JP2001287490A - Ceramic ball for ballpoint pen, manufacturing method for the same and ballpoint pen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic ball for a ballpoint pen capable of obtaining further better writing performance by optimizing a balance of the presences between rough air gaps and fine air gaps. SOLUTION: The air gaps of 3 to 30 pieces in size of 2 to 10 μm and the air gaps of 20 to 200 pieces in size of 0.5 to 2 μm are formed per a region of 50 μm×50 μm of a surface of a ceramic ball. The relatively rough air gaps 93 in size of 0.5 to 2 μm and the relatively fine air gaps 94 in size of 0.5 to 2 7 μm are formed in a good balance in a specifically forming density as described above. Thus, smooth writing satisfactoriness is simultaneously assured while ensuring a necessary sufficient ink flow-out amount so as to clearly express a distinct line or particularly a character or a fine line, and a wear of a ball sheet part can be effectively suppressed. In order to manufacture the ball for satisfying such conditions, it is effective to manufacture a spherically formed material by a tumbling granulating method. Simultaneously, a manufacturing efficiency and a material yield are dramatically improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic ball for a ballpoint pen, a method for manufacturing a ceramic ball for a ballpoint pen, and a ballpoint pen.

[0002]

2. Description of the Related Art Conventionally, metal balls are often used as ball-point pens, but in recent years, ball-point pens using ceramic balls that are hard to wear or susceptible to corrosion by ink have been commercialized. ing. For example, JP-A-56-145000, JP-A-59-135
Japanese Patent Publication No. 195 or JP-B-3-23356 discloses ceramic balls for ball-point pens made of various ceramics such as silicon carbide, silicon nitride, sialon, zirconia, alumina, and aluminum nitride.

If the surface of a ceramic ball for a ball-point pen is in a very smooth finished state like a bearing ball, the ink is repelled and the smooth writing quality is impaired. Therefore, it is necessary to maintain a surface state in which voids are appropriately dispersed and formed. For example, Japanese Patent Publication No. 3-23356 discloses an invention in which a ceramic ball for a ballpoint pen made of silicon carbide ceramic has an average pore diameter of 1 to 30 μm on the surface. The reason for adjusting the average hole diameter in this way is to suppress shaving of the ball seat portion,
It describes that a so-called ball drop is suppressed.

[0004]

However, in the ceramic ball for a ballpoint pen, not only the suppression of shaving of the ball seat portion but also a proper ink outflow performance for ensuring a smooth and clear writing quality are naturally compatible. Must be. For example, when only a large number of voids are formed, the amount of ink retained on the ball surface increases, which can increase the amount of ink flowing out. There is a problem that the sliding of the ball on an object (for example, paper) becomes poor, and the writing becomes rough and uncomfortable. In addition, since the amount of the ink flowing out is large, it is difficult to express sharp fine characters even if the ball diameter is considerably reduced. On the other hand, when only minute voids are mainly used, the amount of ink flowing out is insufficient, and fainting is likely to occur particularly when the ball diameter is small or when the writing speed is increased.

In order to solve such a problem, it is necessary to consider the dimensional distribution of surface voids, that is, the existence balance between coarse voids and fine voids.
In Japanese Patent Publication No. 356, the average size of the voids is merely specified, and no attention is paid to the size distribution of the voids. On the other hand, in the publication, as a method of manufacturing a ball, a method is employed in which a square or columnar molded body is formed by press molding, fired, and then subjected to barrel polishing and precision polishing to finish the final shape. ing.
However, in press molding, since the friction between the powder to be molded and the punch or die is large, only a compact having a non-uniform density can be obtained, and as a result, the density distribution of the sintered body tends to be non-uniform. It is very difficult to precisely control the void distribution on the surface of the ball. Therefore, it is almost impossible to form coarse gaps and fine gaps in an optimal balance in order to realize clear and smooth writing taste performance. In addition, in order to finish a square or columnar sintered body into a final ball, a multi-stage polishing process must be performed, so that the production efficiency is extremely poor and a significant reduction in material yield cannot be avoided. There are serious drawbacks.

The material employed in Japanese Patent Publication No. 3-23356 is silicon carbide, but a ball made of silicon carbide is formed of a ball sheet (specifically, an Fe-based metal such as stainless steel). )), When actually used as a ballpoint pen, the surface tends to be rough due to long-term use, and the surface void distribution is naturally also susceptible to the surface roughness, so that the writing taste is slightly There are disadvantages that are easily damaged. In addition, the ball seat portion is liable to be worn out over a long period of time, which also impairs the writing quality.

On the other hand, Japanese Patent Application Laid-Open No. 56-145000 discloses a ballpoint pen ball made of a silicon nitride sintered body. According to the examples, the silicon nitride content is as low as 74% and the strength is low. Also, there is a drawback that the writing performance such as writing taste and sharpness is lacking in sustainability of writing performance and abrasion resistance. Also, since the sintering aid content is expected to be considerably densified during sintering, it is difficult to adjust the amount of surface voids or dimensional distribution by polishing or the like, and chemical resistance is also impaired. However, there is a disadvantage that corrosion and wear are liable to occur due to long-term contact with ink.

[0008] A first object of the present invention is to provide a ceramic ball for a ball-point pen capable of obtaining more excellent writing performance by optimizing the balance between coarse voids and fine voids. Another object of the present invention is to provide a ceramic ball for a ball-point pen made of a silicon nitride ceramic, which solves the drawbacks of the conventional silicon nitride ceramic and has a longer life and excellent writing performance. Further, a third problem is to provide a ceramic ball for a ballpoint pen which is less affected by the surface void distribution even when used for a long period of time, can suppress wear of the ball seat portion, and has excellent writing performance. It is in. A fourth object is to provide a method of manufacturing a ceramic ball for a ballpoint pen, which is extremely excellent in manufacturing efficiency and material yield, and a ceramic ball for a ballpoint pen manufactured by the method.

[0009]

Means for Solving the Problems and Action / Effect In order to solve the above problems, a first structure of the ceramic ball for a ballpoint pen according to the present invention is that at least the surface layer is made of ceramic and the ball surface is made of ceramic. 50 μm × 50
It is characterized in that 5 to 30 voids having a size of 2 μm or more and 10 μm or less and 20 to 200 voids having a size of 0.5 μm or more and less than 2 μm are formed per μm region. Further, the ballpoint pen of the present invention includes a ceramic ball for a ballpoint pen of the present invention (aside from the first configuration, a second or third configuration described later) and a ceramic ball for the ballpoint pen. A ball seat portion rotatably supported at a position, and an ink supply mechanism for supplying ink to the ceramic ball for a ballpoint pen via the ball seat portion.

The present inventors have conducted intensive studies and found that a size of 2 μm was obtained.
a relatively coarse gap of not less than 10 μm and a size of 0.5 μm
It is necessary to form relatively fine voids of m or more and less than 2 μm in a well-balanced manner at the above-mentioned specific formation density, so that clear lines, especially characters and thin lines, can be sufficiently and sufficiently discharged to clearly express ink. The inventors have found that it is possible to secure a smooth writing quality while securing the amount, and it is also possible to effectively suppress the wear of the ball seat portion, thereby completing the present invention. Such a ceramic ball for a ball-point pen can be suitably used particularly for a ball-point pen for writing a character or a fine line having a ball diameter of about 0.5 to 1.4 mm. Thus, the first object of the present invention is solved.

As shown in FIG. 20, the dimensions of the voids (the same applies to the dimensions of the crystal grains described later) mean that the voids (crystal grains) on the observation plane are circumscribed parallel to the voids (crystal grains) without intersecting the inside of the voids (crystal grains). When various lines are drawn while changing the positional relationship with the crystal grains or defects, the average value of the minimum distance dmin and the maximum distance dmax of the parallel lines (that is, d = (dmin + dmax) / 2) Shall be represented.

