Porous superfine silica powder with core-shell structure and preparation method of porous superfine silica powder

Abstract

The invention discloses porous superfine silica powder with a core-shell structure and a preparation method thereof, the silica powder comprises an inner core and an outer shell coating the surface of the inner core, the porosity of the outer shell is larger than that of the inner core, and the ratio of the radius r of the inner core to the layer thickness d of the outer shell is 1: (0.2-0.6); the silica powder has mechanical strength, low dielectric property and high dimensional stability. The preparation method comprises the following steps: coating an amorphous porous silicon oxide outer layer by a sol-gel method on the basis of taking conventional silica powder as an inner core, and adding a dispersing agent to inhibit agglomeration of particles and improve the sphericity of the obtained porous superfine silica powder with the core-shell structure, furthermore, the surfaces of the particles are instantaneously shrunk due to instantaneous high temperature during flash drying, so that the sphericity and the surface bonding strength of the porous superfine silica powder with the core-shell structure are improved, and the flowability and the mechanical strength of the material are further improved.

Description

Technical Field

[0001] The present invention relates to the technical fields of biomedicine and biomaterials. Specifically, it relates to a porous ultrafine silica powder with a core-shell structure and a preparation method thereof. Background Art

[0002] Copper clad laminate (abbreviated in English as: CCL), as the most important carrier of integrated circuits, acts as an industrial basic material in integrated circuits. A copper clad laminate is a plate-like material formed by impregnating a reinforcing material with resins of different properties, adding different fillers (such as silica powder), drying, and then covering one or both sides with copper foil through hot pressing. It mainly consists of three major parts: a substrate, copper foil, and a copper clad laminate adhesive. Among them, the substrate is an insulating laminate composed of a polymer synthetic resin, a reinforcing material, and a filler.

[0003] As a typical inorganic filler, silica powder has excellent properties of "three highs" (high insulation, high heat conduction, high heat stability), "three lows" (low thermal expansion coefficient, low dielectric constant, low raw material cost), and "two resistances" (acid and alkali resistance, wear resistance), and has attracted much attention in recent years.

[0004] When silica powder is used as a filler in copper clad laminates, it is mainly used to improve the heat resistance and dimensional stability of copper clad laminates, and it is a truly functional filler. However, the compatibility between silica powder and the resin system is poor. Therefore, surface modification is usually required using a silane coupling agent to improve the compatibility with the resin. However, the surface modification effect of most silane coupling agents is limited and affects the property performance of silica powder. At the same time, with the rapid development of microelectronics technology, people's requirements for copper clad laminates are becoming more and more stringent. Silica powder prepared by traditional methods has difficulty meeting the requirements of low expansion coefficient, high mechanical strength, and low dielectric constant.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The present invention provides a porous ultrafine silica powder with a core-shell structure. This porous ultrafine silica powder with a core-shell structure has a specific morphology and can improve the mechanical strength, dielectric properties, and thermal stability of the substrate of copper clad laminates.

[0007] The present invention is implemented as follows:

[0008] In a first aspect, the present invention provides a porous ultrafine silica powder with a core-shell structure, including a core and a shell covering the surface of the core. The porosity of the shell is greater than that of the core, and the ratio of the radius r of the core to the layer thickness d of the shell satisfies 1:0.2 - 0.6.

[0009] Among them, the porosity refers to the ratio of the pore area to the total area of the core or the shell; the radius r of the core is 1 / 2 of the average value of the maximum Feret diameter and the minimum Feret diameter of the core.

[0010] In some embodiments, the silica fume satisfies one of the following characteristics:

[0011] Characteristic 1: The circularity C of the silica fume is 0.7 or more; wherein, circularity = 4πA / l 2 , A is the projected area of the particle, and l is the projected perimeter of the particle;

[0012] Characteristic 2: The BET specific surface area B of the silica fume is 6 - 15 m 2 / g, calculated by the BET method through nitrogen adsorption-desorption test;

[0013] In some embodiments, the silica fume satisfies wherein,

[0014] In some embodiments, the silica fume satisfies one of the following characteristics:

[0015] Characteristic 3: The specific pore volume of the silica fume is 0.6 - 1.8 cm 3 / g, wherein the specific pore volume is measured by the nitrogen adsorption-desorption BJH method;

[0016] Characteristic 4: The ratio of the total volume of pores with a pore diameter greater than 50 nm in the silica fume to the total pore volume is less than 40%, wherein the total volume of pores with a pore diameter greater than 50 nm and the total pore volume are measured by the nitrogen adsorption-desorption BJH method.

