JP5426463B2 - Filler - Google Patents

Description

  The present invention relates to a filler made of ceramic particles and a method for producing the same.

  The filler is added to a base material such as plastic, rubber, paint, fiber, paper, glass, metal, and improves the physical properties of the base material and contributes to the improvement of workability and the function of the final product. Among these, ceramic particles have stable physicochemical properties and have been variously studied as fillers.

  For example, Patent Documents 1 and 2 disclose fused spherical silica obtained by flame-melting granular silica gel or hydrous silica, which describes that it can be used as a filler for a semiconductor sealing resin composition.

  Patent Document 3 discloses a silica-based filler for a transparent resin composition obtained by firing polyorganosiloxane particles, and describes that it has a broad refractive index of 1.36 to 1.40.

Japanese Patent Laid-Open No. 2-145415 Japanese Patent Laid-Open No. 2-145416 JP 2007-84606 A

  General-purpose resins such as polyethylene, polypropylene, polystyrene, polyester, polycarbonate, polyamide, polyvinyl chloride, acrylic, and silicone have a refractive index of 1.48 to 1.60. In order to use a base material in which a filler is added to these resins for a transparent member such as a protective cover or a sealing material, it is necessary to improve light transmittance. In that case, the refractive index of the resin and the refractive index of the filler are required. The rate needs to be as close as possible.

  However, the silica particles disclosed in the above patent documents are all amorphous and have a low refractive index of 1.44 or less.

  In the filler used for a transparent member, this invention provides the filler which can improve the light transmittance of a transparent member, and its manufacturing method.

The filler of the present invention is a filler made of ceramic particles, and the ceramic particles satisfy the following requirements (I) to (V).
(I) The content of SiO ₂ is 97.0% by weight or more,
(II) The relative background height in the X-ray diffraction spectrum is 3.0 to 10.0,
(III) The average particle size is 0.01 to 50 μm,
(IV) The sphericity is 0.95 or more,
(V) Refractive index is 1.48-1.60.

  The filler production method of the present invention is a filler production method that satisfies the above requirements (I) to (V), and is prepared by adding an alkali metal compound and an alkaline earth metal compound to amorphous silica particles obtained by a flame melting method. One or more metal compounds selected from the above are added and heat treated.

  The various physical property values in the present invention are specifically values measured by the measurement methods described in the examples.

  According to the filler of the present invention, when it is added to a substrate to form a transparent member, the light transmittance of the transparent member can be improved. Moreover, according to the filler manufacturing method of the present invention, the filler of the present invention can be easily manufactured.

  Hereinafter, the physical properties of the filler (ceramic particles) of the present invention will be described.

[Content of SiO ₂ ]
Ceramic particles used in the present invention is mainly composed of SiO _2. The content of SiO ₂ is to suppress the coloring of the ceramic particles themselves, to improve the light transmittance of the base material to which the filler is added, and to the base material to which the filler is added by adjusting the refractive index within a predetermined range. From the viewpoint of improving the light transmissivity, it is 97.0% by weight or more, preferably 97.5% by weight or more, and more preferably 98.0% by weight or more. Moreover, from the viewpoint of adjusting the refractive index within a predetermined range and improving the light transmittance of the base material to which the filler is added, it is preferably less than 100% by weight, more preferably 99.9% by weight or less, and 99.8%. More preferably, it is not more than% by weight.

  In addition, the content of elements other than Si, for example, transition metal elements such as Fe and Mn is 150 ppm or less from the viewpoint of reducing the coloration of the ceramic particles themselves and improving the light transmittance of the substrate to which the filler is added. Preferably, 100 ppm or less is more preferable, and 80 ppm or less is more preferable. The transition metal element such as Fe may be contained in the raw material silica or may be mixed from the member or the like during the manufacturing process.

[Relative background height in X-ray diffraction spectrum]
The relative background height of the ceramic particles used in the present invention represents the ratio of the amorphous part and the crystalline part of the filler. The higher the value is, the larger the proportion of the amorphous portion is, and the smaller the proportion is, the larger the proportion of the crystalline portion is. The relative background height is 10.0 or less from the viewpoint of making the refractive index 1.48 or more and from the viewpoint of improving the hardness of the ceramic particles themselves to improve the hardness of the substrate to which the filler is added. Yes, 8.5 or less is preferable, and 7.0 or less is more preferable. Further, from the viewpoint of improving the transparency of the ceramic particles themselves, and from the viewpoint of suppressing wear of the mold during molding and reducing contamination, it is 3.0 or more, preferably 3.5 or more, and 4.0 or more. Is more preferable. That is, when these viewpoints are put together, the relative background height is 3.0 to 10.0, preferably 3.5 to 8.5, and more preferably 4.0 to 7.0. Regarding the control of the relative background height within the above range, in the production method described later, by increasing the addition amount of the alkali metal compound and / or alkaline earth metal compound, or increasing the heat treatment temperature, By increasing the heat treatment time, the relative background height can be reduced.

