JP2005263568A - Silicon nitride-based powder, its producing method, and toner external additive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride-based powder which has excellent resistance to hydrolysis and adequate electrostatic charge amount, hardly generates ammonia odors, and contains a small amount of coarse particles; and to provide a method for producing the same, and a toner external additive obtained by using the silicon nitride-based powder. <P>SOLUTION: The silicon nitride-based powder is obtained by treating a silicon nitride powder having an oxide film in an amount of 6-20 mass % expressed in terms of oxygen with a surface treatment agent comprising at least one of a fatty acid or its salt, and characterized in that the average particle diameter is ≤2 μm, the content of coarse particles having particle diameters of ≥25 μm is ≤50 μg/g, and the elution amount of ammonium ions after heating/extracting at 80°C for 15 days is <50 μg per 1 g of the silicon nitride-based powder. Further, the method for producing the silicon nitride-based powder and the toner external additive comprising the silicon nitride-based powder are also provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a silicon nitride powder excellent in hydrolysis resistance, generating little ammonia smell, having an appropriate charge amount, and suitable as, for example, a toner external additive, a method for producing the same, and a toner external additive.

  Silicon nitride powder has excellent properties such as wear resistance, high strength, fracture toughness, low specific gravity, and low thermal expansion, and is used as a raw material for engineering ceramics sintered bodies such as industrial machines and automotive parts, and as a filler for resins, etc. Recently, studies on the use as a toner external additive have been made using the property of high hardness.

Conventional toner external additives include hydrophobic silica fine powder (Patent Document 1), anatase-type titanium oxide (Patent Document 2), a mixture of silica fine particles and aluminum oxide or titanium oxide fine particles (Patent Document 3), and the like. Further, these surface-treated products, for example, hydrophobized products of vapor-phase titanium oxide (Patent Document 4), aluminum oxide-coated titanium oxide (Patent Document 5), treated with a silane coupling agent such as titanium oxide ( Patent Documents 6 and 7) are known.
JP 56-128956 A JP 60-112052 A JP-A-60-238847 JP 59-52255 A JP-A-57-79961 JP-A-4-40467 JP-A-4-348354

  In order to use silicon nitride powder as a toner external additive, coarse particles having a particle diameter of 25 μm or more (hereinafter simply referred to as “coarse particles”), hydrolyzability of silicon nitride, and charge amount must be taken into consideration. I must. The presence of coarse particles damages the surface of the drum of the photoreceptor, and the generation of ammonia by hydrolysis adversely affects the off-flavor and image density. If the charge amount is not appropriate, toner particles do not fly and printing cannot be performed.

  In order to improve the hydrolysis resistance of the silicon nitride powder, it is necessary to modify the surface. In other words, an oxide film is formed on the surface of the silicon nitride powder, the generation of ammonia is suppressed by blocking the contact between silicon nitride and water, and hydrophilic groups such as hydroxyl groups on the oxide film surface are crushed with a coupling agent or the like. That is. In addition, it is important to reduce coarse particles including agglomerated particles.

As a method for forming an oxide film, it has been proposed to repeat a process of pulverizing silicon nitride fine powder after wet oxidation or heat oxidation (Patent Document 8), but the process becomes longer and the cost is increased.
JP 2001-265052 A

  In view of the above, an object of the present invention is to provide a silicon nitride-based powder that is excellent in hydrolysis resistance, has a reduced content of coarse particles, has an appropriate charge amount, and is particularly suitable as a toner external additive. A method and toner external additive are provided. The object of the present invention can be achieved by treating a silicon nitride powder filled with a predetermined packing density and a predetermined thickness with a fatty acid-based surface treatment agent after oxidation treatment at a predetermined temperature.

  That is, according to the present invention, the silicon nitride powder having an oxide film and having an oxygen content of 6 to 20% by mass is treated with a surface treatment agent composed of at least one of a fatty acid and a salt thereof. A silicon nitride material having a particle size of 2 μm or less, a coarse particle content of 50 μg / g or less, and an elution amount of ammonium ions after heating and extraction at 80 ° C. for 15 days is less than 50 μg per gram of silicon nitride powder. It is a powder.

