阅读说明：本技术 低介电二氧化硅粉体、含有该二氧化硅粉体的树脂组合物及低介电二氧化硅粉体的制备方法 (Low dielectric silica powder, resin composition containing the same, and method for producing low dielectric silica powder ) 是由 盐原利夫 糸川肇 于 2021-05-28 设计创作，主要内容包括：本发明的目的在于提供一种介电损耗角正切非常小的二氧化硅粉体及包含该二氧化硅粉体的树脂组合物。本发明的目的还在于提供一种介电损耗角正切低、且与树脂的界面处的粘合也牢固的二氧化硅粉体的制备方法。本发明提供一种低介电二氧化硅粉体,其特征在于,其平均粒径为0.1～30μm、介电损耗角正切(10GHz)为0.0005以下。(The purpose of the present invention is to provide a silica powder having a very low dielectric loss tangent and a resin composition containing the silica powder. It is another object of the present invention to provide a method for producing a silica powder having a low dielectric loss tangent and a strong adhesion to a resin at an interface. The present invention provides a low dielectric silica powder having an average particle diameter of 0.1 to 30 μm and a dielectric loss tangent (10GHz) of 0.0005 or less.)

1. A low dielectric silica powder characterized in that it has an average particle diameter of 0.1 to 30 μm and a dielectric loss tangent (10GHz) of 0.0005 or less.

2. The low dielectric silica powder according to claim 1, wherein the metal selected from the group consisting of aluminum, magnesium and titanium and/or an oxide thereof is 200ppm or less in terms of metal mass, and the alkali metal and the alkaline earth metal are 10ppm or less in terms of mass, respectively, in the inside and on the surface of the low dielectric silica powder.

3. The low dielectric silica powder of claim 1, wherein the low dielectric silica powder has a hydroxyl (Si-OH) content of 300ppm or less.

4. The low dielectric silica powder of claim 2, wherein the low dielectric silica powder has a hydroxyl (Si-OH) content of 300ppm or less.

5. The low dielectric silica powder according to claim 1, wherein the content of B is 1ppm or less, the content of P is 1ppm or less, and the contents of U and Th are each 0.1ppb or less.

6. The low dielectric silica powder according to claim 2, wherein the content of B is 1ppm or less, the content of P is 1ppm or less, and the contents of U and Th are each 0.1ppb or less.

7. The low dielectric silica powder according to claim 3, wherein the content of B is 1ppm or less, the content of P is 1ppm or less, and the contents of U and Th are each 0.1ppb or less.

8. The low dielectric silica powder according to claim 4, wherein the content of B is 1ppm or less, the content of P is 1ppm or less, and the contents of U and Th are each 0.1ppb or less.

9. The low dielectric silica powder according to any one of claims 1 to 8, wherein the maximum particle diameter of the low dielectric silica powder is 100 μm or less.

10. A resin composition containing a low dielectric silica powder, which is a mixture of the low dielectric silica powder according to any one of claims 1 to 9 and a resin.

11. A preparation method of low dielectric silicon dioxide powder is characterized in that,

heating a silica powder at a temperature of 500 to 1500 ℃ so that the dielectric loss tangent (10GHz) of the silica powder is 0.0005 or less, and then etching the surface of the heated silica powder with an etching solution.

12. The method of claim 11, wherein the heat treatment is performed for 30 minutes to 72 hours.

13. The method of claim 11, wherein the etching solution is an aqueous solution selected from the group consisting of hydrofluoric acid, ammonium fluoride, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia, and alkaline electrolyzed water.

14. The method of claim 12, wherein the etching solution is an aqueous solution selected from the group consisting of hydrofluoric acid, ammonium fluoride, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia, and alkaline electrolyzed water.

15. The method of claim 11, wherein an alkaline aqueous solution having a pH of 11 or more is used as the etching solution.

16. The method of claim 12, wherein an alkaline aqueous solution having a pH of 11 or more is used as the etching solution.

17. The method of claim 13, wherein an alkaline aqueous solution having a pH of 11 or more is used as the etching solution.

18. The method of claim 14, wherein an alkaline aqueous solution having a pH of 11 or more is used as the etching solution.

19. The method for producing a low dielectric silica powder according to any one of claims 15 to 18, wherein alkaline electrolyzed water having a pH value of 12 or more is used as the alkaline aqueous solution.

20. The method according to any one of claims 11 to 18, wherein the surface of the etched silica powder is further subjected to a coupling agent treatment.

21. The method of claim 19, wherein the surface of the etched silica powder is further treated with a coupling agent.

Technical Field

The present invention relates to a silica powder having very low dielectric characteristics, particularly a very low dielectric loss tangent in a high-frequency region, a method for producing the same, and a resin composition containing the silica powder.

Background

With the recent trend toward higher performance and higher speed communication of information terminals such as smartphones, there is a strong demand for higher density, thinner thickness, and lower dielectric characteristics, particularly lower dielectric loss tangent, of sealing materials for semiconductors such as printed wiring boards and underfills to be used.

Transmission loss of a signal is as follows Edward a. wolff: transmission lossIt is known that the loss is suppressed as the dielectric constant (. epsilon.) and the dielectric loss tangent (tan. delta.) are smaller. In particular, the dielectric loss tangent (tan δ) greatly contributes to the transmission loss as seen from the above formula.

As a method for reducing the dielectric loss tangent of a sealing material for a semiconductor such as a printed wiring board or an underfill material, a method of adding an inorganic powder having a lower dielectric loss tangent than that of a resin is common. However, an inorganic powder having a dielectric loss tangent of 0.0006 or less and a dielectric constant of 4.0 or less in a high frequency region is not known.

Silica powder, which is one of typical general-purpose inorganic powders, is a material having a small expansion coefficient and excellent insulating properties and dielectric properties as an inorganic powder to be added to a resin.

