Transparent flexible copper-clad plate with high peel strength and production process thereof

Abstract

The invention relates to the technical field of electronic packaging materials, and discloses a high-peel-strength transparent flexible copper-clad plate and a production process thereof.The copper-clad plate comprises a flexible copper foil and an adhesive layer, and the adhesive layer is formed by curing biphenyl epoxy resin, modified polyvinyl butyral resin prefabricated liquid, methylhexahydrophthalic anhydride and a silane coupling agent; the prefabricated liquid is prepared from PVB, a solvent, zinc isoocatanoate and acetylacetone. A latent catalytic system formed by zinc isoocatanoate and acetylacetone is utilized, catalytic activity is shielded through coordination at normal temperature, and the working life of a glue solution is prolonged; during high-temperature lamination, an active center is dissociated and released, and PVB hydroxyl and epoxy resin are catalyzed to be subjected to in-situ chemical grafting. According to the scheme, microscopic phase separation in the curing process is effectively inhibited, the lamination bubble defect is eliminated from the source while the high transparency of the adhesive layer is ensured, and the interface peel strength and heat aging resistance of the copper-clad plate are improved.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging materials technology, specifically to a transparent flexible copper-clad laminate with high peel strength and its manufacturing process. Background Technology

[0002] With the development of flexible display technology, touch panels, and automotive optoelectronic applications, the market has placed higher demands on the optical and mechanical properties of transparent flexible copper clad laminates (FCCLs). Among transparent adhesive systems, epoxy resin is widely used due to its excellent insulation, bonding strength, and optical transparency. However, cured epoxy resin has a high crosslinking density and is brittle and hard, making it difficult to meet the bending resistance requirements of flexible circuit boards. Therefore, it is usually necessary to introduce polymer toughening agents for modification.

[0003] Polyvinyl butyral (PVB) is often used as a toughening modifier for epoxy resins due to its excellent flexibility, adhesion, and optical properties. However, PVB and epoxy resin / anhydride curing systems are thermodynamically incompatible. During the curing process after adhesive coating, as the molecular weight of the epoxy resin increases, the mixing entropy of the system decreases, and microscopic phase separation easily occurs between the components. This phase separation behavior leads to the formation of micro-regions with uneven refractive index within the resin matrix, resulting in light scattering, increased haze, and reduced overall light transmittance, making it difficult to meet the application requirements of high-end optical display scenarios.

[0004] To improve compatibility and enhance interfacial adhesion strength, existing technologies attempt to utilize metal salt catalysts to promote esterification or transesterification reactions between the hydroxyl groups on the PVB molecular chain and epoxy resin or acid anhydride, thereby inhibiting phase separation through chemical bonding. However, traditional metal salt catalysts (such as zinc salts and tin salts) exhibit high Lewis acid activity at room temperature. Direct addition leads to a sharp increase in viscosity of the adhesive solution during storage and coating, resulting in an extremely short pot life, which is difficult to meet the requirements of industrial roll-to-roll continuous coating processes.

[0005] Furthermore, to prevent the adhesive from pre-curing during the coating and drying stage, the drying temperature or time often has to be lowered during production. This results in a higher residual solvent content in the semi-cured adhesive film during stage B. When this type of adhesive film is subsequently laminated at high temperatures, the residual solvent rapidly vaporizes upon heating. At this point, the resin viscosity has not yet decreased sufficiently to allow for degassing, which can easily lead to the formation of microbubbles or delamination at the interface between the copper foil and the resin, affecting the thermal shock resistance and reliability of the copper-clad laminate. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a transparent flexible copper-clad laminate with high peel strength and its manufacturing process. It solves the problems of phase separation during the curing process of the physical blending system of polyvinyl butyral modified epoxy resin adhesive, which leads to a decrease in transparency and makes it difficult to simultaneously achieve high peel strength and excellent heat aging resistance. At the same time, the traditional high residual solvent process is prone to producing bubble defects during high-temperature lamination.

[0007] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a transparent flexible copper-clad laminate with high peel strength, employing the following technical solution: A high peel strength transparent flexible copper-clad laminate includes a flexible copper foil and an adhesive layer attached to the surface of the flexible copper foil. The adhesive layer is cured from components comprising the following parts by weight: 60-80 parts of biphenyl-type epoxy resin; 66.7-133.3 parts of modified polyvinyl butyral resin pre-solution; 31.5-42 parts of methylhexahydrophthalic anhydride; and 1-3 parts of silane coupling agent. The modified polyvinyl butyral resin pre-solution is prepared from raw materials including polyvinyl butyral resin, mixed solvent, zinc isooctanoate, and acetylacetone, and its solid content is 30 wt%.

