Electrostatic charge image developing toner, toner cartridge, and image forming apparatus

Abstract

To provide a toner for electrostatic charge image development excellent in printing durability at normal temperature and normal humidity, excellent also in resistance to high temperature and high humidity, and excellent in stability of printing performance.SOLUTION: The electrostatic charge image developing toner contains toner base particles containing a binder resin and a colorant, and an external additive, wherein the external additive contains a positively chargeable external additive 1 and a negatively chargeable external additive 2, and true specific gravities of the positively chargeable external additive 1 and the negatively chargeable external additive 2 are 1.0g / cm3 or more and 1.3g / cm3 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a toner for developing electrostatic images used for developing latent images formed in electrophotography, electrostatic recording, electrostatic printing, etc. The present invention also relates to a toner cartridge filled with the toner for developing electrostatic images, and an image forming apparatus using the toner for developing electrostatic images. [Background technology]

[0002] Electrostatic image developing toners are used in image forming devices such as printers, copiers, and facsimiles to visualize electrostatic images. For example, in electrophotographic image formation, an electrostatic latent image is first formed on a photoreceptor drum. This electrostatic latent image is then developed with toner, transferred to a printing medium such as transfer paper, and the toner is heated to fix the image.

[0003] In recent years, machines using such toners have been used not only in printers and copiers for office and home printing, but also in commercial printing machines such as label printing machines, and the range of applications is expanding.

[0004] Toners used for developing electrostatic images generally have a structure in which solid fine particles are attached as external additives to the surfaces of toner base particles containing a binder resin, a colorant, wax, etc.

[0005] Patent Document 1 discloses a toner for developing electrostatic images that is suppressed from fogging under low-temperature and low-humidity conditions, the toner containing toner base particles containing a binder resin and a colorant and an external additive, wherein the external additive contains silica particles A whose charging polarity is opposite to that of the toner base particles and whose shape index, expressed as the ratio of the number-average particle diameter to the BET-equivalent particle diameter, is 2.0 or more.

[0006] Furthermore, Patent Document 2 proposes a toner for developing electrostatic images that has low replenishment cohesion and excellent print durability, and that contains colored resin particles containing a binder resin, a colorant, and a charge control agent, as well as external additives, and that the external additives contain a specific amount of a combination of metal oxide particles that have the same charge polarity as the colored resin particles, a specific charge amount per unit surface area, and a specific number-average particle diameter, and resin particles that have a charge polarity opposite to that of the colored resin particles and a specific number-average particle diameter. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-46199 [Patent Document 2] International Publication No. 2019 / 065730 Summary of the Invention [Problem to be solved by the invention]

[0008] The toners for developing electrostatic images described in Patent Documents 1 and 2 do not take into consideration printing performance in high-temperature and high-humidity environments.

[0009] The present invention aims to provide a toner for developing electrostatic images that has excellent print durability under normal temperature and humidity conditions, as well as excellent resistance to high temperatures and high humidity, and excellent stability of print performance, and a toner cartridge and an image forming apparatus that use this toner for developing electrostatic images. [Means for solving the problem]

[0010] As a result of extensive investigations to solve the above problems, the present inventors have discovered a toner for developing electrostatic images, which comprises toner base particles containing a binder resin and a colorant, and external additives, wherein the external additives contain a positively chargeable external additive 1 and a negatively chargeable external additive 2, and the true specific gravity of the positively chargeable external additive 1 and the negatively chargeable external additive 2 is 1.0 g / cm 3 More than 1.3g / cm3 It has been found that the above problems can be solved by using the following toner for developing electrostatic images. That is, the present invention is summarized as follows.

[0011] [1] A toner for developing electrostatic images, comprising toner base particles containing a binder resin and a colorant, and an external additive, the external additives contain a positively chargeable external additive 1 and a negatively chargeable external additive 2, The true specific gravity of the positively chargeable external additive 1 and the negatively chargeable external additive 2 is 1.0 g / cm 3 More than 1.3g / cm 3 A toner for developing electrostatic images, which is:

[0012] [2] The toner for developing electrostatic images according to [1], wherein the toner base particles have an average circularity of 0.95 or more.

[0013] [3] The toner for developing electrostatic images according to [1] or [2], wherein the toner for developing electrostatic images is positively charged.

[0014] [4] The toner for developing electrostatic images according to any one of [1] to [3], wherein the toner base particles have a volume average particle diameter (Dv) of 8 μm or less, and a ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) of 1.2 or less.

[0015] [5] The electrostatic image developing toner according to any one of [1] to [4], wherein the toner base particles are toner base particles produced by an emulsion polymerization aggregation method.

[0016] [6] The toner for positive charge development according to any one of [1] to [5], wherein the external additive 1 and / or the external additive 2 contains a (meth)acrylic resin.

[0017] [7] The true specific gravity of the toner base particles is 0.8 g / cm 3 More than 1.5g / cm 3or less, and the absolute value of the difference in true specific gravity between the external additive 1 and the external additive 2 is 0.2 or less.

[0018] [8] The toner for developing electrostatic images according to any one of [1] to [7], further comprising inorganic particles as an external additive other than the external additive 1 and the external additive 2.

[0019] [9] A toner cartridge filled with the toner for developing electrostatic images according to any one of [1] to [8].

[0020]

[10] An image forming apparatus having an electrophotographic photosensitive member, a charging means for charging the electrophotographic photosensitive member, an image exposure means for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image, a developing means for developing the electrostatic latent image with toner, and a transfer means for transferring the toner from the electrophotographic photosensitive member to a transfer receiving member, wherein the toner is the toner for developing electrostatic images according to any one of [1] to [8]. [Effects of the Invention]

[0021] According to the present invention, there are provided a toner for developing electrostatic images which has excellent print durability at normal temperature and normal humidity, and also has excellent resistance to high temperatures and high humidity, and therefore fogging is suppressed even after continuous printing at normal temperature and normal humidity, and also under high temperature and high humidity conditions, and which has excellent stability of print performance, as well as a toner cartridge and an image forming device which use this toner. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following describes in detail the mode for carrying out the present invention (hereinafter referred to as "embodiments of the invention"). Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention.

[0023] In this specification, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more and Y or less," as well as "preferably larger than X" or "preferably smaller than Y." Furthermore, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the intention that "it is preferable that it is greater than X" or "it is preferable that it is less than Y."

[0024] [Toner for developing electrostatic images] The electrostatic image developing toner according to an embodiment of the present invention (hereinafter may be referred to as "the toner of the present invention" or "the present toner") is a toner for developing electrostatic images containing toner base particles (hereinafter may be referred to as "the toner base particles of the present invention" or "the present toner base particles") containing a binder resin and a colorant, and an external additive, wherein the external additive contains a positively charged external additive 1 and a negatively charged external additive 2, and the true specific gravity of the positively charged external additive 1 and the negatively charged external additive 2 is 1.0 g / cm 3 More than 1.3g / cm 3 The present invention is characterized by the following: The present toner will be described in detail below, but the present toner is not limited to the following embodiments. In the present invention, the chargeability of the external additive, the toner base particles, and the toner, the volume average particle diameter (Dv), number average particle diameter (Dn), true specific gravity, and average circularity of the toner base particles, and the true specific gravity and number average primary particle diameter of the external additive are all measured by the methods described in the Examples section below.

[0025] [mechanism] The toner for developing electrostatic images of the present invention contains at least a positively chargeable external additive 1 and a negatively chargeable external additive 2 as external additives, and the true specific gravity of both external additive 1 and external additive 2 is 1.0 g / cm 3 More than 1.3g / cm 3The following are important constituent requirements, and by having such constituent requirements, the present toner has excellent print durability and suppresses fogging when continuous printing is performed under normal temperature and humidity conditions, and also has excellent resistance to high temperatures and high humidity, so that fogging is suppressed even under high temperature and high humidity environments, and it is possible to realize a toner for developing electrostatic images with excellent stability of printing performance.

[0026] Although the details of the mechanism by which such effects are achieved in the present invention are not clear, it is believed to be as follows. That is, by containing a positively chargeable external additive 1 and a negatively chargeable external additive 2, the positively chargeable external additive 1 prevents the toner from deteriorating even with repeated printing, and the negatively chargeable external additive 1 improves the chargeability of the toner. In addition, by using both external additives 1 and 2, the negatively chargeable external additive 2 rubs against the positively chargeable external additive 1 on the toner surface, thereby more efficiently improving charging performance such as start-up ability. Furthermore, since the true specific gravities of external additives 1 and 2 are both within the above ranges, the difference in specific gravity between external additives 1 and 2 and the toner base particles is small, which makes it easier for the toner base particles and external additives 1 and 2 to mix more uniformly during the stirring step in which external additives 1 and 2 are added.As a result, the toner base particles can be uniformly coated with the external additive particles, which is thought to result in excellent print durability and excellent printing performance even under high temperature and high humidity conditions. In addition, the true specific gravity is 1.0 g / cm 3 More than 1.3g / cm 3 The external additives 1 and 2 below have a lower specific gravity than inorganic particles generally used as external additives, which prevents the external additives 1 and 2 from being embedded in the toner base particles, improving the durability of the toner. This is thought to result in excellent print durability and excellent printing performance even under high temperature and high humidity conditions.

[0027] Toner degradation during continuous printing is primarily caused by external additive particles externally added to the surface of toner base particles becoming embedded in the surface of the toner base particles due to the stress of continuous printing. To prevent this embedding, particularly of small-diameter external additive particles that are prone to embedding, a commonly used technique is to simultaneously add an external additive with a relatively large particle size as a spacer. Another technique is to incorporate a relatively large external additive, which is charged with the opposite polarity to the toner base particles, into the surface of the toner base particles, thereby maintaining the toner's chargeability through friction with the external additive. However, these spacers and external additives of opposite polarity must be properly dispersed on the surface of the toner base particles. Inorganic fine particles, which are generally used as external additives to toner, have a different true specific gravity from the toner base particles, making it difficult to properly mix them with the toner base particles in the dry mixer used in the external addition process. The present inventors have discovered that by making the true specific gravity of these spacers and reversely charged external additives similar to that of the toner base particles, a dispersion form can be obtained that optimally exhibits the effects of each external additive, and have arrived at the present invention.

[0028] The true specific gravity of the external additives 1 and 2 used in this toner is 1.0 g / cm 3 If the density is less than 1.3 g / cm, the specific gravity will be smaller than that of the base particles, making it difficult for the particles to enter the gaps between the base particles during the external addition process. 3 If the specific gravity exceeds 1.0, the external additives 1 and 2 will be concentrated in the lower part of the mixer, making it difficult to uniformly attach them to the entire base particles. 3 , preferably 1.0 to 1.2 g / cm 3 External additives are used.

[0029] [External additives] The toner contains an external additive to improve the fluidity and charge controllability of the toner. The external additive is usually attached to the surface of the toner base particles, but the degree to which the external additive is embedded in the toner base particles may be in any state. That is, a part or all of the external additive may be attached so as to be in contact with the surface of the toner base particles, or may be embedded in the toner base particles, and a part or all of the external additive may be present in a dispersed or aggregated state on the surface of the toner base particles.

[0030] Generally, the external additive can be selected from various inorganic or organic particles as appropriate. From the viewpoint of charge control, conductive particles may also be used as the external additive.

[0031] Examples of inorganic particles commonly used as external additives include various carbides such as silicon carbide, boron carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, tantalum carbide, niobium carbide, tungsten carbide, chromium carbide, molybdenum carbide, and calcium carbide; various nitrides such as boron nitride, titanium nitride, and zirconium nitride; various borides such as zirconium boride; various oxides such as titanium oxide (titania), calcium oxide, magnesium oxide, zinc oxide, copper oxide, aluminum oxide, cerium oxide, silica, and colloidal silica; various titanic acid compounds such as calcium titanate, magnesium titanate, and strontium titanate; phosphate compounds such as calcium phosphate; sulfides such as molybdenum disulfide; fluorides such as magnesium fluoride and carbon fluoride; various metal soaps such as aluminum stearate, calcium stearate, zinc stearate, and magnesium stearate; talc, bentonite, various carbon blacks, conductive carbon black, magnetite, and ferrite.

