JP2005148405A - Electrophotographic toner and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic toner capable of suppressing fogging and preventing filming even after long-term use. <P>SOLUTION: The electrophotographic toner 1 is obtained by locating fine strontium titanate particles 3 and hydrophobic inorganic fine particles 4 whose average particle diameter is 1/10 to 1/3 of that of the fine strontium titanate particles on toner base particles 2 comprising at least a release agent, a colorant and a binder resin and having an average particle diameter of ≤10 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic toner used in an image forming apparatus utilizing an electrophotographic process and a method for producing the same.

  An image forming apparatus using an electrophotographic process forms an image by a charging process, an exposure process, a development process, a transfer process, a cleaning process, a fixing process, and the like. In the charging step, the surface of the photoreceptor is uniformly charged. In the exposure step, the charged photoconductor is exposed to form an electrostatic latent image on the surface of the photoconductor. In the development step, a visible image is formed by attaching a developer such as toner to the electrostatic latent image formed on the surface of the photoreceptor. In the transfer step, the visible image formed on the surface of the photoreceptor is transferred to a recording medium such as paper or sheet. In the fixing step, the visible image transferred to the recording medium is fixed by means such as heating and pressing. In the cleaning process, the developer remaining on the surface of the photoreceptor without being transferred to the recording medium is collected. Through the above steps, an image forming apparatus using an electrophotographic process forms a desired image on a recording medium.

  In recent years, image forming apparatuses using electrophotographic processes such as copying machines and printers have been reduced in size, digitized, and full-colored. There is also a demand for a developer such as a toner used in an image forming apparatus using an electrophotographic process that has performance capable of realizing high image quality and gradation reproducibility. Therefore, in the developing process, the developer such as toner is suitable for the developer such as toner so that the electrostatic force can smoothly adhere to the electrostatic latent image on the photoreceptor and form a clear visible image. It is necessary to impart fluidity and chargeability.

  In order to impart appropriate fluidity and chargeability to a developer such as toner, a charge control agent or the like is added to the toner base particles, or external additives such as silica and titania are added externally. Or The toner base particles are prepared by dispersing a colorant, a release agent, and the like in a binder resin to a predetermined particle size.

  The developing method used in the developing process includes a one-component developing method using a one-component developer consisting only of toner not containing a carrier and a two-component developer using a two-component developer consisting of a toner and a carrier. There is a development method. Since the two-component development method is generally large in apparatus, the one-component development method is often used from the viewpoint of miniaturization.

  Further, the one-component development method includes a magnetic one-component development method using a magnetic toner having magnetism and a non-magnetic one-component development method using a non-magnetic toner having no magnetism. The magnetic toner needs to be added with magnetic powder, and since the magnetic powder is generally black, a non-magnetic one-component developing system using non-magnetic toner is suitable for a full-color image forming apparatus. In addition, in the non-magnetic one-component development method, in order to adjust the charge amount of the toner and the like, it is more desirable to adjust the additive amount of the external additive than to adjust the additive amount of the charge control agent. In many cases, external additives are added.

  However, the toner used in the non-magnetic one-component development method does not use a carrier, and therefore easily deteriorates due to stress. In the non-magnetic one-component developing system, the toner is charged by passing through a gap between the regulating blade and the developing roller. For this reason, a strong stress is applied to the toner. When used repeatedly, the external additive externally added to the toner is embedded in the toner, and the surface state of the toner changes. Since the toner whose surface state has changed has no external additive on the surface, the fluidity and chargeability are lowered, and the cohesive force between the toners is further increased.

  Since the deteriorated toner has low fluidity and high cohesive force, there arises a problem of filming in which the toner adheres to the developing roller and the photoreceptor. Furthermore, in the cleaning process, unnecessary toner adhering to the surface of the photoreceptor cannot be collected, and a problem of fogging occurs. The term “fogging” refers to toner particles adhering to a portion where an image is not formed on a recording medium after image formation. Further, not only the fluidity is lowered but also the chargeability is lowered. Therefore, in the development process, the toner does not uniformly adhere to the electrostatic latent image formed on the surface of the photoreceptor, and image defects are caused. Invite.

  As a countermeasure against problems such as toner fogging and filming, a typical conventional technique is described in Patent Document 1. The developer described in Patent Document 1 is a developer containing a binder resin and a colorant, and externally adds small-sized inorganic fine particles having an average particle diameter of 1 to 70 nm and strontium titanate fine particles having an average particle diameter of 100 to 500 nm. It is characterized by that.

  As another conventional technique, a technique similar to the technique of Patent Document 1 is described in Patent Document 2. In the electrostatic latent image developing toner described in Patent Document 2, strontium titanate fine particles are externally added to toner particles composed of a colorant and a binder resin, and the number of strontium titanate fine particles added externally is The average particle size is 80 to 800 nm, and the content of strontium titanate fine particles having a particle size of 1000 nm or more is 20% by number.

  As another conventional technique, a technique similar to the technique of Patent Document 1 is described in Patent Document 3. Patent Document 3 discloses a toner for developing an electrostatic latent image, in which toner particles composed of a binder resin and a colorant are externally added with composite particles of strontium titanate and strontium carbonate, and strontium titanate and strontium carbonate of the composite particles. The weight ratio is 98: 2 to 80:20, and the number average particle size of the composite particles is 80 to 800 nm.

Japanese Patent Laid-Open No. 11-212293 Japanese Patent Laid-Open No. 10-10770 JP 2003-15349 A

  The electrophotographic toner needs to maintain appropriate fluidity and chargeability so that it can smoothly adhere to the electrostatic latent image formed on the surface of the photoreceptor. This depends on the external additive externally added to the toner particles and the method of externally adding the external additive.

