Process for producing toner for developing electrostatic latent image

Abstract

 A process for producing a toner for developing an electrostatic latent image comprising the step of mixing (a) (a-1) a solventless colorant-dispersed resin comprising a solventless resin and a colorant and (a-2) a resin emulsion, (b) (b-1) a colored resin emulsion comprising a resin emulsion and a colorant and (b-2) a solventless resin, or (c) (c-1) a solventless resin, (c-2) a colorant, and (c-3) a resin emulsion, and removing water from the mixture (a), (b) or (c) simultaneously with or after the mixing to prepare a solventless colored resin composition.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to a process for producing a toner for developing an electrostatic latent image in electrophotography, electrostatic recording, electrostatic printing, and the like.

Description of Related Art

[0002] In recent years, a dry process for developing an electrostatic latent image has shown rapid development.

[0003] Various methods for fixing an image are known for the dry development system. In particular, a contact heat fixing system typically including a fusing roller unit is superior to a non-contact heat fixing system, e.g., a hot plate fixing unit, in thermal efficiency and particularly feasibility of high speed fixing and low temperature fixing.

[0004] In a fusing roller fixing system, a toner image formed on an electrostatic recording medium called a photoreceptor is transferred to a transfer sheet, such as paper, and the sheet is passed under a fusing roller for hot pressing thereby to fuse and fix the toner image onto the sheet. However, if the fusing roller fixing system is applied to a conventional toner, the toner coming into contact in a molten state with the fusing roller is adhered onto the fusing roller and stains the next transfer sheet (called an offset phenomenon).

[0005] A toner for developing an electrostatic latent image is generally made up of a resinous component, a colorant (a pigment or a dye), and additives, such as a parting agent and a charge control agent. In order to solve the above problem, it has been studied to incorporate a binder resin for a toner (a) a low-molecular weight polymer to decrease the viscosity so as to securely accomplish fixing at a fixing temperature and also (b) a high-molecular weight polymer to increase the modulus of elasticity so as to prevent the offset phenomenon (sticking of part of the toner to a contact fusing roller).

[0006] Styrene resins are often used as such a binder resin for a toner which comprises a low-molecular weight polymer and a high-molecular weight polymer, and various methods of polymerization have been studied.

[0007] For example, Japanese Patent Laid-Open No. 48657/90 discloses a method in which a high-molecular weight polymer is produced by suspension polymerization using a polyfunctional initiator, and a low-molecular weight polymer is then produced in the presence of the high-molecular weight polymer. The resulting polymer is dried to provide a solvent-free polymer mixture comprising a high-molecular weight polymer and a low-molecular weight polymer, which is expected to be applicable as a binder resin for a toner.

[0008] In general, it is relatively easy to obtain a high-molecular weight polymer by suspension polymerization using a crosslinking agent, such as divinylbenzene, diethylene glycol dimethacrylate, and trimethylolpropane dimethacrylate. However, in order to obtain a low-molecular weight polymer by suspension polymerization, it is necessary to use a large quantity of a chain transfer agent, such as mercaptans or halogen compounds. In using a chain transfer agent, the polymer must be subjected to post-treatment to remove an undesired odor or a residual halogen compound, which increases the cost. Further, the method involves difficulty in removing unreacted polymerizable monomers.

[0009] Japanese Patent Laid-Open No. 48657/90 discloses a technique comprising dissolving a low-molecular weight polymer obtained by solution polymerization in a polymerizable monomer which is to provide a high-molecular weight polymer and causing the system to produce a high-molecular weight resin by addition of a polyfunctional initiator (having at least trifunctionality) to prepare a binder resin for a toner. However, a solution polymerization system for producing a high-molecular weight resin produces the Weissenberg effect (a phenomenon that a resin rises, clinging to a stirring rod), which makes the production difficult.

[0010] U.S. Patent 5,084,368 teaches combining solution polymerization with bulk polymerization for production of a high-molecular weight polymer.

[0011] Any of these processes based on solution polymerization requires a step of solvent removal for obtaining a solventless resin mixture, which not only needs labor but incurs cost.

[0012] Additionally, since solution polymerization has a difficulty in producing polymers having a high weight average molecular weight of more than 200,000, the resulting polymers have not sufficient molecular weight enough to overcome the problem of offset.

[0013] Further, Japanese Patent Laid-Open No. 118583/90 discloses a process for preparing a toner for developing an electrostatic latent image which comprises compounding a low-molecular weight polymer, a high-molecular weight polymer, and a colorant, and kneading the mixture. However, since polymers having largely different molecular weights and also having different compositions generally have poor compatibility to each other, the toner disclosed has both the drawback of the low-molecular weight polymer, i.e., an offset phenomenon, and the drawback of the high-molecular weight polymer, i.e., insufficient fixing in low temperatures.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to provide a process for efficiently and economically producing a toner for developing an electrostatic latent image in which a low-molecular weight polymer and a high-molecular weight polymer both serving as a binder resin component and a colorant are uniformly dispersed with good compatibility and which has reduced odor and exhibits satisfactory characteristics, such as anti-offset properties, fixing properties, grindability in the production thereof, antiblocking properties (resistance to agglomeration) during storage, and developing properties in image formation.

[0015] The present invention provides a process for producing a toner for developing an electrostatic latent image comprising the step of mixing (1) a solventless colorant-dispersed resin comprising a solventless resin and a colorant and (2) a resin emulsion and removing water from the mixture of (1) and (2) simultaneously with or after the mixing to prepare a solventless colored resin composition (hereinafter referred to as a first invention).

[0016] The present invention further provides a process for producing a toner for developing an electrostatic latent image comprising the step of mixing (1) a colored resin emulsion comprising a resin emulsion and a colorant and (2) a solventless resin and removing water from the mixture of (1) and (2) simultaneously with or after the mixing to prepare a solventless colored resin composition (hereinafter referred to as a second invention).

[0017] The present invention furthermore provides a process for producing a toner for developing an electrostatic latent image comprising the step of mixing (1) a solventless resin, (2) a colorant, and (3) a resin emulsion and removing water from the mixture of (1), (2), and (3) simultaneously with or after the mixing to prepare a solventless colored resin composition (hereinafter referred to as a third invention).

[0018] The present invention additionally provides preferred embodiments of the first, second and third inventions, in which:

the resin of the resin emulsion is different from the solventless resin and/or;

the solventless resin is a polymer obtained by bulk polymerization and/or;

the bulk polymerization is carried out at a temperature of not lower than 100 °C and/or;

the resin emulsion is an emulsion of a polymer obtained by emulsion polymerization and/or;

The solventless resin has a weight average molecular weight (Mw) of not more than 200,000 and/or;

the solventless resin has a peak molecular weight (Mp) of 1,500 to 30,000 and a weight average molecular weight (Mw) to number average molecular weight (Mn) ratio (Mw/Mn) of less than 4.0, the molecular weights being as measured by gel-permeation chromatography (GPC), and/or;

the resin of the resin emulsion has a weight average molecular weight (Mw) of not less than 50,000 and/or;

the resin of the resin emulsion has a peak molecular weight (Mp) of 300,000 to 3,000,000 as measured by GPC.

[0019] According to the present invention, a toner for electrostatic latent image development can be produced efficiently and economically by grinding the solventless colored resin composition prepared by the above-described processes. The toner for electrostatic latent image development obtained by the processes of the present invention exhibits outstandingly excellent characteristics. That is, the low-molecular weight resin and the high-molecular weight resin are uniformly dispersed in the toner with good compatibility; the toner is satisfactory in anti-offset properties, fixing properties, grindability in the production, anti-blocking properties (resistance to agglomeration) during storage, and developing properties in image formation; and the toner gives off little odor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Fig. 1 is a schematic plan of a twin-screw continuous mixer which is used for preference to carry out mixing and water removal according to the present invention.

[0021] Fig. 2 is a schematic side view of the twin-screw continuous mixer of Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The process for producing a toner for developing an electrostatic latent image (hereinafter simply referred to as a toner) according to the present invention will be described below in detail.

[0023] To begin with, the first invention is explained.

[0024] The process for producing a toner according to the first invention comprises the step of mixing (1) a solventless colorant-dispersed resin comprising a solventless resin and a colorant and (2) a resin emulsion and removing water from the mixture of (1) and (2) simultaneously with or after the mixing to prepare a solventless colored resin composition. The resulting solventless colored resin composition is ground to give a toner.

[0025] The method for preparing a solventless colorant-dispersed resin comprising a solventless resin and a colorant is not particularly limited, and any method is employable as long as a solventless colorant-dispersed resin may be obtained. For example, a solventless colorant-dispersed resin can be prepared by a method comprising putting a solventless resin and a colorant in an apparatus having a mixing function and a melt-kneading function and mixing them in the apparatus or a method comprising polymerizing a monomer having dispersed therein a pigment. The former method is preferred for the ease of obtaining a uniform mixture.

[0026] Examples of apparatus having these functions include a pressure kneader, a Banbury mixer, a roll mill, and a single- or twin-screw continuous mixer.

[0027] The solventless colorant-dispersed resin as obtained by mixing a solventless resin and a colorant by means of these apparatus is not particularly limited in shape. For example, it can be flakes, powder, granules, or blocks, or be in a molten state. A molten state is preferred because high thermal efficiency can be obtained when a solventless colorant-dispersed resin while in a high temperature is put into an apparatus for carrying out mixing with a resin emulsion and water removal. Besides, the viscosity is lower at a high temperature, making the mixing easier.

[0028] The mixing of a solventless colorant-dispersed resin and a resin emulsion is a treatment in which the solventless colorant-dispersed resin and the resin emulsion are mixed with stirring by a mechanical means or any other means.

[0029] The mixing is preferably carried out at or above the glass transition point of the solventless resin, particularly at or above a temperature higher than the glass transition point by 20 °C. The mixture of the solventless colorant-dispersed resin and the resin emulsion obtained under this preferred temperature condition has a uniform composition and provides a toner with improved physical properties.

[0030] During the mixing, the resin particles of the resin emulsion come into contact with the solventless resin and united therewith while being in a dispersed state. This mechanism of action seems to be accelerated under the preferred temperature condition to bring about the above-described advantage of the mixing treatment.

[0031] The mixing may be performed either under atmospheric pressure or under pressure so as to suppress evaporation of the water content.

