LED lamp filament and manufacturing method thereof

Abstract

The invention discloses an LED lamp filament and a manufacturing method thereof, and relates to the technical field of LED luminescent devices. The LED lamp filament comprises a substrate, a light-emitting device, a fluorescent layer and a refraction layer, at least one end of the substrate is provided with a light-emitting position, the light-emitting device is embedded in the light-emitting position, the fluorescent layer wraps the outer surface of the substrate and covers the light-emitting position, and the refraction layer wraps the outer surface of the fluorescent layer. The LED lamp filament not only retains the advantage that the flexible lamp filament is easy to shape, but also can protect a light-emitting device from being damaged by external force, and gives consideration to both the light-emitting performance and the structural reliability. The refraction layer can be provided with a high-low refraction film layer and a silane coupling agent transition layer, so that the optical performance and the structural stability are optimized. The manufacturing method of the LED lamp filament is simple in process, accurate forming is achieved through the steps of etching, welding, coating and the like, complex equipment is not needed, large-scale mass production is facilitated, cost is reduced, and the manufacturing method is suitable for various LED light-emitting scenes and has high practical value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LED light emitting devices, in particular to an LED filament and a manufacturing method thereof. BACKGROUND

[0002] The LED filament is an optical device arranged in a filament shape by LED chips, which has the core features of 360-degree full-angle light emission, energy saving, long service life, etc. The LED filament lamp made of the device not only continues the energy-saving advantage, but also has a beautiful retro appearance. Its unique filament shape and soft light can add a unique atmosphere and decoration effect to indoor and outdoor space, which can accurately meet the needs of consumers for lamp aesthetic design, so it is more widely used in the market and is favored by consumers.

[0003] In the prior art, LED filaments are mainly divided into two categories: rigid filaments and flexible filaments. Among them, the rigid filament generally uses a rigid material such as sapphire, ceramic, glass or metal as a substrate board, and the ceramic substrate rigid filament is a typical representative. It has the advantages of stability and durability, but is limited by the characteristics of the rigid material itself, and has poor modeling flexibility and limited application scenarios. The flexible filament is mostly based on copper foil covered with a high polymer film (such as FPC, BT, PE, etc.) as a substrate material, and the FPC substrate flexible filament is a representative. Its core advantage is flexible and easy to model, which can meet the modeling needs of diversification. However, in the modeling process, the internal light emitting chip is prone to breakage and damage due to twisting and other operations, resulting in a decrease in product yield. In summary, the existing LED filament cannot balance the modeling flexibility and structural reliability, which restricts the further popularization and application of the LED filament lamp. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides an LED filament and a manufacturing method thereof.

[0005] The LED filament disclosed by the present application comprises a substrate, a light emitting device, a fluorescent layer and a refractive layer. A light emitting position is arranged at least at one end of the substrate. The light emitting device is arranged in the light emitting position. The fluorescent layer is coated on the outer surface of the substrate, and covers the light emitting position. The refractive layer is coated on the outer surface of the fluorescent layer.

[0006] According to an embodiment of the present application, the refractive layer comprises a high-refraction film layer and a low-refraction film layer. The high-refraction film layer is coated on the outer surface of the fluorescent layer, and the low-refraction film layer is coated on the outer surface of the high-refraction film layer.

[0007] According to an embodiment of the present application, the high-refraction film layer and the low-refraction film layer are coated with a transition layer, and the transition layer is made of a silane coupling agent.

[0008] According to one embodiment of the present invention, the high refractive index film layer is selected from titanium dioxide film, zirconium dioxide film or niobium pentoxide film, and the low refractive index film layer is selected from silicon dioxide film or magnesium difluoride film.

[0009] According to one embodiment of the present invention, the thickness of both the high-refractive-index film layer and the low-refractive-index film layer is no greater than 50 μm, and the surface roughness Ra of both the high-refractive-index film layer and the low-refractive-index film layer is no greater than 0.1 μm.

[0010] According to one embodiment of the present invention, a circuit layer is laid on the side surface of the light-emitting position that is close to the near end of the substrate, and a light-emitting device is disposed on the side where the circuit layer is located within the light-emitting position, with the forward light-emitting surface of the light-emitting device facing the far end of the substrate.

