Silicone coated PTFE anti-dripping agent and preparation method thereof

Abstract

The invention relates to the technical field of high polymer material auxiliaries, and particularly discloses a preparation method of a silicone-coated PTFE anti-dripping agent, which comprises the following steps: 1, preparing an anchoring separant, mixing silicone rubber, inorganic powder and a coupling agent, and carrying out dynamic grafting reaction under the action of an initiator to construct an intermediate with a chemical bonding structure; 2, preparation of an anti-dripping agent: S1, mixing suspension polymerization PTFE with an anchoring separant in a high-speed mixer, and disassembling PTFE aggregate; s2, at a specific rotating speed, spraying a liquid silicone coating agent into the machine through an atomizing nozzle for wet mixing, so that a liquid phase forms a uniform adsorption layer on the surface of the anchoring separant; s3, after cooling, emulsion polymerization PTFE is added for low-speed mixing, and early fibrosis is prevented; and S4, standing and aging to enable the interface to reach adsorption equilibrium. According to the anti-dripping agent, the problem of crystal points caused by easy agglomeration of PTFE in a matrix is solved, so that the prepared anti-dripping agent improves the surface quality and mechanical toughness of a highlight injection molded part while ensuring the flame retardant property.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer material additives, and particularly relates to a silicone-coated PTFE anti-dripping agent and a preparation method thereof. BACKGROUND

[0002] In the field of engineering plastic processing, polytetrafluoroethylene (PTFE) is often used as a flame-retardant synergist. Under high-temperature and high-shear conditions, PTFE can be fibrous to form a network structure to inhibit the generation of melt dripping. Since pure PTFE powder is prone to agglomeration and has poor dispersibility, the industry usually performs coating treatment on the surface of PTFE with a silicone polymer to improve the dispersibility of PTFE in a plastic matrix. Such silicone-coated PTFE additives have been widely applied to thin-walled injection molded products such as computer housings, mobile phone middle frames, and charger housings, which have high requirements for flame-retardant performance and appearance quality.

[0003] In actual applications, in order to balance the cost and anti-dripping efficiency, large-particle suspension polymerization PTFE and small-particle emulsion polymerization PTFE are usually used in combination. The suspension polymerization PTFE has good physical support, but its molecular chain arrangement is compact and is not prone to fibrosis during processing. The emulsion polymerization PTFE is more prone to form a fibrous structure under the action of shearing. The combination of the two 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 a narrow flow channel in a very short time and bear a very high shear stress. Since the coating layers of phenyl silicone and methyl silicone have good compatibility with PC or PC / ABS resin matrix, but the combination with the surface of PTFE mainly depends on physical adsorption, the coating layer is prone to peel off from the surface of the suspension polymerization PTFE under strong shearing conditions. After losing the protection of the coating layer, the suspension polymerization PTFE particles are prone to rapid agglomeration in a high-temperature environment to form a particle group with high crystallinity.

[0005] The agglomerated PTFE particles have a large refractive index difference with the surrounding resin matrix, and light is prone to scattering at the interface, resulting in appearance defects such as white spots, pockmarks, or starlight on the surface of the product. Moreover, because there is a lack of stable interfacial bonding between the agglomerated particles and the resin matrix, microcracks are easily formed and rapidly expanded under external force impact, thereby reducing the impact strength and use reliability of the thin-walled product. The existing technology usually alleviates the problem by increasing the amount of separating agent or prolonging the mixing time, but the former is prone to cause haze of the product, and the latter may damage the fibrous ability of the emulsion polymerization PTFE, which is difficult to balance the appearance and anti-dripping performance. SUMMARY

[0006] The purpose of the present application is to provide a silicone-coated PTFE anti-dripping agent and a preparation method thereof to solve the problems raised in the background.

[0007] To achieve the above object, according to one aspect of the present application, a silicone-coated PTFE anti-dripping agent is provided, raw materials of which include, by weight: PTFE: 20-50 parts, the PTFE being composed of suspension polymerized PTFE and emulsion polymerized PTFE; anchoring release agent: 35-65 parts; liquid silicone coating agent: 10-15 parts, the liquid silicone coating agent including phenyl silicone polymer and polydimethylsiloxane; The preparation of the anchoring release agent includes the following steps: P1. Put silica and talc into a high-speed mixer, spray a coupling agent, and activate the powder by high-speed stirring at 100-110°C for 10-15 minutes; P2. Add methyl vinyl silicone rubber to the product obtained in step P1, and knead uniformly at 60-80°C to obtain a rubber premix; P3. Add initiator 2,5-dimethyl-2,5-di(tert-butylperoxide)hexane to the premix obtained in step P2, and heat to 165-175°C to perform dynamic grafting reaction for 15-20 minutes; P4. After the reaction is completed, the anchoring release agent is prepared by vacuum devolatilization, cooling, and crushing.

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

[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 20-50 μm, and the average particle size of the emulsion polymerized PTFE is 0.2-0.5 μm.