[0032] The water removal is a treatment for removing water from the mixture obtained by the above-mentioned mixing treatment to provide a mixed resin composition from which most of the water content has been removed. Where the mixture contains volatile impurities such as residual monomers and an organic solvent, such impurities can be removed concomitantly by the water removal.

[0033] The water removal can be carried out by heating the mixture at or above the boiling point of water and, more effectively, under reduced pressure. When the treatment is conducted under atmospheric pressure, the heating temperature may be around 100 °C in the initial stage of mixing a solventless colorant-dispersed resin and a resin emulsion but should be increased as the removal of water proceeds to decrease the water content of the mixture.

[0034] The water removal may be performed either after completion of the mixing or simultaneously with the mixing. The latter mode is preferred for efficiency.

[0035] On starting water removal, the water content of the mixture begins to decrease to remove most of the water at last. Where water removal is carried out simultaneously with mixing, evaporation of water from the mixture and reduction in water content start upon starting the mixing.

[0036] Where it is desired for the resulting mixture of the solventless colorant-dispersed resin and the resin emulsion to have a highly uniform composition, the mixing and the water removal are preferably followed by kneading.

[0037] The term "kneading" as used herein means mechanically kneading the mixture from which most of water has been removed.

[0038] In this case, the kneading may be carried out under such a condition that causes a small amount of residual water to be removed.

[0039] It is preferable for securing further improved uniformity of the composition that the kneading be carried out with at least one of the solventless colorant-dispersed resin and the resin of the resin emulsion being in a molten state.

[0040] The method for carrying out mixing of the solventless colorant-dispersed resin and the resin emulsion and water removal, and, if desired, kneading is not particularly limited, and any method can be used as long as the solventless colorant-dispersed resin and the resin emulsion can be mixed and the water content can be removed. For example, the solventless colorant-dispersed resin and the resin emulsion are put in an apparatus having a mixing function, a function of removing water, and a melt-kneading function to carry out mixing and water removal.

[0041] Examples of useful apparatus include a pressure kneader, a Banbury mixer, a roll mill, a single-screw continuous mixer, and a twin-screw continuous mixer. A twin-screw continuous mixer is advantageous in that all the mixing, the water removal, and the kneading can be conducted effectively in a single apparatus in a continuous manner.

[0042] The solventless colorant-dispersed resin and the resin emulsion are put in the apparatus and mixed in the presence of the water of the resin emulsion. Simultaneously with or after the mixing, the water content is removed. In the latter case, the mixing and the water removal may be carried out in the respective apparatus. In either case, it is preferable that addition of raw materials, mixing, water removal, and withdrawal of the resin composition be conducted in a continuous manner.

[0043] While various twin-screw continuous mixers are available, those having two self-cleaning type shafts having fixed thereto a plurality of paddles or two self-cleaning type screws, particularly those in which paddles of each shaft rotate in contact with the inner wall of the barrel of the mixer while the paddles of one shaft come into contact with those of the other, are still preferred for their high mixing effect and satisfactory workability. These twin-screw continuous mixers are preferably capable of delivering a fluid having a viscosity of 10 to 1 x 10⁸ cps from the feed opening to the discharge end through revolution of paddles or screws.

[0044] Twin-screw continuous mixers of this type are known and commercially available, e.g., under a trade name of "KRC kneader" manufactured by Kurimoto, Ltd.

[0045] By use of the above-described apparatus, the mixing and the kneading can be practiced by mixing the mixture with stirring through revolution of the screws or paddles fixed to the stirring shafts, and the water removal can be efficiently carried out by heating the mixture to a temperature not lower than the equilibrium evaporation temperature of water present in the mixture by means of a heating jacket or an electric heater usually set on the apparatus or by heating under reduced pressure. Alternatively, the water removal can be conducted by well-known flash distillation, in which the mixture is, if desired as heated, introduced into a reduced pressure zone to evaporate water to make the mixture into a substantially solventless state.

[0046] The mixing and the water removal can be performed in the same apparatus or separate apparatus, preferably in the same apparatus.

[0047] Where the kneading is conducted, the mixing, the water removal and the kneading can be carried out in the respective apparatus; or the mixing and the water removal can be carried out in the same apparatus (first apparatus) and the kneading in a separate apparatus (second apparatus); or the mixing in the first apparatus and the water removal and the kneading in a separate apparatus (second apparatus); or all of the mixing, water removal and kneading in a single apparatus. Where a particularly uniform mixed resin composition is desired, it is preferable to carry out the mixing and the water removal in a first apparatus and the kneading in a second apparatus. Where weight is put on satisfactory workability, it is preferable to carry out all of the mixing, water removal and kneading in a single apparatus.

[0048] In carrying out the mixing and the water removal in a first apparatus and the kneading in a second apparatus, it is preferable for the mixed resin composition discharged from the discharge end of the first apparatus to have a water content of not more than 20% by weight, particularly not more than 5% by weight.

[0049] Figs. 1 and 2 schematically illustrate the structure of a preferred twin-screw continuous mixer. Fig. 1 provides a schematic plan view, and Fig. 2 a schematic side view. Embodiments for carrying out the mixing and the water removal simultaneously followed by the kneadng by the use of the twin-screw continuous mixer will be explained by referring to Figs. 1 and 2.

[0050] The twin-screw continuous mixer used here has two shafts 2 each having fixed thereto a number of paddles 1. The shafts 2 are revolved by a motor 3, whereby a solventless colorant-dispersed resin and a resin emulsion which are continuously fed through a feed opening 4 is stirred and mixed at a temperature not lower than the glass transition point of solventless resin and forwarded toward a discharge end 5.

[0051] Meanwhile, the mixture is heated by means of a heating jacket 6 through which a heating medium, such as steam or oil, is circulated or an electric heater (not shown) to discharge water of the emulsion from a vent hole 7. The feed rate of the solventless colorant-dispersed resin and the resin emulsion is usually adjusted by a means (not shown) so as to leave space between the upper surface of the moving mixture and the heating jacket so that the evaporated water may pass through the space and discharged from the vent hole 7. While the temperature of the mixture in the vicinity of the feed opening 4 is 100 to 110°C because of a high water content, it gradually increases as the water content decreases. Finally the most of the water content of the mixture is removed. Thereafter, the kneading is conducted preferably at a temperature at which solventless resin melts. Through the kneading the solventless colorant-dispersed resin and resin emulsion are dispersed more uniformly. In the melt zone where the kneading is effected, residual water of the melt is also evaporated and discharged from the vent hole 7.

[0052] Depending on the end use, the mixture (solventless colored resin composition) obtained from the discharge end 5 can be continuously transferred to another apparatus where it is processed into pellets or flakes.

[0053] In the case where the mixing, the water removal and the kneading are performed by means of the above-illustrated twin-screw continuous mixer, such conditions as the heating temperature of the jacket and the retention time vary depending on the kinds of solventless colorant-dispersed resin and the resin emulsion, the water content of the resin emulsion, a desired degree of dispersion of resin or a desired content of residual water in the mixture obtained from the discharge end 5, the throughput capacity of the apparatus, and other factors. Nevertheless it is easy for one skilled in the art to decide these conditions theoretically and experimentally provided that the above-mentioned factors are once specified.

[0054] In general, the time and the length of the zone necessary for achieving the mixing and the water removal can be shortened by increasing the rate of water removal by, for example, raising the heating temperature or reducing the inner pressure. It follows that the time and the length of the zone for conducting the kneading increase.

[0055] For example, when polystyrene resins as the solventless resin and resin in the resin emulsion are treated under atmospheric pressure, the temperature of the heating jacket can be set at 120 to 300°C, preferably 160 to 250°C, and the retention time from the feed opening 4 to the discharge end 5 can be set usually at 1 to 60 minutes, preferably at 5 to 30 minutes, while somewhat varying according to the kneading capacity of the apparatus and other factors.

[0056] With an apparatus having a vent hole 7 for discharging water as in the above-described apparatus, an increase in open area of the vent hole 7 for water discharge leads to an increase in efficiency of water removal from the mixture having a high water content. That is, it is preferable for attaining high efficiency of the water removal that the sum of the open area of the feed opening 4 and that of the vent hole 7, which are provided on the upper part of the barrel, ranges from 15 to 100% of the product of the length and the width of the barrel (corresponding to L and D, respectively, shown in Fig. 1). The sum of the open areas being 100%, the upper part of the barrel of the twin-screw continuous mixer is open over the whole length, which is one of preferred embodiments. In this case, the jacket is not provided on the upper part of the barrel. The jacket is provided only on the lower part, or it is replaced with a heating medium which is to be circulated within the revolving shafts or paddles.

[0057] The term "solventless resin" as used herein means a resin which contains substantially no water nor an organic solvent. That is, the total content of water and an organic solvent of the solventless resin is not more than 10% by weight, preferably not more than 5% by weight, particularly preferably not more than 1% by weight. The solventless resin can take a flaky form, a powdered form, a granulated form, a block form, or a molten state.

[0058] In preparing the binder resin for the toner of the present invention, the solventless resin is preferably used as a low-molecular weight component of the binder resin.

[0059] The solventless resin used as a low-molecular weight component of a binder resin for a toner preferably has a molecular weight of 1,500 to 30,000, particularly 2,000 to 20,000, in terms of peak molecular weight Mp indicating the maximum in the gel-permeation chromatogram (GPC).

[0060] If the peak molecular weight Mp is less than 1,500, the resulting toner is, while satisfactory in fixing properties, apt to agglomerate in a developing machine, resulting in reduction of a developer life, deterioration of storage stability, and caking when stored in high temperatures. If Mp exceeds 30,000, the toner is prevented from getting spent (the degradation of carrier) or excessively finer but exhibits insufficient fixing properties in low temperatures, i.e., the toner has a raised lower limit of fixing temperature and the toner tends to cause cold offset.

[0061] The solventless resin used as a low-molecular weight component preferably has a weight average molecular weight Mw of 1,000 to 200,000, particularly 1,000 to 100,000, especially 1,000 to 40,000.

[0062] If Mw is less than 1,000, the resulting toner is, while satisfactory in fixing properties, apt to agglomerate in a developing machine, resulting in reduction of a developer life, deterioration of storage stability, and caking when stored in high temperatures. If Mw exceeds 200,000, the toner is prevented from getting spent (the degradation of carrier) or excessively finer but exhibits insufficient fixing properties in low temperatures. As a result, the toner has a raised lower limit of fixing temperature and the toner tends to cause cold offset.

