Epoxy curing agent and preparation method thereof, and preparation method of visbreaking uncovering protective film

Abstract

The invention relates to an epoxy hardener and a preparation method thereof and a preparation method of a visbreaking uncovering protective film, and the preparation method of the epoxy hardener comprises the following steps: adding 2, 2 '-(1, 3-phenylene)-dioxazoline and a phenolic hydroxyl group or carboxyl group-containing bifunctional monomer into a first solvent, stirring at normal temperature to obtain a first solution, heating to a first temperature, and stirring at normal temperature to obtain a second solution; the first temperature is 155 DEG C to 165 DEG C, and refluxing for 3.5 hours to 4.5 hours; adding a terminated monomer containing carboxyl or phenolic hydroxyl into a reaction system of the first solution, and continuing to carry out reflux reaction for 2.5-3.5 hours at the first temperature; and after the reaction is finished, purifying and drying to obtain the epoxy curing agent. The epoxy curing agent disclosed by the invention has compatibility with low-polarity glue and has a relatively high curing degree in a high-temperature environment; the viscosity-reducing uncovering protective film has the advantages that the viscosity is reduced at high temperature, and the uncovering design efficiency of different types of PCBs is improved.

Description

Technical Field

[0001] This invention relates to the field of chemical materials in thick and thin film materials for electronic component PCBs, particularly to the field of polymer materials in thick and thin film materials for electronic component PCBs, and especially to epoxy curing agents and their preparation methods in thick and thin film materials for electronic component PCBs. This invention also relates to a method for preparing protective films for electronic component PCBs. Background Technology

[0002] Epoxy resin (EP), a common polymer, possesses excellent properties due to its unique molecular structure, such as high dimensional stability, excellent mechanical properties, corrosion resistance, adhesive properties, and electrical insulation properties. It is one of the most widely used resins and is extensively applied in adhesives, coatings, composite materials, electronic packaging materials, and other industries. With the rapid development of technologies such as 5G and AI, the printed circuit board (PCB) industry is seeing an increasing number of open-cap designs. These include soft area protection and open-capping of rigid-flex PCBs, protection and open-capping of stepped gold fingers, and other high-temperature processes requiring protection. All of these situations necessitate a process protection film to protect specific areas.

[0003] Traditional protective films all have a problem: after high-temperature hot pressing or other high-temperature processes, the adhesion increases due to chemical reactions at high temperatures, which can no longer meet the requirements for easy peeling of protective films in different types of PCB manufacturing processes. Therefore, there is an urgent need for a protective film that can reduce adhesion at high temperatures and play a good protective role in the manufacturing process of different types of PCBs. Summary of the Invention

[0004] The technical problem this invention aims to solve is to overcome the shortcomings of the prior art by providing an epoxy curing agent, its preparation method, and a method for preparing a non-stick protective film. By introducing a dimer acid structure into the curing agent, its compatibility with low-polarity adhesives is improved. Simultaneously, the introduction of amide bonds and aromatic rings reduces the reactivity of amine curing agents at room temperature, ensuring a high degree of curing only at high temperatures. This reduces the tackiness of the protective film after high-temperature, high-pressure bonding. Therefore, the non-stick protective film prepared using this type of curing agent exhibits reduced tackiness at high temperatures, improving the efficiency of various open-top designs for different types of PCBs. In this invention, high temperature refers to a temperature range of 190–220°C.

[0005] The technical solution adopted by the present invention to solve the aforementioned technical problem is as follows: An epoxy curing agent is provided, which contains a dimer acid structure; the structural formula of the epoxy curing agent is: Where x1 + x2 = y + 1; x1 + x2 = 5, y = 4, and x1 and x2 are random numbers greater than 0 and less than 5; or x1 + x2 = 8, y = 7, and x1 and x2 are random numbers greater than 0 and less than 8; R contains a dimer acid structure, and the structural formula of R includes: One of them; the structural formula of R1 is: One of them.

[0006] If R contains the first type of structure mentioned above, then R also contains One of them.

[0007] This invention also provides a method for preparing an epoxy curing agent, comprising the following steps: Step A: 2,2'-(1,3-phenylene)-dioxazoline and a difunctional monomer containing a phenolic hydroxyl or carboxyl group are added to a first solvent. The difunctional monomer containing a phenolic hydroxyl or carboxyl group also contains a dimer acid structure. The mixture is stirred at room temperature to obtain a first solution, which is then heated to a first temperature of 155°C to 165°C and refluxed for 3.5 to 4.5 hours. Then, a terminal monomer containing a carboxyl or phenolic hydroxyl group is added to the reaction system of the first solution, and the mixture is refluxed at the first temperature for another 2.5 to 3.5 hours. After the reaction is complete, the mixture is purified and dried to obtain the epoxy curing agent as described above.

[0008] In step A, the molar ratio of 2,2'-(1,3-phenylene)-dioxazoline: a difunctional monomer containing a phenolic hydroxyl or carboxyl group: a capped monomer containing a carboxyl or phenolic hydroxyl group is 5:4:2 or 8:7:2.

[0009] In step A, the difunctional monomer containing phenolic hydroxyl or carboxyl groups includes dimer acid or hydrogenated dimer acid, or a mixture of hydrogenated dimer acid and 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid), or a mixture of hydrogenated dimer acid and vanillic acid.

[0010] In step A, the end-capped monomer containing a carboxyl or phenolic hydroxyl group includes p-aminobenzoic acid, 3-piperidinecarboxylic acid, 2-piperidinecarboxylic acid, 4-methylaminobenzoic acid, or 1-(4-hydroxyphenyl)piperazine.

[0011] In step A, the first solvent is N,N-dimethylformamide (DMF) or butyl butyrate. When the first solvent is N,N-dimethylformamide (DMF), additional purification is required. The purification method is to distill the DMF in the mixture under reduced pressure to remove most of the DMF, add a certain amount of ethyl acetate and a certain amount of water to the remaining liquid for extraction, and remove the solvent ethyl acetate by rotary evaporation of the extracted organic phase. The resulting brown viscous liquid is the epoxy curing agent, which is then placed in an oven and dried at a certain temperature. When the first solvent is butyl butyrate, the butyl butyrate does not need to be removed and no additional purification is required.