If the number of voids having a size of 2 μm to 10 μm per area of 50 μm × 50 μm (hereinafter, referred to as large-size voids) is less than 5, the amount of ink retained on the ball surface becomes insufficient, and blurring of lines or the like occurs. It is easy to occur. On the other hand, if the number exceeds 30, smooth writing is likely to be lost, and abrasion of the ball seat portion is also likely to progress. It is difficult to avoid ink spots). On the other hand, the upper limit of the number of large-sized voids that plays a leading role in holding ink is kept relatively small in order to maintain writing taste and prevent abrasion of the ball seat portion as described above. A gap smaller than the gap (hereinafter referred to as a small gap) plays a role of compensating the gap and securing the ink holding amount. However, if the number of the gaps is less than 20, the ink holding amount on the ball surface becomes insufficient and the line is blurred. Etc. easily occur. On the other hand, if the number of small-sized voids exceeds 200, the amount of ink retained on the ball surface becomes excessively large, and the sharpness of drawn characters and lines is impaired, and it becomes difficult to write fine characters and fine lines. Problems arise.

Next, a second structure of the ceramic ball for a ballpoint pen of the present invention is characterized in that at least the surface layer portion is made of a silicon nitride ceramic having a silicon nitride content of 85% by weight or more. . In this way, the use of ceramics with a high content of silicon nitride significantly improves strength and wear resistance, and significantly improves the durability of writing performance compared to conventional ballpoint pens made of silicon nitride ceramic. Can be improved. In addition, since the chemical resistance of the ball is also improved, corrosion and wear due to long-term contact with the ink are less likely to occur.

Further, as a result of further intensive studies by the present inventors, when the silicon nitride ceramic having a high silicon nitride content as described above is used for a ceramic ball for a ballpoint pen, the following has not been found. It has been found that such a new effect appears. In other words, when at least a portion (of course, the entirety) of the ball seat portion in contact with the ceramic ball for a ball-point pen is made of an Fe-based material, the surface of the ceramic ball made of silicon nitride ceramic becomes moderate due to continuous use. , And
For example, when a gap for holding ink is formed on the ball surface, the ball surface portion of the adjacent gap can be kept smooth, so that smooth writing quality can be maintained for a long time. The reason for this is that the silicon nitride and the metallic iron component of the ball sheet chemically react to form a very thin composite compound layer on the surface of the ball, which is peeled off by the friction caused by the rotation of the ball. It is presumed that the so-called mechanical and chemical polishing action, which is repeated with continued use and the ball surface is gradually polished (polished), works. In addition, it is conceivable that the components of the ink are involved in the mechanical and chemical polishing action.

In any case, such a phenomenon is peculiarly recognized in silicon nitride ceramics.
For example, it is not remarkable in silicon carbide ceramics. In particular, high-purity silicon nitride ceramics have less grain boundary phases derived from the sintering aid and are more likely to form a homogeneous structure due to the silicon nitride main phase as compared with low-purity silicon nitride ceramics. The effect of smoothing the surface of the ceramic ball by mechanical polishing is remarkable. It is also considered that the reduction in the amount of the grain boundary phase that is relatively vulnerable to corrosion also has an advantageous effect on smoothing the surface. Thus, the second object of the present invention can be solved. That is, by adopting a silicon nitride ceramic as the material of the ball, it becomes possible to maintain the smoothness of writing for a long time at least as compared with the case of employing a silicon carbide ceramic. Naturally, such a smooth writing quality can be advantageously applied to writing of characters and thin lines. Note that by combining the second configuration with the first configuration, the writing performance and the sustainability thereof can be further improved.

A third structure of the ceramic ball for a ball-point pen of the present invention is a porous silicon nitride ceramic in which closed pores of which at least a part has a size of 0.5 μm or more are dispersed and formed therein. It is characterized by having been done.

In a ceramic ball for a ballpoint pen made of the above porous silicon nitride ceramic, even if the surface layer is worn by writing, closed pores existing inside are opened to the surface and a new surface void is formed. Therefore, the surface void distribution is hardly affected even when used for a long period of time, and a ceramic ball for a ballpoint pen having excellent durability of writing performance can be realized. In addition, when the ball seat portion is made of an Fe-based material by adopting a silicon nitride ceramic, the smoothness of the surface of the air gap with the continuous use also progresses, so that the smooth writing durability can be maintained. Excellent. Such an effect can be made more remarkable by combining the above-described second configuration.

In order to ensure the ink retaining property on the ball surface, it is necessary that at least a part of the formed closed pores have a size of 0.5 μm or more.
In this case, by combining with the first configuration described above, that is, when a void is formed by opening pores on the surface, the size of the void has a size distribution satisfying the first configuration. Further, it is more effective to adjust the size distribution of the closed pores.

The silicon nitride porous ceramic as described above has a relative density of, for example, 80 to 98%. Although the absolute density varies depending on the material composition, it is generally 3.0 to 3.5 g / cm.
^{About 3} ). 80% relative density
If it is less than 100%, it is difficult to secure the strength of the ball. If it exceeds 98%, the ball is too dense, and the amount of voids suitable for holding ink on the ball surface cannot be sufficiently secured. The value of the relative density is more desirably 85 to 95%.

The ceramic ball as described above is
For example, when firing a compact formed from a raw material powder, a method of stopping firing at a stage before complete densification, or a range of common-sense firing time that can be employed in industry (for example, 1
(Up to about 0 hours) at a temperature that does not completely densify. It is also possible to employ a method in which a void forming body (for example, carbon particles or polymer material particles) which disappears during firing is mixed into the ceramic raw material powder and fired. For example, in the case of a silicon nitride ceramic, a material having a silicon nitride content of 85% by weight or more and a relatively small content of a sintering aid component is used. Alternatively, a two-stage baking such as performing a first baking in a normal pressure atmosphere and then performing a second baking in a gas pressure atmosphere is generally used. However, in the case of producing a porous silicon nitride-based ceramic, a method of performing firing in only one stage in an atmosphere of 10 atm or less, that is, a two-stage firing process for achieving densification, so-called primary firing has been completed. The method of interrupting at the stage is effective. In this case, it is more preferable to perform normal pressure firing in which firing is performed in an atmosphere containing at least nitrogen of 1 atm or less. The firing temperature is, for example, 1400
It is preferable to set the temperature within a range of 1700 ° C. Firing temperature is 1
If the temperature is lower than 400 ° C., the strength of the sintered body becomes insufficient. On the other hand, if the temperature exceeds 1700 ° C., the densification becomes remarkable, and a sintered body having an intended relative density cannot be obtained.

The silicon nitride-based ceramic is mainly composed of silicon nitride, and the remaining component is a sintering aid component, which is 3A, 4A, 5A, 3B in the periodic table.
(Eg, Al (alumina, etc.)) and 4B (eg, Si
(Silica or the like)) and at least one element selected from the group consisting of Mg and 1 to 15% by weight in terms of oxide. These exist mainly in the oxide state in the sintered body.

If the sintering aid component is less than 1% by weight, the sintering itself becomes difficult, and it becomes difficult to obtain a high-strength ball. On the other hand, if the content exceeds 15% by weight, insufficient strength, toughness or wear resistance is caused. In addition, when the above-mentioned porous ceramic is desired to be formed, the densification of the sintered body proceeds excessively, and an appropriate amount of closed pores ( That is, it is difficult to form a gap on the surface. The content of the sintering aid component is desirably 2 to 2.
The content is preferably 10% by weight. In the present invention,
The term “main component” (also synonymous with “main component” or “mainly”) means that the content of the component in the substance of interest is 50% by weight or more, unless otherwise specified.