[0063] The solventless resin preferably has a weight average molecular weight Mw to number average molecular weight Mn ratio, Mw/Mn, of less than 4. If Mw/Mn is 4 or more, the fixing properties are reduced.

[0064] Any kind of resins can be used as a solventless resin with no particular limitation as long as it is applicable as a binder resin for a toner. Examples of useful resins include acrylic resins, styrene resins, epoxy resins, polyester resins, and styrene-butadiene resins. From the viewpoint of ease of obtaining performance properties as a toner, styrene resins are preferred.

[0065] The styrene resins are homopolymers of a styrene monomer or copolymers mainly comprising a styrene monomer. Suitable styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-t-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, and 3,4-dichlorostyrene. Styrene is the most suitable of them.

[0066] Comonomers to be used in the styrene copolymers are not particularly limited as long as they are copolymerizable with the above-described styrene monomers. Acrylic monomers are preferred. Examples of suitable acrylic monomers are methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, lauryl methacrylate, and stearyl methacrylate. n-Butyl acrylate, ethylhexyl acrylate, n-butyl methacrylate, and lauryl methacrylate are particularly preferred.

[0067] The acrylic monomer is preferably selected so that the copolymer obtained by polymerizing with the styrene monomer under conventional conditions may have a glass transition temperature of from 40 to 80 °C, particularly of from 50 to 70 °C.

[0068] The solventless resin use as a low-molecular weight component of a binder resin for a toner can easily be obtained by bulk polymerization.

[0069] The bulk polymerization is carried out by heating a system comprising the above-described monomer(s) and a catalyst soluble in the monomer(s) substantially in the absence of a solvent, a dispersant, an emulsifying agent, etc. to a polymerization temperature. The bulk polymerization can be conducted either in a batch system or in a continuous system in which addition of the raw materials, polymerization, and withdrawal of the resulting polymer are conducted in a continuous manner. From the standpoint of efficiency, it is preferable to conduct bulk polymerization in a continuous system and to continuously feed the polymer to a mixing apparatus for mixing with the colorant.

[0070] The polymerization temperature for bulk polymerization is preferably 100 °C or higher, still preferably 130 to 250 °C, particularly 170 to 250 °C, especially 190 to 230 °C.

[0071] At temperatures below 130°C, the reaction is slow, and the peak molecular weight Mp of the resulting polymer becomes higher than desired. At temperatures above 250°C, the polymerization reaction is accompanied by depolymerization of the polymer produced, resulting in an increased proportion of oligomers having a molecular weight of 500 or smaller. A toner prepared by using such a resin tends to have poor preservability and is ready to become spent (the degradation of carrier) or be made finer.

[0072] Any conventional oil-soluble polymerization initiator can be used as a catalyst for bulk polymerization. Suitable initiators include benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl hydroperoxide, cumene hydroperoxide, t-hexyl hydroperoxide, p-menthane hydroperoxide, and azobisisobutyronitrile.

[0073] In particular, initiators suitable for high-temperature polymerization at 170°C or higher include t-butyl hydroperoxide and di-t-butyl peroxide.

[0074] The free radical polymerization initiator is preferably used in an amount of 0 to 5% by weight, particularly 0.03 to 3% by weight, especially 0.05 to 1% by weight, based on the total monomer(s).

[0075] In preparing a styrene-based low-molecular weight polymer, the polymerization temperature and time are preferably selected so as to give a conversion of at least 90%, preferably at least 95%, still preferably at least 97%. If desired, the residual monomer(s) can be recovered by means of a molecular distillation or vacuum distillation still, etc.

[0076] The thus obtained bulk polymerization product having a low molecular weight is advantageous for use as a binder resin component for a toner particularly in that the resulting toner exhibits improved charge retention and has little odor.

[0077] The colorant which is mixed with the solventless resin includes inorganic pigments, organic pigments, and synthetic dyes. Inorganic pigments or organic pigments are preferably used. One or more than one pigments and/or one or more dyes may be used in combination.

[0078] Suitable inorganic pigments include metal powder pigments, metal oxide pigments, carbon pigments, sulfide pigments, chromate pigments, and ferrocyanide pigments.

[0079] Examples of the metal powder pigments are zinc powder, iron powder, and copper powder.

[0080] Examples of the metal oxide pigments are magnetite, ferrite, red iron oxide, titanium oxide, zinc oxide, silica, chromium oxide, ultramarine, cobalt blue, cerulean blue, mineral violet, and trilead tetroxide.

[0081] Examples of the carbon pigments are carbon black, thermatomic carbon, and furnace black.

[0082] Examples of the sulfide pigments include zinc sulfide, cadmium red, selenium red, mercury sulfide, and cadmium yellow.

[0083] Examples of the chromium pigments include molybdate red, barium yellow, strontium yellow, and chromium yellow. The ferrocyanide pigments include Milori blue.

[0084] The organic pigments include azo pigments, acid dye lakes, basic dye lakes, mordant dye lakes, phthalocyanine pigments, quinacridone pigments, and dioxane pigments.

[0085] Examples of the azo pigments are Benzidine Yellow, Benzidine Orange, Permanent Red 4R, Pyrazolone Red, Lithol Red, Brilliant Scarlet G, and BON Maroon Light.

[0086] The acid dye lakes and the basic dye lakes include those obtained by precipitating dyes, such as Orange II, Acid Orange R, Eosine, Quinoline Yellow, Tartrazine Yellow, Acid Green, Peacock Blue, and Alkali Blue, with a precipitating agent; and those obtained by precipitating dyes, such as Rhodamine, Magenta, Malachite Green, Methyl Violet, and Victorian Blue, with tannic acid, potassium antimonyl tartrate, phosphotungstic acid, phosphomolybdic acid, phosphotungstomolybdic acid, etc.

[0087] Examples of the mordant dye lakes include metal salts of hydroxyanthraquinone dyes and Alizarin Madder Lake.

[0088] Examples of the phthalocyanine pigments are Phthalocyanine Blue and sulfonated copper phthalocyanine.

[0089] Examples of the quinacridone pigments and dioxane pigments are Quinacridone Red, Quinacridone Violet, and Carbazole Dioxane Violet.

[0090] The synthetic dyes include acridine dyes, Aniline Black, anthraquinone dyes, azine dyes, azo dyes, azomethine dyes, benzo and naphthoquinone dyes, indigo dyes, indophenol, indoaniline, indamine, leuco vat ester dyes, naphtholimide dyes, Nigrosine, Induline, nitro and nitroso dyes, oxazine and dioxazine dyes, oxidation dyes, phthalocyanine dyes, polymethine dyes, quinophthalone dyes, sulfur dyes, tri- and diallylmethane dyes, thiazine dyes, and xanthene dyes. Preferred of these synthetic dyes are Aniline Black, nigrosine dyes, and azo dyes. Still preferred are azo dyes having a salicylic acid, naphthoic acid or 8-oxyquinoline residual group capable of forming a metal complex with chromium, copper, cobalt, iron, aluminum, etc.

[0091] The colorant is preferably used in an amount of 1 to 30 parts by weight, particularly 3 to 20 parts by weight, per 100 parts by weight of the solventless resin.

[0092] The resin emulsion for use in the preparation of the toner according to the present invention is not particularly limited as long as it has a resin dispersed therein in an emulsified state, and any type of resin emulsions can be used. For example, one prepared by mechanically dispersing and emulsifying a resin in water and one obtained by emulsion polymerization can be used. In particular, a resin emulsion as prepared by emulsion polymerization is preferred for its stability during storage and at the time of mixing with the solventless colorant-dispersed resin.

[0093] The resin emulsion is preferably used to serve as a high-molecular weight component of a binder resin for a toner in combination with the solventless resin used as a low-molecular weight component.

[0094] The resin of the resin emulsion used as a high-molecular weight component of a binder resin for a toner preferably has a peak molecular weight Mp (the maximum molecular weight in GPC) of 300,000 to 3,000,000, particularly 500,000 to 2,000,000, especially 600,000 to 1,000,000.

[0095] If Mp is lower than the above lower limit, the resulting toner exhibits satisfactory fixing properties but is apt to cause hot offset, making the fixing temperature latitude narrower.

[0096] The resin of the resin emulsion used as a high-molecular weight component preferably has a weight average molecular weight Mw of not less than 50,000, particularly not less than 100,000, especially not less than 300,000.

[0097] If Mw is lower than the above lower limit, the resulting toner exhibits satisfactory fixing properties but is apt to cause hot offset, making the fixing temperature latitude narrower.

[0098] The kind of the resin of the resin emulsion can be selected from those enumerated as the solventless resin used as a low-molecular weight component of a binder resin for a toner. Styrene resins are particularly preferred.

[0099] The resin used in the resin emulsion is preferably different from the solventless resin. The language "the resin of the resin emulsion is different from the solventless resin" as used herein has a broad meaning covering all the embodiments that the two resins have any difference in their polymeric chains, such as a difference in constituent unit, molecular weight, molecular weight distribution, end group, and the like.

[0100] The particle size of the resin dispersed in the resin emulsion is preferably in the range of from 0.03 to 1 µm. If the particle size of the resin in the resin emulsion exceeds 1 µm, the resin has poor compatibility in mutual dispersion with a low-molecular weight polymer. As a result, the resulting toner has poor fixing properties and tends to cause hot offset, making the fixing temperature latitude narrower. Dispersed particle sizes of smaller than 0.03 µm are not preferred because a large amount of an emulsifying agent should be used in emulsion polymerization in order to obtain such fine particles, which lowers the electrical resistance of the resulting toner.

[0101] Degree of mutual dispersion of the solventless resin and the resin of the resin emulsion is related to fixing properties and durability of a toner. That is, a toner in which these resins are non-uniform in their dispersed state simultaneously causes hot offset and cold offset at the time of fixing. Further, such a toner easily gets spent (the degradation of carrier) and made finer, and a developer using the toner has a short life.

[0102] Where the solventless colorant-dispersed resin containing solventless resin used as a low-molecular component and the resin emulsion used as a high-molecular component are combined, the solventless resin is preferably used in a proportion of 50 to 80 parts by weight, particularly 55 to 75 parts by weight, and the resin in the resin emulsion 20 to 50 parts by weight, particularly 25 to 45 parts by weight, per 100 parts by weight of the total amount of solventless resin and resin in the resin emulsion. If the proportion of solventless resin is less than the above lower limit (i.e., if the proportion of resin in the resin emulsion is more than the above upper limit), the resulting toner, while satisfactory in anti-offset properties, exhibits poor fixing properties in a low temperature region, raising the lower limit of a fixing temperature. If the proportion of solventless resin is more than the above upper limit (i.e., if the proportion of resin in the resin emulsion is less than the above lower limit), the fixing properties are satisfactory, but the toner is apt to cause hot offset, making the fixing temperature latitude narrower.

