JP2007264451A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which stable uniform cleaning performance is ensured, and which allows formation of good full-color images over a prolonged period of time. <P>SOLUTION: In the image forming apparatus using a black magnetic toner and color nonmagnetic toners, 1-3 wt.% of strontium titanate has been externally added to at least the black magnetic toner and the amount of strontium titanate externally added to the color nonmagnetic toners is in a range satisfying the following (I) and (II); (I) the amount of strontium titanate externally added to each color nonmagnetic toner is 0-0.2 wt.%, (II) the total amount of strontium titanate externally added to all the color nonmagnetic toners is ≤(X-1) wt.%, wherein X represents the amount (wt.%) of strontium titanate externally added to the black magnetic toner. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a full-color image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile machine, or a multifunction machine of these.

An image forming apparatus such as a rotary type using a single photosensitive drum has an advantage that the apparatus can be easily downsized. Various types of apparatuses such as a one-drum four-cycle system have been put to practical use so far. Yes.
By the way, when forming a full-color image, the frequency of black is higher than that of color, so magnetic toner that is more durable than non-magnetic is often used as black toner, and non-magnetic as color toner. Toner was often used.

  However, since the magnetic toner has higher polishing performance than the non-magnetic toner, when the magnetic toner and the non-magnetic toner are used in combination in the one-drum / four-cycle image forming apparatus, only the photosensitive drum of the portion to which the magnetic toner is transferred. As a result, the cleaning performance is biased. When an image is formed for a long period in such a state, there is a problem that an image defect such as fogging occurs due to insufficient cleaning of the photosensitive drum.

Therefore, as a technique for controlling the strong polishing performance of the magnetic toner to make the cleaning performance uniform, a technique of adding strontium titanate, which is generally known as a lubricant, to toner particles is known (patent) References 1-4). When strontium titanate is externally added, the polishing performance is controlled and appropriate photoconductor drum polishing becomes possible. Further, by externally adding strontium titanate, a static layer made of strontium titanate particles is formed in the gap between the photosensitive drum and the cleaning blade, and prevents the other external additives from being scraped. The effect that the image noise on the image accompanying the adhering to the drum surface can be suppressed is obtained. Further, since strontium titanate has a weak positive chargeability, it is considered that when externally added to a negatively chargeable non-magnetic one-component toner, it exerts an action of imparting a negative charge to the toner. It is also possible to improve the charge amount of the toner.
JP 2004-191532 A Japanese Patent Laid-Open No. 10-10770 Japanese Patent Laid-Open No. 11-212293 Japanese Patent Laid-Open No. 2003-255609

  However, even if the techniques disclosed in Patent Documents 1 to 4 are used, it is not completely avoided that the cleaning performance of the photosensitive drum is biased. If an image is formed over a long period of time, an image defect may occur. It often occurred.

  Accordingly, an object of the present invention is to provide an image forming apparatus which can obtain a stable and uniform cleaning performance and can form a good full color image over a long period of time.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have formed a specific amount of strontium titanate in the black magnetic toner when forming a full-color image using the black magnetic toner and the color non-magnetic toner. Excessive polishing performance of black magnetic toner is moderately suppressed by external addition, and strontium titanate is not externally added to the color non-magnetic toner, or even when externally added, the amount of external addition is specified or less, Specifically, if the amount of addition to the black magnetic toner is more than a certain amount, the polishing performance of the black magnetic toner and the polishing performance of the color non-magnetic toner are adjusted to be approximately equal. The inventors have found that the problem can be solved all at once, and have completed the present invention.

That is, the image forming apparatus of the present invention is an image forming apparatus using black magnetic toner and color non-magnetic toner, and at least black magnetic toner is externally added with 1 to 3% by weight of strontium titanate, The external addition amount of strontium titanate externally added to the color nonmagnetic toner is in a range satisfying the following (I) and (II).
(I) The amount of external addition per color non-magnetic toner is 0.2% by weight or less (including 0% by weight).
(II) When the external addition amount of strontium titanate of the black magnetic toner is X wt%, the total external addition amount of all colors of the color non-magnetic toner is (X-1) wt% or less.
In a preferred embodiment of the image forming apparatus of the present invention, the black magnetic toner is obtained by a pulverization method, and the color non-magnetic toner is obtained by a polymerization method. In another preferred embodiment of the image forming apparatus of the present invention, the image forming apparatus has a single photosensitive drum.