[0008] By employing the above technical solution, this invention utilizes a latent catalytic system composed of zinc isooctanoate and acetylacetone, combined with the hydroxyl functional groups of polyvinyl butyral (PVB) resin, to achieve in-situ chemical grafting and compatibility control of the resin network. Its mechanism of action is as follows: During room temperature and solvent evaporation, acetylacetone, acting as a chelating ligand, forms a stable coordination structure with the zinc ions at the center of zinc isooctanoate, effectively inhibiting the catalytic activity of zinc ions on the reaction between epoxy resin and anhydride, thereby maintaining the viscosity stability of the adhesive during storage and coating drying. During the high-temperature curing stage, this coordination structure undergoes thermal dissociation, releasing zinc ions that catalyze the hydroxyl groups on the PVB molecular chain to undergo transesterification and esterification reactions with the epoxy resin-anhydride curing network.

[0009] This chemical bonding linkes thermoplastic PVB molecules into the crosslinked network of thermosetting epoxy resin, overcoming microscopic phase separation caused by differences in solubility parameters during curing and eliminating interfacial light scattering, thus obtaining a highly transparent adhesive layer. Simultaneously, the chemical bonding restricts the thermal motion of PVB molecular chains at high temperatures, improving the bonding stability of the interface under high-temperature conditions and preventing a decrease in peel strength due to chain segment relaxation in physically blended systems.

[0010] Preferably, the epoxy equivalent of the biphenyl-type epoxy resin is 280-300 g / eq; the pre-prepared modified polyvinyl butyral resin has a weight-average molecular weight of 100,000-150,000 and a hydroxyl content of 18-25 wt%; and the silane coupling agent is an epoxy-functionalized silane coupling agent.

[0011] By adopting the above technical solution and selecting PVB resin with specific molecular weight and hydroxyl content, sufficient grafting reaction sites can be provided and the toughening effect on the epoxy resin matrix can be guaranteed. The epoxy silane coupling agent connects the inorganic copper foil interface and the organic resin matrix through covalent bonds, further improving the material's resistance to humid heat aging.

[0012] Preferably, the mixed solvent consists of butanone and propylene glycol methyl ether acetate.

[0013] By adopting the above technical solution, the solubility of methyl ethyl ketone and the medium-high boiling point characteristics of propylene glycol methyl ether acetate are used to form a gradient evaporation system, which ensures the leveling of the coating surface during the drying process and avoids surface defects caused by uncontrolled solvent evaporation rate.

[0014] Preferably, the preparation process of the modified polyvinyl butyral resin prepreg includes: first dissolving polyvinyl butyral resin in a mixed solvent, adding zinc isooctanoate for a complexation reaction, cooling down, and then adding acetylacetone for a coordination reaction; wherein the amount of zinc isooctanoate added is 0.5% of the weight of polyvinyl butyral resin.

[0015] By employing the above-described technical solution, this stepwise feeding process ensures that zinc isooctanoate first contacts and disperses with the hydroxyl groups on the PVB chain, followed by the addition of acetylacetone to form coordination protection. This pre-preparation process allows zinc ions to catalyze the reaction of PVB hydroxyl groups nearby during subsequent heat release, improving grafting efficiency.

[0016] Preferably, in the modified polyvinyl butyral resin prepreg, the molar ratio of acetylacetone to zinc isooctanoate is 2:1 to 5:1.

[0017] By adopting the above technical solution, this molar ratio range achieves a balance between ensuring catalyst latency and high-temperature activity, maintaining the pot life of the adhesive while ensuring that the ligands fully dissociate at the curing temperature to initiate the crosslinking reaction.

[0018] Secondly, the present invention provides a manufacturing process for a transparent flexible copper-clad laminate with high peel strength, comprising the following steps: Adhesive preparation: The modified polyvinyl butyral resin prepreg, biphenyl epoxy resin, silane coupling agent and methyl hexahydrophthalic anhydride are mixed and dispersed, and filtered and degassed to obtain the coating adhesive. Coating and drying: The coating adhesive is applied to the surface of the release film, and the solvent is removed by gradient drying to form a semi-cured adhesive film; Reactive lamination: The semi-cured adhesive film is bonded to a flexible copper foil and hot-pressed under high temperature hot rollers; Post-curing: The hot-pressed copper-clad laminate is sent into an oven for curing treatment. After cooling, the release film is removed to obtain the transparent flexible copper-clad laminate with high peel strength.

