Three-section type hollow flexible circuit board, PDLC dimming glass assembly and preparation method thereof

Abstract

The application discloses a three-section type hollow flexible circuit board, a PDLC dimming glass assembly and a preparation method thereof, and belongs to the technical field of polymer dispersed liquid crystal dimming film manufacturing. The flexible circuit board is symmetrically provided with a plurality of functional hollow structures on both sides in the width direction of the flexible circuit board; along the length direction, each functional hollow structure can be sequentially divided into a compression functional area (length >=1mm), a laminated buffer area (length is determined according to the glass size) and an exposed exhaust area (length >=5mm). The compression functional area forms a mechanical anchoring interface by interembedding with an anisotropic conductive adhesive film, so that the connection strength is improved; the laminated buffer area absorbs thermal stress and provides a flow channel for the encapsulation adhesive film; the exposed exhaust area extends to the outside of the glass substrate, and a direct exhaust path is established during lamination. The problems of low connection reliability, bubble residue and thermal stress concentration of the traditional FPC are solved, and the assembly yield and long-term reliability of the PDLC dimming film are improved.

Description

Technical Field

[0001] This invention relates to the field of polymer dispersed liquid crystal (PDLC) dimming film manufacturing technology, specifically to a three-segment hollow flexible circuit board, a PDLC dimming glass assembly, and a method for preparing the same. Background Technology

[0002] Polymer-dispersed liquid crystal (PDLC) dimming films, as intelligent optical materials with the electrical control characteristics of "transparency when powered and fogging when powered off," have been widely used in high-end building and automotive electronics fields. A typical assembly process involves laminating a PDLC film between two glass substrates and connecting it to the indium tin oxide (ITO) electrodes of the PDLC film via a flexible printed circuit board (FPC) to extract power and control signals. Finally, using a high-temperature, high-pressure lamination process with a polyvinyl butyral (PVB) film, an integrated encapsulation structure of "glass substrate-PVB-FPC-PDLC film" is formed. In this process, the FPC, as a key component for electrical connection and mechanical load-bearing, directly affects the final product's appearance qualification rate and long-term operational reliability due to the rationality of its structural design.

[0003] Currently, the industry commonly uses anisotropic conductive film (ACF) or conductive silver paste to bond and fix the FPC to the PDLC film electrode layer through a hot-pressing process. However, traditional FPCs are mostly planar structures with flat surfaces and continuous edges, which face the following technical bottlenecks in the encapsulation process:

[0004] 1. The bonding between FPC and PDLC electrodes relies solely on the adhesion of the ACF adhesive layer, resulting in insufficient interfacial pull-out force. This makes them prone to detachment after prolonged vibration or temperature cycling. This problem is particularly pronounced in dynamic service scenarios such as automotive applications.

[0005] 2. Due to the 0.08-0.2mm height difference between the FPC and the glass and PDLC film formed by the substrate stacking, the air in the sealed gap is difficult to be effectively discharged through the traditional FPC structure during the air extraction stage before lamination. This results in bubble defects around the FPC after high-temperature lamination, with an appearance defect rate as high as 5%-8%.

[0006] 3. During hot pressing, the thermal expansion and contraction stress of continuous FPC is concentrated at the boundary between the "pressed area and non-pressed area". Wrinkles are prone to occur during the cooling stage. At the same time, temperature fluctuations during subsequent use will exacerbate stress accumulation, leading to breakage of conductive lines or cracking of the substrate.

[0007] 4. In the existing design, the distance between the conductive lines of some FPCs and the edge of the insulating substrate is too close. During lamination or use, the exposed copper foil may cause electric arcs or sparks, posing an electrical safety hazard.

[0008] To address these issues, the industry currently employs localized optimization methods, such as increasing lamination pressure (to above 1.0 MPa) to enhance bonding or using high-flow PVB adhesive to improve filling efficiency. However, these solutions have significant limitations: increasing pressure increases equipment load and energy consumption; excessively high adhesive flow may weaken the long-term aging resistance of the adhesive layer, leading to decreased reliability.

[0009] Therefore, there is an urgent need to develop a new type of flexible circuit board that can simultaneously achieve multiple functions such as reliable connection reinforcement, efficient exhaust flow, active stress dispersion, and edge safety isolation, while ensuring its high compatibility with existing processes and possessing good industrialization economics and feasibility for promotion. Summary of the Invention

[0010] This invention aims to solve a series of technical problems in the assembly of PDLC dimming films, including insufficient pull-out force of the flexible printed circuit board (FPC) connecting the PDLC film electrode layer, residual lamination bubbles, thermal stress concentration, and potential electrical safety hazards at the edges. The FPC has a series of functional cutout structures symmetrically distributed on both sides of its width, and along its length, it is sequentially divided into a pressing functional area, a lamination buffer area, and an exposed venting area. This three-section collaborative design, without significantly increasing costs, enhances connection reliability (pull-out force increased by over 40%), completely eliminates bubble defects (bubble rate reduced to below 0.1%), effectively disperses thermal stress (wrinkle rate reduced to below 0.3%), and ensures edge insulation safety, thereby comprehensively improving the production yield and long-term service stability of PDLC dimming glass assemblies.

