JP7461622B2 - Polyimide Film - Google Patents

Description

The present invention relates to polyimide (PI) films.

PI is widely used in electrical and electronic components because of its excellent heat resistance, chemical resistance, electrical properties, and mechanical properties. In particular, a PI precursor is a polyamic acid (hereinafter, a polyamic acid having such a chemical structure may be abbreviated as "PAA") obtained by polymerizing an aromatic tetracarboxylic dianhydride such as pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride with an aromatic diamine such as 4,4'-oxydianiline or p-phenylenediamine, and the like. A PI film obtained by applying a solution containing the polyamic acid to a substrate and thermally curing the coating has excellent heat resistance, dimensional stability, and mechanical properties, and is therefore widely used as a coating material for electric wires, an insulating material for electronic elements (surface protection film, shield film, interlayer insulating film, etc.), and a copier belt (fixing belt, intermediate transfer belt, etc.).

As a method for improving the properties of such PI films, a PI film using dimer diamine (DDA) as the diamine component that makes up the PI has been proposed.

Patent Document 1 discloses a PI film with improved toughness and self-healing properties, which is made of PI using 50% by mass or more of DDA relative to the total diamine components.

Patent Document 2 discloses a PI film with improved dielectric properties, which is made of a PI using 1 to 15 mol% DDA relative to the total diamine components. It discloses that this PI film is suitable for use as a metal clad laminate (CCL) by laminating it to a metal layer such as copper foil.

Japanese Patent No. 6306586 International Publication No. 2014/208644

However, the PI film disclosed in Patent Document 1 has high toughness and good self-healing properties, but is soluble in general-purpose solvents, and therefore has insufficient solvent resistance, making it difficult to use this film as, for example, a coating material for electric wires. In addition, since a large amount of DDA is used, the glass transition point is lowered, and there is a problem that sufficient heat resistance as a PI cannot be obtained.
The PI film disclosed in Patent Document 2 has a low coefficient of linear expansion (CTE) of 1 to 30 ppm/K and is too rigid, which results in a problem of insufficient toughness when used as an insulating coating material for electric wires, for example.If the coating material does not have enough toughness, cracks will occur in the insulating coating when the coated electric wire is twisted or bent.

The present invention aims to solve the above problems by providing a PI film that has excellent dielectric properties, heat resistance, and toughness.

The inventors discovered that the above problem could be solved by specifying the diamine component of the PI and setting the CTE of the PI film in a specific range, which led to the completion of the present invention.

The present invention is a PI film having the following objects.
1) The PI contains, as a diamine component, 10 mol % or more and 25 mol % or less of DDA based on the total diamine components.
2) The CTE of the PI film is greater than 30 ppm/K and less than or equal to 60 ppm/K.

The PI film of the present invention has excellent dielectric properties, heat resistance, and toughness, and can therefore be suitably used as a coating material for electric wires, an insulating material for electronic elements, and the like, and can be particularly suitably used as a coating material for electric wires.

The present invention is described in detail below.

The PI used in the present invention is obtained by reacting a tetracarboxylic acid component containing an aromatic tetracarboxylic dianhydride with a diamine component in a solvent, the diamine component containing an aromatic diamine, and the DDA is in the range of 5 mol% to 25 mol% of the total diamine components. Here, DDA is an aliphatic amine derived from a dimer acid having 24 to 48 carbon atoms, and is obtained by polymerizing unsaturated fatty acids such as oleic acid and linoleic acid to form a dimer acid, which is then reduced and aminated (reductive amination). As DDA, commercially available products such as "Priamine 1074, 1075" (trade names of Croda Japan Co., Ltd.) and "Versamine 551, 552" (trade names of Cognis Japan Co., Ltd.) can be used.

The PI used in the present invention can be obtained by thermally curing the PAA obtained by reacting a tetracarboxylic acid component containing an aromatic tetracarboxylic dianhydride with a diamine component in a solvent, where the diamine component must contain an aromatic diamine and must contain 10 mol % or more and 25 mol % or less of DDA based on the total diamine component.

Examples of the tetracarboxylic acid component include pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, m-terphenyltetracarboxylic dianhydride, and mixtures thereof. Among these, PMDA, BPDA, and mixtures thereof are preferred, and it is particularly preferred to use PMDA in an amount of 80 mol% or more based on the total tetracarboxylic acid component.

Examples of aromatic diamine components include 4,4'-oxydianiline (ODA), p-phenylenediamine (PDA), m-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 1,2-bis(anilino)ethane, diaminodiphenyl sulfone, diaminobenzanilide, diaminobenzoate, diaminodiphenyl sulfide, 2,2-bis(p- Examples of the aromatic diamines include 2,2-bis(p-aminophenyl)propane, 2,2-bis(p-aminophenyl)hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluoride, 1,4-bis(p-aminophenoxy)benzene, 4,4'-bis(p-aminophenoxy)biphenyl, diaminoanthraquinone, 4,4'-bis(3-aminophenoxyphenyl)diphenylsulfone, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-divinyl-4,4'-diaminobiphenyl, and mixtures thereof. These aromatic diamines can be used alone or as a mixture. Among these, ODA, PDA, BAPP, and mixtures thereof are preferred, and it is particularly preferred to use ODA in an amount of 70 mol% or more based on the total diamine components.

The PI film used in the present invention can be obtained by applying, drying, and thermally curing a PAA solution obtained by reacting approximately equimolar amounts of the tetracarboxylic dianhydride and the diamine (containing 5 mol% or more and 25 mol% or less of DDA based on the total diamine components) in a solvent onto a substrate. The amount of DDA blended is preferably 6 mol% or more and 23 mol% or less. By setting the amount of DDA blended in this manner and selecting the type of the tetracarboxylic dianhydride and the diamine, the CTE of the PI film after thermal curing can be made to be greater than 30 ppm/K and less than 60 ppm/K.

