JP2007176747A - Surface-coated silica and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-coated silica synergistically showing the effect which each silicone oil imparts to silica which has not been achieved by silica treated with one kind of silicone oil and conventional silica treated with a mixture of two kinds or more of silicone oil. <P>SOLUTION: The surface-coated silica is provided by being coated with different kinds of two or more silicone oils, wherein an amount of the silicone oil extracted by chloroform is 5 to 95% by mass in a total amount of the silicone oil coated, and at least one kind of silicone oil is not contained in the silicone oil extracted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel surface-coated silica coated with two or more types of silicone oil and a method for producing the novel surface-coated silica. Specifically, the effect that each silicone oil imparts to silica, which could not be achieved with one treated with one type of silicone oil and one with a mixture of two or more types of conventional silicone oils, is synergistic. The present invention relates to a surface-coated silica that can be applied to the surface and a method for producing the surface-coated silica. Specifically, the present invention relates to a surface-coated silica that is excellent in environmental stability such that the change in charge amount is small even at high temperature and high humidity and low temperature and low humidity, and whose charge level is controlled, and a method for producing the surface-coated silica. The present invention also relates to a surface-coated silica having high hydrophobicity, excellent environmental stability, and reduced aggregated particles, and a method for producing the surface-coated silica. Such surface-coated silica is particularly useful as an external additive for electrophotographic dry toners used in copying machines and laser printers.

  In electrophotographic technology that is widely applied to copiers, printers, fax machines, etc., fine silica surface-treated with a hydrophobizing agent is used to provide high fluidity and appropriate chargeability to the dry toner in the developer. It is added and mixed as an additive.

  Organosilicon compounds such as dimethyldichlorosilane, hexamethyldisilazane, and silicone oil have been used as hydrophobizing agents for silica used as external additives for toners. By reacting such an organosilicon compound with a hydrophilic silanol group on the surface of silica fine particles and introducing an organic group, surface-coated silica imparted with hydrophobicity can be obtained. Among them, silica whose surface is coated with silicone oils such as dimethyl silicone oil and modified silicone oil is characterized by particularly high hydrophobicity and low surface energy. These silicone oils can impart various performances to the surface-coated silica depending on the type. For example, dimethyl silicone oil has a function of enhancing the environmental stability of charging because surface-coated silica can be highly hydrophobized. In addition, the amino-modified silicone oil can control the charge level of the surface-coated silica. Furthermore, low molecular weight compounds such as octamethylcyclotetrasiloxane have a feature that they can reduce silica aggregation because they can be surface-coated in a gaseous state.

  In recent years, copiers and printers have become more and more demanding of color, high image quality, miniaturization, high speed, low power consumption, etc. Development is underway to respond. For example, the particle diameter of the toner has been reduced from the conventional 8 to 10 μm to 5 to 7 μm, and the softening temperature of the binder resin constituting the toner tends to be set low.

  As the toner particle size is reduced and the softening point is lowered, the fluidity of the toner is remarkably deteriorated, and a countermeasure for increasing the amount of silica, which is an external additive (fluidizing agent), is increased. The number of cases is increasing. Therefore, for silica external additives located on the outermost surface of the toner, the flow imparting characteristics are improved and the amount of aggregated coarse particles is reduced. There is an increasing demand for imparting various performances such as improvement of environmental stability such as little change.

  First, the case where the charge level is controlled will be described. Specifically, as a means of controlling the charge level of silica, which is generally considered to have strong negative chargeability, the surface is coated with amino-modified silicone oil, and the charge amount of silica is positively chargeable or moderately low negative charge. Technologies for controlling the level and applying it to toner have been proposed (Patent Documents 1 and 2).

  However, silica surface-coated with amino-modified silicone oil does not always maintain a high degree of hydrophobicity because it contains hydrophilic amino groups, and amino-modified silicone oil is used in an amount necessary for charge control. As a result, there is a problem that it is easily affected by environmental fluctuations such as temperature and humidity.

  Attempts have also been made to improve this. For example, there is a technique in which two types of silicone oils having different molecular weights, such as a combination of dimethyl silicone oil and amino-modified silicone oil, are mixed and silica is surface-treated with this mixture. It has been proposed (Patent Document 3). In the technology of finding the optimum combination for each toner by mixing these two types of silicone oil, the release property to the photoreceptor is improved by the high molecular weight oil component, and the aggregated coarse particle amount is reduced by the low molecular weight oil component. Is effective.

  However, even when this method is used as an external additive for toner, environmental fluctuations such as temperature and humidity (hereinafter referred to as environmental stability) are not sufficient, and the charge distribution is widened and the image quality is not stable. However, the effect of treating with two types of silicone oils, dimethyl silicone oil and amino-modified silicone oil, was not fully exhibited, and there was room for improvement.

  Next, a specific example of improving environmental stability and reducing aggregated particles will be described. When silica whose surface is coated with silicone oil is used as an external additive for toner, silicone oil extracted with a solvent such as chloroform (hereinafter sometimes referred to as free silicone oil) exists on the silica surface. By doing so, environmental stability is improved and it can use suitably. However, such a surface-coated silica has a problem that it easily aggregates because silicone oil is a polymer substance.

  Improvements to such problems have also been attempted, and methods for adjusting the amount of silicone oil coated on the surface have been proposed. For example, an attempt has been made to regulate the upper limit value of silicone oil extracted with chloroform so that the silicone oil does not exist excessively on the silica surface (Patent Document 4). There has also been a proposal for improvement by defining a release rate according to a specific surface area rather than an absolute amount of free silicone oil (Patent Document 5).

  However, in the examples of these patent documents, only one type of silicone oil is specifically treated, and simply adjusting the amount of free silicone oil has a certain effect on reducing aggregated coarse particles. Although it can be seen, there has been room for improvement because it has not been possible to sufficiently achieve a reduction in the amount of aggregated coarse particles and environmental stability.

JP 59-201063 A JP-A-62-52564 JP-A-9-166885 JP 2000-66439 A JP 2002-174926 A

  As described above, the silica coated with the conventional silicone oil can impart the performance specific to the silicone oil to the silica, but it is simply treated with one type of silicone oil, or the conventional two types of silicone. In recent years, it has become difficult to cope with various required performances of those treated with an oil mixture.