[0032] As the organic particles, fine particles of styrene-based resin, (meth)acrylic-based resin, epoxy-based resin, melamine-based resin, etc. Charging stability can also be improved by using fine particles containing fluorine atoms. Examples of conductive particles include metal oxides such as conductive titanium oxide, silica, and magnetite, or particles thereof doped with a conductive substance, organic particles of polymers having conjugated double bonds such as polyacetylene, polyphenylacetylene, and poly-p-phenylene doped with a conductive substance such as metal, and carbon such as carbon black and graphite.From the viewpoint of imparting conductivity without impairing the fluidity of the toner, conductive particles such as conductive titanium oxide or particles doped with a conductive substance are more preferred.

[0033] Of these external additives, the toner contains at least one additive having a true specific gravity of 1.0 g / cm 3 More than 1.3g / cm 3 The following positively charged external additive 1 and a true specific gravity of 1.0 g / cm 3 More than 1.3g / cm 3 The negatively charged external additive 2 is contained. The term "positively chargeable external additive" refers to an additive that is positively chargeable in the measurement of chargeability described in the Examples section below, and the term "negatively chargeable external additive" refers to an additive that is negatively chargeable in the measurement of chargeability described in the Examples section below.

[0034] <Positively charged external additive 1> This toner has a true specific gravity of 1.0 g / cm in order to give the toner base particles appropriate charging properties and printing durability. 3 More than 1.3g / cm 3 The positively charged external additive 1 (hereinafter, sometimes simply referred to as "external additive 1") shown below is contained as an essential component. As the positively chargeable external additive 1, (meth)acrylic resin particles or styrene / acrylic resin particles that have been positively charged are suitable. As a method for making the resin particles positively chargeable, any known method can be selected, such as using a positively chargeable monomer as a raw material when producing the particles, or adding a positively chargeable surface treatment agent after producing the resin particles to make them positively chargeable.

[0035] The number-average primary particle diameter of the positively chargeable external additive 1 used in the present invention is preferably 0.05 μm or more and 0.5 μm or less. If the particle diameter is smaller than this range, the effect of the external additive as a spacer will be weak, and printing durability will deteriorate. Conversely, if the external additive is too large, its adhesion to the base particles will be weak, which will actually reduce chargeability and tend to worsen fog.

[0036] External additive 1 has a true specific gravity of 1.0 g / cm 3 More than 1.3g / cm 3 As long as they are positively chargeable, one kind of the following may be used alone, or two or more kinds may be used in combination.

[0037] <Negatively charged external additive 2> In addition to the external additive 1, the present toner has a true specific gravity of 1.0 g / cm in order to maintain chargeability even under high temperature and high humidity conditions where chargeability tends to deteriorate and to obtain high print quality. 3 More than 1.3g / cm 3 The negatively charged external additive 2 (hereinafter, sometimes referred to as "external additive 2") shown below is contained as an essential component. As the negatively chargeable external additive 2, (meth)acrylic resin particles or styrene / acrylic resin particles that have been made negatively chargeable are suitable. As a method for making the resin particles negatively chargeable, any known method can be selected, such as using a negatively chargeable monomer as a raw material when producing the particles, or adding a negatively chargeable surface treatment agent after producing the resin particles to make them negatively chargeable.

[0038] The number average primary particle diameter of the negatively chargeable external additive 2 used in the present invention is preferably 0.1 μm or more and 1 μm or less. If it is smaller than this range, sufficient chargeability cannot be imparted to the toner, and fogging tends to worsen. Conversely, if it is larger than this range, it is more likely to cause contamination of machine components.

[0039] External additive 2 has a true specific gravity of 1.0 g / cm 3 More than 1.3g / cm 3 As long as they are negatively chargeable, one of the following may be used alone or two or more of them may be used in combination.

[0040] <Other external additives> The toner may contain an external additive other than external additive 1 and external additive 2 (hereinafter, sometimes referred to as "other external additives"). In particular, the toner preferably contains silica particles as the other external additive from the viewpoint of toner fluidity and charge stability. Furthermore, from the viewpoint of toner charge stability, particularly under high temperature and high humidity, the silica particles are more preferably hydrophobic silica particles treated with a positively charging surface treatment agent and a hydrophobic treatment agent.

[0041] As the positively charging surface treatment agent, any conventional treatment agent can be used, but in particular, those treated with aminosilane are preferred from the viewpoint of charging stability. As the hydrophobic treatment agent, any conventional treatment agent can be used, but those treated with polydimethylsiloxane or hexamethyldisilane are particularly preferred because they are more easily hydrophobic. The specific surface area of ​​silica particles is set at 30m from the viewpoint of toner fluidity and charging properties. 2 / g or more 300m 2 / g or less, and the number average primary particle diameter is preferably 8 to 50 nm.

[0042] In the present invention, other external additives may be used in addition to silica particles, and one or more of the above-mentioned generally well-known external additives for toner, such as inorganic particles or organic particles, may be used in combination.

[0043] <Surface treatment agent> The external additive may be one in which the surfaces of the inorganic or organic particles have been subjected to a surface treatment such as hydrophobization with a treatment agent such as a silane coupling agent such as hexamethyldisilazane (HMDS) or dimethyldichlorosilane (DMDS), a titanate-based coupling agent, a silicone oil treatment agent such as silicone oil, dimethylsilicone oil, modified silicone oil, or amino-modified silicone oil, a silicone varnish, a fluorine-based silane coupling agent, a fluorine-based silicone oil, or a coupling agent having an amino group or a quaternary ammonium base. Two or more of these treatment agents may be used in combination.

[0044] <Amount of external additives added> The amount of external additive 1 added per 100 parts by mass of toner base particles is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more. If the amount of external additive 1 added is equal to or greater than the above-mentioned lower limit, external additive 1 functions sufficiently as a spacer, and the external additive can be prevented from being embedded. On the other hand, the amount of external additive 1 added per 100 parts by mass of toner base particles is preferably 2 parts by mass or less, more preferably 1.5 parts by mass or less, and even more preferably 1.2 parts by mass or less. If the amount of external additive 1 added is equal to or less than the above-mentioned upper limit, charging becomes appropriate and image density and print quality are not impaired. The amount of external additive 2 added per 100 parts by mass of toner base particles is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more. If the amount of external additive 2 added is equal to or greater than the above-mentioned lower limit, the toner can be effectively charged. On the other hand, the amount of external additive 2 added per 100 parts by mass of toner base particles is preferably 1.5 parts by mass or less, more preferably 1.2 parts by mass or less, and even more preferably 1 part by mass or less. If the amount of external additive 2 added is equal to or less than the above-mentioned upper limit, excess external additive 2 will be prevented from separating from the toner and contaminating machine components.

[0045] The ratio (mass ratio) of the amounts of external additive 1 and external additive 2 added to the toner base particles can be set appropriately depending on the electrophotographic process used, but it is preferable that the ratio of external additive 1 to external additive 2 is 1:0.01 to 5, particularly 1:0.05 to 4, and especially 1:0.1 to 3. When the mass ratio of external additive 1 to external additive 2 added is within the above range, the chargeability is balanced, and images with high print quality can be obtained.

[0046] When an external additive other than external additive 1 and external additive 2 is used as an external additive, the amount of the other external additive added is preferably 50 to 99% by mass, particularly 55 to 95% by mass, and especially 60 to 90% by mass, of the total of external additive 1, external additive 2, and the other external additive. If the amount of the other external additive added is equal to or greater than the lower limit, the charge amount is balanced, images of high print quality can be obtained, and excellent thermal storage stability can be obtained by imparting appropriate fluidity. On the other hand, if the amount of the other external additive added is equal to or less than the upper limit, the aforementioned effects of using external additives 1, 2, and the other external additives can be effectively obtained.

[0047] The other external additives may be positively charged, negatively charged, or uncharged, but from the viewpoint of charging stability, it is preferable that 30% by mass or more, preferably 50% by mass or more and 100% by mass or less, of the other external additives be positively charged external additives.

[0048] The total amount of external additive 1, external additive 2, and other external additives used as needed per 100 parts by mass of toner base particles is preferably 2 parts by mass or more, more preferably 2.5 parts by mass or more, and even more preferably 3 parts by mass or more. If the total amount of external additives added is at least the above-mentioned lower limit, the external additives are less likely to be embedded in the surface of the toner base particles, and the effects of the external additives can be effectively obtained. On the other hand, the total amount of external additive 1, external additive 2, and other external additives used as needed per 100 parts by mass of toner base particles is preferably 10 parts by mass or less, more preferably 9 parts by mass or less, and even more preferably 8 parts by mass or less. If the total amount of external additives added is at most the above-mentioned upper limit, image defects due to removal of particles from the cleaning blade caused by excessive fluidity can be prevented.

[0049] <Method of adding external additives (external addition method)> The present toner is obtained by externally adding external additives including at least the above-mentioned external additive 1 and external additive 2 to the surface of toner base particles described below.

[0050] In the present invention, the method for adding an external additive to the toner base particles and causing it to adhere or fix is ​​not particularly limited, and a mixer generally used in toner production can be used. Specifically, the toner base particles and the external additive are stirred and mixed by a mixer such as a Henschel mixer, a V-type blender, a Loedige mixer, or a Q-mixer.

[0051] The number of external addition steps in producing the toner is not particularly limited as long as the effect of the present invention is not impaired, but it is preferable that external additive 1 and external additive 2 are attached or fixed to the surface of the toner base particles in different external addition steps. The number of external addition steps is usually 2 to 5, and preferably 3.

[0052] Although not particularly limited, examples of the method for adding the external additives 1, 2 and other external additives include a method of carrying out the following external addition step. External addition step 1: A required amount of external additive 1 is added to the toner base particles, and the particles are stirred and mixed. In this step, an external additive other than external additive 1, preferably a positively chargeable external additive, may be mixed together with external additive 1. External Addition Step 2: Other external additives, preferably positively chargeable external additives, are added to the toner base particles that have been subjected to External Addition Step 1, and the mixture is stirred and mixed. External addition step 3: A required amount of external additive 2 is added to the toner base particles that have been subjected to external addition step 2, and the mixture is stirred and mixed.

[0053] As described above, by externally adding the positively charged external additive 1 to the toner base particles in the external addition step 1, the external additive can be firmly attached to the toner base particles, effectively preventing other external additives from being buried. Furthermore, by externally adding other positively charged external additives other than the external additive 1 in the external addition step 1, the fluidity of the toner is improved, and the attachment of the external additives can be made more uniform. Furthermore, as the final external addition step, external addition of negatively chargeable external additive 2 in external addition step 3 is preferable because it prevents the positively chargeable external additive from adhering to the negatively chargeable external additive 2, preventing the negatively chargeable external additive 2 from effectively exhibiting its performance, and effectively increases the chargeability of the toner. Furthermore, the fluidity and chargeability of the toner can be adjusted by externally adding other positively charged external additives between external addition step 1 and external addition step 3. From the viewpoint of the fluidity and chargeability of the toner, it is preferable that the amount of the other positively charged external additives added in external addition step 2 is 20 to 80 mass % of the total amount of external additives, which is the sum of external additive 1, external additive 2, and the other external additives.

[0054] There are no particular restrictions on the stirring and mixing time in each external addition step, but if the amount of external additive to be stirred and mixed is large, the stirring and mixing time should be set relatively long, and if the amount is small, the stirring and mixing time should be set relatively short, and is usually set appropriately between 1 minute and 30 minutes.