  According to the developer disclosed in Patent Document 1, the externally added strontium titanate fine particles reduce the contact probability between toner particles (toner base particles) and prevent the developer from aggregating. In addition, the developer can be charged, so even if it is used repeatedly, the change in the surface state of the developer particles is small, and the fluidity and chargeability that are the characteristics of the developer can be maintained. It is possible to prepare a developer having excellent properties. However, the strontium titanate fine particles also have a property of inducing the adhesion of toner particles to the surface of the photoreceptor, causing problems such as filming and causing image defects.

  According to the electrostatic latent image developing toner disclosed in Patent Document 2, the number average particle diameter of the externally added strontium titanate fine particles and the content of the strontium titanate fine particles having a particle diameter of 1000 nm or more are specified. Thus, the strontium titanate fine particles present free from the toner particles are reduced, and it is possible to prepare a toner for developing an electrostatic latent image that has excellent fluidity and hardly damages the surface of the photoreceptor.

  In addition, according to the electrophotographic toner disclosed in Patent Document 3, by specifying the mixing ratio and number average particle size of the externally added composite particles, the abrasiveness of the composite particles is improved, and repeated copying is possible. In addition, it is possible to prepare a toner for developing an electrostatic latent image, in which a change in the surface state of the toner particles is small and toner characteristics such as fluidity and chargeability can be maintained.

  However, in recent years, developers such as toners are required to have high image quality and long life, but the electrostatic latent image developing toner disclosed in Patent Document 2 and the electronic device disclosed in Patent Document 3 are disclosed. In the case of photographic toner, when the number of printed sheets exceeds 10,000, the frequency of occurrence of filming increases and the problem of fogging also occurs. That is, it is insufficient for improving the image quality and extending the life of a developer such as toner.

  An object of the present invention is to provide an electrophotographic toner capable of suppressing fogging and preventing filming even when used for a long period of time.

The present invention relates to toner base particles having an average particle size of 10 μm or less containing at least a release agent, a colorant and a binder resin,
Strontium titanate fine particles,
Hydrophobic inorganic fine particles having an average particle size of 1/10 or more and 1/3 or less of the average particle size of the strontium titanate fine particles,
An electrophotographic toner characterized by externally adding strontium titanate fine particles and hydrophobic inorganic fine particles to toner base particles.

  The present invention is also characterized in that the hydrophobic inorganic fine particles are fine particles of silica, alumina, or titania.

In the present invention, the weight ratio of the external addition amount of the strontium titanate fine particles to the external addition amount of the hydrophobic inorganic fine particles is 2 or more,
The total of hydrophobic inorganic fine particles and strontium titanate fine particles is 1 to 5 parts by weight with respect to 100 parts by weight of toner base particles.

  The present invention is further characterized by further externally adding hydrophobic silica fine particles having an average particle size of 30 nm or less.

The present invention also includes a preparation step of preparing toner base particles by mixing and pulverizing at least a release agent, a colorant and a binder resin;
A first external addition step of adding hydrophobic silica fine particles having an average particle size of 30 nm or less to the toner base particles and stirring for a predetermined time;
A second external addition step of adding and stirring strontium titanate fine particles and hydrophobic inorganic fine particles after stirring for a predetermined time;
In the second external addition step, the average particle size of the hydrophobic inorganic fine particles is 1/10 or more and 1/3 or less of the average particle size of the strontium titanate fine particles,
An electrophotographic toner manufacturing method comprising adding 100 parts by weight of toner base particles so that a total of hydrophobic inorganic fine particles and strontium titanate fine particles is 1 to 5 parts by weight. .

  Further, in the second external addition step, the present invention stirs between the time when the time differential value of the bulk density changes from negative to positive and the time until the time differential value of the bulk density changes from positive to negative or zero. It is characterized by terminating.

  In the second external addition step, the present invention includes a time at which the secondary differential value with respect to the bulk density time becomes zero after the time at which the time differential value of the bulk density changes from negative to positive, and a time differential value of the bulk density. Stirring is terminated between the time until the value changes from positive to negative or zero.

  According to the present invention, 10,000 or more sheets can be printed by externally adding strontium titanate fine particles and hydrophobic inorganic fine particles having an average particle size of 1/10 or more and 1/3 or less of the average particle size of the strontium titanate fine particles to the toner base particles. Even after this, it is possible to obtain an electrophotographic toner that can maintain the surface state of the toner and maintain toner characteristics such as chargeability and fluidity.

  The strontium titanate fine particles can reduce the contact probability between the toner base particles, and can further impart chargeability to the toner. Therefore, the toner to which the strontium titanate fine particles are externally added can prevent aggregation between the toners, and has appropriate fluidity and chargeability by adjusting the amount of external addition. However, strontium titanate fine particles have the property of inducing the adhesion of toner particles to the surface of the photoreceptor. However, by adding hydrophobic inorganic fine particles having a smaller particle size than strontium titanate fine particles, Hydrophobic inorganic fine particles are attached to the surface of strontium acid fine particles, preventing adhesion to the surface of the photoconductor and damage to the surface of the photoconductor while maintaining fluidity and chargeability when strontium titanate is externally added. be able to.

  As described above, the present invention is a toner for electrophotography that has fluidity and chargeability so that it can smoothly adhere to an electrostatic latent image formed on the surface of a photoreceptor and can prevent fogging and filming. Can provide.

  Further, according to the present invention, the occurrence of fogging and filming can be further prevented by selecting and using fine particles of silica, alumina, or titania as the hydrophobic inorganic fine particles.

  According to the present invention, the weight ratio of the external addition amount of the hydrophobic inorganic fine particles to the external addition amount of the strontium titanate fine particles is 2 or more, and the hydrophobic inorganic fine particles and the strontium titanate fine particles are added to 100 parts by weight of the toner base particles. The toner characteristics such as chargeability and fluidity are made more appropriate by the total amount of 1 to 5 parts by weight.