  Therefore, the object of the present invention is that each silicone oil is imparted to silica, which cannot be achieved by treatment with one type of silicone oil or with a conventional mixture of two or more types of silicone oil. It is an object of the present invention to provide a surface-coated silica capable of synergistically exerting the effect, and a method for producing the silica.

  More specifically, when used as an external additive for toner, the surface-coated silica has excellent charging performance, that is, the charge level is controlled and has environmental stability, and a method for producing the surface-coated silica. Is to provide. Also provided are a surface-coated silica that retains a certain amount of free silicone oil, has high hydrophobicity, exhibits environmental stability and the like, and has a reduced amount of aggregated coarse particles, and a method for producing the surface-coated silica. It is in.

  As a result of intensive studies, the present inventors solved the above problems by adjusting the amount of each silicone oil and the coating state in the silica whose surface was coated with two or more types of silicone oil. The present invention was completed by successfully obtaining surface-coated silica. In addition, the present inventors have found that such surface-coated silica can be obtained by sequentially treating two or more types of silicone oils in stages, and have completed the present invention.

  That is, the present invention is a surface-coated silica coated with two or more different types of silicone oil, and the amount of silicone oil extracted with chloroform is 5 to 95% by mass of the total silicone oil coated. The surface-coated silica is characterized in that at least one kind of silicone oil is not contained in the extracted silicone oil.

  Further, the present invention is a method for producing surface-coated silica, in which silica as a base material is sequentially coated with two or more different types of silicone oils, wherein the first silicone oil is mixed with the base material at 150 ° C. After the coating treatment at the above temperature, the coating treatment is then performed with a silicone oil of a type different from that of the first silicone oil.

  The surface-coated silica of the present invention is coated with two or more types of silicone oils, and can synergistically exhibit the effect that each silicone oil imparts to the silica.

  In particular, the combination of amino-modified silicone oil and dimethyl silicone oil exhibits excellent charging performance, that is, the effect that the charging level is controlled to a moderately low negative charging property and the environmental stability is maintained high. be able to. In addition, the combination of octamethylcyclotetrasiloxane and dimethylsilicone oil retains a certain amount of free silicone oil, is highly hydrophobic, exhibits excellent environmental stability, and has a larger amount of aggregated coarse particles than before. The effect which reduces can be exhibited. For this reason, particularly when used as an external additive for toner, it exhibits an excellent effect on the environmental stability and durability of charging.

  Hereinafter, the present invention will be described in more detail and specifically.

(Silica as the base material)
In the present invention, silica particles obtained by a known method can be used without particular limitation as the silica that is the base material before the coating treatment with the silicone oil. For example, fumed silica, wet method silica, sol-gel method silica and the like are representative. Further, these silicas may be silica partially or wholly melted.

  The fumed silica refers to silica particles produced by burning a silicon compound or metallic silicon in a flame. Typical examples of the silicon compound include silicon halides, alkoxides, and siloxanes. In particular, the silicon halide is generally produced in an oxyhydrogen flame using silicon chloride, usually purified silicon tetrachloride. Fumed silica is sometimes referred to as “dry process silica” to distinguish it from silica produced by a wet process such as precipitated silica.

  The wet process silica is typically precipitated silica generally called “white carbon” in which silica is precipitated by neutralizing sodium silicate with a mineral acid such as sulfuric acid in a solution. Gel silica prepared by synthesizing gel silica by the reaction of sodium silicate and acid, and pulverizing and classifying the silica is also included in the wet silica and can be used as the base silica of the present invention.

  Sol-gel silica is classified as one of wet silicas, and is produced by hydrolyzing silicon alkoxides such as tetramethoxysilane and tetraethoxysilane in an acidic or alkaline water-containing organic solvent. Although silicon alkoxide is expensive, it can be highly purified by distillation, and therefore has a feature that extremely high purity silica can be obtained.

In the silica used as the base material used in the present invention, the physical properties such as specific surface area are not particularly limited. However, when used for fluidizing agents and additives such as external additives for toner, such silica is used. (hydrophilic silica prior to coating treatment) has a specific surface area of 10 to 400 m ² / g, in particular, is suitable as possible 30~380m ² / g available as general-purpose products. Moreover, as a primary particle diameter, 5 nm-1 micrometer, Preferably, 10 nm-300 nm are common. In the present invention, silica obtained by appropriately hydrophobizing such hydrophilic silica with a hydrophobizing agent such as dimethyldichlorosilane, hexamethyldisilazane, or alkylalkoxysilane in advance can be used as a substrate. Furthermore, in the present invention, in addition to the embodiment in which one type of silica as exemplified above is used alone, a plurality of types of silica, for example, a plurality of silicas having different specific surface areas are mixed together in appropriate amounts to form a substrate. The aspect to do is also included.

  In the present invention, it is possible to appropriately select and use a suitable one from the above-mentioned fumed silica and wet silica according to the required characteristics of the individual toner. In particular, fumed silica is excellent in fluidity imparting effect and is suitable as a base silica used in an external additive for electrophotographic toner.

Even when the fumed silica is used as the base silica of the present invention, the physical properties thereof are not particularly limited. For example, the specific surface area which is a representative physical property is preferably 10 to 400 m ² / g, and more preferably 20 ˜380 m ² / g fumed silica is preferably used. A fumed silica having a high specific surface area has a merit that a negative charge amount is high, and a fluidity imparting effect is exhibited even when a small amount is added. Further, fumed silica having a low specific surface area is less likely to be buried in the toner resin and is effective in maintaining fluidity during durability. In this manner, fumed silica having an appropriate specific surface area may be appropriately selected according to the toner and system to be used.

(Silicone oil)
The silicone oil used in the present invention indicates an oily substance having a molecular structure having a siloxane bond as a main chain, and those that are generally available can be used without particular limitation. For example, dimethyl silicone oil, methyl hydrogen silicone oil, methylphenyl silicone oil, alkyl modified silicone oil, chloroalkyl modified silicone oil, α-methylstyrene modified silicone oil, chlorophenyl modified silicone oil, olefin Modified silicone oil, fatty acid modified silicone oil, amino modified silicone oil, alkoxy modified silicone oil, mercapto modified silicone oil, polyether modified silicone oil, carbinol modified silicone oil, fluorine modified silicone oil, terminal reactive silicone oil, etc. In addition to silicone oil consisting of a linear polysiloxane skeleton, hexamethylcyclotrisiloxane, octamethylcyclo Tiger siloxanes, cyclic siloxanes such as decamethylcyclopentasiloxane, and the like.