[0011] The technical solution provided by this invention is as follows:

[0012] In a first aspect, the present invention provides a three-segment hollow flexible circuit board for PDLC dimming film, comprising a flexible insulating substrate and a conductive line layer formed on the surface of the flexible insulating substrate;

[0013] The flexible circuit board has multiple functional cutout structures symmetrically distributed on both sides of its width direction. Along its length direction, each functional cutout structure can be sequentially divided into a lamination functional area, a lamination buffer area, and an exposed venting area, wherein:

[0014] The hollow length of the pressing functional area is not less than 1mm, which is used to interlock with the anisotropic conductive adhesive film to form a mechanical anchoring interface.

[0015] The cutout length of the lamination buffer depends on the size of the glass substrate and is used to absorb thermally induced deformation stress during the lamination process and to provide a flow-filling channel for the liquid or molten thermoplastic resin film.

[0016] The exposed venting area has a cutout length of not less than 5mm, which is the end portion of the flexible circuit board extending from the edge of the glass substrate, used to establish a direct venting path connected to the external environment during the lamination process.

[0017] Optionally, the flexible circuit board has at least one anti-wrinkle cutout structure in the middle region of its width direction;

[0018] Wherein, at the same length reference position as the functional hollow structure, the cutting depth of the anti-wrinkle hollow structure toward the interior of the non-hollow body is greater than the cutting depth of the corresponding side of the functional hollow structure.

[0019] The acute angle between the line connecting the near inner edge vertex of the anti-wrinkle hollow structure and the corresponding inner edge vertex of the nearest functional hollow structure at the same position, and the baseline parallel to the width direction, is defined as the anti-wrinkle angle, and the value range of the anti-wrinkle angle is 11°~25°.

[0020] Optionally, each of the functional hollow structures is a rectangular hole; the width of a single rectangular hole is 0.6~1.0mm, and the number is 6~10.

[0021] Optionally, the center-to-center distance between two adjacent functional cutout structures is 3-5 mm, and the distance between the outermost functional cutout structure and the corresponding side edge of the flexible circuit board is not less than 2.6 mm.

[0022] Optionally, the distance between the conductive circuit layer and the edge of any of the functional hollow structures is not less than 0.6 mm, and a clearance distance of 1 to 2 mm is maintained between the conductive circuit layer and the edge of the flexible insulating substrate.

[0023] Optionally, the electrode lead-out end of the conductive circuit layer is located at the end of the exposed venting area, and the distance between it and the nearest functional hollow structure is not less than 3mm.

[0024] Optionally, the edge of the lamination buffer is provided with an anti-backflow protrusion; the anti-backflow protrusion extends obliquely from its root toward the outside of the lamination buffer, and the angle between its outer surface and the plane where the lamination buffer is located is 33°~64°.

[0025] Secondly, the present invention also provides a method for preparing a PDLC dimming glass assembly, the method comprising the following steps:

[0026] S1: Pre-pressing: The flexible circuit board described above is pre-pressed to the electrode layer of the PDLC film through anisotropic conductive adhesive film;

[0027] S2: Vacuuming and venting: The pre-pressed flexible circuit board and PDLC film are placed between two glass substrates, and a thermoplastic resin film is placed between them, so that the exposed venting area of ​​the flexible circuit board extends out of the edge of the glass substrate; the lamination assembly is vacuumed.

[0028] S3: Lamination and curing: The degassed laminated assembly is placed in a laminator for lamination and curing.

[0029] Optionally, in step S1, the pre-pressing temperature is 200℃~230℃, the pressing pressure is 2.0bar~3.5bar, and the holding time is 10s~25s;

[0030] In step S2, the vacuum degree of the vacuuming process is -80Kpa to -85Kpa, and the evacuation time is not less than 5 minutes.

[0031] In step S3, the curing temperature of the lamination curing is 120℃~140℃, the pressure is 0.8Mpa~1.2Mpa, and the curing time is 60min~90min.

[0032] Thirdly, the present invention also provides a PDLC dimming glass assembly, including the flexible circuit board described above, as well as a PDLC film, a glass substrate and a thermoplastic resin film. The flexible circuit board is connected to the electrode layer of the PDLC film through an anisotropic conductive film, and is integrally bonded to the glass substrate and the thermoplastic resin film through a lamination process.

[0033] By adopting the above technical solution, the three-segment hollow flexible circuit board, PDLC dimming glass assembly and its preparation method provided by the present invention have the following beneficial effects:

[0034] The flexible circuit board provided by the present invention has multiple functional cutout structures symmetrically distributed on both sides of its width direction. Along the length direction, each functional cutout structure is divided into a lamination functional area (length ≥ 1 mm), a lamination buffer area (length adjusted according to the glass size), and an exposed venting area (length ≥ 5 mm).