[0017] It should be noted that the specific pore volume is equal to the total pore volume, which is the same physical quantity, measured by the nitrogen adsorption-desorption BJH method. Specifically, first, the adsorption-desorption isotherm is obtained, and then the BJH method is used to analyze and fit the adsorption-desorption isotherm to obtain the specific pore volume or the total pore volume, as well as the total volume of micropores, mesopores, and macropores.

[0018] In some embodiments, the silica fume satisfies one of the following characteristics:

[0019] Characteristic 5: The Dv50 of the silica fume is 1 - 5.1 μm, and Dv50 refers to the particle diameter when the cumulative volume distribution value is 50%;

[0020] Characteristic 6: The core radius of the silica fume is 0.4 - 2 μm;

[0021] Characteristic 7: The circularity C of the silica fume is 0.7 - 0.85;

[0022] Characteristic 8: The BET specific surface area B of the silica fume is 8.4 - 14.22 m 2 / g;

[0023] Characteristic 9: The specific pore volume of the silica fume is 0.85 - 1.78 cm 3 / g, wherein the specific pore volume is measured by the nitrogen adsorption-desorption BJH method;

[0024] Feature 10: The ratio of the total volume of pores with a pore diameter greater than 50 nm in the silica powder to the total pore volume is 12% - 40%, wherein the total volume of pores with a pore diameter greater than 50 nm and the total pore volume are measured by the nitrogen adsorption-desorption BJH method.

[0025] In a second aspect, the present invention provides a method for preparing a porous ultrafine silica powder with a core-shell structure in any of the above embodiments, comprising the following steps:

[0026] Disperse silica powder A in a solvent, adjust the pH to 3 - 5 with an acid, then add a silicon source and a dispersant, stir and react, and perform solid-liquid separation, flash drying, crushing, sieving, and demagnetization to obtain a porous ultrafine silica powder with a core-shell structure.

[0027] In some embodiments, silica powder A is obtained by grinding quartz sand, and the particle size Dv50 of the silica powder A is 0.4 - 2 μm;

[0028] In some embodiments, calcination is further included after flash drying, and the calcination temperature is 300 - 600 °C and the time is 1 - 3 h.

[0029] In some embodiments, the acid is selected from acetic acid or hydrochloric acid.

[0030] In some embodiments, the above preparation method satisfies one of the following conditions:

[0031] Feature one: The quartz sand is selected from crystalline quartz sand or fused quartz sand with a particle size of 10 - 30 μm;

[0032] Feature two: The solvent is selected from at least one of deionized water, methanol, and ethanol;

[0033] Feature three: The feeding mass ratio of silica powder A, silicon source, and dispersant is 1:0.8 - 1.2:0.05 - 0.1.

[0034] Feature four: The mixing mass ratio of the silicon source and the solvent is 1:3 - 5;

[0035] Feature five: The silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, alkyltrimethoxysilane, alkyltriethoxysilane, dialkyldimethoxysilane, and dialkyldiethoxysilane;

[0036] Wherein, the alkyl group includes a straight-chain or branched-chain alkyl group with 1 - 18 carbon atoms;

[0037] Feature six: The dispersant is selected from at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxypropyl cellulose, chitosan, hydroxypropyl cellulose, sodium alginate, and hyaluronic acid;

[0038] Feature 7: The temperature of the stirring reaction is 40-60°C, and the time is 2-4 h;

[0039] Feature 8: The feeding rate of the flash drying is 1-5 kg / min, the temperature is 250-400°C, the time is 10-30 s, and the air flow rate is 15-30 m / s.

[0040] Feature 9: Crushing means air flow crushing;

[0041] Feature 10: Sieving means sieving through a 300-600 mesh sieve.

[0042] In a third aspect, the present invention provides a copper clad laminate substrate, comprising the porous ultrafine silica powder with a core-shell structure in any of the above embodiments.

[0043] The present invention has the following beneficial effects:

[0044] (1) The present invention provides a porous ultrafine silica powder with a core-shell structure. This silica powder has a porous structure, and the porosity of the outer shell is greater than that of the inner core, enabling it to balance mechanical strength, low dielectric properties, and high dimensional stability. Specifically, the solid or less porous inner core endows the silica powder with good mechanical strength; the outer shell is amorphous porous silica, providing a rich pore structure, which is beneficial to buffering volume changes under heat, thereby reducing the thermal expansion coefficient; in addition, the rich pore structure reduces the conductivity, making it have low dielectric properties.