It is considered that, if the dielectric properties, particularly the dielectric loss tangent of the silica powder can be reduced to the level inherent to silica glass, the silica powder can be widely used as a sealing material for semiconductors for high-speed communications and the like, or as a filler for substrates for high-speed communications, antenna substrates and the like, which are expected to be greatly developed in the future.

In patent document 1, although low silanol silica is produced by heat treatment in an atmosphere with a low partial pressure of water vapor, only the reduction rate of the silanol group is mentioned, the silanol amount of the treated silica is not measured, and the dielectric loss tangent is not mentioned.

In patent document 2, silica glass fibers prepared by a sol-gel method are subjected to a heat treatment to prepare silica glass fibers having a moisture content of 1000ppm or less. Patent document 2 describes the moisture content of the silica glass fiber after the heat treatment, but does not mention the silanol amount and the dielectric loss tangent.

Patent document 2 shows the relationship between the amount of water in the silica glass fiber and the dielectric loss tangent, but does not describe the amount of silanol (Si — OH) and the dielectric loss tangent is a value measured on a printed circuit board using the silica glass fiber and PTFE, and therefore the relationship between the amount of silanol and the dielectric loss tangent of the glass fiber is not clear.

In the case of quartz glass, the amount of hydroxyl groups (OH groups) remaining in the glass is generally correlated with the dielectric loss tangent. Further, it is known that the hydroxyl group is reduced by the high temperature treatment, and the structure of the silica glass is changed (non-patent document 1). However, when the quartz glass containing hydroxyl groups is subjected to a heat treatment at a high temperature, the amount of strain increases, and particularly, the strain on the glass surface increases (non-patent document 2), and the strength is greatly reduced. Therefore, heat-treated silica powder that can be used as a filler whose adhesion strength to a resin is important has not been put to practical use.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2-289416

Patent document 2: japanese laid-open patent publication No. 5-170483

Non-patent document

Non-patent document 1: degrees of OH groups located in thermally processed foods に and うシリカガラス change from the pre-term (35542) of the university of Fujing engineering research, Phi 2011 2 month

Non-patent document 2: シリカガラスブロック thermally induced による structure of the doctor's earlier stage (35542) of the university of Fujing engineering, 2 Yue, 2005

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made to solve the above problems, and an object thereof is to provide a silica powder having a very small dielectric loss tangent and a resin composition containing the silica powder. It is another object of the present invention to provide a method for producing a silica powder having a low dielectric loss tangent and a strong adhesion to a resin at an interface.

Means for solving the problems

In order to solve the above-mentioned problems, the present invention provides a low dielectric silica powder having an average particle diameter of 0.1 to 30 μm and a dielectric loss tangent (10GHz) of 0.0005 or less.

Since the silica powder has a very low dielectric loss tangent, it can be widely used as a sealing material for a semiconductor for high-speed communication or a filler for a substrate for high-speed communication, an antenna substrate, or the like.

In this case, it is preferable that: the low dielectric silica powder has a content of a metal selected from the group consisting of aluminum, magnesium and titanium and/or an oxide thereof in terms of metal mass or less of 200ppm, and an alkali metal and an alkaline earth metal in terms of mass or less of 10ppm, respectively, in the interior and on the surface thereof.

In the case of the silica powder, the electrode is not corroded.

Further, the hydroxyl group (Si-OH) content of the low dielectric silica powder is preferably 300ppm or less.

In the case of the silica powder, the dielectric loss tangent is further lowered.

Further, it is preferable that the content of B is 1ppm or less, the content of P is 1ppm or less, and the contents of U and Th are 0.1ppb or less, respectively.

In the case of the silica powder, dielectric characteristics are preferable, and a failure due to radiation can be prevented.

In the present invention, the maximum particle diameter of the low dielectric silica powder is preferably 100 μm or less.

Thus, coarse particles or agglomerated particles larger than 100 μm are preferably removed and used.

The present invention also provides a resin composition containing the low dielectric silica powder, which is a mixture of the low dielectric silica powder and a resin.

The resin composition containing the low dielectric silica powder can provide a cured product having a very low dielectric loss tangent.

The present invention also provides a method for producing a low dielectric silica powder, which is characterized by heat-treating a silica powder at a temperature of 500 to 1500 ℃ so that the dielectric loss tangent (10GHz) of the silica powder is 0.0005 or less, and then etching the surface of the heat-treated silica powder with an etching solution.

In the above method for producing a low dielectric silica powder, a low dielectric silica powder having a low dielectric loss tangent, high strength and strong adhesion to the interface of the resin can be produced with high productivity.

In this case, the heat treatment is preferably performed for 30 minutes to 72 hours.

By performing the heat treatment in this manner, the dielectric loss tangent of the low dielectric silica powder can be set to an appropriate value.

As the etching solution, an aqueous solution selected from a hydrofluoric acid aqueous solution, an ammonium fluoride aqueous solution, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a sodium carbonate aqueous solution, ammonia water, and alkaline electrolyzed water is preferably used.

The etching solution is preferable from the point of the effect of removing the strained layer of the heat-treated silica powder and the improvement of the adhesion to the resin.

In this case, the etching solution is preferably an alkaline aqueous solution having a pH of 11 or more, and more preferably alkaline electrolyzed water having a pH of 12 or more.

The etching solution is more preferably an alkaline electrolytic water having a pH of 12 or more from the viewpoint of the working environment or the wastewater treatment, because of the etching effect of the silica powder and the improvement of the adhesion between the silica powder and the resin.

Preferably, the surface of the silicon dioxide powder after etching treatment is further subjected to coupling agent treatment.

When the surface of the silica powder is coated with the silane coupling agent and blended into a resin or the like as described above, the adhesion between the resin and the powder surface can be further strengthened.

Effects of the invention

As described above, the low dielectric silica powder of the present invention has a very low dielectric loss tangent, and a resin composition containing the low dielectric silica powder, which is a mixture of the low dielectric silica powder and a resin, can provide a cured product having a very low dielectric loss tangent. In addition, according to the method for producing a low dielectric silica powder of the present invention, a silica powder having a low dielectric loss tangent, high strength, and strong adhesion to the interface with the resin can be produced with excellent productivity.

