A thermally cured bio-based composition and a film prepared therefrom

Abstract

The present application relates to the technical field of structural adhesive, and discloses a thermally curable bio-based composition and a film prepared from the same.The thermally curable bio-based composition comprises an acrylic prepolymer, a flame-retardant cashew phenol-formaldehyde resin and a filler.The flame-retardant cashew phenol-formaldehyde resin is obtained by partially substituting the phenolic hydroxyl groups in cashew phenol-formaldehyde resin with chlorinated diphenyl phosphate.The cashew phenol-formaldehyde resin is generated by blending and reacting cashew phenol, phenol and formaldehyde.The present application combines the flame-retardant cashew phenol-formaldehyde resin with other thermally curable compositions to obtain a thermally cured film containing bio-based and being flame-retardant and applied to the protection of electronic devices.Meanwhile, the bio-based structure of the film, i.e., cashew phenol, makes the film have excellent bending resistance after curing, and the film can be used for the protection of flexible lines which need to be repeatedly bent.

Description

Technical Field

[0001] This invention relates to the field of structural adhesives, specifically to a thermosetting bio-based composition and the adhesive film prepared therefrom. Background Technology

[0002] In recent years, with the increasing awareness of environmental protection, bio-based materials have gradually gained attention. Cashew nut shell phenol is a natural phenolic compound, mainly extracted from cashew nut shell liquid, and has a unique chemical structure and diverse industrial applications. Due to its combination of phenolic activity and long carbon side chain characteristics, it is widely used in resin synthesis, coating production, and biomedicine, and is one of the environmentally friendly alternatives to petrochemical products.

[0003] Flexible printed circuit boards (FPCs) are crucial components in batteries and electronic materials, significantly driving the lightweighting and flexibility of electronic components. Besides the copper-based circuitry that provides conductivity, the protective and adhesive films used for surface protection and component bonding are also important structural materials in FPCs. Their performance characteristics dictate that FPC protective films must possess properties such as flame retardancy, resistance to repeated bending, and resistance to high and low temperatures. Currently, FPC protective films are available in epoxy and acrylic types. Epoxy films generally have better high-temperature resistance, and with adjustments to flame retardants, their overall flame retardancy is further improved. However, they have a high cross-linking density and a high content of rigid structures, resulting in relatively poor overall flexibility. Acrylic films generally have better flexibility, but their corresponding high-temperature resistance and flame retardancy are relatively insufficient, primarily limiting their application to less demanding environments. Gradually, some technicians have tried to balance the two properties mentioned above by compounding phenolic resin into acrylic FPC protective films. However, the introduction of phenolic resin still reduces the overall flexibility of the film. In particular, with the development of foldable screen technology, the film's resistance to repeated bending is still insufficient to meet the application requirements in fields with high requirements for bending resistance.

[0004] The flame-retardant properties of FPC protective films are currently achieved primarily through the addition of flame retardants, which are broadly categorized into inorganic and organic flame retardants. Inorganic flame retardant fillers are readily available, but their flame-retardant effect is inferior to that of organic flame retardants, and excessive addition can negatively impact the adhesive properties of the film. Due to environmental and health concerns, halogen-free flame retardants are becoming the mainstream trend for organic flame retardants; however, the added flame retardants pose a risk of free flame within the system, affecting the aging performance of the film. Therefore, chemically bonding flame retardants into the resin to synthesize intrinsically flame-retardant resins is an increasingly important and promising approach. Summary of the Invention

[0005] Based on the above needs, this invention provides a thermosetting bio-based composition and the resulting adhesive film. It combines flame-retardant cashew nut shell resin with a thermosetting acrylic resin to obtain a bio-based, flame-retardant thermosetting adhesive film for protecting electronic devices. Furthermore, the cashew nut shell structure of the bio-based component in this film gives it excellent bending resistance after curing, making it suitable for protecting flexible circuits that require repeated bending. The technical solution is as follows:

[0006] The first aspect of the present invention provides a thermosetting bio-based composition, comprising, by weight, 100-125 parts of an acrylic prepolymer, 3-30 parts of a flame-retardant cashew nut phenolic resin, and 2-20 parts of a filler.

