Preparation method and application of optical-grade high-transparency flame-retardant PVC / SMMA alloy particles

Abstract

The invention discloses a preparation method and application of optical-grade high-transparency flame-retardant PVC / SMMA (polyvinyl chloride / SMMA) alloy particles, the alloy is prepared by taking optical-grade PVC and SMMA as matrixes, matching with auxiliaries such as a chain extender, a compound flame retardant, a silane coupling agent and an impact modifier, and carrying out pre-dispersion, pre-coupling, blending, extrusion granulation and the like. Wherein the PVC and the SMMA reduce light scattering through refractive index matching; after the compound flame retardant (WSFR-TCPP, F50508 and KR-2710) is modified by KH-570, nanoscale dispersion is realized, and the flame retardant effects of a gas phase and a condensed phase are synergistically exerted. Under the condition that the thickness is 3.2 mm, the light transmittance of the obtained alloy reaches 91.8%, the haze is 0.8%, the flame retardant rating is UL945VA, the oxygen index is 34.2%, and meanwhile the excellent mechanical properties that the tensile strength is 52 MPa and the impact strength is 20 kJ / m are kept. In the production process, a low-shear extrusion and nitrogen protection process is adopted, the crystal point is 0 / 10kg, and the YI chromaticity is 1.5. The material is widely applied to the fields of electronic display screens, transparent fireproof building materials, automotive interiors and the like, and fills the market blank of optical-grade high-flame-retardant materials.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material modification and preparation, and in particular to a method for preparing optical-grade highly transparent flame-retardant PVC / SMMA alloy particles and applications thereof. Background Art

[0002] Optically transparent materials are increasingly used in modern industry, from electronic display screens to architectural decoration. These materials place increasingly stringent demands on their light transmission, mechanical properties, and safety. Flame retardancy, a core safety indicator, is particularly crucial in applications such as electronics, construction, and transportation. However, existing technologies for combining optically transparent materials with high flame retardancy have consistently faced technical bottlenecks.

[0003] At present, traditional flame retardant technologies mainly rely on single systems such as halogen flame retardants, inorganic flame retardants, nitrogen-based, phosphorus-based, boron-based and silicon-based flame retardants, but all of them have significant defects: although halogen flame retardants have high flame retardant efficiency, they release toxic gases when burned, which pose great harm to the environment and human health, and have been strictly restricted by environmental protection laws and regulations of many countries; inorganic flame retardants are environmentally friendly and non-toxic but have poor compatibility with polymers, and need to be added in large quantities to achieve flame retardant effects, resulting in a significant decrease in the mechanical properties and transparency of the material; nitrogen-based flame retardants have unsatisfactory flame retardant effects when used alone, and can easily reduce the impact strength of the material; phosphorus-based flame retardants have poor heat resistance, are easily hydrolyzed, and have the problem of toxic intermediates; boron-based and silicon-based flame retardants face problems such as high cost, low flame retardant efficiency or immature synthesis process.

[0004] The core contradiction of existing technologies lies in the difficulty in balancing flame retardancy with optical and mechanical properties: flame retardants added to enhance flame retardancy often destroy the molecular regularity of the material, resulting in decreased light transmittance and increased haze; at the same time, the introduction of large amounts of additives weakens the bonding between polymer molecules, deteriorating mechanical properties such as tensile strength and impact strength. In addition, the combination of ordinary twin-screw extruders and high-speed mixers in traditional production processes cannot solve the problem of light scattering caused by uneven dispersion of flame retardants, and the insufficient precision of thermal history control can easily cause material degradation and yellowing, further limiting the performance improvement of optical-grade flame retardant materials. These defects make existing materials unable to meet the dual demands of "high transparency + high flame retardancy" in high-end fields, becoming a technical bottleneck for the development of the industry. Summary of the Invention

[0005] The present invention aims to solve the above technical problems and provide a method for preparing optical-grade highly transparent flame-retardant PVC / SMMA alloy particles and their application. The alloy material has both excellent optical properties (high transmittance, low haze) and top flame retardant properties (UL94V-0, 5VA grade). It can be widely used in electronic equipment housings, optical lenses, display light guide plates, transparent fireproof building materials, automotive interiors and architectural decorations, etc., which have strict requirements on material transparency and flame retardant safety. It is especially suitable for high-end application scenarios that need to meet both optical clarity and fire safety standards.

