A silicone-coated ptfc anti-dripping agent and a method for preparing the same

Abstract

The application relates to the technical field of polymer material additives, and particularly discloses a preparation method of a silicone-coated PTFE anti-dripping agent, which comprises the following steps: I. preparing an anchoring isolation agent, mixing silicone rubber, inorganic powder and a coupling agent, and performing a dynamic grafting reaction under the action of an initiator to construct an intermediate with a chemical bonding structure; II. preparing the anti-dripping agent: S1: mixing suspension polymerization PTFE and the anchoring isolation agent in a high-speed mixer to disassemble PTFE agglomerates; S2: under a specific rotating speed, spraying liquid silicone coating agent into the machine through an atomizing nozzle to perform wet mixing, so that a uniform adsorption layer is formed on the surface of the anchoring isolation agent; S3: after cooling, adding emulsion polymerization PTFE to perform low-speed mixing, so as to prevent early fiberization; and S4: standing and aging to make the interface reach adsorption balance. The application solves the problem of crystal points caused by the easy agglomeration of PTFE in a matrix, so that the prepared anti-dripping agent can ensure the flame-retardant performance, and meanwhile, the surface quality and mechanical toughness of high-gloss injection-molded parts are improved.

Description

Technical Field

[0001] This invention belongs to the field of polymer material additives technology, specifically relating to a silicone-coated PTFE anti-dripping agent and its preparation method. Background Technology

[0002] In the field of engineering plastics processing, polytetrafluoroethylene (PTFE) is often used as a flame retardant synergist. Under high temperature and high shear conditions, it can undergo fibrosis to form a network structure that inhibits droplet formation. Because pure PTFE powder is prone to agglomeration and has poor dispersibility, the industry typically uses silicone polymers to coat the surface of PTFE to improve its dispersibility in the plastic matrix. These silicone-coated PTFE additives are widely used in thin-walled injection molded products such as computer casings, mobile phone frames, and charger housings, which require high flame retardancy and aesthetic quality.

[0003] In practical applications, to balance cost and anti-dripping efficiency, large-particle suspension polymerized PTFE is often used in combination with small-particle emulsion polymerized PTFE. Suspension polymerized PTFE offers good physical support, but its dense molecular chain arrangement makes it less prone to fibrosis during processing; emulsion polymerized PTFE, on the other hand, is more likely to form a fibrous structure under shear stress. The combined use of these two materials has become a common technical solution in high-gloss, thin-walled flame-retardant products.

[0004] However, in the injection molding process of high-gloss or thin-walled products, the melt needs to pass through narrow channels in a very short time and withstand extremely high shear stress. While coatings such as phenyl silicone and methyl silicone have good compatibility with the PC or PC / ABS resin matrix, their bonding with the PTFE surface mainly relies on physical adsorption, making them prone to peeling off from the suspension polymerized PTFE surface under strong shear conditions. Without the protection of the coating, the suspension polymerized PTFE particles are prone to rapid agglomeration in high-temperature environments, forming highly crystalline particle clusters.

[0005] The aforementioned agglomerated PTFE particles exhibit a significant refractive index difference with the surrounding resin matrix, leading to light scattering at the interface and resulting in surface defects such as white spots, pitting, or star-like patterns. Furthermore, the lack of a stable interfacial bond between the agglomerated particles and the resin matrix makes them prone to microcracks that propagate rapidly upon impact, reducing the impact strength and reliability of thin-walled products. Existing technologies typically mitigate this problem by increasing the amount of release agent or extending the mixing time; however, the former can easily cause product fogging, while the latter may disrupt the fiberization ability of emulsion-polymerized PTFE, making it difficult to balance appearance and anti-dripping properties. Summary of the Invention

[0006] The purpose of this invention is to provide a silicone-coated PTFE anti-dripping agent and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, according to one aspect of the present invention, a silicone-coated PTFE anti-dripping agent is provided, comprising, by weight, the following raw materials: PTFE: 20-50 parts, wherein the PTFE is composed of suspension polymerized PTFE and emulsion polymerized PTFE; Anchoring and release agent: 35-65 parts; Liquid silicone coating agent: 10-15 parts, wherein the liquid silicone coating agent comprises phenyl silicone polymer and polydimethylsiloxane; The preparation of the anchoring and insulating agent includes the following steps: P1. Add silica and talc powder to a high-speed mixer, spray with coupling agent, and activate the powder by high-speed stirring at 100℃-110℃ for 10-15 minutes; P2. Add methyl vinyl silicone rubber to the product obtained in step P1, and knead evenly at 60℃-80℃ to obtain a rubber premix; P3. Add the initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane to the premix obtained in step P2, and heat to 165℃-175℃ to carry out a dynamic grafting reaction for 15-20 minutes; P4. After the reaction is complete, the anchoring and separating agent is obtained by vacuum devolatilization, cooling and pulverization.

