Preparation method of transparent conductive adhesive sheet by online regulation of resistance through elastic stretching

Abstract

This invention discloses a method for preparing a transparent conductive film with online controllable resistance through elastic stretching, comprising the following steps: S1, forming a trench network on a flexible transparent polymer substrate; S2, elastically stretching the flexible transparent polymer substrate with the trench network, and adjusting the stretching rate according to the target sheet resistance using a stretching device; S3, filling the trench network with conductive material while stretched; S4, releasing the stretching force to allow the flexible transparent polymer substrate to elastically retract. The advantage of this invention is that it enables online, real-time, and continuous control of resistance, allowing the same production line to produce products with different resistance specifications without stopping for product changes.

Description

Technical Field

[0001] This invention relates to the field of functional material preparation technology, and in particular to a method for preparing transparent conductive films by online control of resistance through elastic stretching. Background Technology

[0002] Transparent conductive materials are core functional materials for optoelectronic devices, and their technological development has evolved from controlling the intrinsic properties of materials to designing spatial structures. Based on the fundamental principles of achieving transparent conductivity, existing technologies can be mainly divided into two categories: material-based transparent conductive technology and structural transparent conductive technology.

[0003] In the field of material-based transparent conductive technology, the core idea is to seek a balance between conductivity and transparency through the inherent properties of the material itself. Transparent conductive oxides (TCOs) are a typical example of this technology, with indium tin oxide (ITO) being the most widely used material. The conductivity mechanism of TCOs is achieved by introducing charge carriers (electrons or holes) through doping, allowing them to move freely within the material and form an electric current. However, while increasing the carrier concentration improves conductivity, it also enhances the absorption of visible light (free carrier absorption effect), leading to a decrease in transmittance. Therefore, TCO technology essentially involves a trade-off between conductivity and transparency, precisely controlling the carrier concentration to achieve a critical state of "just enough conductivity, just enough transparency." Besides ITO, fluorine-doped tin oxide (FTO) and aluminum-doped zinc oxide (AZO) are also commonly used TCO materials. The advantages of this type of technology are mature processes and continuous and uniform conductive layers, but it generally suffers from problems such as high brittleness (due to the nature of ceramic materials), scarcity of indium resources (ITO), and high-temperature processes (unsuitable for flexible substrates).

[0004] In recent years, with the rapid development of emerging applications such as flexible electronics, smart windows, and wearable devices, higher requirements have been placed on transparent conductive materials: they not only need high transparency (>85%) and high conductivity (sheet resistance <20Ω / □), but also excellent flexibility (bendable and rollable), compatibility with glass lamination processes (high temperature and high pressure resistance), long-term reliability (resistant to aging and environmental corrosion), and adjustable resistance (multi-specification production). Existing technologies have significant shortcomings in these aspects and are unable to meet the comprehensive needs of high-end applications.

[0005] A comprehensive analysis of existing resistance control technologies reveals the following main shortcomings:

[0006] First, there is a lack of online control capability. Most existing methods adjust resistance before preparation (material formulation) or after preparation (post-processing), failing to provide real-time, online adjustment of resistance values ​​during continuous production. This limits a production line to producing only fixed specifications; different specifications require shutdown and reconfiguration, resulting in low production efficiency and high costs. With increasingly personalized and customized market demands, the lack of online control capability has become a significant bottleneck restricting the development of the transparent conductive materials industry.

[0007] Second, the trade-off between control and performance is difficult to resolve. Existing methods often sacrifice other properties when adjusting resistance. For example, reducing resistance requires increasing the amount of conductive material, leading to decreased transmittance, increased cost, and reduced flexibility; increasing resistance requires reducing conductive material, but this may result in discontinuous conductive networks and poor stability. How to maintain a balance between transmittance, flexibility, stability, and other properties while adjusting resistance is a problem that existing technologies struggle to solve.