Drawings

FIG. 1 is a graph showing the relationship between the silica loading and the dielectric loss tangent (10 GHz).

FIG. 2 is a scanning electron micrograph of a fracture surface obtained by breaking the cured product of example 5.

FIG. 3 is a scanning electron micrograph of a fracture surface obtained by breaking the cured product of example 6.

FIG. 4 is a scanning electron micrograph of a fracture surface obtained by breaking a cured product of comparative example 4.

Detailed Description

As described above, development of a silica powder having a very small dielectric loss tangent is demanded.

The inventors of the present application have made intensive studies on the above-mentioned technical problems, and particularly, have made studies on low dielectric constant, and as a result, have found that: heating the silica powder to a temperature of 500 to 1500 ℃ is effective for lowering the dielectric loss tangent, and further, by forming the etched silica powder in which the surface of the silica powder is further subjected to a slight etching treatment, the surface of the powder becomes firm and adhesion to a resin is improved, thereby completing the present invention.

That is, the present invention is a low dielectric silica powder characterized by having an average particle diameter of 0.1 to 30 μm and a dielectric loss tangent (10GHz) of 0.0005 or less.

The present invention is a method for producing a low dielectric silica powder, characterized by heat-treating a silica powder at a temperature of 500 to 1500 ℃ so that the dielectric loss tangent (10GHz) of the silica powder is 0.0005 or less, and then etching the surface of the heat-treated silica powder with an etching liquid.

The present invention will be described in detail below, but the present invention is not limited thereto.

The present invention relates to a silica powder having an average particle diameter of 0.1 to 30 μm and a dielectric loss tangent (10GHz) of 0.0005 or less. Further, it is preferable to use a silica powder in which the content of each of the alkali metal and the alkaline earth metal is not more than 200ppm in terms of metal mass and not more than 10ppm in terms of mass, in the interior and on the surface of the silica powder, respectively, of a metal selected from the group consisting of aluminum, magnesium, and titanium and/or an oxide thereof. Further, the present invention relates to a silica powder having a hydroxyl group (Si-OH) content of 300ppm or less. Further disclosed is a silica powder having an average particle diameter of 0.1-30 [ mu ] m and preferably a maximum particle diameter of 100 [ mu ] m or less.

Further, the present invention relates to a method for producing a silica powder, which comprises subjecting a silica powder to a heat treatment at a temperature of 500 to 1500 ℃ to thereby adjust the dielectric loss tangent (10GHz) of the silica powder to 0.0005 or less, preferably 0.0004 or less. The content of hydroxyl groups (Si-OH) contained in the silica powder is preferably 300ppm or less, more preferably 280ppm or less, and still more preferably 150ppm or less by the heat treatment, and the silica powder having a low dielectric loss tangent is formed. The silica powder is suitable as a sealing material for semiconductors or a filler for substrates such as high-speed communication substrates and antenna substrates.

When the silica powder having excellent dielectric characteristics is used, a low dielectric resin composition can be easily obtained by blending the silica powder into a resin. In addition, the low dielectric silica powder can also be used as a filler for a low dielectric organic substrate.

As the silica powder which is a raw material of the low dielectric silica powder of the present invention, the following silica powder can be used, but as long as it is a silica powder, the following methods can be used regardless of whether it is a method of producing the silica powder: a spheroidized fused silica powder obtained by pulverizing a naturally-produced crystalline quartz to obtain a powder and passing the powder through a high-temperature flame at about 2000 ℃; silica powder obtained by purifying water glass as a raw material, sintering the water glass at a high temperature, and pulverizing the sintered water glass. In general, even when a silica powder which is easily obtained as a filler for a semiconductor sealing material or the like and which has been treated at a high temperature of about 2000 ℃ is used, a low dielectric silica powder having a dielectric loss tangent of 0.0005 or less which meets the object of the dielectric loss tangent cannot be obtained.

According to the experimental results of the inventors of the present application, when the contents of metals selected from the group consisting of aluminum, magnesium and titanium or metal oxides thereof in the interior or on the particle surface of the silica powder to be heat-treated are 200ppm or less in terms of the metal mass, respectively, the targeted low dielectric silica powder can be obtained without being easily crystallized in the heat treatment step. The content of each of the alkali metal and the alkaline earth metal is preferably 10ppm or less, and more preferably 5ppm or less. Silica powder containing a large amount of alkali metal or alkaline earth metal has a problem of corroding electrodes of a high-speed communication board or a semiconductor device, and silica powder containing a small amount of alkali metal or alkaline earth metal is also required from the viewpoint of preventing corrosion. Further, the content of B (boron) is preferably 1ppm or less and the content of P (phosphorus) is preferably 1ppm or less, and in order to prevent troubles due to radiation, the content of U or Th is preferably 0.1ppb or less. By thus suppressing the impurity concentration to a low level, the dielectric characteristics and the like of the silica powder become more preferable. The concentration of the above-mentioned impurities can be measured by atomic absorption spectrophotometry, Inductively Coupled Plasma (ICP) emission spectrometry, or the like.

In the present invention, alkali metal means lithium, sodium, potassium, rubidium, cesium, francium, among elements belonging to the first main group of the periodic table, excluding hydrogen. The alkaline earth metal means calcium, strontium, barium and radium among elements belonging to the second main group of the periodic table, excluding beryllium and magnesium.

The average particle diameter of the silicon dioxide powder is 0.1-30 mu m. Further, a spherical powder is preferable as a sealing material for a semiconductor because the spherical powder can be highly filled in a resin, but a crushed powder may be used. If the average particle size is less than 0.1 μm, the specific surface area becomes large and the resin cannot be highly filled, and if the average particle size is more than 30 μm, the filling property at the narrow portion becomes poor, and there are problems such as non-filling. Therefore, a powder having an average particle diameter of 0.5 to 20 μm and a maximum particle diameter of 100 μm or less is generally preferred.

