Composite silica particles and method for producing the same

Abstract

This invention provides low dielectric constant composite silica particles and a method for producing the same, which are suitable as fillers for reducing the dielectric constant of laminates used in electronic wiring boards. [Solution] A composite silica particle having T units and Q units of siloxane, with a molar ratio of T units to Q units of 35 / 65 to 70 / 30, and a relative permittivity of 3.4 or less at a frequency of 10 GHz; and a method for producing composite silica particles, comprising hydrolysis and polycondensation of an alkoxysilane in an aqueous medium, wherein the alkoxysilane contains a trialkoxysilane in which a branched alkyl group having 5 or more carbon atoms is bonded to a silicon atom.

Description

[Technical Field]

[0001] The present invention relates to composite silica particles suitable for applications such as electronic wiring boards and a method for producing the same. [Background technology]

[0002] It is known that silica particle fillers are incorporated into resin materials for sealing materials and copper-clad laminates (hereinafter referred to as "laminated boards, etc.") used in electronic wiring boards to improve heat dissipation and reduce thermal expansion. In recent years, with the increasing functionality and miniaturization of electronic component packages, there has been a demand for improved insulation and even lower thermal expansion in laminates and other materials. As a result, various improvements are being considered not only for resin materials but also for silica particle fillers.

[0003] Synthetic silica particles used as fillers are broadly classified into two main types: dry silica such as fumed silica and wet silica produced by methods such as the sol-gel process. As for wet silica, a method is known in which organosilicon compounds having hydrolyzable groups, such as tetraethoxysilane and methyltrichlorosilane, are hydrolyzed and polycondensed (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2022-523589 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Incidentally, there is a growing demand for lower dielectric constants in laminates and the like to meet the requirements for next-generation electronic products, and there is also a need for lower dielectric constants in the fillers themselves. Conventional wet silica for fillers is easy to fill into resin materials, but a lower dielectric constant is desirable.

[0006] The present invention aims to provide low dielectric constant composite silica particles and a method for producing the same, which are suitable as fillers for reducing the dielectric constant of laminates used in electronic wiring boards and the like. [Means for solving the problem]

[0007] This invention is based on the discovery that composite silica particles with a low dielectric constant can be obtained by using a predetermined organosilicon compound as a raw material for wet silica.

[0008] The present invention provides the following means. [1] Composite silica particles having siloxane units of T units and Q units, with a molar ratio of T units to Q units of 35 / 65 to 70 / 30, and a relative permittivity of 3.4 or less at a frequency of 10 GHz. [2] True density is 1.00 to 2.00 g / cm³ 3 The composite silica particles of [1]. [3] Composite silica particles of [1] or [2] having a carbon content of 30% by mass or more. [4] A composite silica particle having carbon atoms inside the particle, one of the [1] to [3]. [5] A spherical composite silica particle of any of the following [1] to [4]. [6] A composite silica particle of any of [1] to [5], which is wet silica.

[0009] A method for producing composite silica particles according to any one of [7][1] to [6], wherein an alkoxysilane is hydrolyzed and polycondensed in an aqueous medium, and the alkoxysilane contains a trialkoxysilane in which a branched alkyl group having 5 or more carbon atoms is bonded to a silicon atom. [8] A method for producing the composite silica particles of [7], wherein the alkoxysilane further comprises a tetraalkoxysilane. [9] A method for producing the composite silica particles of [8], wherein the molar ratio of the trialkoxysilane to the tetrakoxysilane in the alkoxysilane is 35 / 65 to 70 / 30. [Effects of the Invention]

[0010] According to the present invention, composite silica particles having a low relative dielectric constant and a method for producing the same are provided. The composite silica particles of the present invention can be suitably used as a filler for reducing the relative dielectric constant of laminates and the like used in electronic wiring boards. Mode for Carrying Out the Invention

[0011] Definitions and meanings of terms and notations used in the present specification are shown below. Composite silica particles refer to carbon-containing particles having a siloxane bond as the main skeleton. The notation "X to Y" (where X and Y are numerical values) means a numerical range with X as the lower limit and Y as the upper limit. In numerical ranges (for example, ranges of content etc.), the stepwise described lower limits and upper limits may be combined independently of each other. The lower limits and upper limits of numerical ranges may be replaced with the numerical values described in the examples.

