Selective weak base delamination adhesive for transparent display and method of making the same

Abstract

The application discloses a selective weak base film stripping glue for a transparent display screen and a preparation method thereof. The selective weak base film stripping glue is a two-component type, and is mixed according to a weight ratio before use. According to weight parts, the glue comprises component A 95-99 parts and component B 1-5 parts. The component A further comprises, according to weight parts, alkali-soluble acrylate copolymer 60-95 parts, alkali-soluble monomer 1-3 parts, acid-resistant additive 1-3 parts, leveling agent 0.1-1 part, solvent 5-10 parts, photoinitiator 0-6 parts and pigment 0-5 parts. The component B is a crosslinking agent. The components of the component A are prepared according to the above weight parts, and after preparation, the component A is mixed with the component B according to a weight ratio of 95-99:1-5 for use. After the glue is coated on a CPI or PET film, a copper foil is pressed and integrated, and after acid etching, a covered area and a bare area are formed, the glue film of the bare area is dissolved or peeled off during weak base treatment, and the glue film of the covered area remains intact after the same weak base treatment. The glue is applied to the transparent display screen, and the light transmittance is improved.

Description

Technical Field

[0001] This invention relates to an adhesive for the circuit board industry, and more specifically to a selective weak alkali release adhesive for transparent displays and its preparation method. Background Technology

[0002] In the manufacturing process of transparent displays, especially transparent display devices based on transparent polyimide (CPI) or polyethylene terephthalate (PET) flexible substrates, it is often necessary to laminate copper foil circuits onto the substrate and selectively etch the copper foil with an acidic etching solution to form fine conductive patterns.

[0003] Currently, the mainstream processes for patterning copper foil circuits on CPI or PET films in the field of transparent displays mainly include: After plasma bombardment cleaning removes organic impurities from the surface of CPI or PET substrates, the surface is activated by chemical coupling agents, and a high conductivity metal thin film is deposited using magnetron sputtering. The circuit is then formed by combining ultraviolet laser direct writing and wet etching. Alternatively, conductive lines can be directly printed on CPI or PET substrates after surface cleaning and activation (such as silver paste screen printing or inkjet printing).

[0004] The above process has significant shortcomings: High cost: Conductive inks (especially nano silver paste and conductive polymer materials) are expensive, and printing equipment requires high precision; magnetron sputtering is even more expensive and requires huge equipment investment.

[0005] Low yield: The circuit is prone to defects such as broken wires, short circuits, and uneven line width, making it difficult to control the yield during large-scale production.

[0006] Limited conductivity: The conductivity of the above-mentioned circuits is usually lower than that of etched copper foil, which is not conducive to transparent display applications that require high resolution and low resistance.

[0007] Thickness limitations: Due to limitations in ink rheology, printing precision, and drying shrinkage, the thickness of conductive lines that can be obtained in a single printing is limited. Even with multiple overprinting, the actual achievable conductive layer thickness is generally no more than 20–30 μm, and multiple printings significantly increase costs and process complexity, while also easily causing defects such as poor interlayer bonding and linewidth expansion.

[0008] Furthermore, the following problems also exist if existing transparent optical adhesive (OCA) or pressure-sensitive adhesive (PSA) processes are used: Poor acid resistance: In the copper foil etching process (commonly using acidic etching solutions such as FeCl3 / HCl), the existing adhesive layer is easily corroded by the acid, causing the adhesive film to swell, turn white, lose transparency, or even peel off, directly affecting the product yield.

[0009] Lack of selective film removal capability: In the existing technology, no adhesive can achieve the following: the film in the exposed area dissolves rapidly under weak alkaline conditions, while the film in the pressed area (between copper foil and CPI or PET) remains intact and the adhesion does not decrease significantly under the same conditions.

[0010] As transparent displays evolve towards larger sizes, higher brightness, and outdoor applications, the conductive circuitry needs to carry greater current (such as in backlight drivers and high-power LED arrays). The limited thickness of the conductive layer results in higher circuit resistance, leading to significant voltage drops and heat generation under high current, which restricts the application scenarios of transparent displays.

[0011] Therefore, there is a clear industry need and a patent gap in developing an adhesive that combines acid etching resistance, selective peeling with weak alkali, high peel strength to CPI or PET and copper foil, low cost, high light transmittance, and compatibility with thick copper foil. Summary of the Invention

[0012] The purpose of this invention is to address the aforementioned problems in the prior art by providing a selective weak alkali release adhesive for transparent displays and its preparation method.

[0013] The objective of this invention is achieved through the following technical solutions: This invention discloses a selective weak alkaline delamination adhesive for transparent displays. The adhesive is a two-component adhesive, which is mixed by weight before use. By weight, it comprises 95-99 parts of component A and 1-5 parts of component B. Component A, by weight, comprises: 60-95 parts of alkali-soluble acrylate copolymer 1-3 parts of alkali-soluble monomer 1-3 parts of acid-resistant additive Leveling agent 0.1-1 part, Solvent 5-10 parts 0-6 parts of photoinitiator 0-5 parts of pigment; Component B is a crosslinking agent; The components of component A are prepared according to the above weight proportions. After preparation, they are mixed with component B at a weight ratio of 95-99:1-5. The acid value of the alkali-soluble acrylate copolymer is 80-150 mg KOH / g, and the glass transition temperature is -20℃ to 20℃. After the adhesive is applied to the CPI or PET film and copper foil is pressed together, the exposed area and the covered area are formed by acid etching. The adhesive film in the exposed area dissolves or peels off during weak alkali treatment, while the adhesive film in the covered area remains intact after the same weak alkali treatment, and the peel strength retention rate with the CPI or PET film is ≥85%.

[0014] More preferably, the crosslinking agent is selected from epoxy crosslinking agents or aziridine crosslinking agents; the alkali-soluble monomer is selected from one or more of γ-butyrolactone acrylate, γ-butyrolactone methacrylate, dihydrofuran acrylate, dimethylaminopropylacrylamide, and dimethylaminoethyl methacrylate. The crosslinking agent used in component B is selected from epoxy crosslinking agents or aziridine crosslinking agents. Aziridine crosslinking agents (such as trifunctional aziridine and polyfunctional aziridine) have high reactivity and can achieve crosslinking at lower temperatures, making them suitable for thermosetting or UV-assisted curing systems. Epoxy crosslinking agents (such as bisphenol A type epoxy resin, polyfunctional glycidyl ether epoxy resin, aliphatic epoxy resin, etc.) can also be used, but their dosage is still controlled within the range of 1 to 5 parts by weight. When using epoxy crosslinking agents, it is recommended to appropriately increase the curing temperature (usually 130–160°C) or extend the curing time, or add a small amount of epoxy curing accelerator to ensure that the crosslinking density reaches a level comparable to that of aziridine crosslinking agents. This will achieve the same technical effect of rapid film removal from exposed areas in weakly alkaline conditions and a peel strength retention rate of ≥85% in covered areas. Those skilled in the art can make conventional selections and adjustments between the above two types of crosslinking agents according to the specific substrate, coating process, and equipment conditions.

[0015] More preferably, the acid-resistant additive is selected from silane coupling agents or nano-silica dispersions; the photoinitiator is selected from one or more of TPO, TPO-L, 184, ITX, 907 and 819.

[0016] More preferably, after the adhesive is applied to the CPI or PET film and pressed onto the copper foil and cured, the initial peel force between the CPI or PET film and the copper foil is ≥1.3 kgf / cm; the overall light transmittance (550 nm) is ≥90% and the haze is ≤1%.

