Image forming apparatus and image forming method

Abstract

To provide an image forming apparatus and an image forming method that can maintain good image quality because, even if developer approaches the end of its life, the amount of charge of the developer is stabilized.SOLUTION: An image forming apparatus comprises a developer tank filled in advance with a two-component developer including initial toner and carrier, and has the following configuration. A toner cartridge includes a first toner cartridge that is initially mounted and used in the image forming apparatus, and a second toner cartridge that is mounted and used in the second and subsequent replacement at earliest. A toner filled into the first toner cartridge is defined as a first supply toner, and a toner filled into the second toner cartridge is defined as a second supply toner. Of the amounts of external additive added to the initial toner, first supply toner, and second supply toner, when the amounts of small-particle diameter silica particles added are defined as S0, S1, and S2, respectively, and the amount of large-particle diameter silica particles added are defined as L0, L1, and L2, respectively, the relationships of S0≤S1<S2 and L0≥L1>L2 are satisfied.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus and an image forming method.

Background Art

[0002] In image forming apparatuses such as copiers, multifunction peripherals, printers, and facsimile machines that use the electrophotographic method, generally, toner is attached to an electrostatic latent image formed on the surface of a photoreceptor to form a toner image. Since the toner moves from the developing unit to the photoreceptor by the amount used for forming the toner image, a corresponding amount of toner is replenished from the toner cartridge into the developing unit. Further, as the developer filled in the developing unit, a two-component developer containing toner in which an external additive is attached to the surface of toner particles (toner core) and a carrier is widely used.

[0003] Patent Document 1 discloses an image forming apparatus that replenishes toners having different particle diameters such that the particle diameter of the replenishing toner replenished into the apparatus over time is smaller than the particle diameter of the initial replenishing toner initially replenished into the image forming apparatus.

[0004] Patent Document 2 discloses that in an image forming apparatus using a developer containing a negatively charged carrier and a positively charged toner, silica, titanium oxide, or a mixture thereof is used as an external additive for the initial toner pre-filled in the developing unit and the replenishing toner replenished to the apparatus, and the amount of the external additive added to the replenishing toner is larger than that of the initial toner.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a two-component developer, when the carrier deteriorates due to spent, carrier coat peeling, etc., there is a problem that the charge amount decreases as the life (product life) progresses. This problem has become more prominent with the low-temperature fixing (low melting point) and small particle size of the toner, as well as the speeding up of the process of the image forming apparatus. Note that spent is a phenomenon in which the constituent components of the toner adhere to the carrier and contaminate the carrier.

[0007] Conventionally, in order to extend the life of the developer, it has been common to employ a two-layer coated ferrite carrier with high deterioration resistance (resistance to spent, carrier coat peeling, etc.) or to reduce the addition amount of the external additive of the toner. Therefore, it has been difficult to combine an iron powder carrier, which is a carrier that is relatively likely to cause spent, with a low melting point toner.

[0008] The content of the present disclosure has been found in view of such circumstances, and the main object is to provide an image forming apparatus and an image forming method capable of maintaining good image quality because the charge amount of the developer is stable even as the life progresses.

Means for Solving the Problems

[0009] The image forming apparatus of the present disclosure made to solve the above problems is an image forming apparatus in which a two-component developer including an initial toner and a carrier is preliminarily filled in a developing tank, and replenishing toner is replenished from a toner cartridge into the developing tank as development is performed, and is characterized by including the following constituent requirements (A) to (C).

[0010] (A): The toner cartridge for the image forming apparatus includes a first toner cartridge that is first mounted and used with respect to the image forming apparatus, and a second toner cartridge that is mounted and used at least from the second time onward.

[0011] (B): When the toner filled in the first and second toner cartridges is used as the first and second replenishing toners respectively, the initial toner, the first replenishing toner, and the second replenishing toner are toners with external additives attached to the surface of the toner particles.

[0012] (C): Among the amounts [parts by mass] of the external additive added to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner, when the amounts of the small particle size silica particles having an average primary particle diameter of less than 20 nm are S0, S1, and S2 respectively, and the amounts of the large particle size silica particles having an average primary particle diameter of 20 nm or more are L0, L1, and L2 respectively, the relationships of the following formulas (1) and (2) are satisfied. S0 ≦ S1 < S2 ···(1) L0 ≧ L1 > L2 ···(2)

[0013] In the above image forming apparatus, among the initial toner, the first replenishing toner, and the second replenishing toner, it is preferable that at least the second replenishing toner contains titanium oxide particles as an external additive.

[0014] Further, in the above image forming apparatus, when the amounts [parts by mass] of the titanium oxide particles as an external additive added to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner are A0, A1, and A2 respectively, it is preferable that the relationship of A0 ≦ A1 < A2 is satisfied.

[0015] Further, in the above image forming apparatus, it is preferable that the relationships of the following formulas (3), (4), and (5) are satisfied. A0 < S0 < L0 ···(3) A1 < S1 < L1 ···(4) L2 < S2 < A2 ···(5)

[0016] Further, in the above image forming apparatus, when the coating rates of the toner particles by the silica particles as an external additive in the initial toner, the first replenishing toner, and the second replenishing toner are C0, C1, and C2 respectively, it is preferable that C0 and C1 are 80% or more and 110% or less, and C2 is 100% or more and 120% or less.

[0017] Further, in the above image forming apparatus, assuming that the absolute values of the charge amounts [μC / g] of the initial toner, the first replenishing toner, and the second replenishing toner are Q0, Q1, and Q2, respectively, it is preferable that the relationship Q0 ≦ Q1 < Q2 is satisfied.

[0018] Also, in the above image forming apparatus, the external additive of the initial toner and the external additive of the first replenishing toner may have the same composition.

[0019] Also, in the above image forming apparatus, it is preferable that the toner particles of the initial toner, the first replenishing toner, and the second replenishing toner have a glass transition temperature of 50°C or higher and 65°C or lower, and a softening temperature of 105°C or higher and 130°C or lower.

[0020] The image forming method of the present disclosure made to solve the above problems includes an electrostatic latent image forming step of forming an electrostatic latent image on an electrostatic latent image carrier, a developing step of developing the electrostatic latent image formed on the electrostatic latent image carrier as a toner image using a two-component developer including an initial toner and a carrier, a transfer step of transferring the toner image formed on the electrostatic latent image carrier to a recording medium, a fixing step of fixing the toner image transferred to the storage medium, and a toner replenishing step of replenishing a replenishing toner to the two-component developer. The image forming method is characterized by including the following constituent elements (D) to (F).

[0021] (D) The toner replenishing step includes a first replenishing step of replenishing a first replenishing toner as the first toner replenishment to the two-component developer, and a second replenishing step of replenishing a second replenishing toner after the first replenishing step.

[0022] (E): The initial toner, the first replenishing toner, and the second replenishing toner are toners having an external additive attached to the surface of toner particles.

[0023] (F) Among the amounts [parts by mass] of the external additive added to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner, the amounts of the small particle size silica particles having an average primary particle size of less than 20 nm are denoted as S0, S1, and S2, respectively, and the amounts of the large particle size silica particles having an average primary particle size of 20 nm or more are denoted as L0, L1, and L2, respectively. Then, the relationships of the following formulas (1) and (2) are satisfied. S0 ≦ S1 < S2 ··· (1) L0 ≧ L1 > L2 ··· (2)

Advantages of the Invention

[0024] In the image forming apparatus and the image forming method of the present disclosure, even as the life progresses, the charge amount of the developer remains stable. As a result, the occurrence of fogging and toner scattering is suppressed. Consequently, even as the life of the developer progresses, good image quality can be maintained.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0026] Hereinafter, the image forming apparatus and the image forming method of the present disclosure will be described in detail. First, the features as the image forming apparatus and the image forming method will be described, and then the configurations of the toner and the carrier to be used will be described.

