Black silica filler, preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of fillers, and disclosed are a black silica filler, a preparation method therefor and a use thereof. According to the present invention, polysiloxane containing T units is used as initial raw material particles; then under an inert gas atmosphere, heating treatment is performed by controlling the upper limit of the moisture content in the gas atmosphere to be 3500 ppm when the temperature rises above 650°C, causing organic groups in the particles to be thermally decomposed into carbon; and then, surface carbon of the particles is removed under an oxygen-containing gas atmosphere, thereby obtaining a black silica filler having an average particle size of 0.1-1 μm. The black silica filler having the small particle size has excellent properties of few surface defects and low moisture absorption after storage.

Description

A black silica filler and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of fillers, and in particular to a black silica filler and a preparation method and application thereof. Background Art

[0002] In the semiconductor field, when assembling passive components, semiconductor components, electroacoustic devices, display devices, optical devices, and radio frequency devices into devices, circuit board substrate materials such as high-density interconnect boards, high-frequency and high-speed boards, and motherboards are required. These substrate materials are generally composed mainly of fillers and organic polymers such as epoxy resins. The main function of the fillers is to reduce the thermal expansion coefficient of the organic polymers, which are mainly angular or spherical silica. To facilitate laser printing or reduce light aging, pigments are usually added to the substrate materials to dye them gray or black. A commonly used pigment is acetylene black. However, acetylene black is an electron conductor, and its use as a pigment in substrate materials poses a risk of short circuits. Therefore, the preparation of black silica, which also plays a dyeing role during the process of filling the substrate materials, is of great significance.

[0003] Prior art, such as patent application publication number CN102924869A, discloses a black modified silica. This is produced by carbonizing organic matter at high temperatures and adsorbing it into the silica. However, this method has the following disadvantages: ① The carbon in this black silica is adsorbed on the surface, resulting in a high carbon content on the outer surface and a low carbon content inside. This causes surface carbon to aggregate and become conductive; ② To reduce the dielectric properties of black silica, the carbon content is reduced to prevent carbon aggregation, but this also results in a reduction in the blackness of the silica.

[0004] For example, patent application publication number CN113603103A provides a semiconductor packaging material and its preparation method. This patent uses polysiloxane particles containing T units as the starting material. The particles are then heat-treated at 600-800°C in a non-oxidizing atmosphere or vacuum to carbonize the alkyl groups within them and condense the silanol groups on their surfaces. The remaining silanol groups are then calcined at 800-1100°C to condense the remaining silanol groups, resulting in a semiconductor packaging material, namely, black silica powder. The black silica powder provided in this patent has a particle size of 0.8-4.5 μm, but the preparation method has the following problems: Residual carbon in the powder easily causes the silanol groups to form numerous pores, resulting in a high porosity. The powder is also susceptible to moisture absorption from the air. Therefore, when used as a filler in a substrate material, the substrate material exhibits significant dielectric loss.

[0005] With the rapid development of microelectronics and communications technology, semiconductor chips are continuously developing towards high integration, miniaturization, high frequency, and high power, thus placing higher demands on the dielectric properties of electronic packaging materials. The dielectric properties of existing black silica cannot meet the current filler requirements in the semiconductor industry. Therefore, a new method for preparing black silica is urgently needed to address the dielectric loss problem of black silica. Summary of the Invention

[0006] To address the dielectric loss problem of black silica, the present invention provides a black silica filler, a preparation method, and applications thereof. The present invention controls the water content of the atmosphere during the preparation of the black silica filler to produce a black silica powder with an average particle size of 0.1 to 1 μm.

[0007] The specific technical solutions of the present invention are:

[0008] In a first aspect, the present invention provides a black silica filler.

[0009] The carbon mass content of the black silica filler particles provided by the present invention gradually increases from the surface to the inside; the average particle size is 0.1-1 μm, and the carbon mass content is 0.3%-9%.

[0010] Preferably, the carbon content of the black silica filler particles of the present invention is 6% to 9% by mass.

[0011] Preferably, the black silica filler particles of the present invention have a water content of less than 591 ppm / m2 after being placed under environmental conditions of 25°C and 50% RH for 48 hours from the time of preparation.

[0012] Furthermore, from the start of preparation, the moisture content is less than 245ppm / m2 after being placed under environmental conditions of 25°C and 50%RH for 48 hours.

[0013] In the semiconductor field, the filling of substrate materials often requires the use of silica fillers with small particle sizes of 0.5~2μm as the main material for graded filling, while small particles below 0.5μm can be used for graded filling. In order to simultaneously play a dyeing role in the process of filling substrate materials, the present invention provides a black silica filler with a single-layer structure, an average particle size of 0.1~1μm, and a carbon mass content of 0.3%~9%. The filler particles also have other excellent properties, such as: under the environmental conditions of 25°C and 50%RH, after being placed for 48 hours from the time of preparation, its water content is less than 591ppm / m2, and it has a small water absorption capacity. When used as a filler for filling substrate materials, it can make the substrate material have less dielectric loss.

[0014] In the actual application process of silica fillers, they are generally not used directly after preparation. They have a shelf life and therefore absorb water during storage. The black silica provided by the present invention absorbs little water after storage, which has a significant advantage in reducing dielectric loss caused by water absorption.