[0019] By employing the above technical solution, this process utilizes the temperature-sensitive characteristics of the catalytic system to separate solvent removal and chemical crosslinking over time. During the coating and drying stages, the catalyst is in an inactive state, and the resin system maintains a low reaction rate, allowing for deep solvent removal without gelation. During the reactive lamination stage, high temperature rapidly activates the catalyst, causing the resin viscosity to increase and crosslinking to occur, achieving bonding with the copper foil.

[0020] Preferably, in the adhesive preparation step, the adhesive temperature is controlled to be no higher than 35°C; the molar ratio of the anhydride group of the methyl hexahydrophthalic anhydride to the epoxy group of the biphenyl epoxy resin is 0.85-0.95:1.

[0021] By employing the above technical solutions, the low-temperature modulation environment prevents premature ligand dissociation, ensuring the operational stability of the adhesive solution. Maintaining a slightly insufficient molar ratio of acid anhydride to epoxy groups helps regulate the crosslinking density of the cured product and improves the flexibility of the adhesive layer.

[0022] Preferably, in the coating and drying steps, gradient drying is carried out through three temperature zones: the first temperature zone is 75-85℃, the second temperature zone is 105-115℃, and the third temperature zone is 125-135℃; the residual volatile content in the semi-cured adhesive film after drying is controlled to be 0.3-0.8%.

[0023] By adopting the above technical solution, the latent catalytic system of the present invention allows operation at higher drying temperatures without causing resin aging, thereby safely reducing the residual volatiles in the semi-cured film to extremely low levels and reducing the risk of plate bursting caused by solvent vaporization during high-temperature lamination from the source.

[0024] Preferably, in the reactive lamination step, the temperature of the high-temperature hot roller is set to 170-190℃, the linear pressure is 30-50 kgf / cm, and the linear speed is 1.5-2.5 m / min.

[0025] By adopting the above technical solution, the high temperature environment of 170-190℃ can break the coordination equilibrium of zinc isooctanoate-acetylacetone, rapidly release catalytic activity, and enable the resin to complete leveling and establish preliminary chemical connection in a short time when in contact with copper foil.

[0026] Preferably, the post-curing step specifically involves: first curing at 100°C for 2 hours, then raising the temperature to 180°C for 4 hours.

[0027] By adopting the above technical solution, the segmented post-curing process helps to eliminate the thermal stress generated during lamination and ensures the complete progress of the PVB grafting reaction and the epoxy resin curing reaction, ultimately obtaining a copper-clad laminate product with uniform performance.

[0028] This invention provides a transparent flexible copper-clad laminate with high peel strength and its manufacturing process. It has the following beneficial effects: 1. This invention introduces a latent catalytic system composed of zinc isooctanoate and acetylacetone to catalyze an ester exchange reaction between the hydroxyl groups on the polyvinyl butyral (PVB) molecular chain and the epoxy resin anhydride curing network during the high-temperature curing stage. This chemical grafting effect inhibits micro-phase separation caused by differences in component solubility parameters during the curing process, resulting in a cured adhesive layer with a haze of less than 1.0% and a total light transmittance of over 90%. At the same time, the chemical bonding restricts the thermal movement of the PVB flexible chain segments at high temperatures, thereby improving the peel strength retention rate of the copper clad laminate after long-term aging at 150°C. This solves the problem of a significant decrease in interfacial bonding strength in traditional physical blending systems under high-temperature conditions.

[0029] 2. The modified PVB resin prepreg of this invention utilizes acetylacetone as a ligand to form a stable coordination structure with zinc isooctanoate, effectively inhibiting the Lewis acid activity of zinc ions during room temperature and solvent evaporation. Test data shows that the pot life of this adhesive system exceeds 60 hours at 25°C, with slow viscosity growth. This solves the problem of short pot life caused by traditional metal salt catalysts, which makes it difficult to meet the requirements of long-cycle roll-to-roll coating operations in industrial applications, and ensures the process stability of the production process.

