Porous Polyimide Film

Abstract

To provide a porous polyimide film that has low dielectric loss tangent.SOLUTION: A porous polyimide film is a reaction product of a diamine component and a dianhydride component. The diamine component contains an aromatic diamine represented by the following formula (1). (In the formula, Y represents at least one selected from the group consisting of a single bond, -COO-, -S-, -CH(CH3)-, -C(CH3)2-, -CO-, -NH- and -NHCO-.). The porosity is 50% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous polyimide film. [Background technology]

[0002] A porous polyimide film that is a reaction product of a diamine component and an acid dianhydride component is known (see, for example, Patent Document 1 below). In the examples of Patent Document 1, the diamine component includes phenylenediamine (PDA) and oxydianiline (ODA). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2018 / 186486 Summary of the Invention [Problem to be solved by the invention]

[0004] A porous polyimide film is required to have a low dielectric loss tangent. However, there is a limit to how low the dielectric loss tangent of the porous polyimide film described in Patent Document 1 can be.

[0005] The present invention provides a porous polyimide film having a low dielectric loss tangent. [Means for solving the problem]

[0006] The present invention (1) includes a porous polyimide film which is a reaction product of a diamine component and an acid dianhydride component, the diamine component containing an aromatic diamine represented by the following formula (1), and has a porosity of 50% or more.

[0007] [ka] (In the formula, Y represents at least one selected from the group consisting of a single bond, —COO—, —S—, —CH(CH3)—, —C(CH3)2—, —CO—, —NH—, and —NHCO—.)

[0008] The present invention (2) includes the porous polyimide film according to (1), which has a dielectric loss tangent at 10 GHz of 0.0028 or less.

[0009] The present invention (2) includes the porous polyimide film according to (1) or (2), wherein the porosity is 95% or less. [Effects of the Invention]

[0010] In the porous polyimide film of the present invention, the diamine component contains an aromatic diamine represented by formula (1) and the porosity is 50% or more, so the dielectric loss tangent of the porous polyimide film is low. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view of one embodiment of a porous polyimide film of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Porous polyimide film> The porous polyimide film of the present invention will be described. The porous polyimide film has a thickness. The porous polyimide film extends in a plane direction. The plane direction is perpendicular to the thickness direction.

[0013] The porous polyimide film is a porous body (foam) having, for example, a closed-cell structure and / or an open-cell structure.

[0014] <Porosity> The porosity of the porous polyimide film is 50% or more.

[0015] If the porosity of the porous polyimide film is less than 50%, the dielectric loss tangent of the porous polyimide film cannot be sufficiently low. Specifically, if the porosity of the porous polyimide film is less than 50%, the dielectric loss tangent of the porous polyimide film cannot be sufficiently low even if the diamine component as the raw material contains a specific aromatic diamine described below.

[0016] The porosity of the porous polyimide film is preferably 60% or more, more preferably 70% or more, and even more preferably 75% or more.

[0017] The porosity of the porous polyimide film is, for example, 95% or less, preferably 90% or less, more preferably 85% or less, even more preferably 75% or less, and particularly preferably 70% or less. When the porosity of the porous polyimide film is the above-mentioned upper limit or less, the mechanical strength of the porous polyimide film is ensured, and the handling property is excellent.

[0018] The porosity of the porous polyimide film can be determined by inserting the dielectric constant into the following equation:

[0019] Dielectric constant of porous polyimide film = Dielectric constant of air × Porosity + Dielectric constant of polyimide resin × (1 - Porosity)

[0020] The dielectric constant of the porous polyimide film inserted into the above formula is measured using a resonator at a frequency of 10 GHz, at a temperature of 22°C and a relative humidity of 50%.

[0021] <Physical properties other than porosity> The average pore size of the porous polyimide film is, for example, 10 μm or less, preferably 5 μm or less, more preferably 4 μm or less, and for example, 0.1 μm or more, preferably 1 μm or more, more preferably 2 μm or more. The average pore size is measured by image analysis of a cross-sectional SEM photograph.