Further, the present invention is filled with silicon nitride powder having an average particle diameter of 2 μm or less and a particle content of 6 μm or more of 1% by mass or less with a packing density of 1 g / cm ³ or less and a filling thickness of 50 mm or less. A heat treatment is performed at a temperature of 1100 to 1300 ° C. in an oxygen-containing atmosphere to form an oxide film on the silicon nitride powder, and then it is treated with a surface treatment agent comprising at least one of a fatty acid and a salt thereof. This is a method for producing silicon nitride powder. In this case, the treatment with the surface treatment agent is preferably performed by heating to a temperature equal to or higher than the melting point of the surface treatment agent.

  Furthermore, the present invention is a toner external additive comprising the silicon nitride powder of the present invention.

  According to the present invention, silicon nitride powder having excellent hydrolysis resistance, less generation of ammonia odor, low content of coarse particles, an appropriate charge amount, a method for producing the same, and a reduction in image density and high temperature Provided is an external toner additive material which is less likely to cause problems such as a blurred image (ghost image) under humidity.

In the present invention, as a method for suppressing the hydrolysis of the silicon nitride powder, a method of forming an oxide film such as SiO _{2 on the} surface of the silicon nitride powder is employed. The presence of the oxide film can be confirmed by a transmission electron microscope, and the amount of the oxide film is 6 to 20% by mass using the oxygen content of the silicon nitride powder as an index. When the amount of oxide film corresponding to an oxygen content of less than 6% by mass is thin, the film is thin, so that it is destroyed in the next surface treatment process or the like, resulting in a decrease in hydrolysis resistance, and an amount of oxide film exceeding 20% by mass. Many coarse grains remain. A preferable amount of oxide film is 9 to 16% by mass as oxygen content. This value is significantly higher than 1.7% by mass of Patent Document 8.

  The silicon nitride powder of the present invention needs to have an average particle diameter of 2 μm or less and a coarse particle content of 50 μg / g or less. These conditions are acceptable levels that do not damage the photoreceptor when the use of the silicon nitride powder of the present invention is an external toner additive. Preferably, the average particle size is 0.9 to 1.5 μm, and the content of coarse particles is 40 μg / g or less.

  Further, it is necessary that the elution amount of ammonium ions after heating and extraction at 80 ° C. for 15 days is less than 50 μg / g of silicon nitride powder (less than 50 μg / g). This condition is such that when the use of the silicon nitride powder of the present invention is an external toner additive, it is difficult to cause problems such as a decrease in image density and a blurred image (ghost image) under high temperature and high humidity, and an unpleasant odor is allowed. The lowest level you can do.

   Furthermore, in order to have an appropriate charge amount, it is necessary that the surface treatment is performed with a surface treatment agent comprising at least one of a fatty acid and a salt thereof. The degree of surface treatment is preferably set to a charge amount of 80 μC / g or more for both positively and negatively charged toner applications. If this is shown by the usage-amount of a surface treating agent, it will be 0.5-5 mass parts per 100 mass parts of silicon nitride powder, especially 1-2 mass parts. Since the silicon nitride powder before the surface treatment has an oxide film (that is, covered with silanol groups), it is negatively charged (about −20 μC / g). Even if it is charged, it has a strong hydrophilicity, so that it is easy to discharge, and even if it is a toner external additive, there is a possibility that the toner particles do not fly and there is a problem in printing.

  Illustrative examples of the surface treating agent used in the present invention include fatty acids such as stearic acid, lauric acid, and palmitic acid, and alkali metal salts and alkaline earth metal salts thereof. Specific examples of fatty acids are stearic acid, sodium stearate, calcium stearate, magnesium stearate, zinc stearate, aluminum stearate, barium stearate, potassium stearate and the like. Of these, stearic acid and magnesium stearate are preferred.

