Toner and process for preparation thereof

Abstract

 Toner particles are described, each particle comprising a spheroidal resin core, a pigment layer on the surface of said core and a layer of a static electrification controlled resin on the surface of said pigment layer. The state of static electrification of the toner is substantially deter­mined by that of the outermost layer of the static electrification con­trolled resin, and thus can be precisely controlled by simply control­ling the amount of static electrification of the resin particles used to form the outermost layer. Since the state of static electrification of the toner can be precisely controlled, the kind and concentration of the pigment used can be freely selected. The presence of the outermost layer 3 prevents the pigment from breaking away from the toner. Further, it is possible to improve the fluidity and anti-block properties of the toner without any adverse effect. In addition, it is not necessary to use an additional static electrification controlling agent such as silica which might adversely affect the color shade of the toner.

Description

[0001] The present invention relates to a toner and a process for the preparation of the same. More particularly, it relates to such a toner for which its state of static electrification can be precisely controlled and its pigment concentration can be selected at an arbitrary value, and to a process for the preparation of such a toner.

[0002] Electrophotography generally includes the steps of trans­forming an electronic latent image such as a static or electrically con­ductive image to a visible image by means of a toner and fixing the visible toner image on a recording substrate such as a recording sheet of paper. Recently, color electrophotography has been developed and a demand of color toners having various color shades is increasing.

[0003] Toners, including color toners, have heretofore been man­ufactured by melt kneading a resin for toner, a pigment and a static electrification controlling agent, cooling and making the kneaded ma­terial to powder, followed by further pulverization and optional siev­ing to a desired particle size. A fluidizing agent and other appropriate additives are added to the same to provide a final product.

[0004] The prior art toner so manufactured by the process including the steps of pulverization and sieving, however, involves a problem in that variations in toner shape and size of toner particles are inevitable, and in consequence, control of the amount of static electrification of the toner is difficult. For example, even if a static electrification con­trolling agent comprising a particulate inorganic substance such as sil­ica is added to the resin for toner, it is difficult to control precisely the amount of static electrification of the toner. Further posed is a problem in that addition of a relatively large amount of the static electrification controlling agent, although not serious in the case of a black toner, fre­quently changes the color shade in the case of a color toner.

[0005] As described above a fluidizing agent such as silica is added to the prior art toner to improve the fluidity of toner particles or to en­hance the anti-block properties of toner particles. However, silica is hygroscopic and liable to impair a photosensitive body of the em­ployed copy machine.

[0006] To solve the problems discussed above a proposal has been made to add to toner particles a small amount of ultrafine particulate acrylics having a particle size of from 0.2 to 0.5 µm. This proposal, however, poses other problems in that the ultrafine particulate acrylics not only adversely affect the fluidity of the toner but also are likely to break away from the surfaces of toner particles thereby los­ing the effect of the addition thereof.

[0007] Also known in the art is a process for the preparation of toners, including color toners, comprising suspending a monomer of a resin for toner, a pigment and a polymerization initiator for the monomer in water, suspension polymerizing the monomer to produce toner parti­cles, sieving the same, followed by incorporation therein of a static elec­ trification controlling agent and other appropriate additives to provide a product.

[0008] The prior art process including the suspension polymerization to produce toner particles, however, poses a problem in that it is difficult to produce toner of uniform particle size, and in consequence the sieving step is essential, resulting in a reduction of the yield. Further, since a pigment acts as a polymerization inhibitor, limited kinds of pigments are usable on the one hand, and depending upon a nature of a particular pigment an increased concentration of said pigment in the resin is not always realized on the other hand, meaning the fact that a toner having an arbitrary concentration of a particular pigment can not be necessarily prepared.

[0009] The invention sets out to solve the problems associated with the prior art and we have been able to provide a toner in which the state of static electrification can be precisely controlled; any kinds of pigments can be used at any desired concentration; the pigment used does not break away from the toner; and it is possible to improve the fluidity and anti-block properties of the toner without any adverse effect. We have also been able to provide a process for the preparation of such a toner.

[0010] The toner according to the invention comprises composite parti­cles, each of said particles comprising a spheroidal resin core, a pigment layer on the surface of said core and a layer of a static electrification controlled resin on the surface of said pigment layer.