[0008] Preferably, the anchoring and isolating agent comprises, by weight, the following raw materials: 10-20 parts of methyl vinyl silicone rubber, 5-10 parts of silica, 15-30 parts of talc, 0.3-0.6 parts of coupling agent, and 0.01-0.04 parts of initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane.

[0009] Preferably, the weight ratio of the suspension polymerized PTFE to the emulsion polymerized PTFE is 1.5:1 to 3:1.

[0010] Preferably, the average particle size of the suspension polymerized PTFE is 20μm-50μm; and the average particle size of the emulsion polymerized PTFE is 0.2μm-0.5μm.

[0011] Preferably, in the liquid silicone coating agent, the weight ratio of phenyl silicone polymer to polydimethylsiloxane is 2:1 to 4:1.

[0012] Preferably, the coupling agent is vinyltrimethoxysilane.

[0013] According to another aspect of the present invention, a method for preparing a silicone-coated PTFE anti-dripping agent is provided, comprising the following steps: S1. Add the prescribed amount of suspension polymerized PTFE and anchoring release agent into a mixer and mix for 5-8 minutes at a speed of 800-1000 rpm; S2. Maintaining a rotation speed of 600-800 rpm, spray liquid silicone coating agent into the mixture obtained in step S1 through an atomizing nozzle, and wet mix at 60℃-70℃ for 10-15 minutes; S3. Cool down to below 40℃, reduce the rotation speed to 300rpm-500rpm, add the emulsion polymerized PTFE, and mix for 2-3 minutes; S4. Discharge the material and allow it to stand for aging for 12-24 hours to obtain the silicone-coated PTFE anti-dripping agent.

[0014] Preferably, the liquid silicone coating agent in step S2 is a premix of phenyl silicone polymer and polydimethylsiloxane.

[0015] Preferably, the atomizing pressure of the atomizing nozzle in step S2 is 0.2MPa-0.6MPa, and the spraying rate of the liquid silicone coating agent is 2kg / min-10kg / min.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention provides an anchoring and separating agent that chemically bonds silicone rubber to an inorganic carrier by grafting methyl vinyl silicone rubber onto the surfaces of activated silica and talc under the action of an initiator. In this anchoring and separating agent, the silicone rubber no longer exists in a physical coating form but is stably anchored to the surface of the inorganic powder, thus improving the structural stability of the silicone phase during subsequent processing.

[0017] By using the anchoring and isolating agent to coat suspension polymerized PTFE and emulsion polymerized PTFE in steps, the resulting anti-dripping material is less likely to have its silicone layer peel off from the PTFE surface under high-shear injection molding conditions. The PTFE particles can maintain a stable and uniform dispersion in the resin matrix, thereby effectively inhibiting the agglomeration of suspension polymerized PTFE.

[0018] Since PTFE particles do not easily form large-sized aggregates with high crystallinity in products, the resulting flame-retardant parts can significantly reduce light scattering caused by refractive index differences under high-gloss or thin-wall molding conditions, thereby reducing the risk of white spots, pitting, or star-like defects on the product surface and improving the appearance consistency of the products.

[0019] Moreover, the chemical connection structure formed by the silicone rubber and inorganic carrier in the anchoring and release agent creates a stable transition interface between PTFE and the resin matrix, reducing stress concentration and micro-defect generation inside the material, thus improving the impact resistance of the product while maintaining its flame retardant properties. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] I. The core of the design of the anchoring and release agent lies in constructing an organic-inorganic hybrid structure to provide a solid base layer for subsequent PTFE coating.

[0022] P1. In the first stage of preparation, silica and talc are added to a high-speed mixer for powder activation. Vinyltrimethoxysilane coupling agent is then added at a high temperature of 100℃-110℃. This temperature range effectively promotes the hydrolysis of the alkoxy groups in the silane coupling agent and their condensation reaction with the hydroxyl groups on the surface of the inorganic powder. Through 10-15 minutes of high-speed stirring, a large number of active vinyl groups are successfully implanted into the powder surface.

