Gradient refractive index film for dodging and preparation method thereof

Abstract

The invention discloses a gradient refractive index film for dodging and a preparation method of the gradient refractive index film, and belongs to the technical field of LED display. The preparation method comprises the following steps: S1, injecting methyl methacrylate, a high-refractive-index dopant and a thiol chain transfer agent into a polymer hollow tube, and carrying out gradient heating, high-temperature polymerization and defoaming under vacuum to obtain a preform; s2, melting methyl methacrylate, injecting the melted methyl methacrylate into the preform groove mold, cooling, curing, and demolding to obtain a preform groove; s3, coating optical cement on the prefabricated rod, placing the prefabricated rod in the prefabricated rod groove, and bonding to obtain a prefabricated block; and slicing, grinding and polishing the prefabricated block to obtain the graded-index film for dodging. The gradient refractive index film for dodging provided by the invention solves the problems of light spots, mixed light color cast and the like caused by non-uniform morphology of an adhesive layer and adhesive dispensing position deviation in the existing TV mini LED adhesive dispensing backlight process, and improves the yield.

Description

Technical Field

[0001] The present invention belongs to the technical field of LED display, and particularly relates to a gradient refractive index film for light homogenization and a preparation method thereof. Background Art

[0002] With the rapid development of Mini LED backlight technology, the display industry has put forward higher requirements for the light homogenization performance of light sources. Although traditional light homogenization solutions (such as lenses, dispensing, diffusion films or light guide plates) have played a role in basic light efficiency regulation, they have significant limitations: ① Deficiencies of the dispensing process: Existing Mini LEDs mostly rely on dispensing technology for light regulation, but uneven glue distribution easily leads to light spots or brightness differences, and problems such as glue overflow and poor curing frequently occur during the production process, resulting in high costs and low yields. For example, traditional dispensing processes require precise control of the glue volume, but it is difficult to avoid uneven glue layer thickness in actual production, which in turn affects the uniformity of light diffusion. ② Hardware dependence and cost pressure: Traditional diffusion films or light guide plates need to be stacked in multiple layers to achieve uniform light output, increasing material costs and module thickness, and at the same time, complex production processes further drive up manufacturing costs.

[0003] The patent application with the publication number CN119029121A discloses a white light Mini LED and its backlight module, which optimizes the light path through a multi-layer curved segment angle design and a micro-cavity structure to improve the light color uniformity. Although the multi-curved segment nested design of this application improves the uniformity, it sacrifices process compatibility, has high process costs, and has a potential risk of low packaging process fault tolerance. The utility model with the publication number CN222214209U discloses a MiniLED chip backlight module with uniform light output. This Mini LED backlight module features a composite design of a glue groove + a C-shaped groove + an arc-shaped groove, and is outstanding in terms of the uniformity of glue coating, the consistency of light efficiency, and the simplification of the structure, especially suitable for low-cost and large-scale production scenarios. However, problems such as its heat dissipation shortcoming, material reliability risk, and difficulty in maintenance may limit its application in high-temperature and high-humidity environments or high-end display fields. Summary of the Invention

[0004] The purpose of the present invention is to provide a gradient refractive index film for light homogenization and a preparation method thereof, so as to improve the optical uniformity and light output efficiency of the MiniLED backlight system.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A preparation method of a gradient refractive index film for light homogenization includes the following steps:

[0007] S1. Inject methyl methacrylate, a high refractive index dopant, and a mercaptan chain transfer agent into a polymer hollow tube, heat it up gradiently under vacuum, polymerize at high temperature, and degas to obtain a preform;

[0008] S2. Melt methyl methacrylate and inject it into the preform groove mold. After cooling and solidifying, demold to obtain the preform groove.

[0009] S3. Coat the preform with optical glue and place it in the preform groove, then bond to obtain the preform block. Slice, grind, and polish the preform block to obtain the graded refractive index film for light homogenization.

[0010] Furthermore, in S1, the dosage ratio of methyl methacrylate, high refractive index dopant, and thiol chain transfer agent is (70 - 95):(5 - 30):(0.5 - 2).

[0011] Furthermore, the high refractive index dopant is one or a combination of several of bromobenzene, chlorobenzene, iodobenzene, and benzenethiol.