[0022] The dielectric constant of the porous polyimide film at 10 GHz is not limited. The dielectric constant of the porous polyimide film at 10 GHz is, for example, 2.50 or less, preferably 2.00 or less, more preferably 1.80 or less, even more preferably 1.75 or less, particularly preferably 1.70 or less, and most preferably 1.60 or less. The dielectric constant of the porous polyimide film at 10 GHz is greater than 1.00. The dielectric constant of the porous polyimide film is measured using a resonator.

[0023] The dielectric loss tangent of the porous polyimide film at 10 GHz is, for example, 0.0028 or less, preferably 0.0025 or less, more preferably 0.0020 or less, even more preferably 0.0018 or less, particularly preferably 0.0017 or less, and most preferably 0.0016 or less. If the dielectric loss tangent of the porous polyimide film is not more than the above-mentioned upper limit, the porous polyimide film having a low dielectric loss tangent is suitable for use in, for example, fifth-generation (5G) standard wireless communication and / or high-speed flexible printed circuit boards (FPCs).

[0024] The dielectric loss tangent of the porous polyimide film at 10 GHz is greater than 0.0000. The dielectric loss tangent of the porous polyimide film is measured using a resonator.

[0025] The thickness of the porous polyimide film is not limited and is, for example, 2 μm or more, preferably 5 μm or more, and for example, 1,000 μm or less, preferably 500 μm or less.

[0026] <Raw material for porous polyimide film> The porous polyimide film of the present invention is a reaction product of a diamine component and an acid dianhydride component, in other words, the raw material for the porous polyimide film contains a diamine component and an acid dianhydride component.

[0027] <Diamine component> The diamine component contains an aromatic diamine represented by the following formula (1):

[0028] [ka] (In the formula, Y represents at least one selected from the group consisting of a single bond, —COO—, —S—, —CH(CH3)—, —C(CH3)2—, —CO—, —NH—, and —NHCO—.)

[0029] <Types of aromatic diamines> Specifically, examples of the diamine component include 4,4'-diaminodiphenyl where Y is a single bond, 4-aminophenyl-4-aminobenzoate where Y is -COO-, bis(4-aminophenyl)sulfide where Y is -S-, 4,4'-diaminodiphenylethane where Y is -CH(CH3)-, 4,4'-diaminodiphenylprotane where Y is -C(CH3)2-, 4,4'-diaminobenzophenone where Y is CO-, 4,4'-diaminophenyleneamine where Y is -NH-, and 4,4'-diaminobenzanilide where Y is -NHCO-. From the viewpoint of further reducing the dielectric loss tangent of the porous polyimide film, 4-aminophenyl-4-aminobenzoate is preferably used. Note that 4-aminophenyl-4-aminobenzoate is sometimes simply abbreviated as APAB. The above-mentioned aromatic diamines can be used alone or in combination. Preferably, APAB is used alone.

[0030] On the other hand, if the diamine component does not contain the above-mentioned aromatic diamine, the dielectric loss tangent of the porous polyimide film cannot be sufficiently low. Specifically, if the diamine component does not contain the above-mentioned aromatic diamine, the dielectric loss tangent of the porous polyimide film cannot be sufficiently low even if the porosity is increased to 50% or more.

[0031] The molar fraction of the aromatic diamine in the diamine component is, for example, 5 mol% or more, preferably 10 mol% or more, more preferably 15% or more, and for example, 75 mol% or less, preferably 60 mol% or less, more preferably 40 mol% or less.

[0032] <Other diamine components> The other diamine component may contain, for example, a secondary diamine and a tertiary diamine in addition to the above-mentioned aromatic diamine.

[0033] <Secondary diamine> The second diamine contains a single aromatic ring. Examples of the second diamine include phenylenediamine, dimethylbenzenediamine, and ethylmethylbenzenediamine. From the viewpoint of mechanical strength, phenylenediamine is preferred. Examples of the phenylenediamine include o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine. Examples of the phenylenediamine include p-phenylenediamine. p-phenylenediamine is sometimes simply abbreviated as PDA.

[0034] The molar fraction of the second diamine in the diamine component is, for example, 10 mol% or more, preferably 20 mol% or more, more preferably 30 mol% or more, and for example, 80 mol% or less, preferably 70 mol% or less, more preferably 65 mol% or less.