[0027] 1. Image Forming Apparatus and Image Forming Method The image forming apparatus according to the present embodiment is an image forming apparatus in which a two-component developer containing initial toner and carrier is preliminarily filled in a developing tank, and replenishing toner is replenished from a toner cartridge into the developing tank as development is performed. The toner cartridge is detachable from the image forming apparatus, and toner can be continuously replenished by replacing it with a new toner cartridge. The initial toner and the replenishing toner used in the image forming apparatus according to the present embodiment are toners having an external additive attached to the surface of toner particles.

[0028] In the image forming apparatus according to the present embodiment, an electrostatic latent image forming step of forming an electrostatic latent image on an electrostatic latent image carrier (for example, a photoreceptor), a developing step of developing the electrostatic latent image as a toner image using a two-component developer, a transfer step of transferring the toner image formed on the electrostatic latent image carrier to a recording medium (for example, recording paper), a fixing step of fixing the toner image transferred to the recording medium, and a toner replenishing step of replenishing the two-component developer with replenishing toner are performed. An image forming method including these steps is implemented.

[0029] For the image forming apparatus according to the present embodiment, a plurality of toner cartridges filled with toners having different external additive compositions are used. In other words, the toner cartridge for the image forming apparatus according to the present embodiment includes a first toner cartridge that is first attached to and used with the image forming apparatus, and a second toner cartridge that is attached to and used with the image forming apparatus at least for the second time and later. In the present disclosure, the toners filled in the first and second toner cartridges are referred to as the first and second replenishing toners, respectively.

[0030] In the embodiments described below, the first toner cartridge is initially installed in the image forming apparatus, and then the second toner cartridge is installed when the toner cartridge is replaced. However, the usage and replacement patterns of the toner cartridge are not limited to this. For example, it may be a pattern where the first toner cartridge is replaced even in the first replacement and the second toner cartridge is replaced in the replacements after the second time. Also, between the use of the first toner cartridge and the use of the second toner cartridge, it may be a pattern where another toner cartridge filled with a replenishing toner having a composition intermediate between the first and second replenishing toners is used. Furthermore, it may be a pattern where a period for using the first toner cartridge again is provided after using the second toner cartridge, and then a period for using the second toner cartridge again is provided next.

[0031] As an example of realizing such usage and replacement patterns of the toner cartridge, when introducing and installing the image forming apparatus, a service technician installs the first toner cartridge, and then when replacing the toner cartridge, the second toner cartridge is used.

[0032] In the image forming apparatus according to this embodiment, among the addition amounts [parts by mass] of the external additive with respect to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner, when the addition amounts of the silica particles with a small particle diameter having an average primary particle diameter of less than 20 nm are S0, S1, and S2, respectively, and the addition amounts of the silica particles with a large particle diameter having an average primary particle diameter of 20 nm or more are L0, L1, and L2, respectively, the relationships of the following formulas (1) and (2) are satisfied. S0 ≦ S1 < S2 ···(1) L0 ≧ L1 > L2 ···(2)

[0033] Regarding the above formula (1), the value of S2 - S0 or S2 - S1, which is the difference in the addition amounts, is preferably 0.1 part by mass or more and 1 part by mass or less, and more preferably 0.2 part by mass or more and 0.8 part by mass or less. When the difference in the addition amounts is less than the above lower limit, there is a risk that the amount of waste toner increases, and when the difference in the addition amounts exceeds the above upper limit, there is a risk that the image density decreases as the life progresses.

[0034] Regarding the above formula (2), the value of L1 - L2 or L0 - L2, which is the difference in the addition amount, is preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more. If the difference in the addition amount is less than the above lower limit, the amount of waste toner may increase. Also, the upper limit of the value of L1 - L2 or L0 - L2 is preferably 1 part by mass or less.

[0035] By satisfying the above formula (1), the image forming apparatus according to the present embodiment can maintain a high charge amount of the developer, which conventionally decreased as life progressed, even as life progresses. Also, by satisfying the above formula (2), developability at the initial stage of life can be ensured. Consequently, the image forming apparatus according to the present embodiment can maintain good image quality even as life progresses.

[0036] Next, this mechanism will be described with reference to FIGS. 1 to 5. In these figures, the same toner is used for the initial toner and the first replenishing toner, similar to Examples 1-1 to 1-5 (except Example 1-6) described later. In other words, it is the case where the above formula (1) is S0 = S1 < S2 and the above formula (2) is L0 = L1 > L2. In this way, by using the same toner for the initial toner and the first replenishing toner, developability at the initial stage of life can be ensured.

[0037] As in Example 1-6 described later, by using toners with different external additive compositions for the initial toner and the first replenishing toner, an image forming apparatus can be obtained in which the above formula (1) is S0 < S1 < S2 and the above formula (2) is L0 > L1 > L2. In this case, while the cost becomes disadvantageous due to an increase in the types of toners to be prepared, it is considered that the effect of maintaining good image quality even as life progresses can be more easily obtained.

[0038] FIG. 1 is a schematic diagram showing the configuration of the first replenishing toner T1 filled in the first toner cartridge TC1, and FIG. 2 is a schematic diagram showing the configuration of the second replenishing toner T2 filled in the second toner cartridge TC2. As shown in these figures, in the present embodiment, the small particle size silica particles 2 as an external additive are added more to the second replenishing toner T2 than to the first replenishing toner T1, and the large particle size silica particles 3 are added more to the first replenishing toner T1 than to the second replenishing toner T2.

[0039] FIG. 3 is a schematic diagram exemplifying the state of the toner and the carrier in the developing unit at the initial stage of use of the image forming apparatus. As shown in FIG. 3, at this stage, the initial toner, the first replenishing toner T1, and the carrier C are present in the developing unit.

[0040] FIG. 4 is a schematic diagram exemplifying the state of the toner and the carrier in the developing unit immediately after replacing with the second toner cartridge TC2. As shown in FIG. 4, due to the use of the first toner cartridge TC1, spent where the binder resin 1 adheres to the carrier C and external additive contamination where the external additive detaches from the toner T1 and adheres to the carrier C occur partially. If the use of the first toner cartridge TC1 is continued as it is, as in the conventional case, due to the deterioration of the carrier, the charge amount of the developer decreases as the life progresses. However, in the present embodiment, since the second toner cartridge TC2 is replaced here, the toner in the developing unit is gradually replaced with the toner T2.

[0041] FIG. 5 is a schematic diagram exemplifying a state where the toner in the developing unit has been replaced with the second replenishing toner T2 after a lapse of time from the state of FIG. 4. Thus, as the toner in the developing unit is replaced and the toner to be used satisfies the relationships of the above formulas (1) and (2), the charge amount of the developer can be maintained high even as the life progresses. Consequently, the image forming apparatus according to the present embodiment can maintain good image quality even as the life progresses.

