A transparent polyimide encapsulation film and a preparation method and application thereof

Abstract

The application discloses a transparent polyimide encapsulation film and a preparation method and application thereof, and belongs to the technical field of electronic chemicals. The preparation method of the transparent polyimide encapsulation film comprises the following steps: dissolving organic solvent, monomer diaminodiphenyl ether and monomer 1,3-bis(4-aminophenoxy)benzene to obtain mixed solution A; adding monomer bisphenol A type diether dianhydride and monomer hexafluorodinitrile into the mixed solution A to mix and polymerize, until the viscosity of the reaction system is 30-40 thousand mpa.s, to obtain mixed solution B; adding a catalyst into the mixed solution B, uniformly mixing to obtain transparent polyimide adhesive, coating the transparent polyimide adhesive on a support carrier, drying to obtain the transparent polyimide encapsulation film. The transparent polyimide encapsulation film prepared by the application has high light transmittance and can be used for preparing a flexible circuit board.

Description

Technical Field

[0001] This invention relates to the field of electronic chemicals technology, and more specifically to a transparent polyimide encapsulation film, its preparation method, and its application. Background Technology

[0002] With the rapid development of consumer electronics, customers have increasingly higher demands for these products. Beyond traditional features like fast processing speed and slim design, there is also a need for greater transparency. A report by IDTechEx predicts that the transparent electronics industry will exceed $20 billion by around 2040, and its development trajectory is becoming increasingly clear. With advancements in transparent electronics technology, the concept of electronic displays suspended in mid-air is becoming a reality, making it one of the most dynamic and rapidly growing markets.

[0003] Currently, there are relatively few publicly disclosed patents related to transparent circuit board materials, with most concerning copper-clad laminates, such as CN115648760A, CN114133865A, CN111556644B, and CN108102597A, which disclose the preparation of transparent copper-clad laminates. Flexible transparent copper-clad laminates are the substrate for preparing transparent electronic product circuits and are an essential raw material for transparent flexible circuit boards. Transparent encapsulation film is the protective film for these transparent electronic product circuit boards, which is produced along with the development of transparent flexible circuit boards. It is used by hot-pressing the prepared flexible circuit board circuit to protect the circuit board circuit from damage by the external environment, and is an indispensable protective material in the production of flexible transparent electronic circuit boards. Besides their different functions, encapsulation films and copper-clad laminates (CCLs) also differ significantly in product performance. Controlling the adhesive used in encapsulation films is often more difficult than controlling it in CCLs because encapsulation films are semi-cured products; the adhesive is in an unstable state, and its properties change during storage. During application, specific temperature and pressure are required for a strong bond with the materials being bonded. The adhesive layer of encapsulation films exhibits some flow during the hot-pressing process; this is known as flowability. CCLs, on the other hand, are stable products; the adhesive layer is fully cured and does not change during use. Although existing research documents the preparation of transparent CCLs, differences in functional requirements and manufacturing processes mean that CCLs and encapsulation films are not interchangeable materials. Furthermore, existing encapsulation films lack sufficient transparency to meet production needs. Therefore, it is essential to provide a transparent encapsulation film specifically for transparent circuit board materials. Summary of the Invention

[0004] To address the above problems, this invention provides a method for preparing a transparent polyimide encapsulation film. The transparent polyimide encapsulation film prepared by this invention has high light transmittance and can be used to prepare good flexible circuit boards.

[0005] The first objective of this invention is to provide a method for preparing a transparent polyimide encapsulating film, comprising the following steps:

[0006] Mixture A is obtained by dissolving organic solvent, monomer diaminodiphenyl ether, and monomer 1,3-bis(4-aminophenoxy)benzene.

[0007] Add bisphenol A type diether dianhydride and hexafluoro dianhydride monomers to mixture A to carry out a polymerization reaction until the viscosity of the reaction system is 30,000-40,000 mPa·s to obtain mixture B.

[0008] A catalyst was added to mixture B and mixed evenly to obtain a transparent polyimide adhesive. The transparent polyimide adhesive was then coated onto a support and dried to obtain a transparent polyimide encapsulation film.