[0007] The acrylic prepolymer comprises the following components, by mass parts: 50-80 parts of soft acrylic monomers, 25-40 parts of hard acrylic monomers, 3-15 parts of hydroxyl monomers, 0.5-5 parts of functional acrylic monomers, 0.1-0.4 parts of initiator, and 200-300 parts of solvent.

[0008] The flame-retardant cashew phenol-phenolic resin contains unreacted phenolic hydroxyl groups, and the functional propylene monomer contains groups that react with phenolic hydroxyl groups at high temperatures of 150-220°C.

[0009] Preferably, the functional propylene monomer is a propylene monomer containing one or more of carboxyl, amide, and acid anhydride groups. Optional propylene monomers containing carboxyl groups include, but are not limited to, one or more of acrylic acid and methacrylic acid. Optional propylene monomers containing amide groups include, but are not limited to, one or more of acrylamide and hydroxyethyl acrylamide. Optional propylene monomers containing acid anhydride groups include, but are not limited to, one or more of acrylic anhydride and methacrylic anhydride.

[0010] Preferably, the acrylic soft monomer is one or more of butyl acrylate, ethyl acrylate, and isooctyl acrylate; the acrylic hard monomer is one or more of methyl methacrylate, styrene, and acrylonitrile; the hydroxyl-containing acrylic monomer is one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate; the functional acrylic monomer is one or more of acrylic acid, acrylamide, methacrylic acid, and glycidyl methacrylate; and the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile.

[0011] Preferably, the acrylic prepolymer is prepared by the following method: a soft acrylic monomer, a hard acrylic monomer, a hydroxyl monomer, and a functional acrylic monomer are mixed to obtain a monomer mixture; half the mass of the monomer mixture is mixed with ethyl acetate solvent, and a quarter mass of initiator is added. After mixing evenly, the mixture is heated to 70-90°C under a nitrogen atmosphere and reacted for 1-3 hours to obtain a reaction solution; the remaining half mass of the monomer mixture, a quarter mass of initiator, and ethyl acetate solvent are mixed and slowly added dropwise to the above reaction solution, reacted at 80-100°C for 1-3 hours, a quarter mass of initiator is added, and the mixture is reacted at 70-90°C for 1-3 hours; the remaining quarter mass of initiator is added, and the mixture is reacted at 60-80°C for 0.5-1 hours, and kept at this temperature for 1-2 hours to obtain the acrylic prepolymer.

[0012] Preferably, the flame-retardant cashew phenol-phenolic resin is prepared by the following method: cashew phenol, phenol and formaldehyde are first reacted to generate cashew phenol-phenolic resin, and then diphenyl chlorophosphate is used to partially replace the phenolic hydroxyl groups in the cashew phenol-phenolic resin to obtain a phosphorus-containing and phenolic hydroxyl-containing flame-retardant cashew phenol-phenolic resin.

[0013] Preferably, the flame-retardant cashew nut phenol-formaldehyde resin is prepared by the following method: 100 parts by weight of cashew nut phenol-formaldehyde resin and 1-5 parts by weight of triethylamine are dissolved in 100 parts by weight of chloroform, mixed evenly, and 3-10 parts by weight of diphenyl chlorophosphate are added dropwise. The mixture is refluxed at 60°C for 6 hours. After the reaction is completed, the resin is washed, the solvent is removed, dried, and discharged to obtain the flame-retardant cashew nut phenol-formaldehyde resin.

[0014] More preferably, the cashew phenol-phenolic resin is prepared by the following method: cashew phenol, phenol and formaldehyde are added in a mass ratio of (20-50):100:(40-45), mixed evenly, 1-5 parts by mass of ammonia water are added as a catalyst, the temperature is raised to 60-90℃, and the reaction is kept at this temperature for 3 hours. After the reaction is completed, hydrochloric acid is added to neutralize to neutrality, and the mixture is dehydrated under vacuum at 80℃. Butanone is added to dissolve the resin, and the cashew phenol-phenolic resin is obtained by discharging.