[0011] According to one embodiment of the present invention, the substrate is elongated and is made of a colorless and transparent material.

[0012] According to one embodiment of the present invention, the light-emitting position is a cuboid groove structure, and the light-emitting position is opened along the length direction perpendicular to the substrate.

[0013] This invention discloses a method for manufacturing the above-mentioned LED filament, comprising the following steps: S1. Prepare the substrate, etch the substrate to form light-emitting sites, and then lay the circuit layer in the light-emitting sites. S2. Place the light-emitting device in the light-emitting position, connect the electrodes of the light-emitting device to the circuit layer by soldering, and then fix the light-emitting device by dispensing process. After curing, the substrate semi-finished product is obtained. S3. Coat the fluorescent mixture onto the substrate semi-finished product, so that the fluorescent mixture covers the substrate and the light-emitting device to form a fluorescent layer; S4. A refractive film is coated on the outer surface of the fluorescent layer to form a refractive layer, thus obtaining the LED filament.

[0014] According to one embodiment of the present invention, in step S4, when the refractive layer includes a high-refractive film layer and a low-refractive film layer, a high-refractive film is first coated on the surface of the fluorescent layer to form a high-refractive film layer, then a silane coupling agent is coated on the surface of the high-refractive film layer to form a transition layer, and then a low-refractive film is coated on the surface of the transition layer to form a low-refractive film layer, thus completing the coating of the refractive layer.

[0015] Compared with the prior art, the LED filament and its manufacturing method of the present invention have the following advantages: First, the LED filament of the present invention has a light-emitting position arranged at least at one end of the substrate, and the light-emitting device is embedded in the corresponding light-emitting position. On the one hand, it does not require major modifications to the overall structure of the substrate, and can fully retain the core characteristics of flexible filaments that can be bent at will and are easy to shape, adapting to the installation and appearance design requirements of different scenarios. On the other hand, the light-emitting position can form all-round physical protection for the light-emitting device embedded therein, effectively isolating it from external forces such as torsion, compression, and collision, and preventing the light-emitting device from being deformed or damaged by force, thus affecting its light-emitting performance. At the same time, it takes into account excellent light-emitting effect, flexible shaping ability and stable structural reliability, solving the problem of insufficient protection and difficulty in balancing performance stability of traditional flexible filaments.

[0016] Secondly, the LED filament of this invention employs a combination of a high-refractive-index film layer and a low-refractive-index film layer to form a refractive layer. The high-refractive-index film layer coats the outer surface of the phosphor layer, and the low-refractive-index film layer coats the outer surface of the high-refractive-index film layer. These two layers synergistically optimize the refraction and total internal reflection paths of light, significantly improving the luminous efficiency and light uniformity of the filament. Adding a transition layer made of a silane coupling agent between the two film layers greatly enhances the interfacial bonding force between the film layers, effectively suppressing film peeling and detachment problems, and extending the product's lifespan.

[0017] Furthermore, in this invention, a circuit layer is laid on the side surface of the LED filament near the near end of the substrate at the light-emitting position. The light-emitting device is correspondingly positioned on this side, with the front light-emitting surface of the device facing the far end of the substrate. This arrangement not only ensures the reliability of the circuit connection and reduces signal transmission loss, but also optimizes the light emission direction, making the light concentrated and diffused evenly. The substrate is made of a long strip of colorless and transparent material, which is suitable for various installation scenarios and reduces light transmission loss within the substrate, improving light transmittance. The light-emitting position is designed as a cuboid groove structure, opened along the length direction perpendicular to the substrate, which can accurately accommodate the light-emitting device, ensure assembly stability, prevent displacement during use, and also provide convenient conditions for subsequent circuit laying and packaging operations.

[0018] Furthermore, the LED filament manufacturing method of this invention is simple and controllable, with each step closely connected, enabling precise replication of the filament's structural design. The etching process shapes the light-emitting positions and precisely lays the circuit layers, combined with a dual approach of soldering and adhesive bonding, effectively ensuring the assembly accuracy and connection reliability of each component, significantly improving product yield. The fluorescent mixture coating can fully cover the substrate and light-emitting device, and the refractive layer coating process is standardized and orderly. Especially for the composite refractive layer, a step-by-step coating process ensures the forming quality and bonding effect of each film layer. This method does not rely on complex specialized equipment, has moderate operational difficulty, facilitates large-scale mass production, and significantly reduces production input costs, combining practicality and economy. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a top sectional view of the LED filament in Example 1; Figure 2 This is a side sectional view of the LED filament in Example 1; Figure 3 This is a flowchart of the LED filament manufacturing method in Example 2.