[0045] Furthermore, this silica powder has a high sphericity, which is beneficial to improving the processing fluidity and thermal stability of the silica powder; furthermore, this silica powder meets Among them, Since the specific surface area of a sphere is the smallest under the same volume, a high sphericity is not conducive to a high BET. However, due to the porous structure of the silica powder prepared in the present invention, it compensates for the BET loss caused by the high sphericity, and a high BET is beneficial to increasing the bonding strength with the resin. Furthermore, this silica powder also meets that the volume ratio of macropores is below 40%, and macropores are not conducive to dielectric properties and mechanical stability.

[0046] (2) The present invention provides a method for preparing porous ultrafine silica powder with a core-shell structure. Based on silica powder as the core, an amorphous porous silica outer layer is coated by the sol-gel method. A dispersant is added to inhibit particle aggregation and improve the sphericity of the obtained porous ultrafine silica powder with a core-shell structure. A volatile acid is added to cause pores during the drying process while avoiding the residue of impurities. Further, the instantaneous high temperature during flash drying causes the surface of the particles to shrink instantaneously, improving the sphericity and surface bonding strength of the porous ultrafine silica powder with a core-shell structure, thereby improving the fluidity and mechanical strength of the material. And the solvent volatilizes instantaneously, reducing the compressive effect of capillary force on the pore wall, effectively preventing pore collapse, and shortening the drying time is beneficial to inhibiting the formation of aggregation.

[0047] The dispersant has abundant hydroxyl groups and can be dispersed on the outer surface of the silica gel by hydrogen bond force to disperse it and regulate its sphericity. In addition, it acts as a pore-forming agent during the drying or calcination process, which is beneficial to increasing the surface inhomogeneity of the particles and improving the specific surface area. Brief Description of the Drawings

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0049] Figure 1 The SEM panoramic view of the silica powder prepared in Example 1;

[0050] Figure 2 The SEM sectional view of the silica powder prepared in Example 1;

[0051] Figure 3 The pore size distribution curves of the silica powder prepared in Example 1 and Example 4. Detailed Embodiments

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0053] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order, or primary-secondary relationship of the indicated technical features.

[0054] As used herein, the term "embodiment" means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0055] In the embodiments of the present application, the term "or / and" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A or / and B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0056] In addition, in this text, the character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0057] In the embodiments of the present application, the meaning of "a plurality of" refers to two or more (including two). Similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of layers" refers to two or more layers (including two layers), unless otherwise clearly specified and limited.

[0058] In the embodiments of the present application, the meaning of "at least one" refers to one or more than one.

[0059] Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application according to specific circumstances.

[0060] The features and properties of the present invention will be further described in detail below in conjunction with embodiments.

[0061] Embodiment 1

[0062] A method for preparing porous ultrafine silica powder with a core-shell structure, comprising the following steps:

[0063] (1) The crystalline quartz sand with Dv50 of 25 μm (purity > 99.9%) is respectively dry-ground and wet-milled, and then dried and air-crushed to obtain silica powder A with Dv50 of 1.2 μm; the dry grinding is carried out in a horizontal ball mill with zirconium balls as the grinding medium, the mass ratio of material to balls is 1:2, and the ball milling is carried out for 3 h; when wet grinding, ethanol is used as the dispersion medium, and the addition amount of ethanol is 50% of the powder mass.

[0064] (2) Disperse silica powder A in water, add citric acid to adjust the pH value to 5, stir for 0.5 h, then add the silicon source and the dispersant and stir evenly, raise the temperature to 50 °C and carry out a stirring reaction for 3 h. The solid obtained after filtration is flash-dried, then calcined at 600 °C for 1 h, and finally air-crushed and sieved through a 400-mesh sieve, and demagnetized to obtain porous ultrafine silica powder with a core-shell structure.

[0065] Among them, the feeding mass ratio of silica powder A, the silicon source, and the dispersant is 1:0.8:0.08.

[0066] The silicon source is a mixture of tetraethyl orthosilicate and octyl methyl dimethoxysilane with a mass ratio of 4:1.

[0067] The dispersant is chitosan (degree of deacetylation ≥ 95%, viscosity 100 - 200 mPa·s, purchased from Shanghai Macklin Reagent).

[0068] The mixing mass ratio of the silicon source to the solvent is 1:2.

[0069] The flash drying conditions include: a feeding rate of 1 kg / min, a temperature of 400 °C, a time of 30 s, and an air flow rate of 30 m / s.

[0070] Example 2

[0071] A method for preparing porous ultrafine silicon micropowder with a core - shell structure, comprising the following steps:

[0072] (1) The same as in Example 1;

[0073] (2) Disperse silicon micropowder A in water, add acetic acid to adjust the pH value to 4, stir for 0.5 h, then add the silicon source and the dispersant and stir evenly. Heat up to 50 °C and carry out a stirring reaction for 3 h. After filtration, flash dry the obtained solid, then calcine it at 300 °C for 2 h, and finally perform air - flow crushing and pass through a 400 - mesh sieve. After demagnetization, porous ultrafine silicon micropowder with a core - shell structure is obtained.