[0042] 2. Toner Particles The initial toner and the replenishing toner according to this embodiment are those in which an external additive adheres to the surface of toner particles (toner core). The toner particles according to this embodiment are composed of internal additives such as a colorant, a release agent, and a charge control agent and a binder resin, and the internal additives are dispersed in the binder resin. Further, if necessary, optional components may be contained within a range that does not impair the effects according to the present disclosure. The volume average particle diameter of the toner particles in the initial toner and the replenishing toner is, for example, 3 μm or more and 10 μm or less, preferably 4 μm or more and 9 μm or less, and more preferably 5 μm or more and 8 μm or less. When the volume average particle diameter of the toner particles is less than the above lower limit, the adhesion force between the toner and the carrier significantly increases, making it difficult to replace the initial toner with the replenishing toner, and there is a risk that the non-charged toner may cause fogging. When the volume average particle diameter of the toner particles exceeds the upper limit, the adhesion force between the toner and the carrier weakens, the replacement from the initial toner to the replenishing toner proceeds rapidly, and there is a risk that the uniformity of the image density may decrease (non-uniformity occurs in the image density).

[0043] The toner particles according to this embodiment are preferably low melting point toners. Specifically, the glass transition temperature is preferably 50°C or more and 65°C or less, and more preferably 50°C or more and 60°C or less. Further, the softening temperature is preferably 105°C or more and 130°C or less, and more preferably 110°C or more and 125°C or less. The glass transition temperature and the softening temperature of the toner particles can be adjusted by the types and blending ratios of the constituent components, and by being within the above ranges, both low temperature fixability and heat resistant storability can be achieved.

[0044] <Binder resin> The toner particles constituting the initial toner and the replenishing toner according to this embodiment contain a binder resin. The binder resin is not particularly limited, and resins used in the electrophotography field can be used. For example, polyester resins, polystyrene resins such as styrene-acrylic resins, (meth)acrylate resins, polyolefin resins, polyurethane resins, and epoxy resins can be mentioned. These resins may be used alone or in combination of two or more. Among these, polystyrene resins and polyester resins are preferred, and polyester resins are particularly preferred.

[0045] As the polystyrene resin, a styrene-acrylic resin (styrene acrylic copolymer resin) is preferred. Examples of the styrene monomer that can be used as a resin raw material include styrene derivatives such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, and 2,4-dimethylstyrene. Examples of the acrylic monomer include acrylic acid derivatives and methacrylic acid derivatives such as acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, and dimethylaminoethyl methacrylate.

[0046] Furthermore, vinyl monomers such as maleic anhydride, monomethyl maleate, monoethyl maleate, monophenyl maleate, monoallyl maleate, and divinylbenzene may be used as the resin raw materials.

[0047] The polyester resin used for the adhesive resin is usually obtained by subjecting at least one selected from divalent alcohol components and polyhydric alcohol components having a valence of 3 or more and at least one selected from divalent carboxylic acids and polyhydric carboxylic acids having a valence of 3 or more to a polycondensation reaction through an esterification reaction or a transesterification reaction by a known method.

[0048] The conditions in the polycondensation reaction may be appropriately set according to the reactivity of the monomer components, and the reaction may be terminated when the polymer has suitable physical properties. For example, the reaction temperature is about 170°C to 250°C, and the reaction pressure is about 5 mmHg to normal pressure.

[0049] Examples of the divalent alcohol component include alkylene oxide adducts of bisphenol A such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene(6)-2,2-bis(4-hydroxyphenyl)propane; diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A; propylene adduct of bisphenol A; ethylene adduct of bisphenol A; and hydrogenated bisphenol A.

[0050] Examples of the polyhydric alcohol component having a valency of 3 or more include sorbitol, 1,2,3,6 - hexanetetrol, 1,4 - sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4 - butanetriol, 1,2,5 - pentanetriol, glycerol, 2 - methylpropanetriol, 2 - methyl - 1,2,4 - butanetriol, trimethylolethane, trimethylolpropane, 1,3,5 - trihydroxymethylbenzene, and the like.

[0051] In the toner particles according to the present embodiment, one of the above - mentioned divalent alcohol component and polyhydric alcohol component having a valency of 3 or more may be used alone, or two or more thereof may be used in combination.

[0052] Examples of the divalent carboxylic acid 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, azelaic acid, malonic acid, n - dodecenyl succinic acid, n - dodecyl succinic acid, n - octyl succinic acid, isooctenyl succinic acid, isooctyl succinic acid, and their acid anhydrides, lower alkyl esters, and the like.

[0053] Examples of the polyhydric carboxylic acid having a valency of 3 or more include 1,2,4 - benzenetricarboxylic acid, 1,2,5 - benzenetricarboxylic acid, 2,5,7 - naphthalenetricarboxylic acid, 1,2,4 - naphthalenetricarboxylic acid, 1,2,4 - butanetricarboxylic acid, 1,2,5 - hexanetricarboxylic acid, 1,3 - dicarboxyl - 2 - methyl - 2 - methylenecarboxypropane, 1,2,4 - cyclohexanetricarboxylic acid, tetra(methylene carboxyl)methane, 1,2,7,8 - octanetetracarboxylic acid, pyromellitic acid, Empol trimer acid, and their acid anhydrides, lower alkyl esters, and the like.

[0054] In the toner particles according to this embodiment, one of the above-mentioned divalent carboxylic acids and trivalent or higher polyvalent carboxylic acids may be used alone, or two or more thereof may be used in combination.

[0055] The weight average molecular weight of the polyester resin is preferably 3,000 or more and 50,000 or less. If the weight average molecular weight is less than the above lower limit, the peelability on the high temperature side of the fixable region (non-offset region) may deteriorate. On the other hand, if the weight average molecular weight exceeds the above upper limit, the low temperature fixability may deteriorate.

[0056] Also, the polyester resin preferably has an acid value of 5 mgKOH / g or more and 30 mgKOH / g or less. If the acid value is less than the above lower limit, the chargeability of the polyester resin decreases, and it becomes difficult for the charge control agent to disperse in the polyester resin, which may have an adverse effect on the charge rising property and the charge stability during continuous printing. On the other hand, if the acid value exceeds the above upper limit, the hygroscopicity may increase and the chargeability may become unstable.

[0057] <Internal additive> - Wax - The toner particles according to this embodiment may contain wax as a release agent. As the wax, waxes used in the electrophotography field can be used, for example, paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, polypropylene wax, carnauba wax, synthetic ester wax, and the like. These waxes may be used alone or in combination of two or more. The content of wax in the toner particles is preferably 0.5% by mass or more and 10% by mass or less.

[0058] - Colorant - The toner particles according to this embodiment may contain a colorant. As the colorant, organic pigments, organic dyes, inorganic pigments, inorganic dyes, etc. used in the electrophotography field can be used.

[0059] Examples of the black colorant include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, non-magnetic ferrite, magnetic ferrite, magnetite, and the like.

[0060] Examples of the yellow colorant include C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 17, C.I. Pigment Yellow 74, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 138, C.I. Pigment Yellow 180, C.I. Pigment Yellow 185, and the like.

[0061] Examples of the magenta colorant include C.I. Pigment Red 48:1, C.I. Pigment Red 53:1, C.I. Pigment Red 57:1, C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Pigment Red 178, C.I. Pigment Red 222, and the like.

[0062] Examples of the cyan colorant include C.I. Pigment Blue 15, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 16, C.I. Pigment Blue 60, and the like.