[0055] Furthermore, the stirring and mixing temperature (mixer temperature) in the external addition step is preferably 25 to 55°C, particularly 30 to 50°C. If the stirring and mixing temperature is above the lower limit, the external additive can be adhered to the toner base particles with appropriate adhesive strength, preventing contamination of machine components caused by scattering of external additives with weak adhesive strength during printing. On the other hand, if the temperature is below the upper limit, the external additive can adequately coat the surface of the toner base particles, preventing deterioration of the toner's fluidity and storage properties. Therefore, it is preferable to appropriately adjust the temperature during stirring and mixing of the toner base particles and external additives so that it is within the above temperature range.

[0056] [Toner base particles] The toner base particles contain at least a binder resin and a colorant, and may also contain wax, a charge control agent, and the like, as necessary.

[0057] The toner base particles may be a single-layer structure or a multi-layer structure (core-shell structure) having a core and an outer layer (also referred to as a "shell"), but a core-shell structure is preferred from the viewpoint of the balance between the low-temperature fixability and heat storage stability of the toner. In the present invention, the term "core-shell structure" refers to a structure in which the surface of a core component is covered with a shell component, but is not limited to a structure in which the core component is completely covered with the shell component, and the surface of the core component may be partially exposed, or may be partially dispersed in the shell component. In the present invention, the core portion of the core-shell structure is referred to as a core particle, and the particles used to coat the surface of the core particle are referred to as a shell particle. The process of coating core particles with shell particles is sometimes referred to as an encapsulation process, and the control for coating core particles with shell particles is sometimes referred to as encapsulation control.

[0058] <Core particle> The core particles are produced by a pulverization method or a wet polymerization method. The pulverization method includes a process of melting and kneading a binder resin, a colorant, a wax, etc. at high temperature, a pulverization process, and a classification process. Examples of the wet polymerization method include a suspension polymerization method, an emulsion polymerization aggregation method, and a melt suspension method.

[0059] In the suspension polymerization method, a colorant and wax are usually dissolved in a binder resin monomer, and then the resulting monomer solution is suspended as monomer droplets in an aqueous medium by mechanical shearing force, and polymerization is carried out. The emulsion polymerization aggregation method is a method in which a polymerizable monomer of a binder resin is emulsified in an aqueous medium usually containing a polymerization initiator, an emulsifier, and the like, and the polymerizable monomer is polymerized under stirring to obtain primary polymer particles, to which a colorant and, if necessary, a charge control agent, and the like are added to aggregate the primary polymer particles, and the obtained aggregated particles are further aged to produce core particles.

[0060] The melt suspension method is a method in which a binder resin, wax, etc. are dissolved in a normal solvent to obtain an oil phase, and the oil phase is suspended as oil droplets in an aqueous medium, after which the solvent is removed. Among the wet polymerization methods, the emulsion polymerization aggregation method is preferred from the viewpoint of ease of controlling physical properties such as particle size and shape.

[0061] In the present invention, as the monomer component used to produce the binder resin, any monomer that has been used in the production of binder resins for conventional toners can be used appropriately. For example, any of polymerizable monomers can be used, including polymerizable monomers having an acidic group (hereinafter sometimes simply referred to as acidic monomers), polymerizable monomers having a basic group (hereinafter sometimes simply referred to as basic monomers), and polymerizable monomers having neither an acidic group nor a basic group (hereinafter sometimes referred to as other monomers).

[0062] Examples of the acidic monomer include polymerizable monomers having a carboxyl group such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, and cinnamic acid; polymerizable monomers having a sulfonic acid group such as sulfonated styrene; and polymerizable monomers having a sulfonamide group such as vinylbenzenesulfonamide. Examples of basic monomers include aromatic vinyl compounds having an amino group such as aminostyrene, nitrogen-containing heterocycle-containing polymerizable monomers such as vinylpyridine and vinylpyrrolidone, and (meth)acrylic acid esters having an amino group such as dimethylaminoethyl acrylate and diethylaminoethyl methacrylate. These acidic monomers and basic monomers, together with other monomers, contribute to stabilizing the particles in water in the process of producing toner base particles by suspension polymerization, emulsion polymerization aggregation, melt suspension, etc. These may be used alone or in combination, and may also exist as a salt together with a counter ion.

[0063] Examples of other monomers include styrenes such as styrene, methylstyrene, chlorostyrene, dichlorostyrene, p-tert-butylstyrene, pn-butylstyrene, and pn-nonylstyrene; acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, hydroxyethyl acrylate, and 2-ethylhexyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, hydroxyethyl methacrylate, and 2-ethylhexyl methacrylate; and amides such as acrylamide, N-propylacrylamide, N,N-dimethylacrylamide, N,N-dipropylacrylamide, and N,N-dibutylacrylamide. These may be used alone or in combination.

[0064] Furthermore, when the binder resin is a crosslinked resin, a radically polymerizable polyfunctional monomer is used in addition to the above-mentioned polymerizable monomer. Examples of polyfunctional monomers include divinylbenzene, hexanediol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, hexaethylene glycol dimethacrylate, nonaethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate, and diallyl phthalate. Polymerizable monomers having reactive groups in pendant groups, such as glycidyl methacrylate, methylol acrylamide, and acrolein, can also be used. Among these, radically polymerizable bifunctional polymerizable monomers are preferred, with divinylbenzene and hexanediol diacrylate being particularly preferred. These polyfunctional polymerizable monomers may be used alone or in combination.

[0065] The binder resin has a number average molecular weight measured by gel permeation chromatography (hereinafter referred to as GPC) of preferably 2000 or more, more preferably 2500 or more, and even more preferably 3000 or more, and preferably 50,000 or less, more preferably 40,000 or less, and even more preferably 35,000 or less. The weight average molecular weight measured in the same manner is preferably 30,000 or more, more preferably 40,000 or more, and even more preferably 50,000 or more, and preferably 2,000,000 or less, more preferably 1,000,000 or less, and even more preferably 500,000 or less. If the number average molecular weight and weight average molecular weight of the binder resin are within the above ranges, the durability, storage stability, and fixability of the toner are improved, which is desirable.

[0066] When polymerizing the binder resin, one or more known polymerization initiators can be used, if necessary. Examples include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; redox initiators in which these persulfates are combined with a reducing agent such as sodium sulfite; water-soluble polymerization initiators such as hydrogen peroxide, 4,4'-azobiscyanovaleric acid, t-butyl hydroperoxide, and cumene hydroxide; redox initiator systems in which these water-soluble polymerization initiators are combined with a reducing agent such as a ferrous salt; benzoyl peroxide; and 2,2'-azobisisobutyronitrile. These polymerization initiators can be added to the polymerization system before, simultaneously with, or after the addition of the polymerizable monomer, and these addition methods can be combined as necessary.

[0067] In the present invention, a known chain transfer agent can be used as needed. Specific examples of the chain transfer agent include t-dodecyl mercaptan, 2-mercaptoethanol, diisopropyl xanthogen, carbon tetrachloride, trichlorobromomethane, etc. The chain transfer agent may be used alone or in combination of two or more kinds, and is usually used in a proportion of 0 to 5% by mass based on the polymerizable monomer.

[0068] In the present invention, a known suspension stabilizer can be used as needed. Specific examples of the suspension stabilizer include calcium phosphate, magnesium phosphate, calcium hydroxide, magnesium hydroxide, etc. These may be used alone or in combination of two or more, and may be used in an amount of 1 part by mass to 10 parts by mass per 100 parts by mass of the polymerizable monomer.

[0069] The polymerization initiator and the suspension stabilizer may be added to the polymerization system either before, simultaneously with, or after the addition of the polymerizable monomer, and these addition methods may be combined as necessary. In addition, a pH adjuster, a polymerization degree regulator, an antifoaming agent, etc. may be added to the reaction system as appropriate.

[0070] In the present invention, when the binder resin is polymerized by the emulsion polymerization aggregation method, one or more emulsifiers selected from known cationic surfactants, anionic surfactants, and nonionic surfactants can be used in combination as the emulsifier to be used. Examples of cationic surfactants include dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, dodecyl pyridinium bromide, and hexadecyl trimethyl ammonium bromide. Examples of anionic surfactants include fatty acid soaps such as sodium stearate and sodium dodecanoate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, and sodium lauryl sulfate. Examples of nonionic surfactants include polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monooleate ether, and monodecanoyl sucrose.

[0071] In the present invention, the emulsifier is preferably used in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the polymerizable monomer. These emulsifiers may also be used in combination with one or more protective colloids, such as partially or completely saponified polyvinyl alcohols and cellulose derivatives such as hydroxyethyl cellulose.

[0072] In the present invention, the volume average particle size of the polymer primary particles obtained by the emulsion polymerization aggregation method is usually 0.02 μm or more, preferably 0.05 μm or more, and more preferably 0.1 μm or more, and usually 3 μm or less, preferably 2 μm or less, and more preferably 1 μm or less. If the particle size is smaller than the above range, it may be difficult to control the aggregation rate in the aggregation step, and if it is larger than the above range, the particle size of the toner base particles obtained by aggregation tends to be large, and it may be difficult to obtain a toner of the desired particle size.

[0073] In the toner base particles, a wax can be used as an offset preventing agent. In recent years, attempts have been made to improve the low-temperature fixability of toners. However, low-temperature fixability, anti-blocking properties, and high-temperature offset resistance are usually in a trade-off relationship, and in order to achieve both, it is preferable to use a wax as an offset preventing agent.

[0074] The wax used in the toner base particles may be any known wax, and specific examples include olefin waxes such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, and copolymerized polyethylene, paraffin wax, ester waxes having a long-chain aliphatic group such as behenyl behenate, montanic acid ester, and stearyl stearate, vegetable waxes such as hydrogenated castor oil carnauba wax, ketones having a long-chain alkyl group such as distearyl ketone, silicones having an alkyl group, higher fatty acids such as stearic acid, long-chain fatty acid alcohols, long-chain fatty acid polyhydric alcohols such as pentaerythritol, and partial esters thereof, and higher fatty acid amides such as oleic acid amide and stearic acid amide. Preferred examples include hydrocarbon waxes such as paraffin wax or Fischer-Tropsch wax, ester waxes, and silicone waxes. These waxes may be used alone or in combination of two or more.

[0075] Among these waxes, those having a melting point of 120° C. or less are preferred, those having a melting point of 110° C. or less are more preferred, and those having a melting point of 100° C. or less are particularly preferred, in order to improve fixability. The lower limit of the melting point of the wax is preferably 40° C. or more, and more preferably 50° C. or more. If the melting point of the wax is too high, the effect of lowering the fixation temperature may be poor, and if the melting point is too low, problems may arise with caking and storage stability.

[0076] In the present invention, the amount of wax is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of toner base particles. Also, it is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less. If the wax content in the toner base particles is too low, performance such as high-temperature offset resistance may be insufficient. If the wax content is too high, blocking resistance may be insufficient, or the wax may leak from the toner base particles, causing contamination of the device.

[0077] In the present invention, the wax is preferably blended in the emulsion polymerization aggregation method by dispersing the wax in advance in water to a volume average particle size of 0.01 μm or more and 2.0 μm or less, more preferably 1.0 μm or less, and particularly preferably 0.5 μm or less. In the emulsion polymerization aggregation method, it is preferable to add a wax dispersion dispersed to have an average particle size within the above range during emulsion polymerization or during the aggregation step.