[0006] To solve the above technical problems, the present invention provides a technical solution: an optical grade highly transparent flame retardant PVC / SMMA alloy, comprising the following components by weight: 100 parts of PVC resin; 15-25 parts of SMMA resin; 1-3 parts of chain extender; 1-2 parts of heat stabilizer; 10-20 parts of compound flame retardant, including three components: (a) 3-8 parts of WSFR-TCPP, a carbon-forming agent; (b) 3-8 parts of silicone flame retardant F50508; (c) 3-8 parts of organosilicon flame retardant KR-2710; Silane coupling agent KH-570 0.5-1.5 parts; impact modifier 3-8 parts; toughening agent MBS 2-6 parts; light stabilizer UVB390 0.1-0.5 parts; antioxidant 0.1-0.5 parts; lubricant 0.3-1.0 parts.

[0007] Furthermore, the chain extender is an epoxy or acrylate type chain extender; Components (b) and (c) in the composite flame retardant are surface-treated with a silane coupling agent KH-570 to form a nano-coating structure, and the average particle size D90 after coating is ≤200 nm.

[0008] Furthermore, the impact modifier is acrylic rubber grafted with methyl methacrylate; The toughening agent is a methyl methacrylate-butadiene-styrene copolymer (MBS) with a core-shell structure.

[0009] A method for preparing an optical-grade highly transparent flame-retardant PVC / SMMA alloy comprises the following steps: (1) Pre-dispersion: PVC resin, chain extender, part of lubricant and antioxidant are mixed in a vacuum disperser, the temperature is controlled at 40-45°C, the absolute pressure is ≤0.01MPa, and high-speed shearing is performed until the chain extender dispersed particle size D90 is ≤200nm; (2) Pre-coupling: reacting siloxane flame retardant F50508, organosilicon flame retardant KR-2710 and silane coupling agent KH-570 in an ethanol / water medium, controlling the temperature at 45-50°C and the absolute pressure ≤0.01 MPa, and removing the solvent after the reaction to obtain a nano-coated flame retardant with D90 ≤200 nm; (3) Mixing: Add pre-dispersed PVC, SMMA resin, pre-coupled flame retardant, and remaining additives in sequence, blend at 65-70°C in a high-speed and low-speed mixer, and evacuate to a dew point of ≤-40°C and a moisture content of ≤300ppm; (4) Extrusion granulation: The mixed material is melted and extruded through a twin-screw extruder with a barrel temperature of 150-185°C. The melt is filtered through a 400-mesh filter and then pelletized underwater. The pelletizing water temperature is ≤15°C and the dissolved oxygen is ≤0.5ppm under nitrogen protection.

[0010] Furthermore, in the step (1), the vacuum disperser is a butterfly-type biaxial disperser, the speed in the high-speed shearing stage is ≥1500 rpm, and the dispersion time is 15-20 min.

[0011] Furthermore, in the step (3), the high-speed and low-speed mixing unit includes a high-speed hot mixing pot (800-900 rpm) and a low-speed cold mixing pot (50-70 rpm), and the mixture is transferred to the cold mixing pot after hot mixing and cooled to ≤45°C before discharging; The vacuum disperser in step (1) is a butterfly-type double-shaft disperser, and the rotation speed in the high-speed shearing stage is ≥1500rpm.

[0012] A twin-screw extruder for implementing a method for preparing an optical-grade highly transparent flame-retardant PVC / SMMA alloy, comprising: (a) Low shear barrier screw: Contains a toothed disc structure with a toothed disc thickness of 0.5-1.0 mm, an axial spacing of 2-5 mm, and a barrier gap of 0.3-1.0 mm; (b) Dual-channel barrel temperature control system: It has independent oil cooling circuits for the PVC low-temperature zone (150-195°C) and the SMMA high-temperature zone (200-220°C); (c) Melt filtration unit: 400-600 mesh double-tube switchable backflushing metal fiber filter; (d) Nitrogen protection underwater pelletizing module: dissolved oxygen in the pelletizing chamber is ≤0.5ppm, and the nitrogen flow rate is interlocked with the host PLC.