[0063] The content of the colorant in the toner particles is preferably 3 to 10 parts by mass. In addition, the colorant may be used in the form of a masterbatch in order to be uniformly dispersed in the binder resin.

[0064] The masterbatch can be produced, for example, by dry-mixing a binder resin and a colorant with a mixer, then melt-kneading the mixture with a kneader to obtain a kneaded product, and pulverizing (coarse-pulverizing) the kneaded product with a pulverizer.

[0065] Examples of the mixer include Henschel-type mixers such as Henschel mixer (trade name, manufactured by Nippon Coke & Engineering Co., Ltd.), Super mixer (trade name, manufactured by Kawata Co., Ltd.), and Mechanomill (trade name, manufactured by Okada Seiko Co., Ltd.), and Ongmill (trade name, manufactured by Hosokawa Micron Corporation), Hybridization system (trade name, manufactured by Nara Machinery Co., Ltd.), and Cosmos system (trade name, manufactured by Kawasaki Heavy Industries, Ltd.).

[0066] Examples of the kneader include kneaders such as a kneader, a twin-screw extruder, a two-roll mill, a three-roll mill, and a labo blast mill. Specific kneaders include, for example, single-screw or twin-screw extruders such as TEM-100B (trade name, manufactured by Shibaura Machine Co., Ltd.), PCM-65 / 87, and PCM-30 (both trade names, manufactured by Ikegai Corporation), and open-roll kneaders such as Neidex (trade name, manufactured by Nippon Coke & Engineering Co., Ltd.).

[0067] Examples of the pulverizer include a hammer mill, a cutting mill, and a speed mill. The average particle size (e.g., volume average particle size) of the masterbatch is usually about 1 mm to 5 mm.

[0068] -Charge control agent- The toner particles according to this embodiment may contain a charge control agent. The charge control agent is added to impart a preferable charge property to the toner. The charge control agent is not particularly limited, and charge control agents for positive charge control and negative charge control used in the electrophotography field can be used.

[0069] Examples of the charge control agent for positive charge control include quaternary ammonium salts, pyrimidine compounds, triphenylmethane derivatives, guanidine salts, and amidine salts.

[0070] Examples of the charge control agent for negative charge control include metal-containing azo compounds, azo complex dyes, metal complexes and metal salts of salicylic acid and its derivatives (the metal is chromium, zinc, zirconium, etc.), organic bentonite compounds, and boron compounds.

[0071] These charge control agents may be used alone or in combination of two or more. The content of the charge control agent in the toner particles is preferably 0.5% by mass or more and 5% by mass or less.

[0072] 3. External Additive <Silica Particles> The initial toner, the first replenishing toner, and the second replenishing toner used in the image forming apparatus according to the present embodiment include, as external additives, small particle size silica particles having an average primary particle size of less than 20 nm and large particle size silica particles having an average primary particle size of 20 nm or more so as to satisfy the relationships of the above formulas (1) and (2).

[0073] Examples of the average primary particle size of the small particle size silica particles include 4 nm or more and less than 20 nm, and preferably 5 nm or more and 10 nm or less. Examples of the average primary particle size of the large particle size silica particles include 20 nm or more and 50 nm or less, and preferably 25 nm or less and 40 nm or less.

[0074] Examples of the addition amount of the small particle size silica particles with respect to 100 parts by mass of the toner particles include 0.3 part by mass or more and 0.65 part by mass or less in the initial toner and the first replenishing toner, and preferably 0.35 part by mass or more and 0.55 part by mass or less. Further, in the second replenishing toner, it is 0.5 part by mass or more and 0.9 part by mass or less, and preferably 0.6 part by mass or more and 0.8 part by mass or less. By the addition amount being within the above range, the absolute value of the charge amount of the toner can be appropriately increased, the occurrence of fog can be suppressed, and the amount of waste toner can be reduced. If the addition amount exceeds the above upper limit, there is a risk of high-charge fog occurring or the spent on the carrier deteriorating.

[0075] As the addition amount of the large particle size silica particles with respect to 100 parts by mass of the toner particles, in the initial toner and the first replenishing toner, it is 0.8 parts by mass or more and 1.2 parts by mass or less, and preferably 0.9 parts by mass or more and 1.1 parts by mass or less. Further, in the second replenishing toner, it is 0.8 parts by mass or less, preferably 0.5 parts by mass or less, and more preferably not added. By the addition amount being within the above range, the spacer effect is appropriately exhibited, and the developability can be enhanced. When the addition amount exceeds the above upper limit, there is a possibility that the spent on the carrier deteriorates or the amount of waste toner increases.

[0076] As the silica particles as an external additive, silica particles commonly used in the art, for example, fumed silica obtained by burning silicon tetrachloride, dry method silica particles such as arc method silica obtained by atomizing silica in the gas phase with high energy such as plasma; wet method silica particles such as precipitation method silica synthesized under alkaline conditions using an aqueous sodium silicate solution as a raw material, gel method silica synthesized under acidic conditions; colloidal silica particles obtained by polymerizing acidic silicic acid into an alkaline state; sol-gel method silica particles obtained by hydrolysis of an organic silane compound, etc. may be mentioned. In order to improve the electrical characteristics of the photoreceptor, a hydrophobic treatment may be performed by surface coating with a surface treatment agent such as a silane coupling agent.

[0077] As the method of surface coating with a silane coupling agent, surface treatments commonly used in the art such as with hexamethyldisilazane (HMDS), dimethyl-dichlorosilane (DDS), octylsilane (OTAS), polydimethylsiloxane (PDMS), etc. may be mentioned. In the examples described later, those surface-treated with DDS are used as the small particle size silica particles, and those surface-treated with PMDS are used as the large particle size silica particles.

[0078] As the silica particles as an external additive, commercially available hydrophobic-treated silica particles may be used, or non-hydrophobic-treated silica particles may be subjected to treatment and then used.

[0079] Regarding the initial toner, the first replenishing toner, and the second replenishing toner according to this embodiment, when the coating rates of the toner particles by the silica particles as the external additive are C0, C1, and C2 respectively, it is preferable that C0 and C1 are 80% or more and 110% or less, and more preferably 95% or more and 105% or less. Also, it is preferable that C2 is 100% or more and 120% or less, and more preferably 110% or more and 118% or less. By designing the coating rate in the second replenishing toner to be higher than that in the initial toner and the first replenishing toner, the spacer effect by the second replenishing toner becomes higher, so that it is possible to suppress the decrease in the bulk density due to the looseness of the developer as the life progresses, and also to maintain the charge amount of the developer.

[0080] Regarding the absolute values of the charge amounts [μC / g] of the initial toner, the first replenishing toner, and the second replenishing toner according to this embodiment, which are Q0, Q1, and Q2 respectively, it is preferable to satisfy the relationship Q0 ≦ Q1 < Q2. Thereby, the occurrence of fogging and toner scattering can be suppressed.

[0081] When the initial toner and the first replenishing toner are not made common and the relationship Q0 < Q1 < Q2 is satisfied, while the cost becomes disadvantageous due to an increase in the types of toners to be prepared, it is considered that the effect of maintaining good image quality even as the life progresses can be more easily obtained.

[0082] <Titanium oxide particles> Among the initial toner, the first replenishing toner, and the second replenishing toner used in the image forming apparatus according to this embodiment, it is preferable that at least the second replenishing toner contains titanium oxide particles as an external additive. By using titanium oxide particles as the external additive of the second replenishing toner, the charge rising property of the developer is improved, so that the amount of waste toner can be reduced, and the increase in the resistance of the developer as the life progresses can be suppressed.