[0035] This design significantly improves the bonding strength and reliability of the interface. The pressing functional area and the anisotropic conductive film form a mechanically interlocked anchoring interface, increasing the pull-out strength between the flexible circuit board and the PDLC film electrode layer from the conventional 0.8 N / mm to no less than 1.3 N / mm. This fully meets the requirements of the automotive electronics industry standard QC / T 1096-2021 for dynamic vibration testing and reduces the risk of interface delamination by more than 90%. After rigorous temperature cycling tests from -40℃ to 85℃, its pull-out strength retention rate still reaches 92%.

[0036] This design effectively alleviates thermal and mechanical stress, thereby improving product durability. The lamination buffer can absorb more than 65% of thermal expansion stress, ensuring uniform stress distribution across the flexible circuit board during the cooling phase and preventing localized stress concentration. This significantly reduces the wrinkle rate of the flexible circuit board from the conventional 12% to below 0.3%, while effectively preventing breakage of conductive lines due to stress concentration. After 100 repeated 180° bending tests with a bending radius of 5mm, the circuit conductivity remains at 100%.

[0037] Furthermore, this design optimizes the venting path, significantly reducing residual bubbles. The exposed venting area extends directly to the outside of the glass substrate, forming a direct venting path connected to the vacuum system. This reduces the bubble rate around the flexible circuit board after lamination from 5%-8% in existing processes to below 0.1%, increasing the product appearance pass rate to 99.9%. This structure is particularly suitable for packaging curved or large-size PDLC dimming films, completely eliminating interlayer bubble residue and significantly improving packaging quality and product consistency. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A schematic diagram of a flexible circuit board provided in an embodiment of the present invention;

[0040] Figure 2 A partial schematic diagram of a PDLC dimming glass assembly provided in an embodiment of the present invention;

[0041] Figure 3 Provided for embodiments of the present invention Figure 2 Enlarged view of point A in the middle;

[0042] Figure 4 This is a schematic diagram of the anti-rebound protrusion provided in an embodiment of the present invention.

[0043] The following is supplementary explanation of the attached figures:

[0044] 1-Flexible circuit board; 11-Flexible insulating substrate; 111-Functional cutout structure; 112-Anti-wrinkle cutout structure; 113-Non-cutout body; 12-Conductive circuit layer; 13-Anti-wrinkle corner; 14-Anti-rebound protrusion;

[0045] 100 - Lamination functional area; 200 - Lamination buffer zone; 300 - Exposed venting area;

[0046] 2-PDLC membrane;

[0047] 3-Glass substrate;

[0048] 4-Anisotropic conductive adhesive film. Detailed Implementation

[0049] 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0050] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. In the description of the invention, it should be understood that the terms "upper," "lower," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0051] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0052] Please see Figure 1This invention provides a three-segment hollow flexible circuit board 1 for use in PDLC dimming films, comprising a flexible insulating substrate 11 (such as a polyimide (PI) substrate or a polyethylene terephthalate (PET) substrate) and a conductive circuit layer 12 (e.g., copper foil) formed on the surface of the flexible insulating substrate 11. The core improvement of this invention lies in the fact that the flexible circuit board 1 has multiple functional hollow structures 111 symmetrically distributed on both sides of its width direction. Along its length direction, each functional hollow structure 111 can be sequentially divided into a lamination functional area 100 (length ≥ 1 mm), a lamination buffer area 200 (length depends on the glass size), and an exposed venting area 300 (length ≥ 5 mm), with the three segments continuously connected to form a complete channel. Wherein:

[0053] The pressing functional area 100 is the core functional area where the flexible circuit board 1 and the electrode layer of the PDLC film 2 achieve electrical connection through the anisotropic conductive adhesive film 4. The cutout length of the pressing functional area 100 is not less than 1 mm, which is precisely matched with the conventional bonding length of the anisotropic conductive adhesive film 4, thereby ensuring the formation of a sufficiently large and uniform electrical contact interface. During the hot pressing process, the molten anisotropic conductive adhesive film 4 is fully embedded and filled, and after curing, a three-dimensional mechanical interlocking system is formed that penetrates the conductive layer. This anchoring mechanism, similar to a "rivet," not only enhances the reliability of the interface connection, but also effectively improves the peel strength and long-term environmental resistance of the bonded structure by increasing the mechanical interlocking force.

[0054] The lamination buffer zone 200 serves as a transition area between the lamination functional area 100 and the exposed venting area 300, and the length of its cutout area is determined by the size of the glass substrate 3. This section lies within the composite encapsulation range of the glass substrate 3 and the PDLC film 2, providing ample space to meet the flow and filling requirements of encapsulation materials (such as PVB film) during the lamination process. Simultaneously, the lamination buffer zone 200 effectively absorbs and disperses thermal stress generated at the interface due to differences in thermal expansion coefficients, thereby reducing localized deformation concentration of the flexible circuit board 1 and ensuring the long-term mechanical stability and reliability of the encapsulation structure.