[0011] The process for the preparation of a toner particle according to the invention comprises adhering pigment particles to the surface of a spheroidal resin core, microcapsulating said pigment particles to form a pigment layer on the surface of said core, adhering particles of a static electrification controlled resin on the surface of said pigment layer formed on said core and microcapsulating said particles of the static electrification controlled resin to form a layer of the static electrification controlled resin on the surface of said pigment layer formed on said core.

[0012] The state of static electrification of the toner according to the invention is substantially determined by that of the outermost layer of the static electrification controlled resin and therefore, the state of static electrification of the toner can be precisely controlled by simply controlling that of the resin used in the outermost layer, and in turn the kind and concentration of the pigment used may be freely se­lected. The pigment forming a layer lying between the resin core and the outermost resin layer is not likely to break away from the toner particle. Further, it is possible to improve the fluidity and anti-block properties of the toner according to the invention without any adverse effect.

[0013] The toner and the process for the preparation thereof according to the invention will now be described in detail by way of example with reference to the attached drawings, in which:

Fig. 1 is a diagrammatic cross-sectional view of a toner particle according to the invention; and

Figs. 2 and 3 are diagrammatic cross-sectional showings for il­lustrating the steps of the process according to the invention.

[0014] As shown in Fig. 1, the toner particle according to the invention comprises a spheroidal resin core 1, a pigment layer 2 on the surface of said core 1 and a layer 3 of a static electrification controlled resin on the surface of said pigment layer 2.

[0015] The spheroidal resin core 1 may be formed from a thermoplastic resin when the toner is intended to be heat fixed, or it may be formed from either a thermoplastic or thermosetting resin when the toner is intended to be pressure fixed. The thermoplastic resins which can be used to form the spheroidal resin core 1 include styrene resins, acrylics, polyolefin resins such as polyethylene and polypropylene, nylons and other polyamide resins fluorine resins and polyester resins. The thermosetting resins which can be used to form the spheroidal resin core 1 include epoxy resins and phenolic resins.

[0016] The individual spheroidal resin cores 1 should preferably have approximately the same particle size ranging between 0.5 and 50 µm, preferably between 1 and 10 µm.

[0017] Incidentally, it is not necessary to pay particular attention to the state of static electrification of the spheroidal resin core 1, since it is substantially determined by that of the outermost layer of the static electrification controlled resin.

[0018] The spheroidal resin core 1 is provided with a pigment layer 2 on its surface. Depending upon the desired color of the toner, various pigments can be used to form the pigment layer 2. Specifically, in a case wherein a red toner is desired, inorganic pigments such as iron oxide red and cadmium red, organic pigments such as quinacridone red, Brilliant Karmine 6B and azo red, and dyeable lake pigments; in a case wherein a blue toner is desired, inorganic pigments such as prus­sian blue, ultramarine and cobalt blue, organic pigments such as ph­thalocyanine blue and indigo, and dyeable lake pigments; in a case wherein a yellow toner is desired, inorganic pigments such as titanium yellow, yellow lead and iron oxide yellow, organic pigments such as azo yellow, isoindolinone yellow and fast yellow, and dyeable lake pigments; and in a case wherein a metallic color toner is desired, metallic pigments such as aluminum, bronze, gold, silver and nickel, can be used herein.

[0019] The pigment used, prior to being formed into the layer 2, is preferably particulate and has a primary particle size of from 0.01 to 2 µm, preferably, from 0.02 to 0.2 µm.

[0020] The thickness of the pigment layer 2 is determined in accor­dance with the desired pigment concentration of the toner, and the thicker the pigment layer 2 the deeper the color shade of the toner. Normally the thickness of the pigment layer 2 is within the range from 0.05 to 2 µm.

[0021] Incidentally, it is not necessary to pay particular attention to the state of static electrification of the pigment layer 2, since the state of static electrification of the toner according to the invention is sub­stantially determined by that of the outermost layer of the static electrification controlled resin.