[0083] The titanium oxide particles may be anatase-type titanium oxide particles or rutile-type titanium oxide particles. As a method for producing anatase-type titanium oxide particles, for example, as described in JP-A-2000-10335, a solution obtained by dissolving a raw material such as ilmenite ore in sulfuric acid is hydrolyzed and granulated, dried, and then calcined at a high temperature to obtain titanium oxide particles. As a method for producing rutile-type titanium oxide particles, for example, as described in JP-A-2001-26423, an aqueous titanium tetrachloride solution is hydrolyzed to prepare a fine titania sol having rutile nuclei, which is separated and then heat-treated to obtain titanium oxide particles.

[0084] The surface of the titanium oxide particles may be hydrophobized. Examples of the hydrophobization treatment include a treatment of coating the surface with a silane coupling agent. Examples of the method of surface coating with a silane coupling agent include surface treatments commonly used in the art using hexamethyldisilazane (HMDS), dimethyl-dichlorosilane (DDS), octylsilane (OTAS), polydimethylsiloxane (PDMS), etc. In the examples described later, those surface-treated with i-butyltrimethoxysilane are used.

[0085] As the titanium oxide particles as an external additive, commercially available hydrophobized titanium oxide particles may be used, or non-hydrophobized titanium oxide particles may be treated and then used.

[0086] The average primary particle diameter of the titanium oxide particles is preferably 20 nm or more and less than 60 nm, and more preferably 3 nm or more and 50 nm or less.

[0087] The amount of titanium oxide particles added to 100 parts by mass of toner particles is 0.3 parts by mass or more and 1.2 parts by mass or less in the second replenishing toner, preferably 0.5 parts by mass or more and 1.0 parts by mass or less. In the initial toner and the first replenishing toner, it is 0.5 parts by mass or less, preferably 0.3 parts by mass or less, and more preferably not added. When the amount of titanium oxide particles added in the second replenishing toner is within the above range, it is possible to suppress an increase in the resistance of the developer as the life progresses and prevent deterioration of developability. When the amount of titanium oxide particles added in the second replenishing toner is less than the above lower limit, there is a risk that the amount of waste toner increases. When the amount of titanium oxide particles added in the second replenishing toner exceeds the above upper limit, there is a risk that fogging deteriorates.

[0088] In the initial toner, the first replenishing toner, and the second replenishing toner according to the present embodiment, when the amounts [parts by mass] of titanium oxide particles as an external additive added to 100 parts by mass of toner particles are A0, A1, and A2, respectively, it is preferable to satisfy the relationship A0 ≦ A1 < A2. By satisfying this relationship, it is possible to suppress an increase in the resistance of the developer as the life progresses and enhance the charge rising property of the developer. Consequently, the amount of waste toner can be reduced and the occurrence of toner scattering can be suppressed. As the value of A2 - A0 or A2 - A1, which is the difference in the amount of titanium oxide particles added, it is preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more.

[0089] When the initial toner and the first replenishing toner are not made common and the relationship A0 < A1 < A2 is satisfied, while the cost becomes disadvantageous due to an increase in the types of toner to be prepared, it is considered that the effect of maintaining good image quality even as the life progresses can be more easily obtained.

[0090] Regarding the initial toner, the first replenishing toner, and the second replenishing toner according to this embodiment, the relationship of the addition amounts of the small particle size silica particles, the large particle size silica particles, and the titanium oxide particles as external additives preferably satisfies the relationships of the following formulas (3), (4), and (5). When the initial toner and the first replenishing toner are common (when the composition of the external additive is the same) as in Examples 1-1 to 1-5 described later, the following formulas (3) and (4) are the same formula. A0 < S0 < L0 ···(3) A1 < S1 < L1 ···(4) L2 < S2 < A2 ···(5)

[0091] While satisfying the relationships of the above formulas (3) to (5), as the toner in the developing tank of the image forming apparatus is replaced from the initial toner and the first replenishing toner to the second replenishing toner, the developability at the initial stage of the life can be ensured, and the charge amount of the developer can be maintained high even as the life progresses. Consequently, it is possible to maintain better image quality.

[0092] <Magnetic material> The initial toner, the first replenishing toner, and the second replenishing toner according to this embodiment may contain a magnetic material as an external additive. Examples of the magnetic material include magnetite particles, γ - hematite particles, and various ferrite particles. These magnetic materials may be used alone or in combination of two or more.

[0093] Regarding the addition amount of the magnetic material with respect to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner according to this embodiment, it may be 0.5 part by mass or more and 2.5 parts by mass or less, and preferably 1 part by mass or more and 2 parts by mass or less. If the addition amount of the magnetic material is less than the above lower limit, there is a possibility that the image density may decrease as the life progresses. If the addition amount of the magnetic material exceeds the above upper limit, there is a possibility that the amount of waste toner may increase.

[0094] The average primary particle diameter of the magnetic material is not particularly limited, but for example, it may be 0.2 μm or more and 0.3 μm or less.

[0095] 4. Two-Component Developer, Carrier The two-component developer pre-filled in the developing tank of the image forming apparatus according to the present embodiment is composed of initial toner and a carrier. The two-component developer can be manufactured by mixing toner and a carrier using a known mixer. The mass ratio of toner to carrier is not particularly limited, and examples thereof include 3:97 to 12:88.

[0096] The carrier is agitated and mixed with toner in the developing tank, and gives the toner a desired charge. Further, the carrier functions as an electrode between the developing device and the photoreceptor, and transports the charged toner to the electrostatic latent image on the photoreceptor surface to form a toner image. The carrier is held on the developing roller of the developing device by magnetic force, returns to the developing tank again after acting on development, and is repeatedly used until the end of its life after being agitated and mixed with new toner again.

[0097] The carrier preferably has a carrier core material and a resin coating layer covering the carrier core material. The carrier core material is not particularly limited as long as it is used in the electrophotography field. Examples of the material constituting the carrier core material include magnetic metals such as iron, copper, nickel, and cobalt; and magnetic metal oxides such as ferrite and magnetite.

[0098] According to the image forming apparatus of the present disclosure, even when an iron powder carrier, which is a carrier liable to cause spent, is combined with a low melting point toner, the chargeability of the developer can be stabilized throughout its life. From this viewpoint, in the present embodiment, iron is suitable as the material constituting the carrier core material.

[0099] The average primary particle diameter of the carrier core material is not particularly limited, but is preferably 30 μm or more and 100 μm or less. The resin coating layer preferably contains a silicone resin or an acrylic resin. The silicone resin can delay the progress of contamination of the carrier coat layer and is suitable for long-life use.

Example

[0100] Hereinafter, based on Examples and Comparative Examples, the image forming apparatus and the image forming method of the present disclosure will be specifically described. First, various measurement methods and evaluation methods will be described. Among the Examples and Comparative Examples of the present disclosure, in Examples 1-6, the initial toner for the two-component developer filled in the developing tank in advance and the first replenishing toner filled in the first toner cartridge used for the first time were toners of different compositions, and in other Examples and Comparative Examples, the initial toner and the first replenishing toner were toners of the same composition.