[0012] Before step A, there is also step A0, a method for preparing 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid): Under an inert atmosphere, a certain amount of 4,4'-diaminodiphenyl ether and a certain amount of trimellitic anhydride are added to a certain amount of glacial acetic acid. The mixture is reacted at a certain temperature for a period of time. After the reaction is complete, it is purified and dried to obtain 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid), with the following structural formula:

[0013] In step A0, the molar ratio of 4,4'-diaminodiphenyl ether to trimellitic anhydride is 1:(2.0-2.2); the temperature is 120-140°C, and the reaction time is 18-24 hours.

[0014] This invention also provides a method for preparing a non-adhesive protective film for opening lids, comprising the following steps: Step C1: Dissolve the epoxy curing agent according to claim 1 or 2 in ethyl acetate to prepare an epoxy curing agent solution with a certain solid content; Step C2: Take a certain amount of epoxy-modified acrylate adhesive, add a certain amount of a mixed solution of ethyl acetate and anhydrous ethanol, add a certain amount of epoxy curing agent solution from step C1, stir evenly to make the colloid uniform and transparent, then add a certain amount of 2-ethyl-4-methylimidazole, stir evenly to obtain epoxy-modified acrylate adhesive. Step C3: The epoxy-modified acrylic adhesive prepared in step C2 is coated onto a PI film of a certain thickness to form an adhesive layer with a thickness of 13-17 micrometers. A release film of a certain thickness is then added to the adhesive layer, with the release surface of the release film aligned with the adhesive surface of the adhesive layer, to obtain a semi-finished product of the anti-adhesion opening protective film. The semi-finished product of the anti-adhesion opening protective film is placed in an oven and cured at a certain temperature for a period of time. Then it is taken out and cooled to room temperature to obtain the anti-adhesion opening protective film.

[0015] Compared with the prior art, the beneficial effects of the epoxy curing agent and its preparation method and the preparation method of the anti-adhesion opening protective film of the present invention are as follows:

[0016] First, because this invention contains a large-volume nonpolar dimer acid structure, the introduction of the dimer acid structure can effectively reduce the polarity of the curing agent, making it compatible with the adhesive and preventing precipitation. The introduction of aromatic rings can improve the temperature resistance of the curing agent and increase the curing temperature.

[0017] Second, by introducing compounds containing primary or secondary amine groups as end-capping groups of the curing agent, the present invention can react with epoxy groups during the curing process of the adhesive film, effectively preventing small molecules or unreacted curing agents from migrating to the surface of the substrate and thus affecting the quality of the PCB board.

[0018] Third, the epoxy curing agent of this invention is mainly composed of amides, with primary amines and ordinary aliphatic secondary amines only appearing at the end. Therefore, the overall active hydrogen is less, the activity is lower, and the curing temperature is higher. The curing reaction can only occur during high-temperature pressing, reducing the peeling force and making the protective film easily separate from the surface of the adhered object.

[0019] IV. The synthesis of the epoxy curing agent of this invention does not require the addition of any catalyst to enable the reactants to undergo an amidation reaction. The solvent used can be recycled through vacuum distillation, making it environmentally friendly. Conventional amidation reactions usually require the addition of carbodiimide condensing agents, silane condensing agents, or the introduction of acyl chlorides to the solvent, but these reagents are difficult to separate. If no condensing agent is added, high temperature and vacuum are required for polymerization. The synthesis of the epoxy curing agent of this invention utilizes the property that 2,2'-(1,3-phenylene)-dioxazoline and difunctional monomers containing phenolic hydroxyl or carboxyl groups can generate amides upon heating. No other additives are required; high reaction efficiency is achieved simply by heating. Furthermore, most of the first solvent, N,N-dimethylformamide (DMF), can be recovered through vacuum distillation.

[0020] Therefore, the epoxy curing agent prepared using this invention, by introducing a dimer acid structure into the curing agent, can effectively improve the flexibility and solubility of the epoxy curing agent, enhance its compatibility with low-polarity adhesives, and at the same time introduce amide bonds and aromatic rings to reduce the reactivity of amine curing agents at room temperature, so that they only have a high degree of curing under high temperature conditions, reducing the stickiness of the protective film after high temperature and high pressure bonding. Therefore, the anti-sticking protective film prepared using this type of curing agent has reduced stickiness at high temperature, improving the efficiency of various opening designs for different types of PCBs. The synthesis method of this epoxy curing agent is simple and environmentally friendly, providing a new idea for the research of subsequent curing agents. Attached Figure Description

[0021] Figures 1-11 These are the structural formulas of the various chemical substances.

[0022] Figures 12-20 The structural formulas are those of the epoxy curing agents prepared in Examples 1 to 9.

[0023] Figure 21 The 1H NMR spectrum of 2,2'-(oxybis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) synthesized in Example 9 of this invention is shown.

[0024] Figure 22 The image shows the gel permeation chromatogram and molecular weight distribution data for Example 4.

[0025] Figure 23 The gel permeation chromatogram and molecular weight distribution data are for Example 6. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings.

[0027] This invention provides a method for preparing an epoxy curing agent, comprising the following steps: Step A: 2,2'-(1,3-phenylene)-dioxazoline and a difunctional monomer containing a phenolic hydroxyl or carboxyl group are added to a first solvent. The difunctional monomer containing a phenolic hydroxyl or carboxyl group further comprises a dimer acid structure. The mixture is stirred at room temperature to obtain a first solution, which is then heated to a first temperature, 155°C to 165°C (e.g., 160°C), and refluxed for 3.5 to 4.5 hours. Then, a capped monomer containing a carboxyl or phenolic hydroxyl group is added to the reaction system of the first solution, and the reaction is continued at the first temperature for reflux for another 2.5 to 3.5 hours. After the reaction is complete, the mixture is purified and dried to obtain the epoxy curing agent of this invention. Figure 1 The structure formula 1 in the text refers to the epoxy curing agent described below.

[0028] In step A, the molar ratio of 2,2'-(1,3-phenylene)-dioxazoline: a difunctional monomer containing a phenolic hydroxyl or carboxyl group: a capped monomer containing a carboxyl or phenolic hydroxyl group is 5:4:2 or 8:7:2.

[0029] In step A, the difunctional monomer containing phenolic hydroxyl or carboxyl groups includes dimer acid or hydrogenated dimer acid, or a mixture of hydrogenated dimer acid and 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid), or a mixture of hydrogenated dimer acid and vanillic acid.

[0030] In other words, the difunctional monomer containing phenolic hydroxyl or carboxyl groups includes dimer acid or hydrogenated dimer acid. When the difunctional monomer containing phenolic hydroxyl or carboxyl groups contains hydrogenated dimer acid, the difunctional monomer also contains 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) or vanillic acid.

