Waterproof adhesive for flexible circuit board, preparation method and application thereof

Abstract

The application provides a waterproof adhesive for a flexible circuit board, a preparation method and application thereof, and belongs to the technical field of coating mixtures. The waterproof adhesive A agent comprises 40-60 parts of acrylic resin polymer, 20-40 parts of polyurethane acrylate resin, 5-10 parts of modified terpene resin, 0.5-2 parts of a photoinitiator, 0.2-0.8 parts of a defoaming agent and 10-20 parts of a solvent, in terms of weight parts; the B1 agent comprises 60-80 parts of a modified non-blocked isocyanate curing agent and 20-40 parts of a solvent; the B2 agent comprises 60-80 parts of a special acrylic acid oligomer with an isocyanate group and a double bond and 20-40 parts of a solvent; and the weight ratio of the A agent, the B1 agent and the B2 agent is 100:5-8:5-10. The application reduces the heat curing temperature and achieves a waterproof passing rate of more than 90% and a peeling strength of more than 900 gf.

Description

Technical Field

[0001] This invention relates to the technical field of coating mixtures, and in particular to a waterproof adhesive for flexible circuit boards, its preparation method, and its application. Background Technology

[0002] Flexible printed circuit boards (FPCBs), such as those used in computer keyboards and membrane switches, are widely used in modern electronic products, and the requirements for their waterproof performance are increasing. Currently, the market mainly uses a two-component thermosetting pressure-sensitive adhesive combining acrylic resin and isocyanate. This adhesive is screen-printed onto a PET film and then baked at high temperatures (usually exceeding 120°C) before being laminated to another PET film. This type of adhesive must meet performance requirements such as resistance to hot water immersion (60°C, 4-6 hours), high peel strength (≥500gf), and resistance to high temperature and humidity (70°C, 90%RH, 240 hours).

[0003] However, the existing technology still has significant drawbacks: First, the curing temperature is high and the stability is poor. Temperature fluctuations can easily lead to the diffusion or hardening of the colloid, affecting pressure sensitivity and adhesion tightness. Second, a single curing mechanism is difficult to balance the strength and flexibility of the colloid. When the strength is high, the leveling is poor and air bubbles are easily generated. When the strength is low, the adhesion is insufficient, resulting in a decrease in waterproof performance.

[0004] In view of this, a novel waterproof adhesive for flexible circuit boards, its preparation method, and its application are proposed to solve all or part of the above problems. Summary of the Invention

[0005] To address at least one of the aforementioned problems and deficiencies in the prior art, embodiments of the present invention provide a waterproof adhesive for flexible circuit boards, a preparation method thereof, and its application. Through the specific composition and ratio of agent A, agent B1, and agent B2, a synergistic effect of thermosetting and UV curing is achieved. Initial thermosetting ensures the adhesive's shape and initial tack, while subsequent UV curing enhances the crosslinking density. This allows the waterproof adhesive to maintain flexibility while possessing high strength and excellent barrier properties, increasing the waterproof pass-through rate to ≥90% after 12 hours in hot water at 60°C, thereby improving the reliability and service life of the flexible circuit board. The technical solution is as follows:

[0006] According to one aspect of the present invention, a waterproof adhesive for flexible circuit boards is provided, the waterproof adhesive comprising agent A, agent B1 and agent B2, specifically comprising, by weight:

[0007] Agent A: Acrylic resin polymer, 40-60 parts; polyurethane acrylate resin, 20-40 parts; modified terpene resin, 5-10 parts; photoinitiator, 0.5-2 parts; defoamer, 0.2-0.8 parts; solvent, 10-20 parts;

[0008] Agent B1: Modified non-blocked isocyanate curing agent, 60-80 parts; solvent, 20-40 parts;

[0009] Agent B2: 60-80 parts of a special acrylic oligomer with isocyanate groups and double bonds; 20-40 parts of solvent;

[0010] The weight ratio of Agent A, Agent B1, and Agent B2 is 100:5-8:5-10.

[0011] Specifically, the weight-average molecular weight of the acrylic resin polymer is 250,000-350,000, and the standard viscosity is 6,000-10,000 mPa·s; the acrylic resin polymer has hydroxyl and carboxyl functional groups, the resin acid value is 5%-10%, and the hydroxyl value is 10%-15%.

[0012] Specifically, the polyurethane acrylate resin is a polyether-type polyurethane acrylate resin with two functional groups, and its standard viscosity is 4000-12000 mPa·s.