[0101] 1. Measurement Method <Measurement Method for Average Primary Particle Diameter of Exterior Additive> For the average primary particle diameter of the exterior additive, the toner was photographed using a scanning electron microscope (SEM) (manufactured by Hitachi High-Technologies Corporation, model: S-4800), and 100 particle diameters (major diameters) of the exterior additive on the toner surface were arbitrarily measured from the obtained image. The average value of the 100 particle diameters was calculated and taken as the average primary particle diameter.

[0102] <Measurement Method for Glass Transition Temperature of Toner Particles> Using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Corporation, model number: DSC220), in accordance with Japanese Industrial Standard (JIS) K7121-1987, 1 g of the sample was heated at a heating rate of 10 °C / min to measure the DSC curve. In the obtained DSC curve, the temperature at the intersection of the straight line obtained by extending the baseline on the high-temperature side of the endothermic peak corresponding to the glass transition to the low-temperature side and the tangent line drawn at the point where the gradient is maximized with respect to the curve from the rising part to the apex of the peak was taken as the glass transition temperature Tg [°C].

[0103] <Measurement Method for Softening Temperature of Toner Particles> Using a flow property evaluation apparatus (manufactured by Shimadzu Corporation, Flow Tester, model number: CFT-100C), while heating 1 g of the sample at a heating rate of 6 °C / min, a load of 20 kgf / cm 2 (9.8×10 5 Pa) was applied, and the sample was allowed to flow out from the die (nozzle diameter 1 mm, length 1 mm). The temperature at which half of the sample had flowed out was taken as the softening temperature Tm [°C].

[0104] <Method for Measuring Coating Rate of Toner Particles with Silica Particles> Assuming that when the entire surface of the toner particles is coated with the external additive in the closest-packed state is 100%, and all the silica particles of the external additive have the same particle diameter as its average primary particle diameter, the coating rate [%] by the silica particles was calculated from the average primary particle diameter and the surface area of the toner particles. Specifically, the value obtained by dividing the total projected area of the external additive, which was determined as follows, by the total surface area of the toner was defined as the coating rate by the external additive.

[0105] -Calculation of Total Projected Area of External Additive- (1) From the average primary particle diameter of the external additive, the projected area per particle was calculated. The formula for obtaining the area of a circle was used. (2) Next, the weight of the external additive was determined from its specific gravity. The formula for obtaining the volume of a sphere was used, and the value was multiplied by the specific gravity to obtain it. (3) The total weight of the external additive was calculated by multiplying the weight per toner particle by the number of parts by weight of the added external additive, and the number of external additive particles per toner particle was calculated by dividing the total weight by the weight of the external additive per toner particle. The method for obtaining the weight per toner particle is the same as that for obtaining the weight of the external additive. (4) Finally, the total projected area of the external additive per toner particle was calculated from the number of external additive particles per toner particle.

[0106] -Calculation of Total Surface Area of Toner Particles- The surface area of one toner particle was calculated using the formula for obtaining the surface area of a sphere.

[0107] <Method for Measuring Charge Amount of Toner> The two-component developer using the prepared toner was filled into the developing tank of a multi-function machine (manufactured by Sharp Corporation, model: MX-6071) as an evaluation machine, and the two-component developer was sampled when it reached the READY state (before the first image drawing). The charge amount of the toner was measured for the sampled two-component developer using a charge amount measuring instrument (manufactured by TREK JAPAN, model: Model 210HS-2A).

[0108] Specifically, first, 0.2 g of the two-component developer was placed on a table and covered with a stainless steel mesh (#795). Next, a suction nozzle was placed on the mesh to suck the toner. After that, since the charge amount of the sucked toner was displayed, it was divided by the amount of the sucked toner to calculate the charge amount per 1 g of the toner (Q / m, unit: [μC / g]).

[0109] 2. Evaluation method

[0110] <Evaluation method based on image density (ID value)> The above evaluation machine was filled with the two-component developers prepared in the examples and comparative examples. First, the first toner cartridge (the toner cartridge filled with the first replenishing toner) was installed and continuous printing was performed. When 2000 images with a printing rate of 25% were printed on A4-sized recording paper, the toner cartridge was replaced with the second toner cartridge (the toner cartridge filled with the second replenishing toner). Then, printing was further performed for 2000 sheets. The image density (ID value) of the 4000th printed image in total was measured using a spectrocolorimeter (manufactured by X-Rite, model: X-Rite504). The higher the numerical value of the ID value, the higher the image density, and the lower the numerical value, the lower the image density.

[0111] The evaluation criteria based on the measured image density (ID value) are as follows. ◎ (Excellent): The ID value is 1.3 or more. 〇 (Good): The ID value is 1.2 or more and less than 1.3. △ (Fair): The ID value is 1.0 or more and less than 1.2. × (Poor): The ID value is less than 1.0.

[0112] <Evaluation method based on the amount of waste toner> The above evaluation machine was filled with the two-component developers prepared in the examples and comparative examples. First, the first toner cartridge (toner cartridge filled with the first replenishing toner) was installed and continuous printing was performed. When 1000 images with a printing rate of 25% were printed on A4-sized recording paper, the cartridge was replaced with the second toner cartridge (toner cartridge filled with the second replenishing toner). Thereafter, printing was continued for another 15000 sheets. The mass of the waste toner box before and after this continuous printing was measured, and the mass of waste toner per 1000 prints [g / k] was calculated. This calculated value was used as the evaluation criterion for the amount of waste toner.

[0113] The evaluation criteria based on the calculated amount of waste toner are as follows. ◎ (Excellent): The amount of waste toner is less than 5 g / k. 〇 (Good): The amount of waste toner is 5 g / k or more and less than 7 g / k. △ (Fair): The amount of waste toner is 7 g / k or more and less than 9 g / k. × (Poor): The amount of waste toner is 9 g / k or more.

[0114] 3. Production Example [Example 1-1] <Preparation of Masterbatch> A masterbatch containing a part of the binder resin (L component) and a colorant was prepared. The masterbatch was prepared by dry-mixing a part of the binder resin and the colorant and then melt-kneading them.

[0115] Specifically, 100 parts by mass of the amorphous polyester resin of the L component (L component: low molecular weight component, glass transition temperature around 55°C) and 10 parts by mass of carbon black (manufactured by Mitsubishi Chemical Corporation, trade name: MA-77) were mixed and dispersed using a Henschel mixer (manufactured by Nippon Coke Industry Co., Ltd., model: FM20C), and then melt-kneaded using an open roll type kneader (manufactured by Nippon Coke Industry Co., Ltd., trade name: Neodeck). The mixing conditions in the Henschel mixer were a rotation speed of 550 rpm and a rotation time of 2 minutes.

[0116] <Preparation of Toner Particles> -Mixing and Melt-Kneading Step- The toner particles for the examples and comparative examples were prepared as follows. First, 1 part by mass of a charge control agent (product name: LR-147A, manufactured by Nippon Carlit Co., Ltd.), 3.2 parts by mass of microcrystalline wax (product name: Hi-Mic-1090, manufactured by Nippon Seiro Co., Ltd.), 1.5 parts by mass of a magnetic material (product name: BL-220, manufactured by Titanium Industry Co., Ltd.), and 60 parts by mass of an H-form amorphous polyester resin (H-form: high molecular weight component, glass transition temperature around 60°C) were added to the above-described masterbatch, mixed and dispersed using a Henschel mixer, and then melt-kneaded using a twin-screw extruder. The mixing conditions in the Henschel mixer were a rotation speed of 1200 rpm and a rotation time of 5 minutes. The operating conditions of the twin-screw extruder were a cylinder set temperature of 110°C, a barrel rotation speed of 250 rpm, and a raw material supply rate of 10 kg / hour.