[0035] <Tertiary diamine> The tertiary diamine contains multiple aromatic rings and ether bonds between them. Examples of the tertiary diamine include oxydianiline. Examples of the oxydianiline include 3,4'-oxydianiline and 4,4'-oxydianiline. From the viewpoint of mechanical strength, 4,4'-oxydianiline (also known as 4,4'-diaminodiphenyl ether) is preferred. 4,4'-oxydianiline is sometimes abbreviated as ODA.

[0036] The molar fraction of the tertiary diamine in the diamine component is, for example, 5 mol % or more, or preferably 10 mol % or more, and for example, 40 mol % or less, or preferably 30 mol % or less.

[0037] Furthermore, the molar ratio of the aromatic diamine to the total of 100 molar parts of the secondary diamine and the tertiary diamine is, for example, 5 molar parts or more, preferably 10 molar parts or more, more preferably 20 molar parts or more, and for example, 100 molar parts or less, preferably 50 molar parts or less, more preferably 30 molar parts or less.

[0038] <Acid dianhydride component> The acid dianhydride component contains, for example, an acid dianhydride containing an aromatic ring. Examples of the acid dianhydride containing an aromatic ring include aromatic tetracarboxylic dianhydrides. Examples of the aromatic tetracarboxylic dianhydrides include benzenetetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, biphenylsulfonetetracarboxylic dianhydride, and naphthalenetetracarboxylic dianhydride.

[0039] Examples of benzenetetracarboxylic dianhydrides include benzene-1,2,4,5-tetracarboxylic dianhydride (also known as pyromelotic dianhydride). Examples of benzophenonetetracarboxylic dianhydrides include 3,3'-4,4'-benzophenonetetracarboxylic dianhydride. Examples of biphenyltetracarboxylic dianhydrides include 3,3'-4,4'-biphenyltetracarboxylic dianhydride, 2,2'-3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenylethertetracarboxylic dianhydride. Examples of biphenylsulfonetetracarboxylic dianhydrides include 3,3',4,4'-biphenylsulfonetetracarboxylic dianhydride. Examples of naphthalenetetracarboxylic dianhydrides include 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,4,5-naphthalenetetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride. These can be used alone or in combination. From the viewpoint of mechanical strength, the dianhydride component is preferably biphenyltetracarboxylic dianhydride, and more preferably 3,3'-4,4'-biphenyltetracarboxylic dianhydride. 3,3'-4,4'-biphenyltetracarboxylic dianhydride is sometimes abbreviated as BPDA.

[0040] The molar amount of amino groups (-NH2) in the diamine component and the molar amount of acid anhydride groups (-CO-O-CO-) in the acid dianhydride component are, for example, equivalent.

[0041] Next, a method for producing the porous polyimide film 1 will be described with reference to FIG.

[0042] In this method, for example, first, a substrate film 2 (indicated by parentheses and imaginary lines) made of metal is prepared. The substrate film 2 extends in the planar direction. Examples of metals include copper, iron, silver, gold, aluminum, nickel, and alloys thereof (stainless steel, bronze). A preferred example of the metal is copper. The thickness of the substrate film 2 is, for example, 0.1 μm or more, preferably 1 μm or more, and, for example, 100 μm or less, preferably 50 μm or less.

[0043] Next, a varnish containing a polyimide resin precursor, a porosifying agent, a nucleating agent, and a solvent is prepared, and then the varnish is applied to one surface in the thickness direction of the base film 2 to form a coating film. The types and blending ratios of the porosifying agent, nucleating agent, and solvent in the varnish are described, for example, in WO2018 / 186486.

[0044] The polyimide resin precursor is a reaction product of the diamine component and the acid dianhydride component. To prepare the polyimide resin precursor, the diamine component, the acid dianhydride component, and a solvent are mixed to prepare a varnish, and the varnish is heated to prepare a precursor solution. Subsequently, a nucleating agent and a porosifying agent are mixed into the precursor solution to prepare a porous precursor solution.