[0013] Specifically, the modified isocyanate curing agent is a polyether-modified isocyanate curing agent, wherein the content of isocyanate group -NCO is 5%-10%.

[0014] Preferably, after B1 and B2 are mixed with a solvent, the isocyanate group -NCO reacts chemically with the hydroxyl groups in the acrylic resin polymer in agent A, and during thermosetting, a flexible long chain with a double bond structure is introduced into the acrylic main chain to enhance the flexibility of the waterproof adhesive.

[0015] For example, the photoinitiator is any one of 184, 1173, TPO, or any combination thereof; the defoamer is any one of silicone defoamer, defoaming polymer defoamer, polymer defoamer, or any combination thereof.

[0016] For example, the solvents used in agents A, B1 and B2 are any one of ethylene glycol butyl ether acetate, diethylene glycol methyl ether acetate, DBE or any combination thereof.

[0017] According to another aspect of the present invention, a method for preparing a waterproof adhesive for flexible circuit boards is provided, for preparing the waterproof adhesive described above. The preparation method includes the following steps:

[0018] Step S100: Dissolve the modified terpene resin in a solvent to form a solution with a solid content of 50%-55%;

[0019] Step S200: After mixing the solution from step S100 with the photoinitiator and solvent, add the acrylic resin polymer, polyurethane acrylate resin and defoamer in sequence, and stir at 400-600 rpm for 50-70 min. After filtration, obtain agent A.

[0020] Step S300: Mix the modified isocyanate curing agent with the solvent and stir at 250-350 rpm for 20-40 min, then filter to obtain agent B1;

[0021] Step S400: Mix the special acrylic oligomer with isocyanate groups and double bonds with the solvent and stir at 250-350 rpm for 20-40 min. Filter to obtain agent B2.

[0022] Step S500: Mix Agent A, Agent B1 and Agent B2 in a weight ratio of 100:5-8:5-10 until homogeneous to obtain waterproof adhesive.

[0023] Furthermore, agents A, B1, and B2 are mixed and then cured twice to form a waterproof adhesive layer. This second curing process includes heat curing and UV curing. Heat curing involves baking at 80-120°C for 60-120 seconds. UV curing uses UV energy of 800-1000 mJ / cm². 2 .

[0024] According to another aspect of the present invention, an application of a waterproof adhesive on a flexible circuit board is provided, wherein the waterproof adhesive is the waterproof adhesive described in the above aspect or the waterproof adhesive obtained by the preparation method described in the above aspect.

[0025] Specifically, the waterproof adhesive is screen-printed onto a PET film, and then subjected to heat curing and UV curing to form a waterproof adhesive layer with a thickness of 18-22 μm. After immersion in 60℃ hot water for 12 hours, the waterproof adhesive layer has a waterproof pass rate of ≥90% and a peel strength of 900-1000 gf.

[0026] The waterproof adhesive, preparation method, and application for flexible circuit boards provided by embodiments of the present invention have at least one or a portion of the following advantages:

[0027] (1) Through the specific composition and ratio of Agent A, Agent B1 and Agent B2 (100:5-8:5-10), the synergistic effect of thermosetting and UV curing is achieved. The initial thermosetting ensures the shape and initial tack of the colloid, while the later UV curing enhances the crosslinking density, so that the waterproof adhesive has high strength and excellent barrier properties while maintaining flexibility, and the waterproof pass rate is increased to ≥90% after 12 hours in hot water at 60℃.

[0028] (2) By controlling the molecular weight of acrylic resin polymer to 250,000-350,000 and the viscosity to 6,000-10,000 mPa·s, and containing hydroxyl and carboxyl functional groups (acid value 5%-10%, hydroxyl value 10%-15%), the printability of screen printing is ensured (e.g. no stringing or dripping), while providing sufficient crosslinking sites to enhance the adhesion and water resistance of the colloid;

[0029] (3) By using a difunctional polyether polyurethane acrylate resin (viscosity 4000-12000 mPa·s), it plays an internal plasticizing role in the thermosetting stage to improve flexibility, and participates in cross-linking to form a dense network in the UV curing stage, thereby optimizing the fit and improving the colloidal barrier performance.

[0030] (4) By using polyether-modified isocyanate curing agent (-NCO content 5%-10%) and special acrylic oligomer containing double bonds, flexible long chains are introduced during thermosetting to improve the adsorption and adhesion of colloid to PET, reduce bubble defects, and provide crosslinking points for UV curing, thereby achieving a balance between colloid strength and flexibility.