[0055] The exposed venting area 300, as the exposed end portion of the flexible circuit board 1 extending beyond the encapsulation boundary of the glass substrate 3, has a cutout area length designed to be no less than 5mm. During the lamination and vacuuming of multiple layers of materials such as the glass substrate 3, PDLC film 2, FPC, and adhesive film, if... Figure 3 As shown, this area forms an exhaust channel that is directly connected to the external environment, providing a clear escape path for air and volatile substances within the encapsulation gap, effectively preventing air bubble residue. By placing the exhaust zone completely outside the glass lamination area, it is possible to ensure that gases are efficiently discharged during the vacuum suction and hot pressing stages of the lamination process.

[0056] Optional, please continue reading Figure 1 The flexible circuit board 1 has at least one anti-wrinkle cutout structure 112 in the middle region of its width direction. At the same length reference position as the functional cutout structure 111, the cutting depth of the anti-wrinkle cutout structure 112 towards the interior of the non-cutout body 113 is greater than the cutting depth of the corresponding side of the functional cutout structure 111. The acute angle between the line connecting the near-end inner edge vertex of the anti-wrinkle cutout structure 112 and the corresponding inner edge vertex of the nearest functional cutout structure 111 at the same position, and the reference line parallel to the width direction, is defined as the anti-wrinkle angle 13, which ranges from 11° to 25°. The anti-wrinkle cutout structure 112 provides additional deformation release space for the substrate in the lamination area by locally physically separating the flexible circuit board 1 substrate, effectively dispersing local stress concentration caused by thermal expansion and contraction, thereby preventing wrinkles from forming on the flexible circuit board 1 during temperature cycling. Meanwhile, by controlling the anti-wrinkle angle 13 within the range of 11° to 25°, the relative positional relationship between the anti-wrinkle hollow structure 112 and the ends of the adjacent functional hollow structure 111 is precisely defined: the connecting area formed by the end connection constitutes a transition zone that can buffer stress; while the non-hollow body 113 near the pressing functional area is prone to transmitting tangential stress to the upper connecting area when under force, thus affecting the stability of the conductive lines in the pressing area. By using a smaller anti-wrinkle angle 13, the angle between the direction of the tangential stress borne by the transition zone and the adjacent non-hollow body 113 can be kept within a small range. This not only helps to utilize the space between different hollow ends to achieve stress relief, but also the increased effective connection area between the ends improves the overall tensile strength, thereby enhancing the structural stability of the flexible circuit board 1 in the glass lamination area and extending its service life.

[0057] Optionally, each functional cutout structure 111 is a rectangular hole; the width of a single rectangular hole is 0.6~1.0mm, preferably 0.8mm, and the number is 6~10, preferably 8.

[0058] Optionally, the center-to-center distance between two adjacent functional cutout structures 111 is 3-5 mm, which can be adaptively adjusted according to the actual total width of the flexible circuit board 1. Meanwhile, the distance between the outermost functional cutout structure 111 and the corresponding edge of the flexible circuit board 1 is not less than 2.6 mm. This ensures the integrity of the functional structure while effectively maintaining the mechanical strength of the edge area of ​​the flexible circuit board 1, avoiding the risk of structural weakening or processing tearing due to the cutouts being too close to the edge.

[0059] Optionally, the conductive circuit layer 12 is printed on the surface of the flexible insulating substrate 11, and its wiring layout strictly avoids the functional cutout structure 111; the distance between the conductive circuit layer 12 and the edge of any functional cutout structure 111 is not less than 0.6mm, to ensure that the circuit is not damaged during the cutout process, and to avoid squeezing the circuit when the PVB film is filled; at the same time, the conductive circuit layer 12 maintains a clearance distance of 1mm to 2mm from the edge of the flexible insulating substrate 11 (PI or PET), forming a complete covering structure to avoid the risk of arcing caused by the exposure of the conductive circuit layer 12. At the same time, this clearance distance has been verified by insulation testing and can meet the safety requirements of various scenarios.

[0060] Optionally, the electrode leads of the conductive circuit layer 12 are located at the far end of the exposed venting area 300, i.e., at the free end of the functional area; in the length direction of the flexible circuit board 1, the distance between the electrode leads and the nearest functional cutout structure 111 is not less than 3mm, providing a stable and reliable electrical contact area for external wiring or connector installation.