[0023] P2. Then, the premixing stage of the rubber compound begins, where methyl vinyl silicone rubber is added at 60℃-80℃. This temperature range is designed to reduce the viscosity of the silicone rubber, allowing it to better penetrate the microporous structure of silica and talc during kneading, forming a preliminary physical encapsulation.

[0024] P3. The core reaction occurs during the dynamic grafting stage. The temperature is raised to 165℃-175℃, and the initiator DBPH is added. At this temperature, the initiator decomposes to generate free radicals, inducing a free radical addition reaction between the vinyl groups on the silicone rubber molecular chains and the vinyl groups grafted onto the powder surface. This allows the silicone rubber to be tightly anchored to the inorganic carrier through covalent bonds. A reaction time of 15-20 minutes ensures a sufficient grafting rate while avoiding excessive cross-linking that would lead to hardening of the compound. The final anchoring and releasing agent has a surface covered with organosilicon segments, exhibiting extremely strong oil absorption capacity and interfacial bonding strength.

[0025] II. Based on the obtained anchoring and separating agent, the final composite system is constructed by stepwise coating method, which aims to solve the dispersion contradiction between large particle suspended PTFE and micro-emulsion PTFE in the matrix.

[0026] S1. Substrate Construction and Hard Core Dispersion: First, 20-50 parts of the total PTFE (suspended polymeric PTFE) are dry-mixed with 35-65 parts of the anchoring and separating agent. The suspended polymeric PTFE has a relatively large particle size (20μm-50μm) and tightly packed molecular chains. Mixing is carried out at a medium-high speed of 800rpm-1000rpm for 5-8 minutes. The rigid frictional force of the inorganic powder in the anchoring and separating agent is used to forcibly disperse any large PTFE agglomerates, ensuring they are uniformly embedded in the modified powder substrate.

[0027] S2. Liquid-phase impregnation and affinity layer construction: A mixture of phenyl silicone polymer and polydimethylsiloxane is atomized and sprayed into the PTFE at a pressure of 0.2 MPa-0.6 MPa under an environment of 60℃-70℃. The addition of phenyl silicone is to improve the refractive index matching and compatibility between the additive and the downstream PC / ABS resin. The atomization pressure ensures that the liquid silicone can precisely wet the silicone rubber layer on the surface of the anchoring release agent in the form of microdroplets. Due to the similarity in structure between the two, the liquid silicone will quickly penetrate and physically entangle with the chain segments on the surface of the anchoring release agent, thereby forming an extremely stable lubricating film around the suspended PTFE.

[0028] S3. Flexible Network Introduction and Fiber Protection: This is the most temperature- and shear-sensitive step in the process. Emulsion-polymerized PTFE with an average particle size of only 0.2μm-0.5μm is added. Since emulsion-polymerized PTFE undergoes irreversible fiberization prematurely under mechanical shear or at temperatures exceeding 40°C, the temperature must be lowered to below 40°C, and the rotation speed reduced to 300-500 rpm. Gently mix at low speed for 2-3 minutes to ensure these fine particles are uniformly adsorbed into the interparticle spaces of the already coated particles. This design ensures that the anti-drip activity of PTFE is fully preserved into the injection molding stage.

[0029] S4. Maturation and tissue stabilization: Finally, after 12-24 hours of static aging, the liquid silicone is allowed to fully penetrate and rearrange between the microscopic interfaces to eliminate stress.

[0030] Example 1 This embodiment provides a method for preparing a silicone-coated PTFE anti-dripping agent.

[0031] I. Preparation of anchoring and releasing agent: Prepare the following raw materials by weight: 15 parts of methyl vinyl silicone rubber, 8 parts of fumed silica, 25 parts of talc, 0.45 parts of vinyltrimethoxysilane, and 0.02 parts of 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane as an initiator.

[0032] The specific preparation steps include: P1. Add fumed silica and talc powder to a high-speed mixer, atomize and spray vinyltrimethoxysilane, heat to 105°C, and stir at 1500 rpm for 12 minutes to complete the surface activation of the powder.

[0033] P2. Add methyl vinyl silicone rubber to the obtained activated powder, control the temperature at 70℃, and knead for 20 minutes using a kneader to fully impregnate the silicone rubber with the powder to obtain a rubber premix.

[0034] P3. Add an initiator to the premix, rapidly heat to 170°C, and maintain a speed of 40 rpm for a dynamic grafting reaction for 18 minutes to construct a chemically bonded structure.

[0035] P4. After the reaction is complete, turn on the vacuum pump to remove low molecular weight volatiles, cool the discharged material to room temperature, freeze-crush and pass it through a 100-mesh sieve to obtain the anchoring and separating agent.

