Method for bonding liquid crystal display panel to back plate

Abstract

The application discloses a kind of liquid crystal display and back plate bonding method, belong to liquid crystal display technical field.This method includes: the surface pretreatment of liquid crystal display back and back plate bonding surface is coated with primer agent;UV / wet gas double-curing type adhesive is applied on back plate;Two are placed in vacuum chamber and are vacuumed and are positioned and attached;Vacuum state is maintained, and infrared heating plate array integrated in vacuum chamber is used, and center pre-curing, gradient diffusion curing, edge complete curing and post-curing are sequentially carried out from the center of adhesive layer to the edge;During curing, strain is monitored in real time by FBG strain sensor arranged at four corners of the non-display area of display, and when exceeding threshold, corresponding area heating power is adjusted by feedback;Finally, quality detection is carried out.The application cooperates with the synergistic effect of in-situ gradient curing in vacuum cavity and real-time feedback of FBG strain sensor, effectively eliminates curing shrinkage stress and bubble, significantly reduces pressing light leakage and Mura defect, and improves bonding quality and process stability.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal display manufacturing, and more specifically to a method for bonding a liquid crystal display screen to a back panel. Background Technology

[0002] The bonding of the LCD screen to the back panel is a crucial step in display module manufacturing. Currently, the mainstream process uses optical adhesive (OCA) bonding, which involves vacuum lamination followed by a single-step curing process using heat or ultraviolet irradiation. However, this process has the following drawbacks:

[0003] 1. Curing shrinkage stress concentration: During the process of the adhesive layer from liquid to complete curing, the shrinkage internal stress is generated simultaneously and superimposed on each other across the entire surface. It is difficult to control the stress distribution, which can easily lead to local warping of the LCD panel or the Mura effect, especially in medium and large-sized display devices.

[0004] 2. Light leakage due to pressure: Uneven residual stress causes light leakage when the panel is locally pressed, affecting display quality.

[0005] 3. Residual air bubbles: Although vacuum bonding is used, tiny air bubbles may still remain during the one-time curing process, affecting the bonding strength.

[0006] There are already improved solutions, such as the patent application with public number CN120340365A, which improves the bubble absorption capacity through a double-layer adhesive structure. However, it still uses one-time whole-surface curing and does not solve the problem of spatial distribution control of curing shrinkage stress, nor does it involve real-time stress monitoring and feedback adjustment during the curing process.

[0007] Therefore, how to actively control the orderly release of adhesive layer curing shrinkage stress during large-area bonding process, and avoid panel deformation and display defects caused by stress concentration, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The present invention aims to solve at least one of the technical problems mentioned above by providing a method for bonding a liquid crystal display screen to a back panel, which solves the problems of stress concentration and air bubble residue during the large-area bonding process of the liquid crystal display screen and the back panel.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for bonding a liquid crystal display screen to a back panel includes the following steps: S1: Surface pretreatment - Clean the back of the LCD screen and the bonding surface of the back panel respectively, and apply a primer to the bonding surface of the back panel. S2: Adhesive coating - Apply a UV / moisture dual-curing adhesive to the bonding surface of the back panel to form the initial adhesive layer; S3: Vacuum molding and bonding - The LCD screen and the back plate coated with the adhesive layer are placed in a vacuum chamber, and after vacuuming, they are aligned and bonded. S4: Zoned Gradient Curing – Maintaining the vacuum state of the vacuum chamber, an infrared heating plate array integrated within the vacuum chamber is used to cure the adhesive layer in zones from the center to the edge regions sequentially. Specifically, this includes: S4-1: Center pre-curing stage: Heat the center region of the adhesive layer to a first preset temperature and maintain it for a first preset time, so that the adhesive layer in the center region reaches a gel state; S4-2: Gradient diffusion curing stage: Based on the central pre-cured area, the heating area diffuses outward at a preset speed, and the temperature at the heating front edge is distributed in a gradient. S4-3: Edge curing stage: Heat the edge area of ​​the adhesive layer to the second preset temperature to make the adhesive layer in the edge area fully cured; S4-4: Post-curing stage: Place the product in a room temperature environment for a preset time, and use the moisture curing mechanism to complete the residual cross-linking reaction; S5: Real-time stress monitoring and feedback adjustment - During the partitioned gradient curing process in S4, the strain change caused by the curing shrinkage of the adhesive layer is monitored in real time. When the local strain value exceeds the preset threshold, the heating power of the heating device in the corresponding area is adjusted in feedback. S6: Quality Inspection - After curing, the internal bubbles and delamination defects of the adhesive layer are inspected.