The group 3A sintering aid component includes S
c, Y, La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, and Lu are generally used. The content of these elements R is RO only for Ce.
₂ and others are calculated using R ₂ O ₃ type oxides. Of these, oxides of heavy rare earth elements of Y, Tb, Dy, Ho, Er, Tm, and Yb are preferably used because they have the effect of improving the strength, toughness, and wear resistance of the silicon nitride sintered body. used. In addition, magnesia spinel, zirconia and the like can also be used as a sintering aid.

The structure of the silicon nitride-based sintered member has a structure in which main phase crystal grains containing silicon nitride as a main component are bonded by vitreous and / or crystalline binder phases. The main phase has a β conversion of 70% by volume or more (preferably 90% by volume).
(% By volume or more) of Si ₃ N ₄ phase. In this case, the Si ₃ N ₄ phase is a phase in which a part of Si or N is substituted by Al or oxygen, and a phase in which metal atoms such as Li, Ca, Mg, and Y are solid-dissolved. There may be. For example, it can be exemplified Sialon which is expressed by the following general formula; _{beta-sialon: Si 6-z Al z O} z N 8-z (z =
0-4.2) α-sialon: M _x (Si, Al) ₁₂ (O, N)
₁₆ (x = 0 to 2) M: Li, Mg, Ca, Y, R (R is a rare earth element excluding La and Ce).

The above-mentioned sintering aid component mainly constitutes the binder phase, but a part thereof may be taken into the main phase. The binder phase may contain unavoidable impurities, for example, silicon oxide contained in the silicon nitride raw material powder, in addition to components intentionally added as a sintering aid.

It is desirable that the silicon nitride powder used as a raw material has an α-rate (a ratio of α-silicon nitride in the total silicon nitride) of 70% or more. At least one element selected from the group consisting of groups 3A, 4A, 5A, 3B and 4B is 1 to 15 in terms of oxide.
% By weight, preferably 2 to 10% by weight.
In addition, at the time of compounding the raw materials, in addition to oxides of these elements, compounds which can be converted into oxides by sintering, for example, carbonates and hydroxides may be added.

Of the above three configurations, the first configuration, whose material is not limited to silicon nitride ceramics, includes silicon carbide, alumina (aluminum oxide), and zirconia in addition to silicon nitride ceramics. Ceramics such as (zirconium oxide) can be used, but also in this case, as described above, silicon nitride-based ceramics can be more preferably used than other materials.

Next, a method that can be suitably employed in producing the ceramic ball of the present invention will be described in more detail. In the first configuration of the present invention, it is required that the large-sized voids and the small-sized voids on the ball surface are formed in a specific ratio. In particular, in the case of manufacturing a porous ceramic in which pores for forming voids are dispersed and formed inside the sintered body as in the third configuration, the dimensional distribution of the voids formed in the compact is precisely controlled. And the state of dispersion must be as uniform as possible. As a result of further studies, it has been found that it is essential to make the density as high and uniform as possible in the state of the molded body in order to realize the above-mentioned distribution of voids or pores. did. However, only a diameter of.
In the case of manufacturing a ballpoint pen ball having a size of about 5 to 1.4 mm, it is very difficult to obtain the above-described distribution of voids or pores by conventional mold press molding or extrusion molding which tends to cause uneven density. It is not sufficient to use a cold isostatic pressing (CIP) method together. In addition, it is practically impossible to directly form such a small-diameter ball into a spherical shape by press molding, and a method of firing a square or cylindrical shaped body and polishing the sintered body is adopted. As has already been explained, this leads to a drastic reduction in manufacturing efficiency and yield.

As a result of intensive studies, the present inventors have made it possible to achieve high density and uniform pore distribution of a small-diameter molded product, and to directly obtain a spherical molded product. It succeeded in creating an epoch-making method that can eliminate post-processing such as polishing after sintering, and can simplify even if it is necessary, that is, the rolling granulation method. It is. In this method, a green compact is placed in a granulation container by placing a green compact containing the ceramic raw material powder and rolling the aggregate of the green compact in the container while rolling the aggregate into a spherical shape. It is characterized by including a rolling granulation forming step to obtain and a firing step to obtain a ceramic ball for a ballpoint pen by firing the spherical molded body. This method makes it possible to extremely easily produce a high-density and homogeneous ball-point pen ball, which is almost impossible to obtain with high sphericity by conventional press molding or the like. In addition, the production efficiency in obtaining a spherical molded body is high, and unnecessary parts are not generated in the molded body unlike press molding, so that the polishing allowance for the sintered body can be dramatically reduced, and in some cases, the sintered body can be reduced. It can be used as it is as a ballpoint pen ball.

[0030] By the above-described rolling granulation, it is possible to obtain a spherical molded body having a relative density of 61% or more. Producing a spherical molded body having such a high density is extremely effective in achieving a uniform distribution of voids or pores required in the first or third configuration. When the relative density is less than 61%, it is difficult to make the pores dispersed in the molded body uniform, and the variation in the pore size becomes large, and good writing performance is imparted to the sintered ball. It will be difficult to do.

In this case, in order to obtain a high-density and more uniform molded body, a spherical molded body is obtained by supplying a liquid mainly composed of a liquid molding medium to the molded core and adhering a molding base powder thereto. Can be adopted
This is effective in increasing the density of the molded body. The liquid molding medium may be, for example, an aqueous solvent such as water or an aqueous solution in which an additive is appropriately added to water, but is not limited thereto.For example, an organic solvent may be used. . According to the method, when the liquid molding medium and the molding base powder adhere to the uneven portions existing on the surface of the molded body, the powder particles adhere while closely rearranging due to the osmotic pressure of the liquid molding medium. Therefore, it is considered that the density of the molded body can be increased. In order to enhance such an effect, it is desirable to spray the liquid molding medium directly on the molded body. Further, the step of spraying the liquid forming medium may be performed over the entire period of the forming step (for example, the rolling granulation step), or may be performed only during a part of the forming step (for example, only the final stage). Is also good. Also,
The liquid forming medium may be supplied continuously or intermittently.

When the tumbling granulation method is employed, it is more effective to use the following as the molding base powder. That is, the average particle diameter measured by a laser diffraction type particle size analyzer is 0.3 to 2 μm, the 90% particle diameter is 0.7 to 3.5 μm, and the BET specific surface area value is 5 to 5 μm.
A molding base powder of 13 m ² / g is used. In addition,
In the present specification, the relative cumulative frequency from the small particle side of the particles is:
As shown in FIG. 12, the particles to be evaluated are arranged in the order of the particle size, and when the frequency of the particles is counted from the smaller particle size side on the arrangement, the cumulative frequency up to the particle size of interest is obtained. To N
c, assuming that the total frequency of the particles to be evaluated is N0, nrc =
Relative frequency nrc expressed by (Nc / N0) x 100 (%)
Say. The X% particle size refers to a particle size corresponding to nrc = X (%) in the above-described arrangement. For example, 90
The% particle diameter means a particle diameter corresponding to nrc = 90 (%).

By using a molding base powder whose average particle diameter and 90% particle diameter measured by a laser diffraction type particle sizer fall within the above range and whose BET specific surface area value falls within the above range, the bias of the powder can be improved. Defects such as density non-uniformity and discontinuous boundaries due to the above-mentioned factors are unlikely to occur, and as a result, the rate of occurrence of defects due to non-uniform shrinkage of the sintered body, and defects due to cracking or chipping can be greatly reduced. Although the principle of measurement of a laser diffraction type particle sizer is known, in brief, a sample powder is irradiated with laser light, the diffracted light by the powder particles is detected by a photodetector, and the diffracted light obtained from the detected information is obtained. The particle size can be known from the scattering angle and the intensity of the particles.

