Material composition applied to backlight module and preparation method of material composition

Abstract

The invention belongs to the field of new materials, and discloses a material composition applied to a backlight module and a preparation method of the material composition. The material composition comprises 70-85% of polycarbonate resin, 8-12% of glass fiber, 3-8% of a core-shell structure flexibilizer (a core layer is a butadiene-styrene copolymer, and a shell layer is organosilicon modified acrylate), 1.5-4% of a composite opacifying agent (a double-peak combination of carbon black and flaky barium sulfate), 0.5-1.5% of a silicone-polyester composite lubricant, and 0.3-1.2% of a polyfunctional compatilizer. The preparation method comprises the steps of PC pre-drying, segmented feeding extrusion (180-255 DEG C three-zone temperature control) and gradient cooling. The material induces crazing to absorb impact energy through the core-shell toughening agent, and the organic silicon shell layer is used for scattering light to realize high gloss extinction; the composite opacifying agent synergistically absorbs and reflects to improve the shielding rate; the polyfunctional compatilizer is used for bonding the glass fiber and a PC interface, so that light refraction and warping are inhibited. The obtained material has the shielding rate of 99.6% or above, the impact strength of 70 kJ / m < 2 > and the surface glossiness smaller than or equal to 10 GU, and is particularly suitable for ultrathin Mini-LED backlight module light guide plates.

Description

Technical Field

[0001] This invention belongs to the field of new materials, and specifically discloses a material composition for use in backlight modules and its preparation method. Background Technology

[0002] As the core optical component of an LCD display, the backlight module's material properties, such as the light guide plate and diffuser plate, directly determine the display uniformity, brightness, and device reliability. Polycarbonate (PC) has become the preferred material for backlight modules due to its excellent optical transparency, heat resistance, and mechanical strength. However, with the rapid development of Mini-LED / Micro-LED ultra-thin display technology, traditional PC materials face severe challenges: First, it's difficult to balance light-shielding properties with mechanical properties—to meet the requirements of high-contrast displays (light-shielding rate >99.5%), the amount of carbon black added needs to exceed 2wt%, but this leads to a sharp drop in impact toughness of over 30%, while the introduction of conventional toughening agents (such as MBS) causes edge light leakage; Second, glass fiber reinforcement causes optical defects—although 10% glass fiber improves dimensional stability, the difference in refractive index between glass fiber and PC causes interface light scattering, resulting in "bright lines" on the surface (60° gloss >20). GU), traditional compatibilizers cannot effectively suppress it; secondly, thin-wall processing exacerbates dimensional instability—when the edge thickness is ≤0.5mm, glass fiber orientation causes warping (deformation >1.5mm), and the difference in thermal expansion coefficients between PC and glass fiber leads to rapid cooling internal stress cracking; finally, there is a conflict between the dispersion of the opacifier and its rheological properties—nano-opacifiers easily agglomerate into aggregates >5μm under high shear, becoming stress concentration points, while the forced dispersion process (screw speed >500rpm) causes PC degradation (heat distortion temperature decreases by 10-15℃). Current improvement solutions all have obvious shortcomings: for example, although PC / PMMA alloy improves opacity, the heat distortion temperature (HDT) drops below 90℃; silicone powder toughens and reduces brittleness, but increases gloss to over 30 GU; flake talc suppresses glass fiber exposure, but reduces impact strength by 40%. Therefore, there is an urgent need to develop a method that can simultaneously achieve high opacity (>99.5%) and high notched impact strength (>65kJ / m). 2 It is a material system with low gloss (<10 GU) and ultra-thin dimensional stability (warpage <0.5mm), and is suitable for industrial mass production processes. Summary of the Invention

[0003] To address the aforementioned problems in the prior art, this invention discloses a material composition for use in backlight modules and a method for preparing the same.

[0004] To achieve the above objectives, the present invention includes the following technical solutions.

[0005] A material composition for use in backlight modules, comprising the following raw materials in weight percentages: Polycarbonate (PC) resin: 70-85%; Glass fiber (GF): 8-12%; Core-shell toughening agent: 3-8%; Composite light-blocking agent: 1.5-4%; Silicone-polyester composite lubricant: 0.5-1.5%; Multifunctional compatibilizer: 0.3-1.2%; Hydrolysis stabilizer: 0.1-0.5%.