[0022] The pigment layer 2 is provided on its surface with a layer 3 of a static electrification controlled resin. The layer 3 is formed of a thermoplastic resin when the toner is intended to be heat fixed, or may be formed of either a thermoplastic or thermoset­ting resin when the toner is intended to be pressure fixed. The ther­moplastic resins which can be used to form the layer 3 include styrene resins, acrylics, polyolefin resins such as polyethylene and polypropy­lene, nylons and other polyamide resins, fluorine resins and polyester resins. The thermosetting resins which can be used to form the layer 3 include epoxy resins and phenolic resins.

[0023] The layer 3 of a static electrification controlled resin is formed, as described hereinafter in detail, by adhering particles of a static electrification controlled resin to the surface of the pigment layer 2 formed on each of the spheroidal resin cores 1, and microcapsulating the particles of the resin to form the layer 3 on the surface of the pig­ ment layer 2 on each of the core, for example, by subjecting the same to a shock treatment in a gaseous flow to flatten the resin particles to a film. The particles of the static electrification controlled resin used herein are fine particles of the above-illustrated thermoplastic or thermosetting resins which have preferably been finely divided by e.g. a jet mill. The particle size of of the static electrification controlled resin is normally from 0.05 to 5 µm, preferably from 0.1 to 1 µm, and is normally not larger than one fifth, preferably not larger than one tenth of the particle size of the spheroidal resin core 1.

[0024] In order that the state of static electrification of the toner ac­cording to the invention is substantially determined by that of the outermost layer of the static electrification controlled resin, resin par­ticles charged to an appropriate extent in accordance with the desired level of static electrification of the toner are used to form the outer­most layer 3. The resin particles used preferably have an absolute amount of static electrification larger than, preferably at least 2 times, and more preferably at least 3 times that of the spheroidal resin core. More specifically, the absolute amount of static electrification of the resin particles for forming the layer 3 is desirably at least 50 µC/g.

[0025] The static electrification property of the resin particles can be controlled or modified by surface treatment thereof and/or introduc­tion of polar groups thereto. For example, as described in "Technologies of Surface Reforming and Improvement of Surface Functions of Particulate Bodies", SURFACE, Vol. 25, No. 1 (1987), the static electrification property of the resin particles can be controlled by various surface treatments, including, for example, formation of precipitates on the surface of resin particles, treatments of the surface of resin particles with acids, alkalis or salts, solvent treatment, treat­ment with coupling agents, in situ polymerization, steam treatment, plasma treatment, radioactive irradiation, electron beam treatment and treatment with surfactants.

[0026] Alternatively, the static electrification of the resin particles can be controlled or modified by introducing into the resin particles upon manufacture thereof, negatively electrifiable polar groups such as car­boxylic and sulfonic acid groups or positively electrifiable groups such as amino, alkylamino and amide groups.

[0027] In the process for the preparation of a toner according to the invention, as shown in Fig. 2, pigment particles 4 are first adhered to the surface of spheroidal resin cores 1, and mirocapsulated to form a pigment layer 2 on the surface of each of the spheroidal resin core 1.

[0028] The adhesion of the pigment particles 4 to the individual cores 1 can be conveniently done by dry blending the cores 1 with the pig­ment particles 4 whereupon the cores 1 are frictionally charged and attract the pigment particles 4.

[0029] The pigment particles 4 adhered to the individual cores 1 are then microcapsulated to form pigment layers 2 on the individual cores 1 by an impact treatment of the cores 1 having the pigment particles 4 adhered under a gaseous flow. Examples of the gas include, for exam­ple, air, carbon dioxide, nitrogen, argon and other inert gases. The im­ pact treatment may comprise bringing the cores 1 to collide from each other, or applying a mechanical impact to the cores 1.

[0030] This microcapsulation can be conveniently done using a com­mercially available apparatus for reforming surfaces of particulate bodies such as NARA Hybridization system, supplied by NARA Ma­chinery Co., Ltd.

[0031] In the process for the preparation of a toner according to the invention, as shown in Fig. 3, particles 5 of a static electrification con­trolled resin are adhered to the surface of the pigment layer 2 on the spheroidal resin core 1. and then microcapsulated to form the outer­most layer 3 of the static electrification controlled resin on the pig­ment layer 2 of each of the cores 1.

