JP2012027142A - External additive for electrophotographic toner and electrophotographic toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an external additive for toner, the additive comprising a vapor phase method silica powder that includes primary aggregated particles having a large particle diameter and an amorphous form, for solving problems of a vapor phase method silica powder having a large particle diameter such as intrusion into recesses on a toner surface, embedding in the toner, or detaching from the toner surface, and obtaining excellent effects functioning as a spacer and imparting durability to the toner.SOLUTION: The external additive for an electrophotographic toner comprises a vapor phase method silica powder having an STSA (statistical thickness surface area) of 100 m/g or less and a ratio of a BET specific surface area to the STSA of 1.8 or more. The vapor phase method silica powder having a larger BET specific surface area compared to the STSA and having the STSA of a predetermined value or lower has a firm primary aggregation structure having a large particle diameter and an amorphous form, which prevents problems such as separation from a toner surface or intrusion into recesses on the toner surface and is excellent in a spacer effect and an effect of imparting durability to the toner, and thereby, the toner performance can be maintained for a long period of time.

Description

The present invention relates to a toner for electrophotography such as a copying machine, a printer, a facsimile machine, a plate making system using an electrophotographic method, an improvement in fluidity, a control of charging properties, an improvement in long-term storage, a control of cleaning characteristics, and a carrier. Further, the present invention relates to an external additive for an electrophotographic toner comprising a vapor-phase method silica powder used for the purpose of controlling adhesion to the surface of a photoreceptor or controlling the deterioration behavior of a developer.
The present invention also relates to an electrophotographic toner using the external additive for an electrophotographic toner.

  Inorganic oxide powders such as fine silica, titania, and alumina, and surface-modified inorganic oxide powders that have been modified to improve their chargeability and hydrophobicity can be used in copiers, laser printers, plain paper facsimiles, etc. In electrophotography, it is widely used as a toner fluidity improver or a charge control agent.

  Conventionally, among inorganic oxide powders used for such applications, gas phase method silica has a particularly small primary particle size, and silica powder whose surface has been modified to adjust its chargeability and hydrophobicity is not suitable for toners. Since it has an excellent function as an additive, it is most commonly used (for example, Patent Documents 1 to 3).

Vapor phase method silica has several to tens of primary particle diameters with an average particle diameter of several nm to several tens of nm and is bonded to form amorphous primary aggregated particles. Exists in the form. The aggregate particle diameter is usually 10 μm to 200 μm or more.
When such agglomerated particles are used as an external additive for toner, they are loosened by receiving a strong frictional force in the dispersion step for the toner, and dispersed on the surface of the toner particles in units of primary agglomerated particles.

  In recent years, the particle size of toner particles has been reduced due to the high image quality of electrophotography, and in addition to that, the mechanical load on the toner has been increasing due to the increase in speed and color. Therefore, the durability of toner performance over time (control of deterioration behavior) is particularly important, but on the other hand, binder resins (toner base resins) used for toners for the purpose of shortening printing standby time and saving energy. ) Is required to have low-temperature fixability, and tends to soften with development aimed at this. As a result, the toner is more likely to deteriorate with time.

  The performance of the electrophotographic toner appears as a whole of the properties imparted by the internal and external additives in addition to the physical properties inherent in the toner base resin. In particular, since the external additive is a contact point between the toner base resin surface and the external environment, the influence on the toner performance is large even though the content in the composition is only a few%.

  The toner is agitated in an apparatus such as a copying machine, and is charged, that is, charged by friction with a carrier. The developing function is manifested by the highly controlled chargeability. However, when the toner is continuously stirred in the apparatus for a long time, the strong frictional force becomes stress and the deterioration of the toner proceeds. For example, the external additive is buried in the toner surface, thereby losing the intended function as a contact point between the toner surface and the external environment. However, as described above, the mechanical load on the toner has increased in recent years, and the hardness of the toner base has decreased due to the softening of the binder resin of the toner. As a result, the importance of measures against the burying of external additives as described above is increasing.

  Such embedding of the external additive is particularly noticeable when the primary particle diameter of the external additive powder is less than 20 nm. For the purpose of preventing this, external additive particles having a primary particle diameter of 100 nm or more may be used as a supplementary spacer. In particular, wet method silica such as a precipitation method manufactured using sodium silicate as a raw material or a sol-gel method using silicon alkoxide as a raw material is preferable because it has a uniform particle size and is spherical and has a high fluidity-imparting effect. Used. These silicas generally do not form primary aggregates but are dispersed on the toner in the form of primary particles.

  However, at the same time as the above-described advantage of being spherical and having high particle size uniformity, as a feature common to wet-process silica, the charge amount is low and its rise is slow. Furthermore, since spherical silica has a small contact area with the toner base resin, there is a problem that the developer is easily detached from the toner surface in the step of stirring and mixing the developer together with the carrier in the cartridge and tribocharging. If the detached spherical silica scatters in the developing machine and adheres to an unfavorable portion, it may cause a decrease in printing performance. For example, when the detached spherical silica adheres to the carrier, the charging performance of the carrier deteriorates and toner charging failure occurs.