[0009] In one embodiment of the present invention, during the preparation of the transparent polyimide adhesive, the mass fractions of each raw material are as follows:

[0010] In the preparation of transparent polyimide adhesive, the mass ratio of monomers bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene is 1.9778–2.6024:2.2212–2.7543:0.8009–1.0012:1.4617–1.754.

[0011] The amount of catalyst added is 13.9-17.7% of the total mass of the monomers bisphenol A diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene.

[0012] In one embodiment of the present invention, during the preparation of the transparent polyimide adhesive, the mass ratio of the monomers bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene is 1.9778:2.7543:0.8009:1.754.

[0013] The catalyst was added at a rate of 13.9% of the total mass of the monomers bisphenol A diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene.

[0014] In one embodiment of the present invention, the catalyst is quinoline, benzimidazole, or triethylamine.

[0015] In one embodiment of the present invention, the organic solvent includes dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide.

[0016] In one embodiment of the present invention, the reaction temperature of the polymerization reaction is 0-5°C.

[0017] In one embodiment of the present invention, the drying temperature is 80-150°C.

[0018] In one embodiment of the present invention, the thickness of the transparent polyimide encapsulation film is 15-25 μm.

[0019] A second objective of this invention is to provide a transparent polyimide encapsulation film prepared by the above-described preparation method.

[0020] The third objective of this invention is to provide the application of the above-mentioned transparent polyimide encapsulation film in the preparation of a protective film for transparent electronic circuit boards, wherein the transparent polyimide encapsulation film is applied to the transparent electronic circuit board using a hot pressing process.

[0021] Compared with existing technologies, it has the following beneficial effects:

[0022] This invention uses bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene as raw materials to prepare a polyamic acid solution through quaternary copolymerization. A catalyst is added, and after uniform mixing, a transparent polyimide adhesive is prepared. A transparent polyimide film is used as a support carrier, and the synthesized transparent polyimide adhesive is coated onto the film to prepare a transparent polyimide encapsulating film. The transparent polyimide encapsulating film exhibits characteristics such as a hot-pressing process temperature of 180-210℃, a light transmittance of over 85%, high adhesive strength, and the ability to withstand reflow soldering at 288℃.

[0023] The transparent polyimide encapsulation film prepared by this invention can be applied to consumer transparent electronic products such as smart bracelets, transparent connecting cables, transparent displays, and transparent communication terminal devices. The transparent polyimide encapsulation film prepared by this invention can be thermoformed and applied to the circuitry of a prepared flexible circuit board to protect the circuitry from damage by the external environment. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Copper-clad laminates (CCLs) are the substrate for manufacturing transparent electronic circuit boards and are an essential raw material for transparent flexible circuit boards (FLPCBs). Transparent encapsulation films, on the other hand, are protective films for transparent electronic circuit boards. These two materials differ not only in function but also in performance. Encapsulation films are semi-cured products; the adhesive is unstable and its properties change during storage. They require specific temperature and pressure conditions to bond firmly to the materials being bonded. Copper-clad laminates, however, are stable products; the adhesive layer is fully cured and does not change during use. Therefore, controlling the adhesive used in encapsulation films is often more challenging than that used in copper-clad laminates. Currently, most research on transparent circuit board materials focuses on copper-clad laminates. Therefore, providing a transparent encapsulation film is of significant importance.

[0026] Based on this, the present invention provides a method for preparing a transparent polyimide encapsulating film, comprising the following steps:

[0027] Mixture A is obtained by dissolving organic solvent, monomer diaminodiphenyl ether, and monomer 1,3-bis(4-aminophenoxy)benzene. In this step, the use of monomers containing ether bonds and fluorine to synthesize polyimide resin is beneficial to improving the transparency of the target film. The addition of two diamine monomers in the reaction first facilitates monomer dissolution and is conducive to the synthesis of polymers with higher molecular weight.

[0028] Add bisphenol A type diether dianhydride and hexafluorodianhydride monomers to mixture A to carry out a polymerization reaction until the viscosity of the reaction system reaches 30,000-40,000 mPa·s to obtain mixture B. In this step, experimental tests show that when the polymer viscosity is below this range, the film toughness is insufficient and the strength cannot be guaranteed. When it is above this range, the synthesis reaction is very difficult to control and the requirements for the purity of raw materials are particularly high. Therefore, it is more appropriate to control the viscosity to this range while meeting the usage conditions.