[0015] In a second aspect, the present invention provides a method for preparing a black silica filler, specifically:

[0016] Spherical polysiloxane particles comprising T units are provided and subjected to the following steps:

[0017] Step S1: performing a heating treatment under an inert gas atmosphere to thermally decompose the organic groups in the particles into carbon;

[0018] Step S2: calcining the particles in an oxygen-containing gas atmosphere to remove carbon from the particle surface;

[0019] Wherein, the water content of the inert gas atmosphere is controlled to be no more than 3500 ppm when the temperature of the heating process is higher than 650°C; the particle size of the black silica filler is 0.1-1 μm;

[0020] Wherein, T unit = R1SiO3, R1 is a hydrogen atom or an independently selected hydrocarbon group having 1 to 16 carbon atoms.

[0021] The present invention uses polysiloxane particles containing T units as a starting material, then heats them in an inert gas atmosphere at a temperature above 650°C with a moisture content upper limit of 3500 ppm to thermally decompose the organic groups in the particles into carbon. The carbon on the particle surface is then removed in an oxygen-containing gas atmosphere to obtain a black powder, namely the black silica filler. The average particle size of the black silica filler particles is 0.1 to 1 μm. The preparation method provided by the present invention has the advantage of producing a black silica filler with a small particle size and excellent dielectric properties.

[0022] The biggest reason for the above advantages is that the method of the present invention controls the water content of the gas atmosphere during the heat treatment of the particles, so that the water content of the gas atmosphere is controlled at 3500 ppm or below when the temperature is higher than 650°C.

[0023] The inventors discovered through experiments that during the heat treatment of polysiloxane raw material particles, as silanol groups condense, a significant amount of water is generated within the particles, including adsorbed water, surface hydroxyl groups, and internal hydroxyl groups. This results in a certain concentration of water in the atmosphere. At the heat treatment temperature, the water reacts with carbon, removing carbon from the particles. This reaction is the primary factor limiting carbon retention in small-particle polysiloxane raw material particles during heat treatment. If the water concentration of the atmosphere during heat treatment of small-particle polysiloxane raw material particles is not controlled, black silica cannot be produced. Therefore, the inventors conducted further research and discovered that the minimum temperature for the reaction between water and carbon is approximately 700°C. At temperatures above 650°C, controlling the water content of the polysiloxane atmosphere to 3500 ppm or less effectively prevents water from removing carbon derived from the decomposition of organic groups in the small-particle polysiloxane raw material.

[0024] In large-particle polysiloxane raw material particles, the amount of carbon in the particles is relatively large. After water takes away part of the carbon in the particles, a large amount of carbon can still remain in the particles. Therefore, it is possible to decompose the organic groups without controlling the moisture content of the heat treatment gas atmosphere, and then calcine under oxygen-containing conditions to finally prepare black silica. However, if the moisture concentration of the gas atmosphere during heat treatment is not controlled, only large-particle black silica of more than 5μm can be prepared, and small-particle black silica cannot be prepared.

[0025] In order to prepare small-particle black silica, the present invention maintains the water content in the gas atmosphere at no more than 3500 ppm when the temperature is higher than 650°C during heat treatment of polysiloxane, thereby reducing the contact between carbon in the silica spheres and water and preventing the carbon in the small-particle silica spheres from being carried away by water. Then, the silica spheres are calcined under oxygen-containing conditions to remove carbon on the surface, and silanol groups are condensed to repair surface defects of the silica spheres, forming a dense layer on the surface of the silica spheres and improving the density of the product. This reduces the problem of surface carbon shedding during the shelf life or use of the product, forming pores that lead to easy water absorption, and ultimately prepares black silica filler particles with an average particle size of 0.1 to 1 μm.

[0026] In addition, the black silica filler prepared by the method provided above has few surface defects, low water absorption, and excellent performance of low dielectric loss.

[0027] As a preferred embodiment of the above preparation method of the present invention, in step S1, the terminal temperature of the heating treatment is 850-1100°C.

[0028] As a preferred embodiment of the above preparation method of the present invention, the temperature is slowly increased or / and an inert gas is introduced at a high flow rate during the heating process.

[0029] Controlling the moisture content of the atmosphere during the heating process is key to preparing small-particle black silica in this invention. By slowly increasing the temperature and introducing a high flow rate of inert gas during the heating process, the moisture content of the atmosphere in the heating furnace can be controlled within a low range.

[0030] In order to make the black silica density obtained higher, water absorption is less, the present invention preferably controls the moisture in the heating furnace by passing through a large flow of nitrogen during the silanol condensation process in a lower range. The reason is that, the heat treatment process of step S1 under an inert gas atmosphere, the nitrogen of a large flow rapidly takes out the silanol condensation in the polysiloxane raw material to generate moisture, which can affect the arrangement of the R1 group of the T unit, and then has an impact on the overall structure arrangement of the polysiloxane, so that in the back section calcining process, the density of the surface dense layer formed by the silanol condensation is higher. The silica with higher density, in the case of same particle size, has less porosity, i.e., has less specific surface area, and is placed in the air for a long time in the later stage, and water absorption is small. Therefore, the present invention more preferably controls the moisture in the heating furnace by passing through a large flow of nitrogen during the silanol condensation process in a lower range.

