Ceramic filler powder with excellent fluidity and preparation method thereof

Abstract

The invention provides ceramizable filler powder with excellent flowability and a preparation method thereof, and the ceramizable filler powder comprises the following components in parts by weight: 50-70 parts of a flame-retardant base material, 20-35 parts of ceramizable filler, 3-8 parts of a rheology modifier and 2-5 parts of an auxiliary agent, the ceramic filler powder is high-fluidity granular powder subjected to surface chemical modification and heat treatment granulation, the apparent density of the granular powder is 0.4-0.6 g / cm < 3 >, and the angle of repose is not greater than 35 degrees. According to the invention, various fine and irregular powder raw materials are converted into secondary particles with lower specific surface area and more spherical shape, so that the apparent density of the powder is greatly reduced, the angle of repose is greatly reduced, the Carr index is lower than 25%, and the fluidity grade of the filler is improved, thereby improving the filling performance and processability of the filler.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a ceramicizable filler powder with excellent flowability and its preparation method. Background Technology

[0002] With the ever-increasing demands of modern industry on material performance, especially in key fields such as aerospace, rail transportation, new energy vehicles, high-rise buildings, and electronics, the safety performance of materials under extreme environments such as fire and high temperatures has become a critical technical issue. Polymer-based ceramicizable composite materials, as a type of passive fire-resistant material, have emerged to address this need.

[0003] These materials retain the flexibility and processability of polymers at room temperature. When exposed to flames or high temperatures, the inorganic fillers inside undergo a series of complex physicochemical reactions, transforming in situ into a hard, dense ceramic protective layer. This ceramic layer maintains structural integrity, helps prevent flame spread, insulates against heat transfer, and suppresses the release of toxic fumes, thus protecting equipment and personnel. Currently, ceramizable fillers mainly include traditional ceramic powders, glass powders, and composite ceramic powders.

[0004] Currently, the mainstream technical route for preparing ceramicizable composite materials involves directly adding various functional inorganic powders to a polymer matrix (such as silicone rubber, ethylene-vinyl acetate copolymer, etc.) through mechanical blending. These powders typically include: ceramicization skeleton fillers, such as silicate minerals like kaolin, mica, and wollastonite; low-melting-point fluxes to lower the ceramicization reaction temperature, such as glass powder, zinc borate, or phosphates; and synergistic flame retardants, such as aluminum hydroxide and magnesium hydroxide, which decompose and absorb heat and release water vapor when heated.

[0005] Despite advancements in ceramizable formulation design, a common technical challenge remains: achieving good fire resistance and ceramic-forming properties requires a high proportion (e.g., exceeding 150 phr, i.e., more than 150 parts filler per 100 parts polymer) of inorganic fillers in the polymer matrix. However, these traditional fillers, composed of physical blends of various fine powders, typically exhibit characteristics such as uneven particle size, large specific surface area, irregular shape, and strong van der Waals forces and friction between particles. These characteristics directly lead to high overall packing density and poor flowability, making it difficult to achieve high filler loadings.

[0006] In summary, the existing technical field requires a new solution to improve the relationship between "high filling performance" and "poor processability." Currently, no published literature or patent proposes a solution to systematically solve the aforementioned process challenges by pretreating various functional fillers to prepare a highly fluid, granular, high-filling-performance, and easily processed ceramizable filler intermediate. The purpose of this invention is to fill this technological gap. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address the shortcomings of existing technologies, this invention provides a ceramicizable filler powder with excellent flowability and its preparation method, thus solving the problems mentioned in the background section.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the present invention is implemented through the following technical solution: a ceramizable filler powder with excellent flowability, characterized in that: by weight, it comprises 50-70 parts of flame retardant base material, 20-35 parts of ceramizable filler, 3-8 parts of rheology modifier and 2-5 parts of additives.

[0011] The ceramicizable filler powder is a highly fluid granular powder that has undergone surface chemical modification and heat treatment granulation. The loose packing density of the granular powder is 0.4-0.6 g / cm3, and the angle of repose is not greater than 35°.