[0031] (5) Ensure component uniformity through stepwise mixing and filtration, while controlling the conditions for secondary curing (thermal curing 80-120℃, 60-120 seconds, UV curing 800-1000mJ / cm). 2 The crosslinking process has been optimized, enabling the colloid to quickly solidify at lower temperatures and be strengthened by UV radiation, thus ensuring the stability of the waterproof adhesive's performance.

[0032] (6) Through secondary curing, namely thermal curing followed by UV curing, a waterproof adhesive layer of 18-22μm thickness is formed on the PET film, with a peel strength of 900-1000gf. At the same time, it can withstand 60℃ hot water for 12 hours with a pass rate of ≥90%, which is significantly better than the existing products with 4-6 hours of high-efficiency waterproofing, thus meeting the waterproof requirements of high-performance flexible circuit boards. Attached Figure Description

[0033] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0034] Figure 1 This is a product state diagram of a waterproof adhesive cured on a flexible circuit board according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic flowchart illustrating the steps of a method for preparing a waterproof adhesive for a flexible circuit board according to an embodiment of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings. In this specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation thereof.

[0037] This invention provides a waterproof adhesive for flexible circuit boards. Through the specific composition and ratio of agents A, B1, and B2, a synergistic effect of thermosetting and UV curing is achieved. Initial thermosetting ensures the adhesive's shape and initial tack, while subsequent UV curing enhances crosslinking density. This allows the waterproof adhesive to maintain flexibility while possessing high strength and excellent barrier properties, increasing the waterproof pass-through rate to ≥90% after 12 hours in hot water at 60°C, thereby improving the reliability and lifespan of the flexible circuit board.

[0038] This waterproof adhesive is composed of Agent A, Agent B1, and Agent B2 in a weight ratio of 100:5-8:5-10. The specific components of the waterproof adhesive, by weight, are as follows:

[0039] Agent A comprises: 40-60 parts of acrylic resin polymer, 20-40 parts of polyurethane acrylate resin, 5-10 parts of modified terpene resin, 0.5-2 parts of photoinitiator, 0.2-0.8 parts of defoamer, and 10-20 parts of solvent;

[0040] Agent B1 includes: 60-80 parts of modified non-blocked isocyanate curing agent and 20-40 parts of solvent;

[0041] Agent B2 consists of 60-80 parts of a special acrylic oligomer with isocyanate groups and double bonds, and 20-40 parts of solvent.

[0042] See Figure 1 The product form shown is an example of coating and curing the waterproof adhesive of the present invention onto a flexible keyboard circuit board.

[0043] In application, mix Agent A, Agent B1, and Agent B2 in the above proportions, and then perform a second curing process to form a waterproof adhesive layer. The second curing process includes heat curing and UV curing. The heat curing conditions are baking at 80-120℃ for 60-120 seconds, and the UV curing UV energy is 800-1000 mJ / cm². 2 .

[0044] See Figure 2 A process flow diagram of the preparation method of the waterproof adhesive of the present invention is shown. Specifically, the preparation method includes the following steps:

[0045] Step S100: Dissolve the modified terpene resin in a solvent to form a solution with a solid content of 50%-55%;

[0046] Step S200: After mixing the solution from step S100 with the photoinitiator and solvent, add the acrylic resin polymer, polyurethane acrylate resin and defoamer in sequence, and stir at 400-600 rpm for 50-70 min. After filtration, obtain agent A.

[0047] Step S300: Mix the modified isocyanate curing agent with the solvent and stir at 250-350 rpm for 20-40 min, then filter to obtain agent B1;

[0048] Step S400: Mix the special acrylic oligomer with isocyanate groups and double bonds with the solvent and stir at 250-350 rpm for 20-40 min. Filter to obtain agent B2.

[0049] Step S500: Mix Agent A, Agent B1 and Agent B2 in a weight ratio of 100:5-8:5-10 until homogeneous to obtain waterproof adhesive.

[0050] Agents A, B1, and B2 are mixed in a specific ratio and then screen-coated onto a PET film. The film thickness is controlled at 18-22 μm. The mixture is first heat-cured at 80-120℃ for 60-120 seconds, followed by UV curing (energy 800-1000 mJ / cm²). 2 This process ultimately forms a waterproof adhesive layer. After immersing in 60℃ hot water for 12 hours, the waterproof pass rate of this layer is ≥90%, and the peel strength reaches 900-1000gf.

[0051] Agent A serves as the main agent, with the acrylic resin polymer acting as the backbone of the resin system, providing basic adhesion and crosslinking sites; polyurethane acrylate resin serves as a key component for flexibility adjustment and secondary crosslinking; and modified terpene resin is used to enhance affinity and initial tack to substrates such as PET.