[0078] In order to disperse the wax in the toner base particles at a suitable dispersed particle size, it is preferable to add the wax as a seed during emulsion polymerization, i.e., to perform so-called seed polymerization. By adding the wax as a seed, the wax is dispersed finely and uniformly in the toner, and therefore deterioration of the chargeability and heat resistance of the toner can be suppressed. Alternatively, a wax-long-chain polymerizable monomer dispersion can be prepared by dispersing a wax together with a long-chain polymerizable monomer such as stearyl acrylate in an aqueous dispersion medium, and then polymerizing the polymerizable monomer in the presence of the wax-long-chain polymerizable monomer.

[0079] Any known colorant can be used as the colorant contained in the toner base particles. Specific examples of the colorant include carbon black, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa yellow, rhodamine dyes and pigments, chrome yellow, quinacridone, benzidine yellow, rose bengal, triallylmethane dyes, monoazo dyes, disazo dyes, and condensed azo dyes and pigments, which can be used alone or in combination. In the case of full-color toners, it is preferable to use benzidine yellow, monoazo-based, and condensed azo-based dyes and pigments for yellow, quinacridone and monoazo-based dyes and pigments for magenta, and phthalocyanine blue for cyan. The colorant is preferably used in an amount of 3 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the primary polymer particles.

[0080] In emulsion polymerization aggregation, the colorant is typically incorporated in an aggregation step. A dispersion of polymer primary particles and a dispersion of colorant particles are mixed to form a mixed dispersion, which is then aggregated to form particle aggregates. The colorant is preferably dispersed in water in the presence of an emulsifier, and the volume-average particle size of the colorant particles is preferably 0.01 μm or more, more preferably 0.05 μm or more, and preferably 3 μm or less, more preferably 1 μm.

[0081] The core particles may be produced by any polymerization method, such as a suspension polymerization method, an emulsion polymerization aggregation method, or a dissolution suspension method, without any particular limitation. In the suspension polymerization method, a colorant, a polymerization initiator, and, if necessary, additives such as wax, polar resin, charge control agent, and crosslinking agent are added to the binder resin monomer to prepare a uniformly dissolved or dispersed monomer composition. This monomer composition is then dispersed in an aqueous medium containing a dispersion stabilizer and other additives. Granulation is performed, preferably with the stirring speed and time adjusted so that droplets of the monomer composition have the desired core particle size. Polymerization is then performed while stirring is continued to an extent that the particle state is maintained and particle sedimentation is prevented by the action of the dispersion stabilizer. These particles are collected by washing and filtration and dried to obtain core particles. Next, as described below, a process (encapsulation process) is performed in which primary polymer particles are coated on the surfaces of the core particles to form shell particles, thereby obtaining toner mother particles with a core-shell structure.

[0082] Examples of production methods using emulsion polymerization aggregation include a method in which a colorant dispersion, a wax dispersion, etc. are prepared, and primary polymer particles of a binder resin monomer obtained by emulsion polymerization or primary polymer particles of a wax-encapsulated binder resin monomer obtained by emulsion polymerization in the presence of a wax dispersion are mixed with the colorant dispersion, the wax dispersion, etc., and subjected to a step of aggregating by heating or the like, followed by a maturing step; a method in which primary polymer particles of a binder resin monomer obtained by emulsion polymerization in the presence of a colorant or a colorant and a wax are mixed with a wax dispersion, etc., and subjected to a step of aggregating by heating or the like, followed by a maturing step; and a method in which primary polymer particles of a binder resin monomer obtained by emulsion polymerization in the presence of a colorant and a wax are mixed with a wax dispersion, etc., and subjected to a step of aggregating by heating or the like, followed by a maturing step. Core particles can be obtained by these methods. Next, as will be described later, a step (encapsulation step) is carried out in which polymer primary particles are coated on the surfaces of the core particles to form shell particles, thereby obtaining toner base particles having a core-shell structure. Among the above-mentioned emulsion polymerization aggregation methods, when a binder resin monomer is polymerized in the presence of a colorant, the metal in the colorant affects the radical polymerization, making it difficult to control the molecular weight and rheology of the resin, and there is a risk that desired polymer primary particles cannot be obtained. Therefore, the emulsion polymerization aggregation method in which a colorant is not added during emulsion polymerization but a colorant dispersion is added in the aggregation step is preferred.

[0083] In the present invention, in the aggregation step of the emulsion polymerization aggregation method, the blending components such as the polymer primary particles, colorant particles, and, if necessary, the charge control agent and wax are mixed simultaneously or successively. However, from the viewpoint of uniformity of component composition and uniformity of particle size, it is preferable to prepare dispersions of each component in advance, i.e., a polymer primary particle dispersion, a colorant particle dispersion, and, if necessary, a charge control agent dispersion and a wax fine particle dispersion, and then mix these to obtain a mixed dispersion.

[0084] In the emulsion polymerization aggregation method, aggregation is usually carried out in a tank equipped with a stirrer, and there are a heating method, a method of adding an electrolyte, and a combination of these methods. When polymer primary particles are aggregated under stirring to obtain particle aggregates of a desired size, the particle size of the particle aggregates is controlled by the balance between the cohesive force between the particles and the shear force caused by stirring, and the cohesive force can be increased by heating or adding an electrolyte.

[0085] In the present invention, when an electrolyte is added to perform aggregation, the electrolyte may be any of an acid, an alkali, or a salt, and may be either organic or inorganic. Specific examples of acids include hydrochloric acid, nitric acid, sulfuric acid, and citric acid; alkalis include sodium hydroxide, potassium hydroxide, and aqueous ammonia; and salts include NaCl, KCl, LiCl, Na2SO4, K2SO4, Li2SO4, MgCl2, CaCl2, MgSO4, CaSO4, ZnSO4, Al2(SO4)3, Fe2(SO4)3, CH3COONa, and CH5SO3Na. Among these, inorganic salts having a divalent or higher polyvalent metal cation are preferred.

[0086] In the present invention, the amount of electrolyte added varies depending on the type of electrolyte, the target particle size, etc., but is preferably 0.02 parts by mass or more, more preferably 0.05 parts by mass or more, per 100 parts by mass of the solid components of the mixed dispersion. It is also preferably 25 parts by mass or less, more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less. If the amount of electrolyte added is too small, the aggregation reaction may proceed slowly, resulting in problems such as fine powder of 1 μm or less remaining after the aggregation reaction or the average particle size of the resulting particle aggregates not reaching the target particle size. If the amount of electrolyte added is too large, rapid aggregation may occur, making it difficult to control the particle size, and problems such as the resulting aggregated particles containing coarse particles or irregularly shaped particles may occur. When aggregation is carried out by adding an electrolyte, the aggregation temperature is preferably 20°C or higher, more preferably 30°C or higher, and preferably 80°C or lower, more preferably 70°C or lower.

[0087] The time required for aggregation is optimized depending on the equipment configuration and processing scale, but in order for the aggregated particles to reach the target particle size, it is generally desirable to maintain the above-mentioned predetermined temperature for at least 30 minutes. The temperature may be raised to the predetermined temperature at a constant rate or in stages. In the present invention, if necessary, resin fine particles may be attached or fixed to the surface of the particle aggregates after the above-mentioned aggregation treatment. By attaching or fixing resin fine particles with controlled properties to the surface of the particle aggregates, the chargeability and heat resistance of the resulting toner base particles may be improved, and the effects of the present invention may be further enhanced.

[0088] The resin particles preferably have a glass transition temperature higher than that of the polymer primary particles, since this further improves blocking resistance without impairing fixability. The volume average particle diameter of the resin particles is preferably 0.02 μm or more, more preferably 0.05 μm or more. Furthermore, it is preferably 3 μm or less, and even more preferably 1.5 μm or less. The resin particles may be those obtained by emulsion polymerization of the same polymerizable monomers as those used for the polymer primary particles.

[0089] Resin particles are typically dispersed in water or a water-based liquid using a surfactant for use as a dispersion. However, if a charge control agent is added after the aggregation process, it is preferable to add the resin particles after adding the charge control agent to the dispersion containing the particle aggregates. To increase the stability of the particle aggregates obtained in the aggregation process, it is preferable to fuse the aggregated particles in a ripening process following the aggregation process. The temperature in the ripening process is preferably equal to or higher than the glass transition temperature (Tg) of the polymer primary particles, more preferably at least 5°C higher than Tg, and preferably equal to or lower than 80°C higher than Tg, more preferably equal to or lower than 50°C higher than Tg. The time required for the ripening process varies depending on the shape of the desired toner base particles, but it is generally desirable to maintain the temperature for 0.1 to 10 hours, preferably 1 to 6 hours, after the temperature reaches or exceeds Tg of the polymer primary particles.

[0090] After the aggregation step, preferably before or during the aging step, it is preferable to add a surfactant, increase the pH value, or use a combination of these methods. The surfactant used here can be one or more emulsifiers that can be used in producing polymer primary particles, but it is particularly preferable to use the same emulsifier as used in producing the polymer primary particles. When a surfactant is added, the amount added is not limited, but is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the solid components of the mixed dispersion. By adding a surfactant after the aggregation step or increasing the pH value before the completion of the aging step, it is possible to suppress the aggregation of particle aggregates formed in the aggregation step, and in some cases, it is possible to suppress the generation of coarse particles after the aging step.

[0091] The heat treatment in the aging step fuses and integrates the primary polymer particles in the aggregates, and the core particle shape of the aggregates becomes nearly spherical. The particle aggregates before the aging step are considered to be aggregates formed by electrostatic or physical aggregation of the primary polymer particles, but after the aging step, the primary polymer particles constituting the particle aggregates are fused to each other, and the core particle shape becomes nearly spherical. According to this aging step, by controlling the temperature and time of the aging step, it is possible to produce core particles of various shapes depending on the purpose, such as grape-shaped shapes formed by aggregation of primary polymer particles, potato-shaped shapes formed by advanced fusion, and spherical shapes formed by further advanced fusion.

[0092] <Shell particles> In the present invention, the shell particles to be coated on the surface of the core particles may be inorganic particles or resin particles, and are not particularly limited. From the viewpoints of particle production, controllability of particle performance, and improvement of fixing strength during toner fixing, the shell particles are preferably resin particles. When the shell particles are resin fine particles, the resin component is not particularly specified, but may be, for example, a resin used in general toner binder resins such as styrene-based, acrylic-based, or ester-based resins, or a copolymer or blend thereof. Shell particles made of such resins can be produced by directly emulsifying the resin or by a polymerization method such as emulsion polymerization or suspension polymerization. From the viewpoints of particle size control and ease of microparticulation, a polymerization method is preferred, and from the viewpoints of controlling the particle size and particle size distribution of the microparticles, an emulsion polymerization aggregation method is more preferred.

[0093] When resin shell particles are prepared by emulsion polymerization aggregation, they can be prepared by the same emulsion polymerization aggregation method as used for the primary polymer particles of the binder resin monomer used in the emulsion polymerization aggregation method described above. The volume average particle size of the resin shell particles is not particularly limited as long as it does not impair the effects of the present invention, but is preferably 20 nm or more, more preferably 50 nm or more. It is also preferably 500 nm or less, more preferably 150 nm or less.

[0094] The weight-average molecular weight of the resin shell particles is preferably 2,000 to 30,000, more preferably 4,000 to 25,000, and particularly preferably 6,000 to 20,000. The glass transition temperature (Tg) of the resin shell particles is not particularly limited as long as it is within a range that does not impair the effects of the present invention, but the lower limit is preferably 40°C or higher, more preferably 45°C or higher, and the upper limit is preferably 100°C or lower, more preferably 80°C or lower, and even more preferably 75°C or lower.