[0036] II. Preparation of silicone-coated PTFE anti-dripping agent: Prepare the following raw materials by weight: 25 parts of suspension polymerized PTFE (average particle size 35 μm), 15 parts of emulsion polymerized PTFE (average particle size 0.3 μm), 45 parts of anchoring and releasing agent, 11 parts of phenyl silicone polymer, and 4 parts of polydimethylsiloxane (PDMS).

[0037] The specific preparation steps include: S1. Add the prescribed amount of suspended polymerized PTFE and anchoring agent into a high-speed mixer and mix at 900 rpm for 6 minutes to break up the agglomerates of suspended PTFE using the friction of the anchoring agent.

[0038] S2. Keep the mixer speed at 700 rpm, spray the pre-mixed liquid silicone coating agent into the machine through the atomizing nozzle, set the atomization pressure to 0.4 MPa, the spraying rate to 5 kg / min, and wet mix at 65°C for 15 minutes to form a uniform adsorption layer on the surface of the anchoring and releasing agent.

[0039] S3. Adjust the cooling jacket to reduce the material temperature to 35°C, reduce the rotation speed to 400 rpm, add the emulsion polymerized PTFE, and mix at low speed for 2.5 minutes to prevent early fiberization.

[0040] S4. Discharge: Place the obtained powder in the finished product container and let it stand for 24 hours to allow the silicone oil to reach adsorption equilibrium at the interface, thus obtaining the finished product.

[0041] Example 2 This embodiment provides a method for preparing a silicone-coated PTFE anti-dripping agent.

[0042] I. Preparation of anchoring and separating agent: Prepare the following raw materials by weight: 10 parts methyl vinyl silicone rubber, 5 parts fumed silica, 15 parts talc, 0.3 parts vinyltrimethoxysilane, and 0.01 parts initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane.

[0043] The specific preparation steps include: P1. Add fumed silica and talc powder to a high-speed mixer, atomize and spray vinyltrimethoxysilane, heat to 100°C, and stir at 1500 rpm for 15 minutes to complete the surface activation of the powder.

[0044] P2. Add methyl vinyl silicone rubber to the obtained activated powder, control the temperature at 60℃, and knead for 25 minutes using a kneader to fully impregnate the silicone rubber with the powder to obtain a rubber premix.

[0045] P3. Add an initiator to the premix, rapidly heat to 165℃, and maintain a speed of 45 rpm for a dynamic grafting reaction for 20 minutes to construct a chemically bonded structure.

[0046] P4. The steps are exactly the same as in Example 1.

[0047] II. Preparation of silicone-coated PTFE anti-dripping agent: Prepare the following raw materials by weight: 12 parts of suspension polymerized PTFE (average particle size 35 μm), 8 parts of emulsion polymerized PTFE (average particle size 0.3 μm), 65 parts of anchoring and releasing agent, 10 parts of phenyl silicone polymer, and 5 parts of polydimethylsiloxane (PDMS).

[0048] The specific preparation steps include: S1. Add the prescribed amount of suspended polymerized PTFE and anchoring agent into a high-speed mixer and mix at 800 rpm for 8 minutes. Utilize the dilution effect of the high proportion of anchoring agent to thoroughly disperse the suspended PTFE particles.

[0049] S2. Keep the mixer speed at 600 rpm, spray the pre-mixed liquid silicone coating agent into the machine through the atomizing nozzle, set the atomization pressure to 0.2 MPa, the spraying rate to 2 kg / min, and wet mix at 60℃ for 20 minutes.

[0050] S3. Adjust the cooling jacket to reduce the material temperature to 30℃, reduce the rotation speed to 300rpm, add the emulsion polymerized PTFE, and mix at low speed for 3 minutes.

[0051] S4. The steps are exactly the same as in Example 1.

[0052] Example 3 This embodiment provides a method for preparing a silicone-coated PTFE anti-dripping agent.

[0053] I. Preparation of anchoring and separating agent: Prepare the following raw materials by weight: 20 parts methyl vinyl silicone rubber, 10 parts fumed silica, 30 parts talc, 0.6 parts vinyltrimethoxysilane, and 0.04 parts initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane.

[0054] The specific preparation steps include: P1. Add fumed silica and talc to a high-speed mixer, atomize and spray vinyltrimethoxysilane, heat to 110°C, and stir at 1500 rpm for 10 minutes to complete the surface activation of the powder.