[Average particle size]
The average particle size of the ceramic particles used in the present invention is from the viewpoint of suppressing aggregation and coalescence of the ceramic particles, not increasing the particle size distribution of the ceramic particles, and improving the strength of the base material to which the filler is added. 0.01 μm or more, preferably 0.1 μm or more, more preferably 1.0 μm or more, and further preferably 2.0 μm or more. Further, from the viewpoint of improving the light transmittance of the base material to which the filler has been added and from the viewpoint of improving the strength of the base material to which the filler has been added, it is 50 μm or less, preferably 20 μm or less, more preferably 13 μm or less, 10 μm or less is more preferable. That is, taking these viewpoints together, the average particle size of the ceramic particles is 0.01 to 50 μm, preferably 0.1 to 20 μm, more preferably 1.0 to 13 μm, and even more preferably 2.0 to 10 μm. . In order to control the average particle size within the above range, the particle size of the raw material particles introduced into the flame may be adjusted in the production method described later.

[Sphericity]
The sphericity of the ceramic particles used in the present invention suppresses scattering, improves the light transmittance of the substrate to which the filler is added, improves the dispersibility of the filler in the substrate, From the viewpoint of increasing the amount of filler added and from the viewpoint of easily imparting the filler properties to the substrate, it is 0.95 or more, preferably 0.96 or more, and more preferably 0.97 or more. With regard to controlling the sphericity within the above range, the sphericity can be increased by increasing the flame temperature or increasing the residence time in the flame in the production method described later.

[Refractive index]
The refractive index of the ceramic particles used in the present invention is 1.48 to 1.60 from the viewpoint of approximating the refractive index of the base material and improving the light transmittance of the base material to which a filler is added. 49 to 1.59 are preferred. Regarding controlling the refractive index within the above range, in the production method described later, by increasing the addition amount of the alkali metal compound and / or alkaline earth metal compound, or increasing the heat treatment temperature, or setting the heat treatment time. By increasing the length, the refractive index can be increased.

[Production method]
The method for producing the ceramic particles used in the present invention is not particularly limited as long as the above physical properties can be obtained, but the viewpoint that the ceramic particles having the above physical properties can be easily and stably produced, particularly the viewpoint of improving the sphericity of the ceramic particles. Therefore, it is preferable to adopt a flame melting method.

  The flame melting method is a method in which a silica source (starting material) is melted and spheroidized in a flame. According to the flame melting method, amorphous silica particles are usually obtained. Here, the amorphous silica particles refer to particles having a relative background height of 24 or more. As a silica source used as a starting material, silica, silica sand, quartz, cristobalite, amorphous silica, feldspar, pyrophyllite, fumed silica, ethyl silicate, silica sol and the like can be used. In a preferred embodiment, the starting material is dispersed in a carrier gas such as oxygen and charged into the following flame.

  The flame to be used is generated by burning fuel such as propane, butane, methane, liquefied natural gas, LPG, heavy oil, kerosene, light oil, pulverized coal and the like with oxygen. The fuel to oxygen ratio is preferably 1.01 to 1.30 in terms of volume ratio from the viewpoint of complete combustion. From the viewpoint of generating a high-temperature flame, it is preferable to use an oxygen / gas burner. Although the structure of the burner is not particularly limited, the burners disclosed in JP-A-7-48118, JP-A-11-132421, JP-A-2000-205523, JP-A-2000-346318, etc. Can be illustrated.

The concentration of the starting material in the carrier gas is preferably 0.1 to 20 kg / Nm ^{3 and} more preferably 0.2 to 10 kg / Nm ³ from the viewpoint of ensuring sufficient dispersibility of the starting material.