[0020] Explanation of reference numerals in the attached figures: 100, Substrate; 110, Light-emitting position; 200, Light-emitting device; 300, Fluorescent layer; 400, Refractive layer; 410, High-refractive-index film layer; 420, Low-refractive-index film layer. Detailed Implementation

[0021] The following illustrations disclose several embodiments of the present invention. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential. Furthermore, for the sake of simplicity, some conventional structures and components will be shown in a simple schematic manner in the illustrations. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0022] Example 1

[0023] This embodiment provides an LED filament designed to solve the technical problems of easy breakage of the internal light-emitting device 200 and limited shaping of rigid LED filaments during the shaping process of existing flexible LED filaments. At the same time, it ensures that the LED filament can stably achieve a 360° all-angle light-emitting effect. Through reasonable structural design, this LED filament not only retains the core advantages of flexible filaments in terms of flexibility and ease of shaping, but also effectively protects the internal light-emitting device 200 from damage caused by external forces such as torsion and compression. It balances light-emitting performance, shaping flexibility and structural reliability, and is suitable for various indoor and outdoor lighting and decoration scenarios.

[0024] See Figure 1 and Figure 2The LED filament is composed of a substrate 100, a light-emitting device 200, a phosphor layer 300, and a refractive layer 400. The light-emitting device 200 is located in the light-emitting position 110 of the substrate 100, the phosphor layer 300 covers the outer surface of the substrate 100, and the refractive layer 400 covers the outer surface of the phosphor layer 300. Through the adaptive design of each layer structure, the light emitted by the light-emitting device 200 is excited and converted by the phosphor layer 300, and then undergoes multiple refractions and total internal reflections by means of the refractive layer 400 composed of materials with different refractive indices. Finally, it achieves a highly efficient conversion from a point light source to 360° omnidirectional light emission. At the same time, relying on the structural design and flexible material characteristics of the substrate 100, the light-emitting device 200 is prevented from being damaged during the shaping operation.

[0025] The substrate 100 is an elongated strip structure. One end of the substrate 100 has a light-emitting position 110 for housing the light-emitting device 200. This light-emitting position 110 is perpendicular to the length of the substrate 100. A circuit layer is laid on the side surface of the light-emitting position 110 near the end of the substrate 100, enabling the light-emitting device 200 to conduct electricity and providing a stable power supply. In this embodiment, the substrate 100 is made of a colorless and transparent material, preferably a polyimide film or a polyester film. Such materials not only possess excellent flexible mechanical properties, meeting diverse shaping requirements such as bending, winding, and folding, but also have good light transmittance, not obstructing the light propagation path and ensuring light transmission efficiency. To further enhance the installation stability and protective effect of the light-emitting device 200, the width of the base 100 is set to be greater than 1.2 times the length of the light-emitting device 200, and the thickness of the base 100 is set to be greater than 1.2 times the width of the light-emitting device 200. By reserving sufficient structural margin, the deformation of the base 100 during shaping can be effectively prevented from directly squeezing the light-emitting device 200. At the same time, the light-emitting position 110 is designed as a cuboid groove structure, the length, width, and height of which are all greater than the corresponding dimensions of the light-emitting device 200. This ensures that the light-emitting device 200 can be stably embedded and completely contained within the light-emitting position 110, achieving preliminary physical protection for the light-emitting device 200 and reducing the probability of external forces directly acting on the light-emitting device 200.