[0029] A catalyst is added to mixture B, and after thorough mixing, a transparent polyimide adhesive is obtained. The transparent polyimide adhesive is then dried to obtain a transparent polyimide encapsulation film. The addition of the catalyst effectively lowers the temperature of the imidization reaction, thus ensuring that the encapsulation film meets the requirements of the hot-pressing process for circuit boards during subsequent use.

[0030] In some preferred embodiments, during the preparation of the transparent polyimide adhesive, the mass ratio of the monomers bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene is 1.9778–2.6024:2.2212–2.7543:0.8009–1.0012:1.4617–1.754.

[0031] The amount of catalyst added is 13.9-17.7% of the total mass of the monomers bisphenol A diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene.

[0032] In the specific preparation process of this invention, each raw material is weighed according to the following mass proportions:

[0033] The monomers are: 1.9778–2.6024 parts of bisphenol A type diether dianhydride, 2.2212–2.7543 parts of hexafluorodianhydride, 0.8009–1.0012 parts of diaminodiphenyl ether, 1.4617–1.754 parts of 1,3-bis(4-aminophenoxy)benzene, 1.0119–1.2916 parts of catalyst, and 612.78–721.41 parts of organic solvent. It should be noted that during the preparation process, the amount of each component (1 part) is determined according to the required production quantity. One part can represent 1g, 10g, 500g, 1kg, 10kg, or 50kg, etc., and this invention does not impose any limitations on this.

[0034] In some preferred embodiments, during the preparation of the transparent polyimide adhesive, the mass ratio of the monomers bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene is 1.9778:2.7543:0.8009:1.754.

[0035] The catalyst was added at a rate of 13.9% of the total mass of the monomers bisphenol A diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene.

[0036] Furthermore, in the specific preparation process of this invention, each raw material is weighed according to the following mass proportions:

[0037] The monomers are 1.9778 parts of bisphenol A type diether dianhydride, 2.7543 parts of hexafluorodianhydride, 0.8009 parts of diaminodiphenyl ether, 1.754 parts of 1,3-bis(4-aminophenoxy)benzene, 1.0119 parts of catalyst, and 721.41 parts of organic solvent.

[0038] The structural formula of the monomer diaminodiphenyl ether (ODA) used in this invention is shown below:

[0039]

[0040] The structural formula of the monomer hexafluorodianhydride (6FDA) used in this invention is shown below:

[0041]

[0042] The structural formula of the monomer bisphenol A type diether dianhydride (BPADA) used in this invention is shown below:

[0043]

[0044] The structural formula of the monomer 1,3-bis(4-aminophenoxy)benzene (TPER) used in this invention is shown below:

[0045]

[0046] The addition of four monomers—hexafluorodianhydride, bisphenol A diether dianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene—used in this invention can improve the transparency, peel strength, and flexibility of copper-clad laminates. While increasing the amount of hexafluorodianhydride does not improve strength, it does improve transparency; increasing the amount of bisphenol A diether dianhydride improves peel strength. The TPER structure contains two ether bonds, resulting in a more flexible molecular chain. Increasing the amount of this monomer can provide polymer flexibility, lower the glass transition temperature, and facilitate lowering the lamination temperature in the preparation of encapsulation films. Furthermore, improper adjustment of the amount of a certain monomer outside the parameter range may affect the polymer's molecular weight, leading to lower viscosity during synthesis and consequently affecting adhesive strength and other issues.

[0047] In some preferred embodiments, the organic solvents include dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF). The amount of organic solvent component used is related to the solvent properties; different proportions of the mixed solvents affect the azeotropic point of the mixture. Especially in the preparation process of encapsulation films, it is desirable to lower the boiling point of the mixture to facilitate control of the volatile content of the product; therefore, the amount of low-boiling-point solvent is appropriately increased. Meanwhile, high-boiling-point NMP has a high solubility for the polymer; adding an appropriate amount of NMP is beneficial for improving the polymer's solubility.

[0048] In some preferred embodiments, the catalyst is quinoline (QL), benzimidazole (BI), or triethylamine (Et3N).

[0049] The CAS number for quinoline is 91-22-5, the CAS number for benzimidazole is 51-17-2, and the CAS number for triethylamine is 121-44-8.