[0031] The molar ratio of the hydrogenated dimer acid to 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) or vanillic acid is 3:1.

[0032] Dimeric acid, hydrogenated dimeric acid, or 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) are all dicarboxylic acids. Among them, 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) was prepared by the inventor and will be described in detail below. Vanillic acid is also known as 4-hydroxy-3-methoxybenzoic acid, and vanillic acid is also a hydroxy acid.

[0033] In step A, the end-capped monomer containing a carboxyl or phenolic hydroxyl group includes p-aminobenzoic acid, 3-piperidinecarboxylic acid, 2-piperidinecarboxylic acid, 4-methylaminobenzoic acid, or 1-(4-hydroxyphenyl)piperazine.

[0034] In step A, the first solvent is N,N-dimethylformamide (DMF) or butyl butyrate. When the first solvent is N,N-dimethylformamide (DMF), additional purification is required, such as by rotary evaporation and extraction. Otherwise, the tertiary amines in DMF can easily affect the adhesive. The purification method is to distill the DMF in the mixture under reduced pressure to remove most of the DMF, add a certain amount of ethyl acetate and a certain amount of water to the remaining liquid for extraction, and remove the solvent ethyl acetate by rotary evaporation of the organic phase obtained by extraction. The resulting brown viscous liquid is the epoxy curing agent, which is then placed in an oven and dried at a certain temperature. When the first solvent is butyl butyrate, butyl butyrate does not need to be removed and no additional purification is required. The structure of butyl butyrate is similar to that of ethyl acetate and has virtually no effect on the reaction system.

[0035] Before step A, there is also step A0, a method for preparing 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid): Under an inert atmosphere, such as N2 (nitrogen), 4,4'-diaminodiphenyl ether and trimellitic anhydride are added to a certain amount of glacial acetic acid. The reaction is carried out at a certain temperature for a period of time. After the reaction is complete, the mixture is purified and dried to obtain 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid). The structural formula of this 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) is as follows: Figure 11 The structural formula is 11.

[0036] In step A0, the molar ratio of 4,4'-diaminodiphenyl ether to trimellitic anhydride is 1:(2.0-2.2); the temperature is 120-140°C, and the reaction time is 18-24 hours. Generally, the reaction concentration in step A0 is 0.15-0.2 mol / L. For example, the molar ratio of 4,4'-diaminodiphenyl ether to trimellitic anhydride is 1:2, and approximately 1 L of glacial acetic acid is added for every 0.15 mol of 4,4'-diaminodiphenyl ether added. 2,2'-(oxybis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) is a type of dicarboxylic acid. Its function is to improve flexibility through ether bonds and, secondly, to improve the heat resistance of the curing agent through imide bonds.

[0037] The oxazoline group in 2,2'-(1,3-phenylene)-dioxazoline can react with carboxyl and phenolic hydroxyl groups at temperatures above 100°C (the specific reaction temperature depends on the structure), with the carboxyl group showing greater reactivity than the phenolic hydroxyl group. Difunctional monomers (dicarboxylic acids and / or hydroxy acids) containing phenolic or carboxyl groups act as chain extension sites with 2,2'-(1,3-phenylene)-dioxazoline. End-capped monomers containing carboxyl or phenolic hydroxyl groups limit the molecular weight, leaving a secondary or primary amine end as a reaction site for epoxy resins. 2,2'-(1,3-phenylene)-dioxazoline also functions as a chain extender. Vanillic acid, also known as 4-hydroxy-3-methoxybenzoic acid, can react with 2,2'-(1,3-phenylene)-dioxazoline at both ends for chain extension. The carboxyl end reacts to form an ester group, while the phenolic hydroxyl segment reacts to form an ether bond. The ether bond offers better flexibility and can also improve the compatibility between the curing agent and the resin.

[0038] The present invention also provides an epoxy curing agent containing a dimer acid structure; the structural formula of the epoxy curing agent is as follows: Figure 1The structural formula 1, where x1+x2=y+1; x1+x2=5, y=4, and x1 and x2 are random numbers greater than 0 and less than 5; or x1+x2=8, y=7, and x1 and x2 are random numbers greater than 0 and less than 8; R contains a dimer acid structure, and the structural formula of R includes Figure 2 Structural formula 2 or Figure 3 Any one of the structural formulas in 3; Figure 2 Structural formula 2 is a hydrogenated dimer acid. Figure 3 Structural formula 3 is a dimer acid; the structural formula of R1 is... Figure 6 Structural formula 6 Figure 7 Structural formula 7 Figure 8 Structural formula 8 Figure 9 Structural formula 9 or Figure 10 Any one of the structural formulas in 10. x1 and x2 represent the content of oxazoline, and y represents the content of dimer acid or hydrogenated dimer acid.

[0039] If the structural formula of R contains Figure 2 When the structural formula is 2 (hydrogenated dimer acid), then R also contains Figure 4 Structural formula 4 or Figure 5 Any one of the five structural formulas. That is, the structural formula of R includes... Figure 2 Structural formula 2 or Figure 3 Any one of the structural formulas 3, or the structural formula of R contains Figure 2 Structural formula 2 and Figure 4 The combination of structural formula 4, or the structural formula of R containing Figure 2 Structural formula 2 and Figure 5 The combination of structural formula 5.

[0040] Figure 2 Both open ends of structural formula 2 are carboxyl groups; Figure 3 Both open ends of structural formula 3 are also carboxyl groups; Figure 4 The left open end of structural formula 2 is the phenolic hydroxyl port, and the right open end is the carboxyl port; Figure 5 Both open ends of structural formula 5 are also carboxyl groups; Figure 6 Structural formula 6 Figure 7 Structural formula 7 Figure 8 Structural formula 8 and Figure 9 In structural formula 9, the open ends are all carboxyl groups; Figure 10 The open end in structural formula 10 is the phenolic hydroxyl port.