  In the present invention, the viscosity, which is a typical physical property of the silicone oil, is not particularly limited, but usually a viscosity of about 1 to 1000000 cSt can be used at room temperature. Among them, it is preferable to use a silicone oil having a viscosity of 10 to 10000 cSt in order to avoid aggregation of silica particles surface-treated with silicone oil and ensure reactivity with the silica surface. In view of the performance stability, it is preferable to use a silicone oil having a viscosity of 30 to 1000 cSt. In the present invention, when the viscosity of silicone oil is high, dilution with low reactivity with silica such as organic solvents such as alcohol and toluene, and low molecular weight siloxanes such as hexamethyldisiloxane and octamethyltrisiloxane. It can also be used after being diluted with an agent and adjusting its viscosity.

  Further, in the present invention, even when a modified silicone oil is used, there is no limitation on the type or functional group equivalent of the functional group introduced into the side chain or terminal of the siloxane skeleton, depending on the function from those commercially available. Silicone oil can be appropriately selected and used.

  In the present invention, two or more types of silicone oils of different types are not limited to those in which the molecular structures of two or more types of silicone oils are different from each other, and silicone oils having different functionalities and different viscosity and molecular weight distributions are also included. included. Furthermore, when each silicone oil is mixed, if it does not react with each other, a plurality of types of silicone oil compositions, a mixture composition of silicone oils with different types and concentrations, or a combination of diluents, etc. This aspect is also included.

  In the present invention, two or more types of silicone oils having desired properties and different types and compositions are selected from the above silicone oils. What is necessary is just to determine the combination of a silicone oil suitably according to the performance of the target surface-coated silica. In particular, when amino-modified silicone and dimethylsilicone oil are used, a surface-coated silica having a high environmental stability, in which the charge level is appropriately controlled to a low negative chargeability, can be obtained.

Said amino modified silicone oil is not specifically limited, What is necessary is just to select suitably from what is marketed. An amino group introduced into the side chain or terminal of the siloxane skeleton works to suppress the negative chargeability of the silica surface. In the case of low negative charge or a large amount of functional groups, positive charge is possible. It becomes possible and can be controlled to a desired charge level. In this case, the charge level can be generally controlled based on the amount of amino group to be introduced. Moreover, there is no restriction | limiting in the structure of the amino group introduce | transduced into a side chain or the terminal. For example, when R and R ′ are alkyl groups, structures such as —RNH ₂ and —RNHR′NH ₂ can be generally mentioned. Furthermore, there are no particular limitations on the properties such as viscosity and specific gravity of amino-modified silicone oil and equivalents of functional groups such as amino groups, and the formulation may be optimized so that desired performance can be achieved depending on the toner and system. Even a different functional group-modified silicone oil into which a functional group other than an amino group such as an alkoxy group is simultaneously introduced can be used without any problem.

  Further, in the present invention, when octamethylcyclotetrasiloxane and dimethyl silicone oil are combined, it has a certain amount of free silicone oil, is highly hydrophobic, exhibits excellent environmental stability, In comparison, a surface-coated silica with a reduced amount of aggregated coarse particles can be obtained.

(Surface coating silica)
The present invention is a surface-coated silica coated with two or more types of silicone oils of different types. And in this surface-coated silica, the amount of silicone oil extracted with chloroform is 5 to 95% by mass of the total silicone oil coated, and at least one silicone oil is contained in the extracted silicone oil. Is not included. Hereinafter, the silicone oil obtained when the surface-coated silica is extracted with chloroform by the method described in detail in Examples below will be referred to as free silicone oil.

  In the present invention, the surface-coated silica must be coated with two or more types of silicone oil. Various performances can be imparted to silica by coating with two or more types of silicone oil. Although there is no upper limit in particular in the kind of silicone oil used for a coating process, when industrial production is considered, it is economical that it is 3 or less types.

  In the present invention, the amount of the free silicone oil needs to be 5 to 95% by mass of the total silicone oil coated with the surface-coated silica. When the amount of free silicone oil is less than 5% by mass, or when the amount of free silicone oil exceeds 95% by mass, the effect that each silicone oil imparts to silica cannot be exhibited synergistically. Specifically, a combination of an amino-modified silicone oil and a dimethyl silicone oil (when the free silicone oil is a dimethyl silicone oil) is not preferable because toner performance such as environmental stability is hardly exhibited. That is, when the free silicone oil is less than 5% by mass, it is not preferable because the surface of the silica particles cannot be sufficiently covered with dimethyl silicone oil, and it is estimated that the hydrophobicity is insufficient and is easily affected by environmental humidity. When the free silicone oil exceeds 95% by mass, it is considered that most of the coated silicone oil is not chemically attached to the surface of the silica particles, and environmental stability cannot be exhibited. The amount of the free silicone oil is more preferably 10 to 80% by mass because the performance of each silicone oil imparted to silica can be more effectively exhibited.

  In the present invention, at least one silicone oil among the two or more silicone oils used for coating treatment should not be contained in the free silicone oil. That is, the entire amount of at least one silicone oil needs to be chemically attached to the silica surface. Since at least one silicone oil is not included in the free silicone oil, the performance of other silicone oils can be exhibited while maintaining the performance of the silicone oil imparted to silica. In the state where all of the plurality of coated silicone oil species are separated by the chloroform extraction operation, the free components are mixed on the surface of the silica particles, and the intended synergistic effect becomes insufficient. For example, a combination of amino-modified silicone oil and dimethyl silicone oil is not preferable because performance such as environmental stability is insufficient. Further, a combination of octamethylcyclotetrasiloxane and dimethyl silicone oil is not preferable because the cohesion cannot be improved sufficiently.

  In the present invention, at least one kind of silicone oil is not included in the free silicone oil. However, in consideration of industrial production, it is preferable that one type of silicone oil is not included in the free silicone oil. .