[0008] Third, continuous and precise resistance control is not possible. Most existing methods can only switch between limited discrete values ​​(such as 5Ω / □, 10Ω / □, 20Ω / □), and cannot achieve continuous resistance adjustment (such as arbitrary values ​​like 5.5Ω / □, 7.2Ω / □, etc.). This discrete control limits the refined application of the product, especially in high-end applications requiring precise matching of circuit parameters, where existing methods are insufficient.

[0009] Fourth, changeover costs are high and production flexibility is poor. For companies that need to produce multiple specifications of products, existing methods require preparing multiple sets of molds, photomasks, or material formulas. Changeovers require machine downtime, cleaning, and debugging, which can take several hours or even days, severely impacting production efficiency. In addition, small-batch, multi-variety orders are often not accepted due to excessively high changeover costs, limiting the company's market competitiveness.

[0010] Fifth, the control mechanism is disconnected from the product structure. Existing control methods often focus only on the resistance value itself, neglecting the impact of the control mechanism on the product structure, reliability, and long-term stability. For example, reducing resistance by increasing the thickness of the conductive material may lead to a decrease in the adhesion between the conductive layer and the substrate, making it prone to detachment; changing resistance through chemical treatment may introduce impurities or damage the interface. The lack of control methods designed in conjunction with the product structure makes it difficult to achieve high-performance, high-reliability transparent conductive materials. Summary of the Invention

[0011] The purpose of this invention is to provide a method for preparing transparent conductive film with online control of resistance through elastic stretching, so as to realize online, real-time and continuous control of resistance, and enable the same production line to produce products with different resistance specifications without stopping the machine to change the model.

[0012] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for preparing a transparent conductive film with online control of resistance through elastic stretching includes the following steps: S1, forming a trench network on a flexible transparent polymer substrate; S2, elastically stretch a flexible transparent polymer substrate with a grooved network, and adjust the stretching rate according to the target sheet resistance using a stretching device. S3, under tension, the interior of the trench network is filled with conductive material; S4 releases the tensile force, allowing the flexible transparent polymer substrate to elastically retract.

[0013] Preferably, in step S1, the trench network is formed on a flexible transparent polymer substrate by crack mask etching, nanoimprinting or laser direct writing, and the original width of the trench network is 0.01~2μm.

[0014] Preferably, the flexible transparent polymer substrate in step S1 is selected from at least one of polyvinyl chloride butyral, polyurethane, polycarbonate, polyethylene terephthalate, and polymethyl methacrylate.

[0015] Preferably, in step S2, the stretching ratio of the flexible transparent polymer substrate is adjusted within the range of 5% to 30%, and the corresponding sheet resistance of the transparent conductive film is adjusted within the range of 0.005 to 1000 Ω / □.

[0016] Preferably, the conductive material in step S4 is selected from at least one of gold, silver, copper and their alloys.

[0017] Preferably, the sheet resistance is detected by a four-probe method or a non-contact surface resistivity meter.

[0018] Preferably, in step S2, the elastic stretching direction is uniaxial or biaxial, and the stretching rate is 0.1~5% / min.

[0019] Preferably, the acceptable deviation of the target sheet resistance in step S3 is ±5%.

[0020] Preferably, in step S4, the final stretched state needs to be maintained for 30~120s before the conductive material is filled.

[0021] In summary, the present invention has the following beneficial effects: (1) Achieve online, real-time, and continuous control. The control method of this invention is fully integrated into a continuous production line, with the stretching, filling, and shrinking processes carried out continuously without downtime. By adjusting the stretching force in real time, the product resistance can be changed within seconds, achieving true online control. In contrast, existing methods require downtime for model changes (several hours) or material formula changes (several days), resulting in a huge difference in production efficiency. Experiments show that using the method of this invention, the same production line can complete the continuous production of five different resistance specifications (5Ω / □, 10Ω / □, 15Ω / □, 20Ω / □, 30Ω / □) within 30 minutes, while the traditional method requires more than 8 hours (including model changeover time) to complete the same task.