  This phenomenon occurs regardless of the shape of the toner, but especially on the surface of a toner base having a high degree of sphericity and surface smoothness produced by a polymerization method, the contact area with the external additive is small, so the adhesion force Is very small and easily desorbs. Therefore, a problem in toner performance is likely to occur, and further, it is likely to become serious.

  In addition, in the case of toners other than the spherical shape, rolling of spherical silica into the toner surface recess also becomes a problem. That is, immediately after the external addition process performed in the final stage of toner production, spherical silica is excellent in uniform dispersibility on the toner surface. However, the spherical silica tends to move on the toner surface. Therefore, it tends to eventually roll into the concave portion of the toner and accumulate there. The toner is mainly in contact with the convex portion, and the silica that has rolled into the concave portion can no longer function as a spacer.

  As described above, the use of the large particle size spherical silica by the wet method has a new problem that is not present in the conventional external additives.

  The functional advantage of vapor phase silica as a toner external additive over wet silica is also due to strong primary or agglomerated primary agglomeration and extremely weak secondary agglomeration. When vapor-phase process silica is used as an external additive, it is loosened in the step of dispersing in the toner as described above and adheres to the toner surface in units of amorphous primary aggregated particles. Since the primary agglomerated particles adhere at a plurality of contact points, they are not easily rolled into the recesses on the toner surface, embedded in the toner, or detached from the toner surface, and are stable over a long period of time. Disperses on the toner surface and continues to function as an external additive. On the other hand, the agglomerated structure of the wet process silica is completely different from the vapor process silica. In wet-process silica, primary particles having a spherical shape and high particle size uniformity are closely adhered to each other in the production process, particularly the drying process, and aggregate to form a huge aggregate. Unlike the vapor phase silica, this aggregate is not an aggregate of primary aggregated particles, so that the form dispersed by receiving the frictional force in the dispersion process to the toner is spherical primary particles or undispersed aggregates, It is difficult to obtain primary agglomerated particles having the structure as in vapor phase silica.

  Another major advantage of vapor phase silica is the excellent charging performance resulting from the manufacturing process. It is easy to externally add vapor phase silica to impart high charge to the toner, but more importantly, highly hydrophobized vapor phase silica is stable to the toner even under high humidity conditions. It is to give the electrified chargeability. This is directly related to the development performance of the toner described above, and as the primary particle diameter and primary aggregate particle diameter of the external additive become smaller, the effect becomes more and more, and the performance difference from the small particle diameter silica of the wet method is increased. Expanding. On the other hand, when the performance requirement for the large particle size external additive is specialized in the spacer function, the advantages of the wet process silica described above may be fully utilized. However, in this case as well, the above-mentioned problems derived from the shape, that is, problems such as rolling into the recesses on the toner surface, embedding in the toner, and detachment from the toner surface must be solved.

  On the other hand, even when vapor phase silica is used, primary aggregation is particularly weak when the average primary particle diameter exceeds 40 nm, and in the dispersion process with toner, it is resolved to primary particles by a strong frictional force. It is crushed and many particles are dispersed as spherical particles on the surface of the toner. As a result, similarly to the wet method spherical silica, rolling into the recesses on the toner surface, embedding in the toner, and functional deterioration due to detachment from the toner surface occur.

JP 2004-145325 A JP 2006-99006 A JP 2007-34224 A

  The present invention solves the problems of rolling into the recesses on the toner surface of the vapor phase method large particle size silica, embedding in the toner, and detachment from the toner surface, spacer effect and durability imparting effect on the toner It is an object of the present invention to provide an external toner additive composed of a vapor-phase silica powder having primary aggregate particles having a large particle size and an indefinite shape, which is excellent in the above.

  As a result of intensive studies to solve the above problems, the present inventors have obtained a BET specific surface area that is obtained by highly controlling the production conditions of the vapor phase method silica powder with respect to STSA (statistical thickness specific surface area). Gas phase method silica powder having a large STSA of a predetermined value or less has a strong primary particle agglomeration force and forms a desired agglomerated particle. The agglomerated particle has a large average primary particle size of, for example, 30 nm or more. Despite the fact that the primary agglomeration force is strong, the primary agglomeration remains unbroken even after mixing with the toner and disperses as primary agglomerated particles on the toner. Is adhered firmly to the toner base resin at a plurality of points as in the case of the small-particle-size gas phase method silica, and as a result, the toner surface rolls into the recesses and is embedded in the toner. Eliminating the elimination of problems, it is a suitable silica powder as an external additive for toner capable of maintaining the performance of the toner for a long time, been found.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] A silica powder obtained by a vapor phase method, comprising a silica powder having an STSA of 100 m ² / g or less and a ratio of BET specific surface area to STSA of 1.8 or more. An external additive for toner for electrophotography.