[0015] Preferably, the filler is one or more of silicon dioxide, aluminum hydroxide, aluminum oxide, calcium carbonate, and titanium dioxide.

[0016] Preferably, the solvent is one or more of ethyl acetate, toluene, xylene, and butanone.

[0017] A second aspect of the present invention provides a thermosetting bio-based adhesive film, the adhesive film being formed by coating the above-mentioned thermosetting bio-based composition, wherein release material is coated on both sides of the adhesive film or one side is coated with release material and the other side is coated with PI material.

[0018] The third aspect of this invention provides a method for using a thermosetting bio-based adhesive film. One side of the film is peeled off as a release liner / release paper and pre-applied to a first substrate. This pre-application process can be appropriately pressurized and heated to improve the adhesion of the film to the first substrate. The pre-application process is as follows: 2-20 kg, 50-100°C, 5-30 seconds. Then, the other side of the release liner / release paper is peeled off, and a second substrate is applied to this side. A hot press is used to tightly bond the substrates together. The bonding process is as follows: 20-100 kg, 160-180°C, 50-120 seconds. Finally, the film is placed in an oven at 150-160°C for 1-2 hours to complete the final curing.

[0019] A fourth aspect of the present invention provides a flexible circuit board comprising the above-described thermosetting bio-based composition. A thermosetting bio-based adhesive film is prepared from the thermosetting bio-based composition, one layer of which is coated with PI material, serving as a protective film for the flexible circuit board; the thermosetting bio-based adhesive film can also be used to bond two flexible circuit boards.

[0020] Beneficial effects:

[0021] 1) The thermosetting bio-based composition of the present invention includes an acrylic prepolymer and a flame-retardant cashew phenol-phenolic resin. The adhesive film for flexible circuit boards such as FPC prepared from the thermosetting bio-based composition has the advantages of intrinsic flame retardancy and resistance to more than 100,000 bends.

[0022] 2) When the thermosetting bio-based adhesive film of the present invention is used to prepare flexible circuit boards, it needs to be hot-pressed at a high temperature of 150-200℃ first. At this time, the functional groups such as carboxyl groups and acid anhydrides in the acrylic prepolymer and the phenolic hydroxyl groups in the flame-retardant cashew phenol-phenolic resin undergo a cross-linking reaction. The adhesive film and the PI surface of the flexible circuit board achieve a structural bonding strength of more than 30N / inch and can withstand more than 100,000 bending tests.

[0023] 3) The acrylic prepolymer in the composition of this invention participates in the reaction after heating to form a network cross-linked structure, which has high structural strength and good adhesion after the reaction. At the same time, the amide-containing acrylic monomer in the functional monomer has a structural group similar to PI, which makes the cured composition have good adhesion and wetting with PI, ensuring that the film has excellent adhesion strength to PI.

[0024] 4) This invention designs and synthesizes a flame-retardant cashew nut shell resin, wherein cashew nut shell resin is generated through a blending reaction with phenol and formaldehyde. Because cashew nut shell resin contains a flexible structure with long carbon chains, it exhibits better toughness than ordinary phenolic resin, resulting in a cured film with excellent flexural resistance. Furthermore, the cashew nut shell resin is modified with diphenyl chlorophosphate (DPCP) to obtain a phosphorus-containing flame-retardant cashew nut shell resin, thus maintaining good intrinsic flame retardancy.

[0025] 5) Phenolic resin is a widely used material, but its development is limited by its poor toughness and flame retardancy. This invention designs and synthesizes cashew nut shells with flexible long chains into cashew nut shell-phenolic resin, and then modifies it with flame retardancy to obtain an intrinsically flame-retardant bio-based phenolic resin, which can be applied to the flexible circuit board industry such as FPC and FCCL, thus expanding the application fields of phenolic resin.