[0055] P2. Add methyl vinyl silicone rubber to the obtained activated powder, control the temperature at 80℃, and knead for 15 minutes using a kneader to fully impregnate the silicone rubber with the powder to obtain a rubber premix.

[0056] P3. Add an initiator to the premix, rapidly heat to 175°C, and maintain a speed of 40 rpm for a dynamic grafting reaction for 15 minutes to construct a chemically bonded structure.

[0057] P4. The steps are exactly the same as in Example 1.

[0058] II. Preparation of silicone-coated PTFE anti-dripping agent: Prepare the following raw materials by weight: 30 parts of suspension polymerized PTFE (average particle size 35 μm), 20 parts of emulsion polymerized PTFE (average particle size 0.3 μm), 35 parts of anchoring and releasing agent, 7 parts of phenyl silicone polymer, and 3 parts of polydimethylsiloxane (PDMS).

[0059] The specific preparation steps include: S1. Add the prescribed amount of suspended polymerized PTFE and anchoring agent into a high-speed mixer and mix at 1000 rpm for 5 minutes to ensure that the anchoring agent can fully penetrate between the suspended particles in the high-concentration PTFE system.

[0060] S2. Keep the mixer speed at 800 rpm, spray the pre-mixed liquid silicone coating agent into the machine through the atomizing nozzle, set the atomization pressure to 0.6 MPa, the spraying rate to 10 kg / min, and wet mix at 70℃ for 10 minutes.

[0061] S3. Adjust the cooling jacket to reduce the material temperature to 40℃, reduce the rotation speed to 500rpm, add the emulsion polymerized PTFE, and mix at low speed for 2 minutes.

[0062] S4. The steps are exactly the same as in Example 1.

[0063] Comparative Example 1 This comparative example provides a method for preparing a silicone-coated PTFE anti-dripping agent.

[0064] I. Preparation of the release agent: Prepare the following raw materials by weight: 15 parts methyl vinyl silicone rubber, 8 parts fumed silica, 25 parts talc, 0.45 parts vinyltrimethoxysilane, and 0.02 parts initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane.

[0065] The specific preparation steps include: putting all the above raw materials into a high-speed mixer and mixing them at 80°C and 1500 rpm for 30 minutes to ensure that the components are mixed evenly, without high-temperature activation or high-temperature dynamic grafting reaction, discharging and cooling, and then pulverizing to obtain a physical mixed type of release agent.

[0066] II. Preparation of silicone-coated PTFE anti-dripping agent: The following raw materials are prepared by weight: 25 parts of suspension polymerized PTFE (average particle size 35 μm), 15 parts of emulsion polymerized PTFE (average particle size 0.3 μm), 45 parts of the release agent prepared in this comparative example, 11 parts of phenyl silicone polymer, and 4 parts of polydimethylsiloxane (PDMS).

[0067] The specific preparation steps include: Steps S1-S4 are exactly the same as in Example 1.

[0068] Comparative Example 2 This comparative example provides a method for preparing a silicone-coated PTFE anti-dripping agent.

[0069] I. Preparation of anchoring and releasing agent: Prepare the following raw materials by weight: 15 parts of methyl vinyl silicone rubber, 8 parts of fumed silica, 25 parts of talc, 0.45 parts of vinyltrimethoxysilane, and 0.02 parts of 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane as an initiator.

[0070] The specific preparation steps include: Steps P1-P4 are exactly the same as in Example 1.

[0071] II. Preparation of silicone-coated PTFE anti-dripping agent: Prepare the following raw materials by weight: 25 parts of suspension polymerized PTFE (average particle size 35 μm), 15 parts of emulsion polymerized PTFE (average particle size 0.3 μm), 45 parts of anchoring and releasing agent, 11 parts of phenyl silicone polymer, and 4 parts of polydimethylsiloxane (PDMS).

[0072] The specific preparation steps include: S1. Add the formulation amounts of suspension polymerized PTFE, emulsion polymerized PTFE and anchoring and separating agent to a high-speed mixer and dry mix at 1000 rpm for 8 minutes.

[0073] S2. Keep the mixer speed at 700 rpm, spray the pre-mixed liquid silicone coating agent (phenyl silicone polymer and polydimethylsiloxane) into the machine through the atomizing nozzle, set the atomization pressure to 0.4 MPa, the spraying rate to 5 kg / min, and wet mix at 65°C for 15 minutes.

[0074] Steps S3-S4 are exactly the same as in Example 1.

[0075] Comparative Example 3 This comparative example provides a method for preparing a silicone-coated PTFE anti-dripping agent.