[0030] 3. This invention utilizes the latent properties of catalysts to allow the semi-cured adhesive film in stage B to undergo deep drying without pre-curing, controlling the residual volatile content to below 0.8%. This low-volatile process eliminates microbubbles or delamination defects caused by solvent vaporization and accumulation during high-temperature and high-pressure lamination, improving the thermal shock resistance of copper-clad laminates and preventing blistering or board bursting during tin bleaching tests at 300°C, thereby improving the process yield and reliability of the product. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a modified polyvinyl butyral (PVB) resin preform A, the preparation process of which includes the following steps: (1) In a reactor equipped with a reflux condenser, thermometer and mechanical stirrer, add 700 parts of mixed solvent (350 parts of butanone and 350 parts of propylene glycol methyl ether acetate) and 300 parts of polyvinyl butyral resin (PVB). The weight average molecular weight of PVB is 100,000 and the hydroxyl content is 18 wt%.

[0033] (2) Turn on the stirrer and heat the system to 55°C. Stir at a constant temperature for 90 minutes until PVB is completely dissolved to form a homogeneous transparent solution.

[0034] (3) Keep the temperature at 55℃, add 1.5 parts of zinc isooctanoate (purity >98%), and continue to stir at a constant temperature for 45 minutes.

[0035] (4) Reduce the temperature of the reactor to 35°C.

[0036] (5) Slowly add 0.86 parts of acetylacetone (AcAc) (controlling the molar ratio of acetylacetone to zinc isooctanoate to about 2:1) over a period of 10 minutes.

[0037] Stirring was maintained during the dripping process. After the dripping was completed, stirring was continued for 20 minutes. The material was then discharged and filtered through a 300-mesh filter to obtain a modified PVB resin pre-formulated liquid A with a solid content of approximately 30%.

[0038] Preparation Example 2: This preparation example provides a modified polyvinyl butyral (PVB) resin preform B, the preparation process of which includes the following steps: (1) In a reactor equipped with a reflux condenser, thermometer and mechanical stirrer, add 700 parts of mixed solvent (400 parts of butanone and 300 parts of propylene glycol methyl ether acetate) and 300 parts of polyvinyl butyral resin (PVB). The weight average molecular weight of PVB is 120,000 and the hydroxyl content is 20 wt%.

[0039] (2) Turn on the stirrer and heat the system to 60°C. Stir at a constant temperature for 60 minutes until PVB is completely dissolved to form a homogeneous transparent solution.

[0040] (3) Keep the temperature at 60℃, add 1.5 parts of zinc isooctanoate (purity >98%), and continue to stir at a constant temperature for 30 minutes.

[0041] (4) Reduce the temperature of the reactor to 30°C.

[0042] (5) Slowly add 1.50 parts of acetylacetone (AcAc) (controlling the molar ratio of acetylacetone to zinc isooctanoate to be about 3.5:1) over a period of 12 minutes.

[0043] Stirring was maintained during the dripping process. After the dripping was completed, stirring was continued for 20 minutes. The material was then discharged and filtered through a 300-mesh filter to obtain modified PVB resin pre-solution B with a solid content of approximately 30%.

[0044] Preparation Example 3: This preparation example provides a modified polyvinyl butyral (PVB) resin preform C, the preparation process of which includes the following steps: (1) In a reactor equipped with a reflux condenser, thermometer and mechanical stirrer, add 700 parts of mixed solvent (450 parts of butanone and 250 parts of propylene glycol methyl ether acetate) and 300 parts of polyvinyl butyral resin (PVB). The weight average molecular weight of PVB is 150,000 and the hydroxyl content is 25 wt%.

[0045] (2) Turn on the stirrer and heat the system to 65°C. Stir at a constant temperature for 60 minutes until PVB is completely dissolved to form a homogeneous transparent solution.

[0046] (3) Keep the temperature at 65℃, add 1.5 parts of zinc isooctanoate (purity >98%), and continue to stir at a constant temperature for 30 minutes.

[0047] (4) Reduce the temperature of the reactor to 25°C.

[0048] (5) Slowly add 2.15 parts of acetylacetone (AcAc) (controlling the molar ratio of acetylacetone to zinc isooctanoate to about 5:1) over a period of 15 minutes.

[0049] Stirring was maintained during the dripping process. After the dripping was completed, stirring was continued for 30 minutes. The material was then discharged and filtered through a 300-mesh filter to obtain a modified PVB resin pre-formulated liquid C with a solid content of approximately 30%.

[0050] Examples 1-3: Example 1: This example provides a transparent flexible copper-clad laminate with high peel strength and its preparation method, using the modified PVB resin prepreg A obtained in Preparation Example 1.

[0051] Adhesive formulation (by weight): Component A: 80 parts of biphenyl-type epoxy resin (NC-3000H, epoxy equivalent 290g / eq).