[0074] Among them, the feeding mass ratio of silicon micropowder A, the silicon source, and the dispersant is 1:1:0.08.

[0075] The silicon source is tetraethyl orthosilicate.

[0076] The dispersant is chitosan (degree of deacetylation ≥ 95%, viscosity 100 - 200 mPa·s, purchased from Shanghai Macklin Reagent).

[0077] The mixing mass ratio of the silicon source to the solvent is 1:3.

[0078] The flash drying conditions include: a feeding rate of 5 kg / min, a temperature of 300 °C, a time of 20 s, and an air flow rate of 15 m / s.

[0079] Example 3

[0080] A method for preparing porous ultrafine silicon micropowder with a core - shell structure, comprising the following steps:

[0081] (1) The same as in Example 1;

[0082] (2)Disperse silica powder A in an aqueous ethanol solution of 40 wt%, add hydrochloric acid to adjust the pH value to 3, stir for 0.5 h, then add the silicon source and dispersant and stir evenly, raise the temperature to 50 °C and carry out a stirring reaction for 3 h. After filtration, the obtained solid is subjected to flash drying, then calcined at 300 °C for 1 h, and finally air-classified through a 400-mesh sieve and demagnetized to obtain porous ultrafine silica powder with a core-shell structure.

[0083] Among them, the feeding mass ratio of silica powder A, silicon source, and dispersant is 1:1.2:0.1.

[0084] The silicon source is a mixture of tetraethyl orthosilicate and octyl methyl dimethoxysilane with a mass ratio of 4:1.

[0085] The dispersant is hydroxypropyl cellulose (2 wt% aqueous solution, purchased from Shanghai Aladdin Reagent).

[0086] The mixing mass ratio of the silicon source and the solvent is 1:4.

[0087] The flash drying conditions include: a feeding rate of 3 kg / min, a temperature of 300 °C, a time of 30 s, and an air flow rate of 30 m / s.

[0088] Example 4

[0089] A preparation method of porous ultrafine silica powder with a core-shell structure, comprising the following steps:

[0090] (1) Melted quartz sand with a Dv50 of 20 μm (purity > 99.9%) is respectively dry-ground and wet-milled, and then dried and air-classified to obtain silica powder A with a Dv50 of 1.2 μm; for dry grinding, a horizontal ball mill is used with zirconium balls as the grinding medium, the material-to-ball mass ratio is 1:2, and the ball milling is carried out for 3 h; during wet grinding, ethanol is used as the dispersion medium, and the addition amount of ethanol is 50% of the powder mass.

[0091] (2) Disperse silica powder A in an aqueous ethanol solution of 40 wt%, add acetic acid to adjust the pH value to 4, stir for 0.5 h, then add the silicon source and dispersant and stir evenly, raise the temperature to 40 °C and carry out a stirring reaction for 3 h. After filtration, the obtained solid is subjected to flash drying, and finally air-classified through a 400-mesh sieve and demagnetized to obtain porous ultrafine silica powder with a core-shell structure.

[0092] Among them, the feeding mass ratio of silica powder A, silicon source, and dispersant is 1:1:0.08.

[0093] The silicon source is a mixture of tetraethyl orthosilicate and octyl methyl dimethoxysilane with a mass ratio of 2:1.

[0094] The dispersant is polyvinyl alcohol PVA-1788 (purchased from Yinhuan Chemical Industry).

[0095] The mixing mass ratio of the silicon source to the solvent is 1:4.

[0096] The flash drying conditions include: a feeding rate of 3 kg / min, a temperature of 350 °C, a time of 20 s, and an air flow rate of 30 m / s.

[0097] Example 5

[0098] The difference from Example 4 is that the dispersant is hydroxypropyl cellulose (an aqueous solution of 2 wt%, purchased from Shanghai Aladdin Reagent).

[0099] Example 6

[0100] The difference from Example 4 is that the flash drying conditions include: a feeding rate of 5 kg / min, a temperature of 250 °C, a time of 10 s, and an air flow rate of 15 m / s.

[0101] Example 7

[0102] The difference from Example 4 is that the solvent is water and the dispersant is hydroxypropyl cellulose (an aqueous solution of 2 wt%, purchased from Shanghai Aladdin Reagent).