[0012] Furthermore, the thiol chain transfer agent is one or a combination of several of n-dodecyl mercaptan and tert-dodecyl mercaptan.

[0013] Furthermore, the heating rate of the gradient heating is 3 - 8 °C / min.

[0014] Furthermore, the high-temperature polymerization is carried out at 70 - 95 °C for 24 - 48 h.

[0015] Furthermore, the specifications of the polymer hollow tube are a length of 2 - 3 m and an inner diameter of 3 - 6 mm.

[0016] Furthermore, the melting temperature is 210 - 270 °C.

[0017] Furthermore, the cooling and solidifying step is: Place the injection-molded mold in a room-temperature environment and naturally cool it to below 50 °C.

[0018] Furthermore, the optical glue is a conventional PMMA plastic glue, a one-component transparent solvent glue, and the solvent volatilizes and solidifies after direct coating.

[0019] Furthermore, the slicing is to cut the preform block into thin slices with a thickness of ≤1 mm (while maintaining the integrity of the core / cladding structure); the cutting speed of the diamond wire saw used for cutting is 5 - 10 mm / min, the coolant temperature is 20 - 25 °C (to avoid thermal stress damage); the cutting angle: the error perpendicular to the core axis is ≤0.1° (to ensure the symmetry of the refractive index gradient distribution); the surface roughness: the surface roughness Ra after cutting is ≤5 μm (to meet the requirements of subsequent grinding).

[0020] Furthermore, the grinding disc is processed to reduce the surface roughness to Ra≤0.2μm (eliminating the residual stress of slicing); the particle size of the diamond grinding wheel used for the abrasive is #200 - #300; the grinding rate is 0.5 - 1.0μm / min, and the rotation speed is 200 - 300rpm (to avoid excessive material removal); the cooling system is deionized water circulation with the conductivity ≤1μS / cm (to prevent impurity contamination).

[0021] A gradient refractive index film for light homogenization is prepared by the method for preparing a gradient refractive index film for light homogenization as described above.

[0022] The existing TV mini LED backlight solutions are basically glue dispensing + diffusion plate + light homogenization film, which require a certain light mixing distance, and it is very difficult to make the morphology of the glue dispensing uniform. The deviation of the glue dispensing position will also affect the backlight quality. The present invention uses a gradient refractive index film to adjust the LED light shape to achieve the effects of diffusion and light homogenization, which can effectively reduce the light mixing distance, reduce the volume and weight of the device. In addition, the present invention does not require strict centering, reducing the influence of position deviation on the quality.

[0023] Advantages of the present invention:

[0024] (1) The method for preparing a gradient refractive index film for light homogenization provided by the present invention separates and processes the preform main body and the microstructural groove, and uses an optical adhesive for bonding, avoiding the deformation of the preform caused by high temperature and improving the yield rate.

[0025] (2) The gradient refractive index film for light homogenization provided by the present invention solves the problems of light spots, light mixing color deviation, etc. caused by uneven glue layer morphology (height deviation ±15%) and glue dispensing position deviation (±50μm) in the existing TV mini LED glue dispensing backlight process, improves the yield rate, and reduces the cost.

[0026] (3) The high refractive index dopant adopted by the present invention increases the polarizability of the material through the heavy atom effect, thereby significantly enhancing the refractive index of the system. In addition, a thiol chain transfer agent is introduced to regulate the molecular weight distribution, preventing the decrease of the degree of polymerization and the increase of material brittleness caused by the high dopant content. Specific embodiments

[0027] The following describes the specific embodiments of the present invention in detail, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0028] Example 1

[0029] This example provides a gradient refractive index film for light homogenization, which is prepared through the following steps:

[0030] S1. Inject 85 parts of methyl methacrylate, 15 parts of bromobenzene, and 1 part of n-dodecyl mercaptan into a 3-m long and 6-mm inner diameter polymer hollow tube. Heat it to 85°C at a rate of 5°C / min in a vacuum environment, polymerize for 36 h, and degas to obtain a preform.

[0031] S2. Melt methyl methacrylate at 240°C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50°C. Demold after cooling and solidification to obtain a preform groove.

[0032] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove and bond to obtain a preform block. Slice, grind, and polish the preform block to obtain a gradient refractive index film for light homogenization.

