JP3038640B2 - Inorganic powder filler and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic powder filler used for a high-concentration slurry containing a liquid component and an inorganic powder filler at normal temperature or under heating, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a liquid component containing a large amount of an inorganic powder filler at room temperature or under heating is called a high-concentration slurry. And plastic molding materials,
In the field of using plastic casting materials, semiconductor sealing materials, ceramic materials, various varnishes, and the like, the above-mentioned various materials are often used in a state of a high-concentration slurry. In products manufactured through such a high-concentration slurry, in order to more strongly reflect the properties of the inorganic powder filler used in the product, the content of the inorganic powder filler is increased, and the usability is poor. It has become extremely important to keep the slurry viscosity from becoming too high.

As a technique relating to an inorganic powder filler suitable for obtaining such a high-concentration slurry, an empirical formula such as Fuller or Andreasen which gives a close-packed state with a continuous particle size distribution is applied. The average particle diameter of the inorganic powder filler before compression molding disclosed in Japanese Patent Application Laid-Open No. 5-170967 is reduced by utilizing the width of the particle size distribution by utilizing the tapping filling property of the inorganic powder filler. There is a method using an inorganic powder filler having a volume fraction of 75% or more in a molded product obtained by compression-molding the inorganic powder filler at a pressure maintained after molding.

However, even if these techniques are used, when the content of the inorganic powder filler in the high-concentration slurry is extremely increased, it is difficult to keep the viscosity of the slurry low and to secure the fluidity. is there.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention relates to an inorganic powder filler used for a product which is in a slurry state in a manufacturing process or a use process thereof, wherein the inorganic powder filler in the slurry is used. It is an object of the present invention to provide an inorganic powder filler capable of keeping the viscosity of a slurry low and ensuring fluidity even when the content of the powder is increased, and a method for producing the same.

[0006]

In order to achieve the above object, the inorganic powder filler according to the first aspect of the present invention has a pressure (at which the average particle diameter of the inorganic powder filler before compression molding is maintained even after compression molding). In P), the inorganic powder filler having a volume fraction (φ) of 78% or more of the apparent volume of the molded body obtained by compression-molding the inorganic powder filler is 78% or more. The gradient (K) of the following equation that approximates the relationship between the common logarithm of the pressure (P) at which the average particle size of the powder filler is maintained after compression molding and the volume fraction (φ) at the pressure (P) is as follows: An inorganic powder filler, which is 1 to 5.

Φ = KlogP + α (α in the formula represents a constant.) The inorganic powder filler according to claim 2 is the same as the inorganic powder filler according to claim 1, The material is at least one selected from the group consisting of amorphous silica, crystalline silica, alumina, aluminum nitride, boron nitride, and silicon carbide.
It is characterized by containing inorganic powder of various materials.

A third aspect of the present invention is directed to a method for producing an inorganic powder filler according to the first or second aspect, wherein the surface of the inorganic powder is a coupling agent, a ketone or the like. And at least one selected from the group consisting of alcohols.

Hereinafter, the present invention will be described in detail. As the material of the inorganic powder filler used in the present invention, talc, calcium carbonate, barium sulfate, clay, amorphous silica, crystalline silica, alumina, aluminum nitride, boron nitride, silicon carbide, zirconia, titania, silicon nitride, titanium Barium acid or the like can be exemplified, but any inorganic material is acceptable, and the material is not limited to the above-mentioned exemplified materials. In applications where high thermal conductivity is important, the material of the inorganic powder filler is at least one material selected from the group consisting of amorphous silica, crystalline silica, alumina, aluminum nitride, boron nitride and silicon carbide. Desirably.

In the compression molding of the inorganic powder filler in the present invention, only the inorganic powder filler is compression-molded, and the pressure (P) is determined by the average particle diameter of the inorganic powder filler before compression molding. This pressure is maintained after molding. If the pressure is too high, the particles of the inorganic powder filler are destroyed, and the average particle diameter of the inorganic powder filler after compression molding is not maintained at the average particle diameter before compression molding. Is in a state different from that of the inorganic powder filler contained in the slurry. And when the pressure at the time of compression molding is extremely high, the particles are destroyed,
A void is not contained in the obtained molded body, that is, the volume fraction (φ) of the inorganic powder filler occupying the apparent volume of the molded body approaches 100%. Therefore, in the present invention, the pressure (P) during the compression molding is set so that the inorganic powder filler is present in the compact obtained by compression molding in the same state as the inorganic powder filler contained in the slurry. The process is performed so that the average particle diameter of the inorganic powder filler before molding is maintained within a pressure range that can be maintained after compression molding.