  According to the image forming apparatus of the present invention, it is possible to obtain a stable and uniform cleaning performance and to form a good full color image over a long period of time.

The image forming apparatus of the present invention is an image forming apparatus using black magnetic toner (hereinafter also referred to as “magnetic toner”) and color nonmagnetic toner (hereinafter also referred to as “nonmagnetic toner”). .
The magnetic toner in the present invention contains a magnetic powder as will be described later. Specifically, for example, the holding power is 6.0 to 8.5 kA / m when 79.5 to 397.5 kA / m is applied. Yes, a saturation magnetization of 24 to 35 Am ² / kg and a residual magnetization of 2.0 to 3.0 Am ² / kg are preferable. On the other hand, the nonmagnetic toner in the present invention does not contain magnetic powder as will be described later. In the present invention, the magnetic toner is a black toner, and the non-magnetic toner is a color toner, specifically, one or more of cyan toner, magenta toner, yellow toner and the like.
As for the saturation magnetization and the residual magnetization, about 50 mg of magnetic powder-containing resin particles stored at room temperature and normal humidity (20 ° C., 65% RH) are separated and inserted into a cylindrical cell, and a predetermined magnetic field is applied. It is obtained by drawing a hysteresis curve in one minute and performing measurement with a vibrating sample magnetometer (VSM-P7 / 15 type: manufactured by Toei Kogyo Co., Ltd.) in the applied state.

  In the present invention, strontium titanate must be externally added to at least the magnetic toner. This suppresses the high polishing performance of the magnetic toner. Further, at this time, it is important that the amount of strontium titanate added to the magnetic toner is 1 to 3% by weight. Preferably, it is 1 to 2% by weight. If the amount of strontium titanate added to the magnetic toner is less than 1% by weight, the polishing performance cannot be suppressed and the polishing performance cannot be balanced with the color toner. Further, the development performance becomes higher than necessary. On the other hand, if it exceeds 3% by weight, the polishing performance is suppressed more than necessary, and the polishing performance cannot be balanced with the color toner. Further, the development performance becomes lower than necessary.

In the present invention, it is important that strontium titanate is not externally added to the non-magnetic toner, or that the external addition amount is within a specific range when externally added. That is, it is important that the external addition amount of strontium titanate of the nonmagnetic toner is in a range satisfying the following (I) and (II).
(I) The amount of external addition per color non-magnetic toner is 0.2% by weight or less (including 0% by weight).
(II) When the external addition amount of strontium titanate of the black magnetic toner is X wt%, the total external addition amount of all colors of the color non-magnetic toner is (X-1) wt% or less.

The above (I) defines the amount of external addition per color among a plurality of color non-magnetic toners, and the amount of external addition per color is 0.2% by weight or less, preferably 0.1%. It should be less than wt%. Of course, in this case, 0% by weight, that is, the case where strontium titanate is not externally added is included. If there is even one non-magnetic toner whose external additive amount per color exceeds 0.2% by weight, the polishing performance of the color toner is deteriorated and cleaning failure occurs.
On the other hand, (II) defines the difference between the total amount of all the colors of the color non-magnetic toner and the amount of magnetic toner, and the amount of strontium titanate added in the magnetic toner. Is X wt%, the total external addition amount of all colors of the non-magnetic toner is (X-1) wt% or less, preferably (X-1.2) wt% or less. When the total amount of external addition of all the non-magnetic toner colors exceeds (X-1)% by weight, the black toner has a high polishing performance and the color toner has a low polishing performance, resulting in poor cleaning.

  In this specification, the amount of strontium titanate added to the toner (magnetic or nonmagnetic) is the percentage of the weight of strontium titanate in the total toner weight (toner particle weight + total weight of external additives). It is a thing. The same applies to the case where the addition amount (external addition amount) of additives other than strontium titanate is indicated by “% by weight”, where “% by weight” is the total weight of the toner (toner particle weight + external additive total weight). ) Is a percentage of the additive weight.

