Polyimides, polyimide films and laminates, methods of making the same, and flexible copper clad laminates

Abstract

The present application relates to the technical field of high polymer material, and particularly relates to a polyimide, a polyimide film and a laminate, a preparation method of the polyimide, and a flexible copper clad plate. The polyimide comprises residues of a dianhydride and residues of a diamine in a structural unit; wherein the diamine comprises a substituted or unsubstituted biphenyl diamine shown in formula (1), and the biphenyl diamine accounts for 80% to 100% of the total mass of the diamine; in the formula, R1-R8 are independently hydrogen atoms, fluorine atoms, trifluoromethyl groups, chlorine atoms or trichloromethyl groups, and at least one of R1-R8 is not a hydrogen atom; and the dianhydride is selected from one or more of 3,3',4,4'-biphenyl tetracarboxylic dianhydride, pyromellitic dianhydride and hexafluoro dianhydride. The polyimide provided by the present application increases the number of unsaturated conjugate bonds, introduces electron-withdrawing groups, and makes the valence electrons jump between different energy levels to form purple color. Formula (1).

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polyimide, a polyimide film, a polyimide laminate, a method for preparing the same, and a flexible copper-clad laminate. Background Technology

[0002] Polyimide, a high-performance polymer resin, is a key raw material in the flexible printed circuit board (FPC) and electronic circuit industries. It possesses excellent dimensional stability, superior high-temperature resistance, and good resistance to thermal shock; this is closely related to the large number of benzene ring functional groups and imide ring functional groups in its molecular structure, which exhibit high rigidity and high thermal stability. Polyimide materials come in various colors, including yellow, tan, and brown. Polyimides with different optical properties can be applied in various fields: colorless and transparent PI can be used for flexible substrates, black PI for shielding materials, and colored PI for filters, tapes in different colors, labels, and protective films.

[0003] Currently, adding colorants is the mainstream method for preparing colored polyimide (PI). However, the aggregation of pigment particles can easily lead to optical defects. To achieve better dispersion, a time-consuming, expensive, and complex modification and dispersion process is usually required. Furthermore, the low thermal decomposition temperature of organic pigments hinders the application of PI films in high-temperature applications. For example, invention application CN104211974A describes a method for preparing colored polyimide films, which involves dispersing inorganic pigments in an organic solvent to obtain a dispersion, adding monomers to the dispersion to polymerize and obtain a polyamic acid solution, and then imidizing to obtain a colored polyimide film. However, the addition of inorganic pigments affects the heat resistance of polyimide, and dispersing inorganic pigments is time-consuming and costly.

[0004] To address this problem, this invention is proposed. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a polyimide, a polyimide film, a polyimide laminate, a method for preparing the same, and a flexible copper-clad laminate. The polyimide is a purple polyimide. The polyimide provided by the present invention increases the number of unsaturated conjugated bonds in the monomer and introduces electron-withdrawing groups, so that valence electrons transition between different energy levels to form a purple color.

[0006] In a first aspect, the polyimide structural unit provided by the present invention contains dianhydride residues and diamine residues; wherein the diamine comprises substituted or unsubstituted biphenyl diamine as shown in formula (1), wherein the biphenyl diamine accounts for 80% to 100% of the total amount of the diamine.

[0007] Equation (1).

[0008] In the formula, R1 to R8 are independently hydrogen atoms, fluorine atoms, trifluoromethyl atoms, chlorine atoms or trichloromethyl atoms, and at least one of R1 to R8 is not a hydrogen atom.

[0009] The dianhydride is selected from one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and hexafluorodianhydride (6FDA).

[0010] The purple polyimide provided by this invention increases the number of unsaturated conjugated bonds (benzene rings) in the monomer and introduces electron-withdrawing groups (fluorine atoms, trifluoromethyl, chlorine atoms, or trichloromethyl). These design strategies effectively modulate the electronic structure of the polyimide molecule, causing its valence electrons to transition between energy levels within the molecule, thereby producing a specific purple color. This color formation not only adds visual uniqueness to polyimides but also opens up new possibilities for their application in optical materials and other high-performance applications.

[0011] In this invention, the diamine represented by formula (1) accounts for more than 80% of the total amount of diamines used to synthesize the polyimide, such as 85%, 90%, 95%, 98%, etc., and the remaining diamine can be p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), diaminodiphenyl ether (ODA), etc.

[0012] Preferably, the dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride or pyromellitic dianhydride.

[0013] Preferably, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to pyromellitic dianhydride is 9:1 to 7:3; for example, the ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to pyromellitic dianhydride is 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, etc. Controlling this molar ratio significantly improves the color and peel strength of polyimide (PI). Outside this range, the effect is poor; for example, as the proportion of pyromellitic dianhydride increases, the color of PI gradually transitions from purple to yellow (L value increases, a value decreases, b value increases), while its peel strength gradually decreases.

[0014] Preferably, in the benzidine shown in formula (1), at least one of R2, R3, R6 and R7 is selected from fluorine atom, trifluoromethyl, chlorine atom or trichloromethyl.

[0015] More preferably, the benzidine is 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB), 2,2'-dichloro-4,4'-diaminobiphenyl, or 2,2'-difluoro-4,4'-diaminobiphenyl.

[0016] More preferably, the benzidine is 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB).

[0017] In this invention, by using preferred types of biphenyl diamine, especially 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl, not only is the range of suppliers increased, but the Dk / Df value can also be reduced more effectively than with diamines of different substituents.

[0018] More preferably, the polyimide comprises structural units as shown in formula (2).

[0019] Equation (2).