  Further, from the viewpoint of adjusting the refractive index by promoting crystallization, the amorphous silica particles obtained by the flame melting method may be further heat-treated. The temperature of the heat treatment is preferably 1700 ° C. or less, more preferably 1400 ° C. or less, and further preferably 1100 ° C. or less from the viewpoint of not melting the particles obtained by the flame melting method. Moreover, from a viewpoint of promoting crystallization and improving productivity, 600 degreeC or more is preferable, 800 degreeC or more is more preferable, and 1000 degreeC or more is further more preferable. That is, when these viewpoints are put together, the temperature of the heat treatment is preferably 600 to 1700 ° C, more preferably 800 to 1400 ° C, and further preferably 1000 to 1100 ° C. The heat treatment time is related to the heat treatment temperature. If the heat treatment temperature is high, crystallization is promoted in a short heat treatment time, and the refractive index can be increased. The heat treatment time is preferably 0.01 hours or more, more preferably 0.5 hours or more from the viewpoint of promoting crystallization and improving the refractive index. Moreover, from a viewpoint of improving productivity, 100 hours or less are preferable and 24 hours or less are more preferable. That is, taking these viewpoints together, the heat treatment time is preferably 0.01 to 100 hours, and more preferably 0.5 to 24 hours.

  In addition, from the viewpoint of promoting crystallization in the heat treatment step, one or more metal compounds selected from alkali metal compounds and alkaline earth metal compounds are added to the amorphous silica particles as crystallization accelerators for heat treatment. It is preferable to do. As the metal compound, those having high water solubility are preferable, such as chlorides such as sodium, potassium, magnesium and calcium, carbonates, nitrates, sulfates and oxides, or calcium silicate, aluminum silicate, magnesium aluminate and the like. And the like. Of these, calcium nitrate is preferably used as the metal compound from the viewpoint of promoting crystallization.

  The amount of the metal compound added is from the viewpoint of accelerating crystallization of the amorphous silica particles and suppressing melting and fixing, with respect to 100 parts by weight of the amorphous silica particles, alkali metal and / or alkaline earth metal. Is preferably 0.10 parts by weight or more, more preferably 0.15 parts by weight or more, and still more preferably 0.20 parts by weight or more. Further, from the viewpoint of suppressing a decrease in transparency of the ceramic particles themselves due to impurities, and from the viewpoint of improving the sphericity of the ceramic particles, it is preferably 3 parts by weight or less, more preferably 2 parts by weight or less, and 1.5 parts by weight. Part or less is more preferable. That is, when these viewpoints are combined, the amount of the metal compound added is 0.10 to 3 parts by weight in terms of oxide of alkali metal and / or alkaline earth metal with respect to 100 parts by weight of amorphous silica particles. Is preferred, 0.15 to 2 parts by weight is more preferred, and 0.20 to 1.5 parts by weight is even more preferred.

  From the viewpoint of increasing the refractive index, the content of the alkali metal and / or alkaline earth metal oxide in the ceramic particles is preferably 0.10% by weight or more, more preferably 0.15% by weight or more, and 0.20. More preferably by weight. In addition, from the viewpoint of suppressing a decrease in transparency of the ceramic particles themselves due to impurities and improving the sphericity of the ceramic particles, 2.9% by weight or less is preferable, and 2.0% by weight or less is more preferable. More preferably, it is 1.5% by weight or less. That is, taking these viewpoints together, the content of the alkali metal and / or alkaline earth metal oxide in the ceramic particles is preferably 0.10 to 2.9% by weight, preferably 0.15 to 2.0% by weight. % Is more preferable, and 0.20 to 1.5% by weight is more preferable.

  The transparent member obtained by adding the filler of the present invention to a substrate is useful for a protective cover, a sealing material and the like. In this case, the substrate used is not particularly limited as long as it is made of a transparent material, and glass, resin, transparent liquid, and the like can be used. For example, in the case of glass, alkali glass such as soda-lime glass or borosilicate glass is preferably used. Further, as long as the resin is used, an energy ray curable resin such as a thermoplastic resin, a thermosetting resin, or an ultraviolet curable resin can be used. For example, a polyolefin resin such as polyethylene and polypropylene, a polyester resin such as polyethylene terephthalate, Examples thereof include cellulose resins such as cellulose and butyl cellulose, polystyrene, polyurethane, polyvinyl chloride, polyamide, acrylic resin, polycarbonate resin, epoxy resin, phenol resin, and silicone resin. Further, as long as it is a transparent liquid, clove oil, silicon oil, or the like can be used.