[0010] Further, in S4, the first preset temperature is 50℃~70℃, the first preset time is 30s~60s; the second preset temperature is 80℃~120℃, the second preset time is 1min~3min; the diffusion rate of the heating area is 5mm / s~15mm / s, the heating front temperature is 60℃~80℃, and the temperature of the solidified area is maintained at 40℃~50℃.

[0011] Furthermore, in S3, the vacuum level in the vacuum chamber is ≤100Pa; the partitioned gradient curing in S4 is carried out in situ in the vacuum chamber, and the vacuum state is not released before the completion of stages S4-1, S4-2, and S4-3.

[0012] Furthermore, the strain sensor in S5 is an FBG strain sensor, which is arranged at the four corners of the non-display area of ​​the liquid crystal display screen, and the preset threshold is 300 microstrain.

[0013] Furthermore, the infrared heating plate array is an M×N matrix layout, with each heating unit having independent temperature control. The heating unit size is 5mm×5mm~20mm×20mm, and the center distance between adjacent heating units is 10mm~25mm.

[0014] Furthermore, in S1, the surface cleaning treatment employs plasma cleaning and / or ultraviolet ozone cleaning; the primer is a silane coupling agent.

[0015] Furthermore, in step S2, the adhesive layer is coated using slot coating or inkjet printing, and the adhesive layer thickness is 50μm to 200μm.

[0016] By adopting the above technical solution, the present invention has the following beneficial effects: 1. Eliminate curing shrinkage stress, reduce light leakage during pressing and Mura defects. This invention employs a gradient curing strategy that cures from the center to the edge in stages, allowing the curing shrinkage stress to be released radially outward in an orderly manner, thus avoiding stress superposition and concentration.

[0017] 2. Completely eliminate air bubbles in the adhesive layer and improve bonding quality. This invention maintains the vacuum state after vacuum bonding and directly completes the zonal gradient curing in the vacuum chamber, ensuring that the adhesive layer remains in a vacuum atmosphere until it loses its fluidity, thus preventing the generation of air bubbles.

[0018] 3. Real-time monitoring of curing strain enables closed-loop quality control. This invention arranges FBG strain sensors at the four corners of the non-display area of ​​the liquid crystal display screen to monitor the curing strain in real time. When the local strain exceeds a preset threshold, it automatically adjusts the heating power of the corresponding area, upgrading the curing process from "open-loop control" to "closed-loop adaptive control", which significantly improves process robustness and product consistency.

[0019] 4. High equipment integration and continuous process. This invention employs a vacuum bonding device integrated with an infrared heating plate array, which sequentially completes bonding and gradient curing within the same sealed chamber. This eliminates the need to break the vacuum or transfer the workpiece, simplifying the production process and reducing the risk of contamination and positioning errors.

[0020] In summary, this invention effectively solves the problems of stress concentration and bubble residue during the large-area bonding process between the liquid crystal display screen and the back panel by combining the synergistic effect of in-situ gradient curing in a vacuum cavity and real-time strain feedback of FBG. Attached Figure Description

[0021] Figure 1 Schematic diagram of the integrated vacuum bonding device according to Embodiment 1 of the present invention Figure 2 Process flow diagram of the present invention Figure 3 Schematic diagram of the diffusion of the heating zone.

[0022] In the attached diagram, 10 is the sealed chamber, 20 is the upper support platform, 201 is the pressing plate, 21 is the infrared heating plate array, 30 is the lower support platform, 40 is the bonding assembly, and 50 is the FBG strain sensor. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0024] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or it may be centered within another component. When a component is described as "set to" another component, it can be directly set on the other component or it may be centered within another component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this article are for illustrative purposes only.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] Example 1: like Figures 1 to 3 As shown, a preferred embodiment of the present invention provides a method for bonding a liquid crystal display screen to a back panel, applicable to the manufacture of a 9.7-inch liquid crystal display module. The liquid crystal display panel is an IPS type LCD panel, and the back panel is a stamped aluminum alloy back panel with an anodized surface.