[0020] In the formula, Ar is selected from one or more of the residues of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and hexafluorodianhydride (6FDA); R1 to R8 are independently hydrogen atoms, fluorine atoms, trifluoromethyl atoms, chlorine atoms, or trichloromethyl atoms, and at least one of R1 to R8 is not a hydrogen atom.

[0021] This invention enables polyimide materials to exhibit the target color (purple) by selecting diamine and dianhydride monomers with specific structures. It also demonstrates advantages in optical, electrical, mechanical and thermal properties, and has broad application potential. Moreover, the monomers used in this invention have simple structures, are widely available, and have low cost.

[0022] Preferably, the degree of polymerization of the polyimide is not less than 25, for example, it can be 30, 50, 80, 100, 150, 200, 500, 1000, etc.

[0023] In a second aspect, the present invention provides a polyimide film comprising the above-described polyimide.

[0024] Preferably, in the Lab value of the polyimide film, L is 50~80, a is 10~40, and b is -15~20; and / or, the dielectric constant of the polyimide film at a frequency of 10 GHz is not higher than 3.20, and the dielectric loss is not higher than 0.0060; and / or, the CTE of the polyimide film is 19~25 ppm / K.

[0025] More preferably, in the Lab value of the polyimide film, L is 50~70, a is 20~40, and b is -15~5; and / or, the dielectric constant of the polyimide film at a frequency of 10 GHz is not higher than 3.10, and the dielectric loss is not higher than 0.0050; and / or, the CTE of the polyimide film is 21~23 ppm / K.

[0026] Thirdly, the present invention provides a polyimide stack, the polyimide stack comprising:

[0027] First polyimide layer.

[0028] A second polyimide layer is applied to the surface of the first polyimide layer.

[0029] And a third polyimide layer covering the surface of the second polyimide layer.

[0030] Each layer of the polyimide stack includes the above-mentioned polyimide or the above-mentioned polyimide film, wherein the main body of the first polyimide layer and the third polyimide layer is polyimide 1, the main body of the second polyimide layer is polyimide 2, and in the structural unit of the polyimide 2, at least one of Ar and R1 to R8 contains trifluoromethyl groups.

[0031] Preferably, the fluorine content of the polyimide 2 is >20%, and more preferably 24.3%~27.8%. By using the above-mentioned fluorine content of polyimide 2, polyimides with low CTE (coefficient of thermal expansion) can be synthesized more effectively.

[0032] In this invention, the fluorine content of polyimide can be calculated according to the following formula shown in formula (6).

[0033] Equation (6).

[0034] In the above formula, n i n is the molar amount of aromatic diamine i. j M is the molar amount of tetracarboxylic acid dianhydride j. i M is the molecular weight of the aromatic diamine i-imine after dehydration. j F is the molecular weight of the tetracarboxylic dianhydride j-imine after dehydration. i F represents the number of fluorine atoms in one aromatic diamine i molecule. j 19.00 represents the number of fluorine atoms in one tetracarboxylic acid dianhydride molecule, where 19.00 is the atomic mass of fluorine.

[0035] Preferably, in the Lab value of the polyimide stack, L is 50~80, a is 10~40, and b is -15~20.

[0036] Preferably, the dielectric constant of the polyimide stack is not higher than 3.20 and the dielectric loss is not higher than 0.0060 at a frequency of 10 GHz; and / or, the dielectric constant of the first polyimide layer and the third polyimide layer is 3.00~3.30 and the dielectric loss is 0.0040~0.0060 at a frequency of 10 GHz; and / or, the dielectric constant of the second polyimide layer is 2.85~3.05 and the dielectric loss is 0.0050~0.0065 at a frequency of 10 GHz.

[0037] Preferably, the CTE of the polyimide stack is 19~25ppm / K; and / or, the CTE of the first polyimide layer and the third polyimide layer is greater than 17.5ppm / K and the CTE of the second polyimide layer; preferably, the CTE of the first polyimide layer and the third polyimide layer is 30~65ppm / K; and / or, the CTE of the second polyimide layer is 5~17ppm / K.

[0038] More preferably, in the Lab values ​​of the polyimide stack, L is 50~70, a is 20~40, and b is -15~5; and / or, the dielectric constant of the polyimide stack at a frequency of 10 GHz is not higher than 3.10, and the dielectric loss is not higher than 0.0050; and / or, the dielectric constant of the first polyimide layer and the third polyimide layer at a frequency of 10 GHz is 3.00~3.20, and the dielectric loss is 0.0040~0.0. 055; and / or, the dielectric constant of the second polyimide layer is 2.85~3.00 and the dielectric loss is 0.0050~0.0060 at a frequency of 10 GHz; and / or, the CTE of the polyimide stack is 21~23 ppm / K; and / or, the CTE of the first and third polyimide layers is 35~55 ppm / K; and / or, the CTE of the second polyimide layer is 7~15 ppm / K.