  If the weight ratio of the external addition amount of the hydrophobic inorganic fine particles to the external addition amount of the strontium titanate fine particles is smaller than 2, the strontium titanate fine particles cannot be coated with the hydrophobic inorganic fine particles, and fog and filming are sufficient. Cannot be prevented. Further, if the total weight of the hydrophobic inorganic fine particles and the strontium titanate fine particles is less than 1 part by weight, the desired fluidity or chargeability cannot be obtained, and if it exceeds 5 parts by weight, it adheres to the toner particles. Too much strontium titanate fine particles and hydrophobic inorganic fine particles that cannot be produced cause problems such as in-flight contamination.

  According to the present invention, hydrophobic silica fine particles having an average particle size of 30 nm or less are externally added to the toner base particles to improve the fluidity of the toner base particles, and when the external additive is externally added to the toner base particles. In addition, the toner can be smoothly externally added to the toner base particles. By doing so, the toner for electrophotography has more appropriate toner characteristics such as chargeability and fluidity, and can further prevent the occurrence of fogging and filming.

  According to the present invention, hydrophobic silica fine particles having an average particle diameter of 30 nm or less are externally added to the toner base particles, and the fluidity of the toner base particles is improved by stirring for a predetermined time. Thereafter, strontium titanate fine particles and Since the hydrophobic inorganic fine particles are externally added, they can be added smoothly. By doing so, it is possible to manufacture an electrophotographic toner that has appropriate toner characteristics such as chargeability and fluidity and can prevent fogging and filming.

  According to the present invention, when the strontium titanate fine particles and inorganic fine particles are externally added to the toner base particles, the time when the time differential value of the bulk density changes from negative to positive and the time differential value of the bulk density changes from positive to negative or zero. By stirring until the time until the change to, it is possible to produce an electrophotographic toner in which strontium titanate fine particles and inorganic fine particles are uniformly attached to the toner base particles. Thus, it is possible to produce an electrophotographic toner that has more appropriate toner characteristics such as fogging and filming.

  According to the present invention, when the strontium titanate fine particles and inorganic fine particles are externally added to the toner base particles, the secondary differential value with respect to the bulk density time becomes zero after the time when the temporal differential value of the bulk density changes from negative to positive. The strontium titanate fine particles and inorganic fine particles are adhered to the toner particles in a more preferable state by stirring until the time until the time differential value of the bulk density changes from positive to negative or zero. An electrophotographic toner capable of further preventing fogging and filming can be produced.

1. Electrophotographic Toner FIG. 1 is a schematic cross-sectional view showing a simplified configuration of an electrophotographic toner 1 according to an embodiment of the present invention. As shown in FIG. 1, an electrophotographic toner 1 is an electrophotographic image in which strontium titanate fine particles 3 and hydrophobic inorganic fine particles 4 are externally added to toner base particles 2 containing at least a release agent, a colorant, and a binder resin. Toner.

  As shown in FIG. 1, in the electrophotographic toner 1, strontium titanate fine particles 3 are attached to the surface of toner base particles 2, and the strontium titanate fine particles 3 are covered with hydrophobic inorganic fine particles 4. The presence of the strontium titanate fine particles 3 makes it difficult for the toner base particles 2 to come into contact with each other, thereby preventing aggregation of the electrophotographic toner 1. By adjusting the external addition amount of the strontium titanate fine particles 3, appropriate fluidity and chargeability can be imparted. Further, since the strontium titanate fine particles 3 are coated with the hydrophobic inorganic fine particles 4, while preventing fluidity, chargeability and aggregation, the toner adheres to the photoconductor and damages the photoconductor. Can be prevented.

  The electrophotographic toner 1 according to the present invention can be produced by a method as described below. Binder resin, colorant, release agent, charge control agent, etc. are premixed with a high-speed stirrer such as a super mixer, kneaded with a twin-screw continuous extruder, kneader, two rolls, etc. Cooling. After the cooled kneaded material is roughly crushed by a cutter mill or the like, toner base particles 2 are obtained using a jet airflow pulverizer and an airflow classifier. Thereafter, external additives such as strontium titanate fine particles 3 and hydrophobic inorganic fine particles 4 are externally added to the toner base particles 2. The toner base particles 2 and the external additive are blended and stirred using a high-speed stirrer that gives a shearing force such as a Henschel mixer or a super mixer. Next, foreign substances and coarse particles when external additives are externally added to the toner base particles 2 are screened using a vibrating screen such as an ultrasonic screen and a gyro shifter and a rotary screen such as a turbo screener. The toner 1 for electrophotography is obtained by removing.

1-1. External Additive The electrophotographic toner 1 according to an embodiment of the present invention imparts fluidity and chargeability for the purpose of high image quality and gradation reproducibility, and as shown in FIG. It is desirable to externally add two or more kinds of additives. Known external additives can be used. Examples thereof include inorganic fine particles such as silica, alumina, titania, ferrite, zinc oxide, and strontium titanate. Desirable toner fluidity can be obtained by uniformly coating the toner base particles 2 with fine particles. The electrophotographic toner 1 according to an embodiment of the present invention uses strontium titanate fine particles 3 as a first external additive and hydrophobic inorganic fine particles 4 as a second external additive.

1-1-1. Strontium titanate fine particles In the electrophotographic toner 1 according to the embodiment of the present invention, strontium titanate fine particles 3 can be used as the first external additive. A known method can be used as a method for producing the strontium titanate fine particles. For example, it can be obtained by reacting strontium carbonate and titanium oxide, sintering at a low temperature, and pulverizing with a mixer such as a mixer.