[0052] Component B: 66.7 parts of the modified PVB resin pre-solid A obtained in Preparation Example 1 (pre-solid content 30%, equivalent to 20 parts of solid PVB resin).

[0053] Component C: 42 parts of methylhexahydrophthalic anhydride (MHHPA, acid anhydride equivalent 168 g / eq).

[0054] Component F: 1 part of 3-glycidyl etheroxypropyltrimethoxysilane (KBM-403).

[0055] Component G: Appropriate amount of mixed solvent (butanone: propylene glycol methyl ether acetate = 1:1) to adjust the solid content of the adhesive to 40%.

[0056] Preparation steps: Adhesive preparation: Add modified PVB resin pre-mixed solution A to a mixing tank, controlling the temperature below 35℃, and then add components A, F, and C in sequence. Disperse using a high-speed disperser at 1200 rpm for 20 minutes, then filter through a 200-mesh nylon screen and degas under vacuum for 10 minutes to obtain the coating adhesive.

[0057] Coating and Gradient Drying: The adhesive is evenly coated onto the surface of the PET release film and then subjected to gradient drying through three temperature zones of a precision coating machine. The temperature zones are set as follows: Zone 1, 75℃; Zone 2, 105℃; and Zone 3, 125℃.

[0058] B-Stage Control: Adjust the conveyor speed to control the thickness of the semi-cured adhesive film after drying to 25μm. Sampling and testing are conducted to control the residual volatile matter (VC) content in the adhesive film to 0.3%.

[0059] Reactive lamination: The semi-cured adhesive film is bonded to the roughened surface of a 12μm electrolytic copper foil and fed into a high-temperature roller press. The hot roller temperature is set to 170℃, the linear pressure to 30kgf / cm, and the linear speed to 1.5m / min.

[0060] Post-curing: After winding, the product is sent into an oven and cured at 100°C for 2 hours. Then, the temperature is raised to 180°C and cured for 4 hours. After cooling, the PET release film is removed to obtain the flexible copper-clad laminate.

[0061] Example 2: This example provides a transparent flexible copper-clad laminate with high peel strength and its preparation method, using the modified PVB resin prepreg B obtained in Preparation Example 2.

[0062] Adhesive formulation (by weight): Component A: 70 parts of biphenyl-type epoxy resin (NC-3000H, epoxy equivalent 290g / eq).

[0063] Component B: 100 parts of the modified PVB resin pre-solid B prepared in Preparation Example 2 (pre-solid content 30%, equivalent to 30 parts of solid PVB resin).

[0064] Component C: 36.5 parts of methylhexahydrophthalic anhydride (MHHPA, anhydride equivalent 168 g / eq).

[0065] Component F: 2 parts of 3-glycidyl etheroxypropyltrimethoxysilane (KBM-403).

[0066] Component G: Appropriate amount of mixed solvent (butanone: propylene glycol methyl ether acetate = 1.5:1) to adjust the solid content of the adhesive solution to 40%.

[0067] Preparation steps: Adhesive preparation: Add modified PVB resin pre-mixed solution B to a mixing tank, controlling the temperature below 30℃, and then add components A, F, and C in sequence. Disperse using a high-speed disperser at 1500 rpm for 15 minutes, then filter through a 200-mesh nylon screen and degas under vacuum for 15 minutes to obtain the coating adhesive.

[0068] Coating and Gradient Drying: The adhesive is evenly coated onto the surface of the PET release film and then subjected to gradient drying through three temperature zones of a precision coating machine. The temperature zones are set as follows: Zone 1, 80℃; Zone 2, 110℃; and Zone 3, 130℃.

[0069] B-Stage Control: Adjust the conveyor speed to control the thickness of the semi-cured adhesive film after drying to 25μm. Sampling and testing are conducted to control the residual volatile matter (VC) content in the adhesive film to 0.5%.

[0070] Reactive lamination: The semi-cured adhesive film is bonded to the roughened surface of an 18μm electrolytic copper foil and fed into a high-temperature roller press. The hot roller temperature is set to 180℃, the linear pressure to 40kgf / cm, and the linear speed to 2.0m / min.

[0071] Post-curing: After winding, the product is sent into an oven and cured at 100°C for 2 hours. Then, the temperature is raised to 180°C and cured for 4 hours. After cooling, the PET release film is removed to obtain the flexible copper-clad laminate.