[0095] From the viewpoint of enhancing the blocking resistance effect, the Tg of the resin shell particles is preferably higher than the Tg of the binder resin of the core particles. In this case, the Tg of the resin shell particles is preferably (the Tg of the core particles) or higher, more preferably (the Tg of the core particles + 2)°C or higher, and even more preferably (the Tg of the core particles + 5)°C or higher. On the other hand, it is preferably (the Tg of the core particles + 50)°C or lower, more preferably (the Tg of the core particles + 30)°C or lower, and even more preferably (the Tg of the core particles + 20)°C or lower. If the weight average molecular weight and glass transition temperature of the resin shell particles are too low, the blocking resistance of the toner may deteriorate, whereas if they are too high, the low-temperature fixability may deteriorate.

[0096] The content of the shell particles relative to the toner base particles is not particularly limited as long as it does not impair the effects of the present invention, but the lower limit is usually 0.01% by mass or more, and preferably 0.3% by mass or more, while the upper limit is usually 10% by mass or less.

[0097] The shell particles may be either non-chargeable or chargeable depending on the intended use. If the shell particles are chargeable, they may be positively or negatively chargeable. The core-shell toner base particles of the present invention not only achieve both low-temperature fixability and anti-blocking properties, but also control the chargeability of the toner base particles by using chargeable shell particles. The chargeability of the toner base particles is generally adjusted using a charge control agent, binder resin, or external additive. While inorganic charge control agents are generally used as charge control agents, in recent years, research has been conducted into using resins with charge control capabilities (charge control resins) as charge control agents and incorporating various functional groups into binder resins to utilize their properties to improve chargeability. For example, in the case of positively chargeable toner base particles, chargeability is generally imparted by copolymerizing a monomer containing an amino group or an amide bond with the binder resin.

[0098] Charge control agents are typically used by dispersing them in the binder resin of toner particles or copolymerizing a polymerizable monomer with charge control properties (hereinafter sometimes referred to as a charge control resin) with the binder resin and dispersing it in the binder resin. However, uneven dispersion of the charge control agent or charge control resin within the toner particles and on the surface of the toner particles can lead to problems such as increased fogging and toner scattering. Therefore, in recent years, the trend toward smaller toner particle size for the purpose of achieving higher image resolution has led to a greater demand for uniform dispersion of the charge control agent or charge control resin. It is generally believed that the chargeability of toner particles is controlled by the resin properties on the surface of the toner particles. To achieve a uniform dispersion of the charge control agent or charge control resin in the binder resin of the toner particles, a larger amount of the charge control agent or charge control resin must be added to achieve sufficient charge control. Furthermore, the charge control agent or charge control resin may deteriorate the low-temperature fixability of the toner particles.

[0099] Therefore, it is desirable that the charge control agent or charge control resin is present on the surface of the toner base particle. Compared to toner base particles obtained by a pulverization method, in the case of toner base particles obtained by a polymerization method, particularly toner base particles obtained by an emulsion polymerization aggregation method, the positions of the charge control agent or charge control resin in the toner base particle can be controlled by controlling the timing of mixing the charge control agent or charge control resin during the production of the toner base particle, but it is difficult to expose them completely on the surface of the toner base particle.

[0100] Therefore, in the present invention, when chargeability is imparted to the toner base particles, in order to effectively control the chargeability of the toner base particles, it is preferable to form a core-shell structure in which the shell layer has charge control properties by incorporating a charge control agent or charge control resin into the shell particles. When the shell particles are resin fine particles, it is preferable to form resin shell particles in which the resin used for the shell particles is copolymerized with a charge control resin.

[0101] When the shell particles are positively charged resin microparticles, examples of the positively charged charge control resin include resins containing amino groups such as -NH2, -NHCH3, -N(CH3)2, -NHC2H5, -N(C2H5)2, and -NHC2H4OH; and resins containing quaternary ammonium salts of these ammonium salts. Among these, resins containing quaternary ammonium salts are preferred.

[0102] Such positively chargeable charge control resins can be obtained, for example, by copolymerizing an amino group-containing monovinyl monomer with a monomer copolymerizable therewith. Positively chargeable charge control resins can also be obtained by ammonium salting a copolymer containing an amino group. Resins containing quaternary ammonium salts can also be obtained by copolymerizing an ammonium salt group-containing monovinyl monomer with a monovinyl monomer copolymerizable therewith. However, the methods for producing positively chargeable charge control resins are not limited to these methods. Monomers commonly used in binder resins can be used as the copolymerized monomers.

[0103] As the positively chargeable charge control resin, among resins containing a quaternary ammonium salt group, acrylates containing a quaternary ammonium salt represented by the following general formula (1) and acrylamides containing a quaternary ammonium salt represented by the following general formula (2) are preferred, and acrylates containing a quaternary ammonium salt represented by the following general formula (1) are more preferred.

[0104] [ka]

[0105] In the above general formula (1) and general formula (2), R 1 is a hydrogen atom or a methyl group, and R 2 is an alkylene group, and R 3 , R 4 and R 5 are each independently a hydrogen atom or a linear, branched or cyclic alkyl group having 1 to 6 carbon atoms, and X -is a halogen ion, a benzenesulfonate ion, or an alkylbenzenesulfonate ion.

[0106] In the quaternary ammonium salt represented by the general formula (1), X - is preferably a chloride ion or a toluenesulfonate ion, and R 1 is preferably a hydrogen atom or a methyl group, and R 2 is preferably an alkylene group having 1 to 3 carbon atoms such as CH2, C2H4, or C3H6, or a derivative thereof, and R 3 ~R 5 are preferably each independently an alkyl group such as CH3, C2H5, or C3H7.

[0107] Examples of the amino group-containing (meth)acrylate monomer include dimethylaminomethyl (meth)acrylate, diethylaminomethyl (meth)acrylate, dipropylaminomethyl (meth)acrylate, diisopropylaminomethyl (meth)acrylate, ethylmethylaminomethyl (meth)acrylate, methylpropylaminomethyl (meth)acrylate, dimethylamino-1-ethyl (meth)acrylate, diethylamino-1-ethyl (meth)acrylate, dipropylamino-1-ethyl (meth)acrylate, diisopropylamino-1-ethyl (meth)acrylate, ethylmethylamino-1-ethyl (meth)acrylate, methylpropylamino-1-ethyl (meth)acrylate, dimethylamino-2-ethyl (meth)acrylate, diethylamino-2-ethyl (meth)acrylate, dipropylamino-2-ethyl (meth)acrylate, and diisopropylamino-2-ethyl (meth)acrylate. acrylate, ethylmethylamino-2-ethyl (meth)acrylate, methylpropylamino-2-ethyl (meth)acrylate, dimethylamino-1-propyl (meth)acrylate, diethylamino-1-propyl (meth)acrylate, dipropylamino-1-propyl (meth)acrylate, diisopropylamino-1-propyl (meth)acrylate, ethylmethylamino-1-propyl (meth)acrylate, methylpropylamino-1-propyl (meth)acrylate, dimethylamino-2-propyl (meth)acrylate, diethylamino-2-propyl (meth)acrylate, dipropylamino-2-propyl (meth)acrylate, diisopropylamino-2-propyl (meth)acrylate, ethylmethylamino-2-propyl (meth)acrylate, methylpropylamino-2-propyl (meth)acrylate and other N,N-disubstituted aminoalkyl (meth)acrylate compounds.

[0108] Examples of quaternizing agents used to convert the copolymer into an ammonium salt include alkyl halides such as methyl iodide, ethyl iodide, methyl bromide, and ethyl bromide; alkyl paratoluenesulfonates such as methyl paratoluenesulfonate, ethyl paratoluenesulfonate, and propyl paratoluenesulfonate; etc. Commercially available quaternary ammonium salt group-containing (meth)acrylate monomers include Blemmer QA (manufactured by NOF Corporation).

[0109] The amount of chargeable monomer units having functional groups such as amino groups and ammonium salt groups in the charge control resin is preferably 0.5 to 15% by mass, more preferably 1 to 12% by mass, and particularly preferably 2 to 10% by mass. If the amount of chargeable monomer units having such functional groups is too small, a large amount of charge control resin is required to obtain the required amount of charge, which tends to reduce the environmental stability of the toner. If the amount of chargeable monomer units having such functional groups is too large, the amount of charge of the toner will decrease significantly under high temperature and high humidity conditions, which may cause fogging.

[0110] Various commercially available products can be used as the positively charged charge control resin. Examples include "FCA-161P" (styrene / acrylic resin), "FCA-207P" (styrene / acrylic resin), and "FCA-201-PS" (styrene / acrylic resin), both of which are manufactured by Fujikura Kasei Co., Ltd. As the negatively charged charge control resin, any resin can be used, including styrene / acrylic resin and polyester resin, which are generally used in negatively charged toners. Commercially available negative charge control resins can also be used.

[0111] The resin charge controllable shell particles can be produced by directly emulsifying the charge control resin or by a polymerization method such as emulsion polymerization or suspension polymerization. From the viewpoint of particle size control and ease of microparticulation, polymerization methods are preferred, and from the viewpoint of controlling the particle size and particle size distribution of the microparticles, emulsion polymerization aggregation methods are more preferred. When producing resin shell particles by emulsion polymerization aggregation methods, they can be produced by copolymerizing a chargeable monomer with the same production method as for the polymer primary particles of the binder resin monomer used in the emulsion polymerization aggregation method described above.

[0112] When a charge control resin is used in shell particles, core particles, or toner base particles, the amount of chargeable monomer used is not particularly limited as long as it does not significantly impair the effects of the present invention, but the lower limit relative to the toner base particles is usually 0.01% by mass or more, and in order to exert a better charge control function, it is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more, while the upper limit is usually 5% by mass or less, and in order to prevent the charge control resin from affecting toner performance (particularly environmental resistance, fixability, etc.), it is preferably 2% by mass or less, and more preferably 1% by mass or less.

[0113] <Method of coating core particles with shell particles (encapsulation process)> There are two methods for producing toner base particles having a core-shell structure: a method in which a capsule structure is formed by mixing shell particle components in the latter half of the core particle formation process, and a method in which a capsule structure is formed by an encapsulation process in which a shell layer is formed on the surface of completed core particles, separate from the core particle production process.

[0114] In the former case, the core particles are still being formed, and the core particle surfaces are not stable, so the shell particles tend to embed in the core particle layer and the adhesion strength of the shell particles to the core particles is strong. However, because the shell particles are embedded in the core particle surfaces, the core particle components tend to come out onto the surface of the toner base particles, and more shell particles are required to completely cover (encapsulate) the core particles with the shell particles.

[0115] On the other hand, in the latter case, a capsule structure is formed on the surface of the completed core particles through an encapsulation process of shell particles, separate from the core particle formation process, so the shell particles tend to remain on the surface of the core particles, and a uniform capsule structure can be formed with fewer shell particles. The high encapsulation efficiency prevents the core particle components from being exposed to the surface of the toner base particles.

[0116] In the latter method, the charge polarity of the core particles and the charge polarity of the shell particles are set opposite to each other, and the shell particles are electrostatically attached. This electrostatic attachment makes it easier for the shell particles to remain on the surface of the core particles, increasing the adhesion efficiency (encapsulation efficiency) of the shell particles to the core particles, and as a result, preventing exposure of the core particle components to the surface of the toner mother particles. Furthermore, due to the electrostatic repulsion between the shell particles, a uniform coating layer close to a single layer without overlapping shell particles can be formed on the surface of the core particles with fewer shell particles. The thickness of the single shell layer formed by the electrostatic attachment of the shell particles described above is the same as the volume average particle size of the shell particles. It is not particularly limited as long as the effects of the present invention are not significantly impaired, but is usually 20 nm or more, preferably 50 nm or more, and usually 500 nm or less, preferably 150 nm or less.

[0117] Furthermore, a uniform double shell layer can be formed by first forming a shell layer using shell particles with a certain charge polarity, and then forming another shell layer using shell particles with the opposite charge polarity to the shell particles. By repeating this double shell layer formation, a uniform multiple shell layer can also be formed. When a multiple shell layer is employed, the charge of the toner base particles can also be controlled by the charge polarity of the shell particles in the outermost layer.