[0103] Example 8

[0104] The difference from Example 4 is that in step (2), the dispersant is sodium alginate (M / G = 1:2, molecular weight of 30K, purchased from Shanghai Macklin Reagent); the feeding mass ratio of silica powder A, silicon source, and dispersant is 1:1:0.05; the reaction temperature is 60 °C; the flash drying conditions include: a feeding rate of 5 kg / min, a temperature of 250 °C, a time of 10 s, and an air flow rate of 15 m / s.

[0105] Example 9

[0106] A method for preparing a porous ultrafine silica powder with a core-shell structure, comprising the following steps:

[0107] (1) Crystalline quartz sand with a Dv50 of 10 μm (purity > 99.9%) is respectively dry-ground and wet-milled, and then dried and pneumatically crushed to obtain silica powder A with a Dv50 of 0.4 μm; for dry grinding, a horizontal ball mill is used with zirconium balls as the grinding medium, the mass ratio of the material to the balls is 1:4, and the ball milling is carried out for 6 h; during wet grinding, ethanol is used as the dispersion medium, and the addition amount of ethanol is 50% of the powder mass.

[0108] (2) Silica powder A is dispersed in a 40 wt% aqueous ethanol solution, hydrochloric acid is added to adjust the pH value to 3, after stirring for 0.5 h, the silicon source and the dispersant are added and stirred evenly, the temperature is raised to 50 °C and stirring reaction is carried out for 3 h, the obtained solid is flash-dried after filtration, and finally pneumatically crushed and passed through a 400-mesh sieve, and after demagnetization, a porous ultrafine silica powder with a core-shell structure is obtained.

[0109] Among them, the feeding mass ratio of silica powder A, silicon source, and dispersant is 1:1.2:0.1.

[0110] The silicon source is a mixture of methyl orthosilicate and octadecylmethyldimethoxysilane with a mass ratio of 1:1.

[0111] The dispersant is sodium carboxymethyl cellulose (viscosity 50 - 200 mPa·s, purchased from Shanghai Macklin Reagent).

[0112] The mixing mass ratio of the silicon source and the solvent is 1:5.

[0113] The flash drying conditions include: a feeding speed of 3 kg / min, a temperature of 350 °C, a time of 20 s, and an air flow speed of 30 m / s.

[0114] Example 10

[0115] A preparation method of porous ultrafine silica powder with a core - shell structure, comprising the following steps:

[0116] (1) The fused quartz sand with Dv50 of 25 μm (purity > 99.9%) is dry - milled to obtain silica powder A with Dv50 of 2 μm; the dry - milling is carried out using a horizontal ball mill with zirconium balls as the grinding medium, the mass ratio of material to balls is 1:4, and the ball - milling is carried out for 6 h.

[0117] (2) The silica powder A is dispersed in an 80 wt% ethanol - aqueous solution, hydrochloric acid is added to adjust the pH value to 3, after stirring for 0.5 h, the silicon source and the dispersant are added and stirred evenly, the temperature is raised to 50 °C and stirred for reaction for 3 h, after filtration, the obtained solid is flash - dried, then calcined at 300 °C for 1 h, and finally air - crushed and sieved through a 400 - mesh sieve, and demagnetized to obtain the porous ultrafine silica powder with a core - shell structure.

[0118] Among them, the feeding mass ratio of silica powder A, silicon source, and dispersant is 1:1.2:0.1.

[0119] The silicon source is n - octyltriethoxysilane.

[0120] The dispersant is hydroxypropyl cellulose (2 wt% aqueous solution, purchased from Shanghai Aladdin Reagent).

[0121] The mixing mass ratio of the silicon source and the solvent is 1:5.

[0122] The flash drying conditions include: a feeding speed of 5 kg / min, a temperature of 250 °C, a time of 20 s, and an air flow speed of 30 m / s.

[0123] Comparative Example 1

[0124] It is the silica powder A obtained in step (1) of Example 4.

[0125] Comparative Example 2

[0126] (1) The same as in Example 4.

[0127] (2) Disperse silica powder A in an aqueous ethanol solution of 40 wt%, adjust the pH value to 5 with acetic acid, stir for 0.5 h, then add the silicon source and dispersant and stir evenly, raise the temperature to 40 °C and carry out a stirring reaction for 3 h, filter, perform flash drying on the obtained solid, then calcine at 500 °C for 3 h, and finally carry out air jet milling and screen through a 400-mesh sieve, and obtain porous ultrafine silica powder with a core-shell structure after demagnetization.

[0128] Among them, the feeding mass ratio of silica powder A, silicon source, and dispersant is 1:0.4:0.05.

[0129] The silicon source is tetraethyl orthosilicate.

[0130] The dispersant is polyvinyl alcohol PVA-1788 (purchased from Yinhuan Chemical Industry).