As shown in FIG. 11, a plurality of primary particles may be formed in the molding base powder made of a ceramic raw material due to various factors such as the action of an added organic binder and the action of electrostatic force. Often agglomerated to form secondary particles. In this case, the measurement by the laser diffraction type particle sizer does not cause a large difference between the diffraction behavior of the incident laser light by the aggregated particles and the diffraction behavior by the isolated primary particles. It cannot be distinguished from each other whether it is the particle size of the particles or the particle size of the aggregated secondary particles. That is, the particle diameter measured by this method is a value reflecting the secondary particle diameter D in FIG. 11 (in this case, isolated primary particles that do not cause aggregation are also regarded as secondary particles in a broad sense). In addition, the average particle diameter or 90% particle diameter calculated based on this reflects the average particle diameter or 90% particle diameter of the secondary particles.

On the other hand, the specific surface area of the molding base powder is measured by an adsorption method. Specifically, the specific surface area can be determined from the amount of gas adsorbed on the powder surface. In general, an adsorption curve showing the relationship between the pressure of a measurement gas and the amount of adsorption is measured, and a known BET formula (collection of the inventors, Brunauer, Emmett, Teller) for multi-molecule adsorption is obtained. By applying, the adsorption amount vm when the monomolecular layer is completed is obtained, and the BET specific surface area value calculated from the adsorption amount vm is used. However, when approximately equivalent results are obtained, a simple method that does not use the BET equation,
For example, a method of directly reading the adsorption amount vm of the monolayer from the adsorption curve may be adopted. For example, when a section where the adsorption amount is substantially proportional to the gas pressure appears in the adsorption curve, there is a method of reading the adsorption amount corresponding to the end point on the low pressure side of that section as vm (The Journal of American Chemical Society, 57
Volume (1935), p. 1754, Brunauer and Emet
t). In any case, in the specific surface area value measurement by the adsorption method, the gas molecules to be adsorbed also penetrate into the secondary particles and cover the surface of the individual primary particles constituting the secondary particles, and as a result, the specific surface area value is This reflects the specific surface area of the primary particles, and thus the average value of the primary particle diameter d in FIG.

The BET ratio reflecting the primary particle diameter is set so that the compacting of the ceramic sintered body is sufficiently promoted, and a sintered body having few defects and sufficient strength is obtained. The surface area value is set to be as small as 5 to 13 m ² / g. The important point is that the average particle diameter or 9
The 0% particle size is 0.3 to 2 μm or 0.1%, respectively.
7 to 3.5 μm, which is set to a small value of about 1/10 or less as compared with the green body powder for molding obtained by a spray drying method or the like. This means that the agglomeration state as secondary particles in the green body powder for molding and, as a result, the local coarseness of particle packing is eliminated as much as possible. This makes it difficult for the powder to be biased.

The above-mentioned average particle diameter of the base powder for molding exceeds 2 μm, or the 90% particle diameter is 3.5 μm.
If it exceeds, the powder tends to be biased in the molded body,
Failure such as deformation, cracking or chipping of the sintered body due to uneven shrinkage is likely to occur. On the other hand, the average particle diameter is less than 0.3 μm, or the 90% particle diameter is 0.7 μm.
Fine powders of less than a considerable amount of time are required for preparation (for example, pulverization time), which leads to an increase in cost due to a reduction in production capacity.
The average particle diameter of the green body powder for molding is preferably 0.1.
The diameter is preferably 3 to 1 μm, and the 90% particle diameter is desirably 0.7 to 2 μm.

On the other hand, when the BET specific surface area value of the green body powder for molding is less than 5 m ² / g, the primary particle diameter becomes too large, the uniformity of sintering is impaired, and defects are generated in the obtained spherical sintered body. The strength decreases. On the other hand, a green body powder for molding having a BET specific surface area value of more than 13 m ² / g requires a considerably long time for preparation (for example, pulverization time), which leads to an increase in cost due to a reduction in production capacity. In addition, the BET of the base powder for molding
The specific surface area value is desirably 5 to 10 m ² / g.

The step of preparing the molding base powder as described above includes, for example, a step of mixing a ceramic powder and a sintering aid powder together with a solvent to prepare a powder, and a step of preparing a powder in the middle of the hot air flow passage. An aggregate of dry media formed in a granular or lump shape of ceramic or metal is arranged in a flowable or vibrable state within a predetermined space range, and the dried media aggregate is passed through hot air. By flowing or vibrating in a spatial range and supplying the fluid to the flowing or vibrating dry media assembly,
The method includes a drying step of evaporating the solvent while mixing the plasma with a drying medium, and a collecting step of guiding the forming base powder obtained by the drying together with hot air to a downstream side of the drying medium assembly to collect the powder. be able to.

In the above method, the slurry is supplied to the stack of dry media, and the slurry is dried by hot air to become a powder and adhere to the surface of the media to form a powder aggregate layer. Then, the dried media on which the powder agglomeration layer is formed by the flow of hot air vibrate or flow, and collide with each other or cause friction. At this time, the powder agglomeration layer adhering to the media surface is crushed, and is blown away and collected while alleviating the aggregation state. Thereby, the base powder for molding having the above-mentioned particle size range can be obtained easily and with high efficiency. As the drying medium, it is preferable to use a ceramic medium that is hard to wear as much as possible. For example, if a medium mainly composed of alumina, zirconia, or a mixed ceramic thereof is used, the medium is temporarily worn and the molding base material is used. Even if it is mixed in the powder, since it functions as a sintering aid component, the influence of the mixing can be reduced.

In the drying step in the step of preparing the green body powder for molding, the hot air flow path may be formed to include a vertically arranged hot air duct, and hot air is allowed to pass through the middle of the hot air duct, and the drying medium is dried. Can be formed as a media holding portion composed of a gas circulating body such as a net that does not allow the passage of the medium. In this case, the slurry can be supplied from above to the dry media aggregate held on the media holding unit. Further, the hot air can be circulated in the hot air duct so as to move the drying medium upward from the lower side of the drying media assembly while moving the drying medium upward, and the powder after drying passes through the hot air duct together with the hot air to the downstream side. Can be collected by the collection unit arranged in the storage area.

According to this method, a cycle is repeated in which the dry medium is blown up by the hot air blown up from below, moves up, and is dropped on the integrated body. And can be added relatively uniformly. In addition, coarse particles among the crushed aggregated particles are not blown off by the hot air, but are returned to the dry media aggregate again and continuously crushed, so that coarse particles that cause powder unevenness or the like in the subsequent molding process are obtained. The generation of secondary particles can be further reduced.

In the rolling granulation, the green body powder for molding and the molding nucleus are put into a granulation container, and the molding nucleus is rolled in the granulation container while being rolled around the molding nucleus. It is desirable to obtain a spherical molded body by adhering and aggregating the molding base powder in a spherical shape. That is, in the granulation container, for example, while rolling the molding core on the molding base powder layer,
By adhering and aggregating the molding base powder in a spherical shape around the molding core to obtain a spherical molded body, the density of the aggregated layer of the molding base powder growing around the molding core is remarkably increased. In addition, defects such as pores and cracks due to bridging of the powder particles are reduced in the formed aggregated layer. As a method of rolling the molded core (or growing compact) in the granulation container, a method of rotating the granulation container is simple. For example, the method is based on a principle similar to that of the vibration type barrel polishing apparatus. Vibration may be applied to the grain container, and the molded core may be rolled based on the vibration.

In this case, the ceramic ball obtained by sintering has a cross section substantially passing through the center, and
A core portion that can be distinguished from the outer layer portion is formed. The term “identifiable” as used herein does not only mean that it is visually identifiable, but also a specific physical property value (for example, density or hardness) that causes a difference between the core and the outer layer. , Etc.) is included.