[0118] The process of coating core particles with shell particles (encapsulation process) is carried out by directly adding shell particles to a dispersion of core particles and mixing them. For core particles obtained by a pulverization method, a dispersion prepared by dispersing the core particles with an emulsifier can be used as the dispersion of core particles. For core particles obtained by a polymerization method, the slurry used during core particle production can be used as is. From the perspective of more precise encapsulation control, it is preferable to remove the emulsifier present in the core particle dispersion by a method such as washing, to the extent that agglomerations of core particles do not occur.

[0119] For example, when preparing a dispersion of core particles obtained by polymerization, the slurry obtained during the polymerization process is dehydrated and spray-washed to remove water, emulsifiers, and soluble impurities contained in the water, and the resulting cake of core particles is then redispersed in water to produce a core particle dispersion. Regarding the conditions for the encapsulation process, the mixing temperature for the core particles and shell particles is not particularly limited. However, mixing at a temperature 10°C or more lower than the lowest Tg of the core particles and shell particles is preferred, as this prevents the formation of particle aggregates due to rapid aggregation and allows for uniform mixing of the core particles and shell particles. To increase the encapsulation efficiency and strength of the shell particles, the temperature can be controlled by adding a flocculant such as an electrolyte or adjusting the mixing temperature, as necessary.

[0120] To control the encapsulation of shell particles into core particles, the electrolyte concentration or pH of the mixed solution can be adjusted. The electrolyte can be an inorganic or organic acid, alkali, or salt. It can be selected based on the polarity of the shell particle dispersion. For example, if the polarity of the shell particle dispersion is anionic, an acidic electrolyte is preferred. If the polarity of the shell particle dispersion is cationic, an alkaline electrolyte is preferred. If the polarity of the shell particle dispersion is nonionic, either electrolyte is effective.

[0121] The mixing temperature can be controlled to improve the encapsulation efficiency and capsule strength of the shell particles. When adjusting the temperature, the mixing temperature is preferably set to a temperature equal to or lower than the Tg of the core particles + 20°C to prevent the shell particles from embedding in the surface of the core particles. Furthermore, when the surface of the core-shell toner mother particles obtained using the electrostatic adhesion described above is observed by SEM, it can be confirmed that the shell particles are not embedded in the core particle surface but are attached to the core particle surface in a state where the exposed portion of the shell particle is equal to or larger than the radius of the shell particle. The occupancy rate of the projected area of ​​the shell particles relative to the projected area of ​​the core particle is typically 30% or more, and preferably 50% or more from the viewpoint of achieving both toner storage stability and low-temperature fixing performance. However, due to electrostatic repulsion between the shell particles, it is typically 90% or less.

[0122] <Washing and drying of toner base particles> The toner base particles obtained by coating the core particles with the shell particles are separated from the aqueous solvent, washed, dried, and subjected to the above-mentioned external additive treatment, etc., to be used as a toner for developing electrostatic images. Water is used as the liquid used for washing, but washing with an acid or alkali aqueous solution is also possible. Washing with warm water or hot water is also possible, and these methods can be used in combination. This washing process is preferable because it reduces or removes suspension stabilizers, emulsifiers, unreacted residual monomers, etc. In the washing process, the toner base particles are preferably made into a thick slurry or wet cake by, for example, filtering or decanting the washing liquid, and then a new washing liquid is added to this to disperse the toner base particles, repeating this process. It is preferable to collect the toner base particles after washing in the form of a wet cake, in terms of handling in the subsequent drying process.

[0123] In the drying step, fluidized drying methods such as vibration fluidized drying and circulating fluidized drying, flash drying, vacuum drying, freeze drying, spray drying, flash jet drying, etc. The operating conditions in the drying step, such as temperature, air volume, and degree of vacuum, are optimized as appropriate based on the Tg of the toner base particles, the shape, mechanism, size, etc. of the device to be used.

[0124] <Physical properties of the toner base particles> The true specific gravity of the toner base particles is 0.8 g / cm 3 More than 1.5g / cm 3 Preferably, it is 1.0 g / cm or less. 3 More than 1.3g / cm 3 More preferably, it is: In addition, the absolute value of the difference between the true specific gravity of the external additive 1 and that of the external additive 2 is 0.2 (unit: g / cm 3 ) or less. When the absolute value of the difference between the true specific gravity of the toner base particles and the true specific gravity of external additives 1 and 2 is 0.2 or less, the above-mentioned effects of using external additives 1 and 2 with low specific gravities can be more effectively obtained. The smaller the absolute value of this difference, the better, and it is more preferable that it is 0.15 or less.

[0125] The toner base particles preferably have an average circularity of 0.95 to 0.99, and more preferably 0.955 to 0.98. If the average circularity is too small, poor adhesion of external additives to the toner base particles may cause poor charging, resulting in a decrease in image density, while if the average circularity is too large, poor cleaning may occur due to the shape of the toner base particles. The average circularity can be adjusted to the above range relatively easily by producing the particles using the above-mentioned emulsion polymerization flocculation method.

[0126] In the present invention, the circularity is defined as the circumferential length of a circle having the same projected area as the particle image divided by the circumferential length of the projected image of the particle. The average circularity can be measured using a flow particle analyzer "FPIA3000" manufactured by Malvern Instruments, as described in the Examples below.

[0127] The toner base particles preferably have a volume average particle diameter (Dv) of 8 μm or less and a ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) of 1.2 or less. If the volume average particle diameter (Dv) exceeds 8 μm, the image resolution may decrease. From this viewpoint, the volume average particle diameter (Dv) of the toner base particles is preferably 8 μm or less, and more preferably 7 μm or less. If the volume average particle diameter (Dv) is too small, the toner fluidity may decrease, the transferability may decrease, blurring may occur, and the print density may decrease. Therefore, the volume average particle diameter (Dv) of the toner base particles is preferably 4 μm or more, and more preferably 5 μm or more.

[0128] Furthermore, if the ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) is greater than 1.2, blurring may occur, and transferability, print density, and resolution may be reduced. From this viewpoint, the Dv / Dn of the toner base particles is preferably 1.2 or less, and more preferably 1.15 or less. The lower limit of Dv / Dn is usually 1.00.

[0129] The volume average particle diameter (Dv) and number average particle diameter (Dn) of the toner base particles can be measured using, for example, a particle size distribution analyzer, Multisizer (manufactured by Beckman Coulter), as described in the Examples below.

[0130] The toner base particles may be either positively or negatively chargeable, but are preferably positively chargeable from the viewpoint of charge stability.

[0131] [Charge amount of this toner] The toner is preferably positively charged, and the charge amount (Q / M) (μC / g) of the toner, measured by the method described in the Examples section below, is preferably 10 to 50, and particularly preferably 15 to 40. If Q / M is equal to or greater than the lower limit, the occurrence of fog on the image can be prevented. If Q / M is equal to or less than the upper limit, the image density and print quality are not impaired.

[0132] [Cartridges and image forming devices] Next, an embodiment of an image forming apparatus using the toner (image forming apparatus of the present invention) will be described. However, the embodiment is not limited to the following description, and can be modified as desired without departing from the gist of the present invention.

[0133] The image forming apparatus includes an electrophotographic photosensitive member, a charging device (charging means), an exposure device (image exposure means), a developing device (developing means), a transfer device (transfer means), and toner, and may further include a cleaning device and a fixing device as needed.

[0134] The electrophotographic photosensitive member is not particularly limited, but for example, a drum-shaped photosensitive member having a photosensitive layer formed on the surface of a cylindrical conductive support can be used.

[0135] The charging device is a device for uniformly charging the surface of the electrophotographic photosensitive member to a predetermined potential. Typical charging devices include non-contact corona charging devices such as corotrons and scorotrons, and contact charging devices.

[0136] The type of the exposure device is not particularly limited as long as it can expose an electrophotographic photosensitive member to light to form an electrostatic latent image on the photosensitive surface of the electrophotographic photosensitive member.

[0137] The transfer device applies a predetermined voltage (transfer voltage) with a polarity opposite to the charged potential of the toner, and transfers the toner image formed on the electrophotographic photosensitive member onto recording paper (paper, medium). There are no particular limitations on the type of transfer device, and any device using any method, such as corona transfer or roller transfer, can be used.

[0138] The cleaning device scrapes off residual toner adhering to the electrophotographic photosensitive member with a cleaning member and collects the residual toner. However, if there is little or almost no toner remaining on the surface of the electrophotographic photosensitive member, a cleaning device may not be necessary. There are no particular restrictions on the cleaning device, and any cleaning device such as a brush cleaner, a magnetic roller cleaner, or a blade cleaner can be used.

[0139] In the image forming apparatus configured as above, an image is recorded as follows.

[0140] First, the surface (photosensitive surface) of the electrophotographic photoreceptor is charged to a predetermined potential by a charging device. At this time, charging may be performed by a DC voltage or by superimposing an AC voltage on the DC voltage. Next, the charged photosensitive surface of the electrophotographic photoreceptor is exposed by an exposure device in accordance with the image to be recorded, forming an electrostatic latent image on the photosensitive surface, and then the electrostatic latent image formed on the photosensitive surface of the electrophotographic photoreceptor is developed by a development device. The developing device forms a thin layer of toner using a regulating member such as a developing blade, frictionally charges the toner to a predetermined polarity, and transports the toner while carrying it on a developing roller, bringing it into contact with the surface of an electrophotographic photosensitive member.

[0141] When the charged toner carried on the developing roller comes into contact with the surface of the electrophotographic photosensitive member, a toner image corresponding to the electrostatic latent image is formed on the photosensitive surface of the electrophotographic photosensitive member. This toner image is then transferred onto recording paper or the like by a transfer device. After this, toner that has not been transferred and remains on the photosensitive surface of the electrophotographic photosensitive member is removed by a cleaning device. After the toner image is transferred to a printing medium such as recording paper, the toner image is passed through a fixing device to be thermally fixed to the printing medium such as recording paper, thereby obtaining a final image.

[0142] In addition to the above-described configuration, the image forming apparatus may be configured to be capable of performing, for example, a charge removal process, which is a process of removing charge from an electrophotographic photosensitive member by exposing the electrophotographic photosensitive member to light.

[0143] The image forming apparatus may be further modified, for example, to be configured to perform a pre-exposure process, an auxiliary charging process, etc., to perform offset printing, or to be configured as a full-color tandem system using multiple types of toner.

[0144] A component for storing toner may be combined with one or more of a charging device, an exposure device, a developing device, a transfer device, a cleaning device, and a fixing device to form an integrated cartridge (hereinafter referred to as a "toner cartridge" as appropriate), and this toner cartridge may be configured to be detachable from the main body of an image forming device such as a copier or laser beam printer. The toner is applied to this toner cartridge to constitute the toner cartridge of the present invention. [Example]

[0145] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. In the following examples and comparative examples, "parts" simply means "parts by mass." Furthermore, the unit "%" in solid content concentration and aqueous solution concentration means "% by mass."

[0146] [Measurement and evaluation method] The methods for measuring and evaluating various physical properties and characteristics are as follows:

[0147] <True specific gravity> The true specific gravity of the external additive and the toner base particles was measured using a dry automatic density meter, Autopycnometer (manufactured by Yuasa Ionics Co., Ltd.) under the following conditions. Cell: SM cell (10ml) Sample size: 0.05g

[0148] <Volume average particle size (Dv) · Number average particle size (Dn)> The volume average particle diameter (Dv) and number average particle diameter (Dn) of the toner base particles were measured using a Beckman Coulter Multisizer III (aperture diameter 100 μm: hereinafter abbreviated as "Multisizer") and an Isoton II from the same company as the dispersion medium, dispersing the toner base particles to a dispersoid concentration of 0.03 mass%. From the obtained Dv and Dn values, the ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) was calculated.