  The strontium titanate fine particles are usually particles having an average particle size of 0.1 μm to several μm. When externally added to the toner, the spacer effect, that is, contact between toner base particles, strontium titanate fine particles and other external additives This has the effect of suppressing the embedding of the agent in the toner. Further, the strontium titanate fine particles show a positive polarity although they are weak with respect to the negatively chargeable toner. In the non-magnetic one-component development system, the toner is generally charged by charge injection by a charging member or frictional charging. At this time, the charging efficiency and stability are improved by the presence of a substance having a polarity opposite to that of the toner. Therefore, the strontium titanate fine particles have an effect such as stabilization of charging even when developing negatively charged toner. However, strontium titanate fine particles tend to adhere to the surface of the photoconductor, so that it adheres to the surface of the photoconductor so that it cannot be recovered by a cleaning process or the like, and furthermore, it is excellent in polishing properties, so As a result, it is known that fogging and filming problems occur and image defects are caused.

1-1-2. Hydrophobic inorganic fine particles In the electrophotographic toner 1 according to the embodiment of the present invention, a known external additive can be used as the second external additive. Examples thereof include hydrophobic inorganic fine particles 4 such as silica, alumina, titania, tin oxide, magnesium oxide, and zinc oxide. Of these, fine particles of silica, alumina, and titania are preferable. Furthermore, silica fine particles are more preferable.

  When silica fine particles are used, it is desirable that the silica fine particles have been hydrophobized. For the hydrophobization treatment, hydrophobizing agents such as organosilicon compounds, silane compounds, and silazane compounds are reacted or physically adsorbed on the silica fine particles. Examples of the organosilicon compound include silicone oil, and examples of the silane compound include trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, and benzyldimethyl. Chlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilane mercaptan, trimethylsilyl mercaptan, triorganosilyl acrylate, vinyldimethylacetoxysilane, dimethylethoxysilane , Dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinylteto Examples include lamethyldisiloxane and 1,3-diphenyltetramethyldisiloxane. Examples of the silazane compound include hexamethylene disilazane.

  The average particle size of the hydrophobic inorganic fine particles 4 in the present invention is preferably 1/10 or more and 1/3 or less, more preferably 1/8 or more and 1/4 or less, of the strontium titanate fine particles 3. When the average particle size of the hydrophobic inorganic fine particles 4 is smaller than 1/10 of the strontium titanate fine particles 3, the fine particles covering the strontium titanate fine particles 3 are too small, so that the abrasiveness of the strontium titanate fine particles 3 may be reduced. Inability to do so causes filming due to drum damage. When the average particle size of the hydrophobic inorganic fine particles 4 is larger than 1/3 of the strontium titanate fine particles 3, the hydrophobic inorganic fine particles 4 are difficult to adhere to the strontium titanate fine particles 3, and similarly cause filming.

  The external addition amount of the hydrophobic inorganic fine particles 4 and the strontium titanate fine particles 3 in the present invention is preferably an external addition amount satisfying the following relationship. The relationship is that the weight ratio of the hydrophobic inorganic fine particles 4 to the strontium titanate fine particles 3 is 2 or more, and the total of the hydrophobic inorganic fine particles 4 and the strontium titanate fine particles 3 is 1 with respect to 100 parts by weight of the toner base particles. It is not less than 5 parts by weight. When the weight ratio is less than 2, as shown in FIG. 1, the hydrophobic inorganic fine particles 4 cannot completely cover the strontium titanate fine particles 3, and filming occurs. If the total weight part is less than 1 part by weight, sufficient fluidity and chargeability cannot be imparted to the electrophotographic toner 1. When the total weight part is more than 5 parts by weight, the external additive is detached from the electrophotographic toner 1 or it becomes difficult to adhere to it, and the free fine particles cover the developing member such as the developing roll and the regulating blade. 1 causes charging failure and fogging occurs. Further, the free fine particles cause filming by adhering or damaging the surface of the photoreceptor.

1-1-3. Silica having an average particle size of 30 nm or less In the electrophotographic toner 1 according to the embodiment of the present invention, silica having an average particle size of 30 nm or less may be externally added before the external additive is externally added. The fluidity of the toner is improved by externally adding silica having an average particle size of 30 nm or less. Therefore, when silica having an average particle size of 30 nm or less is externally added, other external additives can be smoothly externally added, and the other external additives can be uniformly attached to the toner particles.

1-2. Toner Base Particles The toner base particles 2 are composed of a release agent, a colorant, a binder resin, and a charge control agent. The average particle diameter of the toner base particles 2 is preferably 4 μm or more and 10 μm or less. If the average particle diameter of the toner base particles 2 is smaller than 4 μm, the particle group becomes overly dense, and the number of contact points between the particles per unit weight increases. It becomes difficult to attach the strontium acid fine particles 3. When the average particle diameter of the toner base particles 2 is larger than 10 μm, the formed image becomes rough, and when it is 10 μm or less, a high-definition and reproducible image can be formed.

1-2-1. Binder Resin The electrophotographic toner 1 according to an embodiment of the present invention includes a polyester resin as a binder resin. Known polyester resins can be used. The polyester resin is synthesized from a condensation polymerization of a polyol and a polybasic acid. Moreover, you may use the polyester resin which has a crosslinked structure. The polyester resin having a crosslinked structure is synthesized by polymerizing a trifunctional or higher polyfunctional component with either a polyol or a polybasic acid.

  A well-known thing can be utilized for the polyol used for the synthesis | combination of a polyester resin. For example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, trimethylene glycol, 1,4-butanediol, 1,4-butenediol, neopentyl glycol Diols such as 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, bisphenol A, Examples thereof include bisphenol A alkylene oxide adducts such as hydrogenated bisphenol A and polyoxyethylenated bisphenol A, and phenols such as 1,2,4-benzenetriol and hydroquinone.

  Moreover, a well-known thing can be utilized for the trihydric or more polyol in connection with crosslinking of a polyester resin. For example, glycerin, 1,2,4-butanetriol, 1,2,5-pentanetriol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, penta Examples include erythritol, dipentaerythritol, tripentaerythritol, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, and sucrose.

  A well-known thing can be utilized for the polybasic acid used for the synthesis | combination of a polyester resin. For example, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, 1,5-naphthalenedicarboxylic acid, Examples include 2,6-naphthalenedicarboxylic acid and acid anhydrides or lower alkyl esters thereof.