[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 application, a preparation method of a silicone-coated PTFE anti-dripping agent is provided, including the following steps: S1. Put the formula amount of suspension polymerization PTFE and anchoring release agent into a mixer, mix at 800 rpm-1000 rpm for 5-8 minutes; S2. Keep the speed at 600-800 rpm, spray the liquid silicone coating agent into the mixture obtained in step S1 through an atomizing nozzle, wet mix at 60℃-70℃ for 10-15 minutes; S3. Reduce the temperature to below 40℃, reduce the speed to 300 rpm-500 rpm, add emulsion polymerization PTFE, mix for 2-3 minutes; S4. Discharge and stand for 12-24 hours to obtain the silicone-coated PTFE anti-dripping agent.

[0014] Preferably, the liquid silicone coating agent in step S2 is pre-mixed from phenyl silicone polymer and polydimethylsiloxane.

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

[0016] Compared with the prior art, the beneficial effects of the present application are: The anchoring release agent is prepared by grafting reaction between methyl vinyl silicone rubber and activated silica and talc powder under the action of an initiator. In the anchoring release agent, the silicone rubber no longer exists in the form of physical coating, but is stably anchored on the surface of inorganic powder, improving the structural stability of the silicone phase in the subsequent processing process.

[0017] The suspension polymerization PTFE and emulsion polymerization PTFE are step-by-step coated with the anchoring release agent, and the anti-dripping material obtained is not easy to peel off from the surface of PTFE under high shear injection molding processing conditions, and the PTFE particles can maintain a stable and uniform dispersion state in the resin matrix, thereby effectively inhibiting the agglomeration phenomenon of suspension polymerization PTFE.

[0018] Since the PTFE particles are not easy to form large-size aggregates with high crystallinity in the product, the flame-retardant product prepared can significantly reduce the light scattering phenomenon caused by the difference in refractive index under high light or thin wall molding conditions, reduce the risk of white spots, pitting or starlight defects on the surface of the product, and improve the appearance consistency of the product.

[0019] Moreover, the chemical connection structure formed by the silicone rubber and the inorganic carrier in the anchoring release agent builds a stable transition interface between PTFE and the resin matrix, reduces the stress concentration and micro-defect generation in the material, so that the flame-retardant performance is maintained while the impact resistance of the product is simultaneously improved. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are the preferred embodiments of the present application, and should not be regarded as exclusive to other embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0021] I. The design core of the anchoring isolation agent is to provide a firm base layer for the subsequent PTFE coating by constructing an organic-inorganic hybrid structure.

[0022] P1. In the first stage of preparation, by powder activation, silica and talc powder are put into a high-speed mixer. At a high temperature environment of 100-110°C, vinyl trimethoxysilane coupling agent is added. This temperature range can effectively promote the hydrolysis of the alkoxy group of the silane coupling agent, and condensation reaction with the hydroxyl group on the surface of the inorganic powder. Through 10-15 minutes of high-speed stirring, the powder surface is successfully implanted with a large number of active vinyl groups.

[0023] P2. Then enter the premixing stage of the rubber, add methyl vinyl silicone rubber at 60-80°C. This temperature range is to reduce the viscosity of the silicone rubber, so that it can better penetrate into the microporous structure of silica and talc powder during kneading, forming a preliminary physical wrapping.

[0024] P3. The core reaction occurs in the dynamic grafting stage. The temperature is raised to 165-175°C, and initiator DBPH is added. At this temperature, the initiator decomposes to produce free radicals, inducing the free radical addition reaction between the vinyl groups on the silicone rubber molecular chain and the grafted vinyl groups on the powder surface. This makes the silicone rubber tightly anchored on the inorganic carrier through covalent bonds. A reaction time of 15-20 minutes can ensure sufficient grafting rate, and avoid hardening of the rubber caused by excessive crosslinking. The finally prepared anchoring isolation agent is covered with organosilicon segments on the surface, and has strong oil absorption capacity and interfacial bonding force.

[0025] II. On the basis of obtaining the anchoring isolation agent, the final composite system is constructed by step-by-step coating method, aiming to solve the dispersion contradiction between large particle suspended PTFE and microfine 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 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.

2. The silicone-coated PTFE anti-dripping agent according to claim 1, characterized in that... The anchoring and isolating agent, by weight, comprises 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.

3. The silicone-coated PTFE anti-dripping agent according to claim 1, characterized in that... The weight ratio of the suspension polymerized PTFE to the emulsion polymerized PTFE is 1.5:1 to 3:

1.

4. 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.

5. 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.

6. The silicone-coated PTFE anti-dripping agent according to claim 2, characterized in that... The coupling agent is vinyltrimethoxysilane.

7. A method for preparing a silicone-coated PTFE anti-dripping agent as described in any one of claims 1-6, characterized in that... This 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 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.

8. The method for preparing a silicone-coated PTFE anti-dripping agent according to claim 7, characterized in that... The liquid silicone coating agent described in step S2 is a premix of phenyl silicone polymer and polydimethylsiloxane.

9. The method for preparing a silicone-coated PTFE anti-dripping agent according to claim 7, 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.

Images