[0006] Furthermore, in the above-mentioned material composition, the composite light-blocking agent is a combination of inorganic particles with a bimodal distribution, comprising: Carbon black with an average particle size of 0.1-0.5 μm (accounting for 60-80% of the total weight of the opacifier). Barium sulfate flakes with an average particle size of 1-3 μm (accounting for 20-40% of the total weight of the opacifier).

[0007] Furthermore, in the above-mentioned material composition, the core-shell toughening agent is an acrylate-organosilicon hybrid particle, the core layer of which is a cross-linked butadiene / styrene copolymer, the shell layer is polymethyl methacrylate, and the particle size range is 100-300 nm.

[0008] Furthermore, in the above-mentioned material composition, the core-shell toughening agent is prepared by the following method: (i) Under nitrogen protection, butadiene:styrene:divinylbenzene are mixed at a mass ratio of 60-75:25-40:1.5-3 and emulsion polymerized at 70-80°C to form a cross-linked core layer; (ii) A mixture of methyl methacrylate (MMA) and γ-methacryloyloxypropyltrimethoxysilane is added dropwise to the core emulsion obtained in step (i), wherein the mass ratio of MMA to silane is 95:5~85:15, and the mixture is reacted at 75-85°C to form an organosilicon modified shell layer, wherein the solid mass ratio of the core layer to the shell layer is 50:50~70:30. (iii) After demulsification, washing and drying, core-shell particles with a particle size of 100-300 nm are obtained.

[0009] Furthermore, in the above-mentioned material composition, the silicone-polyester composite lubricant is compounded from polyether-modified silicone oil (accounting for 50-70% of the total weight of the lubricant) and polycaprolactone with a molecular weight of 2000-5000 (accounting for 30-50% of the total weight of the lubricant).

[0010] Furthermore, in the above-mentioned material composition, the multifunctional compatibilizer is an epoxy-maleic anhydride bifunctional polyolefin with an epoxy value of 0.05-0.12 eq / 100g and an acid value of 10-25 mg KOH / g.

[0011] The present invention also discloses a composite material prepared from the above composition, comprising the following steps: (a) Pre-dry the PC resin at 110-120°C for 4-6 hours; (b) The dried PC is mixed with the core-shell toughening agent and the hydrolysis-resistant stabilizer at high speed; (c) The mixture from step (b), glass fiber, and composite opacifier are added to the twin-screw extruder in three stages: Zone 1 (feeding section): 180-200℃, 50% of the total material is fed in; Zone 2 (Melting Section): 220-240℃, feed in 30% of the remaining material and multifunctional compatibilizer; Zone 3 (Dispersion Section): 235-255℃, feed in the remaining material and silicone-polyester composite lubricant; (d) The melt is extruded, cooled and pelletized after vacuum devolatilization.

[0012] Furthermore, in the above-mentioned composite material, the cooling in step (d) adopts a gradient cooling process: the melt strip is first pre-cooled in a 40-50℃ water bath for 10 seconds, and then rapidly cooled and solidified in a 5-10℃ low-temperature ethanol bath.

[0013] Furthermore, the aforementioned composite material satisfies the following performance indicators: Light shading rate: ≥99.5% (thickness 1.0mm); Notched impact strength: ≥65 kJ / m 2 (ISO 180); Heat distortion temperature (1.82MPa): ≥135℃; Surface gloss (60°): ≤10 GU.

[0014] This invention also discloses a backlight module light guide plate, which is made of the aforementioned composite material by injection molding, and still meets the requirement of a shading rate of ≥99.2% when its edge thickness is ≤0.5mm. Compared with the prior art, the present invention has the following outstanding advantages: This invention discloses a material composition and its preparation method for use in backlight modules. From the perspective of synergistic material composition design and preparation process, it solves the multiple contradictions of light shielding, toughness, dimensional stability, and low gloss in the ultra-thinning process of backlight modules. At the mechanistic level: the cross-linked rubber core of the core-shell toughening agent disperses impact stress by inducing shear bands and crazing, while the organosilicon-modified shell scatters incident light using its refractive index difference with PC, simultaneously achieving high toughness and low gloss; in the composite light shielding agent, nano-carbon black efficiently absorbs visible light, and flake barium sulfate extends the optical path through multiple reflections, with both synergistically breaking through the efficiency limit of a single light shielding agent; the epoxy groups and maleic anhydride groups of the multifunctional compatibilizer respectively bond to the PC end groups and the hydroxyl groups on the glass fiber surface, eliminating interfacial light refraction and inhibiting warping caused by thermal shrinkage differences; the polyether silicone oil of the silicone-polyester lubricant reduces the overall melt viscosity, and polycaprolactone selectively migrates to the glass fiber interface to reduce exposure, ensuring high flowability processing. At the application level: This material enables ultra-thin light guide plates (≤0.5mm) to maintain a low warpage of 0.3mm during injection molding, meeting the requirements of Mini-LED modules for precise assembly with narrow bezels; a shading rate >99.5% ensures high-contrast displays without edge light leakage; a low-gloss surface (<10GU) avoids screen glare; and the self-made toughening agent has a simple process and costs only 1 / 3 of imported products, significantly enhancing the self-sufficiency and controllability of the industrial chain. In summary, this invention provides key material support for high-end display devices with a mass-producible, low-cost solution. Attached Figure Description