[0103] Emulsion polymerization for preparing the resin emulsion used as a high-molecular component in a binder resin for a toner is carried out by mixing a monomer(s), a water-soluble catalyst, an emulsifying agent, and water as a polymerization medium and heating the mixture to a polymerization temperature.

[0104] Useful monomers include those described above as examples of monomers providing the solventless resin used as a low-molecular weight component and, in addition, polyfunctional crosslinking monomers having at least two polymerizable double bonds, such as aromatic divinyl compounds (e.g., divinylbenzene and divinylnaphthalene), diethylenic carboxylic acid esters (e.g., ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,6-hexanediol diacrylate, and allyl methacrylate), N,N'-divinylaniline, divinyl ether, and divinyl sulfide. Preferred of them are divinylbenzene, ethylene glycol dimethacrylate, and 1,6-hexanediol diacrylate.

[0105] The proportion of the unit derived from the crosslinking monomer in resin (B) is preferably up to 2% by weight, still preferably 0.01 to 1% by weight, particularly preferably 0.02 to 0.8% by weight.

[0106] In general, in emulsion polymerization, most of the monomer is converted into a polymer, with an extremely small amount of the monomer remaining unreacted. And yet where the residual monomer concentration is not sufficiently low for some uses, the residual monomer can be reduced by, for example, adding one or more initiators or reducing agents or blowing steam or air after polymerization.

[0107] Where an initiator or a reducing agent is added after polymerization, the initiator or reducing agent is added intermittently or continuously in an amount of 0.1 to 2.0 parts by weight, preferably 0.5 to 1.0 part by weight, per 100 parts by weight of the polymerizable residual monomer over a period of 5 minutes to 5 hours, preferably 30 minutes to 4 hours, still preferably 1 to 3 hours.

[0108] If necessary, the resin emulsion can have its pH adjusted by addition of aqueous ammonia, an aqueous amine solution, an aqueous alkali hydroxide solution, etc. The resin emulsion to be used usually has a solids content of 10 to 70% by weight, preferably 20 to 60% by weight, still preferably 30 to 50% by weight.

[0109] It is usually desirable for the resin emulsion to have a viscosity of not more than 10,000 cps (measured with a BH type rotational viscometer at 25°C and 20 rpm; hereinafter the same) and a pH of 2 to 10.

[0110] The polymerization initiator which can be used in the emulsion polymerization is selected arbitrarily from conventional water-soluble polymerization initiators.

[0111] Suitable polymerization initiators include free radical polymerization initiators such as hydrogen peroxide, specific alkyl hydroperoxides, dialkyl peroxides, persulfates, peresters, percarbonates, ketone peroxides, and azo type initiators.

[0112] Specific examples of suitable free radical polymerization initiators include hydrogen peroxide, t-butyl hydroperoxide, ammonium persulfate, potassium persulfate, sodium persulfate, t-amyl hydroperoxide, methyl ethyl ketone peroxide, 2,2'-azobis(2-amidinopropane), and 2,2'-azobis(4-cyanovaleric acid).

[0113] The free radical polymerization initiator is preferably used in an amount of 0.03 to 1% by weight, particularly 0.05 to 0.8% by weight, especially 0.1 to 0.5% by weight, based on the total monomer.

[0114] A water-soluble redox initiator, a combination of a water-soluble peroxide and a water-soluble reducing agent, can also be used. The peroxide of the water-soluble redox initiator includes those enumerated above. The reducing agent includes sodium bisulfite, sodium pyrosulfite, sodium sulfite, a hypophosphite, ascorbic acid, and formaldehyde-sodium sulfoxylate.

[0115] The redox initiator is used in an amount of 0.03 to 1% by weight based on the total monomer.

[0116] If desired, a trace amount of a transition metal (e.g., ferrous sulfate, Mohr's salt, copper sulfate, etc.) may be used in combination of the redox initiator.

[0117] The emulsifying agent to be used in the emulsion polymerization can be any of anionic ones, nonionic ones, cationic ones, and amphoteric ones. These emulsifying agents can be used either individually or as a combination thereof.

[0118] The nonionic emulsifying agents include polyoxyethylene alkyl ethers, e.g., polyoxyethylene lauryl ether and polyoxyethylene stearyl ether; polyoxyethylene alkyl phenyl ethers, e.g., polyoxyethylene octyl phenyl ether and polyoxyethylene nonyl phenyl ether; sorbitan higher fatty acid esters, e.g., sorbitan monolaurate, sorbitan monostearate, and sorbitan trioleate; polyoxyethylene sorbitan higher fatty acid esters, e.g., polyoxyethylene sorbitan monolaurate; polyoxyethylene higher fatty acid esters, e.g., polyoxyethylene monolaurate and polyoxyethylene monostearate; glycerol higher fatty acid esters, e.g., glycerol monooleate and glycerol monostearate; and polyoxyethylene-polyoxypropylene block copolymers.

[0119] The anionic emulsifying agents include higher fatty acid salts, e.g., sodium oleate; alkylarylsulfonates, e.g., sodium dodecylbenzenesulfonate; alkylsulfuric esters, e.g., sodium laurylsulfate; polyoxyethylene alkyl ether sulfuric ester salts, e.g., sodium polyoxyethylene lauryl ether sulfate; polyoxyethylene alkyl aryl ether sulfuric ester salts, e.g., sodium polyoxyethylene nonyl phenyl ether sulfate; and alkylsulfosuccinic acid ester and derivatives thereof, e.g., sodium monooctylsulfosuccinate, sodium dioctylsulfosuccinate, and sodium polyoxyethylene laurylsulfosuccinate.

[0120] The amphoteric emulsifying agents include alkyl betaines, e.g., lauryl betaine.

[0121] Fluorine-containing emulsifying agents derived from the above emulsifying agents by displacing at least a part of the hydrogen atoms of the alkyl moiety thereof with fluorine are also useful.

[0122] The cationic emulsifying agents include octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, dioctadecylsilmethylammonium chloride, didodecyldimethylammonium chloride, dodecylbenzyldimethylammonium chloride, tetradecylbenzyldimethylammonium chloride, octadecylbenzyldimethylammonium chloride, tetradecyltrimethylammonium chloride, dihexadecyldimethylammonium chloride, dioctadecyldimethylammonium chloride hexadecylbenzyldimethylammonium chloride, palmityltrimethylammonium chloride, oleyltrimethylammonium chloride, dipalmitylbenzyltrimethylammonium chloride, and dioleylbenzyltrimethylammonium chloride.

[0123] Cationic emulsifying agents prepared from natural vegetable oil, such as coconut oil, palm oil, safflower oil, cotton seed oil, rape seed oil, and linseed oil, can also be used. Such cationic emulsifying agents include coconut oil alkylbenzyldimethylammonium chloride and coconut oil alkyltrimethylammonium chloride. Amine acetates and hydrochlorides as a cationic emulsifying agent include dodecylamine acetate, tetradodecylamine acetate, octadecylamine acetate, dodecylamine hydrochloride, tetradecylamine hydrochloride, octadecylamine hydrochloride, and hardened beef tallow amine acetate.

[0124] Reactive emulsifying agents having polymerizable double bond in the molecule thereof are also useful. Examples of such reactive emulsifying agents include those represented by the following formulae (1) and (2):

wherein two R¹'s each independently represent a hydrogen atom or a methyl group; R² represents an alkyl, alkenyl, aryl or aralkyl group having 6 to 18 carbon atoms; EO represents -CH₂CH₂O-; X represents a single bond or a methylene group; Z represents a hydrogen atom or SO₃M (wherein M represents an alkali metal, an ammonium group or an organic ammonium group); and m represents a natural number of from 1 to 50.

[0125] Of the reactive emulsifying agents represented by formula (1), anionic ones in which Z is SO₃M include Adekaria Soap SE-10N (produced by Asahi Denka Kogyo K.K.), and nonionic ones in which Z is hydrogen include Adekaria Soap NE-10, Adekaria Soap NE-20, and Adekaria Soap NE-30 (all produced by Asahi Denka Kogyo K.K.).

[0126] Of the reactive emulsifying agents represented by formula (2), anionic ones in which Z is SO₃M include Aquaron HS-10 and Aquaron HS-20 (both produced by Dai-ichi Kogyo Seiyaku Co., Ltd.), and nonionic ones in which Z is hydrogen include Aquaron RN-10, Aquaron RN-20, Aquaron RN-30, and Aquaron RN-50 (all produced by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0127] Other anionic reactive emulsifying agents include alkylsulfosuccinic acid alkenyl ether salts, e.g., Latemul S-120, Latemul S-120A, Latemul S-180, and Latemul S-180A (all produced by Kao Corp.); alkylsulfosuccinic acid alkenyl ester salts, e.g., Eleminol JS-2 (produced by Sanyo Chemical Industries, Ltd.); methylenebispolyoxyethylene alkylphenyl alkenyl ether sulfuric ester salts, e.g., Antox MS-60 (produced by Nippon Nyukazai Co., Ltd.); alkylalkenylsuccinic ester salts, e.g., ASK (produced by Kao Corp.); polyoxyalkylene (meth)acrylate sulfuric ester salts, e.g., Eleminol RS-30 (produced by Sanyo Chemical Industries, Ltd.); polyoxyalkylene alkyl ether fatty acid unsaturated dicarboxylic ester salts, e.g., RA-1120 and RA-2614 (both produced by Nippon Nyukazai Co., Ltd.); (meth)acrylic acid sulfoalkyl ester salts, e.g., Antox MS-2N (produced by Nippon Nyukazai Co. Ltd.); phthalic acid dihydroxyalkyl (meth)acrylate sulfuric ester salts; and mono- or di(glycerol-1-alkylphenyl-3-allyl-2-polyoxyalkylene ether) phosphoric ester salts, e.g., H-3330PL produced by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0128] Other nonionic reactive emulsifying agents include polyoxyalkylene alkyl phenyl ether (meth)acrylates, e.g., RMA-564 and RMA-568 (produced by Nippon Nyukazai Co., Ltd.); and polyoxyalkylene alkyl phenyl ether (meth)acrylates, e.g.,RMA-1114 (produced by Nippon Nyukazai Co., Ltd.).