By adopting a sintered body structure in which such a structure appears, a spherical ceramic sintered body having a high density and a high strength can be realized with a small defect formation rate in the surface layer, which is a key to improving the performance of bearings and the like. Specifically, if the above-mentioned spherical molded body produced by the method of the present invention is fired, the resulting spherical ceramic sintered body is, for example, when a cross-section passing substantially through the center is polished and this is magnified and observed, At the center thereof, a core portion derived from the molded core is formed so as to be distinguishable from an outer layer portion derived from an aggregated layer having high density and few defects.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to a case where a silicon nitride ceramic is used as a material. First, it is desirable to use a silicon nitride powder as a raw material having an α ratio of 70% or more, and a rare earth element, 3A, 4A, 5A, 3B, or an element group of 4B as a sintering aid. At least one of them is converted to oxide
１５15% by weight, preferably 2-8% by weight. In addition, at the time of compounding the raw materials, in addition to oxides of these elements, compounds which can be converted to oxides by sintering, for example, carbonates, hydroxides and the like may be mixed.

Hereinafter, an example of a method for preparing a molding base powder and a molding method will be described, but as described above, the invention is not limited thereto. FIG. 8 shows an embodiment of an apparatus used in the step of preparing a green body powder for molding. In the apparatus, the hot air flow passage 1 is formed to include a vertically arranged hot air duct 4, and a gas flow member that allows hot air to pass therethrough and does not allow the drying medium 2 to pass therethrough, in the middle of the hot air duct 4. For example, a media holding unit 5 formed of a net or a perforated plate is formed. On the medium holding portion 5, a dry medium 2 composed of ceramic spheres mainly composed of alumina, zirconia, or a mixed ceramic thereof is used.
Are stacked to form a layered dry media assembly 3.

On the other hand, the raw material is in the form of a slurry obtained by adding a water-based solvent to a blend of silicon nitride powder and sintering aid powder and wet-mixing (or wet-mixing / grinding) with a ball mill or an attritor. Be prepared. In this case, the size of the primary particles is adjusted so that the BET specific surface area value is 5 to 13 m ² / g.

As shown in FIG. 9, the dry media assembly 3
On the other hand, the hot air is circulated in the hot air duct 4 so as to move upward from the lower side of the medium holding portion 5 while moving the drying medium 2 up. On the other hand, as shown in FIG.
Is pumped up from the slurry tank 20 by the pump P, and is dropped and supplied to the dry media assembly 3 from above. Thereby, as shown in FIG. 10, the slurry is dried by the hot air and adheres to the surface of the drying medium 2 in the form of the powder aggregation layer PL.

Then, due to the flow of hot air, the dry media 2 repeatedly vibrates and falls and strikes each other. Further, the powder agglomeration layer PL is crushed into the base powder particles 9 for molding by rubbing by the impact. You. The crushed base powder particles 9 for molding include those in the form of isolated primary particles, but are mostly secondary particles in which the primary particles are aggregated. The molding base powder particles 9 having a particle size of a certain size or less flow downstream along with the hot air (FIG. 8). On the other hand, the crushed particles larger than a certain size are not blown off by the hot air but fall again to the dry media assembly 3 and are further crushed between the media.

In this way, the molding base powder particles 9 which have flowed to the downstream side together with the hot air pass through the cyclone S to the collecting section 2.
1 is collected as a molding base powder 10. The recovered molding base powder 10 has an average particle size of 0.3 to 2 μm measured by a laser diffraction type particle sizer, a 90% particle size of 0.7 to 3.5 μm, and a BET specific surface area value of 90%. 5 to 13 m ² / g.

In FIG. 8, the diameter of the drying medium 2 is
It is set appropriately according to the flow cross-sectional area of the hot air duct 4. If the diameter is insufficient, the impact force on the powder agglomeration layer formed on the medium is insufficient, and a base powder for molding having a particle diameter within an intended range may not be obtained. On the other hand, if the diameter is too large, even if hot air is circulated, it is difficult for the dry medium 2 to move, so similarly the striking force is insufficient, and there is a case where a molding base powder having an intended particle diameter cannot be obtained. . Note that it is desirable to use a dry medium 2 having a uniform size as much as possible in order to form an appropriate gap between the media and promote the movement of the medium during hot air circulation.

The filling depth t1 of the drying medium 2 in the drying medium assembly 3 is appropriately set according to the flow rate of the hot air within a range where the flow of the medium 2 occurs without excess or deficiency. If the filling depth t1 is too large, the flow of the drying medium 2 becomes difficult, and the impact force is insufficient, so that there is a case where a molding base powder having a particle diameter within a desired range cannot be obtained. On the other hand, if the filling depth t1 is too small, the amount of the dry medium 2 is too small, and the frequency of impact is reduced, leading to a reduction in processing efficiency.

Next, the temperature of the hot air is appropriately set within a range in which the drying of the slurry proceeds sufficiently and no problems such as thermal deterioration occur in the powder. For example, when the solvent of the slurry is mainly water, when the hot air temperature is lower than 100 ° C., the supplied slurry does not sufficiently dry, and the moisture content of the obtained molding base powder becomes too high. Agglomeration is likely to occur, and a powder having an intended particle size may not be obtained.

Further, the flow velocity of the hot air is appropriately set within a range in which the drying medium 2 is not blown to the collection section 21. If the flow velocity is too low, the flow of the drying medium 2 becomes difficult, and the impact force is insufficient, so that there is a case where a molding base powder having an intended particle diameter cannot be obtained. On the other hand, if the flow velocity is too high, the drying medium 2 rises too high and the collision frequency is rather reduced, leading to a reduction in processing efficiency.

The green body powder 10 for molding thus obtained is
It can be formed into a spherical shape by the rolling granulation molding method. That is, as shown in FIG. 1, the green body powder for molding 10 is charged into a granulation container 132, and as shown in FIG. 2, the granulation container 132 is driven to rotate at a constant peripheral speed. In addition, the water W is supplied to the molding base powder 10 in the granulation container 132 by, for example, spraying or the like. As shown in FIG. 5, the injected molding base powder agglomerates in a spherical shape while rolling on an inclined powder layer 10 k formed in a rotating granulation container to form a compact G. The operating conditions of the tumbling granulator 130 are adjusted so that the relative density of the obtained compact G is 61% or more. Specifically, the rotation speed of the granulation container 132 is adjusted at 10 to 200 rpm, and the water supply amount is adjusted so that the moisture content in the finally obtained molded body is 10 to 20% by weight. . By using a molding base powder in which the above-mentioned type of sintering aid powder is blended within a range of 1 to 15% by weight, the density of the molded body is 2.0 to 2.5 g / cm under the above conditions. ^{About 3} can be secured.

At the time of rolling granulation, it is desirable to put the molding core 50 into a granulation container 132 as shown in FIG. This way,
As shown in FIG. 5 (a), while the molding core 50 is rolling on the molding base powder layer 10k, as shown in FIG. The particles are attached and aggregated into a spherical shape to form a spherical molded body 80 (rolling granulation step). Then, when the size of the molded body becomes an appropriate size, the molding is stopped, and the molded body 80 is sintered to form a ceramic ball 90 (for example, 0.5 to 2 mm) as shown in FIG. can get.