[0072] Example 3: This example provides a transparent flexible copper-clad laminate with high peel strength and its preparation method, using the modified PVB resin prepreg C obtained in Preparation Example 3.

[0073] Adhesive formulation (by weight): Component A: 60 parts of biphenyl-type epoxy resin (NC-3000H, epoxy equivalent 290g / eq).

[0074] Component B: 33.3 parts of the modified PVB resin pre-solid C1 obtained in Preparation Example 3 (pre-solid solid content 30%, equivalent to 40 parts of solid PVB resin).

[0075] Component C: 31.5 parts of methylhexahydrophthalic anhydride (MHHPA, anhydride equivalent 168 g / eq).

[0076] Component F: 3 parts of 3-glycidyl etheroxypropyltrimethoxysilane (KBM-403).

[0077] Component G: Appropriate amount of mixed solvent (butanone: propylene glycol methyl ether acetate = 2:1) to adjust the solid content of the adhesive to 40%.

[0078] Preparation steps: Adhesive preparation: Add modified PVB resin pre-mixed solution C to a mixing tank, controlling the temperature below 25℃, and then add components A, F, and C in sequence. Disperse using a high-speed disperser at 1500 rpm for 20 minutes, then filter through a 200-mesh nylon screen and degas under vacuum for 20 minutes to obtain the coating adhesive.

[0079] Coating and Gradient Drying: The adhesive is evenly coated onto the surface of the PET release film and then subjected to gradient drying through three temperature zones of a precision coating machine. The temperature zones are set as follows: Zone 1, 85℃; Zone 2, 115℃; and Zone 3, 135℃.

[0080] B-Stage Control: Adjust the conveyor speed to control the thickness of the semi-cured adhesive film after drying to 25μm. Sampling and testing are conducted to control the residual volatile matter (VC) content in the adhesive film to 0.8%.

[0081] Reactive lamination: The semi-cured adhesive film is bonded to the roughened surface of a 12μm electrolytic copper foil and fed into a high-temperature roller press. The hot roller temperature is set to 190℃, the linear pressure to 50kgf / cm, and the linear speed to 2.5m / min.

[0082] Post-curing: After winding, the product is sent into an oven and cured at 100°C for 2 hours. Then, the temperature is raised to 180°C and cured for 4 hours. After cooling, the PET release film is removed to obtain the flexible copper-clad laminate.

[0083] Comparative Examples 1-5: Comparative Example 1 (lacking catalyst and locking system): Compared with Example 2, the difference is that zinc isooctanoate and acetylacetone were not added when preparing the modified PVB resin prepreg B. Only the PVB dissolution step was performed. The remaining raw material ratios and process steps were the same.

[0084] Comparative Example 2 (lacking locking ligand / no latency): Compared with Example 2, the difference is that acetylacetone (AcAc) was not added when preparing the modified PVB resin prepreg B, only zinc isooctanoate was added, and the rest were the same.

[0085] Comparative Example 3 (Change in preparation process / no pre-complexation step): Compared with Example 2, the difference is that the step of preparing the modified PVB resin prepreg is omitted, and a one-pot method is used for direct mixing.

[0086] Specifically, in the adhesive preparation stage, the solvent, PVB resin, zinc isooctanoate, acetylacetone, epoxy resin, coupling agent and acid anhydride are added to the mixing tank at one time for dispersion and mixing, and the remaining coating and lamination processes are the same.

[0087] Comparative Example 4 (Traditional high-residual-solvent process): Compared with Example 2, the difference is that in B-Stage control, the drying parameters are adjusted so that the residual volatile content (VC) in the dried semi-cured film is 3.0% (simulating the typical residual amount in the traditional FCCL process), while the rest are the same.

[0088] Comparative Example 5 (Prior Technology / Inorganic Packing Route): Compared with Example 2, the difference is that PVB resin and the corresponding catalytic locking system are not used. Instead, they are replaced with an equal amount of nano-spherical silica filler (average particle size 0.5 μm). The remaining epoxy resin and acid anhydride curing agent system remain unchanged, and the process is the same.

[0089] Test Example 1-2: Test Example 1: Verification of the stability and feasibility of the adhesive process Take 500g of each of the fresh adhesive solutions prepared in Examples 1 to 3 and Comparative Examples 1 to 3, and store them in a sealed environment at a constant temperature of 25°C.

[0090] The initial viscosity was measured using a Brinell viscometer (rotor model #4, speed 60 rpm), and then the viscosity was measured every 4 hours thereafter. The time required for the viscosity to reach twice the initial value was recorded, and this time was used to characterize the pot life of the adhesive.