[0041] When the structural formula of R contains Figure 2 Structural formula 2 and Figure 4 When combining structural formula 4, you can refer to Figure 18 Structural formula 18 orFigure 19 Structural formula 19, generally, for example, the oxazoline group of 2,2'-(1,3-phenylene)-dioxazoline and Figure 4 In structural formula 4, the phenolic hydroxyl group and carboxyl group are combined, while the oxazoline group at the other end of 2,2'-(1,3-phenylene)-dioxazoline is combined with... Figure 2 The structure of formula 2 is linked to the carboxyl group at one end. Figure 2 The carboxyl group at the other end of structural formula 2 is recombined with another 2,2'-(1,3-phenylene)-dioxazoline molecule, and the remaining end of 2,2'-(1,3-phenylene)-dioxazoline is recombined with the hydroxyl or carboxyl group of the end-capping monomer to obtain the epoxy curing agent polymer described in this invention.

[0042] Or when the structure of R contains Figure 2 Structural formula 2 and Figure 5 When combining structural formula 5, you can refer to Figure 20 Structural formula 20, generally, for example, 2,2'-(1,3-phenylene)-dioxazoline and Figure 5 The structural formula 5 has carboxyl groups at both ends, while the other end of 2,2'-(1,3-phenylene)-dioxazoline is bound to... Figure 2 The structure of formula 2 is linked to the carboxyl group at one end. Figure 2 The carboxyl group at the other end of structural formula 2 is recombined with another 2,2'-(1,3-phenylene)-dioxazoline molecule, and the remaining end of 2,2'-(1,3-phenylene)-dioxazoline is recombined with the hydroxyl or carboxyl group of the end-capping monomer to obtain the epoxy curing agent polymer described in this invention.

[0043] This invention also provides a method for preparing a non-adhesive protective film for opening lids, comprising the following steps: Step C1: Dissolve the above-mentioned epoxy curing agent in ethyl acetate to prepare an epoxy curing agent solution with a certain solid content; generally, the solid content of the epoxy curing agent solution is about 50%. Step C2: Take a certain amount of epoxy-modified acrylate adhesive, add a certain amount of a mixed solution of ethyl acetate and anhydrous ethanol, add a certain amount of the epoxy curing agent solution from Step C1, and stir it evenly under magnetic stirring to make the colloid uniform and transparent. Then add a certain amount of 2-ethyl-4-methylimidazole and stir evenly to obtain epoxy-modified acrylate adhesive. Generally, the mass ratio of anhydrous ethanol to ethyl acetate is 1:1 or 8:7. Generally, the solid content of epoxy-modified acrylate adhesive is 30% to 35%. The mass ratio of epoxy-modified acrylate adhesive to the mixed solution of ethyl acetate and anhydrous ethanol to the epoxy curing agent solution to 2-ethyl-4-methylimidazole is 20:(14 to 16):(0.6 to 0.8):(0.07 to 0.09). Step C3: The epoxy-modified acrylate adhesive prepared in step C2 is coated onto a PI film of a certain thickness, typically 11.5–13.5 micrometers, forming an adhesive layer of 13–17 micrometers thickness. A release film of a certain thickness is then added to this adhesive layer, with the release surface of the release film aligned with the adhesive surface of the adhesive layer. The thickness of the release film is typically 12.5–75 micrometers. The applicant generally uses release films with thicknesses of 25 micrometers, 36 micrometers, or 50 micrometers. For example, a release film with a thickness of 36 micrometers yields a semi-finished anti-adhesion opening protective film. This semi-finished anti-adhesion opening protective film is placed in an oven and cured at a certain temperature for a period of time, typically 70–80°C. For example, it is cured in an oven at 80°C for 48 hours. Since the oven temperature is low, the curing time needs to be longer. Then, it is removed and cooled to room temperature to obtain the anti-adhesion opening protective film.

[0044] Example 1 A method for preparing an epoxy curing agent includes the following steps: 25 mmol (mmol) of 2,2'-(1,3-phenylene)-dioxazoline and 20 mmol of dimer acid were added to a three-necked flask, along with 100 mL of N,N-dimethylformamide (DMF). The mixture was stirred at room temperature for 30 minutes until completely dissolved. Then, the mixture was heated to 160 °C and refluxed at boiling point for 4 hours. Next, 10 mmol of p-aminobenzoic acid was added, and the reaction was continued at 160 °C for 3 hours. After removing most of the DMF by vacuum distillation, 100 mL of water and 100 mL of ethyl acetate were added for extraction. This extraction was repeated three times, with 100 mL of water and 100 mL of ethyl acetate added for each extraction. The organic phase obtained was subjected to rotary evaporation to remove the organic solvent ethyl acetate, resulting in a brown viscous liquid, which was the product. The product was dried in an oven at 60 °C. The yield of the brown viscous liquid was approximately 16.5 g, with a yield of 91.7%. This brown viscous liquid is the epoxy curing agent of Example 1.

[0045] The structural formula of the epoxy curing agent prepared in Example 1 is as follows: Figure 12 As shown in structural formula 12, in this structural formula 12, x1+x2=y1+1, where x1+x2=5, y1=4, and x1 and x2 are both random numbers greater than 0 and less than 5. x1 and x2 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, and y1 represents the content of dimer acid.

[0046] Example 2 This is essentially the same as Example 1, except that the substances and their contents are slightly different, particularly the replacement of the dimer acid with hydrogenated dimer acid, as detailed below: 40 mmol of 2,2'-(1,3-phenylene)-dioxazoline and 35 mmol of hydrogenated dimer acid were added to a three-necked flask, along with 210 mL of DMF. The mixture was stirred at room temperature for 30 minutes until completely dissolved. The solution was then heated to 160 °C and refluxed at boiling point for 4 hours. 10 mmol of p-aminobenzoic acid was added, and the reaction was continued at 160 °C for 3 hours. Most of the DMF was then removed by vacuum distillation, and 150 mL of water and 150 mL of ethyl acetate were added for extraction. This extraction was repeated three times, with 150 mL of water and 150 mL of ethyl acetate added for each extraction. The organic phase obtained was subjected to rotary evaporation to remove the organic solvent ethyl acetate, resulting in a brown viscous liquid, which was the product. The product was dried in an oven at 60 °C. The yield of the brown viscous liquid was approximately 26.3 g, with a yield of 88.4%. This brown viscous liquid is the epoxy curing agent of Example 2.

[0047] The structural formula of the epoxy curing agent prepared in Example 2 is as follows: Figure 13 As shown in structural formula 13, in which x1+x2=y1+1, x1+x2=8, y1=7, and x1 and x2 are both random numbers greater than 0 and less than 8. x1 and x2 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, and y1 represents the content of hydrogenated dimer acid.