[0031] By reducing the heating rate, the condensation rate of silanol groups in the polysiloxane raw material is reduced, thereby reducing the rate of water generation. The water content in the heat treatment gas atmosphere can also be controlled to be no higher than 3500 ppm. However, controlling the water content in this way will easily cause it to burn white in the later calcination process. Alternatively, by adjusting the calcination process, black silica can be obtained, but the obtained black silica will absorb a large amount of water after being left for a period of time.

[0032] More preferably, in step S1, the flow rate of the inert gas is 100-1000 mL / min.

[0033] The flow rate of the inert gas during heat treatment can be adjusted according to the specific model of the heat treatment device, the amount of heat treatment raw materials, etc., and the water content in the heat treatment gas atmosphere is preferably controlled to be no higher than 3500ppm when the temperature is higher than 650°C.

[0034] More preferably, in step S1, the heating rate of the slow heating is 0.1-1°C / min.

[0035] As a preferred embodiment of the preparation method of the present invention, in step S2, the volume concentration of oxygen in the oxygen-containing gas is 0.3% to 30%.

[0036] More preferably, in step S2, the volume concentration of oxygen in the oxygen-containing gas is 3% to 21%.

[0037] In step S2, the oxygen volume concentration in the oxygen-containing gas atmosphere is 3% to 21%, which can achieve a better densification effect on the particle surface. Along the radial direction of the silica particles, carbon closer to the surface is more likely to come into contact with oxygen in the gas atmosphere and, therefore, more likely to react with it. Therefore, the black silica prepared by the present invention is presumed to have a structure in which the carbon content gradually increases from the surface to the interior, and the carbon content gradually increases from the surface to the interior in a uniform gradient.

[0038] As a preferred embodiment of the preparation method of the present invention, in step S2, the calcination temperature is 850-1200°C.

[0039] More preferably, in step S2, the calcination treatment time is 0.5 to 72 hours.

[0040] As a preferred embodiment of the above preparation method of the present invention, the polysiloxane further comprises Q units, D units and / or M units; wherein, Q units = SiO4, D units = R2R3SiO2, M units = R4R5R6SiO; R2, R3, R4, R5, and R6 are each a hydrogen atom or an independently selectable hydrocarbon group having 1 to 18 carbon atoms.

[0041] More preferably, the T unit raw material of the polysiloxane is a hydrocarbyltrialkoxysilane or a hydrocarbyltrichlorosilane, the Q unit raw material is at least one selected from the group consisting of tetraalkoxysilane, silicon tetrachloride and silicon dioxide, the D unit raw material is at least one selected from the group consisting of dihydrocarbyldialkoxysilane and dihydrocarbyldichlorosilane, and the M unit raw material is at least one selected from the group consisting of trihydrocarbylalkoxysilane, trihydrocarbylchlorosilane and hexahydrocarbyldisilazane.

[0042] In a third aspect, the present invention provides the use of the above-mentioned black silica filler in the preparation of semiconductor packaging materials and substrate materials.

[0043] In the semiconductor industry, the semiconductor chip packaging process requires the use of semiconductor packaging materials such as molding compound, die-stack adhesive, underfill, and chip carriers to protect the semiconductor chips and provide mechanical support. When assembling passive components, semiconductor components, electroacoustic devices, display devices, optical devices, and RF devices into devices, circuit board substrates such as high-density interconnect boards, high-frequency and high-speed boards, and motherboards are required. These semiconductor packaging and substrate materials are often dyed gray or black to facilitate laser printing or laser drilling on the components, to reduce light aging and improve durability, to reduce light reflection, and to minimize color variation between batches. To achieve this, the industry typically uses acetylene black, which does not contain conductive ions, as a dye to dye semiconductor packaging and substrate materials black. However, acetylene black is an electron conductor, so it must be highly dispersed, smaller than the metal spacing of the semiconductor components, to prevent short circuits. However, as the packaging density of semiconductor components increases, the risk of short circuits caused by acetylene black increases. Based on the above preparation method and silica filler, it can replace acetylene black as a pigment for dyeing semiconductor packaging materials and substrate materials black, thereby resolving the short-circuit problem caused by acetylene black. Without any inventive effort, those skilled in the art can use the black spherical or amorphous silica filler provided by the present invention to densely fill resin in place of acetylene black pigment to form semiconductor packaging materials and substrate materials. Therefore, these semiconductor packaging materials and substrate materials should also be included in the scope of protection of the present invention.

[0044] Preferably, the semiconductor packaging material and substrate material can be used for molding compound, patch adhesive, underfill, chip carrier, circuit board, or intermediate semi-finished products thereof. The molding compound is for DIP packaging, SMT packaging, MUF, FO-WLP, or FCBGA packaging. Preferably, the circuit board is an HDI, high-frequency high-speed board, or motherboard.

[0045] Compared with the prior art, the present invention has the following technical effects:

[0046] (1) The present invention provides a black silica filler having a single-layer structure, an average particle size of 0.1 to 1 μm, and a carbon mass content of 0.3% to 9%, which can be used for gradation and tight filling of substrate materials and can also play a dyeing role.

[0047] (2) The black silica filler provided by the present invention has a water content of less than 245 ppm / m2 after being placed under the environmental conditions of 25°C and 50% RH for 48 hours. It has a small water absorption capacity and can reduce the dielectric loss of the substrate material when used as a filler for filling the substrate material.