[0039] According to the present invention, polyimide laminates are commonly used in flexible copper-clad laminates. Traditional flexible copper-clad laminates typically have a dielectric constant between 3.5 and 4.0, and a dielectric loss of approximately 2%. These relatively high dielectric constants and losses cannot meet the demands of high-frequency signal transmission in 5G communication, leading to signal absorption and loss. Therefore, developing flexible circuit boards for high-frequency and high-speed applications has become a new research hotspot in the electronics industry. Common polyimide film materials have a dielectric constant of approximately 3.4 and a dielectric loss of approximately 0.015. However, ordinary polyimide films are insufficient to meet the high dielectric performance requirements of the future 5G era. This invention develops a new polyimide laminate material that not only maintains good dielectric properties but also achieves a purple appearance. The polyimide layer of this invention, especially polyimide 1, increases the number of unsaturated conjugated bonds and introduces electron-withdrawing groups, allowing valence electrons to transition between different energy levels, resulting in the purple color. Simultaneously, polyimide 2 further reduces the dielectric constant by introducing trifluoromethyl groups. Furthermore, polyimide 2 can better bond with polyimide 1, resulting in the entire polyimide laminate not only exhibiting a purple color but also possessing a low dielectric constant and good dimensional stability. Simultaneously, by utilizing the CTE (coefficient of thermal expansion) of different layers in the laminate and its compatibility with the substrate (such as copper foil), wrinkling and peeling phenomena are effectively reduced. This invention, through the use of low-dielectric layer stacking and the synergistic effect of each layer, yields a polyimide laminate material with excellent overall performance. This invention achieves a balance between a purple appearance and low dielectric constant and low dielectric loss, while also ensuring CTE compatibility with the copper substrate, providing a high-quality new material for high-frequency and high-speed applications.

[0040] Preferably, the polyimide 2 comprises the structural unit shown in formula (3).

[0041] Equation (3).

[0042] Preferably, the polyimide 2 further comprises structural units shown in formula (4) and / or formula (5).

[0043] Equation (4).

[0044] Equation (5).

[0045] In the formula, R1 to R8 are independently hydrogen atoms, fluorine atoms, trifluoromethyl atoms, chlorine atoms or trichloromethyl atoms, and at least one of R1 to R8 is not a hydrogen atom.

[0046] Further preferably, in terms of the amount of substance, the molar proportion of the structural unit shown in formula (3) in the polyimide 2 is 20% to 50%, and the balance is preferably the structural unit shown in formula (4) and / or formula (5).

[0047] According to the present invention, polyimide can be prepared by imidizing a polyamic acid resin obtained by mixing an aromatic diamine monomer and a dianhydride monomer.

[0048] Fourthly, the present invention also provides a method for preparing the above-mentioned polyimide stack, comprising molding a first polyimide layer, a second polyimide layer and a third polyimide layer onto a substrate to obtain a polyimide stack; preferably comprising the following steps.

[0049] 1) Prepare the precursor solution of polyimide 1 and the precursor solution of polyimide 2 respectively.

[0050] 2) A portion of the precursor solution of polyimide 1 is coated onto a substrate and dried. Then, the precursor solution of polyimide 2 and the remaining precursor solution of polyimide 1 are simultaneously cast onto the obtained precursor dry film layer and dried to obtain the precursor dry film layer of the polyimide stack.

[0051] 3) The substrate coated with the polyimide laminate precursor dry film layer is thermocured.

[0052] Preferably, step 1) includes mixing the diamine with a solvent to obtain a solution; then adding dianhydride and reacting; and / or, the diamine accounts for 7% to 15% of the total mass of the solution; and / or, the reaction temperature is 0 to 50°C and the reaction time is 8 to 48 hours; and / or, 0.960 ≤ the molar ratio of the dianhydride to the diamine ≤ 1.100.

[0053] Preferably, in step 2), the substrate includes copper foil, aluminum foil, steel strip or polymer support film, the drying temperature is 100~180℃, and the total solvent content in the precursor dry film layer is 15~35wt%.

[0054] Preferably, in step 3), the heat curing temperature is 350~400℃ and the heat curing time is 5~15min.

[0055] In this invention, the type of substrate for the polyimide laminate is not limited. For example, it can be a metal substrate such as copper foil, aluminum foil, or silver foil; an inorganic substrate such as glass sheet; or a polymer support film such as a vulcanized fiber substrate or polyester fiber substrate. The polyimide laminate is obtained by finally removing the substrate. When copper foil is used, a flexible copper-clad laminate can be obtained directly without removing the substrate. The copper foil can be electronic-grade rolled copper foil or electrolytic copper foil, and the thickness of the copper foil is 6~50 μm.

[0056] Fifthly, the present invention also provides a flexible copper-clad laminate, which includes a copper foil and a polyimide layer coated on the surface of the copper foil. The polyimide layer is the polyimide stack described above or a polyimide stack obtained by the above preparation method. The flexible copper-clad laminate provided by the present invention has a surface polyimide layer that forms a purple color by increasing the number of unsaturated conjugated bonds and introducing electron-withdrawing groups to allow valence electrons to transition between different energy levels. The middle polyimide layer uses a fluorinated monomer to reduce the dielectric constant, and the CTE of the three polyimide layers is close to that of the copper foil, resulting in good flatness and dimensional stability of the flexible copper-clad laminate. Preferably, the difference between the CTE of the polyimide stack and the CTE of the copper foil is no greater than 8 ppm / K. In the present invention, the CTE of the copper foil is 16.6~19.6 ppm / K, and the CTE of the polyimide stack is preferably 19.6~24.7 ppm / K.