[2] The external additive for an electrophotographic toner according to [1], wherein the silica powder has an average primary particle size of 30 nm or more.

[3] The external additive for an electrophotographic toner according to [1] or [2], wherein the silica powder has an STSA of 30 to 100 m ² / g.

[4] The external additive for an electrophotographic toner according to any one of [1] to [3], wherein the ratio of the BET specific surface area of the silica powder to STSA is 1.8 to 7.0. .

[5] The external additive for an electrophotographic toner according to any one of [2] to [4], wherein the silica powder has an average primary particle size of 30 to 70 nm.

[6] The external additive for an electrophotographic toner according to any one of [1] to [5], wherein the silica powder is hydrophobized.

[7] The external additive for an electrophotographic toner according to [6], wherein the silica powder has a hydrophobicity of 70% or more.

[8] A toner for electrophotography, wherein the silica powder according to any one of [1] to [7] is externally added.

The gas phase method silica powder having an STSA of 100 m ² / g or less and a ratio of BET specific surface area to STSA of 1.8 or more, which is an external additive for an electrophotographic toner of the present invention, has a large particle size and an irregular shape. It has a strong primary aggregation structure and is excellent in the spacer effect and durability imparting effect on the toner, and can maintain the toner performance high over a long period of time.

  The average primary particle diameter of the silica powder according to the present invention is preferably 30 nm or more, for example, 30 to 70 nm (Claims 2 and 5).

The STSA of the silica powder according to the present invention is preferably 30 to 100 m ² / g (Claim 3), and the ratio of the BET specific surface area to STSA is preferably 1.8 to 7.0 ( Claim 4).

  The silica powder according to the present invention may be hydrophobized (Claim 6), and in that case, the hydrophobicity is preferably 70% or more (Claim 7).

  The toner for electrophotography of the present invention is formed by externally adding such an external additive for toner for electrophotography of the present invention, and has excellent durability and can maintain its performance high over a long period of time. it can.

18 is a SEM photograph of the toner sample of Example 15. 14 is a SEM photograph of a toner sample of Comparative Example 15. 7 is a graph showing changes with time in triboelectric charge amounts of toner samples of Examples 12 to 14 and Comparative Examples 12 to 14.

  Hereinafter, embodiments of the external additive for electrophotographic toner and the electrophotographic toner of the present invention will be described in detail.

[External additive for toner for electrophotography]
The external additive for an electrophotographic toner of the present invention is a silica powder obtained by a vapor phase method, has an STSA of 100 m ² / g or less, and a ratio of BET specific surface area to STSA of 1.8. It consists of the silica powder which is the above. In the following, a gas phase method silica powder having an STSA of 100 m ² / g or less and a ratio of BET specific surface area to STSA of 1.8 or more constituting the external additive for an electrophotographic toner of the present invention is referred to as “silica of the present invention. Sometimes referred to as “powder”.

<Action mechanism>
As a general method for measuring the specific surface area of silica powder, the nitrogen adsorption specific surface area by the BET method, that is, the BET specific surface area is known. Since general vapor phase silica powder does not have micropores, the BET specific surface area almost reflects the specific surface area of the external surface. For example, assuming that the primary particles are spherical, the average primary particle diameter obtained from the BET specific surface area is obtained by actually measuring the primary particle diameter on a photograph by photographing the vapor phase silica using a transmission electron microscope (TEM). It agrees well with the average primary particle size obtained.

  However, in the silica powder according to the present invention, the BET specific surface area is significantly larger than the specific surface area calculated from the particle diameter observed with a TEM or a scanning electron microscope (SEM). This is because the silica powder according to the present invention has a fine pore structure or an irregular structure on the surface, and the BET specific surface area is a method for measuring the total surface area including the inside of the micropore.

  Therefore, the present inventors paid attention to a statistical thickness specific surface area (STSA) expressed as a surface area not including micropores of particles. Here, STSA is a value measured according to the method described in ISO 18852 and JIS K 6217-7, and is expressed as an external surface area that does not contain micropores on the surface of the silica powder.

This STSA correlated better with the primary particle diameter measured on the TEM image of the silica powder according to the present invention, but more importantly, the STSA is smaller than a certain value, and the ratio of the BET specific surface area to the STSA is more important. Is larger than a certain value, it is found that such silica powder is dispersed on the toner surface as primary agglomerated particles even if the primary particles are large, and further exhibits excellent performance as an external additive for toner. It was.
That is, when such silica powder is used as an external additive for toner, primary aggregated particles adhere to the toner base resin at a plurality of contacts, so that they roll into the recesses on the toner surface and are embedded in the toner. It was confirmed that due to the effect of suppressing detachment from the toner surface, the spacer function continued to be exhibited for a longer time than the spherical silica having the corresponding primary particle size, and the toner charging performance was maintained.