[0048] (3) The present invention also provides a method for preparing black silica filler, which uses polysiloxane particles containing T units as starting raw material particles, and then controls the temperature to be higher than 650°C and the water content of the gas atmosphere to be no higher than 3500 ppm to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon, and then calcined in an oxygen-containing gas atmosphere to remove the carbon on the particle surface and densify the particle surface to obtain a small-particle black silica filler with a particle size of 0.1 to 1 μm. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to the following embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0050] Along the radial direction of the silica particles, the carbon closer to the surface is more likely to come into contact with oxygen in the gas atmosphere and, therefore, more likely to react with it. Therefore, the black silica prepared by the present invention is presumed to have a structure in which the carbon content gradually increases from the surface to the inside, and the carbon content gradually increases from the surface to the inside at a uniform gradient.

[0051] In the semiconductor field, the filling of substrate materials often requires the use of silica fillers with small particle sizes of 0.5~2μm as the main material for graded filling, while small particle sizes below 0.5μm can be used for graded filling. In order to simultaneously play a dyeing role in the process of filling substrate materials, the present invention provides a black silica filler with a single-layer structure, an average particle size of 0.1~1μm, and a carbon mass content of 0.3%~9%. The filler particles also have other excellent properties, such as: under the environmental conditions of 25°C and 50%RH, the water content of the particles as they are just prepared can be regarded as basically 0, and after being placed for 48 hours from the beginning of preparation, the water content is less than 591ppm / m2. It can be seen that the filler particles provided by the present invention have a small water absorption capacity, and when used as a filler for filling substrate materials, the substrate material can have less dielectric loss.

[0052] The following examples provide specific implementations of the methods of the present invention, and the detection methods involved include:

[0053] The moisture content of the particles is the Karl Fischer moisture at 200 degrees Celsius, which is tested using a Karl Fischer titrator.

[0054] The average particle size is measured using a laser particle size distribution analyzer LA 700 manufactured by HORIBA. Herein, the average particle size refers to the volume average diameter of the particles.

[0055] The specific surface area was measured using FlowSorb III 2305 manufactured by SHIMADZU.

[0056] The true specific gravity was measured using Microtrac BEL's BELPycno.

[0057] The uranium and thorium contents were determined using an Agilent 7700X ICP MS. The sample preparation method was to burn the sample at 800°C and then dissolve it in hydrofluoric acid.

[0058] The carbon content of silica particles was determined using a CS 8810C carbon-sulfur analyzer from Sichuan Sai En Si.

[0059] The carbon content on the surface of silica particles was determined by X-ray photoelectron spectroscopy.

[0060] The water content of the gas atmosphere in the muffle furnace is characterized by the water content at the furnace's gas outlet. In the present invention, the water content of the gas atmosphere during the heat treatment process in the muffle furnace can be replaced by the water content at the heat treatment furnace's gas outlet. In the present invention, the heating rate or the gas flow rate or rate is adjusted so that the maximum water content at the outlet is 3500 ppm when the temperature is above 650°C. That is, the water concentration in the muffle furnace does not exceed 3500 ppm when the temperature is above 650°C during the entire heat treatment process.

[0061] The water content at the gas outlet of the heat treatment furnace is tested using a thermometer and hygrometer. The manufacturer of the thermometer and hygrometer is Shenzhen Huahanwei Temperature and Humidity Instrument, model TH11R-EX-H.

[0062] Example 1

[0063] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0064] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0065] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 300 mL / min so that the maximum water content at the outlet of the muffle furnace is 1800 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 1800 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 1800 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 1800 ppm.

[0066] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0067] The process parameters of heat treatment and calcination are shown in Table 1.

[0068] Example 2

[0069] The main difference between this embodiment and embodiment 1 is that the water concentration does not exceed 2500 ppm when the temperature in the muffle furnace is higher than 650° C. during the heat treatment process.

[0070] This example uses polysiloxane containing T units as a starting material to prepare black silica in the following steps:

[0071] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0072] S2. Place the spherical polysiloxane powder in a muffle furnace and set the nitrogen flow rate to a relatively large flow rate of 250 mL / min. When the temperature in the muffle furnace is higher than 650°C, the maximum water content at the outlet is 2500 ppm. That is, when the temperature in the muffle furnace is higher than 650°C, the moisture content in the muffle furnace does not exceed 2500 ppm. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept at this temperature for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 2500 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 2500 ppm.

[0073] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C., and calcine for 3 hours to densify the particle surface, thereby obtaining black silica with a carbon content that increases uniformly from the surface to the inside.

[0074] The process parameters of heat treatment and calcination are shown in Table 1.

[0075] Example 3

[0076] The main difference between this embodiment and embodiment 1 is that the water concentration does not exceed 3500 ppm when the temperature in the muffle furnace is higher than 650° C. during the heat treatment process.

[0077] This example uses polysiloxane containing T units as a starting material to prepare black silica in the following steps:

[0078] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0079] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 200 mL / min. When the temperature in the muffle furnace is higher than 650°C, the maximum water content at the outlet is 3500ppm. That is, when the temperature in the muffle furnace is higher than 650°C, the moisture content in the muffle furnace does not exceed 3500ppm. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 3500ppm, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 3500ppm.

[0080] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C., and calcine for 3 hours to densify the particle surface, thereby obtaining black silica with a carbon content that increases uniformly from the surface to the inside.

[0081] The process parameters of heat treatment and calcination are shown in Table 1.