[0131] The mixing mass ratio of the silicon source and the solvent is 1:5.

[0132] The flash drying conditions include: a feeding speed of 1 kg / min, a temperature of 400 °C, a time of 20 s, and an air flow speed of 30 m / s.

[0133] Comparative Example 3

[0134] (1) The same as in Example 4.

[0135] (2) Disperse silica powder A in an aqueous methanol solution of 60 wt%, adjust the pH value to 3 with acetic acid, stir for 0.5 h, then add the silicon source and dispersant and stir evenly, raise the temperature to 40 °C and carry out a stirring reaction for 3 h, filter, perform freeze drying on the obtained solid, and finally carry out air jet milling and screen through a 400-mesh sieve, and obtain porous ultrafine silica powder with a core-shell structure after demagnetization.

[0136] Among them, the feeding mass ratio of silica powder A, silicon source, and dispersant is 1:1.5:0.05.

[0137] The silicon source is tetraethyl orthosilicate.

[0138] The dispersant is polyvinyl alcohol PVA-1788 (purchased from Yinhuan Chemical Industry).

[0139] The mixing mass ratio of the silicon source and the solvent is 1:3.

[0140] The freeze drying conditions include: pre-freezing at -10 °C for 12 h, and then freeze drying at -40 °C for 24 h.

[0141] Perform performance tests on the silica powder prepared in the above examples and comparative examples:

[0142] Test Example 1 SEM

[0143] Figure 1 and Figure 2 are the overall view and sectional view of the silica powder prepared in Example 1 respectively. It can be seen from Figure 1 that the silica powder has a high sphericity. After calculation, the average circularity is 0.85. It can be seen from Figure 2 that the silica powder has a core-shell structure, and the pores on the outer shell are more than those on the inner core. The ratio of the radius of the inner core to the thickness of the outer shell d / r is 0.22.

[0144] Calculation method of circularity: Use ImageJ to analyze the shape of the particles in the overall scanning electron micrograph, collect the circularity of the particles (=4πA / l 2 , where A is the projected area of the particle and l is the projected perimeter of the particle), and finally obtain the average value. The number of measurement samples for each sample is 20, randomly selected.

[0145] Calculation method of the ratio of the radius of the inner core to the thickness of the outer shell d / r: Use ImageJ to measure the inner core diameter r i and the outer shell thickness d i of the particles in the sectional scanning electron micrograph, and then obtain and then calculate the average value The inner core radius r i is 1 / 2 of the average value of the maximum Feret diameter and the minimum Feret diameter, and the outer shell thickness d i is the average value calculated by measuring 5 random positions of the same particle.

[0146] Test Example 2 Nitrogen adsorption and desorption

[0147] Use a Micromeritics physical adsorption instrument to measure the specific surface area according to the BET method of GB / T 19587-2004, and calculate the specific pore volume and pore size distribution using the BJH method according to the adsorption-desorption isotherm curve.

[0148] Figure 3 are the pore size distribution curves of the silica powder prepared in Examples 1 and 4. Pores less than 2 nm are micropores, 2-50 nm are mesopores, and pores greater than 50 nm are macropores. It can be seen from the curve that the proportion of macropores in Example 1 is more than that in Example 4. Integrate the curve parts corresponding to different pores to calculate the volume ratio of micropores, mesopores, and macropores to the total pore volume.

[0149] Test Example 3 Particle size

[0150] Use a Mastersize2000 laser particle size analyzer to test the Dv50 of the silica powder

[0151] Table 1 shows the various properties of the silica powder prepared in the specific embodiments.

[0152] Table 1

[0153]

[0154] As can be seen from Table 1, the preparation method provided by the present invention is conducive to preparing silica powder that meets the parameters of the target product. By adjusting the preparation process conditions, the parameters of the target product can be adjusted.

[0155] Furthermore, the silica powder prepared in the specific embodiments is applied to prepare a copper-clad laminate substrate, and its performance is tested.

[0156] A method for preparing a copper-clad laminate substrate includes the following steps:

[0157] Add 25 g of tetrabromobisphenol A epoxy resin (Changchun resin) and 7.5 g of the silica powder in the specific embodiments to a reaction kettle, control the temperature at 130 - 140 °C, keep warm and stir for 2 h to obtain a mixture; dissolve 0.25 g of dicyandiamide (curing agent) in N,N-dimethylformamide, stir until completely dissolved, then add the above mixture, and then add 0.4 g of accelerator (dimethylimidazole), stir evenly to obtain a glue with a resin content of 50 wt%; apply the above glue to an electronic grade 7628 fiberglass cloth, set the gap of the clamping shaft to 0.35 mm, after the fiberglass cloth is coated with glue, first leave it to dry at room temperature, and then bake it in an oven at 170 °C for 8 min to obtain the copper-clad laminate substrate.