  In the present invention, the particle size was measured in an ethanol solution using a particle size distribution analyzer (manufactured by LEEDS & NORTHUP, trade name “MICROTRAC-II, SPA: MODEL 7997-20”). The oxygen content was measured by putting a sample into a nickel capsule using an oxygen / nitrogen simultaneous analyzer (manufactured by Horiba, Ltd., trade name “EMGA-620W”).

  The content of the coarse particles is 50 g of silicon nitride powder, 250 g of 0.2 mass% distilled water of sodium hexametaphosphate is added and ultrasonically dispersed for 10 minutes, passed through a JIS sieve having an opening of 25 μm, and the top of the sieve is collected. After drying, the mass was measured and calculated.

  The elution amount of ammonium ions was sealed in a fluororesin container (50 ml) with a lid containing 2.5 g of silicon nitride powder and 25 g of distilled water, stored in a dryer set at 80 ° C. for 15 days, and heated. Extraction was performed using an ion chromatograph (trade name “DX-100”, manufactured by DIONEX).

  The charge amount was measured by a suction blow-off method. That is, silicon nitride powder and ferrite powder having an average particle diameter of 100 μm were put in a polyethylene bottle at a mass ratio of 0.1: 19.9, and mixed by shaking 200 times by hand shaking. This mixed powder was charged into a Faraday cage, and measurement was started 5 minutes after mixing. The measurement was performed by sucking only the silicon nitride powder with a suction device through a mesh having a mesh opening of 34 μm from the lower part of the Faraday cage, and detecting the amount of charge remaining in the Faraday cage with an electrometer after 3 minutes. The suction blow-off charge amount [μC / g] was calculated by the formula {(charge amount of ferrite powder remaining in the Faraday cage [μC]) / (suction mass [g] of silicon nitride powder)}.

  The silicon nitride powder production method of the present invention will be described. As the silicon nitride powder to be heat-treated, those produced by a direct nitridation method of metal silicon, a reductive nitridation method of silica, a method using an imide compound, etc. are used. it can. It is necessary that the average particle diameter is 2 μm or less and the content of particles of 6 μm or more is 1% by mass or less. The reason is that if the particle size is coarser than this, fine powder adheres to the surface during the oxidation treatment, resulting in coarse particles. Particularly preferable particle sizes are an average particle size of 0.9 to 1.6 μm and a maximum particle size of 4 μm or less.

Next, the silicon nitride powder is filled into the container with a filling density of 1 g / cm ³ or less and a filling thickness of 50 mm or less. When the packing density is higher than this, the contact points between the powders increase, and strong aggregation tends to occur. Although the filling density may be reduced, the production capacity is lowered, so the lower limit is preferably 0.5 g / cm ³ .

  As for the filling thickness, if it is too thick, reaction heat generated during oxidation accumulates, the temperature of the center of the filling powder rises above the surrounding set temperature, and strong agglomerated particles are produced. To explain further, when the filling thickness is large, the heat dissipation tends to be easier in the center than in the upper part and the end of the powder, and the oxidation reaction of silicon nitride is an exothermic reaction, so that heat tends to be stored. Therefore, from the balance between the oxidation reaction and the heat dissipation, the central portion of the powder has a higher temperature, and the oxygen content of the partially sampled silicon nitride powder tends to vary greatly. In order to form an oxide film uniformly, it is necessary to reduce the variation in oxygen content at each location. According to the results of the study by the present inventors, when the filling thickness is 50 mm or less, the oxygen content is reduced. The variation could be suppressed within 10%. On the other hand, when the filling thickness exceeds 50 mm, the variation in oxygen content exceeds 30%, and a strong agglomeration is generated at a portion where the oxygen content is high, and a new surface appears when crushed at a low portion. It was. Although the filling thickness may be reduced, the production capacity is lowered, so the lower limit is preferably 20 mm.