[0026] 6) Cashew nut shell extract is a bio-based material extracted from the liquid of cashew nut shells. The introduction of bio-based raw materials makes the preparation of the film more green and environmentally friendly, which is of great significance for addressing energy issues and sustainable development. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0028] The raw materials used in the following comparative examples are shown in the table below:

[0029]

[0030] In the specific implementation method, each raw material is added according to its mass percentage.

[0031] Flame-retardant cashew nut phenol-phenolic resin is prepared by the following method:

[0032] 40 parts cashew nut phenol, 100 parts phenol, and 45 parts formaldehyde were added and mixed evenly. Using 2 parts ammonia water as a catalyst, the mixture was heated to 90°C and kept at that temperature for 3 hours. After the reaction was completed, diluted hydrochloric acid was added to neutralize the mixture. The mixture was then dehydrated under vacuum at 80°C. Butanone was added to dissolve the resin, and the cashew nut phenol-phenolic resin was obtained.

[0033] 100 parts of cashew nut phenol-phenolic resin and 3 parts of triethylamine were dissolved in 100 parts of chloroform and mixed evenly. 5 parts of diphenyl chlorophosphate were added dropwise and refluxed at 60°C for 6 hours. After the reaction was completed, the mixture was washed, the solvent was removed, dried, and the flame-retardant cashew nut phenolic resin was obtained.

[0034] Preparation of acrylic prepolymers, Synthesis Examples 1-5

[0035] Synthesis Example 1: 40 parts MA, 50 parts BA, 0.1 parts GMA, 0.3 parts AA, 0.1 parts AM, and 3 parts 2-HEA were mixed in a glass bottle. Nitrogen gas was purged for two minutes to remove oxygen, and the bottle was sealed. Half of the monomer mixture by mass was mixed with ethyl acetate solvent, and 0.05 parts AIBN were added. After mixing thoroughly, the mixture was heated to 70°C under a nitrogen atmosphere and reacted for 1 hour to obtain a reaction solution. The remaining half of the monomer mixture, 0.05 parts AIBN, and ethyl acetate solvent were mixed and slowly added dropwise to the above reaction solution. The mixture was reacted at 80°C for 2 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 90°C for 2 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 60°C for 0.5 hours and then kept at this temperature for 1 hour to obtain an acrylic prepolymer with a solid content of 40% and a viscosity of 7000 cp.

[0036] Synthesis Example 2: 30 parts MA, 80 parts BA, 1 part GMA, 2.5 parts AA, 0.5 parts AM, and 6 parts 2-HEA were mixed in a glass bottle. Nitrogen gas was purged for two minutes to remove oxygen, and the bottle was sealed. Half of the monomer mixture by mass was mixed with ethyl acetate solvent, and 0.1 parts AIBN were added. After mixing thoroughly, the mixture was heated to 80°C under a nitrogen atmosphere and reacted for 2 hours to obtain a reaction solution. The remaining half of the monomer mixture by mass, 0.1 parts AIBN, and ethyl acetate solvent were mixed and slowly added dropwise to the above reaction solution. The mixture was reacted at 100°C for 1 hour, and 0.1 parts AIBN were added. The mixture was reacted at 90°C for 3 hours, and 0.1 parts AIBN were added. The mixture was reacted at 70°C for 0.5 hours and kept at this temperature for 2 hours to obtain an acrylic prepolymer with a solid content of 40% and a viscosity of 4900 cp.

[0037] Synthesis Example 3: 25 parts MA, 70 parts BA, 2 parts GMA, 2 parts AA, 1 part AM, and 5 parts 2-HEA were mixed in a glass bottle. Nitrogen gas was purged for two minutes to remove oxygen, and the bottle was sealed. Half of the monomer mixture by mass was mixed with ethyl acetate solvent, and 0.05 parts AIBN were added. After mixing thoroughly, the mixture was heated to 90°C under a nitrogen atmosphere and reacted for 1 hour to obtain a reaction solution. The remaining half of the monomer mixture by mass, 0.05 parts AIBN, and ethyl acetate solvent were mixed and slowly added dropwise to the above reaction solution. The mixture was reacted at 80°C for 2 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 90°C for 2 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 70°C for 1 hour and kept at this temperature for 1 hour to obtain an acrylic prepolymer with a solid content of 40% and a viscosity of 3900 cp.