[0048] Example 3 This is essentially the same as Example 2, except that the substances and their contents are slightly different. In particular, glacial acetic acid is used as the end-capping monomer instead of p-aminobenzoic acid, as detailed below: 20 mmol of 2,2'-(1,3-phenylene)-dioxazoline and 17.5 mmol of hydrogenated dimer acid were added to a three-necked flask, along with 100 mL of DMF. The mixture was stirred at room temperature for 30 minutes until completely dissolved. The solution was then heated to 160 °C and refluxed at boiling point for 4 hours. 5 mmol of glacial acetic acid was added, and the reaction was continued at 160 °C for 3 hours. Most of the DMF was then removed by vacuum distillation, and 100 mL of water and 100 mL of ethyl acetate were added for extraction. This extraction was repeated three times, with 100 mL of water and 100 mL of ethyl acetate added for each extraction. The organic phase was then subjected to rotary evaporation to remove the organic solvent ethyl acetate, resulting in a brown viscous liquid, which was the product. This product was dried in an oven at 60 °C. The yield of the brown viscous liquid was approximately 12.5 g, with a yield of 86.3%. This brown viscous liquid is the epoxy curing agent of Example 3.

[0049] The structural formula of the epoxy curing agent prepared in Example 3 is as follows: Figure 14As shown in structural formula 14, in which x1+x2=y1+1, x1+x2=8, y1=7, and x1 and x2 are both random numbers greater than 0 and less than 8. x1 and x2 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, and y1 represents the content of hydrogenated dimer acid.

[0050] Example 4 This is essentially the same as Example 2, except that the substances and their contents are slightly different. In particular, 3-piperidinic acid is used as the end-capping monomer instead of p-aminobenzoic acid, as detailed below: 40 mmol of 2,2'-(1,3-phenylene)-dioxazoline and 35 mmol of hydrogenated dimer acid were added to a three-necked flask, along with 210 mL of DMF. The mixture was stirred at room temperature for 30 minutes until completely dissolved. The solution was then heated to 160 °C and refluxed at boiling point for 4 hours. 10 mmol of 3-piperidinic acid was added, and the reaction was continued at 160 °C for 3 hours. Most of the DMF was then removed by vacuum distillation, and 150 mL of water and 150 mL of ethyl acetate were added for extraction. This extraction was repeated three times, with 150 mL of water and 150 mL of ethyl acetate added for each extraction. The organic phase was then subjected to rotary evaporation to remove the organic solvent ethyl acetate, resulting in a brown viscous liquid, which was the product. The product was dried in an oven at 60 °C. The yield of the brown viscous liquid was approximately 26.6 g, with a yield of 89.6%. This brown viscous liquid is the epoxy curing agent of Example 4.

[0051] The structural formula of the epoxy curing agent prepared in Example 4 is as follows: Figure 15 As shown in structural formula 15, in which x1+x2=y1+1, x1+x2=8, y1=7, and x1 and x2 are both random numbers greater than 0 and less than 8. x1 and x2 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, and y1 represents the content of hydrogenated dimer acid.

[0052] Figure 22 The gel permeation chromatogram and molecular weight distribution data of Example 4 are from... Figure 22 As can be seen, the number-average molecular weight of Example 4 is 7273, and the weight-average molecular weight is 8861. Compared to... Figure 23 Smaller; the molecular weight distribution width index is 1.22, which is lower than that of other molecules. Figure 23 A larger value indicates that using DMF for polymerization will result in a smaller molecular weight and a wider molecular weight distribution. Although DMF has better solubility, the reaction uniformity is poor.

[0053] Example 5 This is essentially the same as Example 2, except that the substances and their contents are slightly different. In particular, 2-piperidinic acid is used as the end-capping monomer instead of p-aminobenzoic acid, as detailed below: 40 mmol of 2,2'-(1,3-phenylene)-dioxazoline and 35 mmol of hydrogenated dimer acid were added to a three-necked flask, along with 210 mL of DMF. The mixture was stirred at room temperature for 30 minutes until completely dissolved. The solution was then heated to 160 °C and refluxed at boiling point for 4 hours. 10 mmol of 2-piperidinic acid was added, and the reaction was continued at 160 °C for 3 hours. Most of the DMF was then removed by vacuum distillation, and 150 mL of water and 150 mL of ethyl acetate were added for extraction. This extraction was repeated three times, with 150 mL of water and 150 mL of ethyl acetate added for each extraction. The organic phase was then subjected to rotary evaporation to remove the organic solvent ethyl acetate, resulting in a brown viscous liquid, which was the product. The product was dried in an oven at 60 °C. The yield of the brown viscous liquid was approximately 25.4 g, with a yield of 85.6%. This brown viscous liquid is the epoxy curing agent of Example 5.

[0054] The structural formula of the epoxy curing agent prepared in Example 5 is as follows: Figure 16 As shown in structural formula 16, in which x1+x2=y1+1, x1+x2=8, y1=7, and x1 and x2 are both random numbers greater than 0 and less than 8. x1 and x2 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, and y1 represents the content of hydrogenated dimer acid.

[0055] Example 6 This is essentially the same as Example 4, except that the substances and their contents are slightly different. In particular, butyl butyrate is used as the first solvent instead of DMF, as detailed below: 80 mmol of 2,2'-(1,3-phenylene)-dioxazoline and 70 mmol of hydrogenated dimer acid were added to a three-necked flask, followed by 45 g of butyl butyrate. The mixture was heated to 160°C and refluxed at boiling point for 4 hours. Then, 20 mmol of 3-piperidinic acid was added, and the reaction was continued at 160°C for another 3 hours, yielding a brown viscous liquid. This liquid was cooled to room temperature and brought to a final volume of approximately 118.72 g with 14.36 g of butyl butyrate, resulting in a solid content of approximately 50%. This brown viscous liquid is the epoxy curing agent of Example 6. Since the first solvent in Example 6 is butyl butyrate, and butyl butyrate does not need to be removed, no further purification is required.

[0056] The structural formula of the epoxy curing agent prepared in Example 6 is as follows: Figure 17As shown in structural formula 17, in which x1 + x2 = y1 + 1, x1 + x2 = 8, y1 = 7, and x1 and x2 are both random numbers greater than 0 and less than 8. x1 and x2 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, and y1 represents the content of hydrogenated dimer acid. Butyl butyrate is used as a solvent, and the feed ratio remains unchanged.