  In the present invention, the silicone oil not included in the free silicone oil is not particularly limited, but is preferably an amino-modified silicone oil or octamethylcyclotetrasiloxane. Among these, in the case of an amino-modified silicone oil, since the charge level of silica can be controlled, it can be suitably used for toner external additives. Further, it is preferable that octamethylcyclotetrasiloxane is a silicone oil not included in the free silicone oil because the cohesiveness of the surface-coated silica can be improved. Silicone oil used for other surface treatments is not particularly limited, but dimethyl silicone oil is used in order to impart high hydrophobicity to silica and excellent environmental stability. It is preferable. To specifically illustrate the preferred combination, the free silicone oil is dimethyl silicone oil and the silicone oil not included in the free silicone oil is an amino-modified silicone oil, or the free silicone oil is dimethyl silicone oil, The silicone oil not contained in the free silicone oil is preferably octamethylcyclotetrasiloxane.

  The reason why the surface-coated silica of the present invention can effectively exhibit the performance imparted by each silicone oil is not clear, but is estimated as follows. That is, in the surface-coated silica of the present invention, a coating layer formed of a different type of silicone oil (included in the free silicone oil) is further formed on the silicone oil coating layer not contained in the free silicone oil. It is thought that it is formed in multiple stages. Such a coating layer is considered to have a concentration gradient in which the concentrations of silicone oil not included in the free silicone oil and different types of silicone oil gradually change. As a result, for example, when the amino-modified silicone oil is not included in the free silicone oil and the dimethyl silicone oil is a different type of silicone oil, a coating layer having this concentration gradient is formed. It is presumed that the oil characteristics can be exhibited in a well-balanced manner, and excellent environmental stability can be maintained even though the obtained surface-coated silica has low negative chargeability.

(Method for producing surface-coated silica)
Next, a method for producing the surface-coated silica will be described.

  The surface-coated silica of the present invention can be produced by the following method. In particular, as estimated, in order to be a surface-coated silica that forms a multi-stage coating layer having a concentration gradient, the base silica is sequentially coated with two or more different types of silicone oils. Can be manufactured. In the conventional method of treating a silicone oil in which two types of silicone oils are mixed in an appropriate amount without sequentially treating, the silicone oil on the silica surface may not exist in a uniformly dispersed state. It is considered that the balance of the performance as a whole may be insufficient due to the coexistence of the functions of seeds and the harmful effects. Further, in the study by the present inventors, it is considered that when treated with a mixture of two types of silicone oils, both silicone oils are contained in the free silicone oil, so that the performance balance is lowered. Further, in the method of treating with the mixed silicone oil, a combination that cannot be mixed into the kind of silicone oil, for example, a combination of a fatty acid-modified silicone oil and an amino-modified silicone oil, a gel-like substance is generated and a uniform coating is formed. Processing may be difficult and improvement cannot be expected.

  In the production method of the present invention, the initial silicone oil is mixed with the base silica, heated to a temperature of 150 ° C. or higher, and the silica surface is coated with the silicone oil. It is characterized by coating with silicone oils of different types or compositions.

  In the present invention, the first silicone oil is mixed with the base silica, heated to a temperature of 150 ° C. or higher, and the silica surface is coated with the silicone oil. Silicone oil and silanol groups on the silica surface are combined. This shows a process of reacting and baking silicone oil on the silica surface. The first silicone oil is mixed with the base silica and heated to a temperature of 150 ° C or higher to coat and fix the first silicone oil, and then the same treatment is performed with a silicone oil different from the first silicone oil. By carrying out, 2 types of silicone oil can be reliably coat | covered on the base-material silica surface. When mixed silicone oil is used, if the next contact or mixing process is started before the first silicone oil layer is fixed by coating, the first silicone oil and the next silicone oil will be mixed. It becomes the same mode as that and is not preferred.

  In the present invention, as described above, since the treatment is sequentially performed with two or more types of silicone oil, it is presumed that in the obtained surface-coated silica, the coating layer has a multi-stage concentration gradient. For this reason, the coating layer formed of different types of silicone oil was steadily fixed, and the first silicone oil coating treatment was carried out to ensure a concentration gradient resulting from the difference in composition on the silica surface, as estimated. Later, it is essential to treat the next silicone oil.

  In the present invention, when the base silica is coated with the first silicone oil, it is necessary to carry out the coating at a temperature of 150 ° C. or higher. Even if water-repellent silicone oil is mixed with hydrophilic silica, a slight hydrophobizing effect can be obtained. However, by performing coating treatment at a temperature of 150 ° C. or higher, the silicone oil mixed with silica becomes the surface of silica particles. And a coating layer that is not liberated even by extraction with chloroform is formed. That is, it is considered that an adhesion state having a chemical interaction is realized. When the temperature at the time of the coating treatment is less than 150 ° C., it is considered that the formation of the multi-stage coating layer is not achieved because the chemical adhesion on the surface of the base silica of the silicone oil becomes insufficient. For example, amino modification In the case of a combination of silicone oil and dimethyl silicone oil, environmental stability cannot be obtained, which is not preferable. The temperature during the coating treatment is preferably 180 ° C to 400 ° C, and 200 ° C to 350 ° C is suitable in a practical range.

  In the present invention, when two types of silicone oil are used, the first silicone oil is mixed with silica, and after coating at a temperature of 150 ° C. or higher, the type differs from the first silicone oil. Suppose that it is coated with a second silicone oil. When three types of silicone oil are used, the first silicone oil is brought into contact with or mixed with silica, the coating treatment is performed at a temperature of 150 ° C. or higher, and then the second silicone oil is obtained by the previous treatment. The obtained surface-treated silica (hereinafter, treated with at least one kind of silicone oil and silica that has not been completely treated may be used as surface-treated silica) is mixed and subjected to coating treatment at a temperature of 150 ° C. or higher. Then, it shall treat with a 3rd silicone oil.

  In the present invention, the mixing of the silicone oil with the silica as the base material may be an aspect in which the silicone oil coexists with the base silica as a liquid or vapor to interact with each other, or an aspect in which both are simply mixed. The method is not particularly limited. For example, in the case of silicone oil with a relatively low boiling point, such as octamethylcyclotetrasiloxane, the silica is introduced into the mixer and heated to introduce the vapor into it. In the embodiment of the present invention, there is an embodiment in which a mist-like mist is sprayed onto the silica powder using a spray nozzle, and an embodiment in which the base silica and silicone oil are mixed in a solvent such as toluene. .