[0038] Synthesis Example 4: 35 parts MA, 65 parts BA, 1.5 parts GMA, 2 parts AA, 0.5 parts AM, and 15 parts 2-HEA were mixed in a glass bottle. Nitrogen gas was purged for two minutes to remove oxygen, and the bottle was sealed. Half of the monomer mixture by mass was mixed with ethyl acetate solvent, and 0.05 parts AIBN were added. After mixing thoroughly, the mixture was heated to 70°C under a nitrogen atmosphere and reacted for 3 hours to obtain a reaction solution. The remaining half of the monomer mixture, 0.05 parts AIBN, and ethyl acetate solvent were mixed and slowly added dropwise to the above reaction solution. The mixture was reacted at 90°C for 2 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 80°C for 3 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 70°C for 1 hour and kept at this temperature for 1 hour to obtain an acrylic prepolymer with a solid content of 40% and a viscosity of 8700 cp.

[0039] Synthesis Example 5: 35 parts MA, 60 parts BA, 1.5 parts GMA, 0.5 parts AA, and 3 parts 2-HEA were mixed in a glass bottle. Nitrogen gas was purged for two minutes to remove oxygen, and the bottle was sealed. Half of the monomer mixture by mass was mixed with ethyl acetate solvent, and 0.05 parts AIBN were added. After mixing thoroughly, the mixture was heated to 90°C under a nitrogen atmosphere and reacted for 3 hours to obtain a reaction solution. The remaining half of the monomer mixture by mass, 0.05 parts AIBN, and ethyl acetate solvent were mixed and slowly added dropwise to the above reaction solution. The mixture was reacted at 90°C for 1 hour, and then 0.05 parts AIBN were added. The mixture was reacted at 90°C for 3 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 80°C for 0.5 hours and then kept at this temperature for 1 hour to obtain an acrylic prepolymer with a solid content of 40% and a viscosity of 6600 cp.

[0040] Synthesis Example 6: 35 parts MA, 65 parts BA, and 15 parts 2-HEA were mixed in a glass bottle. Nitrogen gas was purged for two minutes to remove oxygen, and the bottle was sealed. Half of the monomer mixture by mass was mixed with ethyl acetate solvent, and 0.05 parts AIBN were added. After mixing thoroughly, the mixture was heated to 70°C under a nitrogen atmosphere and reacted for 3 hours to obtain a reaction solution. The remaining half of the monomer mixture by mass, 0.05 parts AIBN, and ethyl acetate solvent were mixed and slowly added dropwise to the above reaction solution. The mixture was reacted at 90°C for 2 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 80°C for 3 hours, and then 0.05 parts AIBN were added. The mixture was reacted at 70°C for 1 hour and kept at this temperature for 1 hour to obtain an acrylic prepolymer with a solid content of 40% and a viscosity of 10500 cp.

[0041] A thermosetting bio-based composition and the adhesive film prepared therefrom, Examples 1-4, Comparative Examples 1-5

[0042] Example 1: 100 parts of the acrylic prepolymer (40% solid content) of Synthesis Example 1, 10 parts of flame-retardant cashew phenol-phenolic resin, and 5 parts of aluminum hydroxide were mixed evenly to obtain composition 1;

[0043] Composition 1 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0044] Example 2: 100 parts of the acrylic prepolymer (40% solid content) of Synthesis Example 2, 3 parts of flame-retardant cashew phenol-phenolic resin, and 2 parts of aluminum hydroxide were mixed evenly to obtain composition 2;

[0045] Composition 2 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0046] Example 3: 100 parts of the acrylic prepolymer (40% solid content) of Synthesis Example 3, 30 parts of flame-retardant cashew phenol-phenolic resin, and 10 parts of aluminum hydroxide were mixed evenly to obtain composition 3;