[0012] Composite Silica Particles Composite silica particles (hereinafter also simply referred to as particles) according to an embodiment of the present invention (hereinafter also referred to as the present embodiment) have T-unit and Q-unit siloxane units, wherein the content molar ratio of T units to Q units is 35 / 65 to 70 / 30, and the relative dielectric constant at a frequency of 10 GHz is 3.4 or less. The composite silica particles of the present embodiment have predetermined siloxane units, have a low relative dielectric constant, and can be suitably used as a filler for reducing the relative dielectric constant of laminates and the like used in electronic wiring boards.

[0013] The Q unit in siloxane units is SiO 4 / 2 , which is a unit in which four oxygen atoms are bonded to a silicon atom constituting a siloxane bond. The T unit is RSiO 3 / 2 , which is a unit in which three oxygen atoms and one carbon atom are bonded to a silicon atom constituting a siloxane bond. Here, R is a group containing a carbon atom bonded to an adjacent silicon atom.

[0014] The content molar ratio of T units to Q units (T unit / Q unit molar ratio) is 35 / 65 to 70 / 30, preferably 38 / 62 to 68 / 32, more preferably 40 / 60 to 67 / 33, so that the composite silica particles have a low relative dielectric constant. If the T unit / Q unit molar ratio is 35 / 65 or higher, it is easy to obtain composite silica particles with a sufficiently low relative dielectric constant. In addition, composite silica particles having a T unit / Q unit molar ratio exceeding 70 / 30 are practically difficult to produce.

[0015] The composite silica particles of the present embodiment, in addition to T units and Q units, include D units (R₂SiO 2 / 2 : a unit in which two oxygen atoms and two carbon atoms are bonded to a silicon atom constituting a siloxane bond), M units (R₃SiO 1 / 2 : a unit in which one oxygen atom and three carbon atoms are bonded to a silicon atom constituting a siloxane bond), or may have both D units and M units (R is the same as defined above). In this case, from the viewpoint of obtaining composite silica particles with a low relative dielectric constant, the total content of D units and M units in the composite silica particles is preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 0 mol%, based on all siloxane units.

[0016] The T unit / Q unit molar ratio is determined from solid-state 29 ²⁹Si nuclear magnetic resonance (NMR) spectra measured for the composite silica particles. Specifically, it is determined by the method described in the Examples. The content of D units and M units is also determined from solid-state 29 ²⁹Si NMR spectra in the same manner.

[0017] The composite silica particles of the present embodiment have a relative dielectric constant of 3.4 or less at a frequency of 10 GHz, preferably 2.5 to 3.3, more preferably 2.6 to 3.2. Compared with conventional silica particle fillers, which have a relative dielectric constant of about 4.0, the composite silica particles of the present embodiment have a lower relative dielectric constant. Therefore, when used as a filler for reducing the relative dielectric constant of laminated boards and the like used in electronic wiring boards, it is possible to reduce the relative dielectric constant of laminated boards and the like with a smaller filling amount.

[0018] The relative dielectric constant of the composite silica particles is measured with a dielectric constant measuring apparatus. The relative dielectric constant in the present embodiment is a value measured at a frequency of 10 GHz and room temperature (25°C).

[0019] When the composite silica particles of the present embodiment are used as a filler for reducing the relative dielectric constant of a laminated board or the like used for an electronic wiring board, from the viewpoint of enabling a reduction in the relative dielectric constant of the laminated board or the like with a smaller filling amount, the true density is preferably 1.00 to 2.00 g / cm 3 , more preferably 1.05 to 1.80 g / cm 3 , still more preferably 1.10 to 1.50 g / cm 3 .