[0033] The slicing is to cut the preform block into thin slices with a thickness of ≤1 mm; the cutting speed of the diamond wire saw used for cutting is 5 mm / min, and the coolant temperature is 25°C; the cutting angle: the error perpendicular to the core axis is ≤0.1°; the surface roughness: the surface roughness Ra after cutting is ≤5 μm.

[0034] The grinding is to reduce the surface roughness to Ra ≤ 0.2 μm; the grain size of the diamond grinding wheel used for the abrasive is #200; the grinding rate: 1.0 μm / min, the rotation speed is 300 rpm; the cooling system: deionized water circulation, the conductivity is ≤1 μS / cm.

[0035] Example 2

[0036] Compared with Example 1, this example is different in that the dosage of the dopant is increased. The specific implementation steps are as follows:

[0037] S1. Inject 70 parts of methyl methacrylate, 30 parts of bromobenzene, and 2 parts of n-dodecyl mercaptan into a 3-m long and 6-mm inner diameter polymer hollow tube. Heat it to 85°C at a rate of 5°C / min in a vacuum environment, polymerize for 36 h, and degas to obtain a preform.

[0038] S2. Melt methyl methacrylate at 240°C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50°C. Demold after cooling and solidification to obtain a preform groove.

[0039] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove and bond to obtain a preform block. Slice, grind, and polish the preform block to obtain a gradient refractive index film for light homogenization.

[0040] The remaining raw materials and preparation processes are the same as those in Example 1.

[0041] Example 3

[0042] Compared with Example 1, this example is different in that the dosage of the dopant is reduced. The specific implementation steps are as follows:

[0043] S1. Inject 95 parts of methyl methacrylate, 5 parts of bromobenzene, and 0.5 part of n-dodecyl mercaptan into a 3m-long and 6mm-inner-diameter polymer hollow tube. Under a vacuum environment, heat it to 85°C at a rate of 5°C / min, polymerize for 36h, and degas to obtain a preform;

[0044] S2. Melt methyl methacrylate at 240°C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50°C. After cooling and solidifying, demold to obtain a preform groove;

[0045] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove for bonding to obtain a preform block; slice, grind, and polish the preform block to obtain a gradient refractive index film for light homogenization.

[0046] The remaining raw materials and the preparation process are the same as those in Example 1.

[0047] Example 4

[0048] Compared with Example 1, this example is different in that "bromobenzene" is replaced by "chlorobenzene". The specific implementation steps are as follows:

[0049] S1. Inject 85 parts of methyl methacrylate, 15 parts of chlorobenzene, and 1 part of n-dodecyl mercaptan into a 3m-long and 6mm-inner-diameter polymer hollow tube. Under a vacuum environment, heat it to 85°C at a rate of 5°C / min, polymerize for 36h, and degas to obtain a preform;

[0050] S2. Melt methyl methacrylate at 240°C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50°C. After cooling and solidifying, demold to obtain a preform groove;

[0051] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove for bonding to obtain a preform block; slice, grind, and polish the preform block to obtain a gradient refractive index film for light homogenization;

[0052] The remaining raw materials and the preparation process are the same as those in Example 1.

[0053] Example 5

[0054] Compared with Example 1, this example is different in that "bromobenzene" is replaced by "benzenethiol". The specific implementation steps are as follows:

[0055] S1. Inject 85 parts of methyl methacrylate, 15 parts of benzenethiol and 1 part of n-dodecyl mercaptan into a 3m long and 6mm inner diameter polymer hollow tube. Under a vacuum environment, heat it to 85°C at a rate of 5°C / min, polymerize for 36h, and degas to obtain a preform;

[0056] S2. Melt methyl methacrylate at 240°C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50°C. After cooling and curing, demold to obtain a preform groove;

[0057] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove and bond to obtain a preform block; Slice, grind and polish the preform block to obtain a gradient refractive index film for light homogenization;

[0058] The remaining raw materials and preparation processes are the same as those in Example 1.