  Moreover, a well-known thing can utilize the polybasic acid more than trivalence in connection with crosslinking of a polyester resin. For example, 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid Examples thereof include acids, 1,2,5-hexatricarboxylic acid and acid anhydrides or lower alkyl esters thereof.

1-2-2. Colorant The electrophotographic toner 1 according to an embodiment of the present invention includes a colorant such as a pigment and a dye. A well-known thing can be used as a coloring agent. In the case of electrophotographic toner for monochrome printing, a black pigment is used, and examples thereof include carbon black such as acidic carbon, neutral carbon, basic carbon, and iron black. Carbon black is produced by various methods such as a channel black method, a furnace black method, a lamp black method, and an acetylene black method. In the case of electrophotographic toner for full color printing, ultramarine, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, rhodamine pigment, chrome yellow, quinacridone, benzidine yellow, rose bengal, triallylmethane dye, anthraquinone dye, Examples include monoazo dyes and pigments and disazo dyes and pigments.

  The addition amount of the colorant in the present invention is preferably 4 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the binder resin. When the amount of the colorant added to 100 parts by weight of the binder resin is less than 4 parts by weight, the desired printing density cannot be obtained, and the amount of the colorant added to 100 parts by weight of the binder resin is greater than 20 parts by weight. The colorant will not be mixed uniformly with the binder resin.

1-2-3. Release Agent The electrophotographic toner 1 according to an embodiment of the present invention includes a wax as a release agent. The release agent is dispersed in the electrophotographic toner 1 and is eluted (bleeded) onto the surface of the electrophotographic toner 1 when the image is fixed on the recording medium by heat-pressing with a fixing roller in the fixing step. It exhibits releasability and works as an anti-offset agent. Not only can the offset resistance be improved, but filming problems can be reduced. The offset means that the surface of the fixing roller comes into contact with the toner from which the release agent is eluted when the image is fixed on the recording medium by heat-pressing with the fixing roller, and at that time, a part of the toner is fixed to the fixing roller. The toner adheres to the surface of the toner and the toner is retransferred to the recording medium at the time of the next fixing, and the recording medium is soiled.

  A well-known thing can be used as a mold release agent. Examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax, synthetic waxes such as polyethylene wax, Fischer Tropus wax and amide wax, and animal and plant waxes such as carnauba wax, candelilla wax and rice wax.

  The melting point of the release agent and the dispersion state in the electrophotographic toner 1 are greatly involved in preventing offset. A wax having an endothermic peak value by differential scanning calorimetry (DSC) of 60 ° C. or higher and 100 ° C. or lower is preferred. When the endothermic peak in DSC of the release agent is less than 60 ° C, it is difficult to manufacture such as fusion to the impact plate at the time of toner pulverization. When the endothermic peak exceeds 100 ° C, the release agent is sufficiently used for fixing. Unable to bleed, causing problems such as winding around the fixing roller.

  The acid value of the release agent is preferably 10.0 mgKOH / g or less, more preferably 4.0 mgKOH / g or less. When the acid value of the release agent exceeds 10.0 mgKOH / g, the affinity for the polyester resin increases, and it is difficult to bleed to the toner surface during thermocompression bonding, which causes an offset.

  The amount of the release agent added is preferably 0.5 parts by weight or more and 5.0 parts by weight or less, more preferably 1.5 parts by weight or more and 3.5 parts by weight or less with respect to 100 parts by weight of the binder resin. When the addition amount of the release agent is less than 0.5 parts by weight, the effect of preventing offset cannot be expected, and when it is more than 5.0 parts by weight, a phenomenon such as filming occurs.

1-2-4. Charge Control Agent The electrophotographic toner according to the embodiment of the present invention may include a charge control agent. Known charge control agents can be used. For example, nigrosine dyes, amino group-containing vinyl copolymers, quaternary ammonium salt compounds, polyamine resins, imidazoles, etc. can be used for positive charging, and metals such as chromium, zinc, cobalt, and aluminum can be used for negative charging. Examples thereof include metal-containing azo dyes, salts of salicylic acid or alkylsalicylic acid with the aforementioned metals, metal complexes, and the like.

  The charge control agent in the present invention may not be used, and when used, the amount used is preferably 0.1 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the binder resin. More preferably, it is 0.5 parts by weight or more and 4.0 parts by weight or less. When the amount is less than 0.1 part by weight with respect to 100 parts by weight of the binder resin, the chargeability is not significantly affected, and when the amount exceeds 10 parts by weight, the binder resin cannot be uniformly mixed.

1-3. External Addition (Stirring) Time When an external additive is externally added to the toner base particles, the external additive is added to the toner base particles and stirred by a super mixer or the like. FIG. 2 is a graph showing the relationship between the bulk density AD (Apparent Density) of toner particles and the stirring time. The vertical axis represents the toner particle bulk density AD (g / ml), and the horizontal axis represents the stirring time (min) when the external additive is externally added to the toner base particles. Note that 0 min is the time when silica (silica A) having an average particle size of 30 nm or less was added. A curve 100 is a curve when silica A is used, and a curve 101 is a curve when silica A, strontium titanate fine particles (SrTiO ₃ A) and hydrophobic inorganic fine particles (silica D) are used as external additives. It is. Details of silica A, SrTiO ₃ A and silica D will be described later. The bulk density is a value obtained by filling toner particles in a container having a known volume and dividing the mass of the toner particles by the volume including the space between the toner particles.

  When only silica having an average particle diameter of 30 nm or less is added and stirred, as shown by a curve 100, the bulk density AD increases once and then gradually decreases. When silica having an average particle size of 30 nm or less is added and stirred for a predetermined time, and then strontium titanate fine particles and hydrophobic inorganic fine particles are added and stirred, as shown by curve 101, the bulk density AD is determined by strontium titanate fine particles and It decreases sharply immediately after the addition of hydrophobic inorganic fine particles, then increases once, and then decreases gently.