[0015] Figure 1 The results are from a comparative test of 60° gloss (GU). Figure 2 The results are for comparison of warpage (mm). Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The following is a list of raw materials and instruments used in the examples. These are only preferred options and do not imply that other manufacturers or models cannot be used.

[0018] Table 1 Raw Material Table Table 2. List of Instruments and Equipment .

[0019] Examples 1-5 The formula is shown in Table 3. Table 3: Formulations (wt%) for Examples 1-5 The basic preparation processes for Examples 1-5 are all the same, as follows: Preparation process: 1. Pre-drying: The PC resin is dried in a 115℃ forced-air oven for 5 hours; 2. Initial mixing: Dry PC is mixed with homemade toughening agent and anti-hydrolysis agent in a high-speed mixer at 800 rpm for 3 minutes; 3. Extrusion: Use a twin-screw extruder (L / D=40), with segmented feeding and temperature settings: Zone 1 (feeding section, 180℃): 50% of the total mass of the primary mixture is added; Zone 2 (Melting section, 230℃): Add 30% of the remaining initial mixture + glass fiber + multifunctional compatibilizer; Zone 3 (Dispersion section, 245℃): Add remaining materials + composite opacifier + silicone-polyester lubricant; Screw speed 350 rpm, vacuum devouring (-0.08 MPa); 4. Cooling: The melt strip is first cooled in a 45°C water bath for 8 seconds, and then immersed in an 8°C ethanol bath for rapid cooling and solidification; 5. Dicing: Dicing length 3mm.

[0020] Special: Examples 1-3 use a self-made toughening agent, which is prepared as follows: (i) Under nitrogen protection, butadiene:styrene:divinylbenzene were mixed at a mass ratio of 70:28:2 and emulsion polymerized at 75°C for 6 hours to form a cross-linked core layer; (ii) A mixture of methyl methacrylate (MMA) and γ-methacryloyloxypropyltrimethoxysilane is added dropwise to the core emulsion obtained in step (i), wherein the mass ratio of MMA to silane is 90:10, and the mixture is reacted at 80°C for 4 hours to form an organosilicon modified shell layer, wherein the solid mass ratio of the core layer to the shell layer is 60:40. (iii) After demulsification, washing and drying, a core-shell particle powder with a particle size of 200±50 is obtained.

[0021] It should be noted that Example 4 uses 5% toughening agent Paraaloid EXL-2651 (Dow Chemical, MBS type core-shell toughening agent; note: EXL-2651 has limited heat resistance, and the temperature in Zone 3 drops to 240°C).

[0022] Example 5 uses toughening agent Kane Ace MX-514 3.5% (Kōgen Chemical, organosilicon-acrylate hybrid toughening agent).

[0023] Comparative Examples 1-4 The comparative examples were all modified based on Example 1, as shown in Table 4. Table 4: Formulations of Comparative Examples 1-4 Test case 1. Sample preparation Sample preparation method All composite materials from all groups were granulated by twin-screw extrusion and then tested under the same injection molding conditions: Injection parameters: Barrel temperature 250℃ / 240℃ / 230℃ (front / middle / rear section), mold temperature 80℃, injection pressure 80MPa, holding time 15 seconds; Sample type: Opacity test: 100×100×1.0mm black flat plate (double-sided polished). Impact strength test: 80×10×4mm strip specimen (pre-cut with a V-shaped notch, 2mm deep); Gloss test: 100×100×2.0mm flat plate (no surface texture); Warpage test: 100×100×0.5mm ultra-thin flat plate (let stand for 24 hours after demolding); MFR test: Use dry granules directly (no injection molding required).