[0129] While water is used as a medium of emulsion polymerization, a water-soluble solvent, such as an alcohol, may be used in combination.

[0130] In the production of the toner of the present invention, additives, such as a charge control agent, a parting agent, and a magnetic substance, can be incorporated into the solventless colorant-dispersed resin or the resin emulsion or into the system under the treatment of mixing or water removal.

[0131] The charge control agent includes nigrosine type electron-donating dyes, metal salts of naphthoic acid or higher fatty acids, amine alkoxides, quaternary ammonium salts, alkylamides, chelates, pigments, and fluorine-containing surface active agents for controlling positive chargeability; and electron-accepting organic complexes, chlorinated paraffin, chlorinated polyester, polyester having excess acid radical, and copper phthalocyanine sulfonylamine for controlling negative chargeability.

[0132] Useful parting agents include metal salts of higher fatty acids, such as a cadmium salt, a barium salt, a nickel salt, a cobalt salt, a strontium salt, a copper salt, a magnesium salt or calcium salt of stearic acid, a zinc salt, a manganese salt, an iron salt, a cobalt salt, a copper salt, a lead salt or magnesium salt of oleic acid, a zinc salt, a cobalt salt, a copper salt, a magnesium salt, a silicon salt or a calcium salt of palmitic acid, a zinc salt, a cobalt salt or a calcium salt of linoleic acid, a zinc salt or a cadmium salt of ricinoleic acid, a lead salt of caprylic acid, and a lead salt of caproic acid; natural or synthetic paraffins and fatty acid esters or partially saponified products thereof; and alkylenebisfatty acid amides. These compounds can be used either individually or as a combination of two or more thereof.

[0133] The colored resin composition as obtained by the above-described process in the form of pellets, flakes, etc. is cooled, crushed, and pulverized in a jet mill, etc., followed by classification to obtain a toner having a desired particle size.

[0134] The thus prepared toner can be mixed with generally used external additives, such as a charge control agent and a fluidity improving agent. Any available fluidity improving agent can be used without particular limitation. For example, fine particles of hydrophobic silica, titanium oxide or aluminum oxide can be used. The fluidity improving agent is preferably added in an amount of 0.01 to 5 parts by weight, particularly 0.1 to 1 part by weight, per 100 parts by weight of the toner.

[0135] The toner produced by the process of the present invention can be mixed with a carrier comprising iron powder or glass beads, preferably a carrier having a resin coat, to provide a two-component system developer.

[0136] Usage of the toner is not limited to a two-component system developer. The toner is also applicable to a one-component developer using no carrier, including a magnetic toner containing magnetic powder and a nonmagnetic toner containing no magnetic powder.

[0137] Carriers having a resin coat typically comprise core particles of iron, nickel, ferrite or glass beads coated with an insulating resin. Typical insulating resin materials include fluorine-containing resins, silicone resins, acrylic resins, styrene-acrylate copolymer resins, polyester resins, and polybutadiene resins.

[0138] When the toner obtained by the process of the present invention is used in a two-component developer containing a resin-coated carrier, it is possible to control the triboelectric characteristics of the carrier and the toner so as to markedly reduce developer fatigue due to contamination of the carrier particles by the toner particles. Such a developer with controlled triboelectric characteristics is particularly suited for use in high-speed electrophotographic copying machines for its excellent durability and long life.

[0139] The binder resin according to the present invention can be blended with other auxiliary binder resins, such as styrene resins and polyester resins. In this case, the proportion of the auxiliary binder resins is preferably not more than 30% by weight based on the total binder resin.

[0140] Then the second invention will be explained below.

[0141] The second invention is a process for producing a toner for developing an electrostatic latent image (hereinafter simply referred to as a toner) comprising the step of mixing (1) a colored resin emulsion comprising a resin emulsion and a colorant and (2) a solventless resin and removing water from the mixture of (1) and (2) simultaneously with or after the mixing to prepare a solventless colored resin composition.

[0142] The process of the second invention is different from the first invention in that a colored resin emulsion and a solventless resin are mixed. The resin emulsion, the colorant, and the solventless resin used in the practice of the second invention are the same as those useful in the first invention, and the methods for mixing the materials and removing water from the system are also the same as those adopted in the first invention.

[0143] The colored resin emulsion comprising the resin emulsion and the colorant can be prepared by any method without particular limitation as long as a colored resin emulsion is obtainable. For example, the colored resin emulsion can be prepared by a method of mixing the resin emulsion and the colorant by stirring, kneading, and the like or a method comprising conducting emulsion polymerization in an aqueous solution having dispersed therein the colorant. The method of mixing the resin emulsion and the colorant is preferred for its easiness.

[0144] Dispersive mixing of the resin emulsion and the colorant can be carried out by any method without particular limitation. For example, the resin emulsion and the colorant are dispersed by means of a dispersing apparatus, such as a homogenizer, a sand mill, a disper, or a slasher.

[0145] The colorant to be mixed may be either in a powdered state or in a dispersed state in an aqueous medium.

[0146] The third invention is now explained.

[0147] The third invention is a process for producing a toner comprising the step of mixing (1) a solventless resin, (2) a colorant, and (3) a resin emulsion and removing water from the mixture of (1), (2), and (3) simultaneously with or after the mixing to prepare a solventless colored resin composition.

[0148] The process of the third invention is different from the first and second inventions in that a solventless resin, a colorant, and a resin emulsion are mixed. The resin emulsion, the colorant, and the solventless resin used in the practice of the third invention are the same as those useful in the first invention, and the methods for mixing and removing water are also the same as those used in the first invention.

[0149] The present invention will now be illustrated in greater detail with reference to Examples and Comparative Examples. Unless otherwise noted, all the percents and arts are given by weight.

[0150] Methods of testing carried out in Examples are as follows.

Measurement of Molecular Weight:

[0151] A peak molecular weight Mp of a molecular weight distribution was measured with a gel-permeation chromatograph (GPC) equipped with three columns (GMH, produced by Tosoh Corp.). A resin sample was dissolved in tetrahydrofuran (THF) in a concentration of 0.2% and passed through the columns at 20°C at a flow rate of 1 ml/min. In the molecular weight measurement, measuring conditions were selected so that measurements on several mono-dispersed polystyrene standard samples may form a straight calibration line with the logarithm plotted as an ordinate and the count number as an abscissa.

Measurement of Residual Monomer:

[0152] A residual monomer content of a polymer was measured with a gas chromatograph (GC) equipped with a column 25% Thermon 1,000. A polymer sample was dissolved in chloroform in a concentration of 2.5% and filtered by a glass filter. A 3 µ l portion of the extract was passed through the column.

[0153] The monomer concentration of the sample was calculated from the calibration curve of each monomer.

Resistance to Agglomeration:

[0154] Powder was preserved in a thermostat at 50 °C for 24 hours, and the degree of agglomeration was observed with the naked eye and graded as follows.

A The powder does not agglomerate at all.

B The powder agglomerates into soft cakes.

C The powder agglomerates into hard cakes.

Definition:

[0155] A resolving power chart of Denshi Shyashin Gakkai, N01-R1975 was copied. The 8.0 point test pattern of the toner image was magnified 100 times with an optical microscope, and the definition was evaluated with the naked eye and graded as follows.

5 The fine lines are reproduced with practically no fog between the lines.

4 The fine lines are reproduced. Slight fog is observed between the lines.

3 Reproduction of the fine lines is slightly poor. Slightly considerable fog is observed between the lines.

2 Reproduction of the fine lines is poor. Considerable fog is observed between the lines.

1 The fine lines are not reproduced, only appearing in a single line.

Fog Density:

[0156] The degree of whiteness of paper before printing and that of the white background of the paper after printing were compared by measuring color difference L, a, b with a color-difference meter ND-504DE manufactured by Nihon Denshi Kogyo K.K. A fog density was obtained from the degree of whiteness of paper before printing:

and that of the background after printing:

according to equation:

[0157] The lower the fog density, the better. A fog density 0.3 or lower is judged good, and 0.5 or higher poor.

Fixing Strength:

[0158] A black solid image was copied on a copier SF-7300 (manufactured by Sharp Corp.) which was altered to have a variable fixing temperature, the fixing unit of which was equipped with a temperature sensor. The density of the toner image was measured with a reflective densitometer RD-914. An adhesive tape (Scotch Mending Tape 810) was lightly stuck on the toner image and pressed by a slow double stroke of a cylindrical weight of 1 kg. Thereafter, the adhesive tape was peeled off at a peel angle of 180°, and the density of the residual toner image was measured. The fixing strength was calculated according to equation:

The higher the fixing strength, the better. A fixing strength of 90% or higher was judged good, 80% or lower poor.

EXAMPLE 1

Preparation of Solventless Resin:

[0159] To an autoclave equipped with a stirrer, a heating means, and a cooling means and set at 220 °C was continuously fed a uniform monomer mixture consisting of 100 parts of styrene (St) and 0.5 part of di-t-butyl peroxide over 30 minutes and kept at 220 °C for 30 minutes to obtain a solventless resin.

[0160] The resulting solventless resin had a peak molecular weight Mp of 4,000 and a weight average molecular weight Mw of 4,600.

Preparation of Solventless Colorant-Dispersed Resin:

[0161] A hundred parts of the solventless resin, 8 parts of carbon black (Carbon Black MA-100S, produced by Mitsubishi Chemical Co., Ltd.), 2 parts of polypropylene wax (PP wax) (Viscol 550P, produced by Sanyo Chemical Industries, Ltd.), and 1 part of a nigrosine dye (Bontron N-01, produced by Orient Kagaku K.K.) were mixed for 30 minutes in a heating type three-roll mill (SH-TYPE heating type three-roll mill manufactured by Inoue Seisakusho K.K.) to obtain a solventless colorant-dispersed resin.

Preparation of Resin Emulsion:

[0162] In a container equipped with a stirrer and a dropping pump were put 27 parts of deionized water and 1 part of an anionic reactive emulsifying agent (Aquaron HS-10 produced by Asahi Denka Kogyo K.K.). After dissolving by stirring, a monomer mixture consisting of 77 parts of styrene, 23 parts of butyl acrylate (BA), and 0.05 part of divinylbenzene (DVB) was added thereto dropwise while stirring to prepare a monomer emulsion.