[0052] Meanwhile, photoinitiators are used to initiate the UV curing reaction; defoamers ensure the adhesive layer is free of defects; and solvents are used to adjust the viscosity to suit screen printing.

[0053] Agent B1 is a thermosetting agent. The core function of the modified non-blocked isocyanate curing agent is to provide active isocyanate groups (-NCO) at a lower temperature (80-120℃) to initiate the initial crosslinking reaction.

[0054] Agent B2 is a bridging curing agent. It is a special acrylic oligomer with isocyanate groups and double bonds. This component is the "bridge" connecting thermosetting and UV curing. Its molecular structure contains both -NCO that can react with hydroxyl groups and double bonds that can participate in free radical polymerization.

[0055] In one example, preferably, the acrylic resin polymer has a weight-average molecular weight of 250,000-350,000, a standard viscosity of 6,000-10,000 mPa·s, contains hydroxyl and carboxyl functional groups, and has an acid value of 5%-10% and a hydroxyl value of 10%-15%.

[0056] The molecular weight and functional groups in acrylic resin polymers ensure that there is no stringing or flowing during screen printing, and provide sufficient cross-linking sites to enhance the strength and adhesion of the colloid. This molecular weight and viscosity range is key to ensuring the printability of screen printing. If the molecular weight is too high or the viscosity is too high, stringing is likely to occur during printing; if it is too low, the colloid will easily flow and spread, affecting the accuracy of the lines.

[0057] In addition, the polymer is designed to contain hydroxyl (-OH) and carboxyl (-COOH) functional groups. These functional groups provide sufficient sites for subsequent crosslinking reactions with agents B1 and B2. By forming chemical bonds such as urethane bonds, the polymer significantly improves the cohesive strength and adhesion of the colloid and reduces its hydrophilicity, thereby fundamentally improving its waterproof durability.

[0058] For example, when the molecular weight of the acrylic resin polymer reaches approximately 300,000, the viscosity is approximately 6500-6800 mPa·s, the acid value is 8%, and the hydroxyl value is 12%. The resulting waterproof adhesive film layer produces clear and diffused printed lines when used in flexible circuits.

[0059] In one example, preferably, the polyurethane acrylate resin is a difunctional polyether type with a viscosity of 4000-12000 mPa·s. For example, Changxing DR-U379 (viscosity approximately 10000 mPa·s) can be used. This polyurethane acrylate resin acts as an internal plasticizer during the thermosetting stage, improving the flexibility of the waterproof adhesive and its adhesion to PET. Then, during UV curing, it undergoes a cross-linking reaction with the acrylic resin system, forming a dense network structure. Standard performance tests show that after complete curing, the waterproof adhesive exhibits excellent flexibility and adheres without air bubbles.

[0060] In one example, preferably, agent B1 uses a modified isocyanate curing agent of the polyether modified type with a -NCO content of 5%-10%. For example, Lihuaxin PU532 can be used. Simultaneously, agent B2 is used in conjunction with a special acrylic oligomer containing isocyanate groups and double bonds. For example, Sartoma CN1073 NS, Changxing DR-U272, etc., can be used.

[0061] This component plays a dual role in the resin system as both a "flexibility enhancer" and a "secondary crosslinking agent." During the thermosetting stage, its flexible polyether chains act as an "internal plasticizer," interpenetrating within the initial network of the acrylic resin. This imparts excellent flexibility and pressure sensitivity to the colloid, allowing it to fully wet the substrate surface when laminating PET, reducing air bubbles and improving adhesion. In the subsequent UV curing stage, the acrylic double bonds at both ends of its molecules are activated by a photoinitiator, participating in free radical polymerization. Together with the double bonds grafted onto the acrylic resin via agent B2, they construct a dense interpenetrating network (IPN), significantly enhancing the final strength and moisture barrier properties of the colloid, and increasing the crosslinking density of the waterproof adhesive mixture.

[0062] Experiments have shown that removing agent B2 from the composition of the waterproof adhesive will significantly reduce the peel strength of the final waterproof adhesive and also affect its 12-hour waterproof performance.

[0063] Furthermore, improper use of agent B1 can also significantly reduce the 12-hour water resistance by approximately 50%-60%.

[0064] For example, for the specific resin system other than agent A and agents B1 and B2, those skilled in the art can select the specific components according to conventional technical means and adjust them to an appropriate ratio through experiments.