[0076] I. Preparation of anchoring and releasing agent: Prepare the following raw materials by weight: 15 parts of methyl vinyl silicone rubber, 8 parts of fumed silica, 25 parts of talc, 0.45 parts of vinyltrimethoxysilane, and 0.02 parts of 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane as an initiator.

[0077] The specific preparation steps include: Steps P1-P4 are exactly the same as in Example 1.

[0078] II. Preparation of silicone-coated PTFE anti-dripping agent: Prepare the following raw materials by weight: 40 parts of suspension polymerized PTFE (average particle size 35μm), 45 parts of anchoring and releasing agent, 11 parts of phenyl silicone polymer, and 4 parts of polydimethylsiloxane (PDMS).

[0079] The specific preparation steps include: S1. Add the prescribed amount of suspension polymerized PTFE and anchoring agent into a high-speed mixer and mix for 6 minutes at 900 rpm.

[0080] S2. The steps are exactly the same as in Example 1.

[0081] S3. Adjust the cooling jacket to reduce the material temperature to 35°C, reduce the speed to 400 rpm, and keep stirring for 2.5 minutes (do not add emulsion polymerized PTFE in this step).

[0082] S4. The steps are exactly the same as in Example 1.

[0083] Comparative Example 4 This comparative example provides a method for preparing a silicone-coated PTFE anti-dripping agent.

[0084] I. Preparation of anchoring and releasing agent: Prepare the following raw materials by weight: 15 parts of methyl vinyl silicone rubber, 8 parts of fumed silica, 25 parts of talc, 0.45 parts of vinyltrimethoxysilane, and 0.02 parts of 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane as an initiator.

[0085] The specific preparation steps include: Steps P1-P4 are exactly the same as in Example 1.

[0086] II. Preparation of silicone-coated PTFE anti-dripping agent: Prepare the following raw materials by weight: 25 parts of suspension polymerized PTFE (average particle size 35 μm), 15 parts of emulsion polymerized PTFE (average particle size 0.3 μm), 45 parts of anchoring and releasing agent, 11 parts of phenyl silicone polymer, and 4 parts of polydimethylsiloxane (PDMS).

[0087] The specific preparation steps include: S1. The steps are exactly the same as in Example 1.

[0088] S2. Keep the mixer speed at 700 rpm, pour the pre-mixed liquid silicone coating agent directly into the mixer in one go within 30 seconds without passing through the atomizing nozzle, and wet mix at 65°C for 15 minutes.

[0089] Steps S3-S4 are exactly the same as in Example 1.

[0090] To verify the effectiveness of this invention, the test samples were prepared as follows: Flame-retardant PC / ABS alloy (PC to ABS weight ratio of 4:1) was selected as the base resin. The silicone-coated PTFE anti-dripping agent obtained in the above examples and comparative examples was added to the base resin at a ratio of 0.5%. Granulation was performed using a co-rotating twin-screw extruder at 240℃-260℃. The resulting granules were then fed into an injection molding machine and molded into a high-gloss mirror-finish standard test plate with dimensions of 150mm × 100mm × 1.0mm under a high temperature of 270℃ and a high injection pressure of 120MPa. All samples were then subjected to the following performance tests.

[0091] All performance tests of this invention were conducted in accordance with the relevant Chinese national standards (GB / T), the specific standards of which are as follows: 1. Appearance performance test The evaluation of appearance quality combines visual assessment with instrumental measurement. Gloss testing is conducted according to GB / T8807-1988 "Test Method for Specular Gloss of Plastics," using a gloss meter to measure the proportion of reflected light on the surface of the high-gloss test piece at a 60° incident angle. Higher values ​​indicate a deeper mirror effect; a value exceeding 98 achieves the "piano black" finish required for high-end consumer electronics. The detection of black spots and crystal point count is performed under a 1000 Lux standard light source on a 1dm² surface. 2Surface defects within the specified range are manually counted. The fewer the number of crystal points, the more uniformly the suspended polymerized PTFE is dispersed under the action of the anchoring and releasing agent, and the less secondary agglomeration occurs. This indicator directly determines the pass rate of thin-walled high-gloss products during factory inspection, effectively solving the "starlight point" optical defect mentioned in the background technology.