  The magnetic toner and the non-magnetic toner in the present invention are not particularly limited except that the amount of strontium titanate added is in the above-mentioned range. Both toners are bound similarly to the conventional toner. Various additives are externally added as necessary to toner particles composed of a resin, a colorant, and various additives as required. Hereinafter, each component of the magnetic toner and the non-magnetic toner will be described.

  Examples of the binder resin constituting the magnetic toner and the nonmagnetic toner include styrene polymers, acrylic polymers, styrene-acrylic polymers, olefin polymers such as chlorinated polystyrene, polypropylene, and ionomer, Examples include vinyl chloride, polyester resin, polyamide, polyurethane, epoxy resin, diallyl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, phenol resin, rosin modified phenol resin, xylene resin, rosin modified maleic acid resin, rosin ester, etc. It is done. Of these, styrene polymers, styrene-acrylic polymers, and polyester resins are particularly preferable.

Specific examples of the styrene polymer and the styrene-acrylic polymer include styrene homopolymers and copolymers of styrene and other monomers.
Examples of other monomers copolymerizable with styrene include p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; vinyl chloride, vinyl bromide and vinyl fluoride. Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, acrylic acid (Meth) acrylic acid esters such as n-octyl, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; acrylonitrile, methacrylonitrile, acrylamide, etc. Other acrylic acid derivatives; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl compounds such as N-vinylpyrrolidene; and the like can be used. These other copolymerizable monomers may be used alone or in combination of two or more.

As the polyester-based resin, for example, those obtained by polycondensation of a polyvalent carboxylic acid component and a polyhydric alcohol component can be used.
Examples of the polyvalent carboxylic acid component include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, and azelain. Divalent carboxylic acids such as acid and malonic acid; n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n- Alkyl or alkenyl esters of divalent carboxylic acids such as dodecenyl succinic acid, isododecyl succinic acid, isododecenyl succinic acid; 1,2,4-benzene tricarboxylic acid (trimellitic acid), 1,2,5-benzene Tricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalene Tricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexane Tricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, carboxylic acid having 3 or more valences such as empole trimer acid, and the like can be used. Also, anhydrides of these polyvalent carboxylic acids can be used.

  Examples of the polyhydric alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butene. Diols such as diol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A, Bisphenols such as hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythri , Dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2 , 4-butanetriol, trimethylolethane, trimethylolpropane, polyhydric alcohols of triol or higher such as 1,3,5-trihydroxymethylbenzene, and the like can be used.

As the colorant constituting the magnetic toner and the non-magnetic toner, various pigments may be used alone or in combination depending on the desired color of toner and the necessity of magnetism. Specifically, it is preferable to use a black pigment which is a magnetic powder for the black magnetic toner.
Suitable examples of various pigments are as follows. That is, examples of the black pigment include magnetite, ferrite powder, carbon black, acetylene black, lamp black, and aniline black. Among these, magnetite, ferrite powder and the like are magnetic powders. Yellow pigments include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, naples yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Examples include quinoline yellow lake, permanent yellow NCG, and tartrazine lake. Examples of the orange pigment include red lip yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, and indanthrene brilliant orange GK. Red pigments include bengara, cadmium red, red lead, mercury cadmium sulfide, permanent red 4R, risor red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin. Rake, brilliant carmine 3B, etc. are mentioned. Examples of purple pigments include manganese purple, fast violet B, and methyl violet lake. Examples of blue pigments include bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, and induslen blue BC. Examples of the green pigment include chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G, and the like.

  In the case of a magnetic toner (in this case, the colorant is a magnetic powder), the content of the colorant in the toner particles is preferably 50 to 200 parts by weight with respect to 100 parts by weight of the binder resin. In the case of a non-magnetic toner, the amount is preferably 1 to 20 parts by weight, more preferably 2 to 8 parts by weight with respect to 100 parts by weight of the binder resin.