For this reason, the silica powder of the present invention has an STSA of 100 m ² / g or less, and a ratio of BET specific surface area to STSA (hereinafter referred to as “BET / STSA ratio”) of 1.8 or more. This is an essential requirement.

<STSA>
The silica powder of the present invention has an STSA of 100 m ² / g or less. When STSA exceeds 100 m ² / g, not only the primary particle diameter but also the aggregate particle diameter is too small, and the effect of the present invention cannot be obtained. However, if the STSA of the silica powder is too small, both the primary particles and the agglomerated particles as the external additive for the toner are too large, causing detachment from the toner surface, or inhibiting the effect of the small particle size external additive used at the same time. there's a possibility that. Accordingly, the STSA of the silica powder of the present invention is preferably 30 to 100 m ² / g.

<BET / STSA ratio>
When the BET / STSA ratio of the silica powder is less than 1.8, primary agglomerated particles in which spherical silica is agglomerated that is not much different from the conventional vapor phase method silica powder are obtained. In that case, regardless of the value of STSA, a sufficient advantage is not seen as compared with the conventional vapor phase method silica powder corresponding to the BET specific surface area.
However, since the silica powder having an excessively high BET / STSA ratio has a cohesive force that is too strong, coarse agglomeration is likely to occur. Therefore, the BET / STSA ratio of the silica powder of the present invention is 1.8 or more. It is preferably 8 to 7.0, particularly 1.9 to 6.0.

<BET specific surface area>
The BET specific surface area of the silica powder of the present invention is not particularly limited as long as it is a value satisfying the BET / STSA ratio with respect to the value of the STSA, but it is usually preferably about 45 to 400 m ² / g. .

<Average primary particle size>
The average primary particle diameter of the silica powder of the present invention is usually 30 nm or more, preferably 30 to 70 nm. If the average primary particle size of the silica powder is too large, other external additives do not function effectively, and if it is too small, the spacer effect required for the external additive powder is not sufficient.
In addition, the average primary particle diameter of the silica powder of this invention is a measured value on a TEM photograph.

<Manufacturing method>
The method for producing the silica powder of the present invention is not particularly limited as long as it is a method by which a gas phase method silica powder satisfying the above-mentioned STSA and BET / STSA ratio is obtained. It is done.

  A general method for producing a vapor phase silica powder by flame hydrolysis is, for example, introducing a raw silicon compound gas such as silicon tetrachloride with an inert gas into a mixing chamber of a combustion burner and mixing it with hydrogen and air. In this method, the mixed gas is mixed at a predetermined ratio, and the mixed gas is burned in a reaction chamber at a temperature of 1000 to 3000 ° C. to generate silica, and after cooling, the generated silica is collected by a filter. As a more detailed production method for the flame hydrolysis method, methods described in German Patent Nos. 974,793, 974,974, and 909,339 can be referred to.

  In a preferred method for producing the silica powder of the present invention, amorphous silica is obtained by controlling the supply amount of the primary combustible gas used for the raw silicon compound to less than 1 with respect to the theoretical amount. As the production method, European Patent Publication No. 07108557 can be referred to.

  Below, this manufacturing method is demonstrated.

  First, hydrolysable raw material silicon compound, primary oxygen-containing gas and primary combustible gas are introduced and mixed in the mixing chamber of the combustion burner, and this mixture is ignited to produce a flame, which is sent to the reaction chamber. Combustion is performed at a temperature of 1000 to 3000 ° C. to produce silica powder and a gaseous substance. Silica powder is separated and recovered from the generated gaseous substance.

Here, the introduction amount of the primary combustible gas is set to an amount that is not sufficient to completely hydrolyze the raw silicon compound. That is, the amount of primary combustible gas introduced is less than the stoichiometric amount of combustible gas required to completely hydrolyze the raw silicon compound.
The ratio of the introduction amount of the primary combustible gas to the stoichiometric amount of the combustible gas is calculated by the following formula, and the silica powder of the present invention is primary combustible so that the value of γ (primary) is less than 1. It can manufacture by controlling the amount of gas introduction.
γ (primary) = primary combustible gas introduction amount (mole) / stoichiometric amount of combustible gas (mole)

The value of γ (primary) is preferably 0.20 to 0.90, particularly preferably 0.30 to 0.70.
If γ (primary) is 1 or more, the silica powder of the present invention cannot be produced as described later. However, if γ (primary) is excessively small, the product is undesirably residual in chlorine.

The amount of the primary oxygen-containing gas introduced is preferably not less than the amount necessary for complete reaction with the primary combustible gas (this amount is referred to as “the stoichiometric amount of the primary oxygen-containing gas”). . The ratio λ (primary) of the introduction amount of the primary oxygen-containing gas to the stoichiometric amount of the primary oxygen-containing gas is calculated by the following formula.
λ (primary) = introduction amount of primary oxygen-containing gas (mole) / stoichiometric amount of primary oxygen-containing gas (mole)

  The λ (primary) value is desirably 1 or more and 10 or less, preferably 3 to 10, particularly preferably 3 to 7. If the primary oxygen-containing gas is small and λ (primary) is less than 1, the primary combustible gas and its partially decomposed product remain in the reaction system due to incomplete combustion. On the other hand, if the primary oxygen-containing gas is too much, the combustion rate Is too fast to keep a stable flame.