[0057] This invention utilizes a surface polyimide layer that increases the number of unsaturated conjugated bonds and introduces electron-withdrawing groups (such as fluorine atoms, trifluoromethyl groups, chlorine atoms, and trichloromethyl groups), enabling valence electrons to transition between different energy levels, thus producing a purple color. This design not only endows the polyimide with a unique color but also significantly improves its optical properties and stability. The increase in unsaturated conjugated bonds enhances the material's stability under light, while the introduction of electron-withdrawing groups further strengthens its electronic properties, making it excellent for optoelectronic applications. The intermediate polyimide layer uses a fluorinated monomer, which not only lowers the dielectric constant of the polyimide but also improves its chemical resistance and heat resistance. The fluorinated monomer has low polarizability and high electronegativity, resulting in excellent high-frequency electrical performance of the intermediate polyimide layer. Furthermore, the use of the fluorinated monomer also gives the polyimide better weather resistance and service life. The CTE (coefficient of thermal expansion) of the three-layer polyimide combination is close to that of copper foil, significantly improving the flatness and dimensional stability of the flexible copper-clad laminate under temperature changes. The matching design of thermal expansion coefficients avoids interlayer stress caused by thermal expansion and contraction, thus preventing problems such as material delamination and cracking. This not only improves the mechanical properties of the copper-clad laminate but also ensures its reliability and durability during long-term use. This invention, through ingenious material design and structural optimization, significantly enhances the optical, electrical, and mechanical properties of polyimide materials. The introduction of unsaturated conjugated bonds and electron-withdrawing groups in the surface polyimide, the selection of fluorinated monomers in the middle polyimide, and the matching of thermal expansion coefficients of the three polyimide layers collectively endow the flexible copper-clad laminate with excellent flatness, dimensional stability, and durability, making it suitable for the manufacture and application of high-performance electronic materials.

[0058] Preferably, the thickness of the polyimide laminate is 6~50 μm, and the thickness of the copper foil is 6~50 μm.

[0059] Preferably, the thickness of the polyimide laminate is 12~25μm, and the thickness of the copper foil is 12~25μm.

[0060] Further preferably, the thickness of the first polyimide layer is 1~5μm, the thickness of the third polyimide layer is 1~5μm, and the thickness of the second polyimide layer is 4~40μm.

[0061] More preferably, the thickness of the first polyimide layer is 2~4 μm, the thickness of the third polyimide layer is 2~4 μm, and the thickness of the second polyimide layer is 8~20 μm.

[0062] Sixthly, the method for preparing the flexible copper-clad laminate provided by the present invention includes the following steps.

[0063] 1) Prepare the precursor solution of polyimide 1 and the precursor solution of polyimide 2 respectively.

[0064] 2) A portion of the precursor solution of polyimide 1 is coated onto a strip of copper foil and evaporated. Then, the precursor solution of polyimide 2 and the remaining precursor solution of polyimide 1 are simultaneously cast onto the obtained precursor dry film layer and dried to obtain the copper foil of the precursor dry film layer of the polyimide stack.

[0065] 3) The copper foil coated with the precursor dry film layer of the polyimide stack is thermally cured to obtain a strip of copper foil with the polyimide stack; and optionally, the strip of copper foil with the polyimide stack is wound up.

[0066] Preferably, step 1) includes dissolving the diamine monomer in a solvent to obtain a solution; then adding the dianhydride monomer and reacting.

[0067] Preferably, the solvent is selected from strongly polar solvents, and is preferably one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0068] Preferably, the diamine monomer accounts for 7% to 15% of the total mass of the solution.

[0069] Preferably, the reaction temperature is 0~50℃ and the reaction time is 8~48h.

[0070] Preferably, the molar ratio of the diamine monomer to the dianhydride monomer is 0.960 ≤ 1.000.

[0071] Preferably, in step 2), the evaporation temperature is 100~180℃, and the content of the strong polar solvent after evaporation is 15~30wt%.

[0072] Preferably, in step 3), the thermosetting temperature is 350~400℃ and the thermosetting time is 5~15min.

[0073] The polyimide, polyimide laminate, preparation method, and flexible copper clad laminate provided by this invention have significant technical improvements. The polyimide obtained by this invention can be copolymerized using a variety of monomers, and polyimide films with excellent comprehensive properties such as optical, dielectric, and CTE can be obtained at low cost. Unlike the dye-doped purple polyimide in the prior art, the polyimide of this invention does not have problems such as low thermal stability and film inhomogeneity. Attached Figure Description

[0074] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0075] Figure 1 This is a schematic diagram of the structure of the purple polyimide flexible copper-clad laminate provided in an embodiment of the present invention.

[0076] Wherein, 1-copper foil, 2-first polyimide layer, 3-second polyimide layer, 4-third polyimide layer. Detailed Implementation

[0077] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0078] The following embodiments of the present invention provide a purple polyimide flexible copper-clad laminate, the structure of which is shown in the figure. Figure 1As shown, a copper foil 1 is disposed at the bottom layer, and a polyimide layer is formed on the surface of the copper foil 1. The polyimide layer includes a first polyimide layer 2 in contact with the copper foil 1, a second polyimide layer 3 coated on the surface of the first polyimide layer 2, and a third polyimide layer 4 coated on the surface of the second polyimide layer 3. The first polyimide layer 2 and the third polyimide layer 4 are prepared from a precursor solution of polyimide 1, and the second polyimide layer 3 is prepared from a precursor solution of polyimide 2. The copper foil 1 is a strip-shaped (electronic-grade rolled) copper foil with a thickness of 12~25μm. The thickness of the first polyimide layer 2 is 2~4μm, the thickness of the second polyimide layer 3 is 8~20μm, and the thickness of the third polyimide layer 4 is 2~4μm.

[0079] Example 1

[0080] 1) Precursor solution of polyimide 1: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.05 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.02 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 1.

[0081] 2) Precursor solution of polyimide 2: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g of NMP. After stirring evenly on a stirring table, 0.03 mol of hexafluorodianhydride (6FDA) was added and stirred for 1 h. Then, 0.04 mol of pyromellitic dianhydride (PMDA) was added and stirred for 1 h. Then, the remaining 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 2.