Next, the volume fraction (φ) of the inorganic powder filler in the apparent volume of the compact obtained by compression-molding the inorganic powder filler in the present invention will be described. N species used as the inorganic powder filler (n is an integer of 1 or more) of the respective true specific gravity of d _i of the inorganic powder, an integer in each of the mixing weight W _i (i is 1~n of each inorganic powder ), The true specific gravity d of the entire inorganic powder filler is a value calculated by the following equation (A).

D = ΣW _i / Σ (W _i / d _i ) (A) And, the volume fraction φ (%) of the inorganic powder filler in the apparent volume of the compact obtained by compression molding. Is calculated by the following equation (B), where W (g) is the weight of the inorganic powder filler, and V (cc) is the apparent volume of a molded product obtained by compressing the filler.

[0013] φ = 100 (W / d) / V --- (B) Then, molding is performed under a condition that the average particle diameter of the inorganic powder filler before compression molding is less than the maximum pressure (Pmax) maintained after compression molding. The volume fraction φ of the inorganic powder filler of the molded body thus obtained is always smaller than the volume fraction (φmax) of the inorganic powder filler of the molded body when molded at the above maximum pressure (Pmax).

In the present invention, it is important that the volume fraction φ (%) of the inorganic powder filler occupying 78% or more of the apparent volume of the compact obtained by using the above-mentioned calculation formula (B) is 78% or more. , Less than 78%, the object of the present invention is to increase the content of the inorganic powder filler in the high-concentration slurry, and
It is difficult to keep the viscosity of the slurry low.

Further, in the present invention, the common logarithm of the pressure (P) at which the average particle size of the inorganic powder filler before compression molding is maintained after compression molding and the volume percentage (φ) at that pressure (P) The gradient (K) of the above equation approximating the relationship
It is important that Because the gradient (K) is 5
When the concentration exceeds the above, it becomes difficult to increase the content of the inorganic powder filler in the high-concentration slurry and keep the viscosity of the slurry low, and the inorganic powder filler having a gradient (K) of less than 1 is This is because it is difficult to obtain practically. In addition,
The range for obtaining the approximate expression is preferably a pressure range as wide as possible, but specifically, it may be obtained in a pressure range of about 60 to 300 kgf / cm ² .

In the method for producing an inorganic powder filler according to a third aspect of the present invention, the surface of the inorganic powder filler is coated with at least one member selected from the group consisting of coupling agents, ketones and alcohols. Processing. Examples of the coupling agent used here include so-called silane-based coupling agents and titanate-based coupling agents, and any compound having an atomic group other than an alkoxy group and an alkoxy group bonded to a metal atom may be used. It is not limited to the coupling agents exemplified above. The ketones used here are not particularly limited, and examples thereof include acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK). The alcohol used here is not particularly limited, but examples thereof include methanol, ethanol, propanol, and isopropanol.

[0017]

The dense state of the inorganic powder filler in the compact obtained by compression molding the inorganic powder filler is similar to the state of the inorganic powder filler in the high-concentration slurry. Therefore, the volume fraction of the inorganic powder filler in the compact (φ)
That the content of the inorganic powder filler in the high-concentration slurry is increased.

The fact that the volume fraction (φ) of the inorganic powder filler in the compact is large means that there are few voids remaining between the particles of the inorganic powder filler in the compact. Considering a composite material in which the void portion is filled with a liquid component, when the volume of the liquid component is equal to or smaller than the volume of the void portion, the contact between the particles hinders the deformation of the entire composite material and does not flow at all. On the other hand,
When the volume of the liquid component is larger than the volume of the void portion, the particles are separated by the liquid component, so that the particles can move to some extent freely, and the entire composite can be deformed, that is, a slurry that can flow. State. Therefore, in the case of a high-concentration slurry having the same content of the inorganic powder filler, it is better to use the one having a large volume fraction (φ) of the inorganic powder filler in the formed body of the inorganic powder filler, and the fluidity of the high-concentration slurry is higher. Better and lower viscosity.