[0117] - Crushing and Classifying Process - After cooling the kneaded product obtained in the above melt-kneading process using a cooling belt, it was coarsely crushed using a speed mill having a 1 mm screen to obtain a coarsely crushed product with a particle diameter of 1 mm. This coarsely crushed product was finely crushed using a counter jet mill (product name: AFG, manufactured by Hosokawa Micron Corporation) to obtain a group of finely crushed particles with a volume average particle diameter of 6.4 μm. This group of finely crushed particles was classified using a rotary classifier (product name: TSP separator, manufactured by Hosokawa Micron Corporation) to obtain toner particles (uncoated particles) with a volume average particle diameter of 6.9 μm.

[0118] <Preparation of Initial Toner and First Refill Toner (External Addition Process)> 100 parts by mass of toner particles (uncoated particles) and 0.45 parts by mass of small particle size silica particles with an average primary particle size of 7 nm (manufactured by Nippon Aerosil Co., Ltd., product name: R976S, surface treatment: DDS) as an external additive were put into a Henschel mixer, and stirred and mixed for 2.0 minutes with the peripheral speed of the rotary stirring part set at 40 m / sec. Further, 1.0 part by mass of large particle size silica particles (manufactured by Shin-Etsu Chemical Co., Ltd., product name: X24, surface treatment: HMDS) and 1.5 parts by mass of a magnetic material (0.75 part by mass of the product name "KBC-100-60S" manufactured by Kanto Denka Kogyo Co., Ltd. and 0.75 part by mass of the product name "BL-220" manufactured by Titanium Industry Co., Ltd.) were put into the Henschel mixer, and stirred and mixed for 5.5 minutes with the peripheral speed of the rotary stirring part set at 40 m / sec, to obtain an initial toner and a first replenishment toner having a volume average particle size of 6.9 μm and a softening temperature of 120°C.

[0119] <Preparation of the Second Replenishment Toner (External Addition Step)> 100 parts by mass of toner particles (uncoated particles) and 0.8 part by mass of small particle size silica particles with an average primary particle size of 7 nm (manufactured by Nippon Aerosil Co., Ltd., product name: R976S) as an external additive were put into a Henschel mixer, and stirred and mixed for 0.5 minute with the peripheral speed of the rotary stirring part set at 40 m / sec. Further, 0.7 part by mass of titanium oxide particles (manufactured by Titanium Industry Co., Ltd., product name: ST550R, average primary particle size: 40 nm) and 1.5 parts by mass of a magnetic material (0.75 part by mass of the product name "KBC-100-60S" manufactured by Kanto Denka Kogyo Co., Ltd. and 0.75 part by mass of the product name "BL-220" manufactured by Titanium Industry Co., Ltd.) were put into the Henschel mixer, and stirred and mixed for 1 minute with the peripheral speed of the rotary stirring part set at 40 m / sec, to obtain a second replenishment toner having a volume average particle size of 6.9 μm and a softening temperature of 120°C.

[0120] <Manufacturing Process of Two-Component Developer> The two-component developer to be filled in the developing tank in advance was prepared by mixing the prepared first toner and iron powder carrier (average primary particle size 60 μm) for 20 minutes in a V-type mixer (manufactured by Tokuju Kogyosho Co., Ltd., product name: V-5) so that the toner concentration became 7% by mass.

[0121] [Examples 1-2 to 1-6, Comparative Examples 1-1 to 1-2] Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-2 shown in Table 1 below are examples in which the composition of the first replenishing toner is mainly fixed and the composition of the external additives of the second replenishing toner is changed, and the addition amount of small particle size silica particles is changed.

[0122] In Examples 1-2 to 1-4, toners and two-component developers were prepared in the same manner as in Example 1-1, except that the addition amount of small particle size silica particles in the second replenishing toner was changed as shown in Table 1 below.

[0123] In Example 1-5, toners and two-component developers were prepared in the same manner as in Example 1-1, except that magnetic materials were not added to the initial toner, the first replenishing toner, and the second replenishing toner.

[0124] Example 1-6 is an example in which toners with different compositions are used for the initial toner, the first replenishing toner, and the second replenishing toner. Toners and two-component developers were prepared in the same manner as in Example 1-1, except that the addition amounts of the external additives in each toner were changed as shown in Table 1.

[0125] Comparative Example 1-1 is an example in which the first replenishing toner in Example 1-1 was continuously replenished. In other words, it is an example in which the first replenishing toner and the second replenishing toner have the same composition.

[0126] In Comparative Example 1-2, toners and two-component developers were prepared in the same manner as in Example 1-1, except that the addition amount of small particle size silica particles in the second replenishing toner was changed as shown in Table 1 below. In other words, Comparative Example 1-2 is an example in which S1 > S2 for the addition amount of small particle size silica particles.

[0127] [Examples 2-1 to 2-3, Comparative Example 2-1] In Examples 2-1 to 2-3 and Comparative Example 2-1, toners and two-component developers were prepared in the same manner as in Example 1-2, except that the addition amount of large particle size silica particles in the second replenishing toner was changed as shown in Table 1 below. In other words, Comparative Example 2-1 is an example in which L1 < L2 for the addition amount of large particle size silica particles.

[0128]

Table 1

[0129] [Examples 3-1 to 3-3] In Examples 3-1 to 3-3, except that the composition of the second replenishing toner was fixed and the titanium oxide particles (manufactured by Titanium Industry Co., Ltd., trade name: ST550R) were added to the initial toner and the first replenishing toner in the addition amounts shown in Table 2 below, toner and a two-component developer were prepared in the same manner as in Example 1-2.

[0130]

Table 2

[0131] [Examples 4-1 to 4-9] Examples 4-1 to 4-9 are examples in which the coating rate of the toner particles by the silica particles is changed within the range satisfying the relationships of S1 < S2 and L1 > L2. In Examples 4-1 to 4-5, except that the composition of the second replenishing toner was fixed and the coating rates in the initial toner and the first replenishing toner were changed as shown in Table 3 below, toner and a two-component developer were prepared in the same manner as in Example 1-2.

[0132] Also, in Examples 4-6 to 4-9, except that the compositions of the initial toner and the first replenishing toner were fixed and the coating rate in the second replenishing toner was changed as shown in Table 3 below, toner and a two-component developer were prepared in the same manner as in Example 1-2.

[0133]

Table 3

[0134] As is clear from the evaluation results in Table 1, in the initial toner, the first replenishment toner, and the second replenishment toner, when the addition amounts [parts by mass] of the small particle size silica particles with respect to 100 parts by mass of the toner particles are denoted as S0, S1, and S2, respectively, and the addition amounts [parts by mass] of the large particle size silica particles are denoted as L0, L1, and L2, respectively, in Examples 1-1 to 1-5 and Examples 2-1 to 2-3 that satisfy the relationships S0 = S1 < S2 and L0 = L1 > L2, and in the image forming apparatus and the image forming method of Example 1-6 that satisfy the relationships S0 < S1 < S2 and L0 > L1 > L2, the amount of waste toner was small, and the charge amount of the developer remained stable even as the life progressed. Consequently, good image quality could be maintained even as the life progressed.