[0158] The application examples corresponding to Examples 1 - 10 are Application Examples 1 - 10, and the application examples corresponding to Comparative Examples 1 - 3 are Application Comparative Examples 1 - 3.

[0159] The following performance tests are carried out on the application examples, and the results are listed in Table 2.

[0160] Test Example 4 Dielectric properties

[0161] The dielectric properties measured by a WY2851 type high-frequency Q meter: the test temperature is 25 °C, the test frequency is 1 MHz, and the thickness of the specimen is 1.6 mm.

[0162] Test Example 5 Coefficient of linear expansion

[0163] Obtained by testing with a thermomechanical analyzer.

[0164] Test Example 6 Mechanical strength

[0165] Test the bending performance of the copper-clad laminate substrate according to GB / T 9341 - 2008; test the impact performance of the copper-clad laminate substrate according to GB / T 13525 - 1992.

[0166] Table 2

[0167]

[0168] It can be seen from the results that the example has lower dielectric properties and higher thermal stability compared with the comparative example, and the mechanical strength still meets the application requirements. Thus, it shows that the silica powder provided by the present invention is beneficial to taking into account the dielectric properties, thermal stability and mechanical strength of the copper clad laminate substrate, and has good comprehensive properties.

[0169] Compared with Application Example 1, the silica powder used in Application Example 2 satisfies BET≥6m 2 / g, and the specific pore volume ≥0.52 cm 3 / g. Therefore, the obtained substrate has lower dielectric properties and higher thermal stability, and the flexural strength and impact strength are slightly reduced. The reason is that the pores in the outer layer increase, and the air filled in the pores has a low dielectric constant and poor thermal conductivity. Therefore, it is beneficial to reduce the dielectric properties and thermal deformation.

[0170] Compared with Application Example 2, the silica powder used in Application Example 3 satisfies Therefore, the obtained substrate has lower dielectric properties and higher thermal stability; although the specific pore volume of Application Example 3 is larger than that of Application Example 2, due to the lower macropore content in Application Example 3, the mechanical strength of Application Example 3 is slightly higher than that of Application Example 2, indicating that the distribution of the pore structure has an impact on the mechanical strength.

[0171] The silica powder used in Application Example 4 satisfies both d / r of 0.2 - 0.6 and the specific pore volume of 0.52 - 1.84 cm 3 / g, and the macropore proportion is below 40%. Therefore, it has better comprehensive properties in the specific implementation manner.

[0172] The silica powders used in Application Examples 4, 5, and 6 have similar d / r, Dv50, core radius, and circularity. However, due to the different pore numbers, they have different specific pore volumes and BETs, but the macropore contents are similar. With the increase of the specific pore volume and BET, the dielectric properties of the substrate increase, the thermal stability is enhanced, but the mechanical properties decrease.

[0173] The silica powder used in Application Example 7 has a higher macropore proportion compared with Application Example 4, and its dielectric constant, thermal expansion coefficient, and mechanical properties all decrease. Thus, it can be seen that the size and distribution uniformity of the pores will affect various properties. At the same specific pore volume, due to the larger pore diameter of the macropores, the pore number decreases, making the area of the continuous phase (including silica and resin) larger. Therefore, it is not conducive to reducing the dielectric properties and thermal stability, and at the same time, the macropores are likely to be stress concentration points, resulting in a decrease in mechanical properties.

[0174] The silica powder used in Application Example 8 has a lower circularity compared to Application Example 4, resulting in a reduction in various properties. Specifically, the worse the sphericity of the particles, the worse the binding compatibility with the resin, leading to a reduction in various properties.

[0175] Due to the relatively large particle size of the silica powder used in Application Example 10, even though the specific pore volume is large and the proportion of macropores is small, the properties of the resulting substrate are worse than those of Application Example 4. At the same feed ratio, the larger the particle size of the silica powder, the larger the continuous phase area. Therefore, it is also not conducive to reducing the dielectric properties and thermal stability. At the same time, large particles are likely to act as stress concentration points, resulting in a decrease in mechanical properties.

[0176] The d / r of the silica powder used in Application Comparative Examples 2 and 3 exceeds the range of 0.2 - 0.6. Therefore, Application Comparative Example 2 with a value lower than 0.2 has poor dielectric properties and thermal stability; Application Comparative Example 3 with a value higher than 0.6 has poor mechanical properties.