[0061] Optionally, the edge of the lamination buffer 200 is provided with anti-rebound protrusions 14. For example... Figure 4 Two dashed lines mark the pressing partition line between the pressing functional area 100 and the lamination buffer zone 200, and the exposed partition line between the lamination buffer zone 200 and the exposed venting area 300, respectively. The anti-backflow protrusion 14 is preferably located near the pressing partition line. The anti-backflow protrusion 14 extends obliquely from its root towards the outside of the lamination buffer zone 200, with its outer surface forming an angle of 33° to 64° with the plane of the lamination buffer zone 200. It is used to prevent the thermoplastic resin film from flowing back into the pressing functional area 100 during lamination and to enhance the buffering stress of the pressing functional area 100. The anti-backflow protrusion 14 can effectively guide the thermoplastic resin film (such as PVB) to fill the buffer zone during the lamination process, while preventing the film from flowing back towards the pressing functional area 100, thus avoiding the impact on electrical performance due to adhesive contamination of the bonding interface. In addition, the anti-backflow protrusion 14 enhances the lateral support of the pressing functional area 100 through its geometry during lamination, further improving the ability to buffer local stress.

[0062] This invention also provides a fabrication process for a flexible circuit board with a three-segment hollow structure for PDLC dimming film. The hollow structure is processed by ultraviolet laser cutting (dimensional accuracy ±0.01mm) or precision die punching (dimensional accuracy ±0.03mm). Both processes can ensure that the vertical deviation of the hollow edge is no more than 0.02mm, and the processed surface is free of defects such as burrs, collapsed edges, and material tears. This provides a smooth and vertical structural channel for subsequent processes, ensuring that the PVB film can flow smoothly along the hole wall to fill the gap during lamination, and ensuring that the ACF forms a tight and complete interface with the hollow area during hot pressing, achieving reliable mechanical anchoring and electrical connection.

[0063] This invention also provides a method for preparing a PDLC dimming glass assembly, the method comprising the following steps:

[0064] S1: Pre-pressing: The above-mentioned flexible circuit board 1 is pre-pressed with the electrode layer (such as ITO) of the PDLC film 2 through the anisotropic conductive adhesive film 4 to achieve precise alignment and bonding. During the hot pressing process, the ACF adhesive fully fills the hollow structure and cures to form a mechanically interlocked "anchoring structure". Compared with the traditional planar bonding method, this structure increases the effective electrical contact area by more than 35% and improves the interface pull-out strength by more than 40%, fundamentally overcoming the problem of insufficient connection reliability caused by relying solely on the surface adhesion of the adhesive layer.

[0065] S2: Vacuuming and Exhausting: The pre-pressed flexible circuit board 1 and PDLC film 2 are placed between two glass substrates 3, and a thermoplastic resin film (such as polyvinyl butyral PVB) is placed between them, so that the exposed exhaust area 300 of the flexible circuit board 1 extends beyond the edge of the glass substrate 3; the laminated assembly is vacuumed; the exposed exhaust area 300 is directly connected to the vacuuming equipment, and the originally closed interlayer gaps in the glass substrate-PDLC-FPC composite structure are transformed into efficient exhaust channels with the external environment through the continuous three-segment hollow structure on the flexible circuit board 1. This structure improves the efficiency of interlayer air exhaust by more than 95%, fundamentally eliminating air residue in the encapsulation gaps and preventing the generation of bubble defects from the source.

[0066] S3: Lamination and Curing: The degassed laminated assembly is placed in a laminator for lamination and curing. Under high temperature, the PVB film melts and flows, rapidly filling the micro-gap between the FPC and the glass substrate 3 through the continuous perforated channels of the lamination buffer 200 in the flexible circuit board 1. At the same time, residual air is smoothly guided to the outside of the glass and discharged along the channels. The lamination buffer 200 structure effectively absorbs and disperses the interfacial stress caused by the difference in the thermal expansion coefficients of the materials during this process, preventing the flexible circuit board 1 from buckling or excessively deforming, thereby ensuring the integrity of the encapsulation interface and long-term structural stability.

[0067] Optionally, the pre-pressing in step S1 is the stage of pressing the PDLC film 2 and the flexible circuit board 1 together. Under the conditions of temperature 200℃~230℃, pressing pressure 2bar~3.5bar, and holding for 10s~25s, the anisotropic conductive adhesive film 4 begins to soften and flow, filling the gaps in the hollow structure of the flexible circuit board 1, and then curing to form an adhesive interface. If the temperature is too low (<200℃), the ACF adhesive film has poor fluidity and cannot fully fill the gaps, easily generating bubbles and delamination. If the pressure is too low (<2bar), the adhesive layer and the PDLC film 2 are not pressed tightly together, and gaps are easily generated at the edges, resulting in poor vacuum pumping effect. If the holding time is too short (<10s), the ACF adhesive film is not fully cured, the peel strength is insufficient, and it is easy to delaminate during subsequent high-temperature and high-pressure curing. Excessive temperature (>230℃) causes the ACF film to flow excessively, potentially overflowing and contaminating the electrodes of PDLC film 2. Simultaneously, PDLC film 2 may suffer structural damage due to the excessive temperature. Excessive pressure (>3.5 MPa) causes PDLC film 2 to deform under pressure, affecting its photoelectric performance; in severe cases, it may even cause PDLC film 2 to rupture. Excessive time (>30 seconds) reduces production efficiency and may lead to material aging due to prolonged heating.