[0149] <Number average primary particle diameter> The average primary particle size of the external additives was measured using a transmission electron microscope image. Several thousand particles were randomly selected from the target external additive in the transmission electron microscope image, and the average primary particle size was calculated by averaging the particle sizes by number.

[0150] <Average circularity> The average circularity of the toner base particles was measured by dispersing the toner base particles, which are the dispersoid, in a dispersion medium (Celsius: manufactured by Malvern Instruments) to a concentration of 5720 to 7140 particles / μL, and using a flow particle analyzer ("FPIA3000" manufactured by Malvern Instruments) in HPF mode under conditions of an HPF analysis volume of 0.35 μL and an HPF detection volume of 2000 to 2500 particles.

[0151] <Amount of charge> 9.7 g of carrier (manufactured by Powder Tech Co., Ltd., product name "F150") and 0.3 g of sample (external additive, toner base particles, or toner) were weighed out and placed in a glass bottle with a volume of 30 mL (internal bottom diameter 30 mm, height 65 mm). The bottle was shaken at 500 rpm for 1 minute using a shaker (manufactured by TAITEC Co., Ltd., product name "RECIPRO SHAKER NR1"), and then blown with nitrogen gas at a pressure of 0.25 MPa using a blow-off meter (manufactured by Toshiba Chemical Co., Ltd., product name "TB-203"), followed by suction at a pressure of 350 mmH2O for 3 seconds. The carrier and sample were separated using a 400-mesh wire net, and the blow-off charge amount was measured. The measurements were carried out in an environment with a temperature of 23°C and a relative humidity of 50%. The weight of the mixture of carrier and sample used in the blow-off measurement was defined as M1 (g), the weight of the carrier remaining on the wire mesh after blow-off was defined as M2 (g), and the resulting charge amount was defined as Q (C). The charge amount (Q / M) (μC / g) was calculated using the following formula (1) to obtain the value. Charge amount (Q / M) = -Q / (10 6 ×(M2-M1)) (1)

[0152] <Print durability> Toner was placed in a commercially available non-magnetic single-component development printer (print speed 30 pages / min) equipped with a scorotron and photoreceptor, and left overnight at room temperature and humidity of 23°C and 50% humidity. Subsequently, 3,000 sheets were continuously printed at 4% print density under the same room temperature and humidity environment. A solid white print (0% print density) was then performed, and the printer was stopped midway through the solid white print. The toner in the non-image area on the photoreceptor after development was adhered to adhesive tape (product name "Scotch Mending Tape 810-3-18" manufactured by 3M Japan Co., Ltd.), then peeled off, and the tape was applied at 80 g / m. 2 The toner was pasted onto a sheet of printing paper. For comparison, mending tape was pasted onto the same sheet of paper as it was, and the color difference ΔE between the two was measured using a spectrophotometric densitometer FD-5 (manufactured by Konica Minolta) to evaluate fogging. A smaller color difference ΔE indicates better image quality and a toner with high print durability. A color difference ΔE of 2.0 or less was judged as ◯, and a color difference ΔE of more than 2.0 was judged as x.

[0153] <High temperature and high humidity resistance> Toner was placed in a commercially available non-magnetic single-component development printer (print speed 30 pages / min) equipped with a scorotron and photoreceptor, and left overnight in a high-temperature, high-humidity environment at a temperature of 35°C and humidity of 85%. A solid white print (print density 0%) was then performed, and the printer was stopped midway through the solid white print. The toner in the non-image area on the photoreceptor after development was adhered to adhesive tape (product name "Scotch Mending Tape 810-3-18" manufactured by 3M Japan Co., Ltd.), which was then peeled off and applied to an 80g / m 2The toner was pasted onto a printing paper of the same color. Furthermore, for comparison, mending tape was pasted onto the same paper as it was, and the color difference ΔE between the two was measured using a spectrophotometric densitometer FD-5 (manufactured by Konica Minolta) to evaluate fogging. A smaller color difference ΔE indicates better image quality and a toner with excellent resistance to high temperatures and high humidity. Color difference ΔE that was too high to measure was marked "ND" in the table. Note that toner B4 of Comparative Example 4 was not measured because its printing durability at normal temperature and normal humidity was significantly inferior. A color difference ΔE of 2.0 or less was judged as ◯, and a color difference ΔE of more than 2.0 was judged as x.

[0154] [Production of toner base particles] <Preparation of Colorant Dispersion> A propeller-equipped agitator vessel was fitted with a true density of 1.8 g / cm 3 A pigment premix was prepared by pre-dispersing 20 parts of carbon black (manufactured by Mitsubishi Chemical Corporation, product name: Mitsubishi Carbon Black MA100S) manufactured by the furnace method, 1 part of anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Neogen S-20A), 4 parts of nonionic surfactant (manufactured by Kao Corporation, product name: Emulgen 120), and 75 parts of ion-exchanged water with a conductivity of 2 μS / cm. The carbon black in the dispersion after premixing had a volume cumulative 50% diameter (Dv50) of approximately 90 μm. The premix was fed as raw material slurry to a wet bead mill and subjected to one-pass dispersion. The inner diameter of the stator was 120 mmφ, the diameter of the separator was 60 mmφ, and zirconia beads with a diameter of 50 μm (true density 6.0 g / cm) were used as dispersion media. 3 ) was used. The effective internal volume of the stator was approximately 2 liters, and the media filling volume was 1.4 liters, resulting in a media filling rate of 70%. The rotor rotation speed was kept constant (the peripheral speed of the rotor tip was approximately 11 m / sec), and the premix liquid was fed from the feed port at a feed rate of approximately 40 liters / hr using a non-pulsating metering pump, and once the specified particle size was reached, the product was collected from the discharge port. During operation, cooling water at approximately 10°C was circulated from the jacket, and the colorant dispersion was obtained.

[0155] <Preparation of Wax Dispersion A1: Emulsification Step> The wax used was ester wax 1 (NOF Corporation, product name: WEP-3, melting point peak in the second measurement of Tg measurement by DSC: 71.0 ° C, onset temperature in the second measurement of Tg measurement by DSC: 68.6 ° C, inflection point in the second measurement of Tg measurement by DSC: 69.9 ° C, catalog acid value 0.1 mg KOH / g, catalog hydroxyl value 3 mg KOH / g or less), 30.00 parts (1440 g), decaglycerin decabehenate (Mitsubishi Chemical Corporation, product name: B100D, hydroxyl value 27, melting point 70 ° C), 0.24 parts, 20% aqueous sodium dodecylbenzenesulfonate solution (hereinafter referred to as "20% DBS aqueous solution"), 1.93 parts, and 67.83 parts of demineralized water. The mixture was heated to 90 ° C and mixed for 20 minutes in a CSTR-type agitation bed equipped with a 45-degree inclined three-stage paddle blade. Next, while this dispersion was still heated to 90°C, circulation emulsification was initiated using a valve homogenizer (Gaulin, 15-M-8PA model) under a pressure of 25 MPa. The particle size was measured using a Nanotrac and the particles were dispersed until the volume median diameter reached 245 nm, producing wax dispersion A1 (emulsion solids concentration = 31.2%, wax component concentration 30.8%).

[0156] <Preparation of Wax Dispersion A2: Emulsification Step> 27.30 parts of paraffin wax 1 (Nippon Seiro Co., Ltd., product name: HNP-9, catalog melting point: 75 ° C), 2.70 parts of stearyl acrylate (Toho Chemical Co., Ltd., product name: ST-A), 1.93 parts of 20% DBS aqueous solution, and 68.07 parts of demineralized water were heated to 90 ° C and mixed for 20 minutes in a CSTR-type stirring chamber equipped with a 45-degree inclined three-stage paddle blade. Next, while the dispersion was still heated to 90 ° C, circulation emulsification was initiated at 25 MPa using a valve homogenizer (Gaulin, 15-M-8PA model). The particle size was measured with a Nanotrac and dispersed until the volume median diameter reached 260 nm, producing wax dispersion A2 (emulsion solids concentration = 30.2%, wax component concentration = 29.8%).

[0157] <Preparation of Polymer Primary Particles B1: Polymerization Step> A reactor equipped with a stirrer, a heating / cooling device, a concentrator, and a device for feeding raw materials and auxiliary agents was charged with 10.8 parts of wax dispersion A1 (as the wax component), 256 parts of demineralized water, and 0.02 parts of a 0.5% aqueous solution of iron (II) sulfate heptahydrate, and the temperature was raised to 90°C under a nitrogen stream while stirring.

[0158] Then, with stirring continued, the following mixture of monomers and emulsifier aqueous solution, which had been stirred in advance with a homogenizer for 30 minutes, was added over 240 minutes. The start of polymerization was the point at which the addition of this mixture of monomers and emulsifier aqueous solution began, and the following initiator aqueous solution was added over 480 minutes from 0 minutes after the start of polymerization. 240 minutes after the start of polymerization, the following iron sulfate aqueous solution was added. 300 minutes after the start of polymerization, the temperature was raised to 95°C. Heating and stirring continued until 540 minutes after the start of polymerization.

[0159] [Monomers] Styrene 72.7 parts Butyl acrylate 27.3 parts 0.95 parts acrylic acid Trichlorobromomethane 1.43 parts Hexanediol diacrylate 1.41 parts [Emulsifier aqueous solution] 20% DBS aqueous solution 1.0 part Demineralized water 67.2 parts [Initiator aqueous solution] 28.0 parts of 8% hydrogen peroxide solution 8% L-(+) ascorbic acid aqueous solution 28.0 parts [Ferrous sulfate aqueous solution] 0.5% iron(II) sulfate heptahydrate aqueous solution 0.08 parts

[0160] After 540 minutes from the start of polymerization, the mixture was cooled to 30°C to obtain milky white polymer primary particles B1. The volume median diameter measured using Nanotrac was 243 nm. The number average molecular weight (Mn) was The viscosity was 13,000, the mass average molecular weight (Mw) was 102,000, the solid content was 23.7% by mass, and the glass transition temperature (Tg) was 40°C.

[0161] <Preparation of Shell Particles C1: Polymerization Process> A reactor equipped with a stirrer, a heating / cooling device, a concentrator, and a device for feeding raw materials and auxiliary agents was charged with 10.5 parts of wax dispersion A2 (as the wax component), 282 parts of demineralized water, and 0.02 parts of a 0.5% aqueous solution of iron (II) sulfate heptahydrate, and the temperature was raised to 90°C under a nitrogen stream while stirring.

[0162] Then, with stirring continued, a mixture of the following monomers, emulsifier aqueous solution, and iron sulfate aqueous solution, which had been stirred in advance with a homogenizer for 30 minutes, was added over 300 minutes. The time when the addition of this mixture of monomers, emulsifier aqueous solution, and iron sulfate aqueous solution began was considered the start of polymerization, and initiator aqueous solution 1, shown below, was added over 270 minutes from 30 minutes after the start of polymerization. Then, initiator aqueous solution 2, shown below, was added over 120 minutes from 300 minutes after the start of polymerization. Heating and stirring was continued until 540 minutes after the start of polymerization.

[0163] [Monomers] Styrene 76.8 parts Butyl acrylate 23.2 parts 1.50 parts acrylic acid Trichlorobromomethane 1.00 parts Hexanediol diacrylate 0.70 parts [Emulsifier aqueous solution] 20% DBS aqueous solution 1.0 part Demineralized water 67.1 parts [Initiator aqueous solution 1] 15.5 parts of 8% hydrogen peroxide solution 8% L-(+) ascorbic acid aqueous solution 15.5 parts [Initiator aqueous solution 2] 8% hydrogen peroxide solution 0.00 parts 8% L-(+) ascorbic acid aqueous solution 14.7 parts [Ferrous sulfate aqueous solution] 0.5% iron(II) sulfate heptahydrate aqueous solution 0.02 part

[0164] 540 minutes after the start of polymerization, the mixture was cooled to 30°C to obtain milky white shell microparticles C1. The volume median diameter measured using Nanotrac was 254 nm. The mass average molecular weight (Mw) was 88,000. The solid content was 20.6% by mass, and the glass transition temperature (Tg) was 51°C.