[0017] More preferably, the alkali-soluble acrylate copolymer is copolymerized from carboxyl-containing monomers, (meth)acrylate alkyl esters, and optionally hydroxyl monomers or amide monomers, and has an acid value of 80 to 150 mg KOH / g based on solids.

[0018] The present invention discloses a method for preparing a selective weak alkali release adhesive, comprising the following steps: (1) Dissolve the alkali-soluble acrylate copolymer in a solvent and stir until completely dissolved; (2) Add photoinitiator (if any), acid-resistant additive, leveling agent, alkali-soluble monomer, and pigment (if any) in sequence, and stir until homogeneous; (3) Grind to a fineness ≤5μm, filter and degas to obtain component A, and package it individually; (4) Component B is a crosslinking agent and is packaged separately; (5) Before use, each component of component A is prepared according to the weight parts. After preparation, it is mixed with component B at a weight ratio of 95-99:1-5 to obtain the glue.

[0019] The application of the selective weak alkaline stripping adhesive of this invention in the manufacture of transparent displays includes the following steps: (a) Apply the adhesive to a CPI or PET film and dry it to form an adhesive layer; (b) Press the copper foil onto the adhesive layer and perform heat curing or UV curing to form an adhesive film; (c) Selective acid etching is performed on the copper foil to form a conductive pattern, exposing the adhesive film on the exposed parts; (d) Treat with a weak alkali to remove the film from the exposed area, while retaining the film in the covered area between the copper foil and CPI or PET; The thickness of the copper foil is 9–105 μm; the temperature of the weak alkali treatment in step (d) is 40–60 °C, the weak alkali is a 1–5% NaOH or KOH aqueous solution, and the treatment time is 1–3 minutes.

[0020] More preferably, after pressing and curing, a single exposure / curing can be performed, and after film removal, a second exposure or additional curing can be performed to further enhance the peel strength.

[0021] More preferably, in step (a), the adhesive is applied to a CPI or PET film using a micro-grooving method, using an 80–120 mesh micro-grooving roller, with the cell depth controlled at 30–70 μm and the adhesive layer thickness controlled at 15–25 μm.

[0022] More preferably, step (d) uses a weak alkaline spraying method to remove the adhesive film in the exposed area, while the adhesive film in the covering area between the copper foil and CPI or PET is retained.

[0023] This invention also provides a manufacturing system for forming selectively conductive patterns on flexible transparent films. The system is not limited to using the selective weak-alkali release adhesive of this invention, but can also be applied to other alkali-soluble acrylic or similar functional adhesives that can selectively dissolve under weakly alkaline conditions. The manufacturing system includes a precision adhesive coating device and a multi-stage dynamic parameter gradient spraying device. These two devices work together to achieve high-precision control of the dry adhesive layer thickness and effective suppression of edge etching of fine lines, thereby stably obtaining conductive patterns with high light transmittance and high peel strength retention on flexible transparent substrates such as CPI or PET.

[0024] A manufacturing system for forming selectively conductive patterns on a flexible transparent film material, comprising: (1) An adhesive coating apparatus, wherein the coating apparatus comprises: Material trough, gluing roller with micro-relief pattern on the surface, coarse scraper, coating roller and fine scraper; The coarse scraper presses against the surface of the upper glue roller only by its own weight, and the angle between the blade and the surface of the upper glue roller in the forward direction is 10° to 20°. The fine scraper adopts a reverse scraping method, and the gap between it and the adhesive coating surface of the film material is 2.0 to 2.8 times the target dry adhesive thickness; The coating device applies the adhesive to the surface of CPI or PET film with a dry film thickness of 15-25 μm and a thickness deviation of ≤±2 μm. (2) A multi-stage dynamic parameter gradient spraying device, wherein the spraying device divides the weak alkali treatment into at least three continuous stages: First stage: 3.5-5.0% NaOH or KOH aqueous solution, temperature 55-60℃, spraying pressure 0.12-0.18 MPa, used for rapid surface saponification; The second stage involves a 1.5–2.5% NaOH or KOH aqueous solution at a temperature of 45–50°C and a spraying pressure of 0.06–0.10 MPa, used for controlled permeation dissolution. The third stage: using clean water or an alkaline solution with a concentration of ≤0.5% at a spray pressure of 0.15–0.25 MPa to thoroughly rinse and terminate the reaction; The highly uniform adhesive layer obtained by the coating device, combined with the gradient parameter control of the spraying device, ensures that the edge etching width of the conductive line is ≤2 μm and the peel strength retention rate of the adhesive film in the covered area is ≥85%.

[0025] More specifically, the adhesive is an alkali-soluble acrylic adhesive with an acid value of 80–150 mg KOH / g.

[0026] More specifically, the processing time of the second stage is adjusted according to the amount of crosslinking agent used. For every 0.5 parts by weight increase in the amount of crosslinking agent, the processing time of the second stage is extended by 8 to 12 seconds.

[0027] More specifically, the spraying device also employs a micro-droplet atomizing nozzle, with the median diameter of the droplets D50 controlled between 30 and 80 μm, and the spraying angle being between 5° and 15° and the normal to the substrate.

[0028] Compared with the prior art, the selective weak alkali film-removing adhesive of the present invention has the following beneficial effects: The first-ever selective film removal function: For the first time, it enables the rapid removal of exposed areas in a weak alkali in the same adhesive layer while keeping the covered area intact and the adhesion undiminished (peel strength retention rate ≥85%). This solves the industry's pain point of "removing the film from the entire surface and then re-laminating", simplifying the process and improving the yield.

[0029] Excellent acid resistance: By adding acid-resistant additives, the film can remain stable in acidic etching solutions, and the circuit is fully displayed without whitening, peeling, or side etching.

[0030] Process-friendly: The film removal process uses a weak alkali (1–5% concentration) and low temperature (40–60℃), which does not damage CPI or PET film and requires no organic solvents, making it environmentally friendly and safe.

[0031] High bonding strength: It has high initial peel force on both CPI or PET film and copper foil (initial peel force between CPI or PET film and copper foil ≥ 1.3 kgf / cm), meeting the reliability requirements of flexible transparent display screens.

[0032] Compatible with existing PCB processes: Standard equipment such as coating, hot pressing, screen printing, and UV curing can be used without the need for large-scale additional investment.

[0033] The cost is significantly lower than other processes: This invention uses copper foil etching to form conductive circuits. Copper foil, as a bulk industrial product, has a material cost far lower than that of specialized conductive inks such as nano-silver paste and conductive polymers. The etching process is mature and the equipment is universal, eliminating the need for high-precision inkjet printing or laser direct writing equipment. Calculations show that, without considering the cost of the film material (CPI or PET) and under the condition of equivalent conductivity (sheet resistance <0.1 Ω / □), the material and manufacturing cost of this invention is approximately 150 RMB / ㎡, compared to approximately 250 RMB / ㎡ for silver paste printing and approximately 330 RMB / ㎡ for magnetron sputtering, representing a cost reduction of approximately 40–55%.

[0034] The light transmittance is higher than other processes: This invention can directly use CPI or PET film as the substrate (CPI film itself has a light transmittance of ≥92%, PET film has a light transmittance of ≥90%); and after the adhesive is removed from the film, the light transmittance is basically restored to the light transmittance of the base film itself (overall light transmittance ≥90%, haze ≤1%).

[0035] Wider adaptability and compatibility with subsequent high-temperature processes: The preferred CPI film has excellent high-temperature resistance (long-term operating temperature ≥250℃), low coefficient of thermal expansion, and dimensional stability, making it compatible with subsequent high-temperature processes. The preferred high-temperature resistant PET optical film (≥180℃, light transmittance ≥90%) can be seamlessly integrated with existing flexible display production lines.