[0065] Photoinitiators such as 184, 1173, or TPO, or combinations thereof, can be used to ensure a rapid and complete UV curing reaction.

[0066] Defoamers can be silicone-based (such as Deqian 6800), defoaming polymers, or polymer defoamers to effectively prevent the introduction of air bubbles during stirring and printing, ensuring a continuous and dense adhesive layer.

[0067] The solvents in Agent A, Agent B1, and Agent B2 can be common resin solvent products. The same solvent can be used for all three components, or different solvents can be used depending on the preparation requirements of each component.

[0068] Commonly used solvents include ethylene glycol butyl ether acetate, diethylene glycol methyl ether acetate, or DBE. These solvents have good solubility for all components of the resin system, a moderate evaporation rate, and are conducive to the formation of a smooth film.

[0069] The aforementioned photoinitiator, defoamer, and solvent are essential components in the formulation of waterproof adhesives. These essential components ensure efficient UV curing, a defect-free adhesive layer, and overall adaptability to the manufacturing process.

[0070] Preferably, TPO is used as a photoinitiator and ethylene glycol butyl ether acetate is used as a solvent. Experiments have verified that the viscosity of the waterproof adhesive is stable at 6500-6900 mPa·s, the solid content is 50%-55%, and no bubbles are generated.

[0071] The modified isocyanate curing agent in agent B1 is a polyether-modified non-blocked isocyanate with an isocyanate group (-NCO) content of 5%-10%. The introduction of polyether segments enhances the flexibility of the curing agent itself and enables it to react with the hydroxyl groups in agent A at a lower temperature (80-120℃), overcoming the disadvantage of traditional blocked isocyanates requiring higher dissociation temperatures.

[0072] Specifically, the synergistic effect of agent B1 and agent B2 and the mechanism of the two-stage curing reaction are further explained as follows:

[0073] During the thermosetting stage, the modified isocyanate in agent B1 reacts with the hydroxyl groups (-OH) of the acrylic resin in agent A to form urethane bonds (-NH-COO-), creating a preliminary three-dimensional network structure. This transforms the waterproof adhesive mixture from a fluid state to a solid state, achieving initial shaping. At this stage, the waterproof adhesive acquires a certain strength (peel force of approximately 400-500 gf) and basic pressure-sensitive adhesion.

[0074] Meanwhile, the special acrylic oligomers in agent B2 also participate in the reaction: their -NCO groups react with the -OH groups of the acrylic resin. However, unlike other reactions, this reaction is equivalent to "grafting" a side chain containing both flexible segments and acrylic double bonds at the ends onto the rigid acrylic backbone. The flexible segments further enhance the softness and conformability of the thermosetting colloid; while the introduced double bonds pre-lay crosslinking points for the next stage of UV curing.

[0075] During the UV curing stage, irradiation with UV light of a certain energy intensity causes the photoinitiator in Agent A to decompose and generate free radicals. These free radicals first initiate the polymerization and cross-linking of the double bonds within the polyurethane acrylate resin itself in Agent A. More importantly, the free radicals also initiate a copolymerization reaction between the double bonds of the polyurethane acrylate and the double bonds grafted onto the acrylic resin via Agent B2. This causes the originally relatively independent acrylic resin network and polyurethane acrylate network to be tightly connected together by chemical bonds (CC bonds), forming a highly dense and unified three-dimensional cross-linked network structure.

[0076] This step-by-step, synergistic curing mechanism effectively balances the contradiction between the "initial adhesion" and "final strength / barrier properties" of the waterproof adhesive. Experimental verification (detailed results can be found in the examples and comparative examples below) shows that, for instance, in Comparative Example 1, the lack of B2 agent resulted in the loss of the UV crosslinking bridge, leading to insufficient final strength and waterproofing. In Comparative Examples 3-5, the improper proportion of B1 agent resulted in insufficient thermosetting crosslinking, potentially leading to insufficient setting (adhesive flow) or excessively hard adhesive (poor adhesion), further causing a significant decrease in waterproofing performance (to 50%-70%).

[0077] In one example, after using the component proportions of the waterproof adhesive of the present invention, the final waterproof adhesive product can be obtained through a dual curing process of heat curing and UV curing. Specifically, in the first heat curing stage, due to the use of this waterproof adhesive, the curing temperature can be reduced to 80-120°C, and the preferred heat curing time is 60-120 seconds. Then, in the second UV curing stage, the UV curing energy is controlled at 800-1000 mJ / cm². 2 .