[0012] Preferably, the rheology modifier comprises nano-silica, zinc stearate, and polyethylene wax, wherein the mass ratio of nano-silica, zinc stearate, and polyethylene wax is 1-3:1-2:1-3.

[0013] Preferably, the adjuvants include coupling agents, antioxidants and other adjuvants, and the mass ratio of the coupling agent, antioxidants and other adjuvants is 0.5-1.5:0.5-1.5:1-2.

[0014] Preferably, the ceramizable filler includes kaolin, mica powder and quartz powder, wherein the mass ratio of kaolin, mica powder and quartz powder is 8-15:5-12:7-18.

[0015] Preferably, the flame-retardant base material includes aluminum hydroxide, magnesium hydroxide and zinc borate, wherein the mass ratio of aluminum hydroxide, magnesium hydroxide and zinc borate is 20-35:15-25:5-15.

[0016] A method for preparing a ceramizable filler powder with excellent flowability, characterized by comprising the following steps:

[0017] S1. Kaolin, mica powder and quartz powder are ball-milled and the particle size distribution is controlled. Aluminum hydroxide, magnesium hydroxide and zinc borate are pre-dried.

[0018] S2. Weigh each component according to the proportion, and dry mix the components in S1 using a high-speed mixer at 800-1200 rpm for 15-25 minutes. Add zinc stearate and polyethylene wax, and continue mixing for 10-15 minutes.

[0019] S3. Add coupling agent, antioxidant and other additives, and stir at 80-120℃ for 30-60 minutes, with the stirring speed controlled at 200-400 rpm;

[0020] S4. The modified mixture from step S3 is placed in a rotary kiln and subjected to segmented programmable heat treatment under an inert atmosphere. After heat treatment, the physical morphology of the mixture surface changes from a loose, fluffy aggregate of micro powders to dense, rounded particles.

[0021] S5. The mixture after heat treatment in S4 is pulverized using air jet milling technology, and then precisely classified by air classifier to remove large particles and agglomerates;

[0022] S6. Add nano-silica and mechanically fuse it in a high-speed mixer at 40-60℃ for 20-30 minutes.

[0023] Preferably, the segmented programmable heat treatment in S4 includes the following steps:

[0024] (a) The room temperature is raised to 200°C at a rate of 5-8°C / min;

[0025] (b) Heating from 200℃ to 450℃ at a rate of 3-5℃ / min;

[0026] (c) Keep warm at 450℃ for 60-90 minutes;

[0027] (d) Allow to cool naturally to room temperature.

[0028] Preferably, the coupling agent is a silane coupling agent.

[0029] Preferably, the particle size control range of the mixture in S5 is D50 < 7 μm.

[0030] Preferably, the nano-silica particles are "embedded" or "coated" on the particle surface formed in step S5 and fill the depressions between larger particles.

[0031] (III) Beneficial Effects

[0032] This invention provides a ceramizable filler powder with excellent flowability and its preparation method. It has the following beneficial effects:

[0033] 1. This invention transforms various fine and irregular powder raw materials into secondary particles with lower specific surface area and a shape closer to spheres, thereby significantly reducing the loose density of the powder, greatly reducing the angle of repose, and lowering the Carr index to less than 25%, thus improving the flowability grade of the filler.

[0034] 2. The good fluidity of the present invention allows the filler powder of the present invention to be added to high-viscosity silicone rubber and other matrices relatively smoothly, and can be quickly and uniformly dispersed by shear force, shortening the mixing time and helping to avoid the generation of air bubbles, thereby effectively increasing the filling amount of filler in the matrix, and thus achieving the purpose of improving the fire resistance rating of the composite material.

[0035] 3. Through optimized formulation design and pre-reaction during heat treatment, the filler of this invention ensures that the composite material can initiate a ceramicization reaction at a relatively low temperature (approximately 500°C) to form a protective layer, which is far lower than the ceramicization temperature of traditional fillers (600-800°C), thereby providing timely and effective protection in the early stages of a fire.