[0024] 2. Test methods detailed (1) Shielding rate test Objective: To evaluate the ability of a material to block visible light; a higher value indicates better light-blocking performance. Principle: The degree to which light is absorbed / scattered when it passes through a material determines its light-blocking efficiency; operate: Place the sample in the sample chamber of the spectrophotometer; Transmittance of light in the scanning wavelength range of 400-700nm; Calculate the average transmittance T avg , shading rate = (1-T) avg ) x100%.

[0025] (2) Impact strength test Objective: To measure the toughness of a material against impact damage; Principle: A pendulum impacts a notched specimen, and the energy absorbed during fracture is measured. operate: Fix the specimen to the base of the impact testing machine; Release the pendulum (energy scale 5.5J); Record the impact energy value at the time of specimen fracture (unit: kJ / m). 2).

[0026] (3) Gloss test Objective: To quantify the reflectivity of material surfaces; the lower the value, the better the matting effect. Principle: The specular reflectivity of light rays at a 60° incident angle on a smooth surface; operate: The gloss meter probe is pressed vertically against the sample surface; Read the 60° gloss value (unit: GU) displayed on the instrument.

[0027] (4) Warpage deformation test Objective: To evaluate the dimensional stability of thin-walled products during the cooling process; Principle: The release of internal stress in the material leads to flatness deviation; operate: The ultra-thin flat plate is placed on a horizontal measuring platform; Laser displacement sensors scan the height of the four corners and the center point; Calculate the maximum height difference (in mm).

[0028] (5) Melt Flow Rate (MFR) Test Objective: To characterize the flow properties of the material at high temperatures; Principle: The extrusion rate of melt through a fixed orifice under standard load; operate: The granules are added to the melt flow indexer barrel, which is preheated to 300°C. Apply a 1.2 kg weight; Measure the mass of the extruded melt within 10 minutes (unit: g / 10min).

[0029] The test results are shown in Tables 5 and 6, and Figure 1 and Figure 2 .

[0030] Table 5: Optical and Mechanical Properties The data analysis in Table 5 is as follows: (1) Shielding rate: Example 1 (99.68%) was 0.73% higher than Comparative Example 2 (98.95%), which is attributed to the synergistic effect of nano carbon black (absorption) and flake barium sulfate (reflection) in the bimodal opacifier; Comparative Example 3 (99.67%) is close to Example 1, demonstrating that the multifunctional compatibilizer does not impair the light-shielding function.

[0031] (2) Impact strength: Toughening agent content is dominant: Example 2 (8% self-made, 79.6 kJ / m) 2Example 1 (5% self-made, 71.8%) > Example 3 (3.5% self-made, 68.3%) The homemade toughening agent (71.8%) was 11.0% higher than that of commercially available MBS (64.7) because the silicone shell improved crack propagation resistance; The comparative example 1 (40.9) without toughening agent plummeted by 43%, confirming the key role of the core-shell structure in inducing plastic deformation.

[0032] Table 6: Surface and Machining Properties Table 6 Data Analysis: (1) Gloss: The homemade toughening agent (Example 1: 8.52 GU) was 44.8% lower than that of commercially available MBS (12.31 GU) due to the scattering of light by the organosilicon shell; Comparative Example 3 (lacking compatibilizer) increased to 17.26 GU → glass fiber / PC interface refraction was not suppressed; Comparative Example 1 (without toughening) reached 35.17 GU → Exposed glass fiber forms specular reflection points.

[0033] (2) Warpage and fluidity: Comparative Example 1 (0.912 mm) showed the most severe warping → toughening agent buffered internal stress; Comparative Example 3 (0.608 mm) showed increased warping → Multifunctional compatibilizer inhibited glass fiber orientation; Comparative Example 4 (MFR 9.82) Liquidity Plunge → Zinc stearate fails to lubricate the fiberglass interface.

[0034] As can be seen from the above embodiments and test examples, this solution is achieved using conventional equipment and domestically produced raw materials: Performance breakthrough: Simultaneously achieving >99.5% shading rate (Mini-LED requirement) and 70 kJ / m² 2 Impact strength (higher than automotive parts standards); Implementation efficiency: The self-made toughening agent process requires only 2 reaction steps (emulsion polymerization + spray drying) and does not require precious metal catalysts; Application expansion: In addition to backlight modules, it is also suitable for automotive interior parts (low gloss, high toughness), optical instrument light shields, and other scenarios.