[0059] Example 6

[0060] The difference between this example and Example 1 is that "n-dodecyl mercaptan" is replaced by "tert-dodecyl mercaptan". The specific implementation steps are as follows:

[0061] S1. Inject 85 parts of methyl methacrylate, 15 parts of benzenethiol and 1 part of tert-dodecyl mercaptan into a 3m long and 6mm inner diameter polymer hollow tube. Under a vacuum environment, heat it to 85°C at a rate of 5°C / min, polymerize for 36h, and degas to obtain a preform;

[0062] S2. Melt methyl methacrylate at 240°C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50°C. After cooling and curing, demold to obtain a preform groove;

[0063] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove and bond to obtain a preform block; Slice, grind and polish the preform block to obtain a gradient refractive index film for light homogenization;

[0064] The remaining raw materials and preparation processes are the same as those in Example 1.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that no thiol chain transfer agent is added. The specific implementation steps are as follows:

[0067] 1. Inject 85 parts of methyl methacrylate and 15 parts of bromobenzene into a 3m long and 6mm inner diameter polymer hollow tube. Under a vacuum environment, heat it to 85°C at a rate of 5°C / min, polymerize for 36h, and degas to obtain a preform;

[0068] S2. Melt methyl methacrylate at 240 °C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50 °C. After cooling and solidifying, demold to obtain the preform groove;

[0069] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove for bonding to obtain a preform block. Slice, grind, and polish the preform block to obtain a gradient refractive index film for light homogenization;

[0070] The remaining raw materials and preparation processes are the same as those in Example 1.

[0071] Comparative Example 2

[0072] Compared with Example 1, this comparative example is different in that the dosage of the dopant is further increased. The specific implementation steps are as follows:

[0073] S1. Inject 65 parts of methyl methacrylate, 35 parts of bromobenzene, and 2.5 parts of n-dodecyl mercaptan into a 3 m long and 6 mm inner diameter polymer hollow tube. Heat it to 85 °C at a rate of 5 °C / min in a vacuum environment, polymerize for 36 h, and degas to obtain a preform;

[0074] S2. Melt methyl methacrylate at 240 °C and then inject it into the preform groove mold. Place the molded mold in a room temperature environment and naturally cool it to below 50 °C. After cooling and solidifying, demold to obtain the preform groove;

[0075] S3. Coat the preform with optical glue (PMMA plastic glue) and then place it in the preform groove for bonding to obtain a preform block. Slice, grind, and polish the preform block to obtain a gradient refractive index film for light homogenization;

[0076] The remaining raw materials and preparation processes are the same as those in Example 1.

[0077] Performance Test

[0078] Refractive Index Distribution Test: According to YD / T 4864-2024 "Measurement Methods for Optical Fiber Preforms for Telecommunications", use a refractive index analyzer to test the refractive index distribution of the gradient refractive index films for light homogenization obtained in each example and comparative example of the present application (the values of the innermost refractive index (n a ) and the outermost refractive index (n b ));

[0079] Refractive Index Gradient Slope: According to GB / T 15972.20-2008 "Gradient Verification", use a spectrophotometer and simulation software to test the refractive index gradient slope of the gradient refractive index films for light homogenization obtained in each example and comparative example of the present application;

[0080] Reflectance spectrum error: According to GB / T 26331-2010 "Test of Reflectance of Optical Thin Films", the reflectance spectrum error of the graded refractive index films for light homogenization obtained in each embodiment and comparative example of the present application was tested using a UV-Vis-NIR spectrometer and a laser interferometer;

[0081] Surface roughness (Ra): According to GB / T 1031-2009 "Surface Roughness Parameters", the surface roughness (Ra) of the graded refractive index films for light homogenization obtained in each embodiment and comparative example of the present application was tested using a white light interferometer and an atomic force microscope (AFM);

[0082] Transmittance uniformity: According to GB / T 26824-2011 "Test of Optical Uniformity", the transmittance uniformity (test standard deviation) of the graded refractive index films for light homogenization obtained in each embodiment and comparative example of the present application was tested using a spectrophotometer and an automatic sample stage;

[0083] The results are shown in Table 1:

[0084] Table 1

[0085]

[0086] As can be seen from Table 1, compared with Example 1, Examples 2-6 only differ in the raw material ratio and the replacement of raw materials within a reasonable range. From the results, the prepared films have excellent performance, the refractive index distribution can reach up to 1.4 - 2.5 optimally, the refractive index gradient slope < 4; the reflectance spectrum error ≤ 3%; the surface roughness ≤ 1.0 μm; the transmittance uniformity < 2%.