  In the production of the silica powder of the present invention, secondary and higher higher flammable gases may be supplied at one or more locations in the reaction chamber. Unlike the primary combustible gas introduced into the mixing chamber of the combustion burner, the high-order combustible gas is supplied directly into the reaction chamber. Moreover, it is essential to install each inlet of the high-order flammable gas at a location where the composition and structure of the silica powder can be affected.

The introduction amount of the total combustible gas, which is the sum of the primary combustible gas and the high order combustible gas, is preferably at least the stoichiometric amount necessary for completely hydrolyzing the raw silicon compound. That is, it is preferable that the ratio γ (total) of the total amount of combustible gas calculated by the following formula to the stoichiometric amount of combustible gas is 1 or more.
γ (total) = total amount of combustible gas introduced (mole) / stoichiometric amount of combustible gas (mole)

  The value of γ (total) is preferably 1.05 to 4.0, and particularly preferably 1.1 to 2.0. If γ (total) is less than 1, the generated water vapor is insufficient for completion of the reaction. On the other hand, if this value is too large, the primary particle size of the silica powder becomes small. It becomes difficult to produce powder.

  In the production of the silica powder of the present invention, secondary and higher secondary oxygen-containing gas may be supplied at one or more locations in the reaction chamber. The primary oxygen-containing gas is supplied directly into the reaction chamber, unlike the primary oxygen-containing gas introduced into the mixing chamber of the combustion burner. Moreover, it is essential to install each inlet of the high-order oxygen-containing gas at a location where the composition and structure of the silica powder can be affected.

The total amount of the oxygen-containing gas, which is the sum of the primary oxygen-containing gas and the higher-order oxygen-containing gas, is the amount necessary for complete reaction with all combustible gases (this amount is expressed as “the stoichiometric amount of the oxygen-containing gas”). It is preferable that it is above. The ratio λ (total) of the total oxygen-containing gas introduction amount to the stoichiometric amount of the oxygen-containing gas is calculated by the following equation.
λ (total) = total oxygen-containing gas introduction amount (mole) / stoichiometric amount of oxygen-containing gas (mole)

  λ (total) is 1 or more, particularly preferably greater than 1 and 10 or less, preferably 1.5 to 7.0, particularly preferably 1.8 to 4.0. If λ (total) is less than 1, the primary combustible gas and its partial decomposition products remain in the reaction system due to incomplete combustion. On the other hand, if it is too large, the combustion speed is too high and a stable flame can be maintained. Since it disappears, it is not preferable.

  In addition, the hydrolyzable raw material silicon compound as a starting material includes a hydrolyzable silicon compound that is converted to silica by reaction with water. The raw silicon compound can be introduced either in the vapor state or in the form of a solution dissolved in a solvent that does not react therewith. The raw material silicon compound is desirably introduced in a vapor state.

Examples of the raw material silicon compound include silicon halides, organic silicon halides, and silicon alkoxides. Specific examples include SiCl ₄ , MeSiCl ₃ , Me ₂ SiCl ₂ , Me ₃ SiCl, Me ₄ Si, HSiCl ₃ , and Me _{2. HSiCl, MeEtSiCl 2, Cl 3 SiSiMeCl} 2, Cl 3 SiSiMe 2 Cl, Cl 3 SiSiCl 3, MeCl 2 SiSiMeCl 2, Me 2 ClSiSiMeCl 2, Me 2 ClSiSiClMe 2, Me 3 SiSiClMe 2, Me 3 SiSiMe 3, tetraethoxysilane, Tetramethoxysilane, D4 polysiloxane (cyclic siloxane tetramer), D5 polysiloxane (cyclic siloxane pentamer), etc. (where Me is methyl, Et is ethyl) Represent.). These may be used alone or in combination of two or more. Of these, SiCl ₄ is particularly preferred.

  The combustible gas is a gas that reacts with oxygen and burns, and at the same time generates water necessary for hydrolysis of the raw silicon compound. As the combustible gas (for example, primary combustible gas, secondary combustible gas or higher combustible gas higher than the secondary combustible gas), hydrogen, methane, ethane, propane, butane, and natural gas are preferable. These may be used alone or in combination of two or more. Particularly preferred as a combustible gas is hydrogen.

  The oxygen-containing gas (for example, a primary oxygen-containing gas, a secondary oxygen-containing gas, or a higher-order oxygen-containing gas higher than the tertiary oxygen-containing gas) is preferably air, and can be used by enriching air with oxygen.