[0022] (2) Balancing regulation and performance The resistance control of this invention is achieved solely by changing the geometry of the trench, without altering the type, purity, or amount of the conductive material. Therefore: the transmittance remains essentially unchanged (change <2%) because the total amount of conductive material remains constant, only the distribution density changes; the flexibility remains essentially unchanged because the substrate material and thickness remain constant, and the embedded structure itself possesses excellent flexibility; the stability remains essentially unchanged because the bonding method between the conductive material and the substrate remains unchanged, and the clamping force even increases with retraction. In contrast, existing methods often sacrifice other properties when controlling resistance, such as increasing the thickness of the conductive material reducing transmittance and increasing brittleness; and chemical treatment introducing impurities and reducing stability.

[0023] (3) Continuous and precise control to meet the needs of refined management. The elongation of this invention can be continuously adjusted within the range of 1% to 30%, and the corresponding resistance value can also be continuously varied. Taking the PVB / Ag system as an example, an elongation of 5% corresponds to a sheet resistance of approximately 5 Ω / □, 10% corresponds to approximately 8 Ω / □, 15% corresponds to approximately 12 Ω / □, 20% corresponds to approximately 18 Ω / □, and 30% corresponds to approximately 35 Ω / □. Any value in between (such as 7.5 Ω / □, 13.2 Ω / □) can be achieved by precisely controlling the elongation. This continuous and precise control capability meets the requirements of high-end applications (such as precision circuits, adjustable heaters) for precise resistance matching, which cannot be achieved by existing discrete control methods (which can only switch between standard specifications such as 5 Ω / □, 10 Ω / □, 20 Ω / □).

[0024] (4) Extremely low changeover cost and extremely high production flexibility. The changeover process of this invention involves only adjusting the tensile force, without requiring changes to molds, masks, or materials. Changeover time is reduced from hours to minutes, and changeover costs are reduced by over 90%. This makes small-batch, multi-variety, and customized production economically feasible, allowing companies to accept more diverse orders and improve market competitiveness. For example, a customer needs three specifications of products: 100 square meters of 5Ω / □, 50 square meters of 12Ω / □, and 20 square meters of 25Ω / □. Using the method of this invention, continuous production can be achieved on the same production line in approximately 2 hours; while the traditional method requires three changeovers, with a total time exceeding one day.

[0025] (5) Enhance product structure through regulation process The unique feature of this invention lies in the fact that the regulation process itself enhances the product structure: stretching widens the grooves, facilitating the filling and penetration of conductive materials; after filling, retraction narrows the grooves, generating lateral pressure on the conductive materials and forming an elastic clamping force; the clamping force increases with the amount of retraction (i.e., elongation), thus products with high resistance specifications (high elongation) actually have stronger bonding force. This synergistic effect of "regulation-enhancement" allows the product of this invention to achieve the required resistance while also improving structural reliability, whereas existing methods often require a trade-off between regulating resistance and ensuring reliability.

[0026] (6) Closed-loop control, high precision and good stability The control method of this invention can be combined with an online resistance monitoring system to achieve closed-loop control: real-time monitoring of product resistance → comparison with the target value → feedback adjustment of the tensile force → bringing the actual resistance close to the target value. This closed-loop control can control the resistance deviation within ±5%, which is much higher than open-loop control (±15%) and batch fluctuations (±20%) of traditional methods. Furthermore, due to the rapid stretching-retraction process (within seconds), the system responds quickly, has strong disturbance suppression capabilities, and exhibits good production stability. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below. These embodiments do not constitute a limitation on the present invention.

[0028] Example 1: Quantitative verification of the effect of different elongation rates on electrical resistance Materials preparation: Substrate: PVB film, 0.76 mm thick, with a trench network fabricated on the surface (original trench width approximately 500 nm, depth approximately 300 nm); Conductive material: silver target (99.99% purity).