  The magnetic toner and the non-magnetic toner may be one in which various additives are internally added to toner particles containing the binder resin and the colorant as constituent components. Representative additives among internally added additives include charge control agents and offset preventing agents. Of course, in addition to these, various conventionally known additives such as stabilizers can be internally added as long as the effects of the present invention are not impaired.

The charge control agent is for controlling the triboelectric charging characteristics of the toner, and a charge control agent for positive charge control and / or negative charge control is used according to the charge polarity of the toner. Examples of the charge control agent for controlling positive charge include organic compounds having basic nitrogen atoms such as basic dyes, aminopyrines, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, and fillers surface-treated with these compounds. Etc. On the other hand, examples of charge control agents for controlling negative charge include oil-soluble dyes such as nigrosine base (CI5045), oil black (CI26150), Bontron S, and spiron black; charges such as styrene-styrenesulfonic acid copolymer. Controlling resins; compounds containing a carboxy group (for example, alkyl salicylic acid metal chelates), metal complex dyes, fatty acid metal soaps, resin acid soaps, naphthenic acid metal salts, and the like.
The content of the charge control agent in the toner particles is preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the binder resin.

The offset preventing agent is for imparting an offset preventing effect to the toner. Examples of the offset preventive agent include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Among these, an aliphatic hydrocarbon having a weight average molecular weight of about 1000 to 10,000 is preferable. Specifically, one or a combination of two or more of low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, a low molecular weight olefin polymer composed of olefin units having 4 or more carbon atoms, silicone oil and the like are suitable.
The content of the offset inhibitor in the toner particles is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the binder resin.

There are no particular restrictions on the method for obtaining the toner particles constituting the magnetic toner and the non-magnetic toner. For example, after mixing and kneading the raw materials, the toner particles are obtained by a pulverization method such as coarse pulverization, fine pulverization, and classification. The toner particles can also be obtained by a chemical production method such as a polymerization method. In general, particles obtained by the pulverization method have a lower sphericity and higher polishing performance than particles obtained by the polymerization method. Since magnetic toner is more durable than non-magnetic toner, in the present invention, it is desirable to maintain higher polishing performance for magnetic toner and lower polishing performance for non-magnetic toner. Therefore, in the present invention, the magnetic toner (toner particles in the magnetic toner) is obtained by the pulverization method, and the non-magnetic toner (toner particles in the non-magnetic toner) is obtained by the polymerization method. It is preferable.
The toner particles constituting the magnetic toner and the nonmagnetic toner in the present invention preferably have a volume average particle size of 4 to 12 μm, more preferably 6 to 10 μm.

  In the magnetic toner and the non-magnetic toner according to the present invention, various additives other than strontium titanate are externally added to the toner particles composed of the binder resin and the colorant described above within a range not impairing the effects of the present invention. It may be what was done. Examples of other additives that can be externally added include silica, alumina, titanium oxide, magnetite, and zinc stearate. Further, the above-described charge control agent and offset preventive agent may be externally added as an additive that can be internally added to the toner particles.

The image forming apparatus of the present invention only needs to use the above-described black magnetic toner and color non-magnetic toner, and the image forming system and the like are not particularly limited. An apparatus using the image forming apparatus, that is, a rotary image forming apparatus is an embodiment in which the effects of the present invention can be more utilized, and is particularly preferable.
Hereinafter, a 1-drum 4-cycle image forming apparatus will be described in detail with reference to the drawings as an example of a rotary image forming apparatus.

  As shown in FIG. 1, an image forming unit 10 is provided in the approximate center of the color image forming apparatus 100. The image forming unit 10 includes a photosensitive drum 1, and around the photosensitive drum 1, a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, a roller 8, a cleaning device are sequentially arranged along the moving direction. A blade 6 is provided. A fixing device 7 is disposed downstream of the photosensitive drum 1 in the sheet conveyance direction. A paper feeding unit 20 is provided at the lower part of the image forming apparatus, and a paper feeding roller 9 is disposed downstream of the paper feeding unit 20 in the paper feeding direction.