  The filled silicon nitride powder is oxidized at 1100 to 1300 ° C., preferably 1150 to 1200 ° C. in an atmosphere containing oxygen such as the air. Below 1100 ° C., the oxygen content of the silicon nitride powder is less than 6% by mass, so that a sufficient oxide film cannot be formed, and the elution amount of ammonium ions in the silicon nitride powder is 100 μg / g or more. The reason for this is thought to be that the oxide film formed on the surface of the silicon nitride powder was broken by crushing or the like and a new surface appeared. Even in heat treatment at about 1000 ° C., an oxide film is formed on the surface of the silicon nitride powder, but it is difficult to form a strong oxide film that is not easily broken. When the oxidation treatment temperature exceeds 1300 ° C., the oxygen content exceeds 20% by mass and a thicker oxide film is formed, while the content of coarse particles exceeds 50 μg / g. The holding time in the above temperature range is preferably 5 to 50 hours, particularly 10 to 30 hours.

  Oxidation proceeds to the inside of the silicon nitride particles by the above oxidation treatment, and the powder is agglomerated. Therefore, before the surface treatment with the surface treatment agent is performed, the agglomeration is broken (pulverized) and classified as necessary. The silicon nitride powder preferably has an average particle size of 1 μm or less and a coarse particle content of 50 μg / g or less.

  The treatment with the surface treatment agent may be either a dry mixing method or a wet mixing method, but the wet mixing method requires filtration, drying, and crushing steps, but the content of coarse particles is less than that of dry mixing. There are advantages. Therefore, in order to express the advantage of the wet mixing method that can reduce the content of coarse particles by the dry mixing method, when adopting the dry mixing method, it is preferable to carry out heating at a temperature equal to or higher than the melting point of the surface treatment agent. The wet mixing method is a method in which a stirring blade is placed in a container and mixing is performed in the presence of a medium such as water or an organic solvent.

  An example of the dry mixing method is that the silicon nitride powder and the surface treatment agent are heated to a temperature equal to or higher than the melting point of the surface treatment agent, or after being mixed for 5 to 60 minutes with a mixer such as a Henschel mixer. Depending on the condition, it is further held for 0.5 to 10 hours above the melting point of the surface treatment agent. In this case, a method may be employed in which the surface treatment agent heated to a melting point or higher and brought into a molten state is mixed while being sprayed from a two-fluid nozzle or the like attached to the top of the Henschel mixer. Moreover, if an example of a wet mixing method is shown, after mixing a silicon nitride powder, a medium, such as distilled water, and a surface treating agent with a stirring blade for 0.5 to 5 hours, it is filtered and dried, and then as necessary. Crush.

Examples 1-11 Comparative Examples 1-8
Use a classifier to adjust the particle size of commercially available silicon nitride powder as shown in Tables 1 and 2 and fill it into a silicon carbide container with the packing density and thickness shown in Tables 1 and 2 and then in the atmosphere. The temperature was raised to a heat treatment temperature shown in Tables 1 and 2 at a temperature rate of 250 ° C./h, held at that temperature for 20 hours, and then cooled to form an oxide film on the silicon nitride powder.

This was pulverized using a crusher (trade name “Jet Mill PJM-200SP”, manufactured by Nippon Pneumatic Co., Ltd.), and the average particle diameter, oxygen content, and coarse particle content shown in Tables 1 and 2, A silicon nitride powder having ammonium ion elution amount and charge amount was obtained. As a result of observing the particle surface of the pulverized silicon nitride powder with a transmission electron microscope, the presence of SiO ₂ was observed in all cases.

  Thereafter, surface treatment by dry mixing is performed by adding 1 part by mass of the surface treatment agent shown in Tables 1 and 2 to 100 parts by mass of silicon nitride powder and mixing with a Henschel mixer for 20 minutes. It was. In Example 11, since the melting point of stearic acid was about 70 ° C., it was kept at 100 ° C. for 4 hours after mixing. With respect to the obtained silicon nitride powder, the average particle size, oxygen content, coarse particle content, ammonium ion elution amount, and charge amount were measured in accordance with the above methods. Table 1 shows the results of the examples and Table 2 shows the results of the comparative examples.