[0045] Thereafter, the porous precursor solution is applied to one surface of the substrate film 2 in the thickness direction to form a coating film.

[0046] The coating is then dried by heating to form a precursor film, which is a precursor film having a phase-separated structure of the polyimide resin precursor and the porosifying agent, with the nucleating agent as the core, while the solvent is removed by the heating.

[0047] Thereafter, the porosifying agent is extracted (pulled out or removed) from the precursor film by, for example, supercritical extraction using supercritical carbon dioxide as a solvent.

[0048] Thereafter, the precursor film is cured by heating to form a porous polyimide film 1 made of polyimide resin. The porous polyimide film 1 is formed on one surface of the base film 2 in the thickness direction.

[0049] Thereafter, if necessary, the base film 2 is removed as indicated by the solid line in FIG. 1. For example, the base film 2 is dissolved using a stripping solution. Examples of the stripping solution include FeCl3. This results in a porous polyimide film 1. When producing the metal layer laminate 10 described below, the base film 2 is not removed but remains as the first metal layer 3.

[0050] <Application> Next, a metal layer laminate 10 including a porous polyimide film 1 will be described as shown by the phantom and solid lines in Figure 1. This metal layer laminate 10 includes a porous polyimide film 1 and two metal layers 3 and 4 shown by the phantom lines.

[0051] The porous polyimide film 1 is provided in a metal layer laminate 10. That is, the porous polyimide film 1 is used to laminate two metal layers 3 and 4, which will be described next.

[0052] The two metal layers 3, 4 include a first metal layer 3 and a second metal layer 4. The first metal layer 3 is disposed on the other surface in the thickness direction of the porous polyimide film 1. Examples of materials for the first metal layer 3 include the metals exemplified for the base film 2. Preferably, copper is used. The thickness of the first metal layer 3 is, for example, 0.1 μm or more, preferably 1 μm or more, and for example, 100 μm or less, preferably 50 μm or less.

[0053] The second metal layer 4 is disposed on one surface in the thickness direction of the porous polyimide film 1. The second metal layer 4 may be disposed on one surface in the thickness direction of the porous polyimide film 1 via an adhesive layer (not shown). Examples of materials for the second metal layer 4 include the metals exemplified for the base film 2. The thickness of the second metal layer 4 is the same as that of the first metal layer 3.

[0054] A method for manufacturing the metal layer laminate 10 will be described. First, during manufacturing, a second metal layer 4 is disposed on one surface in the thickness direction of a laminate 20 comprising a base film 2 and a porous polyimide film 1. On the other hand, since the base film 2 is made of metal, it is left as it is as the first metal layer 3 (it is diverted to the first metal layer 3). This results in a metal layer laminate 10 comprising the porous polyimide film 1 and the second metal layer 4 and the first metal layer 3 disposed on one and the other surfaces in the thickness direction, respectively.

[0055] Thereafter, the first metal layer 3 and the second metal layer 4 are patterned by, for example, etching.

[0056] Depending on the application and purpose, the metal layer laminate 10 is pressed before, during, and / or after the formation of the above-mentioned pattern. Specifically, the metal layer laminate 10 is heat-pressed.

[0057] This metal layer laminate 10 is used, for example, in fifth generation (5G) standard wireless communications and / or high-speed flexible printed circuit boards (FPCs).

[0058] <Effects of one embodiment> In the porous polyimide film 1 described above, the diamine component contains the aromatic diamine represented by formula (1) and the porosity is 50% or more, so the dielectric loss tangent of the porous polyimide film is low.

[0059] If the dielectric loss tangent of the porous polyimide film 1 is 0.0028 or less, the porous polyimide film 1 having a low dielectric loss tangent is suitable for use in, for example, fifth-generation (5G) standard wireless communication and / or high-speed flexible printed circuit boards (FPCs).

[0060] Furthermore, if the porosity of the porous polyimide film 1 is 95% or less, the mechanical strength of the porous polyimide film is excellent. [Example]

[0061] The present invention will be described in more detail below with reference to examples and comparative examples. It should be noted that the present invention is not limited to these examples and comparative examples. The specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be substituted with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than" or "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Description of the Invention" above.