[0177] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A porous ultrafine silicon powder with a core-shell structure, characterized in that: It comprises an inner core and an outer shell covering the inner core, wherein the porosity of the outer shell is greater than that of the inner core, and the ratio of the radius r of the inner core to the layer thickness d of the outer shell satisfies 1:0.2-0.

6.

2. The porous ultrafine silicon powder with a core-shell structure according to claim 1, characterized in that: The silicon powder meets one of the following characteristics: Feature 1: The circularity C of the silicon powder is greater than 0.7; Feature 2: The specific surface area of ​​the silicon powder is 6 to 15 m 2 / g.

3. The porous ultrafine silicon powder with a core-shell structure according to claim 1 or 2, characterized in that: The silicon powder satisfies in, 4. The porous ultrafine silicon powder with a core-shell structure according to any one of claims 1 to 3, characterized in that: The silicon powder meets one of the following characteristics: Feature 3: The specific pore volume of the silicon powder is 0.6 to 1.8 cm 3 / g, where the specific pore volume is measured using the nitrogen adsorption-desorption BJH method; Feature 4: The total volume of pores with a pore size greater than 50 nm in the silicon micropowder accounts for less than 40% of the total pore volume, wherein the total volume of pores with a pore size greater than 50 nm and the total pore volume are measured using the nitrogen adsorption-desorption BJH method.

5. The porous ultrafine silicon powder with a core-shell structure according to any one of claims 1 to 4, characterized in that: The silicon powder meets one of the following characteristics: Feature 5: The Dv50 of the silicon powder is 1 to 5.1 μm, where Dv50 refers to the particle size when the cumulative value of volume distribution is 50%; Feature 6: The inner core radius of the silicon powder is 0.4 to 2 μm; Feature 7: The circularity C of the silicon powder is 0.7 to 0.85; Feature 8: The BET specific surface area of ​​the silicon powder is 8.4 to 14.22 m 2 / g; Feature 9: The specific pore volume of the silicon powder is 0.85 to 1.78 cm 3 / g, where the specific pore volume is measured using the nitrogen adsorption-desorption BJH method; Feature 10: The total volume of pores with a pore size greater than 50 nm in the silicon micropowder accounts for 12% to 40% of the total pore volume, wherein the total volume of pores with a pore size greater than 50 nm and the total pore volume are measured using the nitrogen adsorption-desorption BJH method.

6. The method for preparing porous ultrafine silicon powder with a core-shell structure according to any one of claims 1 to 5, characterized in that: The following steps are involved: The silicon micropowder A is dispersed in a solvent, an acid is added to adjust the pH to 3-5, and then a silicon source and a dispersant are added, stirred for reaction, and solid-liquid separation, flash drying, crushing, sieving, and demagnetization are performed to obtain porous ultrafine silicon micropowder with a core-shell structure.

7. The method for preparing porous ultrafine silicon powder with a core-shell structure according to claim 6, characterized in that: The silicon micropowder A is obtained by grinding quartz sand, and the particle size Dv50 of the silicon micropowder A is 0.4 to 2 μm; And / or, the flash drying further includes calcination, the calcination temperature is 300-600° C., and the time is 1-3 hours.

8. The method for preparing porous ultrafine silicon powder with a core-shell structure according to claim 7, characterized in that: The acid is selected from acetic acid or hydrochloric acid.

9. The method for preparing porous ultrafine silicon powder with a core-shell structure according to claim 7 or 8, characterized in that: One of the following conditions is met: Feature 1: The quartz sand is selected from crystalline quartz sand or fused quartz sand with a particle size of 10 to 30 μm; Feature 2: The solvent is selected from at least one of deionized water, methanol and ethanol; Feature 3: The mass ratio of silicon powder A, silicon source and dispersant is 1:0.8~1.2:0.05~0.

1. Feature 4: The mixing mass ratio of silicon source to solvent is 1:3-5; Feature 5: The silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, alkyltrimethoxysilane, alkyltriethoxysilane, dialkyldimethoxysilane and dialkyldiethoxysilane; Feature 6: The dispersant is selected from at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxypropyl cellulose, chitosan, hydroxypropyl cellulose, sodium alginate and hyaluronic acid; Feature 7: The stirring reaction temperature is 40-60°C and the time is 2-4h; Feature 8: The feed rate of the flash drying is 1-5 kg / min, the temperature is 250-400° C., the time is 10-30 s, and the air flow velocity is 15-30 m / s. Feature 9: The crushing refers to air flow crushing; Feature 10: The sieving refers to sieving through a 300-600 mesh sieve.

10. A copper clad laminate substrate, characterized in that: The copper-clad laminate substrate comprises the porous ultrafine silicon powder with a core-shell structure as claimed in any one of claims 1 to 5.

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