  Among the above listed substrates, polyethylene, polypropylene, and polyamide are preferable because they can further improve the light transmittance when combined with the filler of the present invention.

  From the viewpoint of ensuring good light transparency of the transparent member, the refractive index of the base material is preferably 1.48 to 1.60, more preferably 1.50 to 1.58, and 1.52 to 1.56. Further preferred. Further, the difference (absolute value) between the refractive index of the substrate and the refractive index of the ceramic particles is preferably 0.05 or less, and preferably 0.03 or less from the viewpoint of improving the light transmittance of the substrate to which the filler is added. More preferred is 0.01 or less.

  From the viewpoint of ensuring good light transparency of the transparent member, the amount of filler added to 100 parts by weight of the substrate is preferably 900 parts by weight or less, more preferably 500 parts by weight or less, and even more preferably 300 parts by weight or less. . Further, from the viewpoint of improving the mechanical properties (strength, rigidity, hardness) of the transparent member, the amount of filler added to 100 parts by weight of the base material is preferably 25 parts by weight or more, more preferably 40 parts by weight or more, and still more preferably. Is 60 parts by weight or more. That is, taking these viewpoints together, the amount of filler added to 100 parts by weight of the substrate is preferably 25 to 900 parts by weight, more preferably 40 to 500 parts by weight, and even more preferably 60 to 300 parts by weight.

  The method of adding the filler of the present invention to the substrate is not particularly limited. When the substrate is a resin, (a) a method of kneading the filler into the substrate using a kneader, (b) the substrate resin A method of forming a mixture by mixing a filler in a solution, emulsion, dispersion or suspension of (1), and (c) adding a filler to the monomer of the base resin in the step of synthesizing the base resin, and polymerizing. It can add by methods, such as a method. From the viewpoint of versatility, the method (a) is preferable. In this case, a kneader such as a ball mill, a roller mill, or a kneader can be used. When the substrate is a transparent liquid, it can be added by (d) a method of mixing a filler in the substrate using a stirrer.

  Examples and the like specifically showing the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.

<Content of SiO ₂ >
For ceramic particles, X-ray fluorescence method (JIS R2216 "fluorescent X-ray analysis of refractory brick and fire mortar") performing elemental analysis by, to quantify the concentration of Si, containing SiO ₂ by converting the SiO ₂ The amount was determined.

<Content of oxide of alkali metal or alkaline earth metal>
The ceramic particles are subjected to elemental analysis by the fluorescent X-ray method (JIS R2216 “Fluorescent X-ray analysis method for refractory bricks and refractory mortars”), and the concentration of alkali metal or alkaline earth metal is quantified and converted to oxide. The content of alkali metal or alkaline earth metal oxide was determined.

（但し、Ｎは２θ＝１０°〜３５°の範囲で、ＣｕのＫα線を使用し粉末Ｘ線回折スペクトルを測定したときの測定点数で、その数は１５０１である。） <Relative background height>
A sample (ceramic particle) is filled in a glass holder, a powder X-ray diffraction spectrum is measured using RINT 2500 manufactured by Rigaku Corporation and Cu Kα ray is used as an X-ray source, and the obtained diffraction spectrum is described in the literature. In the method (Abraham Savitzky et.al., Analytical Chemistry, 36 (8), 1627 (1964)), smoothing was performed under the condition of 25 points. After that, the background part was extracted according to the method described in the literature (Sonneveld, E. J and Visser, JW, J. Appl. Cryst. 8, 1 (1975)) under the condition of a score interval of 40 points and a repeat count of 32 times. Based on the following formula 1, the background height F of the ceramic particles was calculated. Next, standard alumina (National Institute of Standard & Technology, Standard Reference Material 674a) was filled in a glass holder and measured in the same manner as described above to obtain the background height A of standard alumina. Then, the background height F of the ceramic particles was divided by the background height A of standard alumina, and the obtained value was defined as the relative background height.

(However, N is the number of measurement points when the powder X-ray diffraction spectrum is measured using Cu Kα ray in the range of 2θ = 10 ° to 35 °, and the number is 1501.)

<Average particle size>
For the raw material particles and ceramic particles, D50 (medium particle size of 50% by volume) was measured by a laser diffraction / scattering method using LA-920 manufactured by HORIBA, Ltd., and the obtained value was taken as the average particle size. That is, while applying ultrasonic waves, the particles were dispersed in ion-exchanged water, and the average particle diameter was measured in a state where the transmittance of the dispersion was 80 to 90%. In the measurement, the relative refractive index was not used.