  T1 shown in FIG. 2 is a time at which the time differential value of the bulk density after the addition of the strontium titanate fine particles and the hydrophobic inorganic fine particles has a minimum value. That is, it is the time when the strontium titanate fine particles and the hydrophobic inorganic fine particles begin to adhere uniformly to the toner base particles. t2 is the time indicating the maximum value of the time differential value of the bulk density after the addition of the strontium titanate fine particles and the hydrophobic inorganic fine particles. That is, it is a time when the strontium titanate fine particles and the hydrophobic inorganic fine particles are not buried in the toner base particles. t3 is the time between the t1 and t2 when the secondary differential value with respect to the bulk density time becomes zero, that is, the time indicating the inflection point of the bulk density.

FIG. 2 shows, as an example, the case where SrTiO ₃ A and silica D are added after adding silica A and stirring for 2 minutes, but after adding silica A, the mixture is stirred for 1 to 5 minutes and then SrTiO _3. Even when A and silica D are added, the bulk density after adding SrTiO ₃ A and silica D shows the same tendency as in FIG.

Table 1 shows specific times and bulk densities when SrTiO ₃ A and silica D are added after adding silica A and stirring for 2 minutes. t1 is 4.0 minutes, and the bulk density at that time is 0.394 g / ml. t2 is 12.0 minutes, and the bulk density at that time is 0.410 g / ml. t3 is 6.0 minutes, and the bulk density at that time is 0.403 g / ml.

  The agitation end time is preferably after t1 and before t2, that is, after the time when the strontium titanate fine particles and hydrophobic inorganic fine particles begin to uniformly adhere to the toner base particles and before the time when they are no longer embedded. More preferably, it is before t2 after t3. When the stirring end time is earlier than t1, it easily occurs such as peeling of the external additive to generate free fine particles, causing fogging and filming. After t2, the external additive is excessively embedded in the toner base particles, the toner is likely to deteriorate, and fogging occurs.

  As a recording medium for recording the image by attaching the toner 1 for electrophotography, a conventionally used recording medium can be used, for example, plain paper, postcard, color copy paper, plastic sheet, plastic film, etc. Can be mentioned.

  The toner 1 for electrophotography according to the present invention can be used for any one of monochrome image forming and color use as long as it is a conventionally known one-component developing type image forming apparatus. For example, as shown in FIG. Such a full-color image forming apparatus can be used.

  FIG. 3 is a schematic configuration diagram of the full-color image forming apparatus 11. The full-color image device 11 includes a photoconductor 12, a driving unit that rotates the photoconductor 12 in the direction of an arrow 13, and a conveyance unit that conveys the recording medium 19.

  Around the photosensitive member 12, a charger 14, an exposure device 15, a developing device 16, a transfer device 17, and a cleaner 18 are disposed from the upstream side to the downstream side in the rotational direction of the photosensitive member 12 indicated by an arrow 13. Are provided in this order.

  When the photoconductor 12 is rotationally driven in the direction of the arrow 13 by the driving means, the surface of the photoconductor 12 is uniformly charged by the charger 14. The surface of the charged photoreceptor 12 is neutralized by the exposure device 15 based on a desired image, and an electrostatic latent image is formed on the surface of the photoreceptor 12. The developing device 16 forms a toner image on the surface of the photoreceptor 12 based on the formed electrostatic latent image. The formed toner image is transferred onto the recording medium 19 by the transfer unit 17. The recording medium 19 is conveyed from the paper feed tray 20 to the transfer unit 17 by the conveying roller 21 along the conveying path 22 by the conveying means. The recording medium 21 onto which the toner image has been transferred by the conveying means is conveyed to the fixing device 23. Further, the toner image formed on the recording medium 19 is heated and pressurized by the fixing device 23. As a result, the image is fixed on the recording medium 19 and becomes a robust image. The recording medium 19 on which the image has been fixed is discharged onto a paper discharge tray 24 by the conveying means.

  In the full-color image forming apparatus 11, when the above-described electrophotographic toner 1 is stored in the charger 14 and developed using the electrophotographic toner 1, a full-color image forming apparatus that is less likely to cause fogging and filming can be realized.

2. EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these examples unless it exceeds the gist.

Examples 1-9 and Comparative Examples 1-10
2-1. Preparation of toner for electrophotography 100 parts by weight of a binder resin, 6.0 parts by weight of a colorant, 3.0 parts by weight of a release agent and 1.0 part by weight of a charge control agent are premixed by a super mixer and are continuously biaxial After kneading with an extruder, it is cooled quickly while rolling with two rolls that have been cooled with water. The cooled kneaded product was roughly crushed by a cutter mill, and then toner base particles having an average particle size of about 8.2 μm were prepared using a jet airflow pulverizer and an airflow classifier. The average particle diameter of the toner base particles was measured with a multisizer manufactured by Coulter.

  As the binder resin, a polyester resin having a weight average molecular weight of 60000 to 90000 and a number average molecular weight of 3500 to 4500 was used. Carbon black was used as the colorant. As the release agent, paraffin wax having a weight average molecular weight of 300 to 1000 and a number average molecular weight of 300 to 1000 was used. As the charge control agent, chromate was used.

  The external additives shown in Table 2 were added to 100 parts by weight of the toner base particles obtained by the above method based on the external addition amounts shown in Table 3, and Examples 1 to 9 and Comparative Examples were as follows. 1 to 10 electrophotographic toners were prepared.

In Example 1, 1.5 parts by weight of silica A having an average particle size of 8 nm was added to the toner base particles as the first step, and the mixture was stirred for 3.0 minutes with a supermixer, and the average particle size was 300 nm as the second step. 0.5 part by weight of SrTiO ₃ A, which is strontium titanate fine particles, and 1.5 part by weight of silica C, which is hydrophobic inorganic fine particles having an average particle size of 30 nm, are added for 10.0 minutes using a super mixer. Stir. That is, the total stirring time for external addition is 13.0 minutes. Finally, it was prepared by passing through a 200 mesh vibrating screen.