[0036] The invention significantly expands the range of conductive line thicknesses and enhances current-carrying capacity: using CPI or PET film as the substrate, it can directly bond electrolytic copper foil or rolled copper foil with a thickness of 8–105 μm (preferably 35–70 μm, more preferably 50–70 μm) without intermediate transfer steps. Compared to existing printing processes (thickness limit 15–20 μm), the invention expands the range of conductive line thicknesses by more than three times. The low resistance characteristics of the thick copper foil significantly reduce Joule heating under high current, improving device reliability and lifespan.

[0037] Color adjustable: By adding pigments, the back of the etched circuit can be made to appear in different colors (gold, silver, black, red, yellow, white, blue, etc.) to suit various application scenarios. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the process route of Embodiment 1 for the application of the adhesive of the present invention in the manufacture of transparent displays; Figure 2 This is a schematic diagram of the second embodiment of the process route for the application of the adhesive of the present invention in the manufacture of transparent displays; Figure 3 This is a schematic diagram of an embodiment of the adhesive coating device used in this invention. Detailed Implementation

[0039] To better understand the technical content of the present invention, the technical solution of the present invention will be further introduced and explained below with reference to specific embodiments, but is not limited thereto. Example 1

[0040] This embodiment provides a light-colored thermosetting adhesive suitable for bonding CPI or PET films and copper foils, and capable of alkali-removable film. Its formulation is as follows: Component A (by weight): Main gelling resin (alkali-soluble acrylate copolymer): 81.5 parts Alkali-soluble monomer (dihydrofuran acrylate): 2 parts Acid-resistant additive (KH560): 1.3 parts Leveling agent (BYK-358): 0.2 parts Solvent (PMA): 8 parts Pigment (nano titanium dioxide): 5 parts Component B: Crosslinking agent (trifunctional aziridine): 2 parts (Component A totals 98 parts, which are mixed with 2 parts of component B, and the ratio falls within the range of 95-99:1-5) Preparation method: Dissolve the alkali-soluble acrylate copolymer in a solvent and stir until completely dissolved; Add the acid-resistant additive, leveling agent, alkali-soluble monomer, and nano titanium dioxide in sequence, and continue stirring for 30-60 minutes until homogeneous; The above abrasive material was ground to a fineness of ≤5μm using a nano-grind mill. Filter through a 400-mesh filter, then degas under vacuum or allow to stand to degas, to obtain component A of the adhesive; Package component B, the crosslinking agent, directly according to the above formula ratio. In the above formula ratio, component A is 98 parts and component B is 2 parts.

[0041] Performance testing: Viscosity 25°C, Brookfield DV2T, rotor S64 1250 mPa·s Fineness scraper fineness gauge 4μm Coating suitability Bake in sections at 80℃-120℃ for 3 minutes each. The surface is dry and leaves no mark when pressed. Pressing conditions 30 kgf / cm², 130℃ The CPI or PET film adheres completely to the copper foil without bubbling or separation. Acid-resistant etching <![CDATA[40°C FeCl₃ etching solution, 5 minutes]]> The adhesive surface showed no whitening or peeling; the circuit showed no side corrosion. Alkali removal performance 3% NaOH, 50℃, 2 minutes Complete removal of the adhesive film from exposed areas, leaving no residue; the film remains intact in covered areas. Peel strength IPC-TM-650 2.4.8 90° Vertical Tensile Test ≥1.36 kgf / cm Light transmittance Spectrophotometer GB / T 2410 ≥90%; Haze ≤0.9% Example 2

[0042] This embodiment provides a transparent adhesive suitable for bonding CPI or PET films and copper foil, and which is alkali-removable. Its formulation is as follows: Component A (by weight): Main gelling resin (alkali-soluble acrylate copolymer): 80.2 parts Acid-resistant additive (KH570): 1 part Alkali-soluble monomer (dihydrofuran acrylate): 3 parts Leveling agent (BYK-358): 0.3 parts Solvent (ethyl acetate): 6 parts Photoinitiator (184): 2 parts Photoinitiator (ITX): 1 part Photoinitiator (TPO-L): 2 parts Component B: Crosslinking agent (trifunctional aziridine): 2 parts (Component A totals 95.5 parts, which are mixed with 2 parts of component B, falling within the range of 95-99:1-5) Preparation method: Under light-protected conditions, the alkali-soluble acrylate copolymer was dissolved in a solvent and stirred until completely dissolved; Add the photoinitiator and heat and stir at 45°C until completely dissolved; Add the acid-resistant additive, leveling agent, and alkali-soluble monomer in sequence and continue stirring for 30-60 minutes until homogeneous; Filter through a 400-mesh filter, then degas under vacuum or allow to stand to degas, to obtain component A of the adhesive; The crosslinking agent of component B is packaged directly according to the formula ratio. In the above formula, component A is 95.5 parts and component B is 2 parts.

[0043] Performance testing: Viscosity 25°C, Brookfield DV2T, rotor S64 1300 mPa·s Coating suitability Bake in sections at 80℃-120℃ for 3 minutes each. The surface is dry and leaves no mark when pressed. UV curing 385 LED light source, 800 mJ / cm² The film is completely dry Pressing conditions 30 kgf / cm², 130℃ The CPI or PET film adheres completely to the copper foil without bubbling or separation. Acid-resistant etching <![CDATA[40°C FeCl₃ etching solution, 5 minutes]]> The adhesive surface showed no whitening or peeling; the circuit showed no side corrosion. Alkali removal performance 3% NaOH, 50℃, spray treatment for 2 minutes (multi-row array fan-shaped nozzles, pressure 0.10–0.12MPa, flow rate density 8–10 L / (m²·min)). The adhesive film is completely removed from exposed areas without any residue; the film remains intact in covered areas; and the peel strength retention rate is ≥90%. Peel strength IPC-TM-650 2.4.8 90° Vertical Tensile Test ≥1.62 kgf / cm Light transmittance Spectrophotometer GB / T 2410 ≥90%; Haze ≤0.9% Example 3 (A combination of components with proportions close to the lower limit, thermosetting transparent type)

[0044] This embodiment approximates the lower limits of alkali-soluble acrylate copolymers, alkali-soluble monomers, acid-resistant additives, leveling agents, and solvents, while using component B close to the lower limit, and containing no photoinitiator and no pigments. The formulation, by weight, is as follows: Component A: Alkali-soluble acrylate copolymer: 62 parts Alkali-soluble monomer (dihydrofuran acrylate): 1 part Acid-resistant additive (KH560): 1 part Leveling agent (BYK-358): 0.1 parts Solvent (PMA): 5 parts Photoinitiator: 0 parts Pigment: 0 parts Component B: Crosslinking agent (trifunctional aziridine): 1.2 parts (Component A totals 69.1 parts, which are mixed with 1.2 parts of component B. When converted to percentages, the ratio of component A to component B is 98.3:1.7, falling within the range of 95-99:1-5.) The preparation method is exactly the same as in Example 1 (dissolve → add additives in sequence → grind to fineness ≤5μm → filter and degas to obtain A; B is packaged separately; mix according to proportion before use).