The photosensitive drum 1 has an electrostatic latent image formed on the surface thereof, and for example, an amorphous silicon photosensitive member is preferably used. Amorphous silicon photoreceptors include, for example, a carrier injection blocking layer made of Si: H: B: O, a carrier excitation / transport layer (photoconductive layer) made of Si: H, SiC: H, etc. on a conductive substrate. The surface protective layers are sequentially stacked.
The charging device 2 is installed above the photosensitive drum 1 and is a device for uniformly charging the photosensitive drum 1.
The exposure device 3 is a device for forming an electrostatic latent image on the photosensitive drum 1 based on a document image read from an image data input unit (not shown).

  The developing device 4 is a device that forms a toner image by supplying toner to the surface of the photosensitive drum 1 on which the electrostatic latent image is formed. Here, the developing device 4 includes a rotary rack 41 and a plurality of developing devices 4Y, 4M, 4C, and 4K. The rotary rack 41 rotates the plurality of developing devices 4Y, 4M, 4C, and 4K sequentially to the developing positions facing the photosensitive drum while performing rotation by rotating means (not shown) around the rotating shaft 40. is there. Among the plurality of developing devices, the yellow developing device 4Y, the magenta developing device 4M, the cyan developing device 4C, and the black developing device 4K are held side by side in the circumferential direction of the rotary rack 41 in the order of 4Y, 4M, 4C, and 4K. The developing units are arranged at intervals of about 90 degrees in the circumferential direction.

  The transfer device 5 is a device for transferring the toner image on the photosensitive drum 1 to a sheet, and includes an intermediate transfer belt 51, primary transfer rollers 52 and 53, a driving roller 55, a secondary transfer counter roller 54, and a secondary transfer. A roller 56 is provided. The intermediate transfer belt 51 is wound endlessly around the primary transfer rollers 52 and 53, the drive roller 55, and the secondary transfer counter roller 54, and is driven by the drive roller 55, and the toner image formed on the photosensitive drum 1. Plays the role of a transcript that is transferred and temporarily held. The secondary transfer roller 56 is disposed at a position facing the secondary transfer counter roller 54 on the outer peripheral surface of the intermediate transfer belt 51, and plays a role of secondary transfer of the toner image to the transfer material.

  The cleaning blade 6 is a device for cleaning deposits such as residual developer remaining on the photosensitive drum 1, and a blade made of rubber having a hardness of 60 to 80 degrees (for example, urethane rubber) is linear pressure 10. It is in pressure contact with the photosensitive drum at -40 N / m.

  The roller 8 is in contact with the surface of the photosensitive drum 1 and has a buffer function for collecting and discharging toner. Here, the roller 8 has a configuration in which the peripheral surface of the metal shaft is covered with a rubber layer (for example, a foamed rubber layer) having a hardness of 40 to 70 degrees, and a photoconductor by springs (not shown) at both ends of the bearing. The drum 1 is biased at 500 to 2000 gf (spring piece side 250 to 1000 gf). The rotation speed of the roller 8 is usually set to about 1 to 1.5 times that the surface speed at the contact portion is faster than that of the drum.

  The fixing device 7 is a device for fixing the transferred toner image on a sheet. Reference numeral 11 denotes a scraper for peeling off the toner adhering to the roller 8, and reference numeral 12 denotes a collecting screw for collecting the toner adhering to the roller or the toner scraped off by the blade and dropped onto the roller. It is. The recovery screw discharges the recovered residual toner to a waste toner box (not shown).

  Next, the color image forming operation by the 1-drum 4-cycle image forming apparatus as shown in FIG. 1 will be described. At the time of image formation, after the photosensitive drum 1 is charged by the charging device 2, the rotary rack 41 rotates around the rotary shaft 40 provided at the center thereof. Then, the rotary rack 41 stops at the developing position where the developing device 4K corresponding to the first color, black, faces the photosensitive drum 1. In this state, exposure corresponding to black is performed by the exposure device 3, and an electrostatic latent image corresponding to black is formed on the surface of the photosensitive drum 1. The electrostatic latent image is converted into a toner image by the developing device 4K, and the toner image formed on the surface of the photosensitive drum 1 is transferred onto the transfer belt 51 by a transfer bias applied to the primary transfer rollers 52 and 53. . When the formation of the black toner image on the transfer belt 51 is completed in this way, the rotary rack 41 then rotates around the rotation shaft 40 provided at the center thereof, for example, development corresponding to cyan. The container 4C is positioned at the development position. Such an operation is similarly performed for the other colors, cyan, magenta, and yellow, and a full-color toner image is formed on the transfer belt 51.