<Sphericality>
The ceramic particles are observed with a real surface view microscope VF-7800 manufactured by Keyence Corporation, and the area of the particle projection cross section and the perimeter of the cross section of the obtained SEM image are obtained. Then, [the same area as the area of the particle projection cross section] Of the true circle] / [perimeter of the projected particle cross section] was calculated, and the values obtained for each of the arbitrary 50 ceramic particles were averaged to determine the sphericity.

<Refractive index>
The refractive index of the ceramic particles and the substrate was determined by the B method (immersion method using a microscope (Becke's line method)) in JIS K7142 “Method for measuring the refractive index of plastic”. However, instead of the immersion liquid described in JIS K7142, a Cargill standard solution (manufactured by Moritex Co., Ltd.) was used as the immersion liquid, and the immersion liquid temperature was measured at 15 to 20 ° C. As a microscope, a polarizing microscope “Optiphoto” (manufactured by Nikon Corporation) was used.

Example 1
A natural silica pulverized product having an average particle diameter of 2.0 μm (purity 99) in a flame (approximately 2000 ° C.) in which oxygen is used as a carrier gas and LPG (propane gas) is burned at an oxygen ratio (volume ratio) of 1.1. 0.9%) to obtain amorphous silica particles having an average particle size of 2.2 μm. Next, 4.2 parts by weight of calcium nitrate tetrahydrate (1.00 parts by weight as CaO) was added to 100 parts by weight of the obtained amorphous silica particles, and mixed in ethanol for 30 minutes. Subsequently, after removing ethanol, it heat-processed at 1100 degreeC for 24 hours, and obtained the filler (ceramic particle).

(Example 2)
A filler (ceramic particles) was obtained in the same manner as in Example 1 except that the amount of calcium nitrate tetrahydrate added was changed to 2.1 parts by weight (0.50 parts by weight as CaO).

(Example 3)
A filler (ceramic particles) was obtained in the same manner as in Example 1 except that 1.7 parts by weight of sodium carbonate (1.00 parts by weight as Na ₂ O) was added instead of calcium nitrate tetrahydrate. .

Example 4
A natural silica pulverized product having an average particle size of 5.2 μm (purity 99) in a flame (about 2000 ° C.) in which oxygen is used as a carrier gas and LPG (propane gas) is burned at an oxygen ratio (volume ratio) of 1.1. 0.9%) to obtain amorphous silica particles having an average particle size of 5.9 μm. Next, 3.6 parts by weight of calcium carbonate (2.00 parts by weight as CaO) was added to 100 parts by weight of the obtained amorphous silica particles, and mixed for 30 minutes in ethanol using a ball mill. Subsequently, after removing ethanol, it heat-processed at 1400 degreeC for 4 hours, and obtained the filler (ceramic particle).

(Example 5)
A natural silica pulverized product with an average particle size of 4.4 μm (purity 99) in a flame (approximately 2000 ° C.) in which oxygen is used as a carrier gas and LPG (propane gas) is burned at an oxygen ratio (volume ratio) of 1.1. 0.9%) to obtain amorphous silica particles having an average particle diameter of 4.9 μm. Next, 0.8 parts by weight of calcium nitrate tetrahydrate (0.20 parts by weight as CaO) is added to 100 parts by weight of the obtained amorphous silica particles, and the mixture is distilled in distilled water for 30 minutes using a ball mill. Mixed. Subsequently, after removing distilled water, it heat-processed at 1100 degreeC for 24 hours, and obtained the filler (ceramic particle).

(Example 6)
A natural silica pulverized product having an average particle size of 8.5 μm (purity 99) in a flame (about 2000 ° C.) in which oxygen is used as a carrier gas and LPG (propane gas) is burned at an oxygen ratio (volume ratio) of 1.1. 0.9%) to obtain amorphous silica particles having an average particle diameter of 8.9 μm. Next, 1.8 parts by weight of magnesium sulfate (0.60 parts by weight as MgO) was added to 100 parts by weight of the obtained amorphous silica particles, and mixed in distilled water for 30 minutes using a ball mill. Subsequently, after removing distilled water, it heat-processed at 1200 degreeC for 24 hours, and obtained the filler (ceramic particle).

(Example 7)
A filler (ceramic particles) was obtained in the same manner as in Example 1 except that 0.9 parts by weight of calcium carbonate (0.50 parts by weight as CaO) was added instead of calcium nitrate tetrahydrate.