[0163] In a pressure reactor equipped with a stirrer, a pressure gauge, a thermometer, and a dropping pump was charged 120 parts of deionized water. After displacing the atmosphere with nitrogen, the inner temperature was elevated to 80 °C, and a 5% portion of the above-prepared monomer emulsion was added thereto. Further, 1 part of a 2% potassium persulfate aqueous solution was added to carry out initial polymerization at 80 °C. After completion of the initial polymerization, the temperature was raised to 85 °C, at which the rest of the monomer emulsion and 4 parts of a 2% potassium persulfate aqueous solution were added over a 3 hour period. The reaction system was maintained at that temperature for 2 hours to obtain a styrene resin emulsion having a solids content of 40% and a particle size of 0.2 µm.

[0164] The resulting resin emulsion exhibited a high rate of conversion and stable progress of the polymerization.

[0165] The resin emulsion was subjected to centrifugal separation to separate the resin, which was found, by analysis, to have a weight average molecular weight Mw of 1,000,000 and a peak molecular weight Mp of 750,000.

Preparation of Toner:

[0166] A hundred parts of the above-prepared solventless colorant-dispersed resin and 135 parts of the above-prepared resin emulsion were put in the continuous mixer shown in Figs. 1 and 2 (KRC Kneader, manufactured by Kurimoto, Ltd.) and continuously subjected to mixing and heating to remove water at a jacket temperature of 200 °C to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resulting resin composition had a residual monomer content of 100 ppm. The temperature of the mixture while being mixed and heated for water removal was about 95 °C in the vicinity of the feed opening and about 130 °C at the middle between the feed opening and the discharge end.

[0167] After cooling, the solventless colored resin composition was crushed in a hammer mill and then finely ground in a jet mill. The grinds were classified in an air classifier to obtain particles of 5 to 20 µm. The particles were mixed with 0.2 part of hydrophobic silica (R-972, produced by Nippon Aerosil K.K.) to obtain a toner having an average particle size of 10 µm.

[0168] The resulting toner was mixed with a silicone resin-coated carrier, and the resulting developer was subjected to a copying test on a commercially available copier (SF-7300 manufactured by Sharp Corp.), the fixing unit of which was equipped with a temperature sensor. Fixing of a toner image was possible at or above 145 °C. No contamination of the fusing roller with the toner (offset) occurred even at a fixing temperature of 230 °C. Even after producing 100,000 copies, contamination of the carrier particles with the toner was not observed, and the copies obtained were as clear and free from background stains (fog) as those obtained in the initial stage. These and other test results are shown in Table 2, in which all the parts are by weight.

EXAMPLE 2

Preparation of Solventless Resin:

[0169] Polymerization was carried out in the same manner as in Example 1, except for using a uniform monomer mixture consisting of 87 parts of styrene, 13 parts of butyl acrylate, and 0.1 part of di-t-butyl peroxide, conducting the reaction at 200 °C, and adding the monomer mixture over a 30 minute period. The resulting solventless resin had a peak molecular weight Mp of 10,000 and a weight average molecular weight Mw of 13,000.

Preparation of Solventless Colorant-Dispersed Resin:

[0170] A hundred parts of the solventless resin and 8 parts of carbon black (MA-100S, produced by Mitsubishi Chemical Co., Ltd.) in the same manner as in Example 1 to prepare a solventless colorant-dispersed resin.

Preparation of Resin Emulsion:

[0171] Polymerization was carried out in the same manner as in Example 1, except for using a monomer mixture consisting of 70 parts of styrene, 20 parts of butyl acrylate, 10 parts of butyl methacrylate (BMA), and 0.1 part of 1,6-hexanediol diacrylate (1,6-HDDA), and using 1 part of Neogen R (produced by Kao Corp.) as an anionic emulsifying agent, to obtain a styrene polymer emulsion having a solids content of 40%, a weight average molecular weight of 850,000, a peak molecular weight of 650,000, and a particle size of 0.1 µm.

Preparation of Toner:

[0172] A hundred parts of the solventless resin, 107 parts of the resin emulsion, 2 parts of polypropylene wax (Viscol 550P, produced by Sanyo Chemical Industries, Ltd.), and 1 part of a nigrosine dye (Bontron N-01, produced by Orient Kagaku K.K.) were mixed and heated to remove water in the same manner as in Example 1 to obtain a solventless colored resin composition. The resin composition was found to have a residual monomer content of 85 ppm.

[0173] After the solventless colored resin composition was cooled, a toner was prepared and tested in the same manner as in Example 1. As a result, fixing of a toner image was possible at or above 140 °C. No contamination of the fusing roller (offset) occurred even at a fixing temperature of 225 °C. The copies obtained after producing 100,000 copies were as clear and free from background stains as those obtained in the initial stage.

EXAMPLE 3

Preparation of Toner:

[0174] A hundred parts of the solventless colorant-dispersed resin prepared in Example 1 and melted at 200 °C and 135 parts of the resin emulsion prepared in Example 1 were fed to a twin-screw extruder equipped with a stirring means having two revolving shafts, a heating jacket, and a vacuum water separator (TEX, manufactured by Nippon Seisakusho K.K.) and mixed and heated to remove water at a jacket temperature of 200 °C to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resulting resin composition had a residual monomer content of 150 ppm.

[0175] After the solventless colored resin composition was cooled, a toner was prepared and tested in the same manner as in Example 1. As a result, fixing of a toner image was possible at or above 150 °C. No contamination of the fusing roller by offset occurred even at a fixing temperature of 230 °C. Even after producing 100,000 copies, the copies obtained were as clear and free from background stains as those obtained in the initial stage.

COMPARATIVE EXAMPLE 1

Preparation of Toner:

[0176] The resin emulsion prepared in Example 1 was dried in a drier at 105 °C and crushed to a particle size of about 3 mm in a hammer mill. The resulting particles (54 parts) of a high-molecular weight polymer and 100 parts of the solventless colorant-dispersed resin prepared in Example 1 were mixed in the same continuous mixer as used in Example 1 in the same manner as in Example 1 to obtain a solventless colored resin composition.

[0177] A toner was prepared and tested in the same manner as in Example 1, except for using the above resin composition. As a result, the minimum temperature practical for fixing was as high as 165 °C; considerable offset (contamination of the fusing roller with the toner) was observed at 205 °C; and the resulting copies suffered from considerable fog.

COMPARATIVE EXAMPLE 2

Preparation of Suspension Polymer:

[0178] In a container equipped with a stirrer and a dropping pump were charged 200 parts of deionized water and 1 part of polyvinyl alcohol (PVA117, produced by Kuraray Co., Ltd.). After dissolving by stirring, a monomer mixture consisting of 77 parts of styrene, 23 parts of butyl acrylate, and 0.15 part of di-t-butyl peroxyhexahydroterephthalate (Kaya Ester HTP, produced by Nippon Kayaku Co., Ltd.) was added thereto, followed by stirring to disperse the monomer mixture. The system was heated to 90 °C to start suspension polymerization, and the reaction was continued for 2 hours to obtain a suspension polymer dispersion.

[0179] The resin was separated from the dispersion and dried. The resulting suspension polymer had an average particle size of 180 µm, a weight average molecular weight (Mw) of 650,000, and a peak molecular weight (Mp) of 500,000.

Preparation of Toner:

[0180] The suspension polymer (54 parts) and 100 parts of the solventless colorant-dispersed resin prepared in Example 1 were treated in the same manner as in Example 1 to obtain a solventless colored resin composition.

[0181] The resin composition had a residual monomer content of 980 ppm.

[0182] A toner was prepared using the resulting resin composition and tested in the same manner as in Example 1. As a result, the minimum temperature practical for fixing was as high as 160 °C; considerable offset (contamination of the fusing roller with the toner) was observed at a fixing temperature of 195 °C; and the resulting copies suffered from considerable fog.

EXAMPLE 4

Preparation of Solventless Resin:

[0183] To an autoclave equipped with a stirrer, a heating means, and a cooling means and set at 220 °C was continuously fed a uniform monomer mixture consisting of 100 parts of styrene and 0.5 part of di-t-butyl peroxide over 30 minutes and kept at 220 °C for 30 minutes to obtain a solventless resin.

[0184] The resulting solventless resin had a peak molecular weight Mp of 4,000 and a weight average molecular weight Mw of 4,600.

Preparation of Resin Emulsion:

[0185] In a container equipped with a stiffer and a dropping pump were put 27 parts of deionized water and 1 part of an anionic reactive emulsifying agent (Aquaron HS-10 produced by Asahi Denka Kogyo K.K.). After dissolving by stirring, a monomer mixture consisting of 77 parts of styrene, 23 parts of butyl acrylate, and 0.05 part of divinylbenzene was added thereto dropwise while stirring to prepare a monomer emulsion.

[0186] In a pressure reactor equipped with a stirrer, a pressure gauge, a thermometer, and a dropping pump was charged 120 parts of deionized water. After displacing the atmosphere with nitrogen, the inner temperature was elevated to 80 °C, and a 5% portion of the above-prepared monomer emulsion was added thereto. Further, 1 part of a 2% potassium persulfate aqueous solution was added to carry out initial polymerization at 80 °C. After completion of the initial polymerization, the temperature was raised to 85 °C, at which the rest of the monomer emulsion and 4 parts of a 2% potassium persulfate aqueous solution were added over a 3 hour period. The reaction system was maintained at that temperature for 2 hours to obtain a styrene resin emulsion having a solids content of 40% and a particle size of 0.2 µm.

[0187] The resulting resin emulsion exhibited a high rate of conversion and stable progress of the polymerization. The resin emulsion was subjected to centrifugal separation to separate the resin, which was found, by analysis, to have a weight average molecular weight Mw of 1,000,000 and a peak molecular weight Mp of 750,000.

Preparation of Colored Resin Emulsion:

[0188] The resin emulsion (135 parts), 8 parts of carbon black (Carbon Black MA-100S, produced by Mitsubishi Chemical Co., Ltd.), 2 parts of polypropylene wax (Viscol 550P, produced by Sanyo Chemical Industries, Ltd.), and 1 part of a nigrosine dye (Bontron N-01, produced by Orient Kagaku K.K.) were mixed in a sand mill for 15 minutes to obtain a colored resin emulsion in which the colorant was uniformly dispersed.