[0029] Equipment: Precision tensile testing machine, tensile accuracy ±0.1%, maximum elongation 50%; magnetron sputtering instrument; four-probe sheet resistance tester; ultraviolet-visible spectrophotometer.

[0030] Experimental design: Six groups of samples were prepared with elongation rates of 0% (control group), 5%, 10%, 15%, 20%, and 30%, respectively. Each group had three parallel samples.

[0031] Preparation steps: 1. Fix the grooved PVB sample onto the tensile testing machine fixture; 2. Stretch at a rate of 1 mm / min to the target elongation (0%, 5%, 10%, 15%, 20%, 30%). 3. While maintaining the stretched state, silver was filled into the trench using magnetron sputtering at a power of 80W for a deposition time of 5 minutes; 4. Maintain the stretched state for 10 minutes to allow the silver layer to stabilize; 5. Release the tensile force at a rate of 1 mm / min to allow the sample to retract; 6. Remove the sample and conduct performance testing.

[0032] Test results:

[0033] The table above shows the relationship between resistance and elongation: the sheet resistance R is positively correlated with the elongation ε, and the fitted curve is R = 4.2 × exp(0.12ε), with a correlation coefficient R² = 0.998; the transmittance changes: as the elongation increases, the transmittance slowly increases from 85% to 91%, with a small change range, indicating that the resistance adjustment has little effect on the transmittance; the peel strength changes: as the elongation increases, the peel strength increases from 4.8 N / cm to 6.8 N / cm, indicating that the greater the shrinkage, the stronger the gripping force and the better the bonding force.

[0034] Therefore, it can be concluded that by adjusting the elongation rate within the range of 5% to 30%, the sheet resistance can be continuously and precisely controlled within the range of 5Ω / □ to 45Ω / □, while the light transmittance remains basically unchanged, and the bonding force increases with the increase of elongation rate.

[0035] Example 2: Practical Application of Online Control System System components: Unwinding module: PVB roll material, 300mm wide, with pre-prepared groove network; Tension control module: driven by servo motor, tension accuracy ±0.5N, can achieve precise elongation control of 5%~30%; Filling module: Magnetron sputtering equipment for online silver deposition; Retraction module: tension release mechanism, controllable retraction; Rewinding module: Rewinding finished roll materials; Online monitoring module: Four-probe sheet resistance tester, installed before winding, to measure the product resistance in real time; Feedback control module: PLC controller, receives online monitoring data, calculates deviations, and adjusts the tension control module. Production process flow: 1. Unwinding: The PVB roll is unwound at a speed of 0.5 m / min; 2. Tensioning: The tension control module applies a tensile force to the PVB to make the elongation reach the set value; 3. Filling: Under stretched conditions, magnetron sputtering is used to fill the trench with silver for 4 minutes; 4. Retraction: Tension release, PVB elastically retracts; 5. Online monitoring: A four-probe tester measures the sheet resistance of the finished product in real time; 6. Rewinding: Rewinding the finished product; 7. Feedback control: If the deviation between the monitored sheet resistance and the target value exceeds ±5%, the tension will be automatically adjusted to correct the elongation.

[0036] Production Case: A customer order requires the production of three specifications of products: Specification A: Sheet resistance 8±1Ω / □, quantity 100m²; Specification B: Sheet resistance 15±1.5Ω / □, quantity 50m²; Specification C: Sheet resistance 25±2.5Ω / □, quantity 30m².

[0037] Production process: 1. Production Specification A (8Ω / □): According to the calibration curve, 8Ω / □ corresponds to an elongation of approximately 9%; set the tension to make the elongation = 9%; the average sheet resistance monitored online is 8.2Ω / □, which is within the allowable range; complete specification A by continuous production for 200 minutes (100m² ÷ 0.5m² / minute).