[0036] 4. This invention achieves high-proportion and uniform filling of fillers through the high fluidity of the fillers. The ceramic layer formed by the composite material prepared by the fillers at high temperature is more dense, strong and complete, with good structural support, which greatly increases its high-temperature stability, thereby resisting more severe flame erosion.

[0037] 5. This invention provides a standardized functional filler intermediate product, which simplifies the production process of downstream customers and reduces their dependence on complex powder processing equipment and technology. By using domestically produced raw materials and optimized processes, its overall cost can be reduced by 25-35% compared with imported similar functional products, making it competitive in the market. Attached Figure Description

[0038] Figure 1 This is a scanning electron microscope (SEM) image of the ceramizable filler powder prepared in Example 1 of the present invention. Detailed Implementation

[0039] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0041] This invention provides a ceramicizable filler powder with excellent flowability and its preparation method. To achieve the above objective, this invention is implemented through the following technical solution: A ceramicizable filler powder with excellent flowability, comprising, by weight, 50-70 parts of flame retardant base material, 20-35 parts of ceramicizable filler, 3-8 parts of rheology modifier and 2-5 parts of additives.

[0042] The ceramizable filler powder is a highly fluid granular powder that has undergone surface chemical modification and heat treatment granulation. The loose packing density of the granular powder is 0.4-0.6 g / cm3, and the angle of repose is not greater than 35°.

[0043] The rheology modifiers include nano silica, zinc stearate, and polyethylene wax, with a mass ratio of 1-3:1-2:1-3.

[0044] The additives include coupling agents, antioxidants and other additives, with a mass ratio of 0.5-1.5:0.5-1.5:1-2.

[0045] The ceramizable filler includes kaolin, mica powder and quartz powder, wherein the mass ratio of kaolin, mica powder and quartz powder is 8-15:5-12:7-18.

[0046] The flame-retardant base material includes aluminum hydroxide, magnesium hydroxide and zinc borate, wherein the mass ratio of aluminum hydroxide, magnesium hydroxide and zinc borate is 20-35:15-25:5-15.

[0047] The coupling agent used is a silane coupling agent.

[0048] The particle size of the mixture is controlled within the range of D50 < 7 μm.

[0049] Nano-silica particles are "embedded" or "coated" on the particle surface formed in step S5 and fill the depressions between larger particles, reducing the static electricity or van der Waals forces between particles.

[0050] The preparation method of the present invention includes the following steps:

[0051] S1: Raw material pretreatment

[0052] Pre-dry aluminum hydroxide and magnesium hydroxide at 200-250℃ for 2-4 hours to remove surface moisture.

[0053] Kaolin, mica powder, and quartz powder are ball-milled to control particle size distribution;

[0054] S2: Ingredient Mixing

[0055] Weigh each component according to the formula, dry mix them using a high-speed mixer at 800-1200 rpm for 15-25 minutes, add the rheology modifier, and continue mixing for 10-15 minutes.

[0056] S3: Surface modification treatment

[0057] Add a coupling agent (such as silane coupling agent KH-550) at a rate of 0.5-1.5% of the total weight, and perform surface modification treatment at 80-120℃ for 30-60 minutes, while controlling the stirring speed at 200-400 rpm.

[0058] S4: Heat treatment process

[0059] The modified mixture was placed in a rotary kiln and heated under an inert atmosphere (nitrogen) according to the following procedure:

[0060] (a) Room temperature → 200℃, heating rate 5-8℃ / min;

[0061] (b) 200℃→450℃, heating rate 3-5℃ / min;

[0062] (c) Keep warm at 450℃ for 60-90 minutes;

[0063] (d) Allow to cool naturally to room temperature;

[0064] S5: Grinding and Classification

[0065] Using airflow milling technology, the particle size D50 is controlled to be <7μm, and precise classification is performed by an airflow classifier to remove large particles and agglomerates;

[0066] S6: Liquidity Optimization

[0067] Nano-silica was added as a flow modifier and processed in a high-speed mixer using mechanical fusion technology, with the processing temperature controlled at 40-60℃ and the time at 20-30 minutes.