[0092] 2. Mechanical property testing The notched impact strength test was performed according to GB / T1843-2008 "Determination of Impact Strength of Plastic Cantilever Beams". This index is determined by measuring the energy (kJ / m²) consumed when a specimen with a V-notch fractures upon impact. 2 The impact strength is used to evaluate the toughness of materials. A higher impact strength value means a stronger interfacial bond within the material. In this invention, the magnitude of this index directly reflects the effectiveness of the anchoring and isolating agent as an "elastic bridge." High impact strength means that when the component is subjected to a drop or impact, the area around the PTFE particles will not become a stress concentration point and induce cracks, thereby improving the structural reliability of the thin-walled electronic casing in actual use.

[0093] 3. Flame retardant performance test The evaluation of anti-dripping and flame-retardant properties was strictly conducted according to the vertical burning (Class V) test in GB / T2408-2021 "Determination of Burning Performance of Plastics - Horizontal and Vertical Methods". The test was performed on a 1.0mm thick thin-walled test strip, focusing on compliance with the UL-94 V-0 rating. Quantitative indicators included afterflame time (the time of afterflame following each application of flame) and whether molten droplets ignited the underlying absorbent cotton. A shorter afterflame time indicates a better effect of the fibrous network formed by PTFE in inhibiting thermal decomposition. Achieving a V-0 rating with no dripping means the product meets the most stringent fire safety standards, ensuring that in the event of an internal short circuit or other accident, the casing will not cause a fire to spread due to molten dripping.

[0094] 4. Processing performance testing The powder flowability test is performed according to GB / T11986-1989, "Determination of Angle of Repose of Surfactant Powders and Particles". The angle of repose is measured by stacking the powder into a cone and then measuring the angle between its slope and the horizontal plane. A smaller angle of repose (generally recommended to be less than 40°) indicates better powder dryness and flowability. This indicator directly corresponds to the feeding efficiency in actual production: a smaller angle of repose means that the anti-dripping agent will not adhere or bridge in the automated feeding system, ensuring the continuity and stability of component addition during extrusion processing, thereby reducing equipment maintenance costs in industrial production.

[0095] The performance of the test samples obtained from the above embodiments and comparative examples was tested, and the results are summarized in the table below: When evaluating the optical quality of the test panel surface, the number of crystal points and gloss directly reflect the stability of the release agent's coating on PTFE. The gloss of Examples 1, 2, and 3 all remained above 97 GU, with the number of surface crystal points controlled to within 5. This demonstrates that the anchoring release agent, through dynamic grafting, forms chemical bonds that, under the high shear force of the injection molding process, can firmly lock the silicone layer, preventing it from peeling off from the powder surface, thus effectively isolating the secondary agglomeration of PTFE particles. In contrast, Comparative Example 1, due to the simple physical mixing of raw materials and the lack of chemical bond traction, resulted in the silicone layer detaching during processing, causing the exposed PTFE particles to rapidly aggregate, resulting in 35 obvious crystal point defects on the test panel surface, and the gloss level dropping to 88.4 GU. Even in Comparative Example 4, with complete raw material composition, the absence of the atomization spraying process led to uneven distribution of silicone oil in the powder, causing surface oil spots and localized crystal point accumulation. This indicates that precise atomization is a necessary condition for achieving high surface gloss.

[0096] In the impact strength test, the data changes revealed the influence of interfacial bonding on the material's toughness. The impact strength of Example 1 reached 52.4 kJ / m. 2 It is significantly higher than the 32.6 kJ / m² of Comparative Example 1. 2 This demonstrates that the multi-level interface structure constructed in this invention can act as a stress buffer when the matrix is ​​subjected to impact. In Comparative Example 1, due to only weak physical adsorption at the interface, the bonding surface between PTFE and resin becomes a stress concentration point when subjected to external force. Cracks propagate rapidly along these weakly bonded interfaces, leading to brittle fracture of the material. The data fluctuations in Examples 2 and 3 prove that within the formulation range defined in the claims, this interface locking effect can maintain good mechanical reliability.

[0097] The comparison of flame retardant and anti-dripping performance demonstrates the protective effect of the stepwise gradient process on PTFE activity. Examples 1, 2, and 3 all stably achieved a V-0 rating at a 1.0mm thin-walled specification, with short afterflame times and no dripping. This indicates that the stepwise feeding logic prevents the emulsion-type PTFE from failing due to excessive shearing in the early stages of mixing. Comparative Example 2, although using the exact same raw materials as Example 1, employed a one-time feeding process, causing the emulsion-type PTFE to prematurely fibroinate due to friction with hard particles in the first stage. By the time of the combustion test, it was unable to construct an effective anti-dripping network, resulting in dripping ignition. Comparative Example 3, due to the complete absence of easily fibrous PTFE components, experienced a significant decline in flame retardant performance, which conversely confirms the synergistic necessity of the dual-source system in constructing the flame retardant network in this invention.