  In the present invention, the coating method at a temperature of 150 ° C. or higher is not particularly limited, and may be appropriately performed by a known method or a combination thereof. Specifically, a typical embodiment is that the base silica is fluidized by stirring or the like under heating at 150 ° C. or higher, and the silicone oil is sprayed as fine mist using a spray nozzle or the like as described above. In the case of a silicone oil having a relatively low boiling point, an embodiment in which the silicone oil is vaporized and the vapor is introduced into a reaction tank heated to 150 ° C. or higher and brought into contact with, mixed with, and reacted with the base silica. Also good. Further, the present invention also includes an aspect in which after the base silica and silicone oil are contact-mixed at a low temperature of less than 150 ° C. such as normal temperature, the temperature is raised to 150 ° C. or higher while stirring is continued. Furthermore, the silicone oil is dissolved in a solvent such as toluene, the base silica is dispersed therein, and the solvent is removed while being baked by heating to 150 ° C. or higher, or the base silica and the silicone oil are mixed in the solvent. An embodiment in which the solvent is removed by a depressurization operation and then heated to 150 ° C. or higher. Since industrial solvent removal is often economically disadvantageous, a dry treatment method such as spraying a mist of silicone oil directly onto silica is preferred. Further, the time required for the coating treatment at 150 ° C. or higher is not particularly limited, and may be appropriately determined according to the production scale and method. In general, about 30 minutes to 2 hours is a standard. .

  In the present invention, when the first silicone oil is coated and then treated with the next silicone oil, the first silicone oil and the next silicone oil must not be mixed in the coating treatment system. I must.

In the present invention, the silicone oil used for the first coating treatment is preferably coated so that the resulting surface-coated silica is not extracted by extraction with chloroform described in detail later. That is, it is preferable to perform the coating treatment so that the entire amount of the silicone oil used for the first coating treatment is chemically attached to the silica surface and is not included in the free silicone oil. In order to perform the coating treatment in this way, first, the silica used as the base material is first subjected to a heat reaction or baking treatment using a large amount of silicone oil in advance, and the resulting surface-treated silica is subjected to extraction treatment, and then the silicone oil is obtained. What is necessary is just to obtain the maximum amount of chemicals that can be chemically attached. And what is necessary is just to adjust so that the silicone oil below the maximum amount may be coat | covered. For example, when linear dimethyl silicone oil is coated on hydrophilic fumed silica, the amount of free silicone oil that does not contain the dimethyl silicone oil, that is, the maximum amount that can be chemically attached to the silica surface is It is about 8-10 mass parts per 100 m < ² > of surface area with respect to 100 mass parts of material silica.

In the present invention, the silicone oil used for the coating treatment after the first silicone oil is applied to the surface-treated silica so that the free silicone oil of the obtained surface-coated silica is 5 to 95% by mass of the total silicone oil coated. It is coated. That is, the treatment amount of the silicone oil of a different type from the first silicone oil is determined such that the free silicone oil of the surface-coated silica obtained is 5 to 95% by mass of the total silicone oil coated. Usually, it is about 0.5 to 50 parts by mass, preferably 1 to 30 parts by mass per 100 m ² of the surface area of the hydrophilic silica to be the base material before the silicone oil treatment, Since the performance of silicone oil can be sufficiently imparted to the silica particles, it is preferable. Further, when the third and fourth silicone oils are used, it is a guideline that the total amount of the silicone oil used for the coating treatment is in a range of about 1 to 40 parts by mass with respect to 100 parts by mass of the base silica. .

  In the present invention, it is particularly preferable to use an amino-modified silicone oil as the first silicone oil because environmental stability can be maintained while controlling the chargeability to a low negative charge. For example, while using amino-modified silicone oil as the previous silicone oil to effectively suppress the negative chargeability of the silica particle surface, the next silicone oil is a highly hydrophobic one such as dimethyl silicone oil. It is preferable to use it. By adopting such an embodiment, it is possible to achieve resistance to humidity that could not be realized by the conventional mixing treatment of amino-modified silicone oil and dimethyl silicone oil, and to achieve excellent environmental stability of charging. .

  Furthermore, the surface-coated silica of the present invention retains a certain amount of free silicone oil, is highly hydrophobic, exhibits excellent environmental stability, and reduces the amount of aggregated coarse particles by the following method. Preferably it is manufactured. Silica which is the base material is put in a mixer and stirred, and steam of silicone oil having a relatively low boiling point, such as octamethylcyclotetrasiloxane, is introduced as the first silicone oil under heating, and the surface is less than the chemical adhesion amount. After coating, dimethyl silicone oil having a relatively high boiling point and viscosity, which is effective for transferability and environmental stability, is preferably coated as a free silicone oil so as to have a predetermined free amount.

  The surface-coated silica agglomerated coarse powder is presumed to be formed by mixing a high molecular weight, high molecular weight, liquid silicone oil with silica powder in the coating treatment operation. In the case of treatment, it is relatively easy to reduce the amount of agglomerated coarse powder. On the other hand, there is a certain amount of free silicone oil required for each electrophotographic system to achieve transferability and environmental stability. Therefore, with the above method, the surface of the second dimethyl silicone oil is coated so as to have a predetermined free amount while the surface of the vaporized silicone oil is coated first to suppress the formation of agglomerated coarse particles. It is preferable to exhibit charging performance and the like.

(Toner use)
The surface-coated silica of the present invention is particularly useful as an external additive for electrophotographic dry toners used in copying machines and laser printers. The surface-coated silica obtained by the production method of the present invention is an external additive applicable to both black toner and color toner.

  The method for producing the toner particles is not particularly limited, and may be produced by a kneading pulverization method, or a so-called chemical toner produced by a polymerization method such as suspension polymerization or emulsion polymerization or a dissolution suspension method. May be.