The effect of the pressure (P) at the time of compression molding on the volume fraction (φ) of the inorganic powder filler in the molded body of the inorganic powder filler is expressed by the above approximate expression. The fact that the slope (K) in this approximate expression is small means that even when the pressure applied to the inorganic powder filler increases, the increase in φ is small. Focusing on the process of compression molding from a state where no pressure is applied to the inorganic powder filler to a maximum pressure (Pmax) at which the average particle diameter of the inorganic powder filler before compression molding is maintained even after compression molding. , Pmax, the amount of work required to reach the volume fraction (φmax) is small. Conversely, a large gradient (K) in the approximate expression means that a large amount of work is required to reach the volume fraction (φmax) at Pmax. In other words, the inorganic powder filler having a small gradient (K) in the approximation formula easily deforms the inside of the powder layer with a small amount of work to be in a high filling state, and the gradient (K) is large. With a small amount of work, the inorganic powder filler is less likely to be deformed inside the powder layer and is less likely to be in a highly filled state.

In an ultra-high-concentration slurry having an extremely high content of inorganic powder filler, the distance between the fillers is extremely small because the liquid component is small, so that the properties of the inorganic powder filler as a whole slurry are reduced. It is thought that it appears strongly in the nature of. In addition, in order to prepare a high-concentration slurry based on the inorganic powder filler and the liquid component, both must be mixed and the inorganic powder filler must be dispersed, and the high-concentration slurry other than the characteristics of the inorganic powder filler must be mixed. If the conditions for preparing the slurry are comparable, the amount of work received by the inorganic powder filler in the slurry preparation process is also similar. If the amount of work received by the inorganic powder filler is substantially the same, the inorganic powder filler having a small K tends to be in a high filling state as compared with the one having a large K, and the viscosity of the slurry is low.

Therefore, in the case of an ultrahigh-concentration slurry having an extremely high content of inorganic powder filler, the pressure (P) at which the average particle size of the inorganic powder filler before compression molding is maintained even after compression molding.
The volume fraction (φ) of the inorganic powder filler in the apparent volume of the molded body obtained by compression molding the inorganic powder filler is 7
When the gradient (K) in the above expression is 8% or more and the gradient (K) is 5 or less, the viscosity of the high-concentration slurry is reduced.

Further, the inorganic powder filler is amorphous silica,
Including inorganic powder of at least one material selected from the group consisting of crystalline silica, alumina, aluminum nitride, boron nitride and silicon carbide has the function of increasing the thermal conductivity of a product obtained via a slurry. I do.

One of the causes of the increase in the K of the inorganic powder filler is that the water adsorbed on the particle surfaces causes the inorganic powders to combine with each other by a liquid crosslinking phenomenon to form a strong aggregate consisting of a plurality of particles. It is thought that it is doing. Treating an inorganic powder that is considered to form such an aggregate with a coupling agent, ketones or alcohols, even when the coupling agent, ketones or alcohols displaces water on the particle surface. Alternatively, even when the particles are dissolved in water on the particle surface, the surface tension of the substance covering the particle surface is lower than that of water, so that it functions to reduce the strength of the aggregate. For this reason, when the surface of the inorganic powder is treated with a coupling agent, a ketone or an alcohol, the K of the inorganic powder filler becomes smaller than before the treatment, so that an inorganic powder filler having a small K is easily obtained.

In addition, the surface treatment of the inorganic powder with a coupling agent has the effect of reducing K and, in addition, in a composite material in which the liquid component constituting the slurry is solidified by means such as hardening or coagulation. The so-called coupling effect between the inorganic powder filler and the solidified liquid component improves the adhesion.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Of course, the present invention is not limited to the following examples.

The inorganic powders shown in Table 1 below were used.

[0027]

[Table 1]

In the following Examples and Comparative Examples, inorganic powder
60kgf / cm for compression molding of filler ^Two, 120kgf /
cm^Two, 180kgf / cm^Two, 240kgf / c
m^Two, 300kgf / cm^TwoChange the pressure level
Pressure was applied to obtain a cylindrical molded body. Pressure 300
kgf / cm^TwoPowder obtained by crushing the compact at the time of
As a result of measuring the average particle size of the
Since this was the same as the diameter measurement result, the particle
No destruction has occurred. In addition, the following examples and
Inorganic powder filling in the apparent volume of the compact in Comparative Examples and Comparative Examples
The volume fraction of filler (φ) is calculated from the diameter and thickness of the molded body
Volume V and weight W of the molded product to be filled and inorganic powder filling
This is a value calculated from the true specific gravity d of the material by the above-described equation (B).
And, in the following, the pressure is 300 kgf / cm^TwoMeasured with
Is φ₃₀₀It is written.