[0045] Performance testing (after coating, drying, pressing, and curing): Viscosity 25°C, Brookfield DV2T, rotor S64 Approximately 980 mPa·s Acid-resistant etching <![CDATA[40°C FeCl3 etching solution, 5 minutes]]> The adhesive surface showed no whitening or peeling; the circuit showed no side corrosion. Alkali removal performance 3% NaOH, 50℃, 2 minutes Complete removal of the adhesive film from exposed areas, leaving no residue; the film remains intact in covered areas. Peel strength IPC-TM-650 2.4.8 90° Vertical Tensile Test Initial peel strength against CPI or PET film ≥ 1.25 kgf / cm; peel strength retention rate of the covered area after weak alkali treatment ≥ 87%. Light transmittance Spectrophotometer GB / T 2410, 550 nm ≥92%, haze ≤0.8% This embodiment verifies that even at dosages close to the lower limit, a moderately cross-linked network is still sufficient to achieve selective film removal while maintaining adequate initial adhesion and acid resistance. Example 4 (Combination of components close to their upper limits, UV-cured colored type)

[0046] This embodiment approaches the upper limits of alkali-soluble acrylate copolymers, alkali-soluble monomers, acid-resistant additives, leveling agents, solvents, photoinitiators, and pigments, while using component B close to the upper limit. The formulation, by weight, is as follows: Component A: Alkali-soluble acrylate copolymer: 92 parts Alkali-soluble monomer (dihydrofuran acrylate): 3 parts Acid-resistant additive (KH570): 2.8 parts Leveling agent (BYK-358): 0.9 parts Solvent (ethyl acetate): 9.5 parts Photoinitiator (184 + TPO-L): 5.5 parts Pigment (nano titanium dioxide): 4.5 parts Component B: Crosslinking agent (trifunctional aziridine): 4.5 parts Component A totals approximately 118.2 parts. In actual use, Component A and Component B are mixed by weight at a ratio of approximately 96.3:3.7, falling within the range of 95 to 99:1 to 5.

[0047] The preparation method is exactly the same as in Example 2 (dissolve in the dark → add photoinitiator to dissolve → add the remaining components in sequence → grind to fineness ≤5μm → filter and degas to obtain A; B is packaged separately; mix according to the ratio before use).

[0048] Performance testing (after coating, drying, pressing, and UV curing): Viscosity 25°C, Brookfield DV2T, rotor S64 Approximately 1450 mPa·s UV curing 385 nm LED After the film is completely dry at 800 mJ / cm² Acid-resistant etching <![CDATA[40°C FeCl₃ etching solution, 5 minutes]]> The adhesive surface showed no whitening or peeling; the circuit showed no side corrosion. Alkali removal performance 3% NaOH, 50℃, spray treatment for 2 minutes (multi-row array fan-shaped nozzles, pressure 0.10–0.12 MPa, flow rate density 8–10 L / (m²·min)). The adhesive film is completely removed from exposed areas without any residue; the film remains intact in covered areas; and the peel strength retention rate is ≥88%. Peel strength IPC-TM-650 2.4.8 90° Vertical Tensile Test Initial peel strength against CPI or PET film ≥ 1.55 kgf / cm; peel strength retention rate of the covered area after weak alkali treatment ≥ 88%. Light transmittance Spectrophotometer GB / T 2410, 550 nm ≥90%, haze ≤1% (light white appearance) This embodiment verifies that even when the dosage is close to the upper limit, the balance between a higher crosslinking density and a higher content of alkali-soluble monomers can still ensure rapid film removal in the exposed area, while the covered area maintains integrity and high peel strength after weak alkali treatment. Example 5 (A mixed extreme example where some components are at their upper limit and some components are at their lower limit, thermosetting transparent type)

[0049] In this embodiment, the alkali-soluble acrylate copolymer and acid-resistant additives are taken to be close to or at the upper limit, while the alkali-soluble monomers, leveling agents, solvents, and component B are taken to the lower limit. No photoinitiator and no pigments are present. The formulation is as follows by weight: Component A: Alkali-soluble acrylate copolymer: 95 parts Alkali-soluble monomer (dihydrofuran acrylate): 1 part Acid-resistant additive (KH560): 3 parts Leveling agent (BYK-358): 0.1 parts Solvent (PMA): 5 parts Photoinitiator: 0 parts Pigment: 0 parts Component B: Crosslinking agent (trifunctional aziridine): 1 part Component A totals approximately 104.1 parts. In actual use, component A and component B are mixed at a weight ratio of approximately 99:1, falling within the range of 95 to 99:1 to 5.

[0050] Preparation method: (1) Dissolve the alkali-soluble acrylate copolymer in a solvent and stir until completely dissolved; (2) Add acid-resistant additives, leveling agents, and alkali-soluble monomers in sequence, and stir for 30-60 minutes until homogeneous; (3) Grind the nano-grinding material to a fineness of ≤5μm using a nano-grinding mill, filter it through a 400-mesh filter, and degas it under vacuum to obtain component A, which is then individually packaged. (4) Component B is a crosslinking agent and is packaged separately; (5) Before use, mix component A and component B evenly according to the above ratio to obtain the adhesive of this embodiment.

[0051] Performance testing (after coating, drying, pressing, and thermosetting): Viscosity 25°C, Brookfield DV2T, rotor S64 Approximately 1100 mPa·s Coating suitability Bake in sections at 80-120℃ for 3 minutes each. The surface is dry and leaves no mark when pressed. Pressing conditions 30 kgf / cm², 130℃ The CPI or PET film adheres completely to the copper foil without bubbling or separation. Acid-resistant etching <![CDATA[40°C FeCl3 etching solution, 5 minutes]]> The adhesive surface showed no whitening or peeling; the circuit showed no side corrosion. Alkali removal performance 3% NaOH, 50℃, 2 minutes Complete removal of the adhesive film from exposed areas, leaving no residue; the film remains intact in covered areas. Peel strength IPC-TM-650 2.4.8 90° Vertical Tensile Test Initial peel strength against CPI or PET film ≥ 1.40 kgf / cm; peel strength retention rate of the covered area after weak alkali treatment ≥ 88%. Light transmittance Spectrophotometer GB / T 2410, 550 nm ≥92%, haze ≤0.7% Example 6 (Another extreme example of mixed components with some components at the upper limit and some components at the lower limit, UV-cured light white type)

[0052] In this embodiment, the alkali-soluble monomer, leveling agent, solvent, photoinitiator, pigment, and component B are taken to be close to or at the upper limit, while the alkali-soluble acrylate copolymer and acid-resistant additives are taken to the lower limit. The formulation is as follows, by weight: Component A: Alkali-soluble acrylate copolymer: 60 parts Alkali-soluble monomer (dihydrofuran acrylate): 3 parts Acid-resistant additive (KH570): 1 part Leveling agent (BYK-358): 1 part Solvent (ethyl acetate): 10 parts Photoinitiator (184): 3 parts Photoinitiator (TPO-L): 3 parts Pigment (nano titanium dioxide): 5 parts Component B: Crosslinking agent (trifunctional aziridine): 5 parts Component A contains approximately 86 parts. In actual use, Component A and Component B are mixed at a weight ratio of approximately 94.3:5.7 to approximately 95:5, falling within the range of 95 to 99:1 to 5.

[0053] Preparation method: (1) Under light-protected conditions, dissolve the alkali-soluble acrylate copolymer in a solvent and stir until completely dissolved; (2) Add photoinitiator, heat and stir at 45°C until completely dissolved, then cool to below 25°C; add acid-resistant additive, leveling agent, alkali-soluble monomer and pigment in sequence, and stir for 30 to 60 minutes until uniform; (3) Grind the powder to a fineness of ≤5μm using a three-roll mill or nano-grind mill, filter it through a 400-mesh filter and degas it under vacuum to obtain component A, which is then individually packaged. (4) Component B is a crosslinking agent and is packaged separately; (5) Before use, mix component A and component B evenly according to the above ratio to obtain the adhesive of this embodiment.