[0013] Furthermore, the melt filtration unit is provided with a melt pressure sensor, and the backflushing cycle is dynamically adjusted according to pressure changes.

[0014] A vacuum drying equipment for implementing a method for preparing an optical-grade highly transparent flame-retardant PVC / SMMA alloy, comprising: (10) Single cone spiral structure, cone angle 60°±2°, inner mirror surface Ra≤0.2μm; (11) Three-stage drying process: Stage 1: 45-55°C / -0.090 MPa for 30 min; Stage 2: 65-70°C / -0.092 MPa for 2-2.5 hours; Stage 3: 55-60℃ / -0.095MPa for 30min.

[0015] An application of optical-grade highly transparent flame-retardant PVC / SMMA alloy particles, and products made from the formulation and method, with a light transmittance ≥ 90%, a haze ≤ 1%, a YI chromaticity ≤ 2, a flame retardancy rating of UL94V-0 (1.6mm thickness), and a tensile strength ≥ 48MPa; The product is an optical lens, a display light guide plate or a transparent fireproof building material.

[0016] The advantages of the present invention compared with the prior art are: The innovatively constructed synergistic flame retardant system demonstrates significant advantages in flame retardancy. The synergistic design of the PVC and SMMA substrates, along with a three-component combination of siloxane flame retardant F50508, organosilicon flame retardant KR-2710, and WSFR-TCPP, leverages multiple mechanisms, including the formation of a silicon-carbon protective layer, free radical capture, and enhanced cross-linked network structure, to achieve a flame retardancy rating of UL94V-0 / 5VB / 5VA, a limiting oxygen index of ≥32%, and rapid self-extinguishing properties without ignitable droplets, meeting high-end safety standards.

[0017] A breakthrough balance in transparency and performance is achieved. Surface treatment of the flame retardant with silane coupling agent K-570 significantly improves its compatibility with the substrate, preventing light scattering caused by agglomeration. Simultaneously, the regularity of the PVC molecular chain and the quality of the SMMA raw material are optimized, achieving a light transmittance of ≥90%, successfully resolving the conflict between flame retardant addition and decreased transparency, achieving optical-grade application requirements.

[0018] Synergistic optimization of mechanical and processing properties. The introduction of a core-shell impact modifier significantly improves impact strength while maintaining transparency. A combination of oxidized polyethylene wax and ethylene-vinyl acetate copolymer wax improves processing fluidity. The addition of heat stabilizers and process optimization enhances PVC's high-temperature stability, reduces processing difficulty, and makes it suitable for large-scale production.

[0019] Significant environmental and cost advantages. Halogen-free and bio-based flame retardants are used to reduce environmental and health hazards and comply with environmental regulations. Formula optimization and efficiency improvements reduce raw material and processing costs, enhancing market competitiveness. The addition of UV absorbers and light stabilizers significantly improves the material's weather resistance, ensuring stable long-term performance and extending its service life.

[0020] Its core value lies in a balanced performance and wide application. Building on its high flame retardancy and transparency, it achieves a comprehensive balance of mechanical properties, processing performance, and environmental friendliness, transcending the limitations of single-performance enhancements. It is widely applicable in high-end applications such as electronic device housings, automotive interiors, and architectural decoration. Its market potential is enormous, driving technological advancements and expanding applications for optical-grade PVC / SMMA alloy materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a tensile test report of Example 1 of the present invention.

[0022] Figure 2 This is a tensile test report of Example 2 of the present invention.

[0023] Figure 3 This is a tensile test report of Example 3 of the present invention.