[0091] Separately, the semi-cured B-stage adhesive films of Examples 1 to 3, Comparative Examples 2 and 4, after coating and drying, were continuously hot-pressed onto copper foil. A 10-meter-long copper-clad laminate sample was cut, and the surface of the board was observed with a 10x magnifying glass to see if there were bubbles, white spots or resin flow lines with a diameter greater than 0.1 mm.

[0092] Table 1. Results of adhesive storage stability and lamination appearance tests

[0093] Results analysis: According to the data in Table 1, the differences between Examples 1 to 3 and Comparative Example 2 indicate that acetylacetone, as a ligand, has a regulating effect on the reaction latency of the adhesive. In Comparative Example 2, only zinc isooctanoate was added without acetylacetone. The zinc ions exhibited catalytic activity towards the anhydride system at room temperature, leading to a rapid increase in the adhesive viscosity within a short period, and the pot life could not meet the requirements of the coating process.

[0094] The examples demonstrate how zinc ions form chelates with ligands, shielding the catalytically active centers at room temperature and extending the pot life of the adhesive solution to meet industrial production requirements. A comparison between Example 2 and Comparative Example 4 shows that the low solvent residue in the B-stage adhesive film is related to lamination appearance defects. Comparative Example 4 had a higher residual solvent content; during high-temperature lamination, the solvent vaporized instantaneously and could not be expelled from the gelled resin, resulting in dense bubbles on the board surface.

[0095] This application utilizes the latent properties of the catalyst, allowing the solvent content to be reduced to a low level before lamination without pre-curing, thus reducing the source of volatiles during the lamination process. Comparative Example 3 uses a direct mixing method, and its pot life is shorter than that of Example 2. This is because some zinc ions did not form stable chelates with the ligands in time during the mixing process, and their contact with the resin system triggered a slow polymerization reaction.

[0096] Test Example 2: Comprehensive Performance Test of Copper Clad Laminates Peel strength at 90 degrees Celsius was tested according to IPC-TM-650 2.4.9 standard; another sample was placed in a 150°C oven for 168 hours of aging, then removed and cooled to room temperature to test the peel strength after aging, in order to evaluate the heat resistance of the interface.

[0097] According to the IPC-TM-650 2.4.13 standard, the cut samples were completely immersed in tin baths at 288℃ and 300℃ for 10 seconds respectively, and the presence of bubbles or delamination was observed.

[0098] After removing the copper foil by etching, the total light transmittance and haze of the resin layer were tested using a haze meter according to ASTM D1003 standard. Using a dynamic thermomechanical analyzer, the temperature was increased at a rate of 5°C per minute in tensile mode, and the peak temperature of the loss tangent was taken as the glass transition temperature.

[0099] Table 2. Test results of physical and optical properties of copper clad laminate

[0100] Results analysis: According to the data in Table 2, the haze of Examples 1 to 3 was all below 1.0%, while the haze of Comparative Example 1 was higher. In Comparative Example 1, no catalyst system was added, so PVB and epoxy resin could not undergo chemical grafting; they were only physically blended. During the curing process, as the molecular weight of the epoxy resin increased, the difference in solubility parameters between the two phases led to phase separation, forming a microscopic two-phase structure that caused light scattering.

[0101] This application utilizes the active centers of zinc ions released at high temperatures to catalyze the transesterification reaction between the hydroxyl groups on the PVB molecular chain and the epoxy anhydride-cured network. This chemical bonding inhibits phase separation and achieves homogeneous mixing at the molecular level, thereby obtaining higher transparency.

[0102] Regarding heat aging resistance, Comparative Example 1 showed a significant decrease in peel strength after aging at 150°C, while the Example showed a higher retention rate. In physically blended systems, thermoplastic PVB segments exhibit free creep at high temperatures, making them prone to interfacial migration or stress relaxation. In this application, PVB participates in the crosslinking reaction and integrates into the thermosetting network, restricting the thermal movement of the segments and improving the interfacial bonding stability at high temperatures. Therefore, Comparative Example 1 experienced delamination during dip soldering at 288°C, while the Example withstood dip soldering tests at 300°C.