[0068] Synergistic mechanism between improved liquidity and particle construction:

[0069] The improved flowability achieved by this invention does not rely on a single component or a single process, but rather stems from a multi-step, synergistic physicochemical particle engineering process. The core idea of ​​this process is to reconstruct various primary micropowders with different properties and poor morphology into homogenized secondary particles with good flow characteristics.

[0070] 1. Raw material selection and pretreatment

[0071] The first step of this invention is to ensure that all inorganic powder raw materials have a controlled initial state. Ball milling of kaolin, mica powder, quartz powder, etc., and pre-drying of hydroxides are carried out to eliminate batch-to-batch variations in raw materials, providing a stable and homogeneous material base for subsequent particle construction.

[0072] 2. Surface chemical modification

[0073] After high-speed mixing, a silane coupling agent (such as KH-550) is added, and surface modification is performed at a temperature of 80-120℃. This step serves a dual purpose: firstly, the functional groups (such as amino groups) of the coupling agent can chemically bond or physically entangle with the polymer matrix (such as silicone rubber), thereby improving the interfacial compatibility between the filler and the matrix, which is crucial for enhancing the mechanical properties of the final composite material. Secondly, the coating of the coupling agent molecules on the particle surface initially reduces the surface energy and friction between particles, laying a chemical foundation for subsequent improvements in flowability.

[0074] 3. Heat treatment granulation

[0075] This step is one of the core components of this invention. The surface-modified mixed powder is placed in a rotary kiln and subjected to segmented, programmable heat treatment under an inert atmosphere, particularly by holding at around 450°C. The purpose of this heat treatment is not to completely ceramicize the material, but to achieve "microscopic sintering" and "particle reconstruction".

[0076] The mechanism is as follows:

[0077] Microscopic sintering and binder granulation: At this temperature, the rheology modifiers in the formulation, especially low-melting-point polyethylene wax and zinc stearate, melt or partially decompose, transforming into a viscous liquid or semi-liquid phase. This viscous phase acts as a "binder," binding together surrounding finer, high-melting-point inorganic primary particles (such as aluminum hydroxide, kaolin, quartz powder, etc.) to form larger, more stable, and more spherical secondary aggregates, i.e., "particles," through the "liquid bridge" effect.

[0078] Morphology optimization and specific surface area reduction: This process alters the physical morphology of the powder, transforming it from a loose, fluffy aggregate of micropowders into relatively dense, rounded particles. The formation of these particles reduces the overall specific surface area of ​​the powder, decreasing the contact points and friction between particles, which is the physical basis for improved flowability.

[0079] Dehydration and Pre-reaction: A temperature of 450℃ is sufficient to cause partial dehydration and decomposition of aluminum hydroxide and magnesium hydroxide, i.e., 2Al(OH)3 → Al2O3 + 3H2O and Mg(OH)2 → MgO + H2O. This not only removes the water of crystallization that may cause problems in subsequent processing, but also allows for the formation of more chemically active new oxides on the filler surface, which is beneficial to the subsequent ceramization reaction. At the same time, preliminary solid-phase reactions may have begun between the flux (such as zinc borate) and some of the fillers, creating conditions for low-temperature ceramicization.

[0080] 4. Mechanical fusion and surface finishing

[0081] After heat treatment, the material undergoes air jet milling and classification to break up excessively large agglomerates and achieve a narrow particle size distribution (e.g., D50 < 7 μm). Subsequent mechanical fusion and flowability optimization is a crucial step in achieving the final effect. During this process, high-speed mechanical force firmly "embeds" or "coats" nano-silica particles, acting as flow modifiers, onto the surface of the secondary particles formed in the previous step. These nano-silica particles act as "ball bearings" or "spacers," filling the depressions between larger particles and increasing the distance between them, effectively preventing the particles from re-agglomerating due to electrostatics or van der Waals forces. This ultimately endows the powder with a low angle of repose and good flowability.