[0020] The true density of the composite silica particles is a value obtained by dry density measurement based on the constant volume expansion method using helium gas displacement.

[0021] From the viewpoints that the composite silica particles of the present embodiment have a low relative dielectric constant and can suppress the coefficient of thermal expansion when used as a filler, the carbon content is preferably 30% by mass or more, more preferably 32 to 50% by mass, still more preferably 33 to 48% by mass.

[0022] The carbon content of the composite silica particles is measured by combustion infrared absorption method. Specifically, it is measured by the method described in the Examples.

[0023] In the composite silica particles of the present embodiment, from the viewpoint of improving filling property into a resin even when no surface treatment is performed, it is preferable that the carbon component is uniformly present in the particles. For this reason, the composite silica particles of the present embodiment preferably have carbon atoms inside the particles. Although carbon atoms may be present on the outer surface of the particle, it is preferable that the carbon atoms are also present inside the particle.

[0024] The composite silica particles in this embodiment are preferably spherical. The spherical shape of the composite silica particles allows for good filling properties in resin, making it easier to achieve a low dielectric constant with a smaller filling amount when used as a filler to reduce the dielectric constant of laminates and the like.

[0025] In this context, "spherical" refers to an object that can be visually identified as round in an image obtained using a scanning electron microscope (SEM) at a magnification of 5000x.

[0026] The composite silica particles in this embodiment are preferably wet silica. For example, if wet silica obtained by the sol-gel method or the like is used, composite silica particles with the above-described physical properties are more likely to be obtained. The specific manufacturing method for wet silica is not particularly limited, but the manufacturing method of this embodiment, as described later, can suitably produce the composite silica particles of this embodiment.

[0027] The composite silica particles of this embodiment can be suitably used as a filler compounded into resin in laminates used in electronic wiring boards and the like. The amount of composite silica particles blended into the resin can be adjusted as appropriate according to the required properties of the laminate, such as dielectric constant and heat resistance.

[0028] The resin into which the composite silica particles are incorporated is not particularly limited and may be a thermosetting resin, a thermoplastic resin, or a composite resin thereof. From the viewpoint of heat resistance, a thermosetting resin is preferred.

[0029] Examples of thermosetting resins include silicone resins (including silicone rubber), epoxy resins, phenolic resins, bismaleimide resins, cyanate resins, urethane resins, (meth)acrylic resins, vinyl ester resins, unsaturated polyester resins, and polyvinyl acetal resins. Curing agents and curing accelerators may be added to the thermosetting resins. Of these, silicone resins are preferred from the viewpoint of good flexibility and adhesion. Furthermore, epoxy resins are preferred from the viewpoint of heat resistance, adhesion, and insulation.

[0030] Examples of silicone resins include addition reaction curing type silicone resins, condensation reaction curing type silicone resins, and organic peroxide curing type silicone resins. In laminates and the like, from the viewpoint of excellent flexibility and adhesion, addition reaction curing type liquid silicone resins are preferred because they are less likely to generate bubbles caused by by-products.

[0031] Examples of epoxy resins include: difunctional glucidyl ether type epoxy resins such as bisphenol A type, bisphenol F type, bisphenol S type, hydrogenated bisphenol A type, and biphenyl type; glucidyl ester type epoxy resins such as glycidyl hexahydrophthalate and glycidyl dimer acid; linear aliphatic epoxy resins such as epoxidized polybutadiene and epoxidized soybean oil; heterocyclic epoxy resins such as triglycidyl isocyanurate; N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, N,N, Examples include glucidylamine-type epoxy resins such as N',N'-tetraglycidyl-1,3-benzenedi(methanamine), 4-(glycidyloxy)-N,N-diglycidylaniline, and 3-(glycidyloxy)-N,N-diglycidylaniline; phenol novolac-type epoxy resins; cresol novolac-type epoxy resins; biphenyl aralkyl-type epoxy resins; naphthalene aralkyl-type epoxy resins; tetrafunctional naphthalene-type epoxy resins; and polyfunctional glycidyl ether-type epoxy resins with three or more functions, such as triphenylmethane-type epoxy resins.