[0047] Composition 3 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0048] Example 4: 100 parts of the acrylic prepolymer (40% solid content) of Synthesis Example 4, 20 parts of flame-retardant cashew phenol-phenolic resin, and 20 parts of aluminum hydroxide were mixed evenly to obtain composition 4;

[0049] Composition 4 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0050] Comparative Example 1: 100 parts of the acrylic prepolymer (40% solid content) of Synthetic Example 5, 20 parts of flame-retardant cashew phenol-phenolic resin, and 20 parts of aluminum hydroxide were mixed evenly to obtain Composition 5;

[0051] Composition 5 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0052] Comparative Example 2: 100 parts of the acrylic prepolymer (40% solid content) of Synthetic Example 1, 10 parts of cashew phenol-phenolic resin, and 5 parts of aluminum hydroxide were mixed evenly to obtain composition 6.

[0053] Composition 6 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0054] Comparative Example 3: 100 parts of the acrylic prepolymer (40% solid content) of Synthetic Example 1, 10 parts of phenolic resin 2127, and 5 parts of aluminum hydroxide were mixed evenly to obtain composition 7.

[0055] Composition 7 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0056] Comparative Example 4: 100 parts of the acrylic prepolymer (40% solid content) of Synthetic Example 6, 20 parts of flame-retardant cashew phenol-phenolic resin, and 5 parts of aluminum hydroxide were mixed evenly to obtain Composition 8.

[0057] Composition 8 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0058] Comparative Example 5: 100 parts of the acrylic prepolymer (40% solid content) of Synthetic Example 1, 10 parts of flame-retardant cashew phenol-phenolic resin, and 5 parts of aluminum hydroxide were mixed evenly to obtain Composition 1.

[0059] Composition 1 was coated onto 50 μm PI and dried at 110 °C for 3 min to obtain a dry film thickness of 50 μm. After drying, a release film with a thickness of 30 μm was applied to the surface of the film to obtain PI single-sided adhesive, which was used for subsequent peel force measurement.

[0060] Comparative Example 5: The film prepared was tested for performance using the following methods:

[0061] The peel strength of the adhesive film after thermosetting was tested according to ASTM D3330, as follows: Before the test, the PI surface to be bonded was wiped three times with ethanol; a strip of single-sided adhesive with 50µm PI as the backing material was cut into 1-inch * 15cm pieces, the release film was removed, and the strip was applied to a clean PI sheet, then rolled twice with a force of 2 bar; the sample was then placed under a flatbed press at 100°C and 20 bar for 50 seconds, followed by baking in a 100°C oven for 1 hour; before the peel test, the PI single-sided adhesive was placed in a controlled environment chamber (23°C / 50% relative humidity) for 30 minutes, and tested using an Instron tensile testing machine at a speed of 300 mm / min. Each test was repeated three times and the average value was taken, with the unit being N / inch.

[0062] Multiple bending tests were conducted, as detailed below:

[0063] Before testing, wipe the surface of the FPC to be bonded three times with ethanol; cut single-sided adhesive tape with 50µm PI as the backing material into 3cm*15cm strips, remove the release film, and apply it to a clean FPC, rolling it twice with a force of 2 bar; then place the sample under a flatbed press at 100℃ and 20 bar for 50 seconds, followed by baking in a 100℃ oven for 1 hour; place the test sample in a controlled environment chamber (23℃ / 50% relative humidity) for 30 minutes before testing. During testing, place the sample in a repeated bending tester, and record the number of bends when the material exhibits defects such as delamination, bubbling, or breakage.

[0064] The flame retardancy of the film was characterized by the limiting oxygen index (LOI), which was determined using a limiting oxygen index meter according to the ASTM D2863-97 test standard.