[0057] Figure 23 The gel permeation chromatogram and molecular weight distribution data of Example 6 are from... Figure 23 As can be seen, the number-average molecular weight of Example 6 is 12595, and the weight-average molecular weight is 14089. Compared to... Figure 22 Larger; the molecular weight distribution width index is 1.12, which is larger than... Figure 22 The smaller molecular weight indicates that using butyl butyrate in the polymerization reaction results in a more uniform chain extension reaction and a larger molecular weight.

[0058] Example 7 This is essentially the same as Example 4, except that the substances and their amounts are slightly different, especially the addition of vanillic acid, as detailed below: 80 mmol of 2,2'-(1,3-phenylene)-dioxazoline, 52.5 mmol of hydrogenated dimer acid, and 17.5 mmol of vanillic acid were added to a three-necked flask, along with 350 mL of DMF. The mixture was stirred at room temperature for 30 minutes until completely dissolved. The solution was then heated to 160 °C and refluxed at boiling point for 4 hours. 20 mmol of 3-piperidinic acid was added, and the reaction was continued at 160 °C for 3 hours. Most of the DMF was then removed by vacuum distillation, and 200 mL of water and 200 mL of ethyl acetate were added for extraction. This extraction was repeated three times, with 200 mL of water and 200 mL of ethyl acetate added for each extraction. The organic phase was then subjected to rotary evaporation to remove the organic solvent ethyl acetate, resulting in a brown viscous liquid, which was the product. This product was dried in an oven at 60 °C. The yield of the brown viscous liquid was approximately 43.2 g, with a yield of 82.4%. This brown viscous liquid is the epoxy curing agent of Example 7.

[0059] The structural formula of the epoxy curing agent prepared in Example 7 is as follows: Figure 18As shown in structural formula 18, in this structural formula 18, x1+x2+x3+x4=y1+y2+z+1, where x1+x2+x3+x4=8, x1, x2, x3, and x4 are all random numbers greater than 0 and less than 8, y1+y2+z=7, (y1+y2):z=3:1, y1, y2, and z are all random numbers greater than 0 and less than 7. x1, x2, x3, and x4 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, y1 and y2 represent the content of hydrogenated dimer acid, and z represents the content of vanillic acid.

[0060] Example 8 This is essentially the same as Example 7, except that the substances and their contents are slightly different. In particular, 1-(4-hydroxyphenyl)piperazine is used as the end-capping monomer instead of 3-piperidinecarboxylic acid, as detailed below: 80 mmol of 2,2'-(1,3-phenylene)-dioxazoline, 52.5 mmol of hydrogenated dimer acid, and 17.5 mmol of vanillic acid were added to a three-necked flask, along with 350 mL of DMF. The mixture was stirred at room temperature for 30 minutes until completely dissolved. The solution was then heated to 160 °C and refluxed at boiling point for 4 hours. 20 mmol of 1-(4-hydroxyphenyl)piperazine was added, and the reaction was continued at 160 °C for 3 hours. Most of the DMF was then removed by vacuum distillation, and 200 mL of water and 200 mL of ethyl acetate were added for extraction. Each extraction was performed with 200 mL of water and 200 mL of ethyl acetate, and this process was repeated three times. The organic phase was then subjected to rotary evaporation to remove the organic solvent ethyl acetate, resulting in a brown viscous liquid, which was the product. This product was dried in an oven at 60 °C. The yield of the brown viscous liquid was approximately 43.3 g, with a yield of 81.1%. This brown viscous liquid is the epoxy curing agent of Example 8.

[0061] The structural formula of the epoxy curing agent prepared in Example 8 is as follows: Figure 19 As shown in structural formula 19, in this structural formula 19, x1+x2+x3+x4=y1+y2+z+1, where x1+x2+x3+x4=8, x1, x2, x3, and x4 are all random numbers greater than 0 and less than 8, y1+y2+z=7, (y1+y2):z=3:1, y1, y2, and z are all random numbers greater than 0 and less than 7. x1, x2, x3, and x4 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, y1 and y2 represent the content of hydrogenated dimer acid, and z represents the content of vanillic acid.

[0062] Example 9 This is essentially the same as Example 7, except that the substances and their contents are slightly different. In particular, vanillic acid in Example 7 is replaced with a self-made 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid). The preparation method of this 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) is as follows: Step A0: The 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) in Example 9 was prepared in-house. The preparation method is as follows: Under an inert atmosphere, 0.15 mol of 4,4'-diaminodiphenyl ether and 0.31 mol of trimellitic anhydride were added to 1000 mL of glacial acetic acid. The reaction was carried out at 120°C for 18 hours. After cooling to room temperature, 2000 mL of water was added to the system. The mixture was filtered and the precipitate was collected. The precipitate was washed with hot water to remove residual solvent and raw materials. Finally, the yellow precipitate was dried at 110°C for 12 hours, yielding approximately 73.39 g of the product 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid), with a yield of 89.2%. Its structural formula is as follows: Figure 11 The structural formula is 11.

[0063] Figure 21 The 1H NMR spectrum of 2,2'-(oxybis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) synthesized in Example 9 indicates that the dicarboxylic acid monomer was successfully synthesized.

[0064] Step A: Add 80 mmol of 2,2'-(1,3-phenylene)-dioxazoline, 52.5 mmol of hydrogenated dimer acid, and 17.5 mmol of 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) to a three-necked flask, along with 350 mL of DMF. Stir at room temperature for 30 minutes until completely dissolved. Heat to 160°C and reflux at boiling point for 4 hours. Add 20 mmol of 3-piperidinecarboxylic acid and continue the reaction at 160°C for 3 hours. Most of the DMF was removed by vacuum distillation, and 200 mL of water and 200 mL of ethyl acetate were added for extraction. This extraction was repeated three times, with 200 mL of water and 200 mL of ethyl acetate added each time. The organic phase obtained was subjected to rotary evaporation to remove the organic solvent ethyl acetate, and a brown viscous liquid was obtained as the product. The product was dried in an oven at 60°C. The yield of the brown viscous liquid was approximately 50.3 g, with a yield of 85.1%. This brown viscous liquid is the epoxy curing agent of Example 9.

[0065] The structural formula of the epoxy curing agent prepared in Example 9 is as follows: Figure 20As shown in structural formula 20, in which x1+x2+x3+x4=y1+y2+z+1, where x1+x2+x3+x4=8, x1, x2, x3, and x4 are all random numbers greater than 0 and less than 8, y1+y2+z=7, (y1+y2):z=3:1, y1, y2, and z are all random numbers greater than 0 and less than 7. x1, x2, x3, and x4 represent the content of 2,2'-(1,3-phenylene)-dioxazoline, y1 and y2 represent the content of hydrogenated dimer acid, and z represents the content of self-made 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid).