When used as an underfill material or a filler for a high-speed substrate, the particles have an average particle diameter of 0.1 to 5 μm and a maximum particle diameter of 20 μm or less, and more preferably have an average particle diameter of 0.1 to 3 μm and a maximum particle diameter of 10 μm or less.

In order to improve the properties such as flowability and processability of the low dielectric silica powder, silica powders having different average particle diameters may be mixed.

In the present invention, the maximum particle diameter and the average particle diameter can be measured by a laser diffraction particle size distribution measuring instrument (for example, SALD-3100: manufactured by Shimadzu Corporation), and the mass average value D50 (that is, the particle diameter at a cumulative mass of 50% or the median particle diameter) in the particle size distribution measurement by the laser diffraction method can be determined and used as the average particle diameter.

In order to develop the low dielectric silica powder of the present invention for wide use as a sealing material for a semiconductor for high-speed communication or a filler for a substrate for high-speed communication or an antenna substrate, the dielectric loss tangent (10GHz) is set to 0.0005 or less. Further, the silica powder is heat-treated in advance to obtain the dielectric loss tangent.

The heating temperature for low dielectric constant is desirably 500 to 1500 ℃, more preferably 600 to 1300 ℃, and further preferably 700 to 1000 ℃. As a heating method, the silica powder is put in an electric heating furnace, a muffle furnace or the like and subjected to a heating treatment at 500 to 1500 ℃.

The time for the heat treatment of the silica powder varies depending on the heating temperature, and is preferably 30 minutes to 72 hours, more preferably 1 hour to 24 hours, and further preferably 2 hours to 12 hours, from the viewpoint of practicality.

The cooling to room temperature after heating may be slow cooling or rapid cooling, and the silica in a molten state may be partially crystallized depending on the conditions, and therefore, it is preferable to optimize the heating temperature or the cooling conditions.

The heating atmosphere is not particularly limited, and may be in air or an inert gas such as nitrogen, and may be under normal pressure, vacuum or reduced pressure.

Whether or not the desired dielectric properties were achieved was confirmed by analyzing the hydroxyl group content of the silica powder after the heat treatment by infrared spectroscopy.

It is known that in the GHz band, a polarization-based dipole responds to an electric field and induces a dielectric (). Therefore, the key to low dielectric characterization in the GHz band is to reduce polarization in the structure.

The dielectric constant is expressed by the following Clausius-Mossotti equation, with molar polarizability and molar volume factored. Therefore, the key to lower the dielectric constant is to reduce the polarization and increase the molar volume.

Dielectric constant [1+2(Σ Pm/Σ Vm) ]/[1- (Σ Pm/Σ Vm) ]

(Pm: molar polarizability of atomic group, Vm: molar volume of atomic group)

Further, the dielectric loss tangent (tan δ) is a delay of a dielectric response to an alternating electric field, and in a GHz band, the main cause is orientation relaxation of dipoles (alignment and). Therefore, in order to reduce the dielectric loss tangent, a method of removing the dipole (making a structure close to nonpolarity) is conceivable.

As a way of reducing the dielectric characteristics of the silica particles in the GHz band, the concentration of hydroxyl groups (silanol) as polar groups is suppressed to be low in the present invention.

From the above viewpoint, in the present invention, it is preferable that the concentration of hydroxyl groups (Si — OH) in the silica powder after the heat treatment is in the above range. In the etching treatment described later, it is preferable that the concentration of hydroxyl groups in the silica powder after the heat treatment is lower in order to dissolve and remove the strained layer on the surface of the silica powder.

Thus, a silica powder having a lower dielectric loss tangent can be obtained. The hydroxyl group concentration in the finally obtained silica powder is preferably 300ppm or less, more preferably 280ppm or less, and further preferably 150ppm or less.

As described later, the concentration of hydroxyl groups (Si-OH) in the silica powder was measured by infrared spectrophotometry at 3680cm^-1The transmittance of the peak in the vicinity was determined. Since 3680cm^-1Since the near infrared absorption is attributed to internal silanol (see patent document 1), silanol which is a polar group affecting the dielectric loss tangent is identified and quantified based on the characteristic absorption band. Thereby, the degree of reduction in the dielectric tangent can be estimated more specifically. In addition, since it is assigned to 3740cm^-1Since the infrared absorption of nearby isolated silanols is negligible in the present invention (see patent document 1), the infrared absorption is only 3680cm as described above^-1By measuring the transmittance at the peak in the vicinity, the decrease in the dielectric loss tangent can be sufficiently estimated.

As mentioned above, the transmission loss of a signal is as follows Edward a. wolff: transmission lossAs shown, the smaller the dielectric constant (. epsilon.) and the dielectric loss tangent (tan. delta.), the more the loss is suppressed. In particular, the contribution of the dielectric loss tangent (tan δ) is large for the transmission loss. Therefore, the dielectric loss angle is required to be positiveThe cut is lower.

The dielectric loss tangent of the quartz powder can be set to the original level, that is, 0.0005 or less by the heat treatment of the present invention. More preferably, it is 0.0004 or less, and still more preferably 0.0002 or less.

Since there are some silica powders partially fused depending on the treatment temperature among the silica powders obtained by the heat treatment, they are used after being pulverized by a pulverizing device such as a ball mill and coarse particles or aggregated particles larger than 100 μm are removed by a sieve. The coarse particle removal can be carried out using a 150 mesh screen.

However, since a strain layer is easily formed on the surface of the silica powder by the treatment at a high temperature, the strength of a cured product of the resin composition filled with the silica powder is easily lowered. The strained layer on the surface of the silica powder can be easily removed by immersing the surface in an etching solution or the like.