[0082] Low-temperature ceramization and synergistic flame retardant mechanism:

[0083] Phase 1: Physical and chemical flame retardancy (300-450℃)

[0084] When the composite material is heated, the most abundant flame-retardant binders—aluminum hydroxide (ATH) and magnesium hydroxide (MDH)—respond first. They undergo an endothermic decomposition reaction, releasing a large amount of non-toxic water vapor. This process produces at least three flame-retardant effects: endothermic cooling: the decomposition process absorbs a large amount of heat, lowering the surface temperature of the polymer matrix and delaying its pyrolysis; dilution effect: the generated water vapor dilutes the concentration of oxygen and flammable gases on the material surface and in the surrounding air; barrier effect: the aluminum oxide and magnesium oxide residues generated after decomposition initially form a porous inorganic heat-insulating layer on the material surface.

[0085] Second stage: Low-temperature liquid phase formation (320-500℃)

[0086] Within this temperature range, zinc borate (ZB), as a key flux, begins to play its role. According to relevant research, hydrated zinc borate (such as 2ZnO·3B₂O)... 3.3.5H2O) decomposes at this temperature, releasing its water of crystallization (further synergistically absorbing heat and cooling down), and generating products such as boron oxide (B2O3). B2O3 is a glass phase formation with a low softening point of about 325℃, and it transforms into a viscous liquid phase with a certain degree of fluidity at temperatures close to 500℃.

[0087] Third stage: Liquid phase sintering and ceramization (above 500℃)

[0088] The presence of the B2O3 liquid phase is key to achieving low-temperature ceramization. It acts as a highly efficient "ceramic glue" or "eutectic flux." This viscous liquid phase wets and encapsulates surrounding ceramic framework filler particles with higher melting points, such as kaolin, mica, and quartz powder. This promotes mass migration and reaction between these solid particles, initiating the "liquid phase sintering" process. Compared to solid-phase sintering, which requires higher temperatures (typically >1000°C), liquid phase sintering can "weld" all inorganic components together at a lower temperature (approximately 500°C in this invention), rapidly forming a continuous, dense, and mechanically strong three-dimensional network framework—the ceramic layer.

[0089] Synergistic enhancement effect:

[0090] The lamellar fillers in the formulation, such as mica powder, play a reinforcing role during the ceramization process. They can deflect cracks and absorb energy within the ceramic matrix, thereby improving the toughness and thermal shock resistance of the ceramic layer and preventing it from cracking and peeling under drastic temperature changes. Simultaneously, the high-strength crystalline phases such as mullite (3Al2O3·2SiO2) formed by the decomposition of kaolin at higher temperatures further enhance the high-temperature resistance and structural stability of the ceramic layer, allowing it to remain intact at temperatures up to 1400℃.

[0091] Example 1:

[0092] Raw material ratio (parts by weight):

[0093] Aluminum hydroxide (particle size D50≈2.5μm): 28 parts

[0094] Magnesium hydroxide (particle size D50≈2.0μm): 20 parts

[0095] Zinc borate: 10 parts

[0096] Kaolin (calcined, particle size D50≈1.5μm): 12 parts

[0097] Mica powder (wet process, 200 mesh): 8 parts

[0098] Quartz powder (high purity, 325 mesh): 10 parts

[0099] Nano-silica (vapor phase method, specific surface area 200m²)2 / g): 2 portions

[0100] Zinc stearate: 1.5 parts

[0101] Polyethylene wax (low molecular weight): 2 parts

[0102] Silane coupling agent (KH-550): 1 part

[0103] Antioxidant (Type 1010): 0.5 parts

[0104] Other additives (processing aids, etc.): 2 parts

[0105] Preparation process:

[0106] (a) Raw material pretreatment: Aluminum hydroxide and magnesium hydroxide were placed in a forced-air drying oven and pre-dried at 220°C for 3 hours, then cooled for later use. Kaolin, mica powder, and quartz powder were added to a ball mill and ball-milled for 2 hours to ensure uniform dispersion.