[0066] Table 1 summarizes the substances and amounts used in Examples 1 through 9: Table 1

[0067] A method for preparing a non-adhesive protective film for opening lids includes the following steps: Step C1: Dissolve the epoxy curing agents obtained in Examples 1 to 9 above in ethyl acetate, and prepare 50wt% (i.e., 50% solid content) epoxy curing agent solutions respectively. Step C2: Take 20g of epoxy-modified acrylate adhesive for each product. The solid content of the epoxy-modified acrylate adhesive is 32%. Add 15g of a mixed solution of ethyl acetate and anhydrous ethanol (8g of ethyl acetate and 7g of anhydrous ethanol) to each product. Add 0.7g of the epoxy curing agent solution from Step C1 to each product. Stir the mixture magnetically until it is uniform and transparent. Then add 0.08g of 2-ethyl-4-methylimidazole to each product. Stir until the mixture is uniform to obtain the epoxy-modified acrylate adhesives of Examples 1 to 9. Step C3: The epoxy-modified acrylic adhesives of Examples 1 to 9 prepared in Step C2 are each coated onto a 12.5-micron PI film to form an adhesive layer with a thickness of 15 microns. A release film with a thickness of 36 microns is then added to the adhesive layer, with the release surface of the release film facing the adhesive surface of the adhesive layer. This yields the semi-finished anti-adhesion protective film of Examples 1 to 9. The semi-finished anti-adhesion protective film is placed in an oven and cured at a certain temperature for a period of time. Then it is taken out and cooled to room temperature to obtain the anti-adhesion protective film of Examples 1 to 9. The peel strength of each film is tested. See Table 2 for a summary of performance tests.

[0068] Regarding the test methods in the various embodiments of the present invention, it is worth noting that: the peel force of the adhesive film was tested by preparing sample strips according to the GB / T2792-2014 standard. The tests measured the 180° peel force of the anti-adhesion protective film of Examples 1 to 9 against a steel plate and a PI film at room temperature, and the 180° peel force against a PI film and a copper foil after being pressed at 210°C for 4 hours. The room temperature in this invention generally refers to 21°C to 25°C.

[0069] In Table 2, the unit for the peel force of the room-temperature steel plate, room-temperature PI film, heat-treated copper foil, and heat-treated PI film is gf / inch (grams per inch). gf is a unit of force, representing the gravitational force exerted on 1 gram of a substance. gf / inch is the peel force in grams per inch of protective film. In the overview table of Table 2, heat treatment refers to pressing each sample at 210℃ for 4 hours.

[0070] Table 2 is a summary of various performance tests conducted after the epoxy curing agents prepared in Examples 1 to 9 of this invention were used to formulate new adhesives, which were then coated onto PI films and cured.

[0071] Table 3 is a summary table of the performance test data analysis in Table 2: Table 3

[0072] In Table 3, D1 represents (peel force of steel plate at room temperature - peel force of copper foil after heat treatment) / peel force of steel plate at room temperature; D2 represents (peel force of PI film at room temperature - peel force of PI film after heat treatment) / peel force of PI film at room temperature.

[0073] As can be seen from Tables 2 and 3: First, in each embodiment, the peel force of the copper foil after heat treatment is significantly reduced compared to that of the steel plate at room temperature, with a minimum reduction of 30.26% (Example 3) and a maximum reduction of 76.34% (Example 7), indicating that the high-temperature anti-adhesion effect is good. Second, in each embodiment, the peel force of the PI film after heat treatment is reduced more than that of the PI film at room temperature, with a minimum reduction of 67.53% (Example 8) and a maximum reduction of 96.06% (Example 9). This indicates that the high temperature has a better anti-adhesion effect for PI film, and is particularly suitable for thinner circuit boards, such as FPC (flexible printed circuit boards). Third, for most FPCs (flexible printed circuit boards), based on feedback data collected from customers supplied by the applicant, the peel force of the PI film after heat treatment is ≤30gf / inch at high temperatures (especially 210°C), which has been met in all embodiments; For some very special FPCs (flexible printed circuit boards), according to the feedback data collected from customers supplied by the applicant, the peel force of the PI film after heat treatment is ≤20gf / inch at high temperature (especially 210℃), which is met in Examples 1 to 3 and Examples 6 to 9. This allows for the selection of different formulations to make the protective film as needed, ensuring that when the anti-adhesion protective film of this invention is used in FPCs (flexible printed circuit boards) of different specifications, the FPC will not be deformed and / or damaged when the protective film is torn off. Fourth, comparing Example 1 and Example 2, the dimer acid introduced in Example 1 has a better effect. Although the dimer acid has a better effect, it contains a double bond structure and is easily oxidized and decomposed at high temperature. Fifth, a comparison of Examples 2, 4, and 5, and of Examples 7 and 8, shows that 3-piperidinic acid is the preferred end-capping monomer, as it has a better viscosity-reducing effect. Sixth, comparing Example 4 and Example 7, it can be seen that the introduction of vanillic acid is equivalent to introducing ether bonds into the curing agent, which increases flexibility and improves the viscosity reduction effect. Seventh, comparing Example 7 and Example 9, it can be seen that the peel strength of the PI film after heat treatment with the self-synthesized 2,2'-(oxybis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) is reduced by more than that of the PI film after heat treatment with vanillic acid. Eighth, the self-synthesized 2,2'-(oxybis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) mainly utilizes the high temperature resistance of the imide structure and the flexibility of the ether bond to make the curing agent both temperature resistant and flexible. In all embodiments, the introduction of the self-synthesized 2,2'-(oxybis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid) resulted in the greatest reduction in the peel strength of the PI film after heat treatment, and the best anti-adhesion effect of the high-temperature PI film. This can be used as a reference when the peel strength of the PI film after heat treatment is required for very thin circuit boards. Ninth, the glacial acetic acid in Example 3 is a common end-capping monomer. Apart from glacial acetic acid, the structure of the other end-capping monomers is that one end is a phenolic hydroxyl group or a carboxyl group, and the other end is a primary amine or a secondary amine. From the data of Examples 1 to 9, it can be seen that the epoxy curing agent end-capped with glacial acetic acid in Example 3 has a poor tack reduction effect and lacks active sites. It is easy to be free on the adhesive surface and then transferred to the PCB board, affecting the quality of the PCB board. Tenth, butyl butyrate was only used as the first solvent in Example 6 because butyl butyrate has low polarity; DMF is a better first solvent. Eleventh, based on the test data above, Example 7 showed the best results, exhibiting relatively high adhesion to steel plates at room temperature (59.5 gf / inch). After heating, the adhesion to copper foil decreased to 14.08 gf / inch, a significant reduction (76.34%). This made it easier to open the protective film for reducing adhesion. Both Examples 7 and 8 introduced vanillic acid, which, compared to other examples, introduced ether bonds, achieving lower adhesion at high temperatures and facilitating the peeling of the protective film. In the difunctional monomer combination, hydrogenated dimer acid:vanillic acid = 3:1 was preferred, and 3-piperidinic acid was preferred as the end-capping monomer. The protective film after high-temperature hot pressing showed lower peeling force on both the PI film and the copper substrate than before hot pressing, and possessed good overall performance, meeting the requirements for improved efficiency and reduced manual labor in various opening processes during PCB manufacturing. Twelfth, different formulations can be selected based on the customer's needs for different types of PCBs, from the various embodiments and the test data mentioned above.