The relationship between the common logarithm of the pressure (P) at which the average particle size of the inorganic powder filler before compression molding is maintained after compression molding and the volume fraction (φ) at that pressure (P) is as follows. The slope (K) of the approximating equation is 60 kgf / cm ² , 120 k
gf / cm ² , 180 kgf / cm ² , 240 kgf /
Each φ measured at each pressure (P) of cm ² and 300 kgf / cm ² is plotted on the figure, with the horizontal axis representing the common logarithm of P and the vertical axis representing φ, and calculating the slope of the straight line by the least square method. I asked. As a typical example of a diagram in which the gradient (K) is obtained, FIG.
The figure which calculated | required the gradient (K) in Example 1 is shown in FIG. FIG. 1 shows points where the measured data are plotted and a straight line calculated by the least square method using the data.
The slope of this straight line is K.

In the following, the amounts of each component are parts by weight and all parts are abbreviated. (Examples 1 to 3 and Comparative Examples 1 and 2) Alumina powders A1, A2, A3, A4 and aluminum nitride powder N1 shown in Table 1 were mixed in the amounts shown in Table 2 to obtain a mixed powder (filled with inorganic powder). materials) and compression molded to measure phi ₃₀₀ and slope (K),
Table 2 shows the obtained results. Next, the remaining mixed powder (inorganic powder filler) subjected to the compression molding was weighed by the amount of the mixed powder to obtain the slurry shown in Table 2, and 20 parts of toluene and 20 parts of ethanol were mixed. The mixture was stirred and mixed with a homodisper (manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a slurry. The volume content of the inorganic powder filler in the slurry was 75% by volume in Examples 1 and 3 and Comparative Examples 1 and 2, and was 77% by volume in Example 2. Table 2 shows the results obtained by measuring the viscosity of the obtained slurry with a B-type rotational viscometer.

[0031]

[Table 2]

As is clear from the results in Table 2, φ is 78
% Of the inorganic powder filler, and the slurries of Examples 1 to 3 in which the inorganic powder filler has a gradient (K) of 5 or less, the slurry (K) has a gradient (K) of 5 or less. The viscosity is lower than those of the slurries of Comparative Examples 1 and 2, which use more than these. In particular, in Example 2, the volume content of the inorganic powder filler (alumina powder) in the slurry was as high as 77% by volume, and the slurry was highly filled. However, the viscosity of the slurry was such that the volume content of the alumina powder was 75% by volume. Is lower than Comparative Example 1. As described above, in the inorganic powder filler having φ of 78% or more, the use of the inorganic powder filler having a K of 5 or less increases the content of the inorganic filler in the slurry and reduces the viscosity of the slurry. It was confirmed that it was effective to keep it low.

If it is possible to increase the content of the high thermal conductive ceramic powder such as alumina in the slurry and to keep the viscosity of the slurry low, the production of a sintered body of the inorganic powder is difficult. It is possible to reduce the dimensional change of the sintered body, and in the case of manufacturing a heat conductive paste (grease), it is necessary to maintain good usability of the heat conductive paste and increase the heat conductivity. Since it becomes possible, the present invention is useful in the field of manufacturing ceramic sintered bodies and heat conductive pastes. Further, if the present invention is applied to coal powder as an inorganic powder, coal oil mixture (COM) or coal water
It is also useful in the field of producing liquefied coal fuel such as mixture (CWM).