  In the above manufacturing method, after the produced silica powder is separated from the gaseous substance, the silica powder may be subjected to steam treatment with a mixed gas of steam and air. This steam treatment is usually performed at a temperature of 250 to 750 ° C, preferably 300 to 700 ° C, more preferably 350 to 650 ° C, still more preferably 400 to 600 ° C, and particularly preferably 450 to 550 ° C. The steam treatment is effective, for example, for removing unreacted chloride from the surface of the produced silica powder and reducing agglomerated particles. This water vapor treatment can also be carried out by continuous treatment of the silica powder after separating the gaseous substance with a mixed gas of water vapor and air flowing in the cocurrent or countercurrent direction.

  The reason why the silica powder satisfying the STSA and BET / STSA ratio of the present invention can be easily obtained by the production method in which the primary combustible gas is set to less than the stoichiometric amount as described above is as follows.

That is, when the primary combustible gas is supplied in a stoichiometric amount or more, the BET specific surface area and STSA of the obtained silica powder are substantially equal (BET / STSA ratio≈1). The STSA is remarkably smaller than the BET specific surface area, and at the same time, the primary particle size is larger than that of a general vapor phase silica powder having the same BET specific surface area.
If the primary combustible gas is deficient relative to the stoichiometric amount, particle growth takes precedence over silica particle formation. At the same time, the raw material silicon compound undergoes particle growth without being completely hydrolyzed. Eventually, the combustible gas is supplied in excess of the stoichiometric amount to complete the reaction, but the generated silica particles have many structural defects, and therefore have an irregular structure on the particle surface.
A further important effect is that the irregular structure on the surface increases the cohesive force between the particles. As a result of the study by the present inventors, the gas phase method silica powder produced by the above method is strongly aggregated even when the primary particle diameter is larger than 30 nm, and the primary aggregates are added to the toner. It was confirmed that the aggregate particle diameter of 0.1 μm to 0.5 μm was maintained even after the dispersion step.
And by controlling the aggregated particle diameter optimally, when used as an external additive for toner, the problem of rolling into the concave portion on the toner surface, embedding in the toner, detachment from the toner surface is solved, A silica powder exhibiting an excellent spacer effect that suppresses toner deterioration over a long period of time can be obtained.

<Surface treatment>
As the silica powder of the present invention, the silica powder produced by the vapor phase method can be used as it is, or after being surface-treated.
When the surface treatment is performed, the surface treatment conditions of known vapor phase silica powder can be used, for example, by the method described in WO2009 / 084184. In this case, silanol groups capable of reacting with the surface treatment agent are distributed on both the external surface and the micropore, but the surface treatment agent cannot react with some surfaces due to steric hindrance. The required amount is smaller than the value calculated from the BET specific surface area in ordinary vapor phase silica powder, and can be set between the BET specific surface area and STSA.

  The surface treatment method is not particularly limited. For example, in the case of a hydrophobic treatment, the hydrophobizing agent includes alkylsilazane compounds such as hexamethyldisilazane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, methyl Alkyl alkoxysilane compounds such as trimethoxysilane and butyltrimethoxysilane, chlorosilane compounds such as dimethyldichlorosilane and trimethylchlorosilane, silicone oil, and silicone varnish can be used. One of these hydrophobizing agents may be used alone, or two or more thereof may be mixed and used.

  Moreover, as a concrete processing method, the method of spraying the hydrophobization processing agent on the silica powder of this invention or mixing the vaporized hydrophobizing processing agent, and heat-processing is mentioned, for example. At this time, water, amine, or other catalyst may be used. The dry surface treatment is preferably performed in an inert gas atmosphere such as nitrogen. Alternatively, the hydrophobizing agent is dissolved in a solvent, and the silica powder of the present invention is mixed and dispersed therein, followed by heat treatment as necessary, and further drying treatment to obtain a surface-modified silica powder. . The hydrophobizing agent may be added after silica powder is mixed and dispersed in a solvent or simultaneously.

The degree of hydrophobicity of the hydrophobized silica powder of the present invention (hydrophobized silica powder) is not particularly limited and is determined according to the purpose of use and the required characteristics, but as an external additive for electrophotographic toners. In the above applications, the hydrophobicity is preferably 70% or more, particularly preferably 85% or more. The upper limit of the hydrophobic rate is 100%.
Specifically, the hydrophobicity of the hydrophobized silica powder is measured by the method described in the Examples section below.

[Electrophotographic toner]
The electrophotographic toner of the present invention is obtained by externally adding the external additive for an electrophotographic toner of the present invention comprising the above-described silica powder of the present invention, and there is no particular limitation on the composition and the production method thereof. Known compositions and methods can be employed.