[0135] On the other hand, in Comparative Examples 1-1 to 2-1 that do not satisfy the above relationships, at least one of the evaluation results based on the amount of waste toner and the image density was inferior to those of the examples.

[0136] Next, when examining the addition amount of titanium oxide particles as an external additive using Table 2, in the first replenishment toner and the second replenishment toner, when the addition amounts [parts by mass] of the titanium oxide particles with respect to 100 parts by mass of the toner particles are denoted as A1 and A2, respectively, it can be seen that Examples 1-2 and 3-1 in which A1 < A2 are superior in the evaluation results based on the amount of waste toner and the image density to Example 3-3 in which A1 = A2.

[0137] Next, when examining the relationship between the addition amounts of the small particle size silica particles, the large particle size silica particles, and the titanium oxide particles, according to Table 1, Examples 1-2, 2-1, and 2-2 that satisfy the relationships A1 < S1 < L1 and L2 < S2 < A2 are superior in the evaluation results based on the amount of waste toner to Example 2-3 in which S2 < A2 < L2 and which does not satisfy the above relationships.

[0138] Also, according to Table 2, Examples 1-2 and 3-1 that satisfy the relationships A1 < S1 < L1 and L2 < S2 < A2 are superior in the evaluation results based on the amount of waste toner and the image density to Example 3-2 in which S1 < A1 < L1 and which does not satisfy the above relationships.

[0139] Next, using Table 3, the relationship between the coating rate of toner particles by silica particles will be examined. Assuming that the coating rates in the first replenishing toner and the second replenishing toner are C1 and C2 respectively, first for C1, according to Examples 4-1 to 4-5 and Example 1-2, it can be seen that Examples 1-2, 4-2, and 4-3 where C1 is 80% or more and 110% or less are superior in the evaluation results based on image density to Examples 4-1, 4-4, and 4-5 where C1 is outside the above range.

[0140] For C2, according to Examples 4-6 to 4-9 and Example 1-2, it can be seen that Examples 4-7, 1-2, and 4-8 where C2 is 100% or more and 120% or less are superior in the evaluation results based on the amount of waste toner to Example 4-6 where C2 is less than the above lower limit, and it can be seen that they are superior in the evaluation results based on image density to Example 4-9 where C2 exceeds the above upper limit.

[0141] Furthermore, when examining the relationship of the charge amount of the toner, assuming that the absolute values of the charge amounts [μC / g] in the first replenishing toner and the second replenishing toner are Q1 and Q2 respectively, Examples 1-2, 4-7, etc. that satisfy the relationship Q1 < Q2 are superior in the evaluation results based on the amount of waste toner and image density. On the other hand, in Examples 4-6 and 4-9 that do not satisfy this relationship, it can be seen that one of the two evaluation results is a "△" evaluation.

[0142] All the embodiments disclosed this time are illustrative in all respects and do not serve as a basis for a limiting interpretation. Therefore, the technical scope of the present disclosure is not interpreted only by the above-described embodiments, but is defined based on the description in the claims. Also, all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0143] 1 Binder resin 2 Silica particles with a small particle size 3 Silica particles with a large particle size 4 Titanium oxide particles 5 Magnetic material C Carrier T1 First replenishing toner T2 Second supply toner TC1 First toner cartridge TC2 Second toner cartridge

Claims

1. An image forming apparatus in which a two-component developer containing an initial toner and a carrier is preliminarily filled in a developing tank, and replenishing toner is replenished from a toner cartridge into the developing tank as development is performed, The toner cartridge for the image forming apparatus includes a first toner cartridge that is first mounted and used on the image forming apparatus, and a second toner cartridge that is mounted and used at least from the second time onward, When the toner filled in the first and second toner cartridges is used as the first and second replenishing toners, respectively, the initial toner, the first replenishing toner, and the second replenishing toner are toners with an external additive adhering to the surface of the toner particles, Among the amounts [parts by mass] of the external additive added to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner, when the amounts of small particle size silica particles having an average primary particle diameter of less than 20 nm are S0, S1, and S2, respectively, and the amounts of large particle size silica particles having an average primary particle diameter of 20 nm or more are L0, L1, and L2, respectively, an image forming apparatus characterized by satisfying the relationships of the following formulas (1) and (2). S0 ≤ S1 < S2... (1) L0 ≥ L1 > L2... (2)

2. The image forming apparatus according to claim 1, Among the initial toner, the first replenishing toner, and the second replenishing toner, at least the second replenishing toner contains titanium oxide particles as an external additive. An image forming apparatus characterized by this.

3. The image forming apparatus according to claim 2, When the amounts [parts by mass] of titanium oxide particles as an external additive added to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner are A0, A1, and A2, respectively, an image forming apparatus characterized by satisfying the relationship A0 ≤ A1 < A2.

4. The image forming apparatus according to claim 3, An image forming apparatus characterized by satisfying the relationships of the following formulas (3), (4), and (5). A0 < S0 < L0... (3) A1 < S1 < L1... (4) L2 < S2 < A2... (5)

5. The image forming apparatus according to any one of Claims 1 to 4, wherein, when the coating rates of toner particles by silica particles as external additives in the initial toner, the first replenishing toner, and the second replenishing toner are C0, C1, and C2, respectively, C0 and C1 are 80% or more and 110% or less, and C2 is 100% or more and 120% or less. An image forming apparatus characterized by this.

6. The image forming apparatus according to any one of Claims 1 to 4, wherein, when the absolute values of the charge amounts [μC / g] of the initial toner, the first replenishing toner, and the second replenishing toner are Q0, Q1, and Q2, respectively, an image forming apparatus characterized by satisfying the relationship Q0 ≤ Q1 < Q2.

7. The image forming apparatus according to any one of Claims 1 to 4, wherein the external additive of the initial toner and the external additive of the first replenishing toner have the same composition. An image forming apparatus characterized by this.

8. The image forming apparatus according to any one of Claims 1 to 4, wherein the toner particles of the initial toner, the first replenishing toner, and the second replenishing toner have a glass transition temperature of 50°C or more and 65°C or less, and a softening temperature of 105°C or more and 130°C or less. An image forming apparatus characterized by this.

9. An electrostatic latent image forming step of forming an electrostatic latent image on an electrostatic latent image carrier, A developing step of developing the electrostatic latent image formed on the electrostatic latent image carrier as a toner image using a two-component developer containing an initial toner and a carrier, A transfer step of transferring the toner image formed on the electrostatic latent image carrier to a recording medium, A fixing step of fixing the toner image transferred to the memory medium; A toner supply step of supplying replenishing toner to the two-component developer, the image forming method comprising: The toner supply step includes a first supply step of supplying a first replenishing toner as the first toner supply to the two-component developer, and a second supply step of supplying a second replenishing toner after the first supply step; The initial toner, the first replenishing toner, and the second replenishing toner are toners with an external additive attached to the surface of the toner particles; Among the addition amounts [parts by mass] of the external additive with respect to 100 parts by mass of the toner particles in the initial toner, the first replenishing toner, and the second replenishing toner, the addition amounts of the small particle size silica particles having an average primary particle size of less than 20 nm are S0, S1, and S2, respectively, and the addition amounts of the large particle size silica particles having an average primary particle size of 20 nm or more are L0, L1, and L2, respectively. The image forming method is characterized by satisfying the relationships of the following formulas (1) and (2). S0 ≦ S1 < S2... (1) L0 ≧ L1 > L2... (2)

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