[0032] [Method for manufacturing composite silica particles] The method for producing the composite silica particles of this embodiment involves hydrolysis and polycondensation of an alkoxysilane in an aqueous medium, wherein the alkoxysilane contains a trialkoxysilane in which a branched alkyl group having 5 or more carbon atoms is bonded to a silicon atom.

[0033] The alkoxysilanes used as raw materials in the production of silica particles by the conventional sol-gel method are generally tetrafunctional, such as tetraethoxysilane, which has four alkoxy groups. In contrast, the production method of this embodiment uses a trifunctional trialkoxysilane as a raw material, in which a branched alkyl group with five or more carbon atoms is bonded to a silicon atom, and three alkoxy groups are bonded to the silicon atom. As a result, through hydrolysis and polycondensation of the raw material alkoxysilane, the branched alkyl group bonded to the silicon atom remains bonded to the silicon atom in the synthesized silica particles, and composite silica particles containing carbon atoms derived from the branched alkyl group are obtained.

[0034] The alkyl group bonded to the silicon atom of the trialkoxysilane is a branched alkyl group having 5 or more carbon atoms. Compared to cases where the alkyl group is linear or where the number of carbon atoms in the branched chain is 4 or less, the branched alkyl group, due to its steric hindrance, allows the carbon atoms of the alkyl chain to be distributed in an appropriate manner relative to the silicon atoms. Furthermore, in wet silica produced by the sol-gel method, it is presumed that the carbon atoms derived from the branched alkyl group are uniformly distributed within the composite silica particles, both on the outer surface and inside the particles. Therefore, it is presumed that using the trialkoxysilane as the raw material alkoxysilane will make it easier to obtain composite silica particles with a low dielectric constant.

[0035] Since the branched alkyl group is prone to moderate steric hindrance, it preferably has 6 to 12 carbon atoms, more preferably 7 to 10. A specific example is the 2,4,4-trimethylpentyl group. The trialkoxysilane may be used alone or in combination of two or more types.

[0036] The raw material alkoxysilane preferably contains the trialkoxysilane and, further, tetraalkoxysilane. By using the aforementioned trialkoxysilane and tetraalkoxysilane in combination, the resulting composite silica particles tend to have a lower dielectric constant. The tetraalkoxysilane may be used alone or in combination of two or more types.

[0037] The raw material alkoxysilane may contain dialkoxysilane and monoalkoxysilane, but from the viewpoint of lowering the dielectric constant of the resulting composite silica particles and ease of manufacturing, it is preferable to use only trialkoxysilane and tetraalkoxysilane.

[0038] The molar ratio of trialkoxysilane to tetraalkoxysilane in the raw material alkoxysilane is preferably 35 / 65 to 70 / 30, more preferably 38 / 62 to 68 / 32, and even more preferably 40 / 60 to 67 / 33. The aforementioned blending molar ratio is reflected in the T-unit / Q-unit molar ratio of siloxane units in the resulting composite silica particles, and approximates the T-unit / Q-unit molar ratio. From the viewpoint of achieving a low dielectric constant in the resulting composite silica particles and ease of manufacturing, it is preferable that the blending molar ratio is within the above range.

[0039] The alkoxy groups in the raw material alkoxysilane are hydrolyzable groups. The three alkoxy groups of the trialkoxysilane may be the same or different. The four alkoxy groups of the tetraalkoxysilane may also be the same or different. Furthermore, the alkoxy groups of the trialkoxysilane and the tetraalkoxysilane may each be the same or different. Since the alkoxy group is removed by hydrolysis, it does not remain in the resulting composite silica particles and does not affect the composition of the particles. For this reason, the alkoxy group is not particularly limited, but in consideration of the reaction rate of hydrolysis and by-products, a shorter carbon chain is preferable, and it is a methoxy group, ethoxy group, or propyl group.