  In the production of the electrophotographic toner of the present invention, the addition amount of the silica powder of the present invention (the external additive for electrophotographic toner of the present invention) is such that the desired characteristic improving effect can be obtained. Although not particularly limited, the electrophotographic toner preferably contains 0.1 to 8.0% by weight of the silica powder of the present invention. When the content of the silica powder of the present invention in the electrophotographic toner is less than 0.1% by weight, the effect of improving durability and the stabilizing effect such as chargeability can be sufficiently obtained by adding the silica powder of the present invention. Absent. Further, if the content of the silica powder of the present invention exceeds 8.0% by weight, the toner surface is completely covered and a large amount of silica is still present, which may cause contamination in the apparatus. .

  In general, the toner contains a small amount of a pigment, a charge control agent, and other external additives in addition to a thermoplastic resin (toner base resin). In the present invention, as long as the silica powder of the present invention is blended, the other components may be the same as those in the past, and may be either a magnetic or non-magnetic one-component toner or two-component toner. Further, either negatively chargeable toner or positively chargeable toner may be used, and either monochrome or color may be used.

  In the production of the electrophotographic toner of the present invention, the silica powder of the present invention as an external additive is not limited to being used alone, but may be used in combination with other metal oxide fine powders depending on the purpose. May be. For example, the silica powder of the present invention may be used in combination with other surface-modified dry silica powder, surface-modified dry titanium oxide powder, surface-modified wet titanium oxide powder, or the like.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

In the following, γ (primary), γ (total), λ (primary), and λ (total) are as described above, but γ (secondary) and γ (third order) are values calculated by the following formulae. Means.
γ (secondary) = secondary combustible gas introduction amount (mole) / stoichiometric amount of combustible gas (mole)
γ (tertiary) = amount of introduced tertiary combustible gas (mole) / stoichiometric amount of combustible gas (mole)

[Examples 1 to 4, Comparative Examples 1 to 6 (production of silica powder)]
In Comparative Example 1, 108 Kg / h silicon tetrachloride (SiCl ₄ ), 14 m ³ / h (standard state) hydrogen (primary combustible gas), and 140 m ³ / h (standard state) air (primary oxygen-containing gas) ) Is introduced into the mixing chamber of the combustion burner and mixed, and this mixed gas is injected from the burner and ignited and burned in the reaction chamber, where 21 m ³ / h (standard state) of hydrogen (secondary combustible) Gas) and 40 m ³ / h (standard state) air (secondary oxygen-containing gas) were additionally supplied.
Γ (primary), γ (total), λ (primary), and λ (total) at this time are as shown in Table 1.

In Examples 1 to 4, the amount of SiCl ₄ introduced was 100 kg / h, and γ (primary), γ (secondary), γ (tertiary), γ (total), λ (primary), and λ (total) are shown in Table 1. In the same manner as in Comparative Example 1 except that the introduction amounts of the primary flammable gas, the secondary flammable gas, the tertiary flammable gas, the primary oxygen-containing gas, and the secondary oxygen-containing gas were adjusted so that the values shown in FIG. The reaction was performed.

  In Comparative Examples 2 to 4, primary combustible gas, secondary so that γ (primary), γ (secondary), γ (total), λ (primary), and λ (total) have the values shown in Table 1. The reaction was performed in the same manner as in Comparative Example 1 except that the introduction amounts of the combustible gas, the primary oxygen-containing gas, and the secondary oxygen-containing gas were adjusted.

In Comparative Examples 5 and 6, the amount of SiCl ₄ introduced was 100 kg / h, and γ (primary), γ (secondary), γ (total), λ (primary), and λ (total) are the values shown in Table 1. As described above, the reaction was carried out in the same manner as in Comparative Example 1 except that the introduction amounts of the primary combustible gas, the secondary combustible gas, the primary oxygen-containing gas, and the secondary oxygen-containing gas were adjusted.

  The produced gas phase method silica powder is collected by a filter, and purified by removing hydrogen chloride and other impurity gases by opposingly passing a gas mixture of air and water vapor at 520 ° C. to obtain the desired hydrophilic silica powder. Obtained.

  The average primary particle diameter, STSA and BET specific surface area of the obtained silica powder were measured by the following methods, and the results are shown in Table 1 together with the BET / STSA ratio.

<Average primary particle size>
Each silica powder was photographed with a transmission electron microscope (TEM), and the average primary particle size was determined by measuring 2000 or more particles on the photograph.

<STSA>
It measured based on the method as described in ISO18852 and JISK6217-7.

<BET specific surface area>
It was measured by the BET method.

[Examples 5 to 11 and Comparative Examples 7 to 11 (surface treatment)]
100 parts by weight of the silica powder (hydrophilic silica powder) obtained in Examples 1, 2, 4 and Comparative Examples 1, 3, 5, and 6 was put in a reaction vessel, respectively, and 5 parts by weight of water and Table 2 in a nitrogen atmosphere. The amount of hexamethyldisilazane (abbreviated as “HMDS”) was sprayed. The reaction mixture was stirred at 150 ° C. for 2 hours and further stirred at 220 ° C. for 2 hours under a nitrogen stream and dried. By cooling this, a surface-treated silica powder was obtained.
The hydrophobicity of the obtained surface-treated silica powder was measured by the following method, and the results are shown in Table 2.