  As described above, the secondary transfer roller 56 is separated from the transfer belt 51 in the process of primary transfer of the toner image to the intermediate transfer belt 51. On the other hand, when a full-color toner image is formed on the transfer belt 51, the secondary transfer roller 56 is brought into contact with the transfer belt 51. At that time, the transfer belt 51 is applied to the transfer material (recording medium) conveyed from the paper supply unit 20 to the transfer position by the paper supply roller 9 or the like in accordance with the secondary transfer bias applied to the secondary transfer roller 56. The formed full color toner image is transferred. Further, the full-color toner image transferred to the transfer material is fixed to the transfer material by heating and pressing by the fixing unit 7, and the transfer material is discharged from the paper discharge unit 30.

  The residual developer remaining on the photosensitive drum 1 is cleaned by the cleaning blade 6 and discarded in a waste toner container (not shown). The toner remaining on the transfer belt 51 is cleaned by bringing a cleaning device (not shown) of the transfer belt 51 into contact with the transfer belt 51 after the secondary transfer, and is discarded in a waste toner container (not shown). A cleaning device (not shown) for the transfer belt 51 is separated from the transfer belt 51 after cleaning the entire circumference of the transfer belt 51.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to a following example.
(Production Example 1-Production of magnetic black toner particles)
A reactor equipped with a thermometer, a stirrer, and a nitrogen introduction tube was charged with 300 parts by weight of xylene, and under a nitrogen stream, a mixed monomer of 845 parts by weight of styrene and 155 parts by weight of n-butyl acrylate, and di- Using a mixed solution of 8.5 parts by weight of tert-butyl peroxide (polymerization initiator) and 125 parts by weight of xylene, the solution was added dropwise at 170 ° C. over 3 hours. After dripping, it was made to react at 170 degreeC for 1 hour, and superposition | polymerization was completed. Thereafter, the solvent was removed to obtain a binder resin.
In 49 parts by weight of the obtained binder resin, magnetite as magnetic powder (retention force of 5.0 kA / m when 796 kA / m is applied, saturation magnetization of 82 Am ² / kg, residual magnetization of 11 Am ² / kg, number average particle diameter of 0 .25 μm) 45 parts by weight, 3 parts by weight of a wax (“Sazol Wax H1” manufactured by Sazol) as a release agent, and a quaternary ammonium salt (“Bontron P-” manufactured by Orient Chemical Co., Ltd.) as a positive charge control agent 51 ") 3 parts by weight were mixed with a Henschel mixer, then melt-kneaded with a twin screw extruder, cooled, and coarsely pulverized with a hammer mill. Further finely pulverized by a mechanical pulverizer was classified by an airflow classifier to obtain magnetic black toner particles having a volume average particle diameter of 8.0 μm.

(Production Example 2-Production of non-magnetic color toner particles)
80 parts by weight of the binder resin obtained in Production Example 1, 20 parts by weight of 2-ethylhexyl methacrylate, 5 parts by weight of a colorant, 3 parts by weight of low molecular weight polypropylene, a charge control agent ("Bontron S-" manufactured by Orient Chemical Co., Ltd.) 34 ") 2 parts by weight and a mixed solution of 1 part by weight of divinylbenzene as a crosslinking agent was sufficiently dispersed by a ball mill, and then 2 parts by weight of 2,2-azobis (2,4-dimethylvaleronitrile) as a polymerization initiator. Was added. This was added to 400 parts by weight of ion-exchanged water, and further 5 parts by weight of tribasic calcium phosphate and 0.1 part by weight of sodium dodecylbenzenesulfonate were added as suspension stabilizers. For 45 minutes at a rotational speed of 5000 rpm, and a polymerization reaction was performed at 70 ° C. and 100 rpm for 10 hours in a nitrogen atmosphere. Thereafter, acid washing was performed to remove tricalcium phosphate, and a toner particle dispersion was obtained. This dispersion was filtered, washed, and dried to obtain non-magnetic color toner particles of each color (cyan, magenta, yellow). The obtained toner particles had a volume average particle diameter of 7.5 μm and a sphericity of 0.975.
As a colorant, “Toner Cyan BG” manufactured by Clariant Japan is used in the case of cyan, “Toner Magenta EO2” manufactured by Clariant Japan is used in the case of magenta, and manufactured by Clariant Japan in the case of yellow. “Toner Yellow HG” was used.