(Example 8)
A natural silica crushed material having an average particle size of 0.4 μm (purity 99) in a flame (approximately 2000 ° C.) in which oxygen is used as a carrier gas and LPG (propane gas) is burned at an oxygen ratio (volume ratio) of 1.1. 0.9%) to obtain amorphous silica particles having an average particle diameter of 0.5 μm. The obtained amorphous silica particles were used in the same manner as in Example 2 to obtain fillers (ceramic particles).

Example 9
Natural silica crushed material (purity 99.9) having an average particle size of 35 μm in a flame (approximately 2000 ° C.) in which oxygen is used as a carrier gas and LPG (propane gas) is burned at an oxygen ratio (volume ratio) of 1.1. %) To obtain amorphous silica particles having an average particle diameter of 38 μm. The obtained amorphous silica particles were used in the same manner as in Example 2 to obtain fillers (ceramic particles).

(Comparative Example 1)
A filler (ceramic particles) was obtained in the same manner as in Example 1 except that the heat treatment was performed without using a crystallization accelerator.

(Comparative Example 2)
A filler (ceramic particles) was obtained in the same manner as in Example 1 except that the amount of calcium nitrate tetrahydrate added was 0.2 parts by weight (0.05 parts by weight as CaO).

(Comparative Example 3)
A filler (ceramic particles) was obtained in the same manner as in Example 1 except that the amount of calcium nitrate tetrahydrate added was 21 parts by weight (5.0 parts by weight as CaO).

(Comparative Example 4)
In Example 1, the amorphous silica particles having an average particle diameter of 2.2 μm obtained by the flame melting method were used as they were without heat treatment and without adding calcium nitrate tetrahydrate. Various evaluations were performed.

For the fillers of the obtained Examples and Comparative Examples, the SiO ₂ content, the alkali metal or alkaline earth metal oxide content, the relative background height, the average particle diameter, the sphericity, and the refractive index are measured. did. Moreover, light transmittance was evaluated by the method shown below. The results are shown in Table 1.

<Light transmission test>
50 parts by weight of a sample (filler) and 50 parts by weight of clove oil having a refractive index of 1.53 were mixed using a Hoovermarler (manufactured by Yoshimitsu) with a stirring speed of 100 rotations / minute, an applied load of 2 kg, and a stirring time of 3 minutes. These were mixed and coated on glass to form a 50 μm thick coating film. Next, the total transmittance of the coating film was measured under the conditions of JIS K 7105 using HM150 manufactured by HAZE MURAKAMI COLOR RESEARCH RAB, and judged according to the following criteria.
A: Total transmittance is 95% or more B: Total transmittance is 90% or more and less than 95% C: Total transmittance is 85% or more and less than 90% D: Total transmittance is less than 85%

  As shown in Table 1, the total transmittance of Examples 1 to 9 was 90% or more, and the light transmittance was high. However, the total transmittance of Comparative Examples 1 to 4 was less than 85%, and the light transmittance was inferior compared to the Examples. From this result, according to the filler of this invention, it became clear that the light transmittance of a transparent member can be improved.

Claims (5)

A filler comprising ceramic particles, wherein the ceramic particles satisfy the following requirements (I) to (V).
(I) The content of SiO ₂ is 97.0% by weight or more,
(II) The relative background height in the X-ray diffraction spectrum is 3.0 to 10.0,
(III) The average particle size is 0.01 to 50 μm,
(IV) The sphericity is 0.95 or more,
(V) Refractive index is 1.48-1.60.   The ceramic particles are obtained by adding one or more metal compounds selected from alkali metal compounds and alkaline earth metal compounds to amorphous silica particles obtained by a flame melting method, and heat-treating them. The filler described.   The filler according to claim 1 or 2, wherein the content of an oxide of alkali metal and / or alkaline earth metal in the ceramic particles is 0.10 to 2.9% by weight.   The method for producing a filler according to any one of claims 1 to 3, wherein the amorphous silica particles obtained by the flame melting method are one or more metals selected from alkali metal compounds and alkaline earth metal compounds. A method for producing a filler, wherein a compound is added and heat treatment is performed.   The filler according to claim 4, wherein the addition amount of the metal compound is 0.10 to 3 parts by weight with respect to 100 parts by weight of the amorphous silica particles in terms of oxide of alkali metal and / or alkaline earth metal. Manufacturing method.