[0082] 3) The precursor solution of polyimide 1 is cast onto a strip of copper foil at a linear speed of 5 m / min, and then desolvented in a 160°C oven for 9 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 20±2%, and the thickness of the first polyimide layer obtained by imidization is 3 μm. Then, the precursor solutions of polyimide 2 and polyimide 1 are simultaneously cast onto the precursor dry film layer at a linear speed of 3 m / min, and then desolvented in a 160°C oven for 15 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 25±2%. The thickness of the second polyimide layer obtained by imidization is 19 μm. The thickness of the third polyimide layer obtained by imidization is 3 μm. The total thickness of the polyimide layers obtained by imidization is 25 μm.

[0083] 4) The long strip of copper foil coated with the precursor dry film layer of polyimide resin is heat-treated by heating from 150°C to 370°C at a heating rate of about 10°C / min to imidize the polyamic acid, thereby obtaining a flexible copper-clad laminate.

[0084] Example 2

[0085] The steps of Example 1 were repeated, but the dianhydride compound in polyimide 1 was replaced with 0.07 mol of BPDA and 0.03 mol of PMDA; the order of addition was 0.03 mol of PMDA, 0.04 mol of BPDA, and 0.03 mol of BPDA. The first polyimide layer obtained by imidization had a thickness of 3 μm; the second polyimide layer obtained by imidization had a thickness of 19 μm; the third polyimide layer obtained by imidization had a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization was 25 μm.

[0086] Example 3

[0087] The steps of Example 1 were repeated, but the dianhydride compound in polyimide 1 was replaced with 0.09 mol of BPDA and 0.01 mol of PMDA; the order of addition was 0.01 mol of PMDA, 0.06 mol of BPDA, and 0.03 mol of BPDA. The first polyimide layer obtained by imidization had a thickness of 3 μm; the second polyimide layer obtained by imidization had a thickness of 19 μm; the third polyimide layer obtained by imidization had a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization was 25 μm.

[0088] Example 4

[0089] Repeat the steps of Example 1, but replace the dianhydride compound of polyimide 2 with 0.02 mol of 6FDA and 0.08 mol of PMDA; the order of addition is 0.02 mol of 6FDA, 0.05 mol of PMDA, and 0.03 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0090] Example 5

[0091] Repeat the steps of Example 1, but replace the dianhydride compound of polyimide 2 with 0.05 mol of 6FDA and 0.05 mol of PMDA; the order of addition is 0.05 mol of 6FDA, 0.03 mol of PMDA, and 0.02 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0092] Example 6

[0093] The method is the same as in Example 1, except that...

[0094] 1) Precursor solution of polyimide 1: Under a nitrogen atmosphere, 0.09 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) and 0.01 mol of p-phenylenediamine (PDA) were dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.05 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h. Then, the remaining 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h. Then, 0.02 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 1.

[0095] 2) Precursor solution of polyimide 2: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g of NMP. After stirring evenly on a stirring table, 0.03 mol of hexafluorodianhydride (6FDA) was added and stirred for 1 h. Then, 0.04 mol of pyromellitic dianhydride (PMDA) was added and stirred for 1 h. Then, 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 2.

[0096] 3) The precursor solution of polyimide 1 is cast onto a strip of copper foil at a linear speed of 5 m / min, and then desolvented in a 160°C oven for 9 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 20±2%, and the thickness of the first polyimide layer obtained by imidization is 3 μm. Then, the precursor solutions of polyimide 2 and polyimide 1 are simultaneously cast onto the precursor dry film layer at a linear speed of 3 m / min, and then desolvented in a 160°C oven for 15 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 25±2%. The thickness of the second polyimide layer obtained by imidization is 19 μm. The thickness of the third polyimide layer obtained by imidization is 3 μm. The total thickness of the polyimide layers obtained by imidization is 25 μm.

[0097] 4) The long strip of copper foil coated with the precursor dry film layer of polyimide resin is heat-treated by heating from 150°C to 370°C at a heating rate of about 10°C / min to imidize the polyamic acid, thereby obtaining a flexible copper-clad laminate.

[0098] Example 7

[0099] Repeat the steps of Example 6, but replace the dianhydride compound of polyimide 1 with 0.07 mol of BPDA and 0.03 mol of PMDA; the order of addition is 0.03 mol of PMDA, 0.04 mol of BPDA, and 0.03 mol of BPDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0100] Example 8

[0101] The steps of Example 6 were repeated, but the dianhydride compound in polyimide 1 was replaced with 0.09 mol of BPDA and 0.01 mol of PMDA; the order of addition was 0.01 mol of PMDA, 0.06 mol of BPDA, and 0.03 mol of BPDA. The first polyimide layer obtained by imidization had a thickness of 3 μm; the second polyimide layer obtained by imidization had a thickness of 19 μm; the third polyimide layer obtained by imidization had a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization was 25 μm.

[0102] Example 9

[0103] Repeat the steps of Example 6, but replace the dianhydride compound of polyimide 2 with 0.02 mol of 6FDA and 0.08 mol of PMDA; the order of addition is 0.02 mol of 6FDA, 0.05 mol of PMDA, and 0.03 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0104] Example 10

[0105] Repeat the steps of Example 6, but replace the dianhydride compound of polyimide 2 with 0.05 mol of 6FDA and 0.05 mol of PMDA; the order of addition is 0.05 mol of 6FDA, 0.03 mol of PMDA, and 0.02 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0106] Example 11

[0107] The method is the same as in Example 1, except that...

[0108] 1) Precursor solution of polyimide 1: Under a nitrogen atmosphere, 0.08 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) and 0.02 mol of p-phenylenediamine (PDA) were dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.05 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.02 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 1.