Example 2 is the same as Example 1 except that silica D, which is hydrophobic inorganic fine particles having an average particle diameter of 50 nm, is externally added instead of externally adding silica C. Example 3 is the same as Example 1 except that silica E, which is hydrophobic inorganic fine particles having an average particle diameter of 100 nm, is externally added instead of externally adding silica C. Example 4 is the same as Example 1 except that instead of externally adding silica C, titania A, which is a hydrophobic inorganic fine particle having an average particle diameter of 100 nm, is externally added. Example 5 is the same as Example 2 except that the external addition weight of silica D is 1.0 part by weight. Example 6 is the same as Example 2 except that the external addition weight of SrTiO ₃ A is 0.2 parts by weight. Example 7 is the same as Example 2 except that the external weight of SrTiO ₃ A is 0.1 parts by weight. Example 8 is the same as Example 2 except that the external addition weight of SrTiO ₃ A is 1.5 parts by weight and the external addition weight of silica D is 3.0 parts by weight.

Comparative Example 1 is the same as Example 1 except that silica B, which is hydrophobic inorganic fine particles having an average particle diameter of 20 nm, is externally added instead of externally adding silica C. Comparative Example 2 is the same as Example 1 except that silica F, which is hydrophobic inorganic fine particles having an average particle diameter of 150 nm, is externally added instead of externally adding silica C. Comparative Example 3 is the same as Example 2 except that SrTiO ₃ A is not added. Comparative Example 4 is the same as Example 2 except that the external addition weight of silica D is 0.5 parts by weight. Comparative Example 5 is the same as Example 2 except that the external weight of SrTiO ₃ A is 1.0 part by weight. Comparative Example 6 is the same as Example 2 except that the external addition weight of SrTiO3 A is 1.5 parts by weight and the external addition weight of silica D is 4.0 parts by weight. Comparative Example 7 is the same as Example 2 except that the external addition weight of SrTiO ₃ A is 1.5 parts by weight and the external addition weight of silica D is 5.0 parts by weight. Comparative Example 8 is the same as Example 2 except that silica A is not added.

The electrophotographic toners 1 of Examples 2 and 9 and Comparative Examples 9 and 10 were prepared based on the agitation time shown in Table 4 when the external additive was externally added to the toner base particles. Example 2 is the same as Example 1 except that silica D, which is hydrophobic inorganic fine particles having an average particle diameter of 50 nm, is externally added instead of externally adding silica C as described above. The time is 13 minutes as in Example 1. Example 9 is the same as Example 2 except that the stirring time is 7.0 minutes. Comparative Example 9 is the same as Example 2 except that the stirring time is 7.0 minutes.
Comparative Example 10 is the same as Example 2 except that the stirring time is 23.0 minutes.

2-2. Evaluation of Physical Properties of Toner Examples 1 to 9 and Comparative Examples 1 to 10 were subjected to filming evaluation, fog evaluation, and image density evaluation as follows. The physical properties of the electrophotographic toner 1 prepared by the above method were evaluated by the following evaluation methods, and the results are shown in Table 5.

  Note that symbols such as “◎”, “◯”, “Δ”, and “x” described in the description of each evaluation item are symbols indicating evaluation results used in Table 5. “◎” indicates very good, “○” indicates that it is practical, “Δ” indicates that it is difficult to use, and “×” indicates that it is not practical. It shows that.

2-2-1. Evaluation Machine For the evaluation of the electrophotographic toner 1 in the present invention, a color copier (AR-C260) manufactured by Sharp Corporation which is a full-color image forming apparatus as shown in FIG. 3 was used.

2-2-2. Evaluation method [Filming]
After printing 10,000 sheets of belt-like image with an image area of 5% by the above-mentioned evaluation machine, a solid image, a 16 gradation image, a halftone image, etc. are printed on the transfer paper, and the photoconductor is detached from the machine body and the surface thereof is removed. Visual observation was performed to determine the presence or absence of filming. The trial was performed 5 times and evaluated by the frequency of occurrence.
A: No filming occurred.
○: One occurrence of filming.
Δ: Filming occurred 2 or 3 times.
X: Filming occurred 4 times or more.

[Fog]
Reflection density using the Z-Σ90 COLOR MEASURING SYSTEM made by Nippon Denka Kogyo Co., Ltd. at the same position on the white background of the transfer paper and the white background after printing a strip-like image with an image area of 5% by the evaluation machine. The fog amount Wk was calculated from the reflection density Wr of the white background portion of the transfer paper and the reflection density Ws of the white background portion after printing by the following formula, and evaluated based on the following criteria.
Wk = {100 × (Wr−Ws) / Wr}
However, the initial fogging is obtained by filling the toner in an empty toner cartridge and idling for 4 minutes, and then performing the above measurement. The fog after 10,000 sheets is measured after 10,000 sheets of 5% band images are printed by the evaluation machine.
A: Less than 0.50.
○: 0.50 or more and less than 0.90.
Δ: 0.90 or more and less than 1.10
×: 1.10 or more.

[Image density]
The reflection density of the solid portion printed on the transfer paper was measured with a reflection density meter RD918 manufactured by Macbeth Co., Ltd. and evaluated based on the following criteria. The evaluated image is an image printed after 10,000 belt-like images having an image area of 5% are printed by the evaluation machine.
A: 1.55 or more.
○: 1.45 or more and less than 1.55.
Δ: 1.35 or more and less than 1.45.
X: Less than 1.35.

[Comprehensive evaluation]
Based on the following criteria, the above items were judged comprehensively and used as a comprehensive evaluation.
A: Very good.
○: No problem in practical use.
Δ: There are some problems in practical use.
X: There is a problem in practical use.