As the etching solution, an acidic aqueous solution such as a hydrofluoric acid aqueous solution, an alkaline aqueous solution selected from an ammonium fluoride aqueous solution, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, a sodium carbonate aqueous solution, ammonia water, alkaline electrolytic water, and the like can be used. As the acidic aqueous solution, acidic ammonium fluoride (NH) may also be used₄F.HF) aqueous solution, potassium fluoride acid (KHF)₂) An aqueous solution. From the working environment or the point of wastewater treatment, an alkaline aqueous solution is more preferable, and alkaline electrolyzed water is more preferable.

The temperature of the etching treatment conditions of the silica powder after the heat treatment is preferably from room temperature (23 ℃) to 100 ℃, and more preferably from 40 ℃ to 80 ℃. The treatment time is not particularly limited, since it depends on the etching rate of the silicon dioxide surface depending on the treatment temperature (for example, room temperature to 90 ℃ C., preferably 40 to 80 ℃ C.). The lower the temperature of the etching solution, the less etching proceeds, and the higher the temperature, the higher the etching rate, but in terms of practicality, the temperature at which the treatment is completed within a treatment time of 10 minutes or more to 168 hours is preferable. The treatment time is preferably 1 to 72 hours, more preferably 10 to 24 hours. Further, even under atmospheric pressure or pressurized atmosphere, the treatment can be performed within the above-described temperature and time ranges.

The pH of the etching solution is not particularly limited as long as the strained layer can be removed, and can be adjusted by adding an acid, an alkali, or the like as needed.

When the pH of the alkaline solution was 8.0 or more, the etching effect of the silica powder was sufficient, and it was confirmed that the adhesion between the resin and the surface of the etched silica powder was improved. The pH value is preferably 10.0 to 13.5, and more preferably 11.0 to 13.0.

As the alkaline etching solution, an alkaline aqueous solution having a pH of 11 or more is preferably used, and alkaline electrolyzed water having a pH of 12 or more is more preferably used.

In addition, in the case of a powder which is not sufficiently crushed or spheroidized, sharp edges and the like on the surface of the powder are reduced by etching, and therefore, the powder is effective for highly filling and reducing local stress.

After the etching is completed, the silica powder is separated by a method such as filtration, and further washed repeatedly with ion-exchanged water or pure water until the washing water becomes neutral. After washing, the silica powder is separated by filtration, centrifugal separation or the like, and dried at a temperature of 100 to 200 ℃ to remove water. In general, silica powder is aggregated by drying of moisture, and is pulverized by a pulverizing device such as a ball mill. When the aggregation by drying is strong, the silica powder may be separated by washing with an alcohol such as methanol after washing with ion-exchange water, and then drying by filtration, centrifugal separation, or the like, thereby preventing aggregation.

The low dielectric silica powder obtained in this way is used after coarse particles or agglomerated particles larger than 100 μm are removed by a sieve (for example, 150 mesh sieve).

The coupling agent treatment is a step to be performed as needed, and is a step to treat the surface of the silica powder with a coupling agent or the like. The coupling agent is not particularly limited, and a silane coupling agent is preferred.

This is because, in the case of preparing a resin composition or the like by washing and drying a low dielectric silica powder subjected to a high temperature treatment or an etching treatment and then covering the surface of the silica powder with a silane coupling agent, the surface treatment with the silane coupling agent makes the adhesion between the resin and the surface of the low dielectric silica powder strong.

As the silane coupling agent, a known silane coupling agent can be used, but preferably an alkoxysilane, more preferably one or more selected from the group consisting of γ -aminopropyltrimethoxysilane, γ -aminopropyltriethoxysilane, N- β -aminoethyl- γ -aminopropyltrimethoxysilane, N- β -aminoethyl- γ -aminopropyltriethoxysilane, γ -methacryloxypropyltrimethoxysilane, γ -methacryloxypropyltriethoxysilane, and trifluoropropyltrimethoxysilane.

The concentration of the silane coupling agent is usually 0.1 to 5% by mass in the form of a dilute solution, and is particularly effective when 0.1 to 1% by mass is used. Thus, the silane coupling agent is uniformly adhered to the surface of the silica powder, and the silica powder is more uniformly protected and can be easily handled.

The silica powder subjected to low dielectric loss tangent can be blended with a thermosetting resin or a thermoplastic resin as a filler such as an epoxy resin, a silicone resin, a polyimide resin, a Teflon (registered trademark) resin, a maleimide resin, or a polyphenylene ether resin.

The resin composition containing a low dielectric silica powder, which is a mixture of the low dielectric silica powder and a resin, can provide a cured product having a very low dielectric loss tangent. In particular, by blending the silica powder subjected to the etching treatment (etching silica powder), the strain on the surface of the silica powder is removed and the strength is increased, and the adhesive strength between the resin and the silica powder can be further improved.

The low dielectric silica powder obtained in the above manner is a useful material such as a sealing material for a semiconductor device for high-speed communication or the like, or a filler for a low dielectric organic substrate such as a server or an antenna, which is expected to be greatly developed in the future.

Examples

The present invention will be specifically described below by referring to examples and comparative examples, but the present invention is not limited thereto.

In the present specification, the dielectric loss tangent and the hydroxyl group content of the silica powder prepared in examples or comparative examples are values determined by the following methods.

< method for measuring dielectric loss tangent >

The method for measuring the dielectric loss tangent will be described with reference to the silica powder A1(RS8225 untreated product) as an example.

Silica powder was mixed, dispersed and dissolved in an anisole solvent containing SLK-3000(Shin-Etsu Chemical co., ltd.) as a low dielectric maleimide resin and dicumyl peroxide (PERCUMYL D: NOF CORPORATION) as a radical polymerization initiator as a curing agent at the ratio shown in table 1 below to prepare varnish.

To the resin, silica powder was added in an amount of 0%, 11.1%, 33.3%, 66.7% by volume, the mixture was spread to a thickness of 200mm using a bar coater, and the mixture was put into a dryer at 80 ℃ for 30 minutes, and the anisole solvent was removed, thereby preparing an uncured maleimide resin composition.

