High-gloss polycarbonate fiber-added composite material and preparation method thereof

Abstract

The invention relates to a high-gloss polycarbonate fiber-added composite material and a preparation method thereof. The material comprises the following components in parts by weight: 100 parts of polycarbonate resin, 15-35 parts of PMMA coated modified glass fiber and 1.5-3 parts of a refractive index matching agent, wherein the refractive index difference delta n between a coating layer and a matrix is less than or equal to 0.02. Glass fibers are subjected to surface treatment by adopting a melting mechanical coating method, molding is performed through a double-screw extruder side feeding process, the screw shear strength is in gradient change in the axial direction, and the shear rate ratio of a strong shear area to a low shear area is larger than or equal to 4: 1. The technical problems that glass fiber reinforced polycarbonate is low in surface glossiness and serious in floating fiber are solved, the 60-degree-angle glossiness of a product is larger than or equal to 92 GU, the tensile strength is larger than or equal to 110 MPa, and the surface floating fiber rate is lower than 2%. The preparation method is environment-friendly, free of solvent discharge, stable and reliable in process and suitable for high-end application fields such as consumer electronics shells.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a glass fiber reinforced polycarbonate composite material with high surface gloss, high strength, and excellent appearance quality, and its preparation method. This material is particularly suitable for applications with stringent surface quality requirements, such as consumer electronics casings and high-end home appliance panels. Background Technology

[0002] Polycarbonate resin possesses excellent mechanical properties, heat resistance, and dimensional stability, making it an important type of engineering plastic. To improve the strength and modulus of polycarbonate, glass fiber reinforcement is commonly used. However, significant differences exist between glass fiber and the polycarbonate resin matrix in physical properties such as refractive index and surface tension, leading to strong light scattering at the interface and a substantial decrease in the surface gloss of the finished product. Existing glass fiber reinforced polycarbonate materials typically exhibit a gloss level of only 65 to 70 GU at a 60° angle, with a surface fiber float rate as high as 15% to 20%, failing to meet the high-gloss appearance requirements of the high-end consumer electronics sector.

[0003] Currently, the industry mainly employs two technical approaches to improve surface quality. The first approach is to add brightening agents or surface modifiers, such as ethylene bis-stearamide lubricants. While these substances can slightly improve gloss, they significantly reduce the material's mechanical properties, typically decreasing impact strength by 25% to 30%. The second approach is to optimize the molding process, such as using rapid cooling and heating mold technology. This technology suppresses glass fiber orientation by quickly switching mold temperatures, but the equipment investment is up to ten times that of ordinary molds, energy consumption increases by more than five times, and this technology itself has formed an independent patent system, which is not necessarily related to the material modification of this invention.

[0004] The core contradiction that current technologies have not yet resolved lies in the industry's prejudice that glass fiber reinforcement inevitably leads to a decrease in surface gloss. The prevailing approach among engineers is to seek a compromise between reinforcement and gloss, rather than fundamentally eliminating interfacial light scattering. Furthermore, existing glass fiber surface treatment technologies are limited to coupling agent modification. Coupling agents only improve interfacial bonding and cannot change the refractive index of the glass fiber itself; the refractive index difference Δn at the interface remains greater than 0.15, and the light scattering problem remains unresolved. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned technical deficiencies and provide a high-gloss polycarbonate composite material. This material achieves a significant improvement in surface gloss without sacrificing mechanical properties, while ensuring that the preparation method is industrially feasible and environmentally compliant.

[0006] The high-gloss polycarbonate composite material of the present invention comprises the following components. Polycarbonate resin is used as the matrix material, in an amount of 100 parts by weight. The resin may be a bisphenol A type homopolymer or copolymer, with a melt flow rate preferably of 15 to 25 grams per 10 minutes and a refractive index preferably of 1.582 to 1.586.

[0007] The amount of surface-modified glass fiber used is 15 to 35 parts by weight. The glass fiber is treated by melt mechanical coating, with a polymethyl methacrylate layer uniformly covering its surface. The glass fiber diameter is preferably 9 to 13 micrometers, and the initial length is 3.0 to 4.5 millimeters. The coating thickness is 0.15 to 0.40 micrometers, and the coating coverage is ≥95%. The refractive index difference Δn between the coated glass fiber and polycarbonate resin is ≤0.02, preferably ≤0.01.