[0054] Performance testing (after coating, drying, pressing, and UV curing): Viscosity 25°C, Brookfield DV2T, rotor S64 Approximately 1380 mPa·s Coating suitability Bake in sections at 80-120℃ for 3 minutes each. The surface is dry and leaves no mark when pressed. UV curing 385 nm LED, 800 mJ / cm² The film is completely dry Pressing conditions 30 kgf / cm², 130℃ The CPI or PET film adheres completely to the copper foil without bubbling or separation. Acid-resistant etching <![CDATA[40°C FeCl₃ etching solution, 5 minutes]]> The adhesive surface showed no whitening or peeling; the circuit showed no side corrosion. Alkali removal performance 3% NaOH, 50℃, 2 minutes Complete removal of the adhesive film from exposed areas, leaving no residue; the film remains intact in covered areas. Peel strength IPC-TM-650 2.4.8 90° Vertical Tensile Test Initial peel strength against CPI or PET film ≥ 1.48 kgf / cm; peel strength retention rate of the covered area after weak alkali treatment ≥ 85%. Light transmittance Spectrophotometer GB / T 2410, 550 nm ≥90%, Haze ≤1% Examples 5 and 6 above further demonstrate that even if some components are taken at the upper limit and other components are taken at the lower limit, as long as the whole falls within the scope defined by the claims and the basic balance between alkali solubility and crosslinking density is maintained, all technical effects such as selective weak alkali delamination, acid resistance, high peel force retention rate and high light transmittance can still be stably achieved. When the amount of alkali-soluble monomer or crosslinking agent exceeds the limits of this invention, it is difficult to simultaneously achieve rapid film removal in the exposed area and high peel strength retention in the covered area.

[0055] The application of the adhesive of this invention in the manufacture of transparent displays includes the following steps: (a) Apply the adhesive to a CPI or PET film and dry it to form an adhesive layer; (b) Press the copper foil onto the adhesive layer and perform heat curing or UV curing to form an adhesive film; (c) Selective acid etching is performed on the copper foil to form a conductive pattern, exposing the adhesive film on the exposed parts; (d) Treat with a weak alkali to remove the film from the exposed area, while retaining the film in the covered area between the copper foil and CPI or PET; The thickness of the copper foil is 9–105 μm; the temperature of the weak alkali treatment in step (d) is 40–60 °C, the weak alkali is a 1–5% NaOH or KOH aqueous solution, and the treatment time is 1–3 minutes.

[0056] More specifically, after pressing and curing, one exposure / curing can be performed, and after film removal, a second exposure or additional curing can be performed to further improve the peel strength.

[0057] More specifically, in step (a), the adhesive is applied to a CPI or PET film using a micro-gravure coating method, using an 80–120 mesh micro-gravure roller, with the cell depth controlled at 30–70 μm and the adhesive layer thickness controlled at 15–25 μm.

[0058] More specifically, step (d) involves a weak alkaline spraying process to remove the adhesive film from the exposed areas, while the adhesive film in the covering area between the copper foil and CPI or PET is retained.

[0059] like Figure 1 The specific process sequence of the embodiment shown is as follows: winding → corona treatment → adhesive coating → curing → lamination → maturation → printed circuit → etching → film removal → FPC finished product.

[0060] Curing 80-120℃, 5-stage curing oven, 3 min Pressing 30 kgf / cm², 130℃ ripening Four curing conditions: 60℃ × 4 h, 80℃ × 4 h, 120℃ × 2 h, 160℃ × 30 min Etching <![CDATA[40℃ FeCl3 etching solution, 5 min]]> Film removal 3% NaOH, 50℃, 2 min (weak alkali film removal) Printed circuit 1. Thermosetting / photosensitive circuit inks 2. Dry film lamination, exposure and development like Figure 2 The specific process sequence of the illustrated embodiment is as follows: The process includes winding, corona treatment, adhesive coating, curing, lamination, maturation, printed circuitry, etching, film removal, FPC finishing, and secondary exposure of the film surface using a 385nm LED light source to improve the peel strength of the finished product. Other process parameters are as follows. Figure 1 The content of the example shown.

[0061] More specifically, for the adhesive coating step, to ensure more uniform application, the adhesive coating device provided by this invention (details below) is preferably used to precisely apply the adhesive to the film surface, ensuring that the thickness of the cured dry adhesive layer is stably controlled at 15–25 μm. This device is specifically designed to address the rheological properties of the adhesive used in this process (which has a specific viscosity and solid content) to achieve highly uniform coating and provide a good adhesive layer foundation for subsequent curing, pressing, and 385nm secondary exposure to improve peel strength.

[0062] More specifically, in the weak alkali treatment step, the traditional immersion-type film removal can be replaced with a precise and controllable multi-stage weak alkali spraying system. Relying on the physical barrier effect of the copper foil itself on the alkali solution, the exposed area can be quickly dissolved and the covered area can be almost completely permeated through precise control of the spraying parameters.

[0063] The specific spraying process steps and equipment parameters are as follows: Sprinkler system configuration: Uses multi-row array nozzles (fan-shaped or conical nozzles are recommended, with an orifice diameter of 0.3–0.8 mm), with the nozzles evenly spaced to cover the entire area.

[0064] The nozzle should be installed 80–150 mm above the substrate surface, and the spray angle should be adjustable (vertical or slightly tilted within 15° is recommended) to ensure uniform liquid film coverage without dead corners.

[0065] The spraying method is either reciprocating or continuous, and the substrate passes through the spraying zone at a constant linear velocity (0.5–3 m / min).

[0066] The length of the spray zone is designed to achieve an effective processing time of 1–3 minutes (which can be adjusted according to the production line speed).

[0067] Precise control of spray liquid parameters: Weak alkaline solution: 1–5% NaOH or KOH aqueous solution (preferably 2–4%), with the temperature strictly controlled at 40–60℃ (50±1℃ recommended).

[0068] Online closed-loop control system: Real-time monitoring and feedback of pH (accuracy ±0.1), temperature (accuracy ±0.5℃), and flow rate (accuracy ±2%).

[0069] Spray pressure: 0.05–0.25 MPa (preferably 0.08–0.15 MPa) to ensure that the droplets impact the exposed film evenly, while avoiding excessive penetration at the edges due to high pressure impact.

[0070] Flow rate density: The spray volume per square meter of substrate is controlled at 5–15 L per minute (adjusted slightly according to line speed and film thickness) to form a stable and continuous liquid film coverage.

[0071] Spraying mode: Continuous spraying or pulse spraying (pulse cycle 0.5–2 s on / off) can be used to further control the residence time and penetration depth of the alkali solution on the film surface.

[0072] Processing timing and process window: Pre-spray wetting section (optional, 5–15 s): Low flow rate and low pressure pre-wetting, which allows a hydrophilic salt layer to be quickly formed on the surface of the exposed film.

[0073] Main spray dissolution section: Spray continuously according to the above parameters, with the total effective time controlled within 1–3 minutes (error ±0.1 min). During this time, the exposed area film is rapidly saponified, swollen, dissolved, and washed away by the water flow due to direct contact with the alkaline solution; in the covered area, due to the copper foil barrier, the alkaline solution can only slowly penetrate from the edge of the extremely fine lines and cannot reach the central area in a short time, thus keeping the film intact.

[0074] Immediately after spraying, the solution enters the clean water rinsing section (multi-stage spraying or overflow rinsing) to thoroughly remove residual alkali and prevent secondary reactions.

[0075] Finally, use an air knife or compressed air to dry it (for drying only, not for shielding).