[0050] In some preferred embodiments, the polymerization reaction temperature is 0-5°C. For example, the reaction temperature is 0°C, 1°C, 2°C, 3°C, 4°C, or 5°C, but is not limited to the listed values; other unlisted values ​​within the above range are also applicable.

[0051] In some preferred embodiments, the drying temperature is 80-150°C. During drying, the transparent polyimide adhesive is dried by controlling the temperature of each drying tunnel.

[0052] In some preferred embodiments, the thickness of the transparent polyimide encapsulation film is 15-25 μm.

[0053] The present invention also provides a transparent polyimide encapsulation film, which can be used to prepare a transparent electronic circuit board protective film. In use, the transparent polyimide encapsulation film is applied to the transparent electronic circuit board using a hot pressing molding process.

[0054] The hot pressing process involves pressing at 2MPa and 170℃ for 3 minutes, followed by baking at 180℃-210℃ for 60-120 minutes. These are recommended conditions; the temperature and time will vary depending on the specific product requirements. Performance meets the requirements within these parameters. Temperatures below these levels may result in low strength, while temperatures above these levels are generally outside the required pressing range and therefore unusable.

[0055] The structure of the product obtained after the transparent polyimide encapsulation film undergoes an imidization reaction under the action of a catalyst through a hot-pressing process is shown below:

[0056]

[0057] The present invention will be further described in detail below with reference to specific embodiments. In the following embodiments, the dosage of each component involved in the preparation process of the transparent polyimide adhesive is shown in Table 1, and the unit of dosage is kg.

[0058] Table 1 Formulation of transparent imide encapsulating film

[0059]

[0060] The following is a detailed description of Examples 1-5:

[0061] Example 1

[0062] Step 1: Referring to the formulation ratio of Example 1 in Table 1, add 1.0012 kg of monomer ODA, 1.4617 kg of TPER and organic solvent (organic solvent consists of 432.81 kg of DMAc, 144.27 kg of DMF and 72.14 kg of NMP) to the reactor. Heat appropriately to 80°C to accelerate monomer dissolution. After the reaction solution is homogeneous, cool down to 0°C. Add 2.6024 kg of monomer BPADA and 2.2212 kg of monomer 6FDA in three batches, with an interval of 1 hour between each addition. Stir at a constant speed for 12 hours and start testing the viscosity of the reaction solution. At this time, the viscosity of the reaction solution is about 20,000 mPa·s. Continue stirring until the viscosity reaches 30,000-40,000 mPa·s and then stop the synthesis. Add 1.2916 kg of catalyst QL to the imide resin precursor prepared above and disperse evenly for 24 hours to prepare transparent polyimide adhesive.

[0063] Step 2: Apply the polyimide adhesive prepared above onto a colorless and transparent polyimide film using an air-float coating machine. Control the temperature of the first drying tunnel at 80°C, the second at 100°C, the third at 120°C, the fourth and fifth at 150°C, and the sixth at 120°C. Control the travel speed at 10 m / min and maintain the dry adhesive thickness at 15 μm. Rewind the coating at the end to produce the transparent polyimide encapsulation film.

[0064] Step 3: Lay the transparent polyimide encapsulating film prepared above onto the circuit surface of the flexible printed circuit board, press it under 2 MPa and 170°C for 3 minutes, and bake it at 180°C for 120 minutes to prepare the test sample of the transparent polyimide encapsulating film. The test performance of the sample is shown in Table 2.

[0065] Example 2

[0066] Refer to the formulation and proportions in Example 2 of Table 1 and the preparation of the transparent polyimide encapsulating film in Example 1. The specific preparation steps are as follows:

[0067] Step 1: Add 0.9611 kg of monomer ODA, 1.5201 kg of TPER, and an organic solvent (composed of 360.46 kg of DMAc, 180.23 kg of DMF, and 72.09 kg of NMP) to the reactor. Heat appropriately to accelerate monomer dissolution. After the reaction solution is homogeneous, cool to 0°C. Add 2.4463 kg of monomer BPADA and 2.3545 kg of monomer 6FDA in three batches, with an interval of 1 hour between each addition. Stir at a constant speed for 12 hours and start testing the viscosity of the reaction solution. At this time, the viscosity of the reaction solution is about 20,000 mPa·s. Continue stirring until the viscosity reaches 30,000-40,000 mPa·s and then stop the synthesis. Add 1.1814 kg of catalyst BI to the imide resin precursor prepared above and disperse evenly for 24 hours to prepare a transparent polyimide adhesive.