[0024] Figure 4 This is a tensile test report of Example 4 of the present invention. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] 12. Working principle of the present invention: (1) Synergistic mechanism of matrix materials 1. Optical Performance Control: Specially purified optical-grade PVC resin (such as S-58 and S-60) and highly transparent SMMA resin (such as NAS90 and STYROLUTION90) are used as the matrix. Optical-grade PVC undergoes molecular chain regularization to reduce crystallization defects, resulting in a refractive index of approximately 1.54. SMMA resin, due to its styrene-methyl methacrylate copolymer structure, has a refractive index of 1.56, close to that of PVC, which reduces interfacial light scattering. The epoxy groups of chain extenders (such as ADR4400 and ADR4468) react with the active groups on the PVC molecular chains to repair broken chains, making them more complete and regular, further reducing light scattering losses and ensuring the matrix's basic light transmittance.

[0027] 2. Synergistic Flame Retardancy: PVC contains chlorine in its molecular chains, which decomposes during combustion to produce hydrogen chloride (HCl) gas, which captures free radicals in the combustion reaction and interrupts the chain reaction. SMMA, through molecular chain breakage and rearrangement during combustion, forms a dense carbonized layer, providing heat and oxygen insulation. The two together form a synergistic system of "gas-phase flame retardancy + condensed-phase flame retardancy," providing the alloy with fundamental flame retardancy.

[0028] (2) Action mechanism of compound flame retardant system The present invention adopts the synergistic modification technology of multi-component composite flame retardant and silane coupling agent, which specifically includes: 1. Carbonizing agent WSFR-TCPP: It decomposes at the combustion temperature to produce acidic substances such as phosphoric acid, which catalyzes the dehydration and carbonization reaction on the surface of PVC / SMMA alloy, promotes the formation of a continuous and dense carbon layer, and blocks the transfer of heat and oxygen.

[0029] 2. Siloxane flame retardant F50508: After surface treatment with silane coupling agent KH-570, the silicon-oxygen bonds in its molecular chain break and reorganize at high temperatures to form a dense silicon-carbon protective layer. At the same time, it releases inert gas to dilute the concentration of combustible gas and captures free radicals in the gas phase.

[0030] 3. Organic silicon flame retardant KR-2710: The special structure containing Si-H bonds enables it to form a cross-linked network of carbon-silicon-oxygen bond protective layer when burning, inhibiting the molten material from dripping and enhancing the stability of the carbon layer structure.

[0031] The methacryloyloxy functional group of the silane coupling agent KH-570 reacts with the acrylate structure of SMMA, and the methoxy functional group hydrolyzes and combines with the hydroxyl group on the surface of the flame retardant ( Figure 1 In ⑧), the inorganic flame retardant is connected to the organic matrix through chemical bonds to solve the uneven dispersion problem of traditional flame retardants, so that the particle size of the flame retardant is controlled at D90≤200nm, avoiding light scattering caused by poor dispersion.

[0032] (3) Process performance maintenance mechanism A low-shear barrier screw and a segmented temperature-controlled barrel (PVC section 150-195°C, SMMA section 200-220°C) are used. A toothed disc combination structure (thickness 0.5-1.0mm, axial spacing 2-5mm) achieves gentle mixing of materials to avoid secondary agglomeration of flame retardants. A 400-600 mesh double-barrel switchable backflush filter effectively intercepts impurity particles and reduces the generation of crystal points. Nitrogen protection for underwater pelletizing (dissolved oxygen ≤ 0.5ppm) inhibits oxidative degradation of the material, ensuring that the final pellets have a light transmittance ≥ 90% and a haze ≤ 1%.

[0033] 2. Implementation Methods Example 1: Optical grade highly transparent flame retardant PVC / SMMA alloy (injection molding grade) 13. Recipe 14. Preparation Method (1) Pre-dispersion: PVC resin, ADR4400, PEWO-0530 (0.8 parts), and B215 (0.3 parts) were placed in a SFSD-100 disperser and high-speed sheared at 1500 rpm for 18 min at 40°C and an absolute pressure of 0.01 MPa. The chain extender D90 was measured to be 185 nm. (2) Pre-coupling: F50508, KR-2710 and KH-570 were reacted in ethanol / water (95:5) at 45°C and 0.01 MPa absolute pressure for 20 min. After desolvation, D90 = 192 nm. (3) Mixing: Add pre-dispersed PVC, SMMA, pre-coupled flame retardant and other additives into the SRL-Z500 / 1000 unit, blend at 70°C in a high-speed pot (800 rpm), evacuate to a dew point of -45°C, and a moisture content of 280 ppm. Cool the cold mixing pot to 40°C before discharging. (4) Extrusion granulation: Twin-screw extruder (GoldPowerZE62) temperature zone: 150℃ / 170℃ / 180℃ / 185℃ / 180℃ / 175℃. The melt was filtered through 400 mesh and then pelletized underwater (water temperature 15℃, N2 protection dissolved oxygen 0.3ppm). The powder was removed by vibrating fluidized bed to a dust content of 0.008wt%.