[0026] Correspondingly, the light-emitting device 200 is fixed to the side of the circuit layer within the light-emitting position 110 using an adhesive dispensing process. Simultaneously, the electrodes of the light-emitting device 200 are connected to the circuit layer using soldering to ensure stable circuit connectivity and prevent light-emitting failures or brightness fluctuations due to poor contact. The forward-emitting surface of the light-emitting device 200 faces the far end of the substrate 100, allowing most of the emitted light to be directly transmitted through the transparent substrate 100, significantly improving light utilization. In this embodiment, the light-emitting device 200 uses a flip-chip, and the emitted light can be one or more of red, green, blue, and yellow, providing a basis for achieving diverse color light effects. Furthermore, to ensure the overall brightness and uniformity of the LED filament, two or more light-emitting positions 110 can be set according to the actual length of the substrate 100. Each light-emitting position 110 contains one light-emitting device 200. Through the coordinated emission of multiple light-emitting devices 200, the problem of insufficient local brightness or uneven light is effectively avoided, ensuring uniform overall light emission and meeting brightness standards for the LED filament, adapting to the lighting and decoration needs of different scenarios.

[0027] Meanwhile, the fluorescent layer 300 is fully encapsulated on the outer surface of the substrate 100, completely covering the light-emitting position 110 and the light-emitting device 200 housed therein. This ensures that the light emitted by the light-emitting device 200 can quickly and fully act on the fluorescent layer 300, improving fluorescence conversion efficiency and light mixing effect. In this embodiment, the thickness of the fluorescent layer 300 is set to 0.1~0.5mm. This thickness ensures that the phosphor fully absorbs light and excites light emission, while avoiding excessive thickness that would lead to light attenuation, thus balancing fluorescence conversion effect and light transmittance. The fluorescent layer 300 contains one or more of red, green, blue, and yellow phosphors. By combining it with light-emitting devices 200 of different color light types, LED filaments of different colors, such as white light and warm yellow light, can be precisely tuned to meet the market's demand for diverse lighting colors.

[0028] Furthermore, the refractive layer 400 is composed of a high-refractive-index film layer 410 and a low-refractive-index film layer 420, employing a layered composite structure. The high-refractive-index film layer 410 is directly coated on the outer surface of the fluorescent layer 300, while the low-refractive-index film layer 420 is coated on the outer surface of the high-refractive-index film layer 410. The combination of these two layers with different refractive indices achieves multiple refractions and total internal reflection of light, ensuring uniformity of the 360° light emission effect. In this embodiment, the high-refractive-index film layer 410 can be made of titanium dioxide film, zirconium dioxide film, or niobium pentoxide film, with a thickness controlled to be no greater than 50 μm and a surface roughness Ra controlled to be no greater than 0.1 μm, ensuring film flatness and high refractive performance, and preventing surface defects from affecting light transmission. The low-refractive-index film layer 420 can be made of silicon dioxide film or magnesium difluoride film, with a thickness also controlled to be no greater than 50 μm and a surface roughness Ra controlled to be no greater than 0.1 μm, ensuring close adhesion with the high-refractive-index film layer 410. In addition, due to the significant material difference between the high-refractive-index film layer 410 and the low-refractive-index film layer 420, the interfacial bonding force is weak and interfacial peeling is prone to occur. Therefore, a transition layer is coated between the two film layers. This transition layer is made of silane coupling agent, which can effectively enhance the interfacial bonding force between the two film layers, improve the overall structural stability of the refractive layer 400, ensure that the refractive layer 400 does not peel off or fall off during long-term use of the LED filament, and guarantee the stability of the luminous effect and service life.