  As the binder resin constituting the toner, a synthetic resin that is generally used when the toner is produced can be used without any limitation. Specifically, polystyrene, poly-α-methylstyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-acetic acid Vinyl copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-acrylic acid ester-methacrylic acid ester copolymer, styrene-α-chloroacrylic Homopolymer or copolymer containing styrene or styrene-substituted styrene resin such as acid methyl copolymer, styrene-acrylonitrile-acrylic acid ester copolymer, styrene-vinyl methyl ether copolymer, polyester Resin, epoxy resin, urethane modified epoxy Si resin, silicone modified epoxy resin, vinyl chloride resin, rosin modified maleic acid resin, phenyl resin, polyethylene, polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral Resins, terpene resins, phenol resins, aliphatic or alicyclic hydrocarbon resins and the like can be mentioned, and there is no problem even if these are used alone or in combination depending on the electrophotographic system.

  The surface-coated silica of the present invention may be added to the toner particles thus obtained in such an amount that the desired properties are obtained. Usually, it is added in an amount of 0.05 to 5% by weight, preferably 0.1 to 4% by weight, based on the toner particles. Furthermore, it is externally added by mixing with other fine particles as required using a known method, for example, a high-speed stirrer such as a Henschel mixer.

  When using the surface-coated silica of the present invention as an external additive for toner, as additives other than the toner external additive, hydrophobic silica other than the silica of the present invention, silica such as titania, alumina, zinc oxide, tin oxide, etc. Other metal oxide fine particles, and inorganic fine particles such as barium titanate, strontium titanate, and zinc stearate can be used in combination. In addition, as fine organic particles, fine resin powders such as polyethylene, polypropylene, styrene resin, acrylic resin, epoxy resin, polyester resin, guanamine resin, melamine resin, and fluorine resin are used as fixing aids and resistance control agents. It can also be used in combination as a lubricant.

  Further, when the surface-coated silica of the present invention is used as an external additive for an electrophotographic toner, it can be applied to any one of a magnetic one-component, non-magnetic one-component and two-component electrophotographic system. When used as a two-component developer, the carrier may be a magnetic substance such as iron powder, magnetite powder, or ferrite powder, or a known material such as a resin coating on the surface thereof or a magnetic carrier. As the coating resin of the resin coating carrier, styrene resin, acrylic resin, styrene acrylic copolymer resin, silicone resin, modified silicone resin, fluororesin and the like are generally used.

  Further, when the surface-coated silica of the present invention is used as an external additive for toner, other toner constituent materials can be applied to a toner arbitrarily blended with other known materials. For example, black colorants such as carbon black, color colorants such as cyan, magenta and yellow, positive and negative charge control agents, and release agents such as waxes were also used in materials commonly used in this field. For the toner, the surface-coated silica obtained by the production method of the present invention can be used as an external additive for the toner without any limitation.

  EXAMPLES Hereinafter, examples and comparative examples will be shown to specifically describe the present invention, but the present invention is not limited only to these examples.

  The measuring method of various physical property values in the present invention is as follows.

(Carbon and nitrogen content)
The carbon and nitrogen contents of the surface-coated silica were measured with SUMIGRAPHNC-22 model manufactured by Sumika Chemical Analysis Center.

(Chloroform extraction of silicone oil)
After suspending 1.0 g of the surface-coated silica sample in 40 mL of chloroform and dispersing it with an ultrasonic disperser for 30 minutes, the silica was separated and recovered with a centrifuge. Chloroform was further added to the separated silica, and the operations of ultrasonic dispersion and centrifugation were repeated three times in total. Thereafter, chloroform remaining on the silica recovered by drying under reduced pressure was removed. The carbon content and nitrogen content remaining in the silica thus obtained were measured to confirm the calculation of the amount of free silicone oil and whether the first silicone oil was released.

Specifically, in a silicone oil having a dimethylsiloxane main chain (structural formula: — (Si (CH ₃ ) ₂ —O) _n —), the silicone oil coated with the carbon content obtained by elemental analysis is used. Converted to quantity. From the carbon content of silica before and after extraction with chloroform, the total amount of silicone oil coated and the amount of residual silicone oil after free silicone oil was extracted and removed (ie, chemically adhered silicone), respectively. The amount of free silicone oil was confirmed by calculating the amount of oil).

(Evaluation of hydrophobicity)
In a 250 mL beaker, 50 mL of water and 50 mL of methanol were added, 0.2 g of a silica sample was added, and the mixture was stirred with a magnetic stirrer. To this, methanol was added dropwise using a burette, and titration was performed with the end point when the entire amount of the sample powder was wetted and suspended in the solvent in the beaker. At this time, the tube was introduced into the solution by a tube so that the sample did not directly touch the sample. The volume% of methanol in the methanol-water mixed solvent at the end point was expressed as hydrophobicity (M value).

(Agglomerated coarse powder amount Characteristic as external additive for toner)
In a 100 mL resin bottle, 75 g of glass beads having a particle diameter of 1 mm, 25 g of crosslinked acrylic resin powder (MX-1000 manufactured by Soken Chemical Co., Ltd., average particle diameter of 10 μm), and 0.5 g of a silica sample were placed and mixed with shaking for 3 minutes. The mixed powder was passed through a sieve having 750 μm and 45 μm openings stacked in two stages, and then the weight of silica remaining on the 45 μm openings was measured, and the ratio to the charged silica was calculated. This was the amount of aggregated coarse particles of silica.

(Charge measurement) Properties as an external additive for toner
Styrene-acrylic resin was pulverized and classified, and a resin powder sample having an average particle size of 8 μm was mixed with surface-coated silica so as to be 2% by weight to prepare a pseudo toner. Two sample bottles containing 1 g of this pseudo toner and 99 g of ferrite carrier were prepared and each was conditioned for 24 hours in a constant temperature and humidity chamber under high temperature and high humidity conditions and low temperature and low humidity conditions. The high temperature and high humidity conditions were set to 35 ° C. and 85% relative humidity, and the low temperature and low humidity conditions were set to 10 ° C. and 15% relative humidity. The conditioned sample bottle was rotated and mixed at 100 rpm for 60 minutes with a desktop roller mill, and then blow gas pressure 0.1 MPa, blow time with a blow-off powder electrification measuring device TB-200 type manufactured by Toshiba Chemical Corporation. The charge amount was measured for 30 seconds.