[0068] Step 2: Apply the polyimide adhesive prepared above onto a colorless and transparent polyimide film using an air-float coating machine. Control the temperature of the first drying tunnel at 80°C, the second at 100°C, the third at 120°C, the fourth and fifth at 150°C, and the sixth at 120°C. Control the travel speed at 10 m / min and maintain the dry adhesive thickness at 15 μm. Rewind the coating at the end to produce the transparent polyimide encapsulation film.

[0069] Step 3: Lay the transparent polyimide encapsulating film prepared above onto the circuit surface of the flexible printed circuit board, press it under 2 MPa and 170°C for 3 minutes, and bake it at 180°C for 120 minutes to prepare the test sample of the transparent polyimide encapsulating film. The test performance of the sample is shown in Table 2.

[0070] Example 3

[0071] Refer to the formulation and proportions in Example 3 of Table 1 and the preparation of the transparent polyimide encapsulating film in Example 1. The specific preparation steps are as follows:

[0072] Step 1: Add 0.901 kg of monomer ODA, 1.6078 kg of TPER, and an organic solvent (composed of 324.28 kg of DMAc, 180.16 kg of DMF, and 144.13 kg of NMP) to the reactor. Heat appropriately to accelerate monomer dissolution. After the reaction solution is homogeneous, cool to 0°C. Add 2.2381 kg of monomer BPADA and 2.5322 kg of monomer 6FDA in three batches, with an interval of 1 hour between each addition. Stir at a constant speed for 12 hours and start testing the viscosity of the reaction solution. At this time, the viscosity of the reaction solution is about 20,000 mPa·s. Continue stirring until the viscosity reaches 30,000-40,000 mPa·s and then stop the synthesis. Add 1.0119 kg of catalyst Et3N to the imide resin precursor prepared above and disperse evenly for 24 hours to prepare a transparent polyimide adhesive.

[0073] Step 2: Apply the polyimide adhesive prepared above onto a colorless and transparent polyimide film using an air-float coating machine. Control the temperature of the first drying tunnel at 80°C, the second at 100°C, the third at 120°C, the fourth and fifth at 150°C, and the sixth at 120°C. Control the travel speed at 10 m / min and maintain the dry adhesive thickness at 15 μm. Rewind the coating at the end to produce the transparent polyimide encapsulation film.

[0074] Step 3: Lay the transparent polyimide encapsulating film prepared above onto the circuit surface of the flexible printed circuit board, press it under 2 MPa and 170°C for 3 minutes, and bake it at 180°C for 120 minutes to prepare the test sample of the transparent polyimide encapsulating film. The test performance of the sample is shown in Table 2.

[0075] Example 4

[0076] Refer to the formulation and proportions in Example 4 of Table 1 and the preparation of the transparent polyimide encapsulating film in Example 1. The specific preparation steps are as follows:

[0077] Step 1: Add 0.841g of monomer ODA, 1.6955kg of TPER, and an organic solvent (composed of 288.44kg of DMAc, 216.33kg of DMF, and 216.33kg of NMP) to the reactor. Heat appropriately to accelerate monomer dissolution. After the reaction solution is homogeneous, cool to 0℃. Add 2.0819kg of monomer BPADA and 2.6654kg of monomer 6FDA in three batches, with an interval of 1 hour between each addition. Stir at a constant speed for 12 hours and start testing the viscosity of the reaction solution. At this time, the viscosity of the reaction solution is about 20,000 mPa·s. Continue stirring until the viscosity reaches 30,000-40,000 mPa·s and then stop the synthesis. Add 1.2916kg of catalyst QL to the imide resin precursor prepared above and disperse evenly for 24 hours to prepare a transparent polyimide adhesive.

[0078] Step 2: Apply the polyimide adhesive prepared above onto a colorless and transparent polyimide film using an air-float coating machine. Control the temperature of the first drying tunnel at 80°C, the second at 100°C, the third at 120°C, the fourth and fifth at 150°C, and the sixth at 120°C. Control the travel speed at 10 m / min and maintain the dry adhesive thickness at 15 μm. Rewind the coating at the end to produce the transparent polyimide encapsulation film.