[0029] The working principle of this LED filament is based on the laws of refraction and total internal reflection of light. Relying on the coordinated operation of the substrate 100, the light-emitting device 200, the phosphor layer 300, and the refractive layer 400, it achieves efficient light transmission, conversion, and omnidirectional divergence. The specific process is as follows: After the light-emitting device 200 is powered on through the circuit layer, it emits initial colored light. This initial colored light directly acts on the phosphor layer 300 covering the outside, exciting the phosphor in the phosphor layer 300 to emit corresponding colored light. The initial colored light and the phosphor excitation light mix to form a composite light. After the composite light exits from the phosphor layer 300, it enters the high-refractive-index film layer 410. Due to the difference in refractive index between the phosphor layer 300 and the high-refractive-index film layer 410, the light undergoes its first refraction at the interface, deflecting towards the normal direction, achieving initial convergence and transmission of the light. Subsequently, the light travels from the high-refractive-index film layer 410 to the low-refractive-index film layer. 420. Because the refractive index of the high-refractive-index film layer 410 is higher than that of the low-refractive-index film layer 420, some light rays satisfy the refraction condition at the interface between the two film layers, deflecting away from the normal and passing through the low-refractive-index film layer 420 into the air, thus achieving external light emission. The other part of the light rays satisfy the total internal reflection condition, undergoing total internal reflection at the interface between the high-refractive-index film layer 410 and the low-refractive-index film layer 420. The light rays are reflected back into the high-refractive-index film layer 410 and continue to be transmitted along the extension direction of the film layer. Some of the totally internally reflected light rays will again strike the fluorescent layer 300, mix with the newly excited light rays of the fluorescent layer 300, and participate in the refraction and total internal reflection process again. This cycle repeats, and the light undergoes multiple refractions and total internal reflections inside the refractive layer 400, gradually radiating outwards from the LED filament, ultimately achieving the effect of converting the point light source into a 360° omnidirectional uniform light emission effect. Moreover, the light is softer after being transmitted through the multi-layer structure, improving lighting comfort.

[0030] In summary, the LED filament of this embodiment combines practicality and innovation, effectively overcoming the shortcomings of existing technologies. Its specific advantages are as follows: First, the substrate uses flexible and transparent materials such as polyimide film or polyester film, allowing for flexible bending, winding, and folding operations. Compared to rigid LED filaments, it can adapt to more diverse application scenarios such as indoor decoration, outdoor landscaping, and special-shaped lighting, significantly broadening the product's applicability. Second, the recessed light-emitting positions are used for embedded installation of the light-emitting device. Combined with the light-transmitting characteristics of the transparent substrate, the light from the front-facing light-emitting surface of the device is uniformly diffused after being conducted through the substrate. This avoids the glare caused by direct light and improves the overall uniformity of LED filament illumination. The embedded structure also reduces the corrosion of the light-emitting device by dust and moisture, enhancing environmental adaptability. Third, the light-emitting device is encased in a multi-layered protective system consisting of the light-emitting positions, fluorescent layer, and refractive layer. The external forces generated by substrate deformation during the shaping process do not directly act on the light-emitting device, effectively preventing breakage caused by torsion and compression. This helps improve product yield, extend service life, and reduce total life-cycle costs. Furthermore, the refractive layer employs a layered structure of high and low refractive index films, with an added silane coupling agent transition layer. This not only achieves stable 360° omnidirectional uniform light emission based on the principles of light refraction and total internal reflection, but also enhances the interfacial bonding between film layers, preventing the refractive layer from peeling off and ensuring long-term stable luminous performance. Finally, by matching different types of phosphors in the fluorescent layer with the color of the light-emitting device, various LED filaments with different colors can be formulated to precisely match the lighting and decoration needs of different scenarios, further enhancing the product's market adaptability and core competitiveness.

[0031] Example 2

[0032] This embodiment provides a method for manufacturing an LED filament. The method is simple and the process is controllable, and it is suitable for preparing the LED filament described in Embodiment 1.

[0033] Combination Figure 3 The method for manufacturing this LED filament includes the following steps: S1. Prepare a substrate 100, etch the substrate 100 to form a light-emitting position 110, and then lay a circuit layer in the light-emitting position 110. S2. Place the light-emitting device 200 in the light-emitting position 110, connect the electrodes of the light-emitting device 200 to the circuit layer by soldering, and then fix the light-emitting device 200 by dispensing process. After curing, the substrate 100 semi-finished product is obtained. S3. Coat the fluorescent mixture onto the substrate 100 semi-finished product, so that the fluorescent mixture covers the substrate 100 and the light-emitting device 200 to form a fluorescent layer 300. S4. A refractive film is coated on the outer surface of the fluorescent layer 300 to form a refractive layer 400, thereby obtaining an LED filament.

[0034] In step S4 of this embodiment, when the refractive layer 400 includes a high refractive film layer 410 and a low refractive film layer 420, a high refractive film is first coated on the surface of the fluorescent layer 300 to form a high refractive film layer 410. Then, a silane coupling agent is coated on the surface of the high refractive film layer 410 to form a transition layer. Finally, a low refractive film is coated on the surface of the transition layer to form a low refractive film layer 420, thus completing the coating of the refractive layer 400.