[0008] The amount of refractive index matching agent used is 1.5 to 3 parts by weight. The preferred matching agent is bisphenol A epoxy acrylate with a number-average molecular weight of 800 to 1200 g / mol and a refractive index of 1.585 to 1.588. This substance is in a liquid state during twin-screw extrusion and can penetrate to the glass fiber-matrix interface, forming a refractive index transition layer after curing.

[0009] The compatibility toughening agent is used in an amount of 3 to 8 parts by weight, preferably methyl methacrylate butadiene styrene copolymer, i.e., MBS core-shell rubber. The core-shell ratio is preferably 70:30, and the particle size is 200 to 300 nanometers. This toughening agent can improve the impact strength of the material while maintaining optical transparency.

[0010] The amount of the high-gloss synergist is 1.5 to 3 parts by weight, preferably polyether-modified polydimethylsiloxane. This substance migrates to the surface of the product during processing, reducing surface roughness and contributing approximately 3 to 5 GU to the gloss improvement.

[0011] The composite lubricant is used in an amount of 0.6 to 1.2 parts by weight, preferably a mixture of pentaerythritol stearate and vinyl bis-stearamide in a 7:3 ratio. This lubricant system balances internal and external lubrication and prevents precipitation that could affect gloss.

[0012] The antioxidant is used in an amount of 0.3 to 0.5 parts by weight, preferably a 1:1 mixture of pentaerythritol tetrakis[β-3,5-di-tert-butyl-4-hydroxyphenyl]propionate and tris[2,4-di-tert-butylphenyl]phosphite. The light stabilizer is used in an amount of 0.2 to 0.4 parts by weight, preferably a benzotriazole UV absorber.

[0013] The process flow of each step in the preparation method of this invention is as follows: S1: Preheating treatment of glass fiber. Place alkali-free chopped glass fiber in a high-speed mixer, control the temperature to 110 to 130°C, and preheat for 10 to 15 minutes to remove surface-adsorbed moisture.

[0014] S2: Coupling agent spraying. Apply γ-glycidyl etheroxypropyltrimethoxysilane coupling agent evenly through an atomizing nozzle, at a dosage of 0.5 to 1.0% of the glass fiber mass. Set the mixer speed to 600 to 800 rpm and mix for 3 to 5 minutes to promote the hydrolysis of the coupling agent and the formation of chemical bonds with the silanol groups on the glass fiber surface.

[0015] S3: PMMA micro powder addition. Add polymethyl methacrylate micro powder to the mixer at an amount of 8 to 12% of the glass fiber mass. The micro powder has a particle size of 5 to 10 micrometers and a molecular weight of 80,000 to 120,000.

[0016] S4: Melt Coating Mixing. The mixer jacket is heated to 105 to 115°C, and the rotation speed is increased to 1200 to 1500 rpm, with continuous mixing for 8 to 12 minutes. Under these conditions, the polymethyl methacrylate (PMMA) micropowder softens and adheres to the glass fiber surface through mechanochemical action, forming a uniform coating layer.

[0017] S5: Cooling and Discharging. The material is discharged after natural cooling to below 60°C to obtain surface-modified glass fibers.

[0018] S6: Raw material premixing. Add polycarbonate resin, refractive index matching agent, compatibility toughening agent, high gloss synergist, lubricant, antioxidant and light stabilizer to a high-speed mixer and mix for 3 minutes.

[0019] S7: Main feed melting. The premixed raw material is fed into the main feed port of the twin-screw extruder. The extruder has a length-to-diameter ratio of 40:1, and the screw diameter is 35 to 75 mm. The barrel temperatures from the feed port to the die are 220°C, 240°C, 260°C, 270°C, 265°C, and 260°C, respectively.

[0020] S8: Glass fiber is added via side feeding. Surface-modified glass fiber is added through the side feeding port, located in zones 7 to 9 of the screw, where the polycarbonate has been completely melted.