[0076] Process monitoring and stability assurance Online visual or conductivity detection can be used to determine the completion of film removal in exposed areas in real time.

[0077] Process window curing: Five parameters, namely temperature, concentration, pressure, time, and linear speed, are linked and controlled to ensure the consistency of selective film removal in the same batch and different batches.

[0078] The waste liquid circulation filtration and automatic replenishment system maintains a stable alkali concentration.

[0079] This spraying method relies entirely on the physical barrier of copper foil coverage and the chemical selectivity of the moderately cross-linked network of the adhesive film. Through precise quantitative control of spraying parameters, stable industrial-scale production can be achieved without any additional local shielding structures. Combined with the aforementioned precision micro-recessed coating and segmented curing process, results can be consistently obtained with no residue in the exposed area and a peel strength retention rate of ≥85% in the covered area.

[0080] More specifically, it can also be designed as a multi-stage dynamic parameter gradient spray (achieved by front and rear zone spraying), that is, the spraying process is divided into three continuous stages, with pressure, flow rate, concentration, temperature and time precisely linked in each stage, forming a gradient of "rapid surface saponification first → controlled penetration depth → and finally thorough rinsing": First stage (rapid surface saponification stage): Concentration 3.5–5.0% NaOH / KOH, temperature 55–60℃, spray pressure 0.12–0.18 MPa, flow rate 8–12 L / (m²·min), time 20–40 s.

[0081] Objective: To rapidly form a highly hydrophilic carboxylate layer on the surface of the exposed film, thereby accelerating subsequent dissolution, while avoiding excessive penetration at the edges in a short time and under high pressure.

[0082] Second stage (controlled osmosis and dissolution stage): The concentration was immediately switched to 1.5–2.5%, the temperature dropped to 45–50°C, the pressure dropped to 0.06–0.10 MPa, the flow rate density dropped to 4–7 L / (m²·min), and the time was 40–90 s.

[0083] Objective: To significantly reduce the lateral diffusion rate of alkaline solution from the edge of copper foil to the covered area using lower concentrations and pressures (reducing the lateral etching rate to below 30% of the first stage), while continuing to dissolve the saponified film in the exposed area.

[0084] Third stage (complete flushing and termination): Pure water or very low concentration (≤0.5%) alkaline solution, pressure 0.15–0.25 MPa, flow rate density 10–15 L / (m²·min), time 15–30 s.

[0085] Objective: To mechanically flush away dissolved film fragments and rapidly dilute residual alkali, thereby forcibly stopping any potential slow penetration into the covered area.

[0086] More specifically, a method combining micro-droplet atomization and controlled impact angle spraying can also be used: A specially designed fan-shaped micro-mist nozzle (outlet orifice diameter 0.2–0.4 mm) is used to control the median droplet diameter D50 at 30–80 μm.

[0087] The spray angle is strictly controlled at an angle of 5–15° (preferably 8–12°) with the normal of the substrate to avoid splashing and lateral turbulence caused by vertical impact.

[0088] The nozzle height is fixed at 90–120 mm, and the array spacing controls the overlap of adjacent sprays to 15–25%.

[0089] This combination can significantly reduce the impact of droplet kinetic energy on the edge of the covered area, while ensuring uniform wetting of the exposed area, which is a key hydrodynamic parameter for achieving "selectivity".

[0090] More specifically, real-time optical closed-loop feedback control can also be used: Install online transmittance / haze detection (or high-resolution machine vision) in the middle and rear sections of the spray zone to monitor the dissolution progress of the exposed film in real time.

[0091] When the light transmittance of the exposed area reaches more than 98% of the substrate itself (or the haze is ≤1.5%), the system automatically switches to the third stage in advance or shortens the second stage time.

[0092] Control accuracy: time response ≤ 0.5 s, temperature / concentration fluctuation ≤ ±0.3℃ / ±0.1%.

[0093] This closed loop makes the film removal time no longer a fixed value, but adaptive based on the actual dissolution state, greatly improving the adaptability to different line widths and adhesive thicknesses, and further compressing the permeation window at the edge of the coverage area.

[0094] More specifically, the matching relationship between spraying process parameters and film crosslinking density can also be adopted, that is, the matching relationship between spraying parameters and crosslinking agent dosage (1–5 parts, preferably 2–3.5 parts): for every 0.5 parts increase in crosslinking agent dosage, the allowable treatment time in the second stage can be extended by 8–12 seconds without significant lateral corrosion. Through this quantitative relationship, a joint control window of "formulation-process" is formed, allowing the same adhesive layer to exhibit distinctly different dissolution steps in different regions.

[0095] To verify the quantitative relationship between the crosslinking agent dosage and the allowable treatment time in the second stage of spraying, based on the basic formulation of Example 2 (with the alkali-soluble acrylate copolymer and other components unchanged), only the dosage of the crosslinking agent (trifunctional aziridine) was changed. A multi-stage dynamic parameter gradient spraying process was adopted (first stage: 4% NaOH, 58℃, 0.15 MPa, 30 s; second stage: 2% NaOH, 48℃, 0.08 MPa; third stage: water, 0.20 MPa, 20 s). The longest allowable time without significant lateral corrosion (lateral corrosion width at the edge of the covered area ≤ 2 μm) in the second stage was tested under different crosslinking agent dosages. The results are as follows: 2.0 55 s ≥89% benchmark 2.5 65 s ≥90% Extended by approximately 10 seconds 3.0 76 s ≥91% Extended by approximately 11 seconds 3.5 87 s ≥90% Extended by approximately 11 seconds Another group used the formulation of Example 1 as a baseline (thermosetting system), with only the amount of crosslinking agent changed. The test results are as follows: 1.5 48 s ≥86% benchmark 2.0 58 s ≥87% Extended by approximately 10 seconds 2.5 69 s ≥88% Extended by approximately 11 seconds The above two sets of data show that, within the preferred crosslinking agent dosage range of the present invention, for every 0.5 parts increase in crosslinking agent, the allowable treatment time in the second stage can be stably extended by about 8–12 s, and the peel force retention rate of the covered area is ≥85%, thereby verifying the quantitative matching relationship between crosslinking density and spraying process window.

[0096] This invention also provides an adhesive coating apparatus suitable for flexible transparent films such as PET and CPI. This apparatus can be used not only for the precision coating of the selective weak alkaline stripping adhesive of this invention, but also for the uniform coating of other optical adhesives, pressure-sensitive adhesives, or special functional adhesives with similar viscosity and solid content. The coating apparatus achieves high-precision control of the dry adhesive layer thickness through primary metering by a micro-gravure adhesive roller, stable adhesive removal by a gravity coarse doctor blade, and precise secondary control by a fine doctor blade. This solves the technical problems of poor thickness uniformity and the generation of streaks and bubbles when coating large areas of thin adhesive layers (15–25 μm) using traditional coating methods.

[0097] like Figure 3 As shown, the coating apparatus of this embodiment includes: The material tank 1 is located at the bottom of the device and is used to hold the glue 9. The glue level in the material tank 1 is kept stable so that the lower part of the glue roller is always immersed in the glue.

[0098] The gluing roller 2 is a roller with a micro-gravure pattern on its surface, partially immersed in the glue in the feed trough. As the gluing roller rotates, the micro-gravure indentations carry a measured amount of glue from the feed trough. The rotation direction of the gluing roller is matched with the film feeding direction to achieve direct transfer.

[0099] The coarse scraper 3 is positioned on one side of the gluing roller, with its blade pressed against the roller surface by its own weight. The coarse scraper removes excess glue from the roller surface, leaving only a measured amount of glue within the micro-gravure recesses, thus completing the initial metering. The coarse scraper uses gravity clamping, resulting in uniform pressure and minimal damage to the micro-gravure pattern, making it suitable for the viscosity range of this glue.