Preparation of Toner:

[0189] A hundred parts of the above-prepared solventless resin and 146 parts of the above-prepared colored resin emulsion were put in the continuous mixer shown in Figs. 1 and 2 (KRC Kneader, manufactured by Kurimoto, Ltd.) and continuously subjected to mixing and heating to remove water at a jacket temperature of 200 °C to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resulting resin composition had a residual monomer content of 120 ppm.

[0190] Alter cooling, the solventless colored resin composition was crushed in a hammer mill and then finely ground in a jet mill. The grinds were classified in an air classifier to obtain particles of 5 to 20 µm. The particles were mixed with 0.2 part of hydrophobic silica (R-972, produced by Nippon Aerosil K.K.) to obtain a toner having an average particle size of 10 µm. The resulting toner was mixed with a silicone resin-coated carrier, and the resulting developer was subjected to a coping test on a copier (SF-7300 manufactured by Sharp Corp.) which was altered to have a variable fixing temperature, the fixing unit of which was equipped with a temperature sensor. Fixing of a toner image was possible at or above 145 °C. No contamination of the fusing roller with the toner (offset) occurred even at a fixing temperature of 230 °C. Even after producing 100,000 copies, contamination of the carrier particles with the toner was not observed, and the copies obtained were as clear and free from background stains (fog) as those obtained in the initial stage. These and other test results are shown in Table 4 blow, in which all the parts are by weight.

EXAMPLE 5

Preparation of Solventless Resin:

[0191] Polymerization was carried out in the same manner as in Example 4, except for using a uniform monomer mixture consisting of 87 parts of styrene, 13 parts of butyl acrylate, and 0.1 part of di-t-butyl peroxide, conducting the reaction at 200 °C, and adding the monomer mixture over a 30 minute period. The resulting solventless resin had a peak molecular weight Mp of 10,000 and a weight average molecular weight Mw of 13,000.

Preparation of Resin Emulsion:

[0192] Polymerization was carried out in the same manner as in Example 4, except for using a monomer mixture consisting of 70 parts of styrene, 20 parts of butyl acrylate, 10 parts of butyl methacrylate, and 0.1 part of 1,6-hexanediol diacrylate, and using 1 part of Neogen R (produced by Kao Corp.) as an anionic emulsifying agent, to obtain a styrene polymer emulsion having a solids content of 40%, a weight average molecular weight Mw of 850,000, a peak molecular weight Mp of 650,000, and a particle size of 0.1 µm.

Preparation of Colorant Aqueous Dispersion:

[0193] Eight parts of carbon black (MA-100S, produced by Mitsubishi Chemical Co., Ltd.), 0.5 part of an emulsifying agent (Neogen R, produced by Kao Corp.), and 72 parts of deionized water were dispersed in a horizontal grain mill (GMH-L, produced by Asada Tekkosho K.K.) to obtain a colorant aqueous dispersion.

Preparation of Colored Resin Emulsion:

[0194] The above-prepared resin emulsion (107 parts), 80 parts of the above-prepared colorant aqueous dispersion were dispersed in the same horizontal grain mill as used above to obtain a colored resin emulsion in which the colorant was uniformly dispersed.

Preparation of Toner:

[0195] A hundred parts of the solventless resin, 187 parts of the colored resin emulsion, 2 parts of polypropylene wax (Viscol 550P, produced by Sanyo Chemical Industries, Ltd.), and 1 part of a nigrosine dye (Bontron N-01, produced by Orient Kagaku K.K.) were mixed and heated to remove water in the same manner as in Example 4 to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resin composition was found to have a residual monomer content of 90 ppm.

[0196] After cooling, the solventless colored resin composition was treated in the same manner as in Example 4 to obtain a toner. The resulting toner was tested in the same manner as in Example 4. As a result, fixing of a toner image was possible at or above 140 °C. No contamination of the fusing roller (offset) was observed even at a fixing temperature of 225 °C. The copies obtained after producing 100,000 copies were as clear and free from background stains as those obtained in the initial stage were obtained.

EXAMPLE 6

Preparation of Toner:

[0197] A hundred parts of the solventless resin prepared in Example 4 and melted at 200 °C and 146 parts of the colored resin emulsion prepared in Example 4 were mixed and heated to remove water in a twin-screw extruder equipped with a stirring means having two revolving shafts, a heating jacket, and a vacuum water separator (TEX, manufactured by Nippon Seisakusho K.K.) at a jacket temperature of 200 °C to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resulting resin composition had a residual monomer content of 135 ppm.

[0198] After the resulting solventless colored resin composition was cooled, a toner was prepared and tested in the same manner as in Example 4. As a result, fixing of a toner image was possible at or above 150 °C. No contamination of the fusing roller by offset occurred even at a fixing temperature of 230 °C. Even after 100,000 copies were produced, the copies obtained were as clear and free from background stains as those obtained in the initial stage.

COMPARATIVE EXAMPLE 3

Preparation of Toner:

[0199] The colored resin emulsion prepared in Example 4 was dried in a drier at 105 °C and crushed to about 1 mm in a hammer mill to prepare particles of the high-molecular weight polymer in which the colorant was dispersed. A toner was prepared in the same manner as in Example 4, except for using 65 parts of the above-described colorant-dispersed high-molecular weight polymer particles and 100 parts of the solventless resin prepared in Example 4, and the same copying test as in Example 4 was carried out. The minimum fixing temperature practical for fixing was as high as 165 °C; considerable offset (contamination of the fusing roller with the toner) occurred at a fixing temperature of 205 °C; and the resulting copies suffered from considerable fog.

COMPARATIVE EXAMPLE 4

Preparation of Suspension Polymer:

[0200] In a container equipped with a stirrer and a dropping pump were charged 200 parts of deionized water and 1 part of polyvinyl alcohol (PVA117, produced by Kuraray Co., Ltd.). After dissolving by stirring, a monomer mixture consisting of 77 parts of styrene, 23 parts of butyl acrylate, and 0.15 part of di-t-butyl peroxyhexahydroterephthalate (Kaya Ester HTP, produced by Nippon Kayaku Co., Ltd.) was added thereto, followed by stirring to disperse the monomer mixture. The system was heated to 90 °C to start suspension polymerization, and the reaction was continued for 2 hours to obtain a suspension polymer dispersion.

[0201] The resin was separated from the dispersion and dried to recover the suspension polymer.

[0202] The resulting suspension polymer had an average particle size of 180 µm, a weight average molecular weight Mw of 650,000, and a peak molecular weight Mp of 500,000.

Preparation of Colorant-Mixed Suspension Polymer:

[0203] The suspension polymer (54 parts), 8 parts of carbon black (Carbon Black MA-100S, produced by Mitsubishi Chemical Co., Ltd.), 2 parts of polypropylene wax (Viscol 550P, produced by Sanyo Chemical Industries, Ltd.), and 1 part of a nigrosine dye (Bontron N-01, produced by Orient Kagaku K.K.) were uniformly mixed in a Henschel mixer (MITSUI HENSCHEL, manufactured by Mitsui Mining Co., Ltd.) to obtain a colorant-mixed suspension polymer.

Preparation of Toner:

[0204] Sixty-five parts of the colorant-mixed suspension polymer and 100 parts of the solventless resin prepared in Example 4 were treated in the same manner as in Example 4 to obtain a solventless colored resin composition having the colorant dispersed therein.

[0205] The resulting resin composition had a residual monomer content of 930 ppm.

[0206] A toner was prepared using the resulting solventless colored resin composition and tested in the same manner as in Example 4. As a result, the minimum fixing temperature was as high as 160 °C; considerable offset onto the fusing roller occurred at a fixing temperature of 195 °C; and the resulting copies suffered from considerable fog.

EXAMPLE 7

Preparation of Solventless Resin:

[0207] To an autoclave equipped with a stirrer, a heating means, and a cooling means and controlled at 215 °C was continuously fed a uniform monomer mixture consisting of 100 parts of styrene and 0.7 part of di-t-butyl peroxide over 30 minutes and kept at 215 °C for 30 minutes to obtain a solventless resin.

[0208] The resulting solventless resin had a peak molecular weight Mp of 4,150 and a weight average molecular weight Mw of 4,800.

Preparation of Resin Emulsion:

[0209] In a container equipped with a stirrer and a dropping pump were put 27 parts of deionized water and 1 part of an anionic emulsifying agent (Neogen R produced by Kao Corp.). After dissolving by stirring, a monomer mixture consisting of 75 parts of styrene, 25 parts of butyl acrylate, and 0.05 part of divinylbenzene was added thereto dropwise while stirring to prepare a monomer emulsion.

[0210] In a pressure reactor equipped with a stirrer, a pressure gauge, a thermometer, and a dropping pump was charged 120 parts of deionized water. After displacing the atmosphere with nitrogen, the inner temperature was elevated to 80 °C, and a 5% portion of the above-prepared monomer emulsion was added thereto. Further, 1 part of a 2% potassium persulfate aqueous solution was added to carry out initial polymerization at 80 °C. After completion of the initial polymerization, the temperature was raised to 85 °C, at which the rest of the monomer emulsion and 4 parts of a 2% potassium persulfate aqueous solution were added over a 3 hour period. The reaction system was maintained at that temperature for 2 hours to obtain a styrene resin emulsion having a solids content of 40% and a particle size of 0.15 µm.

[0211] The resulting resin emulsion exhibited a high rate of conversion and stable progress of the polymerization. The resin emulsion was subjected to centrifugal separation to separate the resin, which was found, by analysis, to have a weight average molecular weight (Mw) of 950,000 and a peak molecular weight Mp of 700,000.

Preparation of Mixed Powder Dispersion:

[0212] Eight parts of carbon black (MA-100S, produced by Mitsubishi Chemical Co., Ltd.), 2 parts of polypropylene wax (Viscol 660P, produced by Sanyo Chemical Industries, Ltd.), 1 part of a nigrosine dye (Bontron N-01, produced by Orient Kagaku K.K.), 0.5 part of an emulsifying agent (Neogen R, produced by Kao Corp.), and 72 parts of deionized water were dispersed in a horizontal grain mill (GMH-L, produced by Asada Tekkosho K.K.) to obtain a mixed powder dispersion.

Preparation of Toner:

[0213] A hundred parts of the solventless resin, 135 parts of the resin emulsion, and 83.5 parts of the mixed powder dispersion were put in the continuous mixer shown in Figs. 1 and 2 (KRC Kneader, manufactured by Kurimoto, Ltd.) and continuously subjected to mixing and heating to remove water at a jacket temperature of 215 °C to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resulting resin composition had a residual monomer content of 80 ppm.