[0079] Step 3: Lay the transparent polyimide encapsulating film prepared above onto the circuit surface of the flexible printed circuit board, press it under 2MPa and 170℃ for 3 minutes, and bake it at 180℃-210℃ for 60-120 minutes to prepare the test sample of the transparent polyimide encapsulating film. The test performance of the sample is shown in Table 2.

[0080] Example 5

[0081] The preparation steps are as follows: Refer to the formulation and proportions in Example 5 of Table 1 and the transparent polyimide encapsulation film preparation in Example 1.

[0082] Step 1: Add 0.8009 kg of monomer ODA, 1.754 kg of TPER, and an organic solvent (composed of 288.57 kg of DMAc, 252.49 kg of DMF, and 180.35 kg of NMP) to the reactor. Heat appropriately to accelerate monomer dissolution. After the reaction solution is homogeneous, cool to 0°C. Add 1.9778 kg of monomer BPADA and 2.7543 kg of monomer 6FDA in three batches, with an interval of 1 hour between each addition. Stir at a constant speed for 12 hours and start testing the viscosity of the reaction solution. At this time, the viscosity of the reaction solution is about 20,000 mPa·s. Continue stirring until the viscosity reaches 30,000-40,000 mPa·s and then stop the synthesis. Add 1.0119 kg of catalyst Et3N to the imide resin precursor prepared above and disperse evenly for 24 hours to prepare a transparent polyimide adhesive.

[0083] Step 2: Apply the polyimide adhesive prepared above onto a colorless and transparent polyimide film using an air-float coating machine. Control the temperature of the first drying tunnel at 80°C, the second at 100°C, the third at 120°C, the fourth and fifth at 150°C, and the sixth at 120°C. Control the travel speed at 10 m / min and maintain the dry adhesive thickness at 15 μm. Rewind the coating at the end to produce the transparent polyimide encapsulation film.

[0084] Step 3: Lay the transparent polyimide encapsulating film prepared above onto the circuit surface of the flexible printed circuit board, press it under 2MPa and 170℃ for 3 minutes, and bake it at 180℃-210℃ for 60-120 minutes to prepare the test sample of the transparent polyimide encapsulating film. The test performance of the sample is shown in Table 2.

[0085] Example 6

[0086] Step 1: Referring to the formulation ratio of Example 1 in Table 1, add 0.9217 kg of monomer ODA, 1.6533 kg of TPER, and an organic solvent (composed of 432.81 kg of DMAc, 144.27 kg of DMF, and 72.14 kg of NMP) to the reactor. Heat appropriately to 80°C to accelerate monomer dissolution. After the reaction solution is homogeneous, cool to 5°C and add 2.5207 kg of monomer BPADA and 2.5731 kg of monomer 6FDA in three batches, with an interval of 1 hour between each addition. Stir at a constant speed for 12 hours and start testing the viscosity of the reaction solution. At this time, the viscosity of the reaction solution is about 20,000 mPa·s. Continue stirring until the viscosity reaches 30,000-40,000 mPa·s and then stop the synthesis. Add 1.1836 kg of catalyst QL to the imide resin precursor prepared above and disperse evenly for 24 hours to prepare a transparent polyimide adhesive.

[0087] Step 2: Apply the polyimide adhesive prepared above onto a colorless and transparent polyimide film using an air-float coating machine. Control the temperature of the first drying tunnel at 80°C, the second at 100°C, the third at 120°C, the fourth and fifth at 150°C, and the sixth at 120°C. Control the travel speed at 10 m / min and maintain the dry adhesive thickness at 15 μm. Rewind the coating at the end to produce the transparent polyimide encapsulation film.

[0088] Step 3: Lay the transparent polyimide encapsulation film prepared above onto the circuit surface of the flexible printed circuit board, press it under 2MPa and 170℃ for 3 minutes, and bake it at 210℃ for 60 minutes to prepare a test sample of the transparent polyimide encapsulation film.