[0027] In this embodiment, an integrated vacuum bonding device is used to implement the bonding method. It should be noted that vacuum bonding devices are common existing technology in this field. To adapt to this method, this embodiment makes the following differences and improvements: its structure is as follows. Figure 1 As shown, the device includes a sealed chamber 10, a vacuum system, a CCD vision alignment system, an upper support stage 20, an infrared heating plate array 21, a lower support stage 30, and an FBG strain monitoring system.

[0028] The sealed chamber 10 consists of an upper chamber and a lower chamber, made of stainless steel, with cooling water circulation channels inside the chamber walls. A vacuum system is connected to the sealed chamber 10, achieving an ultimate vacuum of 10 Pa. The CCD vision alignment system consists of four high-resolution CCD cameras mounted on the top of the upper chamber, with an alignment accuracy of ±0.05 mm. The upper support platform 20 is liftable, and a pressing plate 201 is fixedly mounted on its lower surface. An infrared heating plate array 21 is fixedly mounted on the lower surface of the pressing plate 201. The infrared heating plate array 21 adopts an M×N matrix layout, with each heating unit measuring 10 mm × 10 mm and a center-to-center distance of 15 mm. Each heating unit consists of embedded infrared LEDs with a wavelength range of 2–10 μm and a peak wavelength of approximately 4 μm. It is equipped with an independent K-type thermocouple temperature sensor and a PID controller, using a solid-state relay for proportional control of the on / off time. The lower support platform 30 is a vacuum adsorption platform with densely distributed vacuum adsorption micropores on its surface. The platform contains a sealed vacuum chamber, which is connected to a vacuum source pipeline outside the chamber via a vacuum port on its back. The lower support platform 30 supports and fixes the backplate, maintaining its positional stability during the bonding process through vacuum adsorption. The FBG strain monitoring system includes four surface-mount miniature FBG strain sensors 50, optical fibers, a multi-channel fiber optic vacuum feedthrough flange, a fiber optic grating demodulator, and a main controller. The fiber optic vacuum feedthrough flange is installed at the opening in the wall of the sealed chamber, using a soft copper gasket for vacuum sealing. The fiber optic grating demodulator has a wavelength resolution of at least 1 pm and a sampling frequency of 10 Hz, and is connected to the main controller via an industrial Ethernet protocol. The application of the surface-mount miniature FBG strain sensors 50 is a common technique in this field, and its specific principles will not be elaborated here.

[0029] In this embodiment, the method for bonding the liquid crystal display screen to the back panel includes the following steps: S1: Surface pretreatment S1.1 The back of the LCD panel and the bonding surface of the aluminum alloy backplate are placed separately into a plasma cleaner, using argon and oxygen as working gases, RF power 200W, and processing time 90 seconds to remove surface organic contaminants. After treatment, the water droplet contact angle is ≤10°.

[0030] S1.2 A silane coupling agent primer, KH-560, 0.5wt% ethanol solution, is applied to the bonding surface of the aluminum alloy backing plate by spraying. After coating, it is dried at 60°C for 5 minutes to form a uniform primer coating with a thickness of approximately 100nm.

[0031] S2: Adhesive coating A slot coating machine was used to apply a UV / moisture dual-curing adhesive to the bonding surface of the backing plate. The main component of the adhesive is an acrylate prepolymer, containing a photoinitiator and a latent moisture-curing catalyst. The coating parameters were: slot gap 120 μm, coating speed 50 mm / s, and adhesive layer thickness uniformity controlled within ±5 μm. The initial adhesive layer thickness after coating was approximately 100 μm.

[0032] S3: Vacuum molding and bonding A backplate coated with adhesive is placed on the lower support platform 30 and fixed by vacuum adsorption. A liquid crystal display panel is pre-placed at a predetermined position above the lower support platform 30 and fixed by vacuum adsorption from the lower support platform 30. The sealed chamber 10 is closed, and the vacuum system is activated to evacuate the chamber until the pressure is ≤50Pa. Under vacuum conditions, precise alignment is performed using a CCD vision alignment system, followed by pressing down on the upper support platform 20 at a pressure of 0.3MPa for 10 seconds, resulting in an adhesive assembly 40 composed of the liquid crystal display, adhesive layer, and backplate.