2-2-3. Evaluation Results Comparative evaluation was performed on Examples 1 to 9 and Comparative Examples 1 to 10 according to the above-described method. The results are shown in Table 5.

  As can be seen from Table 5, when the average particle size of the hydrophobic inorganic fine particles is smaller than the above range (Comparative Example 1), filming is likely to occur, and a clear image could not be formed. Since the hydrophobic inorganic fine particles are small, it is considered that the polishing property of strontium titanate cannot be lowered and the photoreceptor is damaged. When the average particle size of the hydrophobic inorganic fine particles was larger than the above range (Comparative Example 2), filming was likely to occur. It is considered that the hydrophobic inorganic fine particles were difficult to adhere to the strontium titanate fine particles because the hydrophobic inorganic fine particles were too large. If strontium titanate fine particles were not externally added (Comparative Example 3), fogging was likely to occur after long-term use, and a clear image could not be formed. Since strontium titanate fine particles are not added, it is considered that when used for a long time, the external additive is buried in the toner particles and the toner is deteriorated. When the weight ratio of the hydrophobic inorganic fine particles to the strontium titanate fine particles was smaller than 2 (Comparative Example 4 and Comparative Example 5), fog was likely to occur after long-term use. Since the hydrophobic inorganic fine particles cannot completely cover the strontium titanate, it is considered that the toner has deteriorated. When the total weight part of the hydrophobic inorganic fine particles and the strontium titanate fine particles was more than 5 parts by weight (Comparative Example 6 and Comparative Example 7), fog was likely to occur after long-term use. Since there are too many external additives, it is considered that there are many external additives that are detached from the toner or do not adhere to the toner, and the free external additives have damaged the photoreceptor. If hydrophobic silica fine particles having an average particle diameter of 30 nm or less were not externally added (Comparative Example 8), fog was likely to occur after long-term use. If hydrophobic silica fine particles having an average particle size of 30 nm or less are not externally added to the toner, other external additives are difficult to adhere to the toner, and the amount of external additives that could not be attached increases. The photoconductor is considered damaged. If the stirring time is shorter than the above range (Comparative Example 9), fogging occurs after long-term use. It is considered that the external additive was not sufficiently adhered to the toner, the external additive easily peeled off, and the toner at the time of preparation was easily deteriorated. If the stirring time is longer than the above range (Comparative Example 10), fogging occurs after long-term use. It is considered that the toner was easily deteriorated because the external additive was buried too much at the time of toner preparation.

  In Examples 1 to 9 which are the present invention, filming hardly occurs, and even when used for a long period of time, generation of fog can be suppressed.

  Further, the present invention may be an embodiment that includes a pigment or dye such as magenta, yellow, and cyan as a colorant. In other words, the embodiment of the present invention is not limited to the black electrophotographic toner, but can also be implemented with a full-color electrophotographic toner.

1 is a schematic cross-sectional view showing a simplified configuration of an electrophotographic toner 1 according to an embodiment of the present invention. It is a graph which shows the relationship between the bulk density AD of a toner particle, and stirring time. 1 is a schematic configuration diagram of a full-color image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrophotographic toner 2 Toner base particle 3 Strontium titanate fine particle 4 Hydrophobic inorganic fine particle 11 Full color image forming apparatus 12 Photoconductor 13 Arrow 14 Charger 15 Exposure device 16 Developer 17 Transfer device 18 Cleaner 19 Recording medium 20 Paper feed Tray 21 Conveying roller 22 Conveying path 23 Fixing device 24 Paper discharge tray

Claims (7)

Toner base particles having an average particle size of 10 μm or less containing at least a release agent, a colorant and a binder resin;
Strontium titanate fine particles,
Hydrophobic inorganic fine particles having an average particle size of 1/10 or more and 1/3 or less of the average particle size of the strontium titanate fine particles,
An electrophotographic toner comprising externally adding strontium titanate fine particles and hydrophobic inorganic fine particles to toner base particles.   2. The toner for electrophotography according to claim 1, wherein the hydrophobic inorganic fine particles are fine particles of any one of silica, alumina and titania. The weight ratio of the external addition amount of the strontium titanate fine particles to the external addition amount of the hydrophobic inorganic fine particles is 2 or more,
3. The electrophotographic toner according to claim 1, wherein the total amount of the hydrophobic inorganic fine particles and the strontium titanate fine particles is 1 to 5 parts by weight with respect to 100 parts by weight of the toner base particles.   The electrophotographic toner according to claim 1, wherein hydrophobic silica fine particles having an average particle size of 30 nm or less are further externally added. A preparation step of preparing toner base particles by mixing and pulverizing at least a release agent, a colorant and a binder resin;
A first external addition step of adding hydrophobic silica fine particles having an average particle size of 30 nm or less to the toner base particles and stirring for a predetermined time;
A second external addition step of adding and stirring strontium titanate fine particles and hydrophobic inorganic fine particles after stirring for a predetermined time;
In the second external addition step, the average particle size of the hydrophobic inorganic fine particles is 1/10 or more and 1/3 or less of the average particle size of the strontium titanate fine particles,
A method for producing an electrophotographic toner, comprising adding the hydrophobic inorganic fine particles and the strontium titanate fine particles to 1 to 5 parts by weight with respect to 100 parts by weight of the toner base particles.   In the second external addition step, stirring is terminated between the time when the temporal differential value of the bulk density changes from negative to positive and the time until the temporal differential value of the bulk density changes from positive to negative or zero. The method for producing an electrophotographic toner according to claim 5.   In the second external addition step, after the time when the time differential value of the bulk density changes from negative to positive, the time when the secondary differential value with respect to the time of the bulk density becomes zero, and the time differential value of the bulk density is changed from positive to negative or 6. The method for producing an electrophotographic toner according to claim 5, wherein the stirring is terminated between the time until the time of change to zero.

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