[0040] A specific example of the trialkoxysilane mentioned above is triethoxy(2,4,4-trimethylpentyl)silane. Commercially available trialkoxysilanes can be used.

[0041] Specific examples of the tetraalkoxysilane mentioned above include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane. These compounds can be purchased commercially.

[0042] Hydrolysis and polycondensation of alkoxysilanes are carried out in an aqueous medium. The aqueous medium is water and an organic solvent that is easily miscible with water. The aqueous medium may be a single substance or a mixture of two or more substances. If it is a mixture, a mixture of an organic solvent and water is preferred from the viewpoint of promoting the hydrolysis reaction. Examples of organic solvents include alcohols such as methanol, ethanol, and propanol. Preferably, the organic solvent is the same type of alcohol produced from the leaving group after the hydrolysis of the alkoxysilane. When a mixture of organic solvent and water is used as an aqueous medium, in order to suppress fusion caused by the carbon content of the resulting composite silica particles and to obtain spherical particles, it is preferable that the molar ratio of the organic solvent to water be small, preferably 0.10 to 0.75, more preferably 0.20 to 0.70, and even more preferably 0.30 to 0.65.

[0043] From the viewpoint of ensuring a good reaction, the amount of aqueous medium in the reaction medium is preferably 5 to 200 times by mass, more preferably 10 to 150 times by mass, and even more preferably 15 to 100 times by mass, relative to the total amount of alkoxysilane raw materials.

[0044] Hydrolysis and polycondensation of alkoxysilanes are preferably carried out in the presence of an alkaline catalyst. Examples of catalysts include ammonia, potassium hydroxide, and sodium hydroxide, of which ammonia is preferred. The hydrolysis and polycondensation in the manufacturing method of this embodiment can be carried out under the same reaction conditions as conventional hydrolysis and polycondensation using tetraalkoxysilane as a raw material. For example, composite silica particles can be produced by dropping the alkoxysilane raw material into an aqueous medium containing water in the presence of an ammonia catalyst, reacting the resulting sol to gel, and then drying it. More specifically, it can be produced by the method described in the examples.

[0045] The reaction temperature depends on the aqueous medium used, but from the viewpoint of promoting the reaction and suppressing the volatilization of the aqueous medium, it is preferably 15 to 80°C, more preferably 20 to 75°C, and even more preferably 25 to 70°C. The reaction time is preferably 1 to 48 hours, more preferably 2 to 42 hours, and even more preferably 3 to 36 hours, from the viewpoint of sufficient reaction progress and particle production efficiency.

[0046] Powdered composite silica particles can be obtained by washing the reaction product with an organic solvent such as alcohol (e.g., ethanol) and then drying it. Drying only needs to be done by sufficient evaporation of the organic solvent. From the viewpoint of drying efficiency, heating may be used, but from the viewpoint of suppressing fusion between particles, air drying at room temperature may also be used. After drying, if necessary, the composite silica particles may be obtained by crushing. [Examples]

[0047] The present invention will be specifically described below based on the following examples. The present invention is not limited to the following examples, and various modifications are possible without departing from the spirit of the invention.

[0048] [Manufacturing of composite silica particles] (Example 1) In a 300 mL glass container, combine 16.2 g of tetraethoxysilane (TEOS), 16.2 g of triethoxy(2,4,4-trimethylpentyl)silane (TMP) (TMP / TEOS molar ratio 0.75 / 1), 108 g of ethanol, and 65 g of pure water. Stir at room temperature (25°C) using a stirrer (2-blade, 300 min / second rotation speed). -1The mixture was stirred for 3 hours to carry out the hydrolysis reaction and obtain the reaction raw material solution. In a 1L glass container, 208.8g of pure water and 48g of 10% by mass aqueous ammonia were stirred, and the reaction raw material solution was added at a rate of 4mL / min, followed by a reaction for 3 hours. The reaction product is centrifuged (rotation speed 8000 min⁻¹). -1 After 5 minutes, the solid was collected, washed with ethanol, and centrifuged again. This process was repeated a total of three times. The obtained solid was dried at 150°C for 2 hours, then crushed in a mortar to obtain powdered composite silica particles.