The molding core 50 is made mainly of a ceramic powder like a molding core 50a shown in FIG. 3A, and is made of a material having a composition similar to that of the molding base powder 10, for example. Is the ceramic ball 9 finally obtained.
It is desirable because the nucleus hardly acts as an impurity source with respect to 0. However, when there is no concern that the diffusion of the core component extends to the surface layer of the ceramic ball 90, the molded core is made of a material different from the ceramic powder (inorganic material powder) that is the main component of the molding base powder. It is also possible to use a ceramic powder, a metal core 50d as shown in FIG. 3D, or a glass core 50e as shown in FIG. 3E. It is also possible to form the nucleus with a material that disappears by thermal decomposition or evaporation during firing, for example, a polymer material such as wax or resin. In this case, a void portion corresponding to the core may be formed in the obtained sintered body.

The molded core may have a shape other than a spherical shape as shown in FIG. 3B or 3C, for example.
As shown in (a), it is needless to say that it is desirable to use a spherical one in order to increase the sphericity of the obtained molded body.

The method for producing the molded core is not particularly limited, but when mainly composed of ceramic powder, various methods as shown in FIG. 4 can be exemplified. First, (a)
In the method shown in (1), a core is obtained by compression-molding the ceramic powder 60 with a die 51a and press punches 51b, 51b (of course, other compression methods may be used). In (b), the raw material powder is dispersed in a molten thermoplastic binder to form a molten compound 63, which is spray-solidified to obtain a spherical core 50. In the example shown,
For example, the inner nozzle 61 and the outer nozzle 6 arranged coaxially
The molten compound 63 is supplied into the inner nozzle 61 to the spray nozzle composed of the two nozzles, and while flowing out from the opening on the tip side, the spray compound such as an inert gas or water is passed through the gap 65 between the nozzles 61 and 62. Is sprayed from the opening to spray and solidify the molten compound 63. (C) shows a method of injecting the molten compound 63 into the spherical cavity 70 of the injection mold to form a spherical core. Further, in (e),
The melted compound 63 is dropped freely from the nozzle to make it spherical by surface tension, and cooled and solidified in air to obtain the core 50. Also, a slurry composed of the raw material powder, the monomer (or prepolymer) and the dispersion solvent is
There is also a method of obtaining a spherical molded body by dispersing as droplets in a liquid that is not mixed with the slurry and polymerizing a monomer or prepolymer in that state. Although the form is not spherical but irregular, as a simple method, the powder compact 72 is crushed by pressing or the like,
It is also possible to use as.

On the other hand, in FIG. 2, only the green body powder for molding 10 is charged into the granulation vessel 132, and the vessel is rotated at a lower speed than at the time of growth of the compact to generate agglomerates of the powder. When the amount and the size of the aggregates are generated, the rotation speed of the container 132 is then increased, and the aggregates are
The molded body 80 may be grown so as to be used as zero. In this case, there is no need to intentionally put the nucleus produced in a separate process as described above together with the molding base powder 10 into the container 132.

The molded core body 50 obtained as described above
Can stably maintain its shape without collapse even when some external force acts. As a result, as shown in FIG. 5A, even when rolling on the green body powder layer for molding 10k, a reaction due to its own weight can be reliably received. FIG.
As shown in (e), it is considered that the powder particles rolled up when rolled can be pressed firmly against the surface, so that the powder is appropriately compressed and the dense layer 10a can be grown with high density. On the other hand, as shown in FIG. 5D, when the nucleus is not used, the aggregate 100 corresponding to the nucleus is generated only by an accidental factor, and the agglomeration degree is low and weak. In many cases, the powder is deformed when it rolls on the molding base powder layer 10k, or is crushed in the worst case, and cannot generate a sufficient force to cause the powder to adhere and aggregate. As a result, it takes a long time to grow the compact, and even if it grows, only the one having many defects such as cracks and voids due to bridging of the powder particles may be obtained.

It is preferable that the size of the core 50 be at least about 40 μm (preferably about 80 μm). If the core 50 is too small, the growth of the aggregated layer 10a may be incomplete. Also, if the core is too large, the thickness of the formed cohesive layer is insufficient, and the sintered body may be liable to have defects or the like. Therefore, it is preferable to set the dimension to, for example, 0.3 mm or less. .

The molding core is made of a ceramic powder and a bulk density of a molding base powder (for example, JIS-Z2504 (197)
It is desirable to use an aggregate agglomerated at a higher density than the apparent density specified in 9) in order to reliably receive the pressing force of the powder particles and promote the growth of the aggregate layer 10a. Specifically, it is preferable to use a material that has been agglomerated to 1.5 times or more the bulk density of the molding base powder. in this case,
It is sufficient that the particles are agglomerated to such an extent that they do not collapse due to rolling impact on the molding base powder layer 10k.

In order to achieve more stable growth of the compact, it is desirable to set the size of the core body 50 as follows according to the size of the compact to be obtained. That is, FIG.
As shown in (b), the size of the molded core 50 is represented by the diameter dc of a sphere having the same volume, while (of course, when the core 50 is spherical, the diameter is referred to here). Dc is set so that dc / dg satisfies 1/100 to 1/2, where dg is the diameter of the finally obtained spherical molded body. dc / dg is 1/100
If it is less than 10%, there is a concern that the core is too small, the growth of the cohesive layer 10a is incomplete, or only the one having many defects can be obtained. On the other hand, if it exceeds １ ／, for example, if the density of the core body 50 is not so high, the strength of the obtained sintered body may be insufficient. Note that dc / dg is
Preferably 1/50 to 1/5, more preferably 1/20
It is preferable to adjust in the range of up to 1/10.

For example, if the molded body G is fired by the method described below, the molded body G is made of silicon nitride ceramic (however, when a core other than a material other than silicon nitride ceramic is used, the core corresponding region is nitrided). It goes without saying that the ball can be made of a material other than the silicon ceramic). And if you want to get a porous ceramic ball,
The firing is performed at 1400 to 1700 ° C. in a non-oxidizing atmosphere at a normal pressure or a gas pressure of 10 atm or less containing nitrogen so that the relative density of the sintered body becomes 80 to 98%.

The compact formed by the tumbling granulation method has a relative density increased to 61% or more, and the whole surface is almost uniformly compressed while rolling, so that the distribution of pores is uniform. The relatively large pores and the small pores are formed in a well-balanced manner. Then, the compact is fired under the condition that the compact is not completely densified as described above, so that closed pores 91 and 92 derived from pores formed in the compact are formed in the inside as shown in FIG. The dispersion-formed porous ceramic balls 90 are obtained. Some of the pores 91 and 92 are open to the surface of the ball 90 to form a surface void, and as a dimensional distribution, a relatively large void 93 of 2 to 10 μm per 50 μm × 50 μm area of the ball surface. Is 5-30
And a relatively small gap 94 of 0.5 to 2 μm
Those having a specific ratio of 0 to 200 are obtained.

As shown in FIG. 6, a ceramic ball 90 obtained by firing the spherical compact 80 obtained by the tumbling granulation method was polished at a cross section substantially passing through the center, and was enlarged and observed. In some cases, a core portion 91 derived from the molded core is formed at the center of the core portion so as to be distinguishable from an outer layer portion 92 having a high density and few defects, derived from the aggregated layer. In the polished cross section, the core portion 91 may exhibit a visually recognizable contrast between at least one of the brightness and the color tone between the core portion 91 and the outer portion. This is because the density ρe of the ceramic constituting the outer layer portion 92 is
This is presumed to be different from the density ρc of the ceramic constituting

As shown in FIG. 5B, the diameter dc of the molding core 50 is defined as dg, and the diameter of the spherical sintered body 90 is dg.
dc / dg is 1/100 to 1/2 (preferably 1/50 to
In the case where the adjustment is made in the range of (５, more preferably 1/20 to 1/5), the sectional structure of the sintered body 90 in FIG. 6 is as follows, for example. That is, the core 91
(If the core is made of a material that disappears by thermal decomposition or evaporation during firing, for example, a material composed of wax, resin, or a polymer material, the core 91 becomes a hollow portion.) When the diameter of the ceramic sintered body is Dg, Dc / Dc /
Dg is 1/100 to 1/2 (preferably 1/50 to 1 /
5, more preferably 1/20 to 1/10). When Dc / Dg is less than 1/50,
Defects are likely to occur in the cohesive layer 10a (FIG. 11) that is the basis of the outer layer portion 92, which may lead to insufficient strength or the like.
On the other hand, if it exceeds 1/5, the strength of the sintered body 90 may be insufficient if the density of the core body 50 is not so high, for example. Note that Dc / Dg is more preferably 1/20.
It is preferable to adjust in the range of up to 1/10.