[0033] S4: Partitioned Gradient Solidification After vacuum molding and bonding are completed, the vacuum state within the sealed chamber 10 is maintained unchanged, i.e., the vacuum degree is ≤50Pa. The vacuum is not released, the workpiece is not transferred, and the infrared heating plate array 21 is directly activated to perform in-situ zoned gradient curing within the vacuum chamber. Specifically, it is divided into the following four stages:

[0034] S4-1: Center Pre-curing Stage According to a preset program, the main controller activates only the heating units in the infrared heating plate array 21 that correspond to the central region of the adhesive layer and have a diameter approximately 30% of the total diameter of the adhesive layer. The PID controller of each heating unit sets the temperature to 60℃ and the heating time to 45 seconds. The infrared radiation emitted by the infrared lamp beads directly acts on the central region of the adhesive layer, causing its temperature to rise rapidly to 60℃, and the adhesive layer reaches a gel state with a curing degree of approximately 40%.

[0035] S4-2: Gradient diffusion curing stage Using the central pre-cured area as a reference, the main controller activates the heating units outwards in circles at a preset diffusion rate of approximately 8 mm / s. The target temperature for the newly activated heating units at the heating front is 70°C. The heating units in the pre-cured central area switch to a low-power insulation mode, maintaining a temperature of 50°C. A temperature gradient of approximately 20°C is formed between the heating front and the insulation area. This phase lasts approximately 60 seconds.

[0036] S4-3: Edge fully cured stage When the heating area covers the edge of the adhesive layer, about 5mm from the adhesive layer boundary, the main controller raises the temperature of all activated heating units to 100℃ and holds for 2 minutes, so that the edge area and the entire adhesive layer reach a fully cured state with a curing degree ≥95%.

[0037] S4-4: Post-curing stage Turn off the infrared heating plate array 21 to stop heating. Keep the sealed chamber 10 closed and allow it to cool naturally to room temperature for about 30 minutes; then release the vacuum, turn off the infrared heating plate array 21, and remove the adhesive component 40. Place the adhesive component 40 in an environment with a room temperature of 23±2℃ and a relative humidity of 50%±10% for 24 hours to complete the residual crosslinking reaction using a moisture curing mechanism.

[0038] S5: Real-time stress monitoring and feedback adjustment During the curing process of S4, strain monitoring and feedback control are carried out simultaneously: S5.1 Sensor Arrangement: One FBG strain sensor 50 is attached to the upper surface of each of the four corners of the non-display area of ​​the LCD panel, i.e., the side facing the infrared heating plate array. The sensors are led out of the chamber through an optical fiber via a fiber optic vacuum feedthrough flange and connected to the fiber optic demodulator.

[0039] S5.2 Data Acquisition: Strain values ​​from each FBG sensor are continuously acquired at a sampling frequency of 10Hz, in με. The preset strain threshold is 300με.

[0040] S5.3 Feedback Control Logic: When the real-time strain value monitored by a certain FBG strain sensor 50 exceeds 300με, the main controller determines that the curing shrinkage stress in the area corresponding to the FBG strain sensor 50 is too large, and then executes: ① Reduce the output power of the relevant heating unit in the infrared heating plate array corresponding to the area, so that the temperature in the area drops by 5-10℃; ② Appropriately increase the power of the heating unit in the adjacent outer incompletely cured area, pushing the stress peak area outward. The feedback adjustment response time is ≤2 seconds.

[0041] S5.4 Termination condition: When the strain values ​​monitored by all FBG strain sensors 50 are stable within ±50με for 30 consecutive seconds, it is determined that the curing stress has been basically released and the process enters the S4-4 post-curing stage.

[0042] S6: Quality Inspection After curing, the adhesive assembly 40 was inspected under an ultrasonic scanning microscope. The probe frequency was 50MHz, and the scanning range covered the entire adhesive layer. Inspection standards: equivalent diameter of a single bubble ≤ 0.2mm, and the number of bubbles per square centimeter ≤ 2; no delamination defects. The sample pass rate prepared in this embodiment was 98.5%.

[0043] Here is a table listing the results of the experiment conducted using Example 1: The experimental results show that the method of the present invention has achieved significantly better technical effects than the existing technical solutions in terms of suppressing light leakage under pressure, improving display uniformity and eliminating bubbles, and the process has good robustness when the process parameters fluctuate within a reasonable range.