[0049] (Examples 2-4 and Comparative Examples 1-3) In Example 1, the quantities were changed to achieve the TMP / TEOS molar ratio shown in Table 1, and the composite silica particles were manufactured in the same manner as in Example 1. In the case of Comparative Example 3 (TMP / TEOS molar ratio 3.0 / 1), particles could not be obtained.

[0050] [Measurement and evaluation of particle samples] The following various measurements and evaluations were performed on each particle obtained in the above examples and comparative examples. The results of these measurements and evaluations are shown in Table 1.

[0051] (Molar ratio of T units to Q units) solid 29 Si NMR measurement (Bruker, "AVANCE NEO 400"; 7mmφ probe) 1 H resonance frequency 400MHz, 29 The test was performed with a Si resonance frequency of 79.5 MHz, a magic angle rotation of 5000 Hz, 144 integration cycles, a delay time of 400 sec, and at room temperature (25°C). Solid obtained by the DD / MAS (Dipole Decoupling / Magic Angle Rotation) method 29The ratio of the integral values ​​of the T-unit peak (chemical shift between -80 ppm and -40 ppm) and the Q-unit peak (chemical shift between -120 ppm and -80 ppm) was determined using software analysis of the Si NMR spectrum (Bruker's "TopSpin"). This ratio was expressed as the molar ratio of T-units to Q-units (T-unit / Q-unit molar ratio).

[0052] (Relative permittivity) The relative permittivity of the powder sample was measured using a dielectric constant measuring device (AET Corporation, frequency 10 GHz, room temperature (25°C); "N5222A PNA Microwave Network Analyzer," Keysight Corporation).

[0053] (true density) Measurements were taken using a dry-type automatic densimeter ("AccuPic III 1350," manufactured by Shimadzu Corporation).

[0054] (Carbon content) The measurements were taken using a carbon-sulfur analyzer (EMIA-821FAW, manufactured by Horiba, Ltd.) that employs non-dispersive infrared absorption spectroscopy in a tubular electric furnace.

[0055] (particle shape) In the SEM observation images (magnification 5000x), particles were observed and judged as "round" if they had no corners and appeared to be nearly perfect circles, and as "not round" if they had corners or appeared to be distorted circles.

[0056] [Table 1]

[0057] As shown in Table 1, by producing silica particles using a sol-gel method with a raw material alkoxysilane prepared by blending a predetermined trialkoxysilane and tetraalkoxysilane in a predetermined molar ratio, composite silica particles were obtained in which the T-unit / Q-unit molar ratio was within a predetermined range and the relative dielectric constant was low.

Claims

1. Composite silica particles having siloxane units of T and Q units, with a molar ratio of T units to Q units of 35 / 65 to 70 / 30, and a relative permittivity of 3.4 or less at a frequency of 10 GHz.

2. True density is 1.00 to 2.00 g / cm³ ３ The composite silica particles according to claim 1.

3. The composite silica particles according to claim 1 or 2, wherein the carbon content is 30% by mass or more.

4. The composite silica particle according to claim 1 or 2, having carbon atoms inside the particle.

5. The composite silica particles according to claim 1 or 2, which are spherical in shape.

6. The composite silica particles according to claim 1 or 2, wherein the silica is wet-processed silica.

7. A method for producing composite silica particles according to claim 1 or 2, Alkoxysilanes are hydrolyzed and polycondensed in an aqueous medium. The alkoxysilane includes a trialkoxysilane in which a branched alkyl group having 5 or more carbon atoms is bonded to a silicon atom. A method for producing composite silica particles.

8. The method for producing composite silica particles according to claim 7, wherein the alkoxysilane further comprises a tetraalkoxysilane.

9. The method for producing composite silica particles according to claim 8, wherein the molar ratio of the trialkoxysilane to the tetraalkoxysilane in the alkoxysilane is 35 / 65 to 70 / 30.

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