[0032] The adhesion of the resin particles 5 to the pigment layer 2 of the individual cores 1 can be conveniently done by dry blending the cores 1 having the pigment layer 2 with the resin particles 4, and the microcapsulation of the resin particles 5 can be conveniently done by an impact treatment of the cores 1 having the resin particles 5 ad­hered thereto via the pigment layer 2 under a gaseous flow. The im­pact treatment may comprise bringing the cores 1 to collide from each other, or applying a mechanical impact to the cores 1.

[0033] The state of static electrification of a toner according to the in­vention comprising composite particles each comprising a spheroidal resin core, a pigment layer on the surface of said core and a layer of a static electrification controlled resin on the surface of said pigment layer is substantially determined by that of the outermost layer of the static electrification controlled resin, and thus can be precisely con­trolled by simply controlling the amount of static electrification of the resin particles used to form the outermost layer. Since the state of static electrification of the toner can be precisely controlled, the kind and concentration of the pigment used can be freely selected. The presence of the outermost layer 3 prevents the pigment from breaking away from the toner. Further, it is possible to improve the fluidity and anti-block properties of the toner without any adverse effect. In addi­tion, it is not necessary to use an additional static electrification con­trolling agent such as silica which might adversely affect the color shade of the toner.

[0034] While the invention will now be further described by the fol­lowing examples, which should not be considered as limiting.

Example 1

[0035] To 180 grams of polystyrene particles having a particle diame­ter of about 5 µm and an amount of blow off static electrification of - 83 µC/g,, 20 grams of copper phthalocyanine powder having an amount of blow-off charge of + 55 µC/g were adhered and treated in an apparatus for reforming surfaces of particulate bodies (NHS-1, sup­plied by NARA Machinery Co., Lid.) for a period of 5 minutes to pro­vide colored particles (I) surface coated with copper phthalocyanine. The colored particles had an amount of blow-off charge of - 15 µC/g,

[0036] To 160 grams of the so obtained colored particles (I) surface coated with copper phthalocyanine, 40 grams of polymethyl methacrylate powder having a particle diameter of 0.4 µm and an amount of blow-off charge of - 600 µC/g were adhered and treated in an apparatus for reforming surfaces of particulate bodies of the same type as mentioned above for a period of 8 minutes to provide particles surface coated with polymethyl methacrylate. The particles so ob­tained had an amount of blow-off charge of - 45 µC/g,

Example 2

[0037] To 160 grams of the so obtained colored particles (I) surface coated with copper phthalocyanine of Example 1, 40 grams of cathionic polymethyl methacrylate powder having a particle diameter of 0.4 µm and an amount of blow-off charge of + 700 µC/g were adhered and treated in an apparatus for reforming surfaces of particulate bodies in the manner as in Example 1 to provide particles surface coated with polymethyl methacrylate. The particles so obtained had an amount of blow-off charge of + 115 µC/g,

Example 3

[0038] Example 1 was repeated except that an azo pigment having an amount of blow-off charge of + 33 µC/g was used instead of the copper phthalocyanine.

[0039] The obtained colored particles surface coated with the azo pig­ment had an amount of blow-off charge of - 35 µC/g, The final parti­cles surface coated with polymethyl methacrylate had an amount of blow-off charge of - 54 µC/g.

Example 4

[0040] Example 2 was repeated except that an azo pigment having an amount of blow-off charge of + 33 µC/g was used instead of the copper phthalocyanine. The obtained particles surface coated with polymethyl methacrylate had an amount of blow-off charge of + 108 µC/g.

Example 5

[0041] Example 1 was repeated except that an anthraquinone pigment having an amount of blow-off charge of - 90 µC/g was used instead of the copper phthalocyanine.

[0042] The obtained colored particles surface coated with the an­thraquinone pigment had an amount of blow-off charge of - 80 µC/g, The final particles surface coated with polymethyl methacrylate had an amount of blow-off charge of - 64 µC/g.

Example 6

[0043] Example 2 was repeated except that an anthraquinone pigment having an amount of blow-off charge of - 90 µC/g was used instead of the copper phthalocyanine. The obtained particles surface coated with polymethyl methacrylate had an amount of blow-off charge of + 120 µC/g.