[0021] S9: Gradient Shear Dispersion. The screw assembly design achieves a gradient change in shear strength. Zones 16 to 20 are the strong shear dispersion zone, with a shear rate of 300 to 400 s⁻¹, ensuring uniform dispersion of glass fibers. Zones 32 to 36 are the low shear impregnation zone, with a shear rate of 50 to 80 s⁻¹, reducing glass fiber breakage. The ratio of shear rates between the strong and low shear zones is ≥4:1. The screw speed is constant at 350 to 400 revolutions per minute.

[0022] S10: Vacuum devolatilization. The vacuum devolatilization device is located in zones 21 to 23, with the vacuum level maintained at -0.07 to -0.09 MPa to remove small molecule volatiles.

[0023] S11: Pelletizing. The melt is drawn into pellets, cooled, and then pelletized to obtain the finished pellets.

[0024] S12: Granule drying. The granules are dried at 120℃ for 4 hours.

[0025] S13: Injection temperature setting. Set the injection molding machine barrel temperature to 260 to 280°C and the mold temperature to 80 to 100°C.

[0026] S14: Three-stage injection control. Injection speed is set in stages: Stage 1: 0 to 20% stroke, speed 15 to 25 mm / s; Stage 2: 20 to 80% stroke, speed 60 to 80 mm / s; Stage 3: 80 to 100% stroke, speed 20 to 30 mm / s.

[0027] S15: Pressure holding and cooling. Holding pressure: 50 to 70 MPa; holding time: 3 to 4 seconds; back pressure: 5 to 8 MPa. Mold cavity surface roughness Ra ≤ 0.1 micrometers; material preferably S136H mirror steel.

[0028] S16: Demolding and part removal. After cooling and solidification, the part is demolded to obtain the final product. Beneficial effects

[0029] This invention achieves the following significant technical effects: Regarding surface gloss, the gloss at a 60° angle is ≥92 GU, reaching a maximum of 94 GU, representing an improvement of over 35% compared to conventional glass fiber reinforced polycarbonate. Regarding mechanical properties, tensile strength is ≥110 MPa, reaching a maximum of 132 MPa; notched impact strength is 8 to 11 kJ / m²; flexural strength is 150 to 180 MPa; and flexural modulus is 5000 to 7000 MPa. Regarding appearance quality, the surface fiber floating rate is less than 2%, and no obvious glass fiber exposure is observed under an 8x magnifying glass. Regarding process stability, the coefficient of variation (CV) for gloss is ≤2% for five consecutive batches, and the coefficient of variation (CV) for tensile strength is ≤2%, proving the reliability of the process.

[0030] This invention resolves the inherent contradiction between glass fiber reinforcement and high surface gloss. The polymethyl methacrylate (PMMA) coating increases the effective refractive index of the glass fiber to 1.575-1.585, reducing the refractive index difference with the matrix by over 90%, and lowering the interfacial light scattering intensity by 70-80%. A refractive index matching agent fills microscopic voids, further eliminating scattering centers. A gradient shearing process ensures glass fiber dispersion while maintaining a length retention rate of ≥85%, preventing short fiber aggregation that leads to surface roughness. The synergistic effect of these three elements achieves simultaneous improvement in both mechanical and optical properties. Attached Figure Description

[0031] Figure 1 This is a flowchart of the overall process for preparing the material of this invention; Figure 2 A detailed flow chart for the preparation of modified glass fibers by melt mechanical coating; Detailed Implementation Example 1

[0032] Prepare the raw materials according to the following formula: 100 parts by weight of bisphenol A type polycarbonate resin, melt flow rate 18 g / 10 min; 15 parts by weight of PMMA-coated modified glass fiber, glass fiber diameter 9 μm, initial length 3.5 mm, coating thickness 0.20 μm, coating rate 96%; 1.5 parts by weight of bisphenol A type epoxy acrylate refractive index matching agent, number average molecular weight 1000 g / mol; 3 parts by weight of MBS core-shell rubber compatibility toughening agent, core-shell ratio 70:30, particle size 250 nm; 1.5 parts by weight of polyether-modified polydimethylsiloxane high-gloss synergist; 0.6 parts by weight of composite lubricant, composed of pentaerythritol stearate and vinyl bis-stearamide in a 7:3 ratio; 0.3 parts by weight of antioxidant, composed of pentaerythritol tetrakis[β-3,5-di-tert-butyl-4-hydroxyphenyl]propionate and tris[2,4-di-tert-butylphenyl]phosphite in a 1:1 ratio. 0.2 parts by weight of light stabilizer, selected from benzotriazole ultraviolet absorbers.