[0078] The thermosetting stage allows the waterproof adhesive to initially take shape (at this point, the peel strength is 400-500 gf). In particular, the -NCO in agents B1 and B2 reacts with the hydroxyl groups in the resin system of agent A to form urethane bonds, which initially shapes the adhesive. At the same time, agent B2 introduces a double bond structure into the acrylic chain.

[0079] Then, during the UV curing stage, the photoinitiator initiates the free radical polymerization of the double bonds of polyurethane acrylate, which bonds with the acrylic resin to form a dense network, thereby improving strength and barrier properties. After the UV curing stage, its peel strength increases to 900-1000 gf.

[0080] The process parameters for both curing stages are crucial. The thermosetting conditions, baking at 80-120℃ for 60-120 seconds, are sufficient to activate the reactivity of the non-blocked isocyanate, achieving colloidal setting with low energy consumption. UV curing energy should be controlled at 800-1000 mJ / cm². 2 The energy is too low (e.g., 600-700 mJ / cm³ in Comparative Example 6). 2 This can lead to insufficient free radicals generated by the photoinitiator, and the double bonds introduced by agent B2 and the double bonds of polyurethane acrylate cannot be fully crosslinked. Ultimately, the colloidal crosslinking density decreases, resulting in the peel strength (700gf) and water resistance (70%) failing to meet the standards.

[0081] See Table 1, which shows the different component ratios of the waterproof adhesives in Examples 1-5 and the specific proportions of the three components.

[0082] Table 1. Formulation ratios and dual-curing parameters for Examples 1-5

[0083] Element Example 1 Example 2 Example 3 Example 4 Example 5 acrylic resin polymer 50 copies 60 copies 40 copies 60 copies 60 copies Changxing's DR-U379 30 copies 20 copies 40 copies 20 copies 20 copies SYLVARES™ 1150 modified terpene resin 5 copies 5 copies 5 copies 5 copies 5 copies Photoinitiator TPO 0.8 copies 0.8 copies 0.8 copies 0.8 copies 0.8 copies Defoamer Deqian 6800 0.5 copies 0.5 copies 0.5 copies 0.5 copies 0.5 copies Ethylene glycol butyl ether acetate 13.7 copies 13.7 copies 13.7 copies 13.7 copies 13.7 copies Modified isocyanates 70 copies 70 copies 70 copies 70 copies 70 copies Ethylene glycol butyl ether acetate 30 copies 30 copies 30 copies 30 copies 30 copies Special acrylic oligomers with isocyanate groups and double bonds CN1073 NS70 copies of Shadomar DR-U27270 copies from Changxing CN1073 NS70 copies of Shadomar CN1073 NS70 copies of Shadomar CN1073 NS70 copies of Shadomar Ethylene glycol butyl ether acetate 30 copies 30 copies 30 copies 30 copies 30 copies Mixing ratio 100:5:5 100:5:5 100:5:5 100:8:5 100:8:10 Dual curing parameters <![CDATA[Bake at 120 °C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120 °C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120°C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120°C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120°C for 90 s; UV energy 800 - 1000 mJ / cm 2 >

[0084] See Table 2, which shows the different component ratios of the waterproof adhesives in Comparative Examples 1-6 and the specific ratios of the three components.

[0085] Table 2. Mixing ratios and dual-curing parameters of Comparative Examples 1-6

[0086] Element Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 acrylic resin polymer 50 copies 80 copies 50 copies 50 copies 50 copies 50 copies Changxing's DR-U379 30 copies none 30 copies 30 copies 30 copies 30 copies SYLVARES™ 1150 modified terpene resin 5 copies 5 copies 5 copies 5 copies 5 copies 5 copies Photoinitiator TPO 0.8 copies 0.8 copies 0.8 copies 0.8 copies 0.8 copies 0.8 copies Defoamer Deqian 6800 0.5 copies 0.5 copies 0.5 copies 0.5 copies 0.5 copies 0.5 copies Ethylene glycol butyl ether acetate 13.7 copies 13.7 copies 13.7 copies 13.7 copies 13.7 copies 13.7 copies Modified isocyanate 70 copies 70 copies 70 copies 70 copies 70 copies 70 copies Ethylene glycol butyl ether acetate 30 copies 30 copies 30 copies 30 copies 30 copies 30 copies Special acrylic oligomers with isocyanate groups and double bonds none none 70 copies of CN1073NS from Shadomar 70 copies of CN1073NS from Shadomar 70 copies of CN1073NS from Shadomar 70 copies of CN1073NS from Shadomar Ethylene glycol butyl ether acetate none none 30 copies 30 copies 30 copies 30 copies Mixing ratio 100:5 100:5 100:3:5 100:10:5 100:3:10 100:5:5 Dual curing parameters <![CDATA[Bake at 120°C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120 °C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120 °C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120°C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120°C for 90 s; UV energy 800 - 1000 mJ / cm 2 > <![CDATA[Bake at 120°C for 90 s; UV energy 600 - 700 mJ / cm 2 >

[0087] See Table 3, which shows the test standards or indicators used for performance testing of Examples 1-5 and Comparative Examples 1-6, as well as the operating instruments or test methods used.