[0098] In processing performance evaluation, the angle of repose of the powder directly reflects the dryness and flowability of the product. In Examples 1 and 2, the angles of repose remained around 32° and 30°, respectively, indicating good dryness of the powder. This is because the anchoring agent precisely confines the liquid silicone within the powder, preventing adhesion caused by oil precipitation. In contrast, Comparative Example 4, due to the direct pouring of silicone oil, resulted in uneven distribution of the liquid phase in the system. Some powder was impregnated by excessive oil, and the particles severely agglomerated due to liquid bridging forces, causing the angle of repose to increase sharply to 48°. Such viscous powder is highly prone to causing blockages in the feeding system or fluctuations in the feed rate in automated production. This invention, by controlling the atomization pressure and rate, ensures that the silicone oil achieves nanoscale uniform spreading on the surface of each anchoring agent particle, improving the performance of the end product while ensuring the continuity of industrial production.

[0099] The descriptions of the foregoing specification and embodiments are used to explain the scope of protection of the present invention, but do not constitute a limitation on the scope of protection of the present invention. Modifications, equivalent substitutions, or other improvements to the embodiments of the present invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of the present invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of the present invention.

Claims

1. A silicone-coated PTFE anti-dripping agent, characterized in that, By weight, its raw materials include: PTFE: 20-50 parts, wherein the PTFE is composed of suspension polymerized PTFE and emulsion polymerized PTFE; Anchoring and release agent: 35-65 parts; Liquid silicone coating agent: 10-15 parts, wherein the liquid silicone coating agent comprises phenyl silicone polymer and polydimethylsiloxane; The preparation of the anchoring and insulating agent includes the following steps: P1. Add silica and talc to a high-speed mixer, spray with coupling agent, and stir at high speed for 10-15 minutes at 100℃-110℃ to activate the powder; P2. Add methyl vinyl silicone rubber to the product obtained in step P1, and knead it evenly at 60℃-80℃ to obtain a rubber premix. P3. Add the initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane to the premix obtained in step P2, and heat to 165℃-175℃ to carry out a dynamic grafting reaction for 15-20 minutes. P4. After the reaction is complete, the anchoring and separating agent is obtained by vacuum devolatilization, cooling and pulverization; The anchoring and isolating agent comprises, by weight, the following raw materials: 10-20 parts methyl vinyl silicone rubber, 5-10 parts silica, 15-30 parts talc, 0.3-0.6 parts coupling agent, and 0.01-0.04 parts initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane; The weight ratio of the suspension polymerized PTFE to the emulsion polymerized PTFE is 1.5:1 to 3:1; The coupling agent is vinyltrimethoxysilane; The preparation method of the silicone-coated PTFE anti-dripping agent includes the following steps: S1. Add the prescribed amount of suspension polymerized PTFE and anchoring release agent into a mixer and mix for 5-8 minutes at a speed of 800rpm-1000rpm; S2. Maintain a rotation speed of 600-800 rpm, spray liquid silicone coating agent into the mixture obtained in step S1 through an atomizing nozzle, and wet mix at 60℃-70℃ for 10-15 minutes. S3. Cool down to below 40℃, reduce the rotation speed to 300rpm-500rpm, add emulsion polymerized PTFE, and mix for 2-3 minutes; S4. Discharge the material and allow it to stand for aging for 12-24 hours to obtain the silicone-coated PTFE anti-dripping agent.

2. The silicone-coated PTFE anti-dripping agent according to claim 1, characterized in that, The average particle size of the suspension polymerized PTFE is 20μm-50μm; the average particle size of the emulsion polymerized PTFE is 0.2μm-0.5μm.

3. The silicone-coated PTFE anti-dripping agent according to claim 1, characterized in that, In the liquid silicone coating agent, the weight ratio of phenyl silicone polymer to polydimethylsiloxane is 2:1 to 4:

1.

4. The silicone-coated PTFE anti-dripping agent according to claim 1, characterized in that, The liquid silicone coating agent described in step S2 is a premix of phenyl silicone polymer and polydimethylsiloxane.

5. The silicone-coated PTFE anti-dripping agent according to claim 1, characterized in that, In step S2, the atomizing pressure of the atomizing nozzle is 0.2MPa-0.6MPa, and the spraying rate of the liquid silicone coating agent is 2kg / min-10kg / min.

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