[0214] After cooling, the solventless colored resin composition was crushed in a hammer mill and then finely ground in a jet mill. The grinds were classified in an air classifier to obtain particles of 5 to 20 µm. The particles were mixed with 0.2 part of hydrophobic silica (R-972, produced by Nippon Aerosil K.K.) to obtain a toner having an average particle size of 10 µm. The toner was mixed with a silicone resin-coated carrier, and the resulting developer was subjected to a copying test on a commercially available copier (SF-7300 manufactured by Sharp Corp.) the fixing unit of which was equipped with a temperature sensor. Fixing of a toner image was possible at or above 140 °C. No contamination of the fusing roller with the toner (offset) occurred even at a fixing temperature of 225 °C. Even after producing 100,000 copies, contamination of the carrier particles with the toner was not observed, and the copies obtained were as clear and free from background stains (fog) as those obtained in the initial stage. These and other test results are shown in Table 6 blow, in which all the parts are by weight.

EXAMPLE 8

Preparation of Solventless Resin:

[0215] Polymerization was carried out in the same manner as in Example 7, except for using a uniform monomer mixture consisting of 87 parts of styrene, 13 parts of butyl acrylate, and 0.1 part of di-t-butyl peroxide, conducting the reaction at 200 °C, and adding the monomer mixture over a 30 minute period. The resulting solventless resin had a peak molecular weight Mp of 10,000 and a weight average molecular weight Mw of 13,000.

Preparation of Resin Emulsion:

[0216] Polymerization was carried out in the same manner as in Example 7, except for using a monomer mixture consisting of 75 parts of styrene, 15 parts of butyl acrylate, 10 parts of butyl methacrylate, and 0.1 part of 1,6-hexanediol diacrylate, and using 1 part of an anionic emulsifying agent (Aquaron HS-10 produced by Asahi Denka Kogyo K.K.) to obtain a styrene resin emulsion having a solids content of 40%, a weight average molecular weight Mw of 880,000, a peak molecular weight Mp of 670,000, and a particle size of 0.20 µm.

Preparation of Mixed Powder:

[0217] Eight parts of carbon black (MA-100S, produced by Mitsubishi Chemical Co., Ltd.), 2 parts of polypropylene wax (Viscol 660P, produced by Sanyo Chemical Industries, Ltd.), and 1 part of a nigrosine dye (Bontron N-01, produced by Orient Kagaku K.K.) were mixed in a Henschel mixer (MITSUI HENSCHEL Mixer FM10B, manufactured by Mitsui Miike Kakoki K.K.) to obtain a mixed powder.

Preparation of Toner:

[0218] A hundred parts of the solventless resin, 107 parts of the resin emulsion, and 11 parts of the mixed powder were mixed and heated to remove water in the same manner as in Example 7 to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resulting resin composition had a residual monomer content of 100 ppm.

[0219] After cooling the resulting solventless colored resin composition, a toner was prepared and tested in the same manner as in Example 7. As a result, fixing of a toner image was possible at or above 140 °C. No contamination of the fusing roller by offset occurred even at a fixing temperature of 230 °C. The copies obtained even after 100,000 copies were produced were as clear and free from background stains as those obtained in the initial stage.

EXAMPLE 9

Preparation of Toner:

[0220] A hundred parts of the solventless resin prepared in Example 7 and melted at 200 °C, 135 parts of the resin emulsion prepared in Example 7, and 83.5 parts of the mixed powder dispersion prepared in Example 7 were mixed and heated to remove water in a twin-screw extruder equipped with a stirring means having two revolving shafts, a heating jacket, and a vacuum water separator (TEX, manufactured by Nippon Seisakusho K.K.) at a jacket temperature of 200 °C to obtain a solventless colored resin composition having a water content of not more than 0.1%. The resulting resin composition had a residual monomer content of 150 ppm.

[0221] Alter cooling the resulting solventless colored resin composition, a toner was prepared and tested in the same manner as in Example 7. As a result, fixing of a toner image was possible at or above 145 °C. No contamination of the fusing roller by offset occurred even at a fixing temperature of 230 °C. The copies obtained even after 100,000 copies were produced were as clear and free from background stains as those obtained in the initial stage.

COMPARATIVE EXAMPLE 5

Preparation of Toner:

[0222] The resin emulsion prepared in Example 7 was dried in a drier at 105 °C and crushed to about 3 mm in a hammer mill to prepare high-molecular weight resin particles. The resulting resin particles (54 parts), 100 parts of the solventless resin prepared in Example 7, and 83.5 parts of the mixed powder dispersion prepared in Example 7 were mixed in the same continuous mixer as used in Example 7 in the same manner as in Example 7 to prepare a solventless colored resin composition.

[0223] A toner was prepared and tested in the same manner as in Example 7, except for using the above-prepared solventless colored resin composition. As a result, the minimum fixing temperature practical for fixing was as high as 165 °C; considerable offset onto the fusing roller occurred at a fixing temperature of 205 °C; and the resulting copies suffered from considerable fog.

COMPARATIVE EXAMPLE 6

Preparation of Suspension Polymer:

[0224] In a container equipped with a stirrer and a dropping pump were charged 200 parts of deionized water and 1 part of polyvinyl alcohol (PVA117, produced by Kuraray Co., Ltd.). After dissolving by stirring, a monomer mixture consisting of 78 parts of styrene, 22 parts of butyl acrylate, and 0.15 part of di-t-butyl peroxyhexahydroterephthalate (Kaya Ester HTP, produced by Nippon Kayaku Co., Ltd.) was added thereto, followed by stirring to disperse the monomer mixture. The system was heated to 90 °C to start suspension polymerization, and the reaction was continued for 2 hours to obtain a suspension polymer dispersion.

[0225] The resin was separated from the dispersion and dried to recover the suspension polymer.

[0226] The resulting suspension polymer had an average particle size of 185 µm, a weight average molecular weight Mw of 640,000, and a peak molecular weight Mp of 500,000.

Preparation of Toner:

[0227] The suspension polymer (54 parts), 100 parts of the solventless resin prepared in Example 7, and 83.5 parts of the mixed powder dispersion prepared in Example 7 were treated in the same manner as in Example 7 to obtain a solventless colored resin composition.

[0228] The resulting solventless colored resin composition had a residual monomer content of 950 ppm.

[0229] A toner was prepared using the resulting resin composition and tested in the same manner as in Example 7. As a result, the minimum fixing temperature practical for fixing was as high as 160 °C; considerable offset onto the fusing roller occurred at a fixing temperature of 195 °C; and the resulting copies suffered from considerable fog.

Table 6

Formulation and Toner Properties
	Example			Comparative Example
	7	8	9	5	6
Formulation of Mixed Powder Dispersion (or Mixed Powder) :
Carbon Black	8	(8)	8	8	8
PP Wax	2	(2)	2	2	2
Nigrosine Dye	1	(1)	1	1	1
Emulsifying Agent	0.5		0.5	0.5	0.5
Deionized Water	72		72	72	72

Formulation of Solventless Colored Resin Composition :
Solventless Resin	100	100	100	100	100
Resin Emulsion	135	107	135		135
Dried Resin Emulsion				54
Suspension Polymer					54
Mixed Powder Dispersion (or Mixed Powder)	83.5	(11)	83.5	83.5	83.5
Residual Monomer Content of Composition (ppm)	80	100	150	880	950

Copying Test Results :
Minimum Fixing Temp. (°C)	140	140	145	165	160
Offset Initiating Temp. (°C)	> 225	> 230	> 230	205	195
Fog Density	0.13	0.19	0.23	1.10	0.79
Definition	5	5	5	2	3
Fixing Strength (%)	94	98	91	71	77
Resistance to Agglomeration	A	A	A	B	B
Note : All the units for compositions are part by weight.

Claims

1. A process for producing a toner for developing an electrostatic latent image comprising the step of mixing (1) a solventless colorant-dispersed resin comprising a solventless resin and a colorant and (2) a resin emulsion and removing water from the mixture of (1) and (2) simultaneously with or after the mixing to prepare a solventless colored resin composition.

2. A process for producing a toner for developing an electrostatic latent image comprising the step of mixing (1) a colored resin emulsion comprising a resin emulsion and a colorant and (2) a solventless resin and removing water from the mixture of (1) and (2) simultaneously with or after the mixing to prepare a solventless colored resin composition.

3. A process for producing a toner for developing an electrostatic latent image comprising the step of mixing (1) a solventless resin, (2) a colorant, and (3) a resin emulsion and removing water from the mixture of (1), (2), and (3) simultaneously with or alter the mixing to prepare a solventless colored resin composition.

4. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein the resin of said resin emulsion is different from said solventless resin.

5. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein said solventless resin is a polymer obtained by bulk polymerization.

6. A process for producing a toner for developing an electrostatic latent image according to claim 5, wherein said bulk polymerization is carried out at a temperature of not lower than 100°C.

7. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein said resin emulsion is an emulsion of a polymer obtained by emulsion polymerization.

8. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein said solventless resin has a weight average molecular weight (Mw) of not more than 200,000.

9. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein said solventless resin has a peak molecular weight (Mp) of 1,500 to 30,000 and a weight average molecular weight (Mw) to number average molecular weight (Mn) ratio of less than 4.0, said Mp, Mw, and Mn being measured by gel-permeation chromatography.

10. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein the resin of said resin emulsion has a weight average molecular weight (Mw) of not less than 50,000.

11. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein the resin of said resin emulsion has a peak molecular weight (Mp) of 300,000 to 3,000,000 as measured by gel-permeation chromatography.

12. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein said mixing and water removal are carried out in a twin-screw continuous mixer.

13. A process for producing a toner for developing an electrostatic latent image according to claim 12, wherein said twin-screw continuous mixer is equipped with a heating jacket having an evaporation chamber and/or a vent hole.

14. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein said solventless resin and the resin of said resin emulsion are a styrene resin.

15. A process for producing a toner for developing an electrostatic latent image according to any one of claims 1 to 3, wherein said solventless colored resin composition comprises 50 to 80 parts by weight of said solventless resin and 20 to 50 parts by weight of the resin originated in said resin emulsion per 100 parts by weight of the total amount of said solventless resin and said resin originated in said resin emulsion.

Drawing