[0038] Switch to specification B (15Ω / □): According to the calibration curve, 15Ω / □ corresponds to an elongation of approximately 15%. Adjust the tension to increase the elongation from 9% to 15% (adjustment time is about 30 seconds). The average sheet resistance during online monitoring is 15.3 Ω / □; Production continued for 100 minutes to complete specification B.

[0039] Switch to specification C (25Ω / □): According to the calibration curve, 25Ω / □ corresponds to an elongation of approximately 22%; Adjust the tension to increase the elongation from 15% to 22% (adjustment time is about 30 seconds). The average sheet resistance during online monitoring is 24.8 Ω / □; Production continued for 60 minutes to complete specification C.

[0040] Total production time: 200 + 100 + 60 = 360 minutes (6 hours), including two changeovers (30 seconds each, which can be ignored).

[0041] Compared to traditional methods: If the traditional downtime changeover method is used, each changeover requires: downtime: 5 minutes; mold / mask replacement: 30 minutes; equipment cleaning: 20 minutes; readjustment: 15 minutes; total: 50 minutes / time.

[0042] Producing three specifications requires two model changes, with a total model change time of 100 minutes. The production time is the same (360 minutes), for a total time of 460 minutes (approximately 7.7 hours).

[0043] Efficiency improvement: The total time of the method of this invention is 6 hours, while the traditional method is 7.7 hours, which is an efficiency improvement of about 28%. More importantly, the method of this invention generates no waste (waste generated during changeover and debugging), while the traditional method generates about 5m² of waste per changeover, and a total of 10m² of waste for two changeovers, which increases material costs.

[0044] Example 3: Accuracy Verification of Closed-Loop Control System System Configuration: Target resistance setting: 20Ω / □; allowable deviation: ±5% (i.e., 19~21Ω / □); online monitoring frequency: measurement every 10 seconds; feedback adjustment cycle: tension adjustment every 30 seconds.

[0045] Testing process: The sheet resistance value was recorded during 4 hours of continuous production.

[0046] Results: Average sheet resistance: 20.1 Ω / □; Standard deviation: 0.6 Ω / □; Maximum value: 21.2 Ω / □ (deviation +6%, exceeding the allowable range once, lasting 20 seconds); Minimum value: 19.1 Ω / □ (deviation -4.5%, within the allowable range); Pass rate (within the range of 19~21 Ω / □): 99.2%.

[0047] Compared to open-loop control (without feedback adjustment): Average sheet resistance: 20.5Ω / □; Standard deviation: 2.1Ω / □; Maximum value: 25.3Ω / □ (deviation +26.5%); Minimum value: 16.8Ω / □ (deviation -16%); Pass rate: approximately 75%.

[0048] Conclusion: The closed-loop control system can improve the resistance control accuracy from ±20% (open loop) to ±5% (closed loop) and the pass rate from 75% to over 99%, meeting the requirements of high-end applications for resistance accuracy.

[0049] Example 4: Continuous multi-specification rapid changeover production Production task: An electronics manufacturer needs small batches of transparent conductive films in various specifications for R&D testing. Requirements: Specification 1: 5Ω / □, 10m², Specification 2: 12Ω / □, 10m², Specification 3: 18Ω / □, 10m², Specification 4: 30Ω / □, 10m², Specification 5: 45Ω / □, 10m².

[0050] The method of this invention: Production line speed: 0.5 m² / min; Production time for each specification: 20 minutes (10 m² ÷ 0.5 m). 2 / minute), changeover time: 30 seconds each time (adjust tension), number of changeovers: 4 times (4 changes are required for 5 specifications), total changeover time: 2 minutes, total production time: 100+2=102 minutes (approximately 1.7 hours).

[0051] Traditional method (downtime for changeover): Production time per specification: 20 minutes; Changeover time: 50 minutes per changeover (cleaning + mold change + debugging); Number of changeovers: 4; Total changeover time: 200 minutes (3.3 hours); Total production time: 100 + 200 = 300 minutes (5 hours); Scrap generated: 5m³ per changeover. 2 Scrap materials, totaling 20m 2 (Equivalent to producing two more specifications).