[0088] Based on the standard performance tests shown in Table 3, the performance test results of Examples 1-5 and Comparative Examples 1-6 are shown in Tables 4-5, respectively.

[0089] Table 3 Performance testing standards and testing methods

[0090]

[0091] Table 4 Performance test results of Examples 1-5

[0092]

[0093] Table 5 Performance test results of Comparative Examples 1-6

[0094]

[0095] Examples 1-5 demonstrate the performance of waterproof adhesives after secondary curing under appropriate formulations. The waterproof adhesives in all examples achieved viscosities of 6500-6800 mPa·s, solid content of 50-55%, peel strength of 920-990 gf, no change under high temperature and humidity, and waterproof performance of over 90% (92%-94%).

[0096] The waterproof adhesive in Comparative Example 1 lacked B2 agent, resulting in a peel strength of only 420gf and a waterproof performance reduced to 80%.

[0097] The waterproof adhesive in Comparative Example 2 lacked polyurethane acrylate in its A component, resulting in a significant decrease in its waterproof performance to 40%.

[0098] The improper proportion of agent B1 in the waterproof adhesives of Comparative Examples 3-5 resulted in a significant decrease in their waterproof performance to 50%-70%.

[0099] The waterproof adhesives of various embodiments of the present invention (composed of agent A, agent B1 and agent B2) solve the problems of high curing temperature, large fluctuations in finished product performance, and imbalance between adhesion and strength in existing products in stages through the synergistic mechanism of thermosetting and UV curing (dual curing) by their appropriate component ratio (by weight 100:5-8:5-10). This enables the preparation and application of high-performance waterproof adhesives, especially in the application on flexible circuit boards.

[0100] The waterproof adhesive, preparation method, and application for flexible circuit boards provided by embodiments of the present invention have at least one or a portion of the following advantages:

[0101] (1) Through the specific composition and ratio of Agent A, Agent B1 and Agent B2 (100:5-8:5-10), the synergistic effect of thermosetting and UV curing is achieved. The initial thermosetting ensures the shape and initial tack of the colloid, while the later UV curing enhances the crosslinking density, so that the waterproof adhesive has high strength and excellent barrier properties while maintaining flexibility, and the waterproof pass rate is increased to ≥90% after 12 hours in hot water at 60℃.

[0102] (2) By controlling the molecular weight of acrylic resin polymer to 250,000-350,000 and the viscosity to 6,000-10,000 mPa·s, and containing hydroxyl and carboxyl functional groups (acid value 5%-10%, hydroxyl value 10%-15%), the printability of screen printing is ensured (e.g. no stringing or dripping), while providing sufficient crosslinking sites to enhance the adhesion and water resistance of the colloid;

[0103] (3) By using a difunctional polyether polyurethane acrylate resin (viscosity 4000-12000 mPa·s), it plays an internal plasticizing role in the thermosetting stage to improve flexibility, and participates in cross-linking to form a dense network in the UV curing stage, thereby optimizing the fit and improving the colloidal barrier performance.

[0104] (4) By using polyether-modified isocyanate curing agent (-NCO content 5%-10%) and special acrylic oligomer containing double bonds, flexible long chains are introduced during thermosetting to improve the adsorption and adhesion of colloid to PET, reduce bubble defects, and provide crosslinking points for UV curing, thereby achieving a balance between colloid strength and flexibility.

[0105] (5) Ensure component uniformity through stepwise mixing and filtration, while controlling the conditions for secondary curing (thermal curing 80-120℃, 60-120 seconds, UV curing 800-1000mJ / cm). 2 The crosslinking process has been optimized, enabling the colloid to quickly solidify at lower temperatures and be strengthened by UV radiation, thus ensuring the stability of the waterproof adhesive's performance.