[Examples 1-9 and Comparative Examples 1-18]
External addition amounts of strontium titanate shown in Table 1 were externally added to the magnetic black toner particles obtained in Production Example 1 and the non-magnetic color toner particles of each color (cyan, magenta, yellow) obtained in Production Example 2. (When the amount of external addition is 0% by weight, it is not added.) Further, 1.0% by weight of silica and 1.0% by weight of titanium oxide are externally added and mixed with a Henschel mixer. Each color of non-magnetic color toner (non-magnetic cyan toner, non-magnetic magenta toner, non-magnetic yellow toner) was obtained.

  Next, in the one-drum four-cycle image forming apparatus shown in FIG. 1, the magnetic developer obtained above is applied to the black developer 4K, and the non-magnetic cyan toner obtained above is applied to the cyan developer 4C. A full color image was formed using the nonmagnetic magenta toner obtained above for the developing unit 4M and the nonmagnetic yellow toner obtained above for the yellow developing unit 4Y. Specifically, an image evaluation pattern is printed at the initial time in a normal temperature and humidity environment (20 ° C., 65% RH) to obtain an initial image, and then 300,000 sheets are continuously printed (printing rate of about 5%), and the image evaluation pattern is again printed. It was printed and used as a post-endurance image. Then, the following evaluation was performed on the initial image and the post-endurance image, respectively. The results are shown in Table 1.

<Image density (ID)>
With respect to the solid image of the initial image and the post-durability image, image density (ID) measurement was performed using a Macbeth reflection densitometer (“RD914” manufactured by Macbeth Co., Ltd.). 1.20 or more and less than 1.30 were evaluated as “Δ”, and less than 1.20 were evaluated as “x”.
<Cover (FD)>
For the solid image of the initial image and the post-durability image, the fog (FD) measurement was performed using a reflection densitometer (“TC-6D” manufactured by Tokyo Electric Decoration Co., Ltd.), and “○” indicates that the fog (FD) is 0.010 or less. More than 0.010 and less than 0.020 were evaluated as “Δ”, and 0.020 or more were evaluated as “x”.

<Cleaning performance>
When the initial image was obtained and when the post-durability image was obtained, the surface of the photoreceptor drum was visually observed and evaluated according to the following criteria.
○: No deposit is formed on the surface of the photosensitive drum.
Δ: A deposit is formed on the surface of the photosensitive drum, but does not appear in the image.
X: A deposit is formed on the surface of the photosensitive drum and is completely fixed.

  Table 1 shows the following. That is, in Examples 1 to 9, since the amount of strontium titanate added in each color toner is within the range of the present invention, excellent cleaning performance can be obtained over a long period of time and good over a long period of time. It was clear that full color images could be formed with image quality.

  On the other hand, Comparative Example 1 is a case where strontium titanate is not added to either the black toner or each color toner. In this case, the photosensitive drum is excessively shaved due to the remarkable polishing performance of the black toner, and the cleaning performance deteriorates due to the influence (the drum film thickness decreases and the pressure contact force between the cleaning blade and the photosensitive drum decreases). Deterioration in quality (degradation of image density (ID), fogging, dash mark associated with deterioration in cleaning performance) occurred. Therefore, in Comparative Example 1, the printing durability evaluation was stopped at about 50,000 sheets.