[0034] 3. Performance Testing Light transmittance: 90.68% (ASTM D1003); Haze: 0.9% (ASTM D1003); YI color: 1.8 (ASTM E313); Flame retardancy: UL94 V-0 (1.6mm, ASTM D3801), OI=34%; Tensile strength: 54 MPa (ASTM D638); Impact strength: 19 kJ / m² (notched, ASTM D256); Weather resistance: Light transmittance decreases by 4.2% after 1000 hours of UV irradiation, ΔYI=1.5.

[0035] Example 2: High-gloss injection-molding grade alloy 1. Recipe

[0036] 2. Process optimization The speed was increased to 1600 rpm in the pre-dispersion stage, and the dispersion time was 17 min (D90 = 178 nm); The temperature of the second zone of the extruder was raised to 172°C (otherwise the same as in Example 1).

[0037] 3. Performance Improvement Light transmittance: 91.0%; Haze: 0.7%; OI: 35% → UL945VA grade; Impact strength: 22kJ / m².

[0038] Example 3: Extrusion Grade Alloy 15. Recipe 16. Process adjustment Adjust the speed of the cold mixer to 60 rpm and extend the cooling time to 25 min (discharge temperature 38°C); After pelletizing, the dust removal strength is increased and the dust residue is 0.005wt%.

[0039] 3. Performance characteristics Tensile strength: 58 MPa; Strength: 35 kJ / m² (suitable for extruded sheets); OI: 33% → UL94V-0 grade.

[0040] Example 4: Blow molding grade alloy 1. Recipe 2. Blow molding adaptability The extruder die head temperature was lowered to 170°C (to avoid melt fracture); the underwater pelletizing size was adjusted to φ2×3mm (suitable for blow molding feed).

[0041] 3. Performance data Light transmittance: 89.78%; impact strength: 42kJ / m² (anti-drop of hollow products); elongation at break: 23% (blow molding ductility requirements).

[0042] in conclusion: Example 1-4 formula statistics: Performance test table of Examples 1-4: Through collaborative material design and process innovation, this solution successfully resolves the core contradiction in existing technologies, which is the difficulty in balancing flame retardancy, transparency, and mechanical properties. The prepared optical-grade, highly transparent, flame-retardant PVC / SMMA alloy provides a safe and efficient material solution for industries such as electronics, construction, and transportation, and has broad market application prospects.

[0043] The present invention and its embodiments are described above. This description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs structures and embodiments similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. An optical grade highly transparent flame retardant PVC / SMMA alloy, characterized by: The components by mass are as follows: 100 parts of PVC resin; 15-25 parts of SMMA resin; 1-3 parts of chain extender; 1-2 parts of heat stabilizer; 10-20 parts of compound flame retardant, including three components: (a) 3-8 parts of WSFR-TCPP, a carbon-forming agent; (b) 3-8 parts of silicone flame retardant F50508; (c) 3-8 parts of organosilicon flame retardant KR-2710; Silane coupling agent KH-570 0.5-1.5 parts; impact modifier 3-8 parts; toughening agent MBS 2-6 parts; light stabilizer UVB390 0.1-0.5 parts; antioxidant 0.1-0.5 parts; Lubricant 0.3-1.0 parts.

2. The optical-grade highly transparent flame-retardant PVC / SMMA alloy according to claim 1, characterized in that: The chain extender is an epoxy or acrylate type chain extender; Components (b) and (c) in the composite flame retardant are surface-treated with a silane coupling agent KH-570 to form a nano-coating structure, and the average particle size D90 after coating is ≤200 nm.