[0065] Experiment: The performance of the films prepared in Examples 1 to 4 and Comparative Examples 1 to 4 was tested, and the data obtained are shown below:

[0066] The peel strength of the adhesive film after thermosetting was tested according to ASTM D3330, as follows: Before the test, the PI surface to be bonded was wiped three times with ethanol; a strip of single-sided adhesive with 50µm PI as the backing material was cut into 1 inch * 15cm pieces, the release film was removed, and the strip was applied to a clean PI sheet, and rolled twice with a force of 2 bar; then the sample was placed under a flatbed press at 180°C and 20 bar for 50 seconds, followed by baking in a 160°C oven for 1 hour; before the peel test, the PI single-sided adhesive was placed in a controlled environment chamber (23°C / 50% relative humidity) for 30 minutes, and tested using an Instron tensile testing machine at a speed of 300 mm / min. Each test was repeated three times and the average value was taken, with the unit being N / inch.

[0067] Multiple bending tests were conducted, as detailed below:

[0068] Before testing, wipe the surface of the FPC to be bonded three times with ethanol; cut single-sided adhesive tape with 50µm PI as the backing material into 3cm*15cm strips, remove the release film, and apply it to a clean FPC, rolling it twice with a force of 2 bar; then place the sample under a flatbed press at 180℃ and 20 bar for 50 seconds, followed by baking in a 160℃ oven for 1 hour; place the test sample in a controlled environment chamber (23℃ / 50% relative humidity) for 30 minutes before testing. During testing, place the sample in a repeated bending tester, and record the number of bends when the material exhibits defects such as delamination, bubbling, or breakage.

[0069] The flame retardancy of the film was characterized by the limiting oxygen index (LOI), which was determined using a limiting oxygen index meter according to the ASTM D2863-97 test standard.

[0070] The test results are shown in the table below:

[0071]

[0072] Conclusions: The data in the table show that in Comparative Example 1, the acrylic resin was not modified with amide-containing monomers, resulting in relatively weak adhesion to the PI and low adhesive strength of the cured film. Comparative Example 2 did not contain flame-retardant cashew nut shell resin, thus the cured film had poor flame retardancy. Comparative Example 3 did not contain flame-retardant cashew nut shell resin, and the phenolic resin was not modified with cashew nut shell resin, resulting in poor flame retardancy and low repeated bending performance of the cured film. In Comparative Example 4, the acrylic resin was not modified with functional acrylic monomers (acrylic monomers containing carboxyl, amide, and anhydride groups), therefore the film failed to cross-link with the flame-retardant cashew nut shell resin, and the adhesion to the PI was relatively weak, resulting in low adhesive strength of the final film. The processing temperature of Comparative Example 5 was 100℃, lower than the required processing temperature (>150℃), therefore the film did not fully cross-link and cure, leading to decreased adhesive strength and flame retardancy. Examples 1 to 4 prepared according to the method provided by the present invention have good flame retardancy and excellent mechanical properties.

[0073] The above description is merely an optional embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A thermosetting bio-based composition, characterized in that: By weight, it includes 100-125 parts of acrylic prepolymer, 3-30 parts of flame-retardant cashew nut phenol-phenolic resin, and 2-20 parts of filler. The preparation method of the acrylic prepolymer includes the following raw materials, by mass parts: 50-80 parts of soft acrylic monomer, 25-40 parts of hard acrylic monomer, 3-15 parts of hydroxyl-containing acrylic monomer, 0.5-5 parts of functional acrylic monomer, 0.1-0.4 parts of initiator, and 200-300 parts of solvent. The flame-retardant cashew phenol-phenolic resin contains unreacted phenolic hydroxyl groups, and the functional propylene monomer contains groups that react with phenolic hydroxyl groups at high temperatures of 150-220°C. The flame-retardant cashew phenol-phenolic resin is prepared by the following method: cashew phenol, phenol and formaldehyde are mixed and reacted to generate cashew phenol-phenolic resin, and then diphenyl chlorophosphate is used to partially replace the phenolic hydroxyl groups in the cashew phenol-phenolic resin to obtain a phosphorus-containing and phenolic hydroxyl-containing flame-retardant cashew phenol-phenolic resin. The filler is one or more of the following: silicon dioxide, aluminum hydroxide, aluminum oxide, calcium carbonate, and titanium dioxide.