[ Table 1]

The obtained uncured maleimide resin composition was placed in a mold of 60 mm. times.60 mm. times.100. mu.m, cured at 180 ℃ for 10 minutes and 30MPa using a hand press (hand press), and then completely cured at 180 ℃ for 1 hour using a dryer to prepare a resin cured sheet. The resin cured sheet was cut into a size of 50mm × 50mm, and the dielectric loss tangent at 10GHz was measured using SPDR (Split post dielectric resonators) for dielectric constant measurement at a split dielectric resonator frequency of 10GHz (manufactured by Keysight Technologies Co., Ltd.).

The values of the obtained dielectric loss tangent were plotted on a graph with the horizontal axis representing the volume% of the silica powder and the vertical axis representing the measured dielectric loss tangent as shown in FIG. 1, and a line of the dielectric loss tangent was drawn from the graph in terms of the volume% vs of the silica powder. The dielectric loss tangent of 100% of the silica powder was extrapolated to the value of the dielectric loss tangent of the silica powder.

Although there is a measuring instrument capable of directly measuring silica powder, since the measurement is performed by filling silica powder in a measurement tank (pot), it is difficult to remove air mixed therein. In particular, silica powder having a large specific surface area is more difficult because it is greatly affected by air. Therefore, in order to obtain a value in a state close to an actual use form by eliminating the influence of the air mixed, in the present invention, the dielectric loss tangent of the silica powder is determined by the above-described measurement method.

< method for measuring hydroxyl group (Si-OH) content >

A sample filled with silica powder until filled in an aluminum pan (aluminum pan) having a thickness of 1.5mm was prepared, and 3680cm derived from hydroxyl groups was measured for the infrared absorption spectrum of the sample by a diffuse reflection method using a Fourier transform infrared spectrophotometer (IRaffinity-1S) and a diffuse reflectance measuring device (DRS-8000A)^-1Transmittance T of the nearby peak. Based on the obtained value of the transmittance, absorbance a was obtained by applying lambert beer's law shown below.

Absorbance a ═ Log₁₀T

T＝3680cm^-1Transmittance in the vicinity

Then, the molar concentration C (mol/L) of the hydroxyl group is determined by the following formula based on the absorbance determined by the formula.

·C＝A/εL

Epsilon: molar absorptivity (molar absorptivity of hydroxyl group ∈ 77.5 dm)³/mol·cm)

C: molarity (mol/L)

L: thickness of sample (optical path length) (1.5mm)

From the obtained absorbance a, the molar concentration C was obtained by using the above formula.

Using the obtained molar concentration C, the hydroxyl group content (ppm) in the silica powder was determined by the following formula.

The content of hydroxyl groups (ppm) { (C × M)/(d × 1000) } × 10⁶

The specific gravity d of the silica powder was 2.2g/cm³

Molecular weight of hydroxyl group M (Si-OH) ═ 45g/mol

Examples 1 to 4 and comparative examples 1 to 3

A resin composition was prepared in the following manner, and the dielectric loss tangent of the cured product of the obtained resin composition was measured. The results are shown in tables 2 and 3.

(example 1)

5Kg of silica powder A1(TATSUMORI LTD., RS8225) having an average particle diameter of 15 μm, a dielectric loss tangent of 0.0006 and a hydroxyl group content of 370ppm was put in an alumina container, heated in a muffle furnace (AS ONE Corporation) at 900 ℃ for 5 hours in air, and then cooled to room temperature over 6 hours. The heated silica powder was put into a plastic container containing 20 liters of alkaline electrolyzed water (pH 13) and stirred for 2 hours while being heated to 60 ℃ to thereby remove the strained layer on the particle surface. Then, the silica powder was separated by a centrifugal separator, washed with methanol, and dried. The dried silica powder was pulverized by a ball mill, and the hydroxyl group content of silica powder LK-1 from which coarse particles were removed by a 150-mesh sieve was reduced to 270ppm, and the dielectric loss tangent was 0.0002.

(example 2)

Using silica powder B (SO-E5, manufactured by Admatechs Corporation) having an average particle diameter of 1.5 μm, a dielectric loss tangent of 0.0011 and a hydroxyl group content of 290ppm, 5Kg of the silica powder B was put in an alumina container, heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 900 ℃ for 12 hours, and then cooled to room temperature over 6 hours. The heated silica powder was put into a plastic container containing 20 liters of alkaline electrolyzed water (pH 13) and stirred for 2 hours while being heated to 60 ℃ to thereby remove the strained layer on the particle surface. Then, the silica powder was separated by a centrifugal separator, washed with methanol, and dried to obtain silica powder LK-2. The silica powder had a dielectric loss tangent of 0.0003 and a hydroxyl group content of 240 ppm.

(example 3)

Using a silica powder C having an average particle diameter of 0.1 μm, a dielectric loss tangent of 0.0053 and a hydroxyl group content of 475ppm (EMIX-100, manufactured by TATSUMORI LTD.), 5Kg of the silica powder C was put in an alumina container, heated in a muffle furnace (manufactured by AS ONE Corporation) in air at 900 ℃ for 12 hours, and then cooled to room temperature over 6 hours. The heated silica powder was put into a plastic container containing 20 liters of alkaline electrolyzed water (pH 13) and stirred for 2 hours while being heated to 60 ℃ to thereby remove the strained layer on the particle surface. Then, the silica powder was separated by a centrifugal separator, washed with methanol, and dried to obtain silica powder LK-3. The silica powder had a dielectric loss tangent of 0.0004 and a hydroxyl group content of 135 ppm.