[0109] 2) Precursor solution of polyimide 2: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g of NMP. After stirring evenly on a stirring table, 0.03 mol of hexafluorodianhydride (6FDA) was added and stirred for 1 h. Then, 0.04 mol of pyromellitic dianhydride (PMDA) was added and stirred for 1 h. Then, the remaining 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 2.

[0110] 3) The precursor solution of polyimide 1 is cast onto a strip of copper foil at a linear speed of 5 m / min, and then desolvented in a 160°C oven for 9 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 20±2%, and the thickness of the first polyimide layer obtained by imidization is 3 μm. Then, the precursor solutions of polyimide 2 and polyimide 1 are simultaneously cast onto the precursor dry film layer at a linear speed of 3 m / min, and then desolvented in a 160°C oven for 15 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 25±2%. The thickness of the second polyimide layer obtained by imidization is 19 μm. The thickness of the third polyimide layer obtained by imidization is 3 μm. The total thickness of the polyimide layers obtained by imidization is 25 μm.

[0111] 4) The long strip of copper foil coated with the precursor dry film layer of polyimide resin is heat-treated by heating from 150°C to 370°C at a heating rate of about 10°C / min to imidize the polyamic acid, thereby obtaining a flexible copper-clad laminate.

[0112] Example 12

[0113] Repeat the steps of Example 11, but replace the dianhydride compound of polyimide 1 with 0.07 mol of BPDA and 0.03 mol of PMDA; the order of addition is 0.03 mol of PMDA, 0.04 mol of BPDA, and 0.03 mol of BPDA. The thickness of the first polyimide layer obtained by imidization is 3 μm; the thickness of the second polyimide layer obtained by imidization is 19 μm; the thickness of the third polyimide layer obtained by imidization is 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0114] Example 13

[0115] Repeat the steps of Example 11, but replace the dianhydride compound of polyimide 1 with 0.09 mol of BPDA and 0.01 mol of PMDA; the order of addition is 0.01 mol of PMDA, 0.06 mol of BPDA, and 0.03 mol of BPDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0116] Example 14

[0117] Repeat the steps of Example 11, but replace the dianhydride compound of polyimide 2 with 0.02 mol of 6FDA and 0.08 mol of PMDA; the order of addition is 0.02 mol of 6FDA, 0.05 mol of PMDA, and 0.03 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0118] Example 15

[0119] Repeat the steps of Example 11, but replace the dianhydride compound of polyimide 2 with 0.05 mol of 6FDA and 0.05 mol of PMDA; the order of addition is 0.05 mol of 6FDA, 0.03 mol of PMDA, and 0.02 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0120] Example 16

[0121] 1) Precursor solution of polyimide 1: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.05 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.02 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 1.

[0122] 2) Precursor solution of polyimide 2: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g of NMP. After stirring evenly on a stirring table, 0.03 mol of hexafluorodianhydride (6FDA) was added and stirred for 1 h. Then, 0.04 mol of pyromellitic dianhydride (PMDA) was added and stirred for 1 h. Then, the remaining 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 2.

[0123] 3) Precursor solution of polyimide 3: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.04 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 3.

[0124] 4) The precursor solution of polyimide 1 is cast onto a strip of copper foil at a linear speed of 5 m / min, and then the solvent is removed in a 160°C oven for 9 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 20±2%, and the thickness of the first polyimide layer obtained by imidization is 3 μm. Then, the precursor solutions of polyimide 2 and polyimide 3 are simultaneously cast onto the precursor dry film layer at a linear speed of 3 m / min, and then the solvent is removed in a 160°C oven for 15 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 25±2%. The thickness of the second polyimide layer obtained by imidization is 19 μm. The thickness of the third polyimide layer obtained by imidization is 3 μm. The total thickness of the polyimide layers obtained by imidization is 25 μm.

[0125] 5) The strip of copper foil coated with the precursor dry film layer of polyimide resin is heat-treated by heating from 150°C to 370°C at a heating rate of about 10°C / min to imidize the polyamic acid, thereby obtaining a flexible copper-clad laminate.

[0126] Example 17

[0127] 1) Precursor solution of polyimide 1: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.05 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.02 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 1.

[0128] 2) Precursor solution of polyimide 2: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.02 mol of hexafluorodianhydride (6FDA) was added and stirred for 1 h; then 0.01 mol of biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.04 mol of pyromellitic dianhydride (PMDA) was added and stirred for 1 h; then 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 2.

[0129] 3) Precursor solution of polyimide 3: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.04 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 3.

[0130] 4) The precursor solution of polyimide 1 is cast onto a strip of copper foil at a linear speed of 5 m / min, and then the solvent is removed in a 160°C oven for 9 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 20±2%, and the thickness of the first polyimide layer obtained by imidization is 3 μm. Then, the precursor solutions of polyimide 2 and polyimide 3 are simultaneously cast onto the precursor dry film layer at a linear speed of 3 m / min, and then the solvent is removed in a 160°C oven for 15 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 25±2%. The thickness of the second polyimide layer obtained by imidization is 19 μm. The thickness of the third polyimide layer obtained by imidization is 3 μm. The total thickness of the polyimide layers obtained by imidization is 25 μm.

[0131] 5) The strip of copper foil coated with the precursor dry film layer of polyimide resin is heat-treated by heating from 150°C to 370°C at a heating rate of about 10°C / min to imidize the polyamic acid, thereby obtaining a flexible copper-clad laminate.