[0082] Example 4

[0083] The main difference between this embodiment and embodiment 1 is that the particle size of the polysiloxane raw material of the T unit is 0.73 μm. Other aspects are the same as those of embodiment 1.

[0084] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0085] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 60 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. After standing for 1 hour, filter and dry to obtain spherical polysiloxane powder with an average particle size of 0.73 μm.

[0086] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 300 mL / min so that the maximum water content at the outlet of the muffle furnace is 1800 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 1800 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 1800 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 1800 ppm.

[0087] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0088] The process parameters of heat treatment and calcination are shown in Table 1.

[0089] Example 5

[0090] The main difference between this embodiment and embodiment 1 is that the particle size of the polysiloxane raw material of the T unit is 0.35 μm. Other aspects are the same as those of embodiment 1.

[0091] This example uses polysiloxane containing T units as a starting material to prepare black silica in the following steps:

[0092] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 100 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 0.35 μm.

[0093] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 300 mL / min so that the maximum water content at the outlet of the muffle furnace is 1800 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 1800 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 1800 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 1800 ppm.

[0094] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0095] The process parameters of heat treatment and calcination are shown in Table 1.

[0096] Example 6

[0097] The main difference between this embodiment and embodiment 1 is that the particle size of the polysiloxane raw material of the T unit is 0.18 μm. Other aspects are the same as those of embodiment 1.

[0098] This example uses polysiloxane containing T units as a starting material to prepare black silica in the following steps:

[0099] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 160 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 0.18 μm.

[0100] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 300 mL / min so that the maximum water content at the outlet of the muffle furnace is 1800 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 1800 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 1800 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 1800 ppm.

[0101] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0102] The process parameters of heat treatment and calcination are shown in Table 1.

[0103] Example 7

[0104] The main difference between this embodiment and embodiment 1 is that the particle size of the polysiloxane raw material of the T unit is 0.11 μm. Other aspects are the same as those of embodiment 1.

[0105] This example uses polysiloxane containing T units as a starting material to prepare black silica in the following steps:

[0106] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 160 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 0.11 μm.

[0107] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 300 mL / min so that the maximum water content at the outlet of the muffle furnace is 1800 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 1800 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 1800 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 1800 ppm.

[0108] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0109] The process parameters of heat treatment and calcination are shown in Table 1.

[0110] Example 8

[0111] The main difference between this embodiment and embodiment 1 is that the method for controlling the moisture content of the gas atmosphere during the heat treatment process is to increase the temperature at a low rate.

[0112] This example uses polysiloxane containing T units as a starting material to prepare black silica in the following steps:

[0113] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0114] S2. Place the spherical polysiloxane powder in a muffle furnace, set the nitrogen flow rate to 50 mL / min, and under a nitrogen atmosphere, raise the temperature in the furnace to 850°C at a rate of 1°C / min, keep warm for 10 hours, and heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. The temperature is raised at a rate of 1°C / min to ensure that the maximum water content at the outlet is 1800 ppm when the furnace temperature is higher than 650°C. During the heating process, the water concentration at the gas outlet of the muffle furnace is continuously monitored. When the water concentration increases to more than 1800 ppm when the furnace temperature is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the maximum water concentration at the gas outlet of the muffle furnace is continuously monitored to be 1800 ppm. During this period, the nitrogen flow rate does not exceed 100 mL / min, that is, when the temperature in the muffle furnace is higher than 650°C, the water content in the furnace does not exceed 1800 ppm.

[0115] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0116] The process parameters of heat treatment and calcination are shown in Table 1.

[0117] Example 9

[0118] The main differences between this embodiment and embodiment 1 are that the method for controlling the moisture content of the gas atmosphere during the heat treatment process is to increase the temperature at a low rate, and the calcination treatment time is 0.5 hours.

[0119] This example uses polysiloxane containing T units as a starting material to prepare black silica in the following steps:

[0120] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0121] S2. Place the spherical polysiloxane powder in a muffle furnace, set the nitrogen flow rate to 50 mL / min, and raise the furnace temperature to 850°C at a rate of 1°C / min under a nitrogen atmosphere. Hold the temperature for 10 hours to heat-treat the particles, causing the organic groups in the particles to thermally decompose into carbon. The temperature is raised at a rate of 1°C / min to ensure that the maximum water content at the outlet is 1800 ppm when the furnace temperature is above 650°C. During the heating process, continuously monitor the moisture concentration at the gas outlet of the muffle furnace. When the moisture concentration increases to more than 1800 ppm when the furnace temperature is above 650°C, increase the nitrogen flow rate appropriately. In this embodiment, the maximum moisture concentration at the gas outlet of the muffle furnace is continuously monitored to be 1800 ppm. During this period, the maximum nitrogen flow rate does not exceed 100 mL / min. That is, when the temperature in the muffle furnace is above 650°C, the moisture content in the furnace does not exceed 1800 ppm.

[0122] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C., and calcine for 0.5 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0123] The process parameters of heat treatment and calcination are shown in Table 1.

[0124] Example 10

[0125] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0126] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0127] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 300 mL / min so that the maximum water content at the outlet of the muffle furnace is 1800 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 1800 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 1800 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 1800 ppm.

[0128] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C., and calcine for 0.5 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0129] The process parameters of heat treatment and calcination are shown in Table 1.