  The following can be understood from the comparison between Table 1 and Table 2. In the examples, the silicon nitride powder raw material was heat-treated at 1100 to 1300 ° C. and subjected to surface treatment by forming an oxide film. As a result, the oxygen content of the silicon nitride powder was 6 to 20% by mass, and the inclusion of coarse particles after pulverization The amount was 50 ppm or less, and the amount of ammonium ions eluted was less than 50 ppm. In addition, as the heat treatment temperature increased, the content of coarse particles tended to increase and the elution amount of ammonium ions tended to decrease. As for the charge amount, as a result of the surface treatment with the surface treatment agent, all of them were remarkably improved. This was particularly noticeable when stearic acid was used.

  Further, as a result of observing the finally obtained silicon nitride powder with a scanning electron microscope, in Examples 1 to 10, there was a portion where the surface treatment agent remained without being coated on the surface of the silicon nitride powder. However, in Example 11, it was not observed and was processed more uniformly.

  On the other hand, in Comparative Example 1, since the heat treatment temperature was less than 1100 ° C., the oxygen content was less than 8%, and the elution amount of ammonium ions was at the 100 ppm level. In Comparative Example 2, since heat treatment was performed at a temperature exceeding 1300 ° C., the elution amount of ammonium ions was less than 50 ppm, but the content of coarse particles exceeded 100 ppm. In Comparative Examples 3 and 4, since the filling thickness exceeded 50 mm, the oxygen content tends to decrease in proportion to the thickness, and the elution amount of ammonium ions tends to increase accordingly, both at 50 ppm or more. there were.

  In Comparative Example 5 in which the particle size of the nitrogen silicon powder raw material deviated from the scope of the present invention and Comparative Example 6 in which the packing density deviated, not only the content of coarse particles but also the elution amount of ammonium ions increased. . This is probably because coarse grains were crushed and a new surface appeared.

  Next, in order to evaluate the silicon nitride-based powder produced as a toner external additive, a printing durability test for confirming the printing condition was performed by continuous printing. As a result, in the toner external additives using the silicon nitride-based powders of the examples, printing defects such as a decrease in printing density did not occur, but in the comparative examples 1 to 6. Further, in Comparative Examples 7 and 8 treated with a surface treating agent different from the present invention, as a result of the printing durability test, the toner did not fly and a printing defect due to a decrease in printing density occurred.

  The silicon nitride powder of the present invention can be used as various dispersants, fillers, toner external additives and the like, and further as a raw material for producing a silicon nitride sintered body.

Claims (4)

  A silicon nitride powder having an oxide film and having an oxygen content of 6 to 20% by mass is treated with a surface treatment agent comprising at least one of a fatty acid and a salt thereof, and the average particle diameter is 2 μm or less, A silicon nitride-based powder, wherein the content of coarse particles of 25 μm or more is 50 μg / g or less, and the amount of ammonium ions eluted after 15 days of heat extraction at 80 ° C. is less than 50 μg per 1 g of silicon nitride-based powder. A silicon nitride powder having an average particle diameter of 2 μm or less and a particle content of 6 μm or more of 1% by mass or less is filled with a filling density of 1 g / cm ³ or less and a filling thickness of 50 mm or less, and contains oxygen. A silicon nitride-based powder characterized in that after heat treatment is performed at a temperature of 1100 to 1300 ° C. in an atmosphere to form an oxide film on the silicon nitride powder, the silicon nitride powder is treated with a surface treatment agent comprising at least one of fatty acids and salts thereof. Production method. The method for producing a silicon nitride-based powder according to claim 2, wherein the treatment with the surface treatment agent is performed by heating to a temperature equal to or higher than the melting point of the surface treatment agent. A toner external additive comprising the silicon nitride powder according to claim 1.