In Comparative Example 2, the amount of external addition of strontium titanate in the black toner is too small. In this case, as in Comparative Example 1, it was clear that the photosensitive drum was excessively shaved due to the polishing performance of the black toner, and that the image quality deteriorated as the image formation lasted for a long time.
In Comparative Examples 3 to 5, strontium titanate is blended in all colors, and the amount of strontium titanate added to the toner of any one color is too large, and the total amount of toner of each color is out of the total amount. This is the case when the amount added exceeds the specified range. It was found that the polishing performance of the color toner deteriorated by adding an excess of strontium titanate to the color toner, and cleaning failure occurred when the image formation was performed for a long time. It has also been found that color image density (ID) is reduced and fogging occurs as a result of long-term image formation due to the effect of mixing strontium titanate in the color toner.

  In Comparative Examples 6 to 11, an excessive amount of strontium titanate is blended with one or two of the color toners, and the total amount of toner added for each color color exceeds the specified range. Is the case. It was found that the polishing performance of the color toner deteriorated by adding an excess of strontium titanate to the color toner, and cleaning failure occurred when the image formation was performed for a long time. In addition, the effect of blending strontium titanate into one or two colors instead of all colors causes the development performance of each color to be unbalanced, resulting in a decrease in color image density (ID) and fogging. It was.

  In Comparative Example 12, strontium titanate is not blended in the black toner, but excess strontium titanate is blended in the color toner of all colors. Since black toner does not contain strontium titanate, the black toner exhibits high polishing performance and also improves development performance. On the other hand, since the color toner contains an excess of strontium titanate in all colors, the color polishing performance is lowered and the development performance is also lowered. As a result, the photoconductive drum is excessively shaved, and the cleaning performance deteriorates due to the influence. Also, when the image formation is performed for a long time, the image quality deteriorates (image density (ID) decreases, fogging, a dash mark associated with the cleaning performance decreases). I found it to happen.

  Comparative Examples 13 to 18 are cases where strontium titanate is excessively blended only in one or two color toners among the respective colors. Since black toner does not contain strontium titanate, the black toner exhibits high polishing performance and improves development performance. In addition, since strontium titanate is blended only in one or two color toners instead of all color colors, the polishing performance is reduced and development performance is not as great as when blended in all color colors. Also decreases. As a result, the photoconductive drum is excessively shaved, and the cleaning performance deteriorates due to the influence. Also, when the image formation is performed for a long time, the image quality deteriorates (image density (ID) decreases, fogging, a dash mark associated with the cleaning performance decreases). I found it to happen.

1 is a schematic diagram of a one-drum four-cycle color image forming apparatus according to an embodiment of the present invention.

Explanation of symbols

1: photosensitive drum, 2: charging device, 3: exposure device, 4: developing device, 4Y: yellow developing device, 4M: magenta developing device, 4C: cyan developing device, 4K: black developing device, 5: transfer device, 6: cleaning blade, 7: fixing device, 8: roller, 9: paper feed roller, 10: image forming unit, 11: scraper, 12: recovery screw, 20: paper feed unit, 30: paper discharge unit, 40: rotation Shaft, 41: Rotary rack, 51: Intermediate transfer belt, 52 and 53: Primary transfer roller, 54: Secondary transfer counter roller, 55: Drive roller, 56: Secondary transfer roller, 100: Color image forming apparatus

Claims (3)

In an image forming apparatus using black magnetic toner and color non-magnetic toner,
At least 1% by weight of strontium titanate is externally added to the black magnetic toner, and the external addition amount of strontium titanate externally added to the color nonmagnetic toner is the following (I) and (II). An image forming apparatus characterized by being in a satisfactory range.
(I) The amount of external addition per color non-magnetic toner is 0.2% by weight or less (including 0% by weight).
(II) When the external addition amount of strontium titanate of the black magnetic toner is X wt%, the total external addition amount of all colors of the color non-magnetic toner is (X-1) wt% or less.   The image forming apparatus according to claim 1, wherein the black magnetic toner is obtained by a pulverization method, and the color non-magnetic toner is obtained by a polymerization method. The image forming apparatus according to claim 1, wherein the image forming apparatus has a single photosensitive drum.

Images