[0033] Preparation of surface-modified glass fiber: Glass fiber was placed in a high-speed mixer and preheated to 110℃ for 12 minutes. 0.5% (by weight of the glass fiber) of KH-560 coupling agent was sprayed on, and the mixture was stirred at 700 rpm for 4 minutes. 8% (by weight of the glass fiber) of PMMA micropowder (6 micrometers particle size) was added. The temperature was raised to 105℃, the stirring speed was increased to 1200 rpm, and the mixture was stirred for 10 minutes. The mixture was then cooled to 55℃ and discharged.

[0034] Melt blending: Polycarbonate resin, matching agent, toughening agent, synergist, lubricant, antioxidant, and light stabilizer are mixed at high speed for 3 minutes. The mixture is then fed into the main feed port of a twin-screw extruder with a length-to-diameter ratio of 40:1. Surface-modified glass fiber is added from the side feed port in zone 7. The screw speed is 350 rpm, and the barrel temperatures are 220℃, 240℃, 260℃, 270℃, 265℃, and 260℃. Zones 16 to 20 are the high-shear dispersion zone with a shear rate of 320 seconds to the power of -1. Zones 32 to 36 are the low-shear impregnation zone with a shear rate of 65 seconds to the power of -1. Vacuum devolatilization is performed at a vacuum degree of -0.08 MPa. The product is then drawn into strands and granulated to obtain the final product.

[0035] Injection molding: The granules are dried at 120℃ for 4 hours. The injection molding machine barrel temperature is 260 to 280℃. The mold temperature is 85℃. The injection speed is controlled in three stages: 20 mm / s for the first stage, 65 mm / s for the second stage, and 25 mm / s for the third stage. The holding pressure is 55 MPa, the holding time is 3 seconds, and the back pressure is 6 MPa. The surface roughness of the mold cavity is Ra 0.08 micrometers.

[0036] Performance testing: The product has a gloss level of 92 GU at a 60° angle, a tensile strength of 108 MPa, a notched impact strength of 11.5 kJ / m², a flexural strength of 152 MPa, and a flexural modulus of 5200 MPa. The surface fiber content is 1.2%. Under 8x magnification, the surface is smooth and no visible glass fibers are observed. Example 2

[0037] Prepare the raw materials according to the following formula: 100 parts by weight of bisphenol A type polycarbonate resin, melt flow rate 20 g / 10 min; 25 parts by weight of PMMA-coated modified glass fiber, glass fiber diameter 11 μm, initial length 4.0 mm, coating thickness 0.25 μm, coating rate 97%; 2.0 parts by weight of bisphenol A type epoxy acrylate refractive index matching agent, number average molecular weight 1000 g / mol; 5 parts by weight of MBS core-shell rubber compatibility toughening agent; 2.0 parts by weight of polyether-modified polydimethylsiloxane high-gloss synergist; 0.8 parts by weight of composite lubricant; 0.4 parts by weight of antioxidant; 0.3 parts by weight of light stabilizer.

[0038] Preparation of surface-modified glass fiber: Preheat the glass fiber to 120℃ for 13 minutes. Spray 0.7% (by weight of the glass fiber) of KH-560 coupling agent and mix at 750 rpm for 4 minutes. Add 10% (by weight of the glass fiber) of PMMA micropowder with a particle size of 8 micrometers. Increase the temperature to 110℃, increase the rotation speed to 1350 rpm, and mix for 10 minutes. Cool to 50℃ and discharge.

[0039] Melt blending: Side feed position 8 of the twin-screw extruder. Screw speed 380 rpm. Shear rate 350s -1 for zones 16 to 20, and 70s -1 for zones 32 to 36. The rest is the same as in Example 1.