[0130] Example 11

[0131] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0132] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0133] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 100 mL / min so that the maximum water content at the outlet of the muffle furnace is 3000 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 3000 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 3000 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 3000 ppm.

[0134] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0135] The process parameters of heat treatment and calcination are shown in Table 1.

[0136] Example 12

[0137] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0138] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0139] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 1000 mL / min so that the maximum water content at the outlet of the muffle furnace is 1400 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 1400 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 1400 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 1400 ppm.

[0140] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C. and calcine for 3 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0141] The process parameters of heat treatment and calcination are shown in Table 1.

[0142] Example 13

[0143] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0144] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0145] S2. Place the spherical polysiloxane powder into a muffle furnace and set the nitrogen flow rate to a larger flow rate of 100 mL / min so that the maximum water content at the outlet of the muffle furnace is 2000 ppm when the temperature in the muffle furnace is higher than 650°C. That is, the moisture content in the muffle furnace does not exceed 2000 ppm when the temperature in the muffle furnace is higher than 650°C. Under a nitrogen atmosphere, the temperature in the furnace is raised to 1000°C at a rate of 10°C / min and kept warm for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the moisture concentration at the gas outlet of the muffle furnace is continuously monitored. When the moisture concentration increases to more than 2000 ppm when the temperature in the furnace is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the moisture content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum moisture content is 2000 ppm.

[0146] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 1200° C. and calcine for 10 hours to remove carbon on the particle surface and densify the particle surface to obtain black silica with a carbon content that increases uniformly from the surface to the inside.

[0147] The process parameters of heat treatment and calcination are shown in Table 1.

[0148] Comparative Example 1

[0149] The main difference from Example 1 is that during the heat treatment in step S2, the nitrogen flow rate is 50 mL / min, so that the water content in the furnace is within the range of 3500 ppm to 4200 ppm. Other aspects are the same as in Example 1.

[0150] The silicon dioxide particles of this comparative example were prepared by the following method:

[0151] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0152] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0153] S2. Place the spherical polysiloxane powder in a muffle furnace, set the nitrogen flow rate to 50 mL / min, and raise the temperature in the furnace to 850°C under a nitrogen atmosphere. Hold the temperature for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, continuously monitor the water concentration at the gas outlet of the muffle furnace. In this embodiment, the water concentration at the gas outlet of the muffle furnace is continuously monitored and is in the range of 2000ppm to 4200ppm. After the furnace temperature reaches above 650°C, the water concentration is in the range of 3500ppm to 4200ppm for a total of 5.3 hours.

[0154] S3. Switch the gas in the muffle furnace to air, adjust the temperature to 850° C., and calcine for 3 hours to obtain silicon dioxide particles.

[0155] The process parameters of heat treatment and calcination are shown in Table 1.

[0156] Comparative Example 2

[0157] The main difference from Example 1 is that in step S3, the gas is not switched to air. Other steps are the same as in Example 1.

[0158] The silicon dioxide particles of this comparative example were prepared by the following method:

[0159] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0160] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0161] S2, spherical polysiloxane powder is placed in a muffle furnace, and the nitrogen flow rate is set to a larger flow rate, 300 mL / min, so that the maximum water content at the outlet is 1800ppm, that is, during the heat treatment process, when the temperature in the muffle furnace is higher than 650°C, the moisture content in the furnace does not exceed 1800ppm. Under a nitrogen atmosphere, the temperature in the furnace is raised to 850°C at a rate of 5°C / min, and the particles are heat-treated so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, the water concentration at the gas outlet of the muffle furnace is continuously monitored. When the water concentration increases to more than 1800ppm when the temperature is higher than 650°C, the nitrogen flow rate is appropriately increased. In this embodiment, the water content at the gas outlet of the muffle furnace is continuously monitored. When the temperature in the muffle furnace is higher than 650°C, the maximum water content is 1800ppm.

[0162] S3. Continue calcining for 3 hours to obtain black silica.

[0163] Comparative Example 3

[0164] The main differences from Example 1 are that during the heat treatment in step S2, the nitrogen flow rate is 50 mL / min, so that the water content is less than 4200 ppm when the furnace temperature is above 650°C; and in step S3, the gas is not switched to air. Other aspects are the same as in Example 1.

[0165] The silicon dioxide particles of this comparative example were prepared by the following method:

[0166] Starting with a polysiloxane containing T units, black silica is prepared as follows:

[0167] S1. Place 1300 parts by weight of deionized water at room temperature into a stirred reactor. Stirring is initiated. Add 200 parts by weight of methyltrimethoxysilane and a small amount of acetic acid to adjust the pH to approximately 5. After dissolving the methyltrimethoxysilane, add 30 parts by weight of 5% aqueous ammonia, stir for 10 seconds, and then stop stirring. Allow the mixture to stand for 1 hour, then filter and dry to obtain spherical polysiloxane powder with an average particle size of 1.31 μm.

[0168] S2. Place the spherical polysiloxane powder in a muffle furnace, set the nitrogen flow rate to 50 mL / min, and raise the temperature in the furnace to 850°C under a nitrogen atmosphere. Hold the temperature for 10 hours to heat-treat the particles so that the organic groups in the particles are thermally decomposed into carbon elements. During the heating process, continuously monitor the water concentration at the gas outlet of the muffle furnace. In this embodiment, the water concentration at the gas outlet of the muffle furnace is continuously monitored and is in the range of 2000ppm to 4200ppm. After the furnace temperature reaches above 650°C, the water concentration is in the range of 3500ppm to 4200ppm for a total of 5.3 hours.