3. The optical-grade highly transparent flame-retardant PVC / SMMA alloy according to claim 1, characterized in that: The impact modifier is acrylic rubber grafted with methyl methacrylate; The toughening agent is a methyl methacrylate-butadiene-styrene copolymer (MBS) with a core-shell structure.

4. A method for preparing an optical-grade highly transparent flame-retardant PVC / SMMA alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: (0) Pre-dispersion: PVC resin, chain extender, part of lubricant and antioxidant are mixed in a vacuum disperser, the temperature is controlled at 40-45°C, the absolute pressure is ≤0.01MPa, and high-speed shearing is performed until the chain extender dispersed particle size D90 is ≤200nm; (1) Pre-coupling: reacting siloxane flame retardant F50508, organosilicon flame retardant KR-2710 and silane coupling agent KH-570 in an ethanol / water medium, controlling the temperature at 45-50°C and the absolute pressure ≤0.01 MPa, and removing the solvent after the reaction to obtain a nano-coated flame retardant with a D90 ≤200 nm; (2) Mixing: Add pre-dispersed PVC, SMMA resin, pre-coupled flame retardant, and remaining additives in sequence, blend at 65-70°C in a high-speed and low-speed mixer, and evacuate to a dew point of ≤-40°C and a moisture content of ≤300ppm; (3) Extrusion granulation: The mixed material is melted and extruded through a twin-screw extruder with a barrel temperature of 150-185°C. The melt is filtered through a 400-mesh filter and then pelletized underwater. The pelletizing water temperature is ≤15°C and the dissolved oxygen is ≤0.5ppm under nitrogen protection.

5. The method for preparing an optical-grade highly transparent flame-retardant PVC / SMMA alloy according to claim 4, characterized in that: In the step (1), the vacuum disperser is a butterfly-type biaxial disperser, the speed in the high-speed shearing stage is ≥1500 rpm, and the dispersion time is 15-20 min.

6. The method for preparing an optical-grade highly transparent flame-retardant PVC / SMMA alloy according to claim 4, characterized in that: In the step (3), the high-speed and low-speed mixing unit includes a high-speed hot mixing pot (800-900 rpm) and a low-speed cold mixing pot (50-70 rpm). After hot mixing, the mixture is transferred to the cold mixing pot and cooled to ≤45°C before discharging. The vacuum disperser in step (1) is a butterfly-type double-shaft disperser, and the rotation speed in the high-speed shearing stage is ≥1500rpm.

7. A twin-screw extruder for implementing the method of claims 4 to 6, characterized in that: include: (a) Low shear barrier screw: Contains a toothed disc structure with a toothed disc thickness of 0.5-1.0 mm, an axial spacing of 2-5 mm, and a barrier gap of 0.3-1.0 mm; (b) Dual-channel barrel temperature control system: It has independent oil cooling circuits for the PVC low-temperature zone (150-195°C) and the SMMA high-temperature zone (200-220°C); (c) Melt filtration unit: 400-600 mesh double-tube switchable backflushing metal fiber filter; (d) Nitrogen protection underwater pelletizing module: dissolved oxygen in the pelletizing chamber is ≤0.5ppm, and the nitrogen flow rate is interlocked with the host PLC.

8. The twin-screw extruder according to claim 7, characterized in that: The melt filtration unit is provided with a melt pressure sensor, and the backflushing cycle is dynamically adjusted according to pressure changes.

9. A vacuum drying apparatus for use in the method of claims 4-6, characterized in that: include: (7) Single cone spiral structure, cone angle 60°±2°, inner mirror surface Ra≤0.2μm; (8) Three-stage drying process: Stage 1: 45-55°C / -0.090 MPa for 30 min; Stage 2: 65-70°C / -0.092 MPa for 2-2.5 hours; Stage 3: 55-60℃ / -0.095MPa for 30min.

10. A product prepared from the alloy according to any one of claims 1 to 3 or the method according to claims 4 to 6, characterized in that: Light transmittance ≥ 90%, haze ≤ 1%, YI chromaticity ≤ 2, flame retardant grade UL94V-0 (1.6mm thickness), tensile strength ≥ 48MPa; The product is an optical lens, a display light guide plate or a transparent fireproof building material.

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