[0107] (b) Ingredient mixing: According to the above proportions, accurately weigh all powder components except nano silica and coupling agent, put them into a high-speed mixer, and dry mix at 1000 rpm for 20 minutes.

[0108] (c) Surface modification treatment: Reduce the mixer speed to 300 rpm, slowly add the metered silane coupling agent KH-550 by spraying, and at the same time raise the jacket temperature to 100°C. Perform surface modification treatment at this temperature for 45 minutes.

[0109] (d) Heat treatment process: The modified mixture is transferred to a rotary kiln under nitrogen atmosphere protection. The heating program is set as follows: the temperature is increased from room temperature to 200°C at a rate of 6°C / min; then increased to 450°C at a rate of 4°C / min, and held at 450°C for 75 minutes. After completion, the mixture is allowed to cool naturally to room temperature.

[0110] (e) Crushing and grading: The blocky material obtained after heat treatment is crushed by an air jet mill and graded by an online classifier to control the product particle size D50 to be 6.2 μm and D90 to be less than 15 μm.

[0111] (f) Flowability optimization: The graded powder and 2 parts of nano silica were put into a mechanical fusion machine and treated at 50°C and high speed for 25 minutes to make the nano silica uniformly coat the particle surface.

[0112] (g) Finished product: discharge, sieve, and package to obtain the finished powder of Example 1.

[0113] Example 2:

[0114] The following adjustments were made based on Example 1: the amount of nano-silica and polyethylene wax was increased to 3 parts. Correspondingly, the amount of other additives was adjusted to 3.5 parts, while the remaining components and preparation process remained unchanged. The increased amount of nano-silica further improved the flowability of this invention.

[0115] Example 3:

[0116] The following adjustments were made based on Example 1: the proportion of mica powder was increased to 10 parts, and an additional 2 parts of nano-zirconia (D50 < 100 nm) were added as a high-temperature stabilizer. Correspondingly, the amount of quartz powder was adjusted to 8 parts, and the amount of other additives was adjusted to 4.5 parts. The remaining components and total amounts remained unchanged.

[0117] Example 4:

[0118] Raw material ratio (parts by weight):

[0119] Aluminum hydroxide: 35 parts;

[0120] Magnesium hydroxide: 15 parts;

[0121] Zinc borate: 6 parts;

[0122] Kaolin: 10 parts;

[0123] Mica powder: 5 parts;

[0124] Quartz powder: 17 parts;

[0125] Nano-silica: 1.5 parts;

[0126] Zinc stearate: 1.5 parts;

[0127] Polyethylene wax: 2.5 parts;

[0128] Silane coupling agent (KH-550): 1 part;

[0129] Antioxidant: 0.5 parts;

[0130] Other adjuvants: 4 parts;

[0131] This formulation aims to explore a balance between cost and performance by increasing the amount of lower-cost aluminum hydroxide and quartz powder while reducing the amount of relatively expensive magnesium hydroxide and zinc borate.

[0132] Example 5:

[0133] The raw material ratio is exactly the same as that in Example 1.

[0134] The preparation process is basically the same as that in Example 1, except that in step (c) surface modification, the silane coupling agent KH-550 (aminosilane) is replaced with an equal amount of KH-560 (epoxysilane). This example aims to verify that the filler of the present invention can be adapted to other polymer matrices (such as epoxy resin fire-retardant coatings) by adjusting the surface chemical properties, demonstrating its wide applicability.

[0135] Comparative Example 1:

[0136] The raw material ratio is exactly the same as that in Example 1.

[0137] Preparation process: All powder components (including 2 parts of nano-silica) except for the coupling agent in Example 1 were added to a high-speed mixer at once and simply physically mixed at 1000 rpm for 30 minutes. No surface modification, heat treatment, pulverization and classification, or mechanical fusion steps were performed.