[0103] Compared with Example 2 and Comparative Example 3, the example showed higher peel strength and lower haze. In the direct mixing method (Comparative Example 3), zinc isooctanoate was randomly dispersed throughout the resin system. Some zinc ions were surrounded by acid anhydrides, resulting in a lower probability of contact with PVB hydroxyl groups compared to the pre-mixed method, leading to differences in grafting efficiency. Some PVB remained in a physically entangled form. Comparative Example 5 used inorganic silica filler. Although it had a higher glass transition temperature, the inorganic filler lacked the toughening effect of long-chain polymers, and the rigid interface was prone to stress concentration during deformation, resulting in lower peel strength than the example.

Claims

1. A transparent flexible copper-clad laminate with high peel strength, characterized in that, It includes a flexible copper foil and an adhesive layer attached to the surface of the flexible copper foil, the adhesive layer being cured from components comprising the following parts by weight: Biphenyl-type epoxy resin: 60-80 parts; Modified polyvinyl butyral resin premix: 66.7-133.3 parts; Methylhexahydrophthalic anhydride: 31.5-42 parts; Silane coupling agent: 1-3 parts; The modified polyvinyl butyral resin prepreg is prepared from raw materials including polyvinyl butyral resin, mixed solvent, zinc isooctanoate and acetylacetone, and its solid content is 30wt%.

2. The high peel strength transparent flexible copper-clad laminate according to claim 1, characterized in that, The biphenyl-type epoxy resin has an epoxy equivalent of 280-300 g / eq; the modified polyvinyl butyral resin prepreg has a weight-average molecular weight of 100,000-150,000 and a hydroxyl content of 18-25 wt%; the silane coupling agent is an epoxy-functionalized silane coupling agent.

3. The high peel strength transparent flexible copper-clad laminate according to claim 1, characterized in that, The mixed solvent consists of butanone and propylene glycol methyl ether acetate.

4. The high peel strength transparent flexible copper-clad laminate according to claim 3, characterized in that, The preparation process of the modified polyvinyl butyral resin prepreg includes: First, dissolve polyvinyl butyral resin in a mixed solvent, add zinc isooctanoate to carry out a complexation reaction, cool down, and then add acetylacetone to carry out a coordination reaction. The amount of zinc isooctanoate added is 0.5% of the weight of polyvinyl butyral resin.

5. The high peel strength transparent flexible copper-clad laminate according to claim 4, characterized in that, In the modified polyvinyl butyral resin prepreg, the molar ratio of acetylacetone to zinc isooctanoate is 2:1-5:

1.

6. A manufacturing process for a high peel strength transparent flexible copper-clad laminate, characterized in that, The method for preparing a transparent flexible copper-clad laminate with high peel strength as described in any one of claims 1-5 includes the following steps: Adhesive preparation: The modified polyvinyl butyral resin prepreg, biphenyl epoxy resin, silane coupling agent and methyl hexahydrophthalic anhydride are mixed and dispersed, and filtered and degassed to obtain the coating adhesive. Coating and drying: The coating adhesive is applied to the surface of the release film, and the solvent is removed by gradient drying to form a semi-cured adhesive film; Reactive lamination: The semi-cured adhesive film is bonded to a flexible copper foil and hot-pressed under high temperature hot rollers; Post-curing: The hot-pressed copper-clad laminate is sent into an oven for curing treatment. After cooling, the release film is removed to obtain the transparent flexible copper-clad laminate with high peel strength.

7. The manufacturing process of the high peel strength transparent flexible copper-clad laminate according to claim 6, characterized in that, In the adhesive preparation step, the adhesive temperature is controlled to be no higher than 35°C; the molar ratio of the anhydride group of the methyl hexahydrophthalic anhydride to the epoxy group of the biphenyl epoxy resin is 0.85-0.95:

1.

8. The manufacturing process of the high peel strength transparent flexible copper-clad laminate according to claim 6, characterized in that, In the coating and drying process, gradient drying is carried out through three temperature zones: the first temperature zone is 75-85℃, the second temperature zone is 105-115℃, and the third temperature zone is 125-135℃; the residual volatile content in the semi-cured film after drying is controlled to be 0.3-0.8%.

9. The manufacturing process of the high peel strength transparent flexible copper-clad laminate according to claim 6, characterized in that, In the reactive lamination step, the temperature of the high-temperature hot roller is set to 170-190℃, the linear pressure is 30-50 kgf / cm, and the linear speed is 1.5-2.5 m / min.

10. The manufacturing process of the high peel strength transparent flexible copper-clad laminate according to claim 6, characterized in that, The post-curing step specifically involves: first curing at 100°C for 2 hours, then raising the temperature to 180°C and curing for 4 hours.

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