[0169] S3. Continue calcining for 3 hours to obtain silicon dioxide particles.

[0170] The process parameters of heat treatment and calcination are shown in Table 1.

[0171] Table 1 Process parameters of Examples and Comparative Examples

[0172]

[0173] Performance Characterization

[0174] The silica particles prepared in Examples 1 to 13 and Comparative Examples 1 to 3 were tested for particle size, carbon content, and moisture content. The analytical results are shown in Table 2. The 48-hour moisture content refers to the moisture content measured after the particles were exposed to the environment at 25°C and 50% RH for 48 hours from the time of preparation. The 100-day moisture content refers to the moisture content measured after the particles were exposed to the environment at 25°C and 50% RH for 100 days.

[0175] Table 2 Performance characterization results of the examples and comparative examples

[0176]

[0177] Data Analysis:

[0178] ① As can be seen from the data of Examples 1 to 13, the present invention uses polysiloxane particles containing T units as the starting material, then heat-treats them in an inert gas atmosphere at a temperature above 650°C with a water content of less than 3500 ppm to thermally decompose the organic groups in the particles into carbon elements, and then calcines them in an oxygen-containing gas atmosphere to densify the particle surface. This produces a black silica filler with an average particle size of 0.1 to 1 μm. This small-particle black silica filler has the excellent properties of few surface defects and low water absorption after standing.

[0179] ② Comparative Example 1 and Example 1 show that the main difference between Comparative Example 1 and Example 1 is that the water content is no more than 4200 ppm when the temperature in the inert gas atmosphere is above 650°C, and the carbon content of the resulting silica particles is greatly reduced. This shows that the moisture content of the preparation environment needs to be controlled during the heat treatment of small-particle carbon-containing particles, otherwise the carbon content of the product will be reduced. Further analysis shows that during the heat treatment of polysiloxane raw material particles, as the silanol groups condense, a large amount of water is generated in the particles, including adsorbed water, surface hydroxyl groups, internal hydroxyl groups, etc., resulting in a certain concentration of water in the gas atmosphere. At the heat treatment temperature, water reacts with carbon to remove carbon from the particles. The presence of this reaction is the main factor limiting the retention of carbon in the particles during the heat treatment of small-particle polysiloxane raw material particles. Studies have found that the temperature at which water reacts with carbon is around 700°C. Therefore, during the heat treatment, the organic groups are thermally decomposed into carbon. Controlling the water concentration when the temperature is above 650°C can prevent water from removing carbon from the particles.

[0180] ③ At the same time, from the comparative analysis of Comparative Example 1 and Examples 1 to 3, it can be seen that the main difference between Comparative Example 1 and Examples 1 to 3 is the water content when the temperature in the inert gas atmosphere during heat treatment is higher than 650°C. The black silicon dioxide obtained in Example 1, which has the lowest water content during the heat treatment process, has the lowest water content after being placed, and the black silicon dioxide obtained in Comparative Example 1, which has the highest water content, has the highest water content after being placed. This shows that controlling the water content in the environment during the heat treatment process is beneficial to improving the density of the prepared silicon dioxide. Further analysis shows that the reason is that defect sites are formed after the organic group is converted into carbon. The defect sites have strong water absorption. After the defect sites absorb water, the number of defect points on the surface increases, which in turn leads to a reduction in the surface density of the particles, which is manifested as an increase in the water content of the particles obtained in Comparative Example 1 compared to Examples 1 to 3 after being placed.

[0181] ④ From the comparative analysis of Comparative Example 2 and Example 1, it can be seen that the main difference between Comparative Example 2 and Example 1 is that Comparative Example 2 is calcined in an inert gas atmosphere. The water content of the silica particles obtained in Comparative Example 2 increases greatly after placement, which shows that if the particles are not calcined in an oxygen-containing atmosphere, the surface of the particles cannot be densified, which will lead to an increase in the water absorption of the product after placement. Further analysis shows that the reason is that by calcining under oxygen-containing conditions, the carbon on the surface of the silica spheres can be taken away, and the defects on the surface of the silica spheres can be repaired by condensation of silanol groups, forming a dense layer on the surface of the silica spheres, improving the density of the product, and thus avoiding the problem of easy water absorption caused by the shedding of carbon on the surface of the product during the shelf life or use period.

[0182] ⑤ From the comparative analysis of Comparative Example 1, Comparative Example 3 and Example 1, it can be seen that the main difference between Comparative Example 3 and Example 1 is that the water content in the inert gas atmosphere during heat treatment reaches 4200ppm, which is relatively large, and calcination is carried out in an inert gas atmosphere; the main difference between Comparative Example 3 and Comparative Example 1 is that Comparative Example 3 is calcined in an inert gas atmosphere; the difference between Comparative Example 1 and Example 1 is that the water content in the inert gas atmosphere during heat treatment of Comparative Example 1 reaches 4200ppm, which is relatively large. From the performance characterization results of the three products, it can be seen that although the carbon content of Comparative Example 1 is small, its water content is not significantly increased compared with Example 1, indicating that the moisture control of the gas atmosphere during heat treatment mainly affects the carbon content of the product; the carbon content of Comparative Example 3 is significantly lower than that of Example 1, and the water content after placement is also significantly increased, that is, the density of the product decreases, which indicates that the density of the product surface is affected by the calcination atmosphere.