<Measurement of hydrophobicity>
1 g of the surface-treated silica powder sample was weighed into a 200-mL separatory funnel, 100 mL of pure water was added thereto, the stopper was plugged, and the mixture was shaken with a tumbler mixer for 10 minutes. After shaking, it was allowed to stand for 10 minutes. After standing, after removing 20-30 mL of the lower layer from the funnel, the lower layer mixed solution is dispensed into a 10 mm quartz cell, subjected to a colorimeter using pure water as a blank, and the light transmittance (%) at a wavelength of 500 nm is obtained. The hydrophobicity was assumed.

  The surface-treated silica powder was evaluated for a sufficient amount of the surface treatment agent for each sample by measuring the hydrophobicity as described above. In each sample, a high hydrophobicity of 95% or more was obtained when a sufficient amount of treatment agent was used.

[Examples 12-14, Comparative Examples 12-14 (Preparation of Toner Composition)]
Using a commercially available negatively charged polyester toner base powder (manufactured by Sinnar) manufactured by a polymerization method, this toner, a hydrophobized silica powder shown in Table 3, and a commercially available surface-treated silica powder (Nippon Aerosil Co., Ltd.) Product name “AEROSIL (registered trademark) RX200”) is mixed at a weight ratio of 97.5: 2.0: 0.5, and stirred with a Henschel mixer at 5000 rpm for 1 minute to make silica powder into toner. A toner sample for measuring the triboelectric charge amount was prepared by dispersing the toner sample.

  With respect to the obtained toner sample for measuring the triboelectric charge amount, the triboelectric charge amount was measured by the following method, and the results are shown in Table 3 and FIG.

<Measurement of frictional charge>
2 g of toner sample for triboelectric charge measurement and 48 g of iron powder carrier are placed in a glass container (75 ml capacity) and left for 24 hours at a temperature of 20 ° C. and a humidity of 60%. After shaking for a predetermined time, 0.2 g of this mixture was collected, and the value after nitrogen blowing with a blow-off charge measuring device (product of Toshiba Chemical Co., Ltd .: Model TB-200) for 1 minute was used as the triboelectric charge amount of the toner sample. did.
The triboelectric charge amounts were measured as shaking times of 1 minute, 3 minutes, 10 minutes, 30 minutes, and 90 minutes, respectively, and the change in the triboelectric charge amount with respect to the shaking time was defined as the time-dependent change in the triboelectric charge amount. A toner having a smaller change in triboelectric charge with time and a smaller triboelectric charge quantity can be evaluated as a toner having excellent durability and performance stability.

Example 15
In the above, toner samples were prepared in the same manner as in Examples 12 to 14, except that a commercially available negatively charged polyester toner base powder and the hydrophobized silica powder of Example 6 were mixed at a weight ratio of 97: 3.

[Comparative Example 15]
In the above, toner samples were prepared in the same manner as in Comparative Examples 12 to 14 except that a commercially available negatively charged polyester toner base powder and the hydrophobized silica powder of Comparative Example 10 were mixed at a weight ratio of 97: 3.

The SEM photographs of the toner sample of Example 15 and the toner sample of Comparative Example 15 at this time are shown in FIGS.
1 and 2, it can be seen that in the silica powder of the example of the present invention, the primary aggregated particles are uniformly dispersed and adhered to the surface of the toner base particle as compared with the silica powder of the comparative example. On the other hand, in the toner of FIG. 2, many silica powders are dispersed as spherical primary particles, and further, rolling into the recesses on the toner surface occurs. Those particles cannot function as spacers.

Based on the above results, a toner using gas phase method silica powder having an STSA of 100 m ² / g or less and a BET / STSA ratio of 1.8 or more has improved durability and stability over time. It turns out that it is excellent.

Claims (8)

Electron characterized by comprising a silica powder obtained by a vapor phase method and having a STSA of 100 m ² / g or less and a ratio of BET specific surface area to STSA of 1.8 or more. External additive for photographic toner.   2. The external additive for an electrophotographic toner according to claim 1, wherein the silica powder has an average primary particle diameter of 30 nm or more. 3. The external additive for an electrophotographic toner according to claim 1, wherein the silica powder has an STSA of 30 to 100 m < ² > / g.   The external additive for an electrophotographic toner according to any one of claims 1 to 3, wherein the ratio of the BET specific surface area of the silica powder to STSA is 1.8 to 7.0.   5. The external additive for an electrophotographic toner according to claim 2, wherein the silica powder has an average primary particle size of 30 to 70 nm.   6. The external additive for an electrophotographic toner according to claim 1, wherein the silica powder is hydrophobized.   7. The external additive for an electrophotographic toner according to claim 6, wherein the silica powder has a hydrophobicity of 70% or more.   An electrophotographic toner comprising the silica powder according to any one of claims 1 to 7 externally added.

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