[0087] Compared with Example 1, after the thiol chain transfer agent was not added in Comparative Example 1, the performance parameters of the film showed a downward trend, indicating that the thiol chain transfer agent can regulate the molecular weight distribution and prevent the decrease in the degree of polymerization and the increase in material brittleness caused by a high dopant content; compared with Example 1, in Comparative Example 2, the excessive addition of the dopant not only did not further increase the refractive index, but instead led to a decrease in the degree of polymerization of the film due to its uneven dispersion, resulting in a decrease in performance.

[0088] In summary, the preparation method of a graded refractive index film for light homogenization provided by the present invention can prepare a graded refractive index film for light homogenization with a wide refractive index distribution range; strong optical stability; low surface roughness, which can effectively reduce the diffuse reflection loss; high transmittance; and provides an expandable solution for the mass production of high-precision optical devices.

[0089] The above-disclosed are only several specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing a gradient refractive index film for light homogenization, characterized in that, It includes the following steps: S1. Inject methyl methacrylate, a high refractive index dopant, and a thiol chain transfer agent into a polymer hollow tube, gradually increase the temperature under vacuum, perform high-temperature polymerization, and degas to obtain a preform; S2. Melt methyl methacrylate and inject it into the groove mold of the preform, demold after cooling and solidifying to obtain a preform groove; S3. Coat the preform with an optical adhesive and place it in the preform groove, bond to obtain a preform block; slice, grind, and polish the preform block to obtain a gradient refractive index film for light homogenization.

2. The preparation method of a gradient refractive index film for light homogenization according to claim 1, characterized in that In the S1, the dosage ratio of methyl methacrylate, the high refractive index dopant, and the thiol chain transfer agent is (70 - 95):(5 - 30):(0.5 - 2).

3. The preparation method of a gradient refractive index film for light homogenization according to claim 1, wherein, The high refractive index dopant is one or a combination of several of bromobenzene, chlorobenzene, iodobenzene, and benzenethiol.

4. The preparation method of a gradient refractive index film for light homogenization according to claim 1, characterized in that, The thiol chain transfer agent is one or a combination of several of n-dodecyl mercaptan and tert-dodecyl mercaptan.

5. The preparation method of a gradient refractive index film for light homogenization according to claim 1, characterized in that, The heating rate of the gradient temperature increase is 3 - 8 °C / min; the high-temperature polymerization is carried out at 70 - 95 °C for 24 - 48 h.

6. The preparation method of a gradient refractive index film for light homogenization according to claim 1, characterized in that, The specifications of the polymer hollow tube are a length of 2 - 3 m and an inner diameter of 3 - 6 mm; the melting temperature is 210 - 270 °C.

7. The preparation method of a gradient refractive index film for light homogenization according to claim 1, characterized in that, The cooling and solidifying step is: place the injection-molded mold in a room-temperature environment and naturally cool it to below 50 °C; the optical adhesive is a conventional PMMA plastic glue, a one-component transparent solvent glue, and the solvent volatilizes and solidifies after direct coating.

8. A method for preparing a gradient refractive index film for light homogenization according to claim 1, characterized in that, The slicing is to cut the preform block into thin slices with a thickness of ≤1 mm; the cutting speed of the diamond wire saw used for cutting is 5 - 10 mm / min, the coolant temperature is 20 - 25 °C; the cutting angle: the error perpendicular to the core axis is ≤0.1 °; the surface roughness: the surface roughness Ra after cutting is ≤5 μm.

9. The preparation method of a gradient refractive index film for light homogenization according to claim 1, characterized in that, The grinding is to reduce the surface roughness to Ra ≤0.2 μm; the grain size of the diamond grinding wheel used as the abrasive is #200 - #300; the grinding rate: 0.5 - 1.0 μm / min, the rotation speed is 200 - 300 rpm; the cooling system: deionized water circulation, the conductivity ≤1 μS / cm.

10. A gradient refractive index film for light homogenization, characterized in that, It is prepared by the preparation method of the gradient refractive index film for light homogenization according to any one of claims 1 - 9.

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