[0100] The coating roller 4 is positioned parallel above the adhesive roller, forming a controllable gap with it. The coating roller acts as both a back pressure roller and a guide roller, providing stable support and contact pressure for the film material.

[0101] The fine scraper 5 is positioned on one side of the coating roller, maintaining a precisely adjustable gap with the roller surface, and employs a reverse scraping method. The fine scraper performs a secondary precision trimming on the coating roller surface or the adhesive layer already transferred to the film surface, further controlling the wet film thickness and eliminating any possible streaks or excess adhesive.

[0102] Uncoated film material 7 enters the gap between the coating roller and the applicator roller from the feeding direction. At the gap, the adhesive in the micro-recessed pits on the surface of the coating roller is directly transferred to the surface of the film material. The film material then passes over the applicator roller and is pulled away in the discharge direction to form coated film material 8.

[0103] The working process is related to the adhesive: During use, the adhesive prepared according to this invention is injected into the feed trough 1. The coating roller 2 rotates, and the micro-gravure pits carry the adhesive; the coarse scraper 3 scrapes away excess adhesive in the forward direction by gravity, completing the initial quantitative measurement. The film material 7 contacts the coating roller 2 in the gap between the coating roller 2 and the applicator roller 4, and the adhesive is directly transferred to the surface of the film material 7. The fine scraper 5 trims in the reverse direction with a set gap, precisely controlling the wet film thickness within the target range.

[0104] Based on the characteristics of the adhesive formulated in this invention (solid content and viscosity matching the required dry adhesive thickness of 15–25 μm), by adjusting the fine doctor blade gap, the pressure between the two rollers, and the roller speed ratio, a stable, uniform dry adhesive layer of 15–25 μm can be formed after curing. This highly uniform adhesive layer is beneficial for subsequent curing and lamination processes and provides a more consistent interfacial crosslinking foundation during secondary exposure with 385 nm LEDs, thereby effectively improving the peel strength of the finished product.

[0105] This embodiment achieves a graded metering and transfer structure for the adhesive by using a micro-gravure gluing roller for primary metering, a gravity coarse scraper for stable adhesive removal, a coating roller for back pressure support, and a fine scraper for precise secondary control. This results in a coating effect with controllable thickness and uniform surface.

[0106] Building upon the aforementioned embodiments, a further implementation involves limiting the forward gravity of the coarse doctor blade: the coarse doctor blade rests against the surface of the glue roller solely on its own weight, without applying additional active pressure from a cylinder or spring; simultaneously, the forward tangential angle between the coarse doctor blade and the surface of the glue roller is limited to 10°–20°. This structure enables the coarse doctor blade to stably scrape off excess glue within the viscosity range of this adhesive, while significantly reducing wear on the microgravure pattern and ensuring long-term consistency of the initial metering. Compared to conventional actively pressurized doctor blades or large-angle doctor blades, this feature is specifically adapted to the rheological properties of this adhesive, avoiding uneven thickness caused by pressure fluctuations.

[0107] Building upon the aforementioned embodiments, a further implementation involves the following matching relationship between the fine squeegee gap and the target dry adhesive thickness: the gap between the fine squeegee and the adhesive-coated surface of the film is set according to the solid content of the adhesive, ensuring that the wet film thickness after secondary trimming by the fine squeegee is strictly controlled within 2.0 to 2.8 times the target dry adhesive thickness (15–25 μm) (determined based on an adhesive solid content of approximately 40–55%); and the fine squeegee employs a reverse scraping method. This limitation establishes a clear two-level matching relationship between the initial quantitative measurement of the microgravure pits and the secondary precise measurement of the film surface by the fine squeegee, enabling the dry adhesive layer thickness deviation after curing to be stably controlled within ±2 μm. The uniform dry adhesive layer thickness further ensures the consistency of cross-linking between the adhesive layer and the substrate interface during subsequent 385 nm LED secondary exposure, thereby improving the stability of the finished product's peel strength.

[0108] The core structural feature of the above-mentioned coating device is that: the coarse doctor blade presses against the surface of the glue roller solely by its own weight, and the tangential angle between the blade and the surface of the glue roller is limited to 10° to 20°; the gap between the fine doctor blade and the coating surface of the film is set to 2.0 to 2.8 times the target dry adhesive thickness according to the solid content of the adhesive, and a reverse scraping method is adopted. These features work together to ensure that the thickness deviation of the cured dry adhesive layer can be stably controlled within ±2 μm, while significantly reducing wear on the microgravure pattern and extending the service life of the equipment. Those skilled in the art should understand that the above-mentioned coating device itself constitutes an independent technical solution, and its protection scope is not limited to its use in conjunction with the adhesive of this invention.

[0109] This invention also provides a manufacturing system for forming selectively conductive patterns on flexible transparent films. The system is based on a precision adhesive coating device and a multi-stage dynamic parameter gradient spraying device, which work together. It is not limited to the selective weak-alkali film-removing adhesive of this invention, but can also be applied to other acrylate or similar functional adhesives that are alkali-soluble and can achieve regional selective dissolution under weakly alkaline conditions.

[0110] Specifically, the coating device uses a micro-gravure roller for initial metering, a coarse doctor blade that relies solely on its own weight to press against the surface with a tangential angle of 10°–20°, and a reverse fine doctor blade with a gap strictly controlled at 2.0–2.8 times the target dry adhesive thickness. This process achieves a high-precision, uniform coating of adhesive onto the surface of CPI or PET film with a dry film thickness of 15–25 μm and a thickness deviation of ≤±2 μm. This highly uniform adhesive layer provides a stable foundation for subsequent spray-coating and film removal, significantly reducing edge penetration differences caused by thickness fluctuations.

[0111] Based on this, the multi-stage dynamic parameter gradient spraying device divides the weak alkali treatment into three continuous stages: the first stage uses a higher concentration (3.5–5.0%), higher temperature (55–60℃), and higher pressure (0.12–0.18 MPa) to achieve rapid surface saponification of the adhesive film in the exposed area; the second stage switches to a lower concentration (1.5–2.5%), lower temperature (45–50℃), and lower pressure (0.06–0.10 MPa), effectively dissolving the exposed area while significantly inhibiting the lateral diffusion of the alkali solution into the covered area; the third stage uses clean water or an extremely low concentration of alkali solution for thorough rinsing and forcibly terminating the reaction. The highly uniform adhesive layer obtained by the coating device, precisely matched with the gradient parameters of the spraying device, can stably control the lateral etching width of the conductive line edge to ≤2 μm, and maintain the peel strength retention rate of the adhesive film in the covered area to ≥85%. Even under the conditions of mainstream high-transparency lines with a line width of 8–18 μm, it can still ensure minimal loss of effective bonding width and meet product reliability requirements.

[0112] Those skilled in the art can make routine adjustments within the above-mentioned coating parameter window and spray gradient parameter range according to the rheological properties, line width requirements, and production line speed of the actual adhesive, so that the manufacturing system can be stably applied to the selective conductive pattern preparation process of different alkali-soluble functional adhesives.

[0113] In summary, this invention pioneers a selective film removal function: for the first time, it enables rapid removal of exposed areas in a weak alkali within the same adhesive layer while maintaining the integrity of the covered area and ensuring no decrease in adhesion (peel strength retention rate ≥85%). This solves the industry's pain point of "removing the entire film and then re-laminating," simplifying the process and improving yield.