[0089] Example 7

[0090] Step 1: Add 1.0012 kg of monomer ODA, 1.673 kg of TPER, and an organic solvent (composed of 288.57 kg of DMAc, 252.49 kg of DMF, and 180.35 kg of NMP) to the reactor. Heat appropriately to accelerate monomer dissolution. After the reaction solution is homogeneous, cool to 3°C. Add 2.0241 kg of monomer BPADA and 2.6234 kg of monomer 6FDA in three batches, with an interval of 1 hour between each addition. Stir at a constant speed for 12 hours and start testing the viscosity of the reaction solution. At this time, the viscosity of the reaction solution is about 20,000 mPa·s. Continue stirring until the viscosity reaches 30,000-40,000 mPa·s and then stop the synthesis. Add 1.1385 kg of catalyst Et3N to the imide resin precursor prepared above and disperse evenly for 24 hours to prepare a transparent polyimide adhesive.

[0091] Step 2: Apply the polyimide adhesive prepared above onto a colorless and transparent polyimide film using an air-float coating machine. Control the temperature of the first drying tunnel at 80°C, the second at 100°C, the third at 120°C, the fourth and fifth at 150°C, and the sixth at 120°C. Control the travel speed at 10 m / min and maintain the dry adhesive thickness at 15 μm. Rewind the coating at the end to produce the transparent polyimide encapsulation film.

[0092] Step 3: Lay the transparent polyimide encapsulation film prepared above onto the circuit surface of the flexible printed circuit board, press it under 2MPa and 170℃ for 3 minutes, and bake it at 200℃ for 100 minutes to prepare a test sample of the transparent polyimide encapsulation film.

[0093] Table 2 Performance Test Table of Transparent Polyimide Encapsulation Film Samples

[0094]

[0095] As shown in Table 2, the transparent polyimide encapsulation film prepared by this invention exhibits excellent performance, with a light transmittance of 85.2-88.4% and good transparency. Meanwhile, the catalyst used has a significant impact on adhesive properties such as peel strength; currently, the catalysts used in this invention basically meet the application requirements.

[0096] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0097] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for producing a transparent polyimide encapsulating film, characterized by, Includes the following steps: Mixture A is obtained by dissolving organic solvent, monomer diaminodiphenyl ether, and monomer 1,3-bis(4-aminophenoxy)benzene. Add bisphenol A type diether dianhydride and hexafluoro dianhydride monomers to mixture A to carry out a polymerization reaction until the viscosity of the reaction system is 30,000-40,000 mPa·s to obtain mixture B. A catalyst was added to mixture B and mixed evenly to obtain a transparent polyimide adhesive. The transparent polyimide adhesive was coated on a support and dried to obtain a transparent polyimide encapsulation film. In the preparation of transparent polyimide adhesive, the mass ratio of monomers bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene is 1.9778~2.6024:2.2212~2.7543:0.8009~1.0012:1.4617~1.

754. The amount of catalyst added is 13.9-17.7% of the total mass of the monomers bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene.

2. The method for preparing a transparent polyimide encapsulating film according to claim 1, characterized in that, In the preparation of transparent polyimide adhesive, the mass ratio of monomers bisphenol A type diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene is 1.9778:2.7543:0.8009:1.

754. The catalyst was added at a rate of 13.9% of the total mass of the monomers bisphenol A diether dianhydride, hexafluorodianhydride, diaminodiphenyl ether, and 1,3-bis(4-aminophenoxy)benzene.

3. The method for preparing a transparent polyimide encapsulating film according to claim 1, characterized in that, The catalyst is quinoline, benzimidazole, or triethylamine.

4. The method for preparing a transparent polyimide encapsulating film according to claim 1, characterized in that, Organic solvents include dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide.

5. The method for preparing a transparent polyimide encapsulating film according to claim 1, characterized in that, The reaction temperature for polymerization is 0-5℃.

6. The method for preparing a transparent polyimide encapsulating film according to claim 1, characterized in that, The drying temperature is 80-150℃.

7. The method for preparing a transparent polyimide encapsulating film according to claim 1, characterized in that, The thickness of the transparent polyimide encapsulation film is 15-25 μm.

8. A transparent polyimide encapsulating film prepared by the preparation method according to any one of claims 1-7.

9. The application of the transparent polyimide encapsulation film according to claim 8 in the preparation of a transparent electronic circuit board protective film, characterized in that, A transparent polyimide encapsulation film is applied to a transparent electronic circuit board using a hot-press molding process.

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