[0106] (6) Through secondary curing, namely thermal curing followed by UV curing, a waterproof adhesive layer of 18-22μm thickness is formed on the PET film, with a peel strength of 900-1000gf. At the same time, it can withstand 60℃ hot water for 12 hours with a pass rate of ≥90%, which is significantly better than the existing products with 4-6 hours of high-efficiency waterproofing, thus meeting the waterproof requirements of high-performance flexible circuit boards.

[0107] While some embodiments of the present general inventive concept have been shown and described, those skilled in the art will understand that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A waterproof adhesive for flexible circuit boards, said waterproof adhesive comprising agent A, agent B1, and agent B2, characterized in that, By weight, Agent A comprises: acrylic resin polymer, 40-60 parts; polyurethane acrylate resin, 20-40 parts; modified terpene resin, 5-10 parts; photoinitiator, 0.5-2 parts; defoamer, 0.2-0.8 parts; solvent, 10-20 parts; wherein, The acrylic resin polymer has a weight-average molecular weight of 250,000-350,000 and a standard viscosity of 6,000-10,000 mPa·s. The acrylic resin polymer has hydroxyl and carboxyl functional groups, an acid value of 5%-10%, and a hydroxyl value of 10%-15%. The polyurethane acrylate resin is a polyether-type polyurethane acrylate resin with two functional groups, and its standard viscosity is 4000-12000 mPa·s. The B1 agent comprises: 60-80 parts of a modified non-blocked isocyanate curing agent; and 20-40 parts of a solvent; wherein... The modified non-blocked isocyanate curing agent is a polyether-modified isocyanate curing agent, and the content of isocyanate group -NCO is 5%-10%; The B2 agent comprises: a special acrylic oligomer with isocyanate groups and double bonds, 60-80 parts; and a solvent, 20-40 parts; wherein... The weight ratio of agent A, agent B1, and agent B2 is in the range of 100:5-8:5-10.

2. The waterproof adhesive according to claim 1, characterized in that, After the B1 agent and the B2 agent are mixed in a solvent, the isocyanate group -NCO undergoes a chemical cross-linking reaction with the hydroxyl groups in the acrylic resin polymer in the A agent. During thermosetting, a flexible long chain with a double bond structure is introduced into the acrylic main chain to enhance the flexibility of the waterproof adhesive.

3. The waterproof adhesive according to claim 2, characterized in that, The photoinitiator is any one of 184, 1173, and TPO, or any combination thereof. The defoamer is any one of silicone defoamers, defoaming polymer defoamers, polymer defoamers, or any combination thereof.

4. The waterproof adhesive according to claim 3, characterized in that, The solvents used in Agent A, Agent B1, and Agent B2 are any one of ethylene glycol butyl ether acetate, diethylene glycol methyl ether acetate, DBE, or any combination thereof.

5. A method for preparing a waterproof adhesive for flexible circuit boards, the method being used to prepare the waterproof adhesive according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: Step S100: Dissolve the modified terpene resin in a solvent to form a solution with a solid content of 50%-55%; Step S200: After mixing the solution from step S100 with the photoinitiator and solvent, add the acrylic resin polymer, polyurethane acrylate resin and defoamer in sequence, and stir at 400-600 rpm for 50-70 min. After filtration, obtain agent A. Step S300: Mix the modified isocyanate curing agent with the solvent and stir at 250-350 rpm for 20-40 min, then filter to obtain agent B1; Step S400: Mix the special acrylic oligomer with isocyanate groups and double bonds with the solvent and stir at 250-350 rpm for 20-40 min. Filter to obtain agent B2. Step S500: Mix Agent A, Agent B1 and Agent B2 in a weight ratio of 100:5-8:5-10 until homogeneous to obtain waterproof adhesive; The mixture of agent A, agent B1, and agent B2 undergoes a second curing process to form a waterproof adhesive layer. This second curing process sequentially includes heat curing and UV curing. The thermosetting conditions are baking at 80-120°C for 60-120 seconds. The UV energy for UV curing is 800-1000 mJ / cm². 2 .

6. The application of a waterproof adhesive on a flexible circuit board, wherein the waterproof adhesive is the waterproof adhesive according to any one of claims 1-4 or the waterproof adhesive is the waterproof adhesive obtained by the preparation method according to claim 5, characterized in that, The waterproof adhesive is screen-printed onto a PET film, and then subjected to heat curing and UV curing to form a waterproof adhesive layer with a thickness of 18-22 μm. The waterproof adhesive layer has a waterproof pass rate of ≥90% after being immersed in hot water at 60℃ for 12 hours. The peel strength of the waterproof adhesive layer is 900-1000gf.

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