[0138] Comparative Example 2:

[0139] Raw material ratio (parts by weight):

[0140] Methyl vinyl silicone rubber (base): 100 parts;

[0141] Low melting point glass powder (softening point ~600℃): 60 parts;

[0142] Mica powder: 40 parts;

[0143] Aluminum hydroxide: 50 parts;

[0144] Fumed silica (reinforcing filler): 30 parts;

[0145] Vulcanizing agent (DCP): 1.5 parts;

[0146] Preparation process: A traditional silicone rubber compounding process is adopted. On a two-roll mill, the silicone rubber base is rolled, and fumed silica, aluminum hydroxide, mica powder, and glass powder are added sequentially. After uniform mixing, a vulcanizing agent is finally added, and the mixture is sheeted. This method simulates the common practice in existing technologies of directly mixing various fillers into the rubber.

[0147] Performance testing and data comparison analysis:

[0148] 1. Physical properties of powder:

[0149] Loose packing density: Tested using a loose packing density meter in accordance with GB / T1479.1-2011 standard.

[0150] 2. Angle of repose: Measured using the fixed funnel method according to ASTM D6393 standard.

[0151] Carr index: Calculated by measuring the loose density (ρb) and tapped density (ρt) according to the formula CarrIndex = 100 × (ρt - ρb) / ρt.

[0152] 3. Composite material properties:

[0153] Preparation: Take 100 parts of methyl vinyl silicone rubber (110-2 compound), add the specified amount of filler powder to be tested on a two-roll mill, mix evenly, add 1.5 parts of vulcanizing agent (double 2,5), and mold and vulcanize at 170℃ for 10 minutes to make standard sample pieces.

[0154] 4. Maximum filling amount: The filling material is continuously added to the open mill until it can be mixed normally, produced into sheets, and the sample sheet surface is smooth without obvious agglomeration.

[0155] 5. Ceramicization temperature: The starting temperature of the ceramization reaction is determined by differential scanning calorimetry (DSC) or thermogravimetric analysis (TGA).

[0156] 6. High temperature stability: Place the sample in a muffle furnace, heat it to the specified temperature (e.g., 1400℃) and keep it at that temperature for 30 minutes, then observe the morphology of the residue.

[0157] 7. Flame retardancy rating: based on UL94 vertical burning test standard.

[0158] Table 1

[0159]

[0160]

[0161] Data Analysis and Discussion:

[0162] 1. The Role of the Process: Comparing the data from Example 1 and Comparative Example 1, one of the core conclusions of this invention can be drawn. Both have identical chemical compositions, yet their performance differs significantly. The powder of Comparative Example 1, having undergone only simple physical mixing, exhibits flowability indicators such as bulk density, angle of repose, and Carr index at the same level as the "existing technology product" benchmark, indicating poor flowability (Carr index > 40% is classified as "extremely poor"). In contrast, the powder of Example 1, processed by the process of this invention, shows a significant improvement in all flowability indicators, achieving an "excellent" flowability level. This comparison demonstrates that the innovation of this invention lies in its preparation method, not merely in the component ratio.

[0163] 2. Transformation of Processing Performance: The excellent powder flowability directly translates into processing advantages. As shown in the table, the maximum filling amount of the powders in Examples 1-3 in silicone rubber can reach over 200 phr, while the powders in Comparative Examples 1 and 2 become difficult to process and cannot be added further when the filling amount reaches 130-150 phr. This demonstrates that the present invention improves the contradiction between high filling amount and poor processability, providing a technical basis for the preparation of higher-performance fire-retardant materials.

[0164] 3. Advantages of ultimate fire resistance:

[0165] Low-temperature ceramic formation: The ceramic formation temperature in all embodiments of the present invention is below 500°C, which is lower than that of Comparative Example 2 (glass powder system) and the existing technology benchmark. This means that effective protection can be formed earlier in the event of a fire.

[0166] Ceramic layer quality: Judging from the morphology of the residue, the ceramic layer formed in the embodiments of the present invention is dense, strong, and intact. In contrast, in Comparative Example 1, due to the uneven dispersion of the filler in the matrix, the ceramic layer formed after combustion has a loose structure and uneven stress distribution, leading to cracking and limited protective ability. Although the glass powder system in Comparative Example 2 can form a relatively dense ceramic layer, microcracks still exist, confirming the literature's assertion regarding its poor interfacial properties.