[0068] In step S2, the vacuuming process ensures that the air and moisture between the PDLC film 2 and the glass substrate 3 are fully removed in a vacuum environment, ensuring that the adhesive layer is free of bubbles and improving the bonding strength and optical performance. If the vacuum level is insufficient (>-80Kpa), the bubbles cannot be completely removed, resulting in defects such as bubbles and cloud marks in the finished product. If the time is too short (<5min), the venting is insufficient, and the residual bubbles expand during the subsequent high-temperature curing, leading to delamination or bubbles. If the vacuum level is too high (<-85Kpa), the equipment energy consumption increases, and the equipment sealing requirements are extremely high, but the improvement effect is limited.

[0069] In step S3, lamination curing is carried out at a temperature of 120℃~140℃, a pressure of 0.8Mpa~1.2Mpa, and a curing time of 60min~90min. Under these conditions, the PVB film is completely cured, forming a strong adhesive layer. At the same time, the liquid crystal microdroplets in the PDLC film 2 form a stable dispersion structure in the polymer network. If the temperature is too low (<120℃), the polymer cross-linking is insufficient, the adhesive strength is insufficient, and the product is prone to delamination and delamination. If the pressure is too low (<0.8Mpa), the interlayer bonding is not tight, residual air bubbles cannot be discharged, and the optical performance is poor. If the time is too short (<60min), the curing is incomplete, the adhesive strength is low, and the product life is shortened. If the temperature is too high (>140℃), the liquid crystal material may undergo thermal degradation, the dimming function may decrease or even fail, and the polymer may become brittle due to excessive cross-linking. If the pressure is too high (>1.2Mpa), the PDLC film 2 will be deformed under pressure, the liquid crystal microdroplet structure will be destroyed, the photoelectric performance will deteriorate, and the glass may also break. If the time is too long (>90min), energy consumption will increase, production efficiency will decrease, and the material may age due to prolonged high temperature.

[0070] This invention also provides a PDLC dimming glass assembly, including a flexible circuit board 1 with a three-segment hollow structure for PDLC dimming film, a PDLC film 2, a glass substrate 3, and a thermoplastic resin film. The flexible circuit board 1 is connected to the electrode layer of the PDLC film 2 through an anisotropic conductive film 4, and is solidified into a whole with the glass substrate 3 and the thermoplastic resin film through a lamination process.

[0071] The following detailed description of examples of the present invention is exemplary and is used only to explain the present invention, and should not be construed as limiting the present invention.

[0072] Example 1

[0073] A flexible circuit board with a three-segment hollow structure for PDLC dimming films is disclosed. It uses a 0.1mm thick polyimide flexible insulating substrate (model KaptonHN) with overall dimensions of 80mm (width) × 90mm (length). An 18μm thick electrolytic copper foil is used as the conductive circuit layer, printed on both edges of the polyimide flexible insulating substrate. The circuit width is 2mm and the spacing between the circuits is 2mm. A strict 2mm clearance is maintained between the copper foil edge and the edge of the polyimide flexible insulating substrate, and a 0.6mm distance is maintained between the copper foil edge and the edge of the functional hollow area. The electrode lead-out end is located at the end of the exposed venting area, with a length of 10mm. The flexible circuit board has eight functional hollow structures symmetrically distributed on both sides along its width, and one anti-wrinkle hollow structure distributed in the middle. The eight functional cutout structures are divided along their length into a lamination zone (1mm long), a lamination buffer zone (12mm long), and an exposed venting zone (5mm long). The total cutout length is 18mm, and the non-cutout body length is 72mm. Each functional cutout structure and anti-wrinkle cutout structure measures 0.8mm (width) × 18mm (length). The center-to-center distance between adjacent functional cutout structures is approximately (80mm - 36mm - 4 × 4.6mm) / 6 ≈ 4.27mm (meaning the distance from the boundaries of the two outer and two inner functional cutout structures to the edge of the flexible circuit board is 4.6mm, the total width of the flexible circuit board is 80mm, and the distance between the inner boundaries of the two lamination zones is 36mm). The distance between the edge of the outermost functional cutout structure and the corresponding edge of the flexible circuit board is 2.6mm. The cutout structure is processed using a 30W ultraviolet laser at a cutting speed of 50mm / s. After cutting, the perpendicularity deviation of the cutout edge is no greater than 0.01mm and there are no burrs. The anti-wrinkle cutout structure in the middle area is 6mm longer than the corresponding ends of the functional cutout structures on both sides near the non-cutout body. The anti-wrinkle angle between the line connecting the end of this anti-wrinkle cutout structure to the ends of the adjacent functional cutout structures and the baseline parallel to the width direction of the flexible circuit board is 15°. The edge of the lamination buffer zone has an anti-adhesion protrusion that extends obliquely from its root towards the outside of the lamination buffer zone, with its outer surface forming a 45° angle with the plane of the lamination buffer zone.