[0074] The above-described embodiments are merely preferred embodiments of the present invention, and are described in a relatively specific and detailed manner. However, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. Therefore, all equivalent transformations and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.

Claims

1. An epoxy curing agent, characterized in that: This epoxy curing agent contains a dimer acid structure; the structural formula of this epoxy curing agent is: Where x1+x2=y+1; x1+x2=5, y=4; or x1+x2=8, y=7; R contains a dimer acid structure, and the structural formula of R includes: One of them; the structural formula of R1 is: One of them.

2. The epoxy curing agent according to claim 1, characterized in that: If R contains the first type of structure mentioned above, then R also contains One of them.

3. A method for preparing an epoxy curing agent, characterized in that, Includes the following steps: Step A: 2,2'-(1,3-phenylene)-dioxazoline and a difunctional monomer containing a phenolic hydroxyl or carboxyl group are added to a first solvent. The difunctional monomer containing a phenolic hydroxyl or carboxyl group further comprises a dimer acid structure. The mixture is stirred at room temperature to obtain a first solution, which is then heated to a first temperature of 155°C to 165°C and refluxed for 3.5 to 4.5 hours. Then, a capping monomer containing a carboxyl or phenolic hydroxyl group is added to the reaction system of the first solution, and the reaction is continued to be refluxed at the first temperature for 2.5 to 3.5 hours. After the reaction is completed, the mixture is purified and dried to obtain the epoxy curing agent as described in claim 1 or 2.

4. The method for preparing the epoxy curing agent according to claim 3, characterized in that: In step A, the molar ratio of 2,2'-(1,3-phenylene)-dioxazoline: a difunctional monomer containing a phenolic hydroxyl or carboxyl group: a capped monomer containing a carboxyl or phenolic hydroxyl group is 5:4:2 or 8:7:

2.

5. The method for preparing the epoxy curing agent according to claim 3, characterized in that: In step A, the difunctional monomer containing phenolic hydroxyl or carboxyl groups includes dimer acid or hydrogenated dimer acid, or a mixture of hydrogenated dimer acid and 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid), or a mixture of hydrogenated dimer acid and vanillic acid.

6. The method for preparing the epoxy curing agent according to claim 3, characterized in that: In step A, the end-capped monomer containing a carboxyl or phenolic hydroxyl group includes p-aminobenzoic acid, 3-piperidinecarboxylic acid, 2-piperidinecarboxylic acid, 4-methylaminobenzoic acid, or 1-(4-hydroxyphenyl)piperazine.

7. The method for preparing the epoxy curing agent according to claim 3, characterized in that: In step A, the first solvent is N,N-dimethylformamide (DMF) or butyl butyrate. When the first solvent is N,N-dimethylformamide (DMF), additional purification is required. The purification method is to distill the DMF in the mixture under reduced pressure to remove most of the DMF, add a certain amount of ethyl acetate and a certain amount of water to the remaining liquid for extraction, and remove the solvent ethyl acetate by rotary evaporation of the extracted organic phase. The resulting brown viscous liquid is the epoxy curing agent, which is then placed in an oven and dried at a certain temperature. When the first solvent is butyl butyrate, the butyl butyrate does not need to be removed and no additional purification is required.

8. The method for preparing the epoxy curing agent according to claim 3, characterized in that: Before step A, there is also step A0, a method for preparing 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid): Under an inert atmosphere, a certain amount of 4,4'-diaminodiphenyl ether and a certain amount of trimellitic anhydride are added to a certain amount of glacial acetic acid. The mixture is reacted at a certain temperature for a period of time. After the reaction is complete, it is purified and dried to obtain 2,2'-(oxobis(1,4-phenylene))-bis(1,3-dioxoisoindoline-5-carboxylic acid), with the following structural formula:

9. The method for preparing the epoxy curing agent according to claim 8, characterized in that: In step A0, the molar ratio of 4,4'-diaminodiphenyl ether to trimellitic anhydride is 1:(2.0-2.2); the temperature is 120-140°C, and the reaction time is 18-24 hours.

10. A method for preparing a non-adhesive protective film for opening lids, characterized in that, Includes the following steps: Step C1: Dissolve the epoxy curing agent according to claim 1 or 2 in ethyl acetate to prepare an epoxy curing agent solution with a certain solid content; Step C2: Take a certain amount of epoxy-modified acrylate adhesive, add a certain amount of a mixed solution of ethyl acetate and anhydrous ethanol, add a certain amount of epoxy curing agent solution from step C1, stir evenly to make the colloid uniform and transparent, then add a certain amount of 2-ethyl-4-methylimidazole, stir evenly to obtain epoxy-modified acrylate adhesive. Step C3: The epoxy-modified acrylic adhesive prepared in step C2 is coated onto a PI film of a certain thickness to form an adhesive layer with a thickness of 13-17 micrometers. A release film of a certain thickness is then added to the adhesive layer, with the release surface of the release film aligned with the adhesive surface of the adhesive layer, to obtain a semi-finished product of the anti-adhesion opening protective film. The semi-finished product of the anti-adhesion opening protective film is placed in an oven and cured at a certain temperature for a period of time. Then it is taken out and cooled to room temperature to obtain the anti-adhesion opening protective film.

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