[0062] Example 1 A reactor equipped with a stirrer and thermometer was charged with 64.88 g (0.60 mol) of PDA (secondary diamine), 40.05 g (0.20 mol) of ODA (tertiary diamine), and 45.65 g (0.20 mol) of APAB (aromatic diamine represented by formula (1) where Y- is -COO-), and 2300 g of N-methyl-2-pyrrolidone (NMP) was added as a solvent. The mixture was stirred at 40°C for 20 minutes to prepare an NMP solution of PDA, ODA, and APAB. The NMP solution contained 1.00 mol of the diamine component.

[0063] Next, 294.2 g (1.00 mol) of 3,3'-4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added to the above-mentioned NMP solution, and 18 g of N-methyl-2-pyrrolidone (NMP) was further added, and the temperature was raised to 80°C, followed by stirring for 10 hours to obtain a polyimide precursor solution.

[0064] To 100 parts by mass of the solids content of the polyimide precursor solution, 3 parts by mass of PTFE powder with a median diameter of 1 μm or less as a nucleating agent, 150 parts by mass of polyoxyethylene dimethyl ether (manufactured by NOF Corporation, grade: MM400) with a weight average molecular weight of 400 as a porosifying agent, and 4 parts by mass of 2-methylimidazole (manufactured by Shikoku Chemicals Corporation, 2Mz-H) were added to obtain a porous precursor solution. The obtained porous precursor solution was applied to a substrate film 2 made of copper to form a coating film. The coating film was then dried at 135°C for 15 minutes to produce a precursor film.

[0065] This precursor film was immersed in carbon dioxide pressurized to 30 MPa at 60°C and passed through for 4 hours to promote the extraction and removal of the porosifying agent, phase separation of the remaining NMP, and the formation of pores.The carbon dioxide pressure was then reduced.

[0066] The precursor film was then heated under vacuum at 390°C for approximately 185 minutes to remove residual components and promote imidization, thereby obtaining a porous polyimide film 1 disposed on one surface in the thickness direction of the base film 2. The base film 2 and the porous polyimide film 1 (laminate 20) were then immersed in an FeCl3 solution to remove the base film 2.

[0067] The grams and parts by mass of each component are listed in Table 1. Table 2 lists the mole fractions of the diamine component and the acid dianhydride component.

[0068] <Examples 2 to 6 and Comparative Examples 1 to 3> Porous polyimide film 1 was produced in the same manner as in Example 1, except that the formulation was changed according to Tables 1 and 2.

[0069] <Evaluation> The following items were measured for the porous polyimide films 1 of Examples 2 to 6 and Comparative Examples 1 to 3. The results (excluding the average pore size) are shown in Table 2.

[0070] <Dielectric constant and dielectric loss tangent> The dielectric constant and dielectric loss tangent of the porous polyimide film 1 were measured at a frequency of 10 GHz using a resonator at a temperature of 22°C and a relative humidity of 50%.

[0071] <Porosity> The porosity of the porous polyimide film 1 was calculated by inserting the dielectric constant calculated above into the following formula.

[0072] Dielectric constant of porous polyimide film = Dielectric constant of air × Porosity + Dielectric constant of polyimide resin × (1 - Porosity)

[0073] <Average vacancies> The average pore size of each of the porous polyimide films 1 of Example 1 and Comparative Example 1 was measured by image analysis of cross-sectional SEM photographs.

[0074] As a result, the average pore diameter of the porous polyimide film 1 of Example 1 was 3.6 μm, while the average pore diameter of the porous polyimide film 1 of Comparative Example 1 was 5.3 μm.

[0075] [Table 1]

[0076] [Table 2] [Explanation of symbols]

[0077] 1. Porous polyimide film

Claims

1. It is a reaction product of a diamine component and an acid dianhydride component, the diamine component contains 4-aminophenyl-4-aminobenzoate; A porous polyimide film having a porosity of 50% or more.

2. 2. The porous polyimide film according to claim 1, which has a dielectric loss tangent at 10 GHz of 0.0028 or less.

3. 3. The porous polyimide film according to claim 1, wherein the porosity is 95% or less.

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