The environmental stability was evaluated by calculating an index according to the following formula 1. It can be evaluated that the smaller the index value, the less the influence of the charge amount due to environmental fluctuations and the higher the stability.
(Environmental stability index) = (LL−HH) / (LL + HH) × 2 (Formula 1)
Here, LL represents a charge amount in a low temperature and low humidity environment, and HH represents a charge amount in a high temperature and high humidity environment.

Example 1
100 parts by mass of hydrophilic fumed silica having a specific surface area of 200 m ² / g was placed in a mixer, stirred, and replaced with a nitrogen atmosphere, and simultaneously heated to 250 ° C. 4 parts by mass of the first amino-modified silicone oil (KF-857, manufactured by Shin-Etsu Chemical Co., Ltd.) is sprayed as the first silicone oil using a spray nozzle while maintaining the flow state of silica by continuing stirring and heat retention. , Mixed. Thereafter, the coating treatment was carried out by continuing heating and stirring for 1 hour. Subsequently, 16 parts by mass of a second dimethyl silicone oil (KF-96-50CS, manufactured by Shin-Etsu Chemical Co., Ltd.) was sprayed as a different type of silicone oil, and the coating treatment was further performed for 1 hour. Coated silica was obtained. As a result of extracting the obtained surface-coated silica with chloroform, the nitrogen content of the surface-coated silica before and after the chloroform extraction was not changed, and the amino-modified silicone oil was not extracted. Moreover, the carbon content before and after chloroform extraction was measured, and the amount of free silicone oil in the total silicone oil coated was determined. The results are shown in Table 1. Table 2 shows the results of measuring the charge amount by the above method using the obtained surface-coated silica.

Example 2
A surface-coated silica was obtained by carrying out the same treatment operation as in Example 1 except that 9 parts by mass of the first amino-modified silicone oil and 11 parts by mass of the second dimethyl silicone oil were used. The characteristics of the obtained surface-coated silica are shown in Table 1, and the results of measuring the charge amount are shown in Table 2.

Example 3
The same operation as in Example 1 except that KF-393 manufactured by Shin-Etsu Chemical Co., Ltd. is used as the first amino-modified silicone oil, and this is 3 parts by mass and the second dimethyl silicone oil is 17 parts by mass. To obtain surface-coated silica. The characteristics of the obtained surface-coated silica are shown in Table 1, and the results of measuring the charge amount are shown in Table 2.

Comparative Example 1
100 parts by mass of hydrophilic fumed silica having a specific surface area of 200 m ² / g was placed in a mixer, stirred, and replaced with a nitrogen atmosphere, and simultaneously heated to 250 ° C. 20 parts by mass of dimethyl silicone oil (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.) was sprayed and mixed using a spray nozzle while maintaining the fluid state of silica by continuing stirring and heat retention. Then, the coating process was implemented by continuing the heating and stirring at 250 degreeC for 1 hour. The characteristics of the obtained surface-coated silica are shown in Table 1, and the results of measuring the charge amount are shown in Table 2.

Comparative Examples 2-4
The concentration of amino-modified silicone oil (KF-857 manufactured by Shin-Etsu Chemical Co., Ltd.) is 10% by weight, 30% by weight, and 45% by weight with respect to 100 parts by mass of hydrophilic fumed silica having a specific surface area of 200 m ² / g. Thus, except having processed 20 mass parts of mixed silicone oil process liquids mixed with dimethyl silicone oil (KF-96-50CS by Shin-Etsu Chemical Co., Ltd.), operation similar to the comparative example 1 was implemented. The characteristics of the obtained surface-coated silica are shown in Table 1, and the results of measuring the charge amount are shown in Table 2.

Comparative Example 5
The same operation as in Example 2 was performed except that the treatment temperature was room temperature. The characteristics of the obtained surface-coated silica are shown in Table 1, and the results of measuring the charge amount are shown in Table 2.

Comparative Example 6
For 100 parts by mass of hydrophilic fumed silica having a specific surface area of 200 m ² / g, 4 parts by mass of first amino-modified silicone oil (KF-857 manufactured by Shin-Etsu Chemical Co., Ltd.) and then second dimethyl silicone oil (Shin-Etsu) The same operation as in Example 1 was carried out except that 6 parts by mass of KF-96-50CS manufactured by Chemical Industry Co., Ltd. was coated. The characteristics of the obtained surface-coated silica are shown in Table 1, and the results of measuring the charge amount are shown in Table 2.

  As shown in Table 1, the nitrogen content after solvent extraction with chloroform does not change before and after extraction. Therefore, it was confirmed that the amino acid-modified silicone oil treated first was chemically attached in its entirety. On the other hand, in Comparative Examples 2 to 5, the nitrogen content was greatly reduced after solvent extraction, indicating that amino-modified silicone oil was contained in the free component. In Comparative Example 6, the carbon content and the nitrogen content were not changed before and after the chloroform extraction, and silicone oil was not liberated.

  FIG. 1 is a plot of the environmental stability index with respect to the charge levels of Examples 1 to 3 and Comparative Examples 1 to 4 (average of measured charge amount under low temperature and low humidity and high temperature and high humidity environment). . As can be seen from FIG. 1, in the example, the environmental stability index at the same charge level is smaller than in the comparative example. When an amino group is introduced to adjust the charge level to a low negative charge amount, it can be said that the environmental stability of charging is higher when manufactured by the method of the present invention than when surface treatment is performed with mixed silicone oil. Moreover, it is clear that the environmental stability of Comparative Examples 5 and 6 is inferior to that of the Examples.

Example 4
100 parts by mass of hydrophilic fumed silica having a specific surface area of 200 m ² / g was placed in a mixer, stirred, and replaced with a nitrogen atmosphere, and simultaneously heated to 250 ° C. While continuing stirring and keeping the temperature and maintaining the fluid state of silica, 2.5 parts by mass of the first amino-modified silicone oil (KF-857 manufactured by Shin-Etsu Chemical Co., Ltd.) was sprayed and mixed using a spray nozzle. Thereafter, heating and stirring were continued for 1 hour for coating treatment. Subsequently, 1.5 parts by mass of a second carboxyl-modified silicone oil (X-22-3710 manufactured by Shin-Etsu Chemical Co., Ltd.) was sprayed, and further coated for 1 hour. Furthermore, similarly, the coating process of 16 mass parts of 3rd dimethyl silicone oil (Shin-Etsu Chemical Co., Ltd. KF-96-50CS) was implemented, and the surface-coated silica was obtained. The characteristics of the obtained surface-coated silica are shown in Table 1, and the results of measuring the charge amount are shown in Table 2.