[0035] The LED filament manufacturing method of this embodiment possesses significant technical advantages and outstanding process benefits: First, the overall process is simple and controllable, with moderate operational difficulty in each step, eliminating the need for complex specialized equipment. This reduces production input costs and improves production efficiency, making it suitable for large-scale mass production. Second, the process steps are closely linked and logically coherent. Standardized operations allow for precise control of the dimensional parameters and molding quality of each structure, effectively ensuring the consistency of performance and precision in mass-produced LED filaments and improving product qualification rates. Third, the entire manufacturing process carries an extremely low risk of damage to the light-emitting device. Precise positioning and assembly, reliable welding, and stable adhesive fixation maximize the preservation of the original performance of the light-emitting device, ensuring that the finished LED filament possesses excellent luminous efficiency and uniformity. Finally, this method is highly adaptable. Parameters such as the ratio of the fluorescent mixture and the material and thickness of the refractive film can be flexibly adjusted according to actual application needs to prepare LED filaments with different colors and luminous effects, fully meeting diverse market application demands.

[0036] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. An LED filament, characterized in that, The device includes a substrate, a light-emitting device, a fluorescent layer, and a refractive layer. At least one light-emitting position is provided at one end of the substrate, and a light-emitting device is provided in each of the light-emitting positions. The fluorescent layer covers the outer surface of the substrate and covers the light-emitting positions. The refractive layer covers the outer surface of the fluorescent layer.

2. The LED filament according to claim 1, characterized in that, The refractive layer includes a high-refractive-index film layer and a low-refractive-index film layer. The high-refractive-index film layer covers the outer surface of the fluorescent layer, and the low-refractive-index film layer covers the outer surface of the high-refractive-index film layer.

3. The LED filament according to claim 2, characterized in that, The high-refractive-index film layer and the low-refractive-index film layer are coated with a transition layer, which is made of a silane coupling agent.

4. The LED filament according to claim 2, characterized in that, The high-refractive-index film is selected from titanium dioxide film, zirconium dioxide film, or niobium pentoxide film, and the low-refractive-index film is selected from silicon dioxide film or magnesium difluoride film.

5. The LED filament according to claim 2, characterized in that, The thickness of both the high-refractive-index and low-refractive-index films is no greater than 50 μm, and the surface roughness Ra of both the high-refractive-index and low-refractive-index films is no greater than 0.1 μm.

6. The LED filament according to any one of claims 1 to 5, characterized in that, A circuit layer is laid on the side surface of the light-emitting position that is close to the near end of the substrate. The light-emitting device is located on the side of the circuit layer within the light-emitting position, and the forward light-emitting surface of the light-emitting device faces the far end of the substrate.

7. The LED filament according to any one of claims 1 to 5, characterized in that, The substrate is elongated and made of a colorless and transparent material.

8. The LED filament according to any one of claims 1 to 5, characterized in that, The light-emitting position is a cuboid groove structure, and the light-emitting position is opened along the length direction perpendicular to the base.

9. A method for manufacturing an LED filament as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Prepare the substrate, etch the substrate to form light-emitting sites, and then lay the circuit layer in the light-emitting sites. S2. Place the light-emitting device in the light-emitting position, connect the electrodes of the light-emitting device to the circuit layer by soldering, and then fix the light-emitting device by dispensing process. After curing, the substrate semi-finished product is obtained. S3. Coat the fluorescent mixture onto the substrate semi-finished product, so that the fluorescent mixture covers the substrate and the light-emitting device to form a fluorescent layer; S4. A refractive film is coated on the outer surface of the fluorescent layer to form a refractive layer, thus obtaining the LED filament.

10. The method for manufacturing an LED filament according to claim 9, characterized in that, In step S4, when the refractive layer includes a high-refractive film layer and a low-refractive film layer, a high-refractive film is first coated on the surface of the fluorescent layer to form a high-refractive film layer. Then, a silane coupling agent is coated on the surface of the high-refractive film layer to form a transition layer. Finally, a low-refractive film is coated on the surface of the transition layer to form a low-refractive film layer, thus completing the coating of the refractive layer.

Images