(example 4)

5Kg of silica powder A1(RS8225, manufactured by TATSUMORI LTD., Inc.) having an average particle diameter of 15 μm and a dielectric loss tangent of 0.0006 was placed in an alumina container and subjected to a heat treatment in a muffle furnace (manufactured by AS ONE Corporation) at a temperature, for a time and in an atmosphere AS described in Table 3. After heating, the mixture was cooled to room temperature for 6 hours to obtain silica powders LK-4, LK-5, LK-6, LK-7 and LK-8 (examples 4-1 to 4-5). The dielectric loss tangent (10GHz) and the hydroxyl group content of each of the silica powders obtained by pulverizing the heat-treated silica powder with a ball mill and removing the coarse particles with a 150-mesh sieve were measured and shown in Table 3.

Comparative example 1

5Kg of silica powder A1(TATSUMORI LTD., RS8225) having an average particle diameter of 15 μm and a dielectric loss tangent of 0.0006 was put in an alumina container, heated in a muffle furnace (AS ONE Corporation) at 400 ℃ for 12 hours in air, and then cooled to room temperature over 6 hours. The heated silica powder was put into a plastic container containing 20 liters of alkaline electrolyzed water (pH 13) and stirred for 2 hours while being heated to 60 ℃ to thereby remove the strained layer on the particle surface. Then, the silica powder was separated by a centrifugal separator, washed with methanol, and dried. The dried silica powder was pulverized by a ball mill, and coarse particles were removed by a 150-mesh sieve. The dielectric loss tangent of the silica powder was 0.0006, and no improvement in the dielectric loss tangent was observed. The hydroxyl group content was 355 ppm.

Comparative example 2

5Kg of silica powder A1(TATSUMORI LTD., RS8225) having an average particle diameter of 15 μm and a dielectric loss tangent of 0.0006 was put in an alumina container, heated in a muffle furnace (AS ONE Corporation) at 1600 ℃ for 12 hours in air, and then cooled to room temperature over 6 hours. The silica powder after heat treatment was partially fused and could not be pulverized.

Comparative example 3

5Kg of silica powder A1(TATSUMORI LTD., RS8225) having an average particle diameter of 15 μm and a dielectric loss tangent of 0.0006 was put in an alumina container, heated in a muffle furnace (AS ONE Corporation) at 900 ℃ for 10 minutes in air, and then cooled to room temperature over 6 hours. The dielectric loss tangent of the silica powder was 0.0006, and no improvement in the dielectric loss tangent was observed. The hydroxyl group content was 365 ppm.

[ Table 2]

[ Table 3]

Examples 5 to 7 and comparative example 4

A resin composition was prepared in the following manner, and the dielectric loss tangent of the cured product of the obtained resin composition was measured. The results are shown in Table 4.

(example 5)

65 parts by mass of a cresol novolak type epoxy resin (EOCN1020 Nippon Kayaku Co., Ltd., manufactured by Ltd.), 35 parts by mass of a phenol novolak resin (H-4Gunei Chemical Industry Co., manufactured by Ltd.), 400 parts by mass of LK-1 (heat + etching treated silica powder) of example 1, 0.2 parts by mass of a catalyst TPP (triphenylphosphine HOKKO CHEMICAL INDUSTRY CO., manufactured by LTD.), and 0.5 parts by mass of a silane coupling agent (KBM403 Shin-Etsu Chemical Co., manufactured by Ltd.) were sufficiently mixed by a high-speed mixing apparatus, and then heated and kneaded by a continuous kneading apparatus, and the mixture was sheeted and cooled. The sheet is pulverized into a granular powder to obtain a thermosetting resin composition comprising an epoxy resin.

The composition was cured by transfer molding at 175 ℃ for 2 minutes under curing conditions. Further post-curing at 180 ℃ for 2 hours to obtain a cured product. The interface between the silica and the resin at the fracture surface was observed by breaking the cured product (fig. 2), and as a result, the resin was strongly bonded to the silica powder, and therefore the silica powder was not observed at the fracture surface, and the fracture of the resin portion was large. The dielectric loss tangent of the cured product was 0.004 and good.

(example 6)

After fully mixing 65 parts by mass of a cresol novolak type epoxy resin (EOCN1020 Nippon Kayaku co., ltd.) with 35 parts by mass of a phenol novolak resin (H-4Gunei Chemical Industry co., ltd., LK-6 of example 4 (silica powder which was heat-treated and was not subjected to etching treatment), 0.2 parts by mass of a catalyst TPP (triphenylphosphine HOKKO Chemical Industry co., ltd., ltbm 403), and 0.5 parts by mass of a silane coupling agent (KBM403 Shin-Etsu Chemical co., ltd, the components were heated and kneaded by a continuous kneader, and the components were formed into a sheet and cooled. The sheet is pulverized into a granular powder to obtain a thermosetting resin composition comprising an epoxy resin.

The composition was cured by transfer molding at 175 ℃ for 2 minutes under curing conditions. Further, post-curing was carried out at 180 ℃ for 2 hours, whereby a cured product was obtained. The cured product was broken and the interface between the silica powder and the resin at the broken surface was observed (fig. 3), and as a result, no resin was adhered to the surface of the silica powder, and the interface between the silica powder and the resin was broken. The dielectric loss tangent of the cured product was 0.004 and good.

(example 7)

100 parts by mass of SLK-3000(Shin-Etsu Chemical Co., Ltd., manufactured by Ltd.) of a low dielectric maleimide resin, 400 parts by mass of LK-6 of example 4, and 2 parts by mass of dicumyl peroxide (PERCUMYL D: NOF CORPORATION) as a curing agent and a radical polymerization initiator were mixed with 150 parts by mass of an anisole solvent, and dispersed and dissolved to prepare a maleimide resin composition varnish. Next, the resin composition was spread to a thickness of 200mm using a bar coater, and put into a dryer at 80 ℃ for 30 minutes, and the anisole solvent was removed, thereby preparing an uncured maleimide resin composition.

The prepared uncured maleimide resin composition was put into a mold of 60mm × 60mm × 100 μm, cured at 180 ℃ for 10 minutes and 30MPa by a manual press, and then completely cured at 180 ℃ for 1 hour by a dryer to prepare a resin cured sheet. The dielectric loss tangent was measured using the resin cured sheet. The dielectric loss tangent of the cured product was 0.0007, which is better than that of the untreated silica powder A1 blend.