[0114] Excellent acid resistance: By adding acid-resistant additives, the film can remain stable in acidic etching solutions, and the circuit is fully displayed without whitening, peeling, or side etching.

[0115] Process-friendly: The film removal process uses a weak alkali (1–5% concentration) and low temperature (40–60℃), which does not damage CPI or PET film and requires no organic solvents, making it environmentally friendly and safe.

[0116] High bonding strength: It has high initial peel force on both CPI or PET film and copper foil (initial peel force between CPI or PET film and copper foil ≥ 1.3 kgf / cm), meeting the reliability requirements of flexible transparent display screens.

[0117] Compatible with existing PCB processes: Standard equipment such as coating, hot pressing, screen printing, and UV curing can be used without the need for large-scale additional investment.

[0118] The cost is significantly lower than other processes: This invention uses copper foil etching to form conductive circuits. Copper foil, as a bulk industrial product, has a material cost far lower than that of specialized conductive inks such as nano-silver paste and conductive polymers. The etching process is mature and the equipment is universal, eliminating the need for high-precision inkjet printing or laser direct writing equipment. Calculations show that, without considering the cost of the film material (CPI or PET) and under the condition of equivalent conductivity (sheet resistance <0.1 Ω / □), the material and manufacturing cost of this invention is approximately 150 RMB / ㎡, compared to approximately 250 RMB / ㎡ for silver paste printing and approximately 330 RMB / ㎡ for magnetron sputtering, representing a cost reduction of approximately 40–55%.

[0119] The light transmittance is higher than other processes: This invention can directly use CPI or PET film as the substrate (CPI film itself has a light transmittance of ≥92%, PET film has a light transmittance of ≥90%); and after the adhesive is removed from the film, the light transmittance is basically restored to the light transmittance of the base film itself (overall light transmittance ≥90%, haze ≤1%).

[0120] Wider adaptability and compatibility with subsequent high-temperature processes: The preferred CPI film has excellent high-temperature resistance (long-term operating temperature ≥250℃), low coefficient of thermal expansion, and dimensional stability, making it compatible with subsequent high-temperature processes. The preferred high-temperature resistant PET optical film (≥180℃, light transmittance ≥90%) can be seamlessly integrated with existing flexible display production lines.

[0121] The invention significantly expands the range of conductive line thicknesses and enhances current-carrying capacity: using CPI or PET film as the substrate, it can directly bond electrolytic copper foil or rolled copper foil with a thickness of 9–105 μm (preferably 35–70 μm, more preferably 50–70 μm) without intermediate transfer steps. Compared to existing printing processes (thickness limit 15–20 μm), the invention expands the range of conductive line thicknesses by more than three times. The low resistance characteristics of the thick copper foil significantly reduce Joule heating under high current, improving device reliability and lifespan.

[0122] Color adjustable: By adding pigments, the back of the etched circuit can be made to appear in different colors (gold, silver, black, red, yellow, white, blue, etc.) to suit various application scenarios.

[0123] The above examples are merely illustrative of the technical content of the present invention to facilitate easier understanding by the reader, but do not imply that the implementation of the present invention is limited to these examples. Any technical extensions or re-creations made based on the present invention are protected by the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A selective weak alkaline release adhesive for transparent displays, characterized in that, The adhesive is a two-component mixture, which should be mixed by weight before use; by weight, it contains 95-99 parts of component A and 1-5 parts of component B. Component A, by weight, comprises: 60-95 parts of alkali-soluble acrylate copolymer 1-3 parts of alkali-soluble monomer 1-3 parts of acid-resistant additive Leveling agent 0.1-1 part Solvent 5-10 parts 0-6 parts of photoinitiator 0-5 parts of pigment; Component B is a crosslinking agent; The components of component A are prepared according to the above weight proportions. After preparation, they are mixed with component B at a weight ratio of 95-99:1-5. The acid value of the alkali-soluble acrylate copolymer is 80-150 mg KOH / g, and the glass transition temperature is -20℃ to 20℃. After the adhesive is applied to the CPI or PET film and copper foil is pressed together, the exposed area and the covered area are formed by acid etching. The adhesive film in the exposed area dissolves or peels off during weak alkali treatment, while the adhesive film in the covered area remains intact after the same weak alkali treatment, and the peel strength retention rate with the CPI or PET film is ≥85%.

2. The selective weak alkali delamination adhesive according to claim 1, characterized in that, The crosslinking agent is selected from epoxy crosslinking agents or aziridine crosslinking agents; the alkali-soluble monomer is selected from one or more of γ-butyrolactone acrylate, γ-butyrolactone methacrylate, dihydrofuran acrylate, dimethylaminopropylacrylamide, and dimethylaminoethyl methacrylate.

3. The selective weak alkali delamination adhesive according to claim 1, characterized in that, The acid-resistant additive is selected from silane coupling agents or nano-silica dispersions; the photoinitiator is selected from one or more of TPO, TPO-L, 184, ITX, 907, and 819.

4. The selective weak alkali delamination adhesive according to claim 1, characterized in that, After the adhesive is applied to the CPI or PET film and pressed with copper foil and cured, the initial peel force between the CPI or PET film and the copper foil is ≥1.3 kgf / cm; the overall light transmittance (550 nm) is ≥90% and the haze is ≤1%.

5. The selective weak alkali delamination adhesive according to claim 1, characterized in that, The alkali-soluble acrylate copolymer is copolymerized from carboxyl-containing monomers, (meth)acrylate alkyl esters, and optionally hydroxyl monomers or amide monomers, and has an acid value of 80–150 mg KOH / g based on solids.

6. A method for preparing the selective weak alkali release adhesive according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Dissolve the alkali-soluble acrylate copolymer in a solvent and stir until completely dissolved; (2) Add photoinitiator (if any), acid-resistant additive, leveling agent, alkali-soluble monomer, and pigment (if any) in sequence, and stir until homogeneous; (3) Grind to a fineness ≤5μm, filter and degas to obtain component A, and package it individually; (4) Component B is a crosslinking agent and is packaged separately; (5) Before use, each component of component A is prepared according to the weight parts. After preparation, it is mixed with component B at a weight ratio of 95-99:1-5 to obtain the glue.

7. The application of the adhesive according to any one of claims 1 to 5 in the manufacture of a transparent display screen, characterized in that, Includes the following steps: (a) Apply the adhesive to a CPI or PET film and dry it to form an adhesive layer; (b) Press the copper foil onto the adhesive layer and perform heat curing or UV curing to form an adhesive film; (c) Selective acid etching is performed on the copper foil to form a conductive pattern, exposing the adhesive film on the exposed parts; (d) Treat with a weak alkali to remove the film from the exposed area, while retaining the film in the covered area between the copper foil and CPI or PET; The thickness of the copper foil is 9–105 μm; the temperature of the weak alkali treatment in step (d) is 40–60 °C, the weak alkali is a 1–5% NaOH or KOH aqueous solution, and the treatment time is 1–3 minutes.

8. The application according to claim 7, characterized in that, After pressing and curing, it can be exposed / cured once. After film removal, it can be exposed a second time or cured again to further improve the peel strength.

9. The application according to claim 7, characterized in that, Step (a) The adhesive is applied to a CPI or PET film using a micro-gravure coating method, using an 80–120 mesh micro-gravure roller, with the cell depth controlled at 30–70 μm and the adhesive layer thickness controlled at 15–25 μm.

10. The application according to claim 7, characterized in that, Step (d) involves a weak alkaline spraying process to remove the adhesive film from the exposed areas, while the adhesive film in the covering area between the copper foil and CPI or PET is retained.

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