[0074] A method for preparing a PDLC dimming glass assembly includes the following steps: A flexible circuit board with a three-segment hollow structure is hot-pressed and bonded to the ITO electrode layer of the PDLC film at 215°C and 2.2 bar for 15 seconds using an anisotropic conductive film (ACF); subsequently, the bonded assembly is assembled with two glass substrates and a polyvinyl butyral (PVB) film, extending the exposed venting area of ​​the flexible circuit board beyond the edge of the glass substrate; the assembled assembly is then vacuum-treated at a vacuum level of -83 kPa; finally, the assembly is placed in a laminator and laminated and cured at 130°C and 1.2 MPa for 75 minutes to obtain a bubble-free, low-stress PDLC dimming glass assembly with a strong interfacial bond.

[0075] Example 2

[0076] Referring to the three-segment hollow structure of the flexible circuit board in Embodiment 1, the difference is that two functional hollow structures are set on each side of the flexible circuit board, and the size of each hollow structure is 1.2mm (width) × 28mm (length).

[0077] Example 3

[0078] The flexible circuit board with a three-segment hollow structure as described in Example 1 differs in that the center-to-center distance between two adjacent functional hollow structures is 8 mm.

[0079] Example 4

[0080] The flexible circuit board with a three-segment hollow structure as described in Example 1 differs in that the distance between the outermost functional hollow structure and the corresponding side edge of the flexible circuit board is 2.2 mm.

[0081] Example 5

[0082] Referring to the three-segment hollow structure of the flexible circuit board in Example 1, the difference is that the electrode lead-out end of the conductive line layer is not located at the far end of the exposed venting area, but is moved to the inside of the lamination buffer zone, and the distance between it and the nearest functional hollow structure is 1.5mm.

[0083] Example 6

[0084] Referring to the three-section hollow structure of the flexible circuit board in Embodiment 1, the difference is that the eight functional hollow structures and the anti-wrinkle hollow structures are set flush with the end face of the end of the flexible circuit board that is close to the non-hollow body.

[0085] Example 7

[0086] The flexible circuit board with a three-section hollow structure, as described in Example 1, differs in that the edge of the lamination buffer zone does not have an anti-backflow protrusion structure.

[0087] Comparative Example 1:

[0088] The flexible circuit board with a three-section hollow structure, as described in Example 1, differs in that it is simply hollowed out without functional zoning design for the hollowed-out area.

[0089] Comparative Example 2:

[0090] Referring to the three-section hollow structure of the flexible circuit board in Example 1, the difference is that the hollow length of the lamination functional area is reduced to 0.5mm, the hollow length of the lamination buffer is correspondingly extended to 12.5mm, and the hollow length of the exposed venting area remains at 5mm.

[0091] Comparative Example 3:

[0092] The flexible circuit board with a three-section hollow structure, as described in Example 1, differs in that the hollow length of the lamination functional area is 1mm, the hollow length of the lamination buffer zone is 14mm, and the hollow length of the exposed venting area is 3mm.

[0093] Test example:

[0094] Systematic testing and reliability evaluation were conducted on the PDLC dimming glass assemblies prepared in Examples 1-7 and Comparative Examples 1-3. The tests included appearance integrity, interfacial bonding strength, environmental tolerance, and long-term electromechanical reliability. Specifically, this included: macroscopic defect detection after lamination according to GB / T 17468, evaluating appearance quality such as bubbles and wrinkles through visual and microscopic observation; accelerated environmental aging testing according to IEC 60068-2-67, continuously treating at 85℃ / 85%RH for 1000 hours to simulate a harsh service environment, and retesting the pull-out force after aging to evaluate long-term reliability; and bonding strength pull-out force testing of the flexible circuit board and PDLC film interface according to IPC-TM-650, using a tensile testing machine to quantify the mechanical strength of the ACF bonding interface. The test results are summarized in Table 1.

[0095] Table 1:

[0096]

[0097] Test results show that, compared to the traditional structure (Comparative Example 1), the pull-out force of Example 1 increased significantly from 0.85 N / mm to 1.4 N / mm, an increase of over 64%, while the bubble rate decreased from 4.5% to 0.08% and the wrinkle rate decreased from 10.5% to 0.2%. Furthermore, the pull-out force retention rate reached 92% after rigorous aging tests, fully verifying the comprehensive advantages of this design in enhancing interface anchoring strength, completely eliminating lamination bubbles, effectively dispersing thermal stress, and ensuring long-term reliability. Specifically, insufficient length of the pressing functional area in Comparative Example 2 leads to a significant decrease in pull-out force and aging retention rate, while insufficient length of the exposed venting area in Comparative Example 3 causes a sharp increase in the bubble rate to 2.8%. This, in turn, confirms the necessity of the three-section partition size collaborative design. Simultaneously, the lack of optimized features such as anti-wrinkle corners and anti-rebound protrusions in the examples (not adopted or optimized in Examples 6 and 7) also affects the anti-wrinkle and venting effects to some extent, further highlighting the systematic nature of the overall technical solution of this invention.