[0132] Example 18

[0133] Repeat the steps of Example 17, but replace the dianhydride compound of polyimide 2 with 0.02 mol of 6FDA, 0.02 mol of BPDA, and 0.06 mol of PMDA; the order of addition is 0.02 mol of 6FDA, 0.02 mol of BPDA, 0.03 mol of PMDA, and 0.03 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0134] Comparative Example 1

[0135] The method is the same as in Example 1, except that...

[0136] 1) Precursor solution of polyimide 1: Under a nitrogen atmosphere, 0.05 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) and 0.05 mol of p-phenylenediamine (PDA) were dissolved in 200 g NMP. After stirring evenly on a stirring table, 0.05 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.03 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and stirred for 1 h; then 0.02 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 1.

[0137] 2) Precursor solution of polyimide 2: Under a nitrogen atmosphere, 0.10 mol of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl (TFMB) was dissolved in 200 g of NMP. After stirring evenly on a stirring table, 0.03 mol of hexafluorodianhydride (6FDA) was added and stirred for 1 h. Then, 0.04 mol of pyromellitic dianhydride (PMDA) was added and stirred for 1 h. Then, 0.03 mol of pyromellitic dianhydride (PMDA) was added and stirred at 25 °C for 12 h to obtain a polyamic acid solution, which is the precursor solution of polyimide 2.

[0138] 3) The precursor solution of polyimide 1 is cast onto a strip of copper foil at a linear speed of 5 m / min, and then desolvented in a 160°C oven for 9 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 20±2%, and the thickness of the first polyimide layer obtained by imidization is 3 μm. Then, the precursor solutions of polyimide 2 and polyimide 3 are simultaneously cast onto the precursor dry film layer at a linear speed of 3 m / min, and then desolvented in a 160°C oven for 15 min to obtain a precursor dry film layer of polyimide resin. The solvent content in the precursor dry film layer is 25±2%. The thickness of the second polyimide layer obtained by imidization is 19 μm. The thickness of the third polyimide layer obtained by imidization is 3 μm. The total thickness of the polyimide layers obtained by imidization is 25 μm.

[0139] 4) The long strip of copper foil coated with the precursor dry film layer of polyimide resin is heat-treated by heating from 150°C to 370°C at a heating rate of about 10°C / min to imidize the polyamic acid, thereby obtaining a flexible copper-clad laminate.

[0140] Comparative Example 2

[0141] Repeat the steps of Comparative Example 1, but replace the diamine compound of polyimide 1 with 0.07 mol of TFMB and 0.03 mol of PDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0142] Comparative Example 3

[0143] Repeat the steps of Comparative Example 1, but replace the diamine compound of polyimide 1 with 0.03 mol of TFMB and 0.07 mol of PDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0144] Comparative Example 4

[0145] Repeat the steps of Comparative Example 1, but replace the diamine compound of polyimide 1 with 0.10 mol of PDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0146] Comparative Example 5

[0147] Repeat the steps of Comparative Example 1, but replace the dianhydride compound in polyimide 2 with 0.10 mol of pyromellitic dianhydride (PMDA); the order of addition is 0.05 mol PMDA, 0.03 mol PMDA, and 0.02 mol PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0148] Comparative Example 6

[0149] Repeat the steps of Comparative Example 1, but replace the dianhydride compounds in polyimide 2 with 0.03 mol of pyromellitic dianhydride (PMDA) and 0.07 mol of hexafluorodianhydride (6FDA); the order of addition is 0.04 mol of 6FDA, 0.03 mol of 6FDA, and 0.03 mol of PMDA. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0150] Comparative Example 7

[0151] Repeat the steps of Comparative Example 1, but replace the diamine compound in polyimide 1 with 0.10 mol of 2,2'-difluoro-4,4'-diaminobiphenyl. The first polyimide layer obtained by imidization has a thickness of 3 μm; the second polyimide layer obtained by imidization has a thickness of 19 μm; the third polyimide layer obtained by imidization has a thickness of 3 μm; and the total thickness of the polyimide layers obtained by imidization is 25 μm.

[0152] Performance tests were conducted on the above embodiments and comparative examples.

[0153] Lab value test: Instrument: spectrophotometer, instrument model: Konica Minolta CM-36dg, test conditions: reflectance measurement (SCI), wavelength 360~740nm.

[0154] Coefficient of Thermal Expansion (CTE) Test: Referring to the IPC-TM-650 2.4.41.3 test standard, for the polyimide layer in the polyimide film and the support film, 3mm × 15mm samples were cut out respectively. Using a thermomechanical analysis (TMA) apparatus (TA Instruments Q400 TMA), a tensile test was conducted in the temperature range of 30–300℃ while applying a 0.02N load and heating at a constant rate (10℃ / min). The coefficient of thermal expansion (CTE) was determined by the amount of stretching of the sample relative to the temperature. -6 / K).

[0155] Dielectric properties (Dk / Df) test: Refer to the IEC61189-2-721-2015 test standard and use a network analyzer (NOV ONTROL wide-temperature, wide-frequency impedance analyzer from Germany) for testing; cut out 7cm×7cm samples, treat the samples in a 150℃ circulating oven for 2h, after drying, let the samples stand in an environment of 25±2℃, 50±3RH% for 2h, and then test and record the test results.