[0044] Example 2: This embodiment is basically the same as Embodiment 1, except that: First, the LCD panel is a 12.3-inch automotive LCD panel, and the back panel is a magnesium alloy die-cast back panel; Second, the adhesive layer coating in S2 is applied using inkjet printing with a printhead resolution of 600dpi and an adhesive layer thickness of 150μm. Third, the vacuum degree in S3 is ≤80Pa; Fourth, the parameters for each stage in S4 are adjusted as follows: S4-1 center pre-curing temperature 55℃, time 60 seconds; S4-2 gradient diffusion rate 10mm / s, heating front temperature 65℃, cured area temperature 45℃; S4-3 edge complete curing temperature 110℃, time 90 seconds. Fifth, the strain threshold in S5 is set to 250 με.

[0045] After testing, the sample prepared in this embodiment showed no delamination or bubble formation at the bonding interface after thermal cycling tests at -40℃ to 85℃, for example, after 100 cycles, and the light leakage rate under pressure was 0%, meeting the reliability requirements of the vehicle display device.

[0046] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the technical spirit of the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for bonding a liquid crystal display screen to a back panel, characterized in that, Includes the following steps: S1: Surface pretreatment - Clean the back of the LCD screen and the bonding surface of the back panel respectively, and apply a primer to the bonding surface of the back panel. S2: Adhesive coating - Apply a UV / moisture dual-curing adhesive to the bonding surface of the back panel to form the initial adhesive layer; S3: Vacuum molding and bonding - The LCD screen and the back plate coated with the adhesive layer are placed in a vacuum chamber, and after vacuuming, they are aligned and bonded. S4: Zoned Gradient Curing – Maintaining the vacuum state of the vacuum chamber, an infrared heating plate array (21) integrated within the vacuum chamber is used to sequentially cure the adhesive layer from the center region to the edge region, specifically including: S4-1: Center pre-curing stage: Heat the center region of the adhesive layer to a first preset temperature and maintain it for a first preset time, so that the adhesive layer in the center region reaches a gel state; S4-2: Gradient diffusion curing stage: Based on the central pre-cured area, the heating area diffuses outward at a preset speed, and the temperature at the heating front edge is distributed in a gradient. S4-3: Edge curing stage: Heat the edge area of ​​the adhesive layer to the second preset temperature to make the adhesive layer in the edge area fully cured; S4-4: Post-curing stage: Place the product in a room temperature environment for a preset time, and use the moisture curing mechanism to complete the residual cross-linking reaction; S5: Real-time stress monitoring and feedback adjustment - During the partitioned gradient curing process in S4, the strain change caused by the curing shrinkage of the adhesive layer is monitored in real time. When the local strain value exceeds the preset threshold, the heating power of the heating device in the corresponding area is adjusted in feedback. S6: Quality Inspection - After curing, the internal bubbles and delamination defects of the adhesive layer are inspected.

2. The method for bonding a liquid crystal display screen to a back panel as described in claim 1, characterized in that: In step S4, the first preset temperature is 50℃~70℃, and the first preset time is 30s~60s; the second preset temperature is 80℃~120℃, and the second preset time is 1min~3min; the diffusion rate of the heating area is 5mm / s~15mm / s, the temperature of the heating front is 60℃~80℃, and the temperature of the solidified area is maintained at 40℃~50℃.

3. The method for bonding a liquid crystal display screen to a back panel as described in claim 1, characterized in that: In S3, the vacuum level in the vacuum chamber is ≤100Pa; the partitioned gradient curing in S4 is carried out in situ in the vacuum chamber, and the vacuum state is not released before the completion of stages S4-1, S4-2, and S4-3.

4. The method for bonding a liquid crystal display screen to a back panel as described in claim 1, characterized in that: The strain sensor in S5 is an FBG strain sensor (50), which is arranged at the four corners of the non-display area of ​​the liquid crystal display screen, and the preset threshold is 300 micro-strain.

5. The method for bonding a liquid crystal display screen to a back panel as described in claim 1, characterized in that: The infrared heating plate array (21) is an M×N matrix layout, with each heating unit having independent temperature control. The heating unit size is 5mm×5mm~20mm×20mm, and the center distance between adjacent heating units is 10mm~25mm.

6. The method for bonding a liquid crystal display screen to a back panel as described in claim 1, characterized in that: In step S1, the surface cleaning treatment employs plasma cleaning and / or ultraviolet ozone cleaning; the primer is a silane coupling agent.

7. The method for bonding a liquid crystal display screen to a back panel as described in claim 1, characterized in that: In step S2, the adhesive layer is applied using slot coating or inkjet printing, and the adhesive layer thickness is 50μm to 200μm.

Images