[0183] ⑥ Comparison and analysis of Examples 8 and 9 with Example 1 show that the main difference between Example 8 and Example 1 is that the method for controlling the moisture concentration of the heat treatment gas atmosphere is slow heating. The characterization results of the product of Example 8 show a certain degree of reduction in carbon content and a significant increase in water absorption after standing, which demonstrates the advantage of achieving a low moisture concentration in the gas atmosphere through rapid purging with a large flow of nitrogen. Example 9 can increase the carbon content of the product compared to Example 8 by shortening the calcination time in an oxygen atmosphere, but the water absorption still increases significantly after standing.

[0184] The advantage of achieving a low moisture concentration in the atmosphere through rapid nitrogen purge with a high flow rate is that during the heating process in an inert atmosphere, the high flow of nitrogen rapidly removes moisture generated by the condensation of silanol groups in the polysiloxane raw material. This affects the arrangement of the R1 groups of the T units, and thus the overall structural arrangement of the polysiloxane. This results in a higher density of the surface layer formed by condensation of silanol groups during the subsequent calcination process. Denser silica, at the same particle size, has a lower porosity, meaning a smaller specific surface area. This reduces water absorption when exposed to air for extended periods.

[0185] The uranium and thorium contents of all samples in Examples 1 to 13 were less than 1 ppb. The samples obtained in Examples 1 to 13 can be surface treated. Specifically, treatment with a vinyl silane coupling agent, epoxy silane coupling, disilazane, or the like can be performed as needed. More than one treatment can be performed as needed.

[0186] The "main powder" mentioned in the present invention refers to the powder of large particle segments of the total filler filled in the resin.

[0187] Unless otherwise specified, the raw materials and equipment used in the present invention are commonly used in the art; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0188] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A black silica filler, characterized in that: The carbon mass content of the black silica filler particles gradually increases from the surface to the inside; The average particle size of the black silica filler particles is 0.1-1 μm, and the mass content of carbon is 0.3%-9%.

2. The black silica filler according to claim 1, wherein: From the preparation, under the environmental conditions of 25°C and 50% RH, the water content of the black silica filler particles is less than 591 ppm / m 2 .

3. The black silica filler according to claim 1, wherein: From the preparation, under the environmental conditions of 25°C and 50% RH, the water content of the black silica filler particles is less than 245 ppm / m 2 .

4. A method for preparing a black silica filler, characterized in that: Spherical polysiloxane particles comprising T units are provided and subjected to the following steps: Step S1: performing a heating treatment under an inert gas atmosphere to thermally decompose the organic groups in the particles into carbon; Step S2: calcining the particles in an oxygen-containing gas atmosphere to remove carbon from the particle surface; Wherein, the water content of the inert gas atmosphere is controlled to be no more than 3500 ppm when the temperature of the heating process is higher than 650°C; the particle size of the black silica filler is 0.1-1 μm; Wherein, T unit = R1SiO3-, R1 is a hydrogen atom or an independently selected hydrocarbon group having 1 to 16 carbon atoms.

5. The method for preparing a black silica filler according to claim 4, wherein: In step S1, the terminal temperature of the heating treatment is 850-1100°C.

6. The method for preparing a black silica filler according to claim 5, wherein: During the heating process, the temperature is increased slowly or / and an inert gas is introduced at a high flow rate.

7. The method for preparing a black silica filler according to claim 6, wherein: The heating rate of the slow heating is 0.1-1°C / min.

8. The method for preparing a black silica filler according to claim 6, wherein: The flow rate of the inert gas is 100-1000 mL / min.

9. The method for preparing a black silica filler according to claim 4, wherein: In step S2, the volume concentration of oxygen in the oxygen-containing gas is 0.3% to 30%.

10. The method for preparing a black silica filler according to claim 9, wherein: In step S2, the volume concentration of oxygen in the oxygen-containing gas is 3% to 21%.

11. The method for preparing a black silica filler according to claim 4, wherein: In step S2, the calcination temperature is 850-1200°C.

12. The method for preparing a black silica filler according to claim 4, wherein: The polysiloxane further comprises Q units, D units and / or M units; wherein, Q unit = SiO4-, D unit = R2R3SiO2-, M unit = R4R5R6SiO-; R2, R3, R4, R5, and R6 are each a hydrogen atom or an independently selectable hydrocarbon group having 1 to 18 carbon atoms.

13. The method for preparing a black silica filler according to claim 12, wherein: The T unit raw material of the polysiloxane is a hydrocarbyltrialkoxysilane or a hydrocarbyltrichlorosilane, the Q unit raw material is at least one selected from the group consisting of tetraalkoxysilane, silicon tetrachloride and silicon dioxide, the D unit raw material is at least one selected from the group consisting of dihydrocarbyldialkoxysilane and dihydrocarbyldichlorosilane, and the M unit raw material is at least one selected from the group consisting of trihydrocarbylalkoxysilane, trihydrocarbylchlorosilane and hexahydrocarbyldisilazane.

14. Use of the black silica filler according to any one of claims 1 to 3, or the black silica filler prepared by the preparation method according to any one of claims 4 to 13, in the preparation of semiconductor packaging materials or substrate materials.

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