Claims

1. A three-segment hollow flexible circuit board for use in PDLC dimming film, comprising a flexible insulating substrate (11) and a conductive line layer (12) formed on the surface of the flexible insulating substrate (11), characterized in that: The flexible circuit board has multiple functional cutout structures (111) symmetrically distributed on both sides of its width direction. Along its length direction, each functional cutout structure (111) is sequentially divided into a lamination functional area (100), a lamination buffer area (200), and an exposed venting area (300), wherein: The hollow length of the pressing functional area (100) is not less than 1 mm, and it is used to interlock with the anisotropic conductive adhesive film (4) to form a mechanical anchoring interface. The cutout length of the lamination buffer (200) depends on the size of the glass substrate (3) and is used to absorb thermally induced deformation stress in the lamination process and to provide a flow-filling channel for liquid or molten thermoplastic resin film. The exposed exhaust area (300) has a cutout length of not less than 5 mm. It is the end part of the flexible circuit board extending from the edge of the glass substrate (3) and is used to establish a direct exhaust path that communicates with the external environment during the lamination process.

2. The flexible circuit board according to claim 1, characterized in that, The flexible circuit board has at least one anti-wrinkle cutout structure (112) in the middle region of its width direction. Among them, at the same length reference position as the functional hollow structure (111), the cutting depth of the anti-wrinkle hollow structure (112) toward the interior of the non-hollow body (113) is greater than the cutting depth of the corresponding side of the functional hollow structure (111). The acute angle between the line connecting the near inner edge vertex of the anti-wrinkle hollow structure (112) and the corresponding inner edge vertex of the nearest functional hollow structure (111) at the same position, and the baseline parallel to the width direction, is defined as the anti-wrinkle angle (13). The value range of the anti-wrinkle angle (13) is 11°~25°.

3. The flexible circuit board according to claim 1, characterized in that, Each of the aforementioned functional hollow structures (111) is a rectangular hole; the width of each rectangular hole is 0.6~1.0mm, and the number of such holes is 6~10.

4. The flexible circuit board according to claim 1, characterized in that, The center-to-center distance between two adjacent functional cutout structures (111) is 3~5mm, and the distance between the outermost functional cutout structure (111) and the corresponding side edge of the flexible circuit board is not less than 2.6mm.

5. The flexible circuit board according to claim 1, characterized in that, The distance between the conductive circuit layer (12) and the edge of any of the functional hollow structures (111) is not less than 0.6 mm, and a clearance distance of 1~2 mm is maintained between the conductive circuit layer (12) and the edge of the flexible insulating substrate (11).

6. The flexible circuit board according to claim 1, characterized in that, The electrode lead-out end of the conductive circuit layer (12) is located at the end of the exposed venting area (300), and the distance between it and the nearest functional hollow structure (111) is not less than 3 mm.

7. The flexible circuit board according to claim 1, characterized in that, The edge of the laminated buffer zone (200) is provided with anti-rebound protrusions (14); the anti-rebound protrusions (14) extend obliquely from their roots toward the outside of the laminated buffer zone (200), and the angle between their outer surface and the plane of the laminated buffer zone (200) is 33°~64°.

8. A method for preparing a PDLC dimming glass assembly, characterized in that, The method Includes the following steps: S1: Pre-pressing: The flexible circuit board according to any one of claims 1-7 is pre-pressed to the electrode layer of the PDLC film through an anisotropic conductive adhesive film (4); S2: Vacuuming and venting: The pre-pressed flexible circuit board and PDLC film are placed between two glass substrates (3), and a thermoplastic resin film is placed therebetween, so that the exposed venting area (300) of the flexible circuit board extends out of the edge of the glass substrate (3); the lamination assembly is vacuumed. S3: Lamination and curing: The degassed laminated assembly is placed in a laminator for lamination and curing.

9. The preparation method according to claim 8, characterized in that: In step S1, the pre-pressing temperature is 200℃~230℃, the pressing pressure is 2.0bar~3.5bar, and the holding time is 10s~25s; In step S2, the vacuum degree of the vacuuming process is -80Kpa to -85Kpa, and the evacuation time is not less than 5 minutes. In step S3, the curing temperature of the lamination curing is 120℃~140℃, the pressure is 0.8Mpa~1.2Mpa, and the curing time is 60min~90min.

10. A PDLC dimming glass assembly, characterized in that, The flexible circuit board includes any one of claims 1-7, a PDLC film (2), a glass substrate (3), and a thermoplastic resin film. The flexible circuit board is connected to the electrode layer of the PDLC film (2) through an anisotropic conductive film (4), and is solidified into a single unit with the glass substrate (3) and the thermoplastic resin film through a lamination process.

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