[0052] Advantages Analysis: Time Saving: This invention takes 1.7 hours, compared to the traditional 5 hours, saving 66% of the time; Material Saving: This invention produces no waste, compared to the traditional 20m² waste, saving material costs; Flexibility: This invention can switch to any specification at any time. Traditional methods tend to produce large batches of single specifications due to high changeover costs, making it difficult to meet the needs of small batches and multiple varieties.

[0053] Example 5: Application of fine resistance control (precision circuits) Application Background: A precision electronic device requires a transparent heating film with a sheet resistance of 18.5Ω / □ (with an allowable deviation of ±2%) to achieve precise power control.

[0054] Traditional methods have limitations: standard specifications only include 15Ω / □ and 20Ω / □, and cannot provide 18.5Ω / □; if a custom mold is used to produce 18.5Ω / □, the mold cost is high (about 50,000 yuan), and it can only be used once, which is not economical.

[0055] The method of this invention: According to the calibration curve, 18.5Ω / □ corresponds to an elongation of approximately 17.2%; the elongation is set to 17.2%; the average sheet resistance is monitored online to be 18.4Ω / □, with a deviation of -0.5%, which meets the ±2% requirement; no custom molds are required, and production can proceed directly, with costs only the cost of standard products.

[0056] Result: A transparent heating film of 100m² with a sheet resistance of 18.4Ω / □ was successfully produced, meeting the customer's precise matching requirements. Such fine control cannot be achieved economically using traditional methods.

[0057] Comparative Experiment: A Comprehensive Comparison of the Invention with Existing Control Methods Comparison dimensions: 1. Online control capability: Whether it can be adjusted in real time during continuous production; 2. Adjustable range: The achievable range of resistance variation; 3. Control precision: Deviation is controlled by resistance; 4. Changeover time: The time required to switch specifications; 5. Impact on other properties: Do transmittance, flexibility, etc., change when the resistance is adjusted? Comparison results:

[0058] Conclusion: The stretching control method of the present invention is superior to existing methods in terms of online control capability, control range, control accuracy, changeover speed, and performance maintenance. It is particularly suitable for production scenarios that require multiple specifications, high precision, and rapid changeover.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A method for preparing a transparent conductive film with online controllable resistance through elastic stretching, characterized in that... The steps include the following: S1, forming a trench network on a flexible transparent polymer substrate; S2, elastically stretch a flexible transparent polymer substrate with a grooved network, and adjust the stretching rate according to the target sheet resistance using a stretching device. S3, under tension, the interior of the trench network is filled with conductive material; S4 releases the tensile force, allowing the flexible transparent polymer substrate to elastically retract.

2. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: In step S1, the trench network is etched onto a flexible transparent polymer substrate using a crack mask, and the original width of the trench network is 0.01~2μm.

3. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: In step S1, the flexible transparent polymer substrate is selected from at least one of polyvinyl chloride butyral, polyurethane, polycarbonate, polyethylene terephthalate, and polymethyl methacrylate.

4. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: In step S2, the stretching ratio of the flexible transparent polymer substrate is adjusted within the range of 5% to 30%, and the corresponding sheet resistance of the transparent conductive film is varied within the range of 0.005 to 1000 Ω / □.

5. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: In step S4, the conductive material is selected from at least one of gold, silver, copper and their alloys.

6. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: The sheet resistance is detected by a four-probe method or a non-contact surface resistivity meter.

7. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: In step S2, the elastic stretching direction is uniaxial or biaxial, and the stretching rate is 0.1~5% / min.

8. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: The acceptable deviation of the target sheet resistance in step S3 is ±5%.

9. The method for preparing a transparent conductive film with online control of resistance by elastic stretching according to claim 1, characterized in that: In step S4, the final stretched state needs to be maintained for 30~120s before the conductive material is filled.

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