2. The thermosetting bio-based composition according to claim 1, characterized in that: The functional propylene monomers are propylene monomers containing one or more of the following groups: carboxyl, amide, and acid anhydride.

3. The thermosetting bio-based composition according to claim 1, characterized in that: The acrylic soft monomer is one or more of butyl acrylate, ethyl acrylate, and isooctyl acrylate; the acrylic hard monomer is one or more of methyl methacrylate, styrene, and acrylonitrile; the hydroxyl-containing acrylic monomer is one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate; the functional acrylic monomer is one or more of acrylic acid, acrylamide, methacrylic acid, and glycidyl methacrylate; and the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile.

4. The thermosetting bio-based composition according to claim 1, characterized in that: The acrylic prepolymer is prepared as follows: A mixture of acrylic soft monomers, acrylic hard monomers, hydroxyl monomers, and functional acrylic monomers is obtained. Half the mass of this monomer mixture is mixed with ethyl acetate solvent, and a quarter mass of initiator is added. After mixing thoroughly, the mixture is heated to 70-90℃ under a nitrogen atmosphere and reacted for 1-3 hours to obtain a reaction solution. The remaining half mass of the monomer mixture, a quarter mass of initiator, and ethyl acetate solvent are mixed and slowly added dropwise to the above reaction solution. The mixture is reacted at 80-100℃ for 1-3 hours, a quarter mass of initiator is added, and the mixture is reacted at 70-90℃ for 1-3 hours. The remaining quarter mass of initiator is added, and the mixture is reacted at 60-80℃ for 0.5-1 hours and kept at this temperature for 1-2 hours to obtain the acrylic prepolymer.

5. The thermosetting bio-based composition according to claim 1, characterized in that: The flame-retardant cashew nut phenol-formaldehyde resin is prepared as follows: 100 parts by weight of cashew nut phenol-formaldehyde resin and 1-5 parts by weight of triethylamine are dissolved in 100 parts by weight of chloroform and mixed evenly. 3-10 parts by weight of diphenyl chlorophosphate are added dropwise and refluxed at 60°C for 6 hours. After the reaction is completed, the resin is washed, the solvent is removed, dried, and discharged to obtain the flame-retardant cashew nut phenol-formaldehyde resin.

6. The thermosetting bio-based composition according to claim 1, characterized in that: The cashew phenol-phenolic resin is prepared as follows: cashew phenol, phenol and formaldehyde are added in a mass ratio of (20-50):100:(40-45), mixed evenly, 1-5 parts by mass of ammonia water are added as a catalyst, the temperature is raised to 60-90℃, and the reaction is kept at this temperature for 3 hours. After the reaction is completed, hydrochloric acid is added to neutralize to neutrality, and the mixture is dehydrated under vacuum at 80℃. Butanone is added to dissolve the resin, and the cashew phenol-phenolic resin is obtained by discharging.

7. The thermosetting bio-based composition according to claim 1, characterized in that: The solvent is one or more of ethyl acetate, toluene, xylene, and butanone.

8. A thermosetting bio-based adhesive film, characterized in that: The adhesive film is formed by coating the thermosetting bio-based composition according to any one of claims 1-7, and the adhesive film is coated with release material on both sides or with release material on one side and PI material on the other side.

9. The method of using the thermosetting bio-based adhesive film as described in claim 8, characterized in that: Peel off one side of the release film / release paper and pre-apply it to the first substrate. During this pre-application process, appropriate pressure and heat can be applied to improve the adhesion of the film to the first substrate. The pre-application process is as follows: 2-20KG, 50-100℃, 5-30s. Then peel off the other side of the release film / release paper and apply the second substrate to this side. Use a hot press to tightly bond the substrates together. The bonding process is as follows: 20-100KG, 160-180℃, 50-120s. Finally, place it in an oven at 150-160℃ for 1-2 hours to complete the final curing.

10. A flexible circuit board, characterized in that, Includes the thermosetting bio-based composition according to any one of claims 1-7.

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