(Examples 4 to 7 and Comparative Examples 3 to 5) The silica powders S1 to S4 and the alumina powder A4 shown in Table 1 were used in Table 3
Were mixed in the amounts shown in the resulting mixed powder (inorganic powder filler) was compression molded to measure the phi ₃₀₀ and slope (K),
Table 3 shows the obtained results. Next, a molding material was prepared by using the remaining mixed powder (inorganic powder filler), epoxy resin, curing agent, curing accelerator, and release agent used in the compression molding in the amounts shown in Table 3. Generally, even if the molding material is solid at room temperature, the resin component becomes liquid during the manufacturing process and the molding process, and becomes a slurry state. The epoxy resin is ESCN195 manufactured by Sumitomo Chemical Co., Ltd.
XL, Tamanol 752 (trade name) manufactured by Arakawa Chemical Industry Co., Ltd. as a hardening agent, triphenylphosphine manufactured by Hokuko Chemical Industry Co., Ltd. as a hardening accelerator, and natural carnauba wax as a release agent. Was used. As for the production of the molding material, a mixture of each raw material in a predetermined amount was kneaded with a mixing roll at 90 ° C. for 10 minutes, cooled to room temperature, and pulverized to obtain a molding material. The volume percentage of the inorganic powder filler in these molding materials in terms of the true specific gravity was 73% by volume in Example 5, and 70% by volume in Examples 4, 6, 7 and Comparative Examples 3 to 5. there were. The performance of the obtained molding material was measured by the following method, and the obtained results are shown in Table 3.

(Gel time): Measured at 175 ° C. using a Curastometer V type manufactured by Orientec Co., Ltd. (Melt viscosity): Flow tester CF manufactured by Shimadzu Corporation
Using T500A type, temperature 175 ° C, load 10kgf,
The minimum melt viscosity was determined with a nozzle size of 1 mm (diameter) x 10 mm. (Spiral flow): The flow length of the sample during transfer molding at 175 ° C. was measured using a mold dedicated to spiral flow in accordance with the EMMI standard.

[0036]

[Table 3]

As is clear from the measurement results of the melt viscosity and the spiral flow shown in Table 3, the inorganic powder filler having φ of 78% or more was used, and the gradient (K) of the inorganic powder filler was 5 or less. Examples 4, 6, and 7 using
Has a lower melt viscosity and a longer spiral flow than the slurries of Comparative Examples 3 to 5 in which the gradient (K) exceeds 5. Also, in Example 5, the volume content of the inorganic powder filler in the molding material was less than that of Comparative Examples 3 to 5.
It is higher and more filled, but has a lower melt viscosity and a longer spiral flow. This allows
Φ is 78% for products that have undergone high-concentration slurry
As described above, the use of the inorganic powder filler having a K of 5 or less is effective in increasing the content of the inorganic powder filler and maintaining a low viscosity (melt viscosity) of the slurry. Was confirmed.

As long as the content of the inorganic powder filler in the molding material is high, the packing is high, and the fluidity can be kept high, the use of amorphous silica as the inorganic powder filler will reduce the linear expansion coefficient. It is possible to obtain molded products with small dimensional changes, and if high thermal conductive ceramic powders such as crystalline silica, alumina, aluminum nitride, silicon nitride, etc. are used as the inorganic powder filler, molding with high thermal conductivity and high heat dissipation The present invention is also useful in the field of molding materials, since it is possible to obtain articles.

(Examples 8 and 9) Alumina powders A1, A2, A3, A4 and aluminum nitride powder N1 shown in Table 1 were mixed in the amounts shown in Table 4 to obtain mixed powders. Example 8
Is obtained with the same formulation as Comparative Example 1,
Example 9 was obtained with the same formulation as Comparative Example 2. 10 g of the organic solvent shown in Table 4 was sprayed and mixed with 1000 g of the obtained mixed powder to perform a surface treatment of the inorganic powder. The resulting surface treated mixed powder (inorganic powder filler) was compression molded to measure the phi ₃₀₀ and slope (K), the results are shown in Table 4. Next, the remaining surface-treated mixed powder (inorganic powder filler) subjected to the compression molding was weighed by the “mixed powder blending amount for obtaining a slurry” shown in Table 4, and the amount of toluene shown in Table 4 was measured. And ethanol were stirred and mixed with a homodisper (manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a slurry. The volume content of the inorganic powder filler in each of the obtained slurries was 75% by volume as in Comparative Examples 1 and 2. The results of measuring the viscosity of the obtained slurry with a B-type rotational viscometer were shown in Comparative Examples 1 and 2.
(Same as data in Table 2) are shown in Table 4.