[0040] Injection molding: Mold temperature 90℃. Injection speed in three stages: 22, 70, and 28 mm / s. Holding pressure 60 MPa, holding time 3.5 seconds. The rest is the same as in Example 1.

[0041] Performance testing: The product has a gloss level of 94 GU at a 60° angle, a tensile strength of 121 MPa, a notched impact strength of 9.8 kJ / m², a flexural strength of 168 MPa, and a flexural modulus of 6200 MPa. Surface fiber float rate is 0.8%. Example 3

[0042] Prepare the raw materials according to the following formula: 100 parts by weight of bisphenol A type polycarbonate resin, melt flow rate 22 g per 10 minutes; 35 parts by weight of PMMA-coated modified glass fiber, glass fiber diameter 13 μm, initial length 4.5 mm, coating thickness 0.35 μm, coating rate 95%; 3.0 parts by weight of bisphenol A type epoxy acrylate refractive index matching agent; 8 parts by weight of MBS core-shell rubber compatibility toughening agent; 3.0 parts by weight of polyether-modified polydimethylsiloxane high-gloss synergist; 1.2 parts by weight of composite lubricant; 0.5 parts by weight of antioxidant; 0.4 parts by weight of light stabilizer.

[0043] Preparation of surface-modified glass fiber: Preheat the glass fiber to 130℃ for 15 minutes. Spray 1.0% (by weight of the glass fiber) of KH-560 coupling agent and mix at 800 rpm for 5 minutes. Add 12% (by weight of the glass fiber) of PMMA micropowder with a particle size of 10 micrometers. Increase the temperature to 115℃, increase the rotation speed to 1500 rpm, and mix for 12 minutes. Cool to 45℃ and discharge.

[0044] Melt blending: Side feed position 9 of the twin-screw extruder. Screw speed 400 rpm. Shear rate of 380s -1 / 20 in zones 16 to 20, and 75s -1 / 20 in zones 32 to 36. The rest is the same as in Example 1.

[0045] Injection molding: Mold temperature 95℃. Injection speed in three stages: 25, 75, and 30 mm / s. Holding pressure 65 MPa, holding time 4 seconds. The rest is the same as in Example 1.

[0046] Performance testing: The product has a gloss level of 90 GU at a 60° angle, a tensile strength of 132 MPa, a notched impact strength of 8.2 kJ / m², a flexural strength of 178 MPa, and a flexural modulus of 6800 MPa. The surface fiber floating rate is 1.8%.

[0047] Comparative Example 1 25 parts by weight of unmodified alkali-free chopped glass fiber were used, with the remaining formulation identical to that of Example 2. The glass fiber was added from the main feed port during twin-screw extrusion. The resulting product had a gloss level of 68 GU at a 60° angle, a tensile strength of 105 MPa, and a notched impact strength of 7.2 kJ / m². The surface fiber float rate was 18%, and obvious glass fiber exposure was visible under an 8x magnifying glass.

[0048] Comparative Example 2 25 parts by weight of PMMA-coated modified glass fiber were used, but no refractive index matching agent was added to the formulation; otherwise, it was the same as in Example 2. The resulting product had a gloss level of 75 GU at a 60° angle, a tensile strength of 118 MPa, and a notched impact strength of 9.5 kJ / m². Microscopic voids existed at the interface, and light scattering was not completely eliminated.

[0049] Comparative Example 3 25 parts by weight of glass fiber treated with KH-560 coupling agent were used, without PMMA coating, and the amount of refractive index matching agent was increased to 5 parts by weight, otherwise the same as in Example 2. The resulting product had a gloss of 70 GU at a 60° angle, a tensile strength of 110 MPa, an interfacial Δn of 0.15, and severe light scattering.

[0050] Comparative Example 4 The formulation of Example 2 of this invention was used, but the twin-screw extruder employed a constant screw speed of 380 rpm, with moderate shear throughout the screw element operation and no gradient variation. The resulting product had a gloss level of 82 GU at a 60° angle, and the average glass fiber length retention rate was only 65%, with severe fiber breakage leading to a rough surface.