As a state in which a visually discernible contrast occurs between the core portion 91 and the outer layer portion 92 in the ceramic ball 90, for example, a difference in brightness or color tone is formed in the radial direction of the sphere and formed in the circumferential direction. A state that has not been performed can be exemplified. As a specific mode, the layered pattern 9 surrounding the core 91 is provided on the outer side in the polished cross section.
3 may be formed concentrically.

This is one of the characteristic structures that can occur when the tumbling granulation method is employed (naturally, it is also carried over to the polished ceramic balls). The cause of the formation is as follows. I can guess. That is, as shown in FIG. 5A, the compact 80 grows the agglomerated layer 10a while rolling on the green body powder layer for molding 10k. It does not exist on the molding base powder layer 10k. That is, due to the avalanche flow of the powder accompanying the rotation of the granulation container, the base powder layer 10 k
When it comes to the lower side, it sneaks into the forming base powder layer 10k, is taken up by the wall surface of the granulation container, is carried to the upper side of the forming base powder layer 10k, and rolls down again on the forming base powder layer 10k. When sunk into the molding base powder layer 10k, the surroundings are pressed down by the powder, and the impact due to rolling and falling is relatively unlikely to be applied, and the powder particles adhere relatively loosely. On the other hand, the molding base powder layer 10
When rolling on k, impacts due to rolling and falling are applied, and the liquid spray medium W such as water is easily sprayed, and the powder is easily tightened tightly. Then, the molding base powder layer 10
Since the rolling form on the base member k and the sneaking into the molding base powder layer 10k are periodically repeated, the form of powder attachment changes periodically. It is considered that a layered pattern is formed as a result of the occurrence of the tightness, which appears as a slight difference in density or the like even after firing. For example, it is considered that the above-mentioned layered pattern is formed by alternately laminating concentric arc-shaped portions and remaining portions having higher densities in the radial direction.

FIG. 7 shows that a spherical molded core 50 is formed by spray drying using silicon nitride powder, and an aggregated layer is formed therearound by a rolling granulation method to obtain a molded body. 3 is an optical microscopic observation image of a fractured surface of a ceramic ball obtained by firing in a nitrogen atmosphere at 1200 ° C. under normal pressure. The relative density of the molded body is 70%, and the relative density of the ceramic ball (sintered body) is about 90% (the observation surface is colored with iron oxide). At the center, a circular region corresponding to the molded core 50 is clearly observed. Also, a concentric layered pattern is observed around it,
Further, when the region of the layered pattern was enlarged and observed, it was confirmed that the layer was a porous silicon nitride ceramic in which a large number of closed pores corresponding to those having a size of 1 μm or more were dispersed and formed therein.

The spherical sintered body 90 obtained by the above-described steps can be used as a ballpoint pen ball after polishing for dimensional adjustment. Hereinafter, the manufacturing process of the ballpoint pen will be described. First, as shown in FIG. 14, a wire 100 serving as a material is made of, for example, stainless steel (ferritic material such as SUS430 or austenitic material such as SUS304 in consideration of workability) or other corrosion-resistant Fe-based material. The wire rod 100 is forged by a forging die 101 into a primary processed body 1 having a schematic shape of a holder.
Process to 02. The primary processing body 102 has a tapered portion 102b for forming a ball seat portion formed on the front end side, and a flange portion 102a for locking the ink shaft is formed at an intermediate portion in the axial direction.

As shown in FIG. 15, the primary workpiece 10
An ink guide hole 103 is formed in the axial direction from the rear end side of the nozzle 2 by a drill DR. The ink guide hole 103 has a shape whose diameter gradually decreases toward the tip. Further, a counterbore portion 102e communicating with the ink guide hole 103 is also drilled on the tip side where the tapered portion 102a is formed.
(The bottom surface 102d is a tapered surface). Then, as shown in FIG. 16, the bottom surface 10 of the counterbore 102e is formed.
2d, a radial ink groove 106 is formed by broaching using the blade B. In this way, as shown in FIG. 17A, the counterbore portion 102e becomes the ball seat portion 107 having the ink groove 106, and the primary processed body 102 becomes the holder 105. The inner surface of the ball seat portion 107 is subjected to finishing such as deburring by a rod-shaped jig R. Note that the holder 105 may be manufactured by a metal injection molding method in which a compound obtained by kneading a metal powder with a binder is injection-molded, and the compound is sintered after removing the binder.

Next, as shown in FIG. 17B, a ceramic ball 95 for a ballpoint pen based on the ceramic ball 90 is press-fitted into the ball seat portion 107 of the holder 105 by a press-fitting punch IP. As shown in FIG. 18C, a crimping portion 102h for retaining is formed at the tip of the outer peripheral surface of the holder by a crimping punch JP as shown in FIG.
As shown in (a), the pen point 110 for a ballpoint pen is completed. The ink shaft IJ is inserted into the rear end of the pen tip 110, and the pen shaft case 111 is further assembled to complete the ballpoint pen 120.

When the ball 95 is pressed against paper or the like and rolled,
The ink INK guided to the ink groove 106 via the ink guide hole 103 is guided to the ball surface. At this time,
The gaps 93 and 94 shown in FIG. 13 function as ink holding holes. In the ceramic ball 95 for a ballpoint pen, the closed pores 91 and 92 are uniformly dispersed and formed even inside, so even if worn due to use, the closed pores inside are newly opened to the surface and new ink is retained. Since the air gap is used, the density of formation and the size distribution of the air gap are hardly affected, and good writing performance can be maintained for a long time. In addition, the size distribution of the voids per 50 μm × 50 μm area on the surface of the ball 95,
5 to 30 voids 93 of 2 to 10 μm, and 0.5 to
Since the 2 μm gap is adjusted to a specific ratio of 20 to 200, a sufficient amount of ink flowing out and a smooth writing quality necessary for clearly expressing characters, thin lines, and the like can be achieved, and the ball sheet can be used. Wear of the portion 107 can also be effectively suppressed.

The following experiment was conducted to confirm the effects of the present invention. Silicon nitride powder (purity of silicon nitride: 98% by weight, average particle diameter: 0.5 μm, 90% particle diameter: 1.0 μm, BET specific surface area: 10 m ² / g) as a raw material powder, and yttria powder as a sintering aid component (Average particle size 0.6μ
m, 90% particle diameter 1.0 μm, BET specific surface area 10 m
² / g). The average particle size was measured using a laser diffraction type particle size analyzer (manufactured by Horiba, Ltd., product number: LA-500).
The BET specific surface area was measured using a BET specific surface area measuring device (Multi Soap 12, manufactured by Yuasa Ionics Inc.).