[0156] Table 1

[0157]

[0158] In summary, the polyimide of the present invention can be copolymerized using a variety of monomers to obtain a polyimide film with excellent comprehensive properties such as optical, dielectric, and CTE. Unlike the purple polyimide doped with dyes in the prior art, the polyimide of the present invention does not have problems such as low thermal stability and film inhomogeneity.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polyimide laminate, characterized in that, include: First polyimide layer; A second polyimide layer is applied to the surface of the first polyimide layer; And a third polyimide layer covering the surface of the second polyimide layer; The first polyimide layer and the third polyimide layer are mainly composed of polyimide 1, which is obtained by imidization of polyamic acid resin obtained by mixing aromatic diamine monomers and dianhydride monomers; the diamine contains 80% to 100% of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl in total amount of the diamine. The dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride in a molar ratio of 9:1 to 1:

9. The main body of the second polyimide layer is polyimide 2; the polyimide 2 includes the structural unit shown in formula (3), and also includes the structural units shown in formula (4) and / or formula (5): Equation (3); Equation (4) Equation (5) In formulas (4) and (5), R3 and R7 are trifluoromethyl groups, and R1, R2, R4, R5, R6, and R8 are hydrogen atoms; in the polyimide 2, the molar percentage of the structural unit shown in formula (3) is 20% to 50%.

2. The polyimide laminate according to claim 1, characterized in that, The molar ratio of the 3,3',4,4'-biphenyltetracarboxylic dianhydride and the pyromellitic dianhydride is 9:1 to 7:

3.

3. The polyimide laminate according to claim 1 or 2, characterized in that, The degree of polymerization of the polyimide 1 is not less than 25.

4. The polyimide laminate according to claim 1, characterized in that, In the polyimide film containing the polyimide 1, the Lab value of the polyimide film is L = 50~80, a = 10~40, and b = -15~20; and / or, the dielectric constant of the polyimide film is not higher than 3.20 and the dielectric loss is not higher than 0.0060 under 10GHz frequency conditions.

5. The polyimide laminate according to claim 4, characterized in that, In the Lab value of the polyimide film, L is 50~70, a is 20~40, and b is -15~5; and / or, the dielectric constant of the polyimide film at a frequency of 10GHz is not higher than 3.10, and the dielectric loss is not higher than 0.0050.

6. The polyimide laminate according to claim 1, characterized in that, In the Lab value of the polyimide stack, L is 50~80, a is 10~40, and b is -15~20; And / or, the dielectric constant of the polyimide stack is not higher than 3.20 and the dielectric loss is not higher than 0.0060 at a frequency of 10 GHz; and / or, the dielectric constant of the first polyimide layer and the third polyimide layer is 3.00~3.30 and the dielectric loss is 0.0040~0.0060 at a frequency of 10 GHz; and / or, the dielectric constant of the second polyimide layer is 2.85~3.05 and the dielectric loss is 0.0050~0.0065 at a frequency of 10 GHz; And / or, the CTE of the polyimide stack is 19~25ppm / K; and / or, the CTE of the first polyimide layer and the third polyimide layer is greater than 17.5ppm / K and the CTE of the second polyimide layer is greater than that of the third polyimide layer.

7. The polyimide laminate according to claim 6, characterized in that, The CTE of the first and third polyimide layers is 30~65 ppm / K; and / or, the CTE of the second polyimide layer is 5~17 ppm / K.

8. The polyimide laminate according to claim 7, characterized in that, In the Lab values ​​of the polyimide stack, L is 50~70, a is 20~40, and b is -15~5; and / or, the dielectric constant of the polyimide stack at a frequency of 10 GHz is not higher than 3.10, and the dielectric loss is not higher than 0.0050; and / or, the dielectric constant of the first polyimide layer and the third polyimide layer at a frequency of 10 GHz is 3.00~3.20, and the dielectric loss is 0.0040~0.

005. 5; and / or, the dielectric constant of the second polyimide layer is 2.85~3.00 and the dielectric loss is 0.0050~0.0060 at a frequency of 10 GHz; and / or, the CTE of the polyimide stack is 21~23 ppm / K; and / or, the CTE of the first polyimide layer and the third polyimide layer is 35~55 ppm / K; and / or, the CTE of the second polyimide layer is 7~15 ppm / K.

9. The method for preparing the polyimide laminate according to any one of claims 1-8, characterized in that, This includes molding a first polyimide layer, a second polyimide layer, and a third polyimide layer onto a substrate to obtain a polyimide stack.

10. The preparation method according to claim 9, characterized in that, Includes the following steps: 1) Prepare the precursor solution of polyimide 1 and the precursor solution of polyimide 2 respectively; 2) A portion of the precursor solution of polyimide 1 is coated onto a substrate and dried. Then, the precursor solution of polyimide 2 and the remaining precursor solution of polyimide 1 are simultaneously cast onto the obtained precursor dry film layer and dried to obtain the precursor dry film layer of the polyimide stack. 3) The substrate coated with the polyimide laminate precursor dry film layer is thermocured.

11. The preparation method according to claim 10, characterized in that, Step 1) includes mixing the diamine with a solvent to obtain a solution; then adding dianhydride and reacting; and / or, the diamine accounts for 7% to 15% of the total mass of the solution; and / or, the reaction temperature is 0 to 50°C; and / or, 0.960 ≤ the molar ratio of the dianhydride to the diamine ≤ 1.

100. And / or, in step 2), the substrate includes copper foil, aluminum foil, steel strip, or polymer support film, the drying temperature is 100~180℃, and the total solvent content in the precursor dry film layer is 15~35wt%; And / or, in step 3), the thermosetting temperature is 350~400℃.

12. A flexible copper-clad laminate, characterized in that, It includes a copper foil and a polyimide layer covering the surface of the copper foil; the polyimide layer is a polyimide laminate as described in any one of claims 1-8 or a polyimide laminate obtained by the preparation method described in any one of claims 9-11.

13. The flexible copper-clad laminate according to claim 12, characterized in that, The difference between the CTE of the polyimide laminate and the CTE of the copper foil is no greater than 8 ppm / K.

Images