[0051] Comparative Example 5 The commercially available high-end competitor, SABICLUX9132C, has a glass fiber content of 25% and uses a spray coating post-treatment process. The product has a gloss level of 75 GU at a 60° angle and a tensile strength of 105 MPa, but its production cost is 40% higher than that of Example 2 of this invention.

[0052] Comparative Example 6 The formulation of Example 2 was used, but the compatibility toughening agent was replaced with 5 parts by weight of maleic anhydride-grafted polypropylene. The resulting product had a gloss of 89 GU, but the notched impact strength decreased to 6.1 kJ / m², a reduction of 38%, demonstrating the necessity of MBS core-shell rubber.

[0053] Comparative Example 7 The formulation of Example 2 was used, but the PMMA coating thickness was increased to 0.6 micrometers. The resulting product had a gloss of 78 GU and a tensile strength of 115 MPa. The excessive coating thickness led to decreased adhesion to the substrate and a 30% reduction in interfacial peel strength.

[0054] Comparative Example 8 The formulation and process of Example 2 were used, but the injection mold employed RHCM technology with temperature control ranging from 130 to 150°C. The resulting product achieved a gloss level of 93 GU, only 2 GU higher than the 91 GU achieved at a normal mold temperature of 90°C, demonstrating that the present invention can achieve a high-gloss effect without relying on RHCM technology.

[0055] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-gloss polycarbonate composite material, characterized in that, It comprises the following components: 100 parts by weight of polycarbonate resin; 15 to 35 parts by weight of surface-modified glass fiber, wherein the surface of the glass fiber has a polymer coating layer; and 1.5 to 3 parts by weight of refractive index matching agent; wherein the difference between the refractive index of the polymer coating layer and the refractive index of the polycarbonate resin is Δn ≤ 0.

02.

2. The high-gloss polycarbonate composite material according to claim 1, characterized in that, The polymer coating is polymethyl methacrylate and its copolymers, and the refractive index difference Δn ≤ 0.

01.

3. The high-gloss polycarbonate composite material according to claim 1 or 2, characterized in that, The thickness of the polymer coating layer is 0.15 to 0.40 micrometers, and the coating rate is ≥95%.

4. The high-gloss polycarbonate composite material according to claim 1, characterized in that, The refractive index matching agent is bisphenol A type epoxy acrylate with a number average molecular weight of 800 to 1200 g / mol and a refractive index of 1.585 to 1.

588.

5. The high-gloss polycarbonate composite material according to claim 1, characterized in that, The composite material has a gloss level of ≥92 GU at a 60° angle, a tensile strength of ≥110 MPa, and a surface fiber floating rate of less than 2%.

6. A method for preparing the high-gloss polycarbonate composite material according to any one of claims 1 to 5, characterized in that, Includes the following steps: Surface-modified glass fibers are obtained by surface treatment of glass fibers using melt mechanical coating method; polycarbonate resin, refractive index matching agent and other processing aids are added to the main feed port of a twin-screw extruder; surface-modified glass fibers are added through the side feed port, located in zones 7 to 9 of the twin screw; after melt extrusion granulation, injection molding is performed.

7. The method according to claim 6, characterized in that, The melt mechanical coating method includes the following operations: Preheat the glass fiber to 110 to 130°C; spray 0.5 to 1.0% of the glass fiber mass with γ-glycidyl etheroxypropyltrimethoxysilane coupling agent; add 8 to 12% of the glass fiber mass with polymethyl methacrylate micro powder, with a particle size of 5 to 10 micrometers; mix at high speed for 8 to 12 minutes at 105 to 115°C and a rotation speed of 1200 to 1500 rpm; cool to below 60°C and discharge.

8. The method according to claim 6, characterized in that, The shear intensity of the twin-screw extruder varies in a gradient along the screw axis, with a shear rate of 300 to 400 seconds negative 1 in the strong shear zone and a shear rate of 50 to 80 seconds negative 1 in the low shear zone, and a shear rate ratio of ≥4:1 between the strong and weak shear zones.

9. The method according to claim 6, characterized in that, During injection molding, the mold surface temperature is controlled at 80 to 100°C, and the injection speed is controlled in three stages: 15 to 25 mm per second in the first stage, 60 to 80 mm per second in the second stage, and 20 to 30 mm per second in the third stage.

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