Comparative example 4

After fully mixing 65 parts by mass of a cresol novolak type epoxy resin (EOCN1020 Nippon Kayaku co., ltd.) with 35 parts by mass of a phenol novolak resin (H-4 knee Chemical Industry co., ltd.), 400 parts by mass of silica powder a1 (non-heat-treated silica powder: RS8225, manufactured by tatsumoi ltd.), 0.2 parts by mass of a catalyst TPP (triphenylphosphine HOKKO Chemical Industry co., ltd.), and 0.5 parts by mass of a silane coupling agent (KBM403 Shin-Etsu Chemical co., ltd.) with a high-speed mixing device, heating and kneading were performed with a continuous kneading device, and sheeting and cooling were performed. The sheet is pulverized into a granular powder to obtain a thermosetting resin composition comprising an epoxy resin.

The composition was cured by transfer molding at 175 ℃ for 2 minutes under curing conditions. Further, post-curing was carried out at 180 ℃ for 2 hours, whereby a cured product was obtained. The cured product was broken and the interface between silica and resin at the broken surface was observed (fig. 4), and as a result, cohesive failure occurred in the resin at the interface between silica and resin. The dielectric loss tangent of the cured product was 0.005, which was inferior to that of the present invention (examples 5 and 6).

Comparative example 5

100 parts by mass of SLK-3000(Shin-Etsu Chemical Co., Ltd., manufactured by Ltd.) of a low dielectric maleimide resin, 400 parts by mass of silica powder A1(TATSUMORI LTD., manufactured by RS8225) and 2 parts by mass of dicumyl peroxide (PERCUMYL D: NOF CORPORATION) as a curing agent and a radical polymerization initiator were mixed with 150 parts by mass of an anisole solvent, and dispersed and dissolved to prepare a maleimide resin composition varnish. Next, the resin composition was spread to a thickness of 200mm using a bar coater, placed in a desiccator at 80 ℃ for 30 minutes, and the anisole solvent was removed, thereby preparing an uncured maleimide resin composition.

The prepared uncured maleimide resin composition was put into a mold of 60mm × 60mm × 100 μm, cured at 180 ℃ for 10 minutes and 30MPa by a manual press, and then completely cured at 180 ℃ for 1 hour by a dryer to prepare a resin cured sheet. The dielectric loss tangent was measured using the resin cured sheet. The dielectric loss tangent of the cured product was 0.001, which was inferior to that of the invention (example 7).

[ Table 4]

The blending amount of each component in the table is part by mass.

As is clear from tables 2 and 3, the silica powders of the present invention (examples 1 to 3 and 1 to 5 of example 4) had a significantly lower dielectric loss tangent (tan. delta.) than the untreated silica powders. On the other hand, in the case where the heat treatment temperature was low (comparative example 1) or the case where the heat treatment was insufficient (the treatment time was short) (comparative example 3), no improvement in the dielectric loss tangent was observed. If the heat treatment temperature is too high, the particles partially fuse and cannot be pulverized (comparative example 2). The dielectric loss tangent was improved regardless of whether the heat treatment atmosphere was air or nitrogen, but when the high-temperature treatment was performed in a nitrogen atmosphere, the amount of hydroxyl groups in the powder tended to further decrease (4 and 5 in examples 4). In this manner, a silica powder having a desired low dielectric loss tangent can be obtained by subjecting the silica powder to an appropriate heat treatment.

From the results of example 1(LK-1) and example 4 (LK-6), it was found that the dielectric loss tangent and the hydroxyl group content of the powder were hardly changed before and after the etching treatment. On the other hand, when the cured product of the composition obtained by blending each powder with the resin was broken and the fracture surface was observed, the former (example 5) observed more cracks than the resin portion because the resin and the silica powder were strongly bonded, while the latter (example 6) observed cracks at the interface between the silica powder and the resin. From this, it is found that the etching treatment hardly affects the dielectric loss tangent of the powder after the heat treatment, and has an effect of improving the adhesive strength with the resin.

Further, it is understood from examples 6 and 7 that the dielectric loss tangent of the cured product can be easily reduced by using a resin composition in which the low dielectric silica powder of the present invention is blended with a low dielectric resin.

Further, when the results of example 6 and comparative example 4, and example 7 and comparative example 5 were observed, it was found that: by using the resin composition containing the heat-treated low dielectric silica particles, the dielectric loss tangent of the cured product can be easily reduced.

It has been known that low silanol silica can be obtained by heat treatment, but it is considered that when silica powder is treated at a high temperature, a strain layer is formed on the surface, and the strength of a cured product of a resin composition filled with the heat-treated silica powder is lowered. Therefore, heat-treated silica powder that can be used as a filler whose adhesion strength to a resin is important has not been put to practical use.

However, according to the studies of the inventors of the present application, it was found for the first time that a resin composition obtained by blending heat-treated silica particles into a resin has sufficient strength even if cured. Further, it has been found that the dielectric loss tangent of a cured product can be easily reduced by heat treatment. Further, according to further studies by the inventors of the present application, it was found for the first time that the strained layer on the surface of the silica powder can be easily removed by immersing in an etching solution as described above. By combining the heat treatment and the etching treatment, the selection range of the raw material silica powder is widened, which contributes to cost reduction, and a silica powder (etching silica powder) having a low dielectric loss tangent and excellent adhesion to a resin can be efficiently produced. As described above, the method for producing a low dielectric silica of the present invention can produce a silica powder having a low dielectric loss tangent and strong adhesion to the interface of the resin with high productivity, and therefore has a high industrial value.

The present invention is not limited to the above embodiments. The above embodiments are illustrative, and any embodiments having substantially the same configuration as the technical idea described in the claims of the present invention and having the same effects are included in the scope of the present invention.