The above material powders were blended so that the composition ratio was 100 parts by weight of silicon nitride powder, 4 parts by weight of yttria powder, and 4 parts by weight of alumina powder.
50 parts by weight of pure water as a solvent and an appropriate amount of an organic binder were added to parts by weight, and the mixture was mixed by an attritor mill for 30 hours to obtain a slurry of a molding base powder. The slurry was made into a green body powder for molding by the apparatus shown in FIG. Specifically, alumina spheres having a diameter of 2 mm were used as the drying medium, and other conditions were set as follows: A hot air duct 4 in which the drying medium holding portion 5 was formed.
Inner diameter R2: about 200 mm; filling depth t1 of the drying medium 2: about 150 mm; temperature of hot air: 160 ° C .; flow rate of hot air: 3 m / s. The 50% particle size of the obtained green body powder for molding was 0.6.
The 90% particle diameter was 1.0 μm, and the BET specific surface area value was 10 m ² / g.

Next, a spherical molded body having a diameter of about 1.5 mm was prepared by subjecting the green body powder for molding to tumbling granulation. The obtained spherical molded body was subjected to 14 atmospheric pressure nitrogen atmosphere.
After firing at 00 ° C, 1500 ° C, 1600 ° C, and 1700 ° C for 3 hours, a ball having a diameter of about 1 mm was obtained by polishing.

While calculating the volume from the diameter of the obtained ball, the density is obtained by dividing the weight W (unit: g) by the volume, and the relative density is obtained by dividing the weight by the true density. Was. In addition, the structure of the polished spherical surface was observed with a scanning electron microscope (SEM: magnification of 1000), and from the observed image, a void having a size of 2 μm to 10 μm and a size of 0.5 μm in a visual field of 50 μm × 50 μm. The number of voids smaller than 2 μm was measured. FIG. 19 is an optical microscope observation image of each ball surface ((a) 1400 ° C., (b) 1500 ° C., (c) 16).
00 ° C, (d) 1730 ° C). The frame line in the image is 50μ
Represents the field of view mx 50 μm.

The ball obtained was assembled into a ballpoint pen shown in FIG. 18, and a writing test was performed by drawing a straight line with an aqueous ink. The test was performed by visually observing the state of the drawn line after writing 1000 m.
In addition, the judgment was made according to the following: "線": line drawing with little blur, etc .; "X": blurred line. Table 1 shows the above results.

[0082]

[Table 1]

From the above results, it was found that the size was 2 μm to 10 μm.
The following voids have 5 to 30 balls, and the voids having dimensions of 0.5 μm or more and less than 2 μm use balls having 20 to 200 balls.
It can be seen that good results have been obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a process of rolling granulation.

FIG. 2 is a process explanatory view following FIG. 2;

FIG. 3 is an explanatory view illustrating some molded cores.

FIG. 4 is an explanatory view illustrating some examples of a method for producing a molded core.

FIG. 5 is a view for explaining the progress of a rolling granulation forming step.

FIG. 6 is a schematic diagram showing a cross-sectional structure of a ball manufactured by a rolling granulation method.

FIG. 7 is an optical microscope observation image showing an example of a cross-sectional structure of a ball.

FIG. 8 is a longitudinal sectional view conceptually showing an example of an apparatus for producing a green body powder for molding.

FIG. 9 is a diagram for explaining the operation of the apparatus of FIG. 1;

FIG. 10 is an operation explanatory view following FIG. 2;

FIG. 11 is a diagram illustrating the concept of a primary particle diameter and a secondary particle diameter.

FIG. 12 is an explanatory diagram showing the concept of a relative cumulative frequency.

FIG. 13 is a schematic view showing an example of a form of forming pores or voids in a ceramic ball.

FIG. 14 is an explanatory view showing an example of the manufacturing process of the ballpoint pen.

FIG. 15 is an explanatory view following FIG. 14;

FIG. 16 is an explanatory view following FIG. 15;

FIG. 17 is an explanatory view following FIG. 16;

FIG. 18 is an explanatory view showing an example of the ballpoint pen of the present invention.

FIG. 19 is an optical microscope observation image of a ball surface used in an effect confirmation experiment of the present invention.

FIG. 20 is a view for explaining the definition of the gap size.

[Explanation of symbols]

 10k Molding base powder 50 Molding core 90 Ball (spherical sintered body) 91,92 Closed pore 93,94 Void 95 Ceramic ball for ballpoint pen 107 Ball seat part 120 Ballpoint pen

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C04B 35/58 102Y F term (reference) 2C350 GA03 HA09 HA12 NC01 NC02 NC14 NE01 4G001 BA03 BA09 BA32 BB03 BB09 BB32 BC11 BC13 BC22 BC71 BD12 BE15 BE34 4G019 FA11 FA13 4G030 AA12 AA36 AA52 CA07 CA09 GA04 GA19 GA32

Claims (14)

[Claims] At least a surface layer portion is made of ceramic, and a void having a size of 2 μm or more and 10 μm or less per 50 μm × 50 μm area of a ball surface is provided.
30 voids having a size of 0.5 μm or more and less than 2 μm
A ceramic ball for a ballpoint pen, wherein 200 ceramic balls are formed. 2. The ceramic having a silicon nitride content of 8%.
The ceramic ball for a ball-point pen according to claim 1, wherein the ceramic ball is at least 5% by weight of silicon nitride ceramic. 3. A ceramic ball for a ballpoint pen, characterized in that at least the surface layer is made of a silicon nitride ceramic having a silicon nitride content of 85% by weight or more. 4. A ceramic ball for a ballpoint pen, comprising a porous silicon nitride ceramic in which closed pores having at least a part of a size of 1 μm or more are dispersed and formed therein. 5. A ceramic ball for a ballpoint pen, comprising a porous silicon nitride ceramic having a relative density of 80 to 98%. 6. A void having a size of 2 μm or more and 10 μm or less per 5 μm × 50 μm area of the ball surface is 5 to 3 μm.
0, 20 to 2 voids with dimensions of 0.5 μm or more and less than 2 μm
The ceramic ball for a ball-point pen according to claim 4 or 5, wherein 00 ceramic balls are formed. 7. A ceramic for a ball-point pen, wherein the outer layer portion is made of at least ceramic, and has a core which is distinguishable from the outer layer portion at the center in a cross-section passing substantially through the center. ball. 8. A spherical molded body is obtained by placing a molding base powder containing a ceramic raw material powder in a granulation container and rolling the aggregate of the molding base powder in the container while rolling the aggregate. A method for producing a ceramic ball for a ballpoint pen, comprising: a rolling granulation forming step of obtaining a ceramic ball for a ballpoint pen; and a firing step of obtaining a ceramic ball for a ballpoint pen by firing the spherical molded body. 9. A molding base powder including a ceramic raw material powder and a molding nucleus coexist in the granulation container, and the molding nucleus is rolled in this state while surrounding the molding nucleus. 9. The method for producing a ceramic ball for a ball-point pen according to claim 8, wherein the molding base powder is adhered and aggregated in a spherical shape to obtain the spherical molded body. 10. The method for producing a ceramic ball for a ballpoint pen according to claim 8, wherein a spherical molded body having a relative density of 61% or more is obtained in the rolling granulation molding step. 11. The spherical molded body having a relative density of 80 to 80.
The method for producing a ceramic ball for a ball-point pen according to any one of claims 8 to 10, wherein the ceramic ball is fired to 98%. 12. The ceramic having a silicon nitride content of 8
The method for producing a ballpoint pen ceramic ball according to claim 11, wherein the ceramic ball is a silicon nitride ceramic of 5% by weight or more, and the firing is performed in a single-stage firing in an atmosphere containing nitrogen at 10 atm or less. 13. The ball-point pen ceramic ball according to claim 1, a ball-seat portion rotatably supporting the ball-point pen ceramic ball at a pen tip position, and the ball-point pen via the ball-seat portion. An ink supply mechanism for supplying ink to a ceramic ball for use. 14. The ball-point pen ceramic ball is made of a silicon nitride ceramic, and at least a portion of the ball seat portion that is in contact with the ball-point ceramic ball is made of an Fe-based material.
The described ballpoint pen.