[0167] High temperature resistance: The high temperature stability of all embodiments of the present invention exceeds 1400℃, especially in embodiment 3 which introduces nano-zirconia, reaching 1450℃, showing good high temperature ablation resistance potential, which is higher than the existing technology level.

[0168] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A ceramizable filler powder with excellent flowability, characterized in that: By weight, it includes 50-70 parts of flame retardant base material, 20-35 parts of ceramizable filler, 3-8 parts of rheology modifier and 2-5 parts of additives. The ceramicizable filler powder is a highly fluid granular powder that has undergone surface chemical modification and heat treatment granulation. The loose packing density of the granular powder is 0.4-0.6 g / cm3, and the angle of repose is not greater than 35°.

2. The ceramizable filler powder with excellent flowability according to claim 1, characterized in that: The rheology modifier comprises nano-silica, zinc stearate, and polyethylene wax, wherein the mass ratio of nano-silica, zinc stearate, and polyethylene wax is 1-3:1-2:1-3.

3. The ceramizable filler powder with excellent flowability according to claim 2, characterized in that: The additives include coupling agents, antioxidants, and other additives, wherein the mass ratio of the coupling agent, antioxidant, and other additives is 0.5-1.5:0.5-1.5:1-2.

4. The ceramizable filler powder with excellent flowability according to claim 3, characterized in that: The ceramizable filler includes kaolin, mica powder and quartz powder, wherein the mass ratio of kaolin, mica powder and quartz powder is 8-15:5-12:7-18.

5. The ceramizable filler powder with excellent flowability according to claim 3, characterized in that: The flame-retardant base material includes aluminum hydroxide, magnesium hydroxide and zinc borate, wherein the mass ratio of aluminum hydroxide, magnesium hydroxide and zinc borate is 20-35:15-25:5-15.

6. A method for preparing a ceramizable filler powder with excellent flowability according to any one of claims 1 to 5, characterized in that: Includes the following steps: S1. Kaolin, mica powder and quartz powder are ball-milled and the particle size distribution is controlled. Aluminum hydroxide, magnesium hydroxide and zinc borate are pre-dried. S2. Weigh each component according to the proportion, and dry mix the components in S1 using a high-speed mixer at 800-1200 rpm for 15-25 minutes. Add zinc stearate and polyethylene wax, and continue mixing for 10-15 minutes. S3. Add coupling agent, antioxidant and other additives, and stir at 80-120℃ for 30-60 minutes, with the stirring speed controlled at 200-400 rpm; S4. The modified mixture from step S3 is placed in a rotary kiln and subjected to segmented programmable heat treatment under an inert atmosphere. After heat treatment, the physical morphology of the mixture surface changes from a loose, fluffy aggregate of micro powders to dense, rounded particles. S5. The mixture after heat treatment in S4 is pulverized using air jet milling technology, and then precisely classified by air classifier to remove large particles and agglomerates; S6. Add nano-silica and mechanically fuse it in a high-speed mixer at 40-60℃ for 20-30 minutes.

7. The method for preparing a ceramizable filler powder with excellent flowability according to claim 6, characterized in that: The segmented programmable heat treatment in S4 includes the following steps: (a) The room temperature is raised to 200°C at a rate of 5-8°C / min; (b) Heating from 200℃ to 450℃ at a rate of 3-5℃ / min; (c) Keep warm at 450℃ for 60-90 minutes; (d) Allow to cool naturally to room temperature.

8. The method for preparing a ceramizable filler powder with excellent flowability according to claim 6, characterized in that: The coupling agent is a silane coupling agent.

9. The method for preparing a ceramizable filler powder with excellent flowability according to claim 6, characterized in that: The particle size control range of the mixture described in S5 is D50 < 7 μm.

10. The method for preparing a ceramizable filler powder with excellent flowability according to claim 6, characterized in that: The nano-silica particles are "embedded" or "coated" on the particle surface formed in step S5 and fill the depressions between larger particles.

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