Comparative Example 7
Amino-modified silicone oil (KF-857, manufactured by Shin-Etsu Chemical Co., Ltd.) and carboxyl-modified silicone oil (X-22-3710, manufactured by Shin-Etsu Chemical Co., Ltd.) were transferred in equal amounts to each other and mixed to form a gel substance.

  Furthermore, 100 g of dimethyl silicone oil (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.) is placed in a container, and 10 g of amino-modified silicone oil (KF-857 manufactured by Shin-Etsu Chemical Co., Ltd.) is added to prepare a mixed oil. Furthermore, 10 g of carboxyl-modified silicone oil (X-22-3710 manufactured by Shin-Etsu Chemical Co., Ltd.) was added and mixed. When observed after standing for about 1 hour, the formation of a gel-like substance was observed, and it did not dissolve even after vigorous stirring.

  In Example 4, amino-modified silicone oil, carboxyl-modified silicone oil, and dimethylsilicone oil were sequentially treated in three stages. On the other hand, as can be seen from Comparative Example 7, even when these three types of silicone oils were mixed, a gel-like substance composed of an amino-modified silicone oil and a carboxyl-modified silicone oil was produced, so that the coating treatment could not be performed. .

  The measured values of Example 4 are also shown in Table 1, and the environmental stability index with respect to the charge level is also plotted in FIG. This ternary system is a combination that could not be realized by the conventional mixing of silicone oil, and it can be seen that the environmental stability of charging is improved.

Example 5
Using 100 parts by mass of hydrophilic fumed silica having a specific surface area of 60 m ² / g as a base material, 3 parts by mass of first amino-modified silicone oil (KF-857 manufactured by Shin-Etsu Chemical Co., Ltd.), second dimethyl silicone oil Surface-coated silica was obtained in the same manner as in Example 1 except that 17 parts by mass (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.) was used. The characteristics of the obtained surface-coated silica are shown in Table 3, and the results of measuring the charge amount are shown in Table 4.

Comparative Example 8
Dimethyl silicone oil (Shin-Etsu Chemical Co., Ltd.) so that the concentration of amino-modified silicone oil (KF-857 manufactured by Shin-Etsu Chemical Co., Ltd.) is 15% by weight with respect to 100 parts by mass of hydrophilic fumed silica having a specific surface area of 60 m ² / g. The same operation as in Comparative Example 1 was carried out except that 20 parts by mass of the mixed processing solution diluted with KF-96-50CS manufactured by K.K. The characteristics of the obtained surface-coated silica are shown in Table 3, and the results of measuring the charge amount are shown in Table 4.

Example 6
100 parts by mass of hydrophilic fumed silica having a specific surface area of 200 m ² / g was placed in a mixer, stirred, and replaced with a nitrogen atmosphere, and simultaneously heated to 280 ° C. The mixer was sealed while continuing stirring and heat-retaining and the silica fluid state was maintained, and the first silicone oil was heated and vaporized octamethylcyclotetrasiloxane (KF-994 manufactured by Shin-Etsu Chemical Co., Ltd.) with a gauge pressure of 100 kPa. It was introduced until it became. After heating and stirring were continued for 1 hour, the mixer was opened and the pressure was released.

  When a part was sampled in the middle of this treatment, the carbon content was 2.2%, and the carbon content did not change even after solvent extraction. No octamethylcyclotetrasiloxane was contained in chloroform.

  Subsequently, 15 parts by mass of second-stage dimethyl silicone oil (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.) was sprayed using a spray nozzle, and collected after baking for 1 hour. The characteristics of the obtained surface-coated silica are shown in Table 5, and the charge amount data and the amount of aggregated coarse powder are shown in Table 6 in accordance with the above method.

Comparative Example 9
Comparative example except that 30 parts by mass of dimethyl silicone oil (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.) is sprayed and coated on 100 parts by mass of hydrophilic fumed silica having a specific surface area of 200 m ² / g. The same operation as 1 was performed. The characteristics of the surface-coated silica thus obtained are shown in Table 5, and the charge amount data and the amount of the aggregated coarse powder are shown in Table 6.

  The measured values of the surface-coated silica obtained in Example 6 and Comparative Example 9 are summarized in Tables 5 and 6. In Example 6 and Comparative Example 9, it was confirmed that the amount of free silicone oil was the same from the extraction operation with chloroform. In Example 6, compared with Comparative Example 9, the degree of hydrophobicity was about the same, the charge level was not different, and the environmental stability was about the same, but the amount of agglomerated coarse powder was reduced.

The figure which plotted the environmental stability parameter | index with respect to the average value of the charge amount in the low temperature low humidity environment and high temperature high humidity environment of the pseudo toner which added Examples 1-4 and Comparative Examples 1-4.

Claims (6)

  Surface-coated silica coated with two or more different types of silicone oil, wherein the amount of silicone oil extracted with chloroform is 5 to 95% by mass of the total coated silicone oil, and at least one type The surface-coated silica is characterized in that the silicone oil is not contained in the extracted silicone oil.   The surface-coated silica according to claim 1, wherein the silicone oil not contained in the extracted silicone oil is an amino-modified silicone oil.   A method for producing surface-coated silica in which silica as a base material is sequentially coated with two or more different types of silicone oils. The first silicone oil is mixed with the base material and coated at a temperature of 150 ° C. or higher. Then, a method for producing a surface-coated silica, which is then coated with a silicone oil different from the first silicone oil.   After the first silicone oil is coated so that it is not extracted with chloroform, a silicone oil of a different type from the first silicone oil is then applied. The method for producing a surface-coated silica according to claim 3, wherein the coating treatment is performed so as to be -95 mass%.   The method for producing a surface-coated silica according to claim 3 or 4, wherein the first silicone oil contains an amino-modified silicone oil. An external toner additive comprising the surface-coated silica according to claim 1.

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