[0040]

[Table 4]

As is clear from the results shown in Table 4, the inorganic powder filler obtained by treating the surface of the inorganic powder filler with alcohols or ketones is more effective than the inorganic powder filler without surface treatment. It was also confirmed that the value of K also decreased, and as a result, the viscosity of the slurry decreased.

(Examples 10 and 11) With respect to 1000 g of the mixed powder obtained in the same manner as in Comparative Example 3, Table 5
10 g of an organic solvent (ethanol) or a coupling agent [Epoxy silane coupling agent manufactured by Nippon Unicar Co., Ltd., product number A187] shown in (1) was sprayed and mixed to perform surface treatment of the inorganic powder. The resulting surface treated mixed powder (inorganic powder filler) was compression molded, phi ₃₀₀
And the gradient (K) were measured, and the obtained results are shown in Table 5.
Next, the same as Comparative Example 3 described above except that the remaining mixed powder (inorganic powder filler), epoxy resin, curing agent, curing accelerator, and release agent used in the compression molding were used in the amounts shown in Table 5. Preparation and evaluation of the molding material were performed by the method described in (1). The epoxy resin is ESCN195XL manufactured by Sumitomo Chemical Co., Ltd.
As a curing agent, Tamanol 7 manufactured by Arakawa Chemical Industry Co., Ltd.
52 (trade name), triphenylphosphine manufactured by Hokuko Chemical Industry Co., Ltd. as a curing accelerator, and natural carnauba wax as a release agent. The volume content of the inorganic powder filler in the obtained molding materials of Examples 10 and 11 in terms of the true specific gravity was 70% by volume. The performance of the obtained molding material was measured in the same manner as in Example 4, and the measurement results are shown in Table 5.

[0043]

[Table 5]

As is evident from the results in Table 5, the inorganic powder filler obtained by treating the surface of the inorganic powder filler with an alcohol or a coupling agent is the same as the inorganic powder filler without the surface treatment. It was confirmed that the value of K was lower than that, and as a result, the viscosity of the slurry (melt viscosity) was lower.

[0045]

When the inorganic powder filler according to the first aspect of the present invention is used in a product which is in a slurry state during the production process or the use process, the content of the inorganic powder filler in the slurry is increased. Also, the viscosity of the slurry is kept low, and the fluidity of the slurry can be ensured.

According to the inorganic powder filler of the second aspect of the present invention, in addition to the above effects, the thermal conductivity of a product using the inorganic powder filler can be increased.

In the method for producing an inorganic powder filler according to claim 3 of the present invention, the inorganic powder is treated with at least one selected from the group consisting of coupling agents, ketones and alcohols. The strength of the aggregate in the inorganic powder filler is reduced. Therefore, according to this method for producing an inorganic powder filler, an inorganic powder filler having a small K can be obtained as compared with the case without treatment.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the inorganic powder filler of Example 1;
4 is a graph showing a relationship between a common logarithm of pressure (P) and a filler volume fraction (φ) in an apparent volume of a molded body obtained by compression-molding an inorganic powder filler at the pressure (P).

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C04B 35/58 104S 103R (56) References JP-A-5-170967 (JP, A) JP-A-6-144915 (JP, A) JP-A JP-A-7-82037 (JP, A) JP-A-5-267505 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/622 C04B 35/10 C04B 35/14 C04B 35 / 626 C04B 35/628

Claims (3)

(57) [Claims] 1. An inorganic powder filler having an average particle diameter before compression molding, which is maintained at a pressure (P) after compression molding. In an inorganic powder filler in which the volume fraction (φ) of the powder filler is 78% or more, the average particle size of the inorganic powder filler before compression molding and the common logarithm of the pressure (P) maintained after compression molding are as follows: An inorganic powder filler characterized in that the gradient (K) of the following equation approximating the relationship of the volume fraction (φ) at the pressure (P) is 1 to 5. φ = KlogP + α −−−− (α in the formula represents a constant) 2. The method according to claim 1, wherein the inorganic powder filler contains at least one inorganic powder selected from the group consisting of amorphous silica, crystalline silica, alumina, aluminum nitride, boron nitride and silicon carbide. The inorganic powder filler according to claim 1, wherein 3. The method for producing an inorganic powder filler according to claim 1, wherein the surface of the inorganic powder is at least one selected from the group consisting of coupling agents, ketones and alcohols. A method for producing an inorganic powder filler, characterized in that the method is performed by the following method.