[0035] The above are merely a few preferred embodiments of the present invention, described in a relatively specific and detailed manner, but 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 all fall within the protection scope of the present invention.

Claims

1. A material composition for use in backlight modules, characterized in that, It consists of the following raw materials by weight percentage: Polycarbonate (PC) resin: 70-85%; GF (Glass Fiber) : 8-12%; Core-shell toughening agent: 3-8%; Composite light-blocking agent: 1.5-4%; Silicone-polyester composite lubricant: 0.5-1.5%; Multifunctional compatibilizer: 0.3-1.2%; Hydrolysis stabilizer: 0.1-0.5%.

2. The composition according to claim 1, characterized in that, The composite opacifier is a combination of inorganic particles with a bimodal distribution, comprising: Carbon black with an average particle size of 0.1-0.5 μm accounts for 60-80% of the total weight of the opacifier; Flaky barium sulfate with an average particle size of 1-3 μm accounts for 20-40% of the total weight of the opacifier.

3. The composition according to claim 1, characterized in that, The core-shell toughening agent is an acrylate-organosilicon hybrid particle, with a core layer of cross-linked butadiene / styrene copolymer and a shell layer of polymethyl methacrylate, and a particle size range of 100-300 nm.

4. The composition according to claim 3, characterized in that, The core-shell toughening agent is prepared by the following method: (i) Under nitrogen protection, butadiene:styrene:divinylbenzene are mixed at a mass ratio of 60-75:25-40:1.5-3 and emulsion polymerized at 70-80°C to form a cross-linked core layer; (ii) Add dropwise a mixture of methyl methacrylate (MMA) and γ-methacryloyloxypropyltrimethoxysilane to the core emulsion obtained in step (i), wherein the mass ratio of MMA to silane is 95:5 to 85:15, and react at 75-85°C to form an organosilicon-modified shell layer, wherein the solid mass ratio of the core layer to the shell layer is 50:50 to 70:30; (iii) After demulsification, washing and drying, core-shell particles with a particle size of 100-300 nm are obtained.

5. The composition according to claim 1, characterized in that, The silicone-polyester composite lubricant is formulated by compounding polyether-modified silicone oil, accounting for 50-70% of the total weight of the lubricant, with polycaprolactone with a molecular weight of 2000-5000, accounting for 30-50% of the total weight of the lubricant.

6. The composition according to claim 1, characterized in that, The multifunctional compatibilizer is an epoxy-maleic anhydride bifunctional polyolefin with an epoxy value of 0.05-0.12 eq / 100g and an acid value of 10-25 mg KOH / g.

7. A composite material, characterized in that, Prepared from the composition according to any one of claims 1-6, characterized in that it comprises the following steps: (a) Pre-dry the PC resin at 110-120°C for 4-6 hours; (b) The dried PC is mixed with the core-shell toughening agent and the hydrolysis-resistant stabilizer at high speed; (c) The mixture from step (b), glass fiber, and composite opacifier are added to the twin-screw extruder in three stages: Feeding section 1: 180-200℃, 50% of total material is fed in; Second melting zone: 220-240℃, feed in 30% of the remaining material and multifunctional compatibilizer; Three-zone dispersion section: 235-255℃, feed in the remaining material and silicone-polyester composite lubricant; (d) The melt is extruded, cooled and pelletized after vacuum devolatilization.

8. The composite material according to claim 7, characterized in that, The cooling process in step (d) adopts a gradient cooling process: the melt strip is first pre-cooled in a 40-50℃ water bath for 10 seconds, and then rapidly cooled and solidified in a 5-10℃ low-temperature ethanol bath.

9. The composite material according to claim 7, characterized in that, The material meets the following performance indicators: Light shading rate: ≥99.5%; Notched impact strength: ≥65 kJ / m 2 ; Heat distortion temperature: ≥135℃; Surface gloss: ≤10 GU.

10. A light guide plate for a backlight module, characterized in that, The composite material described in claim 7 is injection molded, and its edge thickness is ≤0.5mm, yet it still meets the requirement of a shielding rate of ≥99.2%.

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