[0165] <Preparation of Polymer Primary Particle Dispersion D1> A reactor equipped with a three-blade stirrer, heating / cooling device, concentrator, and various raw material and auxiliary feed devices was charged with 0.6 parts of a cationic surfactant (Kao Corporation, product name: Sanisol B-50, solids concentration 50%) and 335 parts of demineralized water, and the mixture was heated to 70°C under a nitrogen stream while stirring. Subsequently, while continuing to stir, initiator solution 1 (shown below) was added, and five minutes later, a mixed emulsion of monomers 1 and an emulsifier solution and monomers 2 (shown below) were added over 200 minutes. The polymerization initiation time was the start of the dropwise addition of this monomer / emulsifier solution mixture, and initiator solution 2 (shown below) was simultaneously added over 200 minutes. Initiator solution 3 was then added over 60 minutes, and the temperature was raised to 90°C simultaneously with the addition. After the addition of initiator solution 3, the internal temperature was maintained at 90°C for 1 hour with stirring.

[0166] [Monomers 1] Styrene 74.5 parts Butyl acrylate 25.5 parts [Emulsifier aqueous solution] Sanisol B-50 (Kao, solid content 50%) 0.6 parts 71.8 parts demineralized water [Monomers 2] Blenmar QA (NOF 50% solution) 10.0 parts [Initiator aqueous solution 1] 8.0% 2,2'-azobis(2-methylpropionamidine) dihydrochloride (Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution 3.2 parts [Initiator aqueous solution 2] 8.0% 2,2'-azobis(2-methylpropionamidine) dihydrochloride (Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution 10.5 parts [Initiator aqueous solution 3] 8.0% 2,2'-azobis(2-methylpropionamidine) dihydrochloride (Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution 3.2 parts

[0167] After the polymerization reaction was completed, the mixture was cooled to obtain a milky white polymer primary particle dispersion D1. The volume median diameter (D50) measured using Nanotrac was 93 nm. The glass transition temperature (Tg) measured using DSC was 56°C.

[0168] <Preparation of Core Particle Dispersion E1: Aggregation Step> To a mixer equipped with a stirrer, a heating / cooling device, and a device for feeding raw materials and auxiliary agents, 60.9 parts (solid content) of the polymer primary particles B1 obtained above, 0.12 parts (solid content) of a 20% DBS aqueous solution, 19 parts of deionized water, 0.53 parts (solid content) of a 5% iron (II) sulfate heptahydrate aqueous solution, and 6.0 parts of the colorant dispersion were added in this order with stirring and mixed uniformly. Then, 41 parts of deionized water was added over 6 minutes. The internal temperature was then raised to 40°C and further raised stepwise until the volume median diameter reached 4.9 µm. This temperature (primary aggregation temperature) was 40°C.

[0169] The temperature was quickly lowered by 2°C below the primary aggregation temperature, and 6.8 parts (solids) of polymer primary particles B1 were added at the same time. 90 minutes later, 32.3 parts (solids) of shell microparticles C1 were added. 60 minutes later, 4.0 parts (solids) of a 20% DBS aqueous solution and 23 parts of deionized water were added, and the temperature was then raised to 77°C over 80 minutes, and then gradually raised until the average circularity reached 0.966. The temperature at which the average circularity reached 0.966 (final circularization temperature) was 80°C. The mixture was then cooled to 30°C, yielding core particle dispersion E1.

[0170] The slurry of core particles E1 was cooled to 30°C over 20 minutes, extracted, and filtered by suction with an aspirator using No. 5C filter paper manufactured by Toyo Roshi Co., Ltd. The cake remaining on the filter paper was transferred to a stainless steel container equipped with a stirrer (propeller blade), and ion-exchanged water with an electrical conductivity of 1 μS / cm was added and stirred at 50 rpm to disperse the cake uniformly, followed by stirring for 30 minutes.

[0171] The mixture was then again filtered using No. 5C filter paper under suction with an aspirator, and the solid matter remaining on the filter paper was transferred to a mixer equipped with a heating / cooling device, a concentrator, and a device for feeding raw materials and auxiliary agents. Ion-exchanged water with an electrical conductivity of 1 μS / cm was added, and the mixture was stirred at 50 rpm to uniformly disperse the mixture. The dispersion concentration was adjusted to 20% (solids content), yielding a dispersion of core particles E1.

[0172] While stirring, 3 parts (solids equivalent) of polymer primary particle dispersion D1 was added dropwise to the dispersion of core particles E1 and the mixture was maintained at room temperature for 60 minutes. Then, 1N NaOH solution was added dropwise in an amount of 7.5 g / 1 L of dispersion volume and the mixture was maintained at room temperature for another hour. The dispersion was then heated to an internal temperature of 55°C over 30 minutes and maintained for 30 minutes. The resulting slurry was then cooled to 30°C over 10 minutes and filtered by suction using a No. 5C filter paper manufactured by Toyo Roshi Kaisha, Ltd. The cake remaining on the filter paper was transferred to a stainless steel container equipped with a stirrer (propeller blade), and ion-exchanged water with an electrical conductivity of 1 μS / cm was added and the mixture was stirred at 50 rpm to uniformly disperse the mixture. The mixture was then left stirring for 30 minutes.

[0173] The mixture was again filtered by aspirator using No. 5C filter paper, and the solid matter remaining on the filter paper was transferred to a stainless steel container equipped with a stirrer (propeller blade) containing ion-exchanged water with an electrical conductivity of 1 μS / cm, and uniformly dispersed by stirring at 50 rpm. This process was repeated twice, and the electrical conductivity of the filtrate became 2 μS / cm.

[0174] The cake thus obtained was dried for 48 hours in a blower dryer set at 40° C. to obtain toner base particles. The toner base particles have an average circularity of 0.961, a volume average particle diameter (Dv) of 6.0 μm, a number average particle diameter (Dn) of 5.55 μm, a Dv / Dn ratio of 1.08, and a true specific gravity of 1.1 g / cm 3 The toner base particles were positively charged with a charge amount of 6.4 μC / g.

[0175] [External additives] As external additives, particles shown in Table 1 were prepared.

[0176] [Table 1]

[0177] [Example 1] 100 parts of the positively charged toner base particles obtained above, 0.89 parts of positively charged silica particles A, 0.4 parts of positively charged silica particles B, and 0.5 parts of resin particles A as positively charged external additive 1 were added to a sample mill (manufactured by Kyoritsu Riko Co., Ltd.) in external addition step 1, and the mixture was mixed for 6 minutes at a rotation speed of 5500 rpm. After stopping the mill, 2.88 parts of positively charged silica particles A were added in external addition step 2, and the mixture was mixed for another 6 minutes at 5500 rpm. Then, 0.3 parts of resin particles B as negatively charged external additive 2 were added in external addition step 3, and the mixture was mixed for 1 minute at 5500 rpm. After mixing, the toner was sieved using a sieve with 75 μm openings to remove coarse particles, yielding toner A1. In each external addition step, the sample mill was heated to 40°C.

[0178] The obtained toner A1 was subjected to the above-mentioned evaluations, and the results are shown in Table 2.

[0179] [Examples 2 to 4, Comparative Examples 1 to 5] Toners A2 to A4 and B1 to B5 were obtained in the same manner as toner A1 in Example 1, except that the external additives shown in Table 2 were used in the amounts shown in Table 2 in each external addition step. However, in Example 3, the mixing time in external addition step 1 was 10 minutes, and the mixing time in external addition step 2 was 4 minutes. In Example 4, the mixing time in external addition step 1 was 4 minutes, and the mixing time in external addition step 2 was 10 minutes. The obtained toners A2 to A4 and B1 to B5 were subjected to the above-described evaluations, and the results are shown in Table 2.

[0180] [Table 2]

[0181] Table 2 reveals the following: Toner B1 of Comparative Example 1, which does not use either positively chargeable external additive 1 or negatively chargeable external additive 2, is inferior in both print durability and high-temperature and high-humidity resistance. Toner B2 of Comparative Example 2 is excellent in resistance to high temperatures and high humidity because it contains negatively chargeable external additive 2, but is inferior in print durability because it does not contain positively chargeable external additive 1. Toner B3 of Comparative Example 3 has good print durability because it contains external additive 1 which is positively charged, but has poor resistance to high temperatures and high humidity because it does not contain external additive 2 which is negatively charged. Toner B4 of Comparative Example 4, which uses positively chargeable inorganic particles A having a large true specific gravity instead of positively chargeable external additive 1, is significantly inferior in print durability. Toner B5 of Comparative Example 5, which uses negatively chargeable inorganic particles B having a large true specific gravity instead of negatively chargeable external additive 2, is inferior in both print durability and resistance to high temperatures and high humidity. In contrast, the true specific gravity is 1.0 to 1.3 g / cm 3 and a positively charged external additive 1 having a true specific gravity of 1.0 to 1.3 g / cm 3 In the toners A1 to A4 of Examples 1 to 4 in which the negatively charged external additive 2 is used together, good results are obtained in both print durability and high temperature and high humidity resistance. From these results, it is apparent that the present invention provides a toner for developing electrostatic images that is excellent in print durability and resistance to high temperatures and high humidity.

Claims

1. A toner for developing electrostatic images, comprising toner base particles containing a binder resin and a colorant, and an external additive, the external additives contain a positively chargeable external additive 1 and a negatively chargeable external additive 2, The true specific gravity of the positively chargeable external additive 1 and the negatively chargeable external additive 2 is 1.0 g / cm ３ 1.3g / cm or more ３ A toner for developing electrostatic images, which is:

2. 2. The toner for developing electrostatic images according to claim 1, wherein the toner base particles have an average circularity of 0.95 or more.

3. 2. The toner for developing electrostatic images according to claim 1, wherein the toner for developing electrostatic images is positively charged.

4. 2. The toner for developing electrostatic images according to claim 1, wherein the toner base particles have a volume average particle diameter (Dv) of 8 μm or less, and a ratio (Dv / Dn) of the volume average particle diameter (Dv) to the number average particle diameter (Dn) of 1.2 or less.

5. 2. The toner for developing electrostatic images according to claim 1, wherein the toner base particles are toner base particles produced by an emulsion polymerization aggregation method.

6. 2. The toner for positive charge development according to claim 1, wherein the external additive 1 and / or the external additive 2 contains a (meth)acrylic resin.

7. The true specific gravity of the toner base particles is 0.8 g / cm ３ 1.5g / cm or more ３ 2. The positive charge developing toner according to claim 1, wherein the absolute value of the difference in true specific gravity between said external additive 1 and said external additive 2 is 0.2 or less.

8. 2. The toner for developing electrostatic images according to claim 1, further comprising inorganic particles as an external additive other than the external additive 1 and the external additive 2.

9. A toner cartridge filled with the toner for developing electrostatic images according to any one of claims 1 to 8.

10. 9. An image forming apparatus comprising: an electrophotographic photosensitive member; charging means for charging the electrophotographic photosensitive member; image exposure means for exposing the charged electrophotographic photosensitive member to light to form an electrostatic latent image; developing means for developing the electrostatic latent image with toner; and transfer means for transferring the toner from the electrophotographic photosensitive member to a transfer receiving member, wherein the toner is the toner for developing electrostatic images according to any one of claims 1 to 8.

Images