[0044] From the foregoing the following can be seen. Colored particles comprising the same polystyrene core surface with copper ph­thalocyanine, azo pigment and anthraquinone pigment have an amount of blow-off charge of - 15, -35 and -80 µC/g, respectively, indicating the fact that the amount of blow-off charge of colored particle drastically varies depending upon the nature of the pigment. Whereas when these colored particles having copper phthalocyanine, azo pig­ment and anthraquinone pigment are surface coated with polymethyl methacrylate having an amount of blow-off charge of - 600 µC/g. the coated particles have an approximately the same amount of blow-off charge of - 45 , -55 and -64 µC/g, respectively. Further, when these colored particles having copper phthalocyanine, azo pigment and an­thraquinone pigment are surface coated with polymethyl methacrylate having an amount of blow-off charge of + 700 µC/g. the coated parti­cles have an approximately the same amount of blow-off charge of + 115, +108 and + 120 µC/g, respectively.

[0045] The amount of blow-off charge reported herein was determined by means of a device for measuring amounts of blow-off charge of particulate bodies TB-20, supplied by TOSHIBA Chemical Industries Co., Ltd. This method of measurement is described in detail in Partic­ulate Bodies and Industry, Vol. 18, No. 6. June, 1986.

Example 7

[0046] To 180 grams of polystyrene particles having a particle diame­ter of about 5 µm and an amount of blow-off charge of - 83 µC/g,, 20 grams of copper phthalocyanine powder having an amount of blow-off charge of + 55 µC/g were adhered and treated in an apparatus for re­forming surfaces of particulate bodies (NHS-1, supplied by NARA Ma­chinery Co., Lid.) for a period of 5 minutes to provide colored particles (I) surface coated with copper phthalocyanine. The colored particles had an amount of blow-off charge of - 15 µC/g,

[0047] Polymethyl methacrylate having a particle diameter of 0.4 µm and an amount of blow-off charge of - 600 µC/g and polymethyl methacrylate having a particle diameter of 0.4 µm and an amount of blow-off charge of + 700 µC/g were mixed together in weight ratios of 100 : 0,70 : 30,40 : 60 and 0 : 100, to provide powder mixtures (II), (III), (IV) and (V), respectively. 160 Grams of the above obtained col­ored particles (I) was admixed with 40 grams of each powder mixture (II). (III). (IV) or (V), and the resulting admixture was treated in an apparatus for reforming surfaces of particulate bodies (NHS-1, sup­plied by NARA Machinery Co., Lid.) for a period of 8 minutes to pro­vide particles surface coated with polymethyl methacrylate. The amounts of blow-off charge of the products were - 45 µC/g in the case of powder mixture (II), +2 µC/g in the case of powder mixture (III), + 43 µC/g in the case of powder mixture (IV) and + 115 µC/g in the case of powder mixture (V),.

Claims

1. Toner particles,each particle comprising a spheroidal resin core, a pigment layer on the surface of said core and a layer of a static electrification controlled resin on the surface of said pigment layer.

2. Toner particles as claimed in claim 1 wherein the core diameter is between 0.5 and 50µm, preferably between 1 and 10µm.

3. Toner particles as claimed in claim 1 or claim 2 wherein the pigment layer is formed from a particulate pigment having a primary particle size of from 0.01 to 2µm, preferably from 0.02 to 0.2µm, and the layer has a thickness of from 0.05 to 2µm.

4. Toner particles as claimed in any of claims 1 to 3 wherein the particle size of the resin which forms the surface is from 0.05 to 5µm, preferably from 0.1 to 1.0µm, and does not exceed one fifth of the particle size of the spheridal core.

5. Toner particles as claimed in any of claims 1 to 4 wherein the absolute amount of static electrification of the resin particles forming the surface is at least 50µC/g.

6. A process for the preparation of a toner particle compris­ing the steps of adhering pigment particles to the surface of a spheroidal resin core, microcapsulating said pigment particles to form a pigment layer on the surface of said core, adhering particles of a static electrification controlled resin on the surface of said pigment layer formed on said core and microcapsulating said particles of the static electrification controlled resin to form a layer of the static electrification controlled resin on the surface of said pigment layer formed on said core.

Drawing