The solvent used in the production of PAA is not limited, and amide-based solvents, ester-based solvents, ether-based solvents, alcohol-based solvents, water, etc. can be used. Among these solvents, amide-based solvents can be preferably used. Specific examples of amide-based solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide (DMAc). These solvents can be used alone or in a mixture of two or more. Among these, NMP, DMAc, and mixtures thereof are preferred.

The reaction temperature during the production of the PAA solution is preferably 10°C to 100°C, and the solids concentration of PAA is preferably 5 to 30% by mass relative to the PAA solution.

If necessary, known additives such as various surfactants, leveling agents, silane coupling agents, etc. can be added to the PAA solution.

The PAA solution thus obtained is applied to a substrate, dried, and thermally cured to form a coating of a PI film on the substrate. Examples of substrates that can be used include metal foils such as aluminum foil and copper foil, inorganic substrates such as glass plates, linear substrates such as copper wires and aluminum wires, and plastic films such as PI films. For drying and thermal curing, it is preferable to gradually increase the temperature from 40°C to about 500°C using a normal hot air dryer or infrared lamp. It is also preferable to dry and thermally cure in an inert gas atmosphere such as nitrogen. In this way, a PI film with a uniform surface can be obtained without causing foaming of the coating film. The PI coating formed on the substrate can be used as a laminate that is still in contact with the substrate, or as a single PI film peeled off from the substrate. In particular, the copper wire on which the PI coating is formed can be suitably used as an electric wire with an insulating coating (enameled wire).

The PI film thus obtained must have a CTE of more than 30 ppm/K and not more than 60 ppm/K, and preferably more than 32 ppm/K and not more than 55 ppm/K. This ensures the toughness of the PI film while ensuring the dimensional stability of the PI film. The CTE can be measured by TMA (temperature range 100°C to 200°C) in a tensile mode based on the standard of JIS K7197. The toughness of the PI film can be evaluated by measuring the tensile elongation based on JIS C 2151:2006. The PI film of the present invention preferably has a tensile elongation of 50% or more and 90% or less. This ensures good toughness while ensuring appropriate rigidity, and can be suitably used, for example, as an electric wire coating material.

The PI film of the present invention has DDA copolymerized within a predetermined range, so that its dielectric constant can be reduced compared to that of a non-copolymerized PI film. The dielectric constant is preferably 3.3 or less, more preferably 3.0 or less. In this way, when the PI film of the present invention is used as an insulating coating for an enameled wire, its inverter surge resistance can be improved. Here, the inverter surge refers to a steep and high voltage applied to an inverter-driven motor. If this inverter surge voltage exceeds the partial discharge inception voltage (PDIV) of the enameled wire used in the motor coil, partial discharge occurs between the enameled wires, and the insulating coating is eroded, which may cause insulation breakdown of the motor. An enameled wire with improved inverter surge resistance refers to an enameled wire that has high resistance to partial discharge here. It is known that the PDIV of an enameled wire can be increased by lowering the dielectric constant of the coating.

The present invention will be described in detail below with reference to examples, but is not limited to these examples.

Example 1
In a glass reaction vessel, 0.51 mol of ODA, 0.09 mol of DDA ("Priamine 1075" manufactured by Croda Japan Co., Ltd., molecular weight: 549), and dehydrated NMP (polymerization solvent) were charged under a nitrogen atmosphere and stirred to dissolve ODA and DDA. While cooling this solution to 30° C. or less with a jacket, PMDA (0.606 mol) was gradually added, and then polymerization reaction was carried out at 60° C. for 100 minutes to obtain a PAA solution with a PAA solid content concentration of 20% by mass. Next, this solution was applied onto a glass substrate (20 cm square) using a table coater, dried at 120° C. for 30 minutes, and then heated to 350° C. at a heating rate of 5° C./min under a nitrogen atmosphere to obtain a laminate in which a PI film (A-1) having a thickness of about 25 μm was formed on the glass substrate. A-1 was peeled off from the glass substrate, and the CTE and elongation were measured based on the above-mentioned JIS standard. The results are shown in Table 1.
Next, after leaving it in a thermo-hygrostat at a temperature of 25° C. and a humidity of 50% for 50 hours, metal electrodes were vapor-deposited on both sides of the sample, and the capacitance between the metal electrodes was measured using a commercially available impedance analyzer (frequency: 1 kHz) to calculate the relative dielectric constant of A-1. The results are shown in Table 1.

Example 2
A PI film (A-2) was obtained in the same manner as in Example 1, except that 0.54 mol of ODA and 0.06 mol of DDA were used as the diamine components. The film properties of A-2 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 3
A PI film (A-3) was obtained in the same manner as in Example 1, except that 0.468 mol of ODA and 0.132 mol of DDA were used as the diamine components. The film properties of A-3 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 4
A PI film (A-4) was obtained in the same manner as in Example 1, except that 0.528 mol of ODA and 0.072 mol of DDA were used as the diamine components. The film properties of A-4 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

< Reference Example 5>
A PI film (A-5) was obtained in the same manner as in Example 1, except that 0.558 mol of ODA and 0.042 mol of DDA were used as the diamine components. The film properties of A-5 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 6
A PI film (A-6) was obtained in the same manner as in Example 1, except that 0.44 mol of ODA, 0.1 mol of BAPP, and 0.06 mol of DDA were used as the diamine components. The film properties of A-6 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

Example 7
A PI film (A-7) was obtained in the same manner as in Example 1, except that 0.506 mol of PMDA and 0.1 mol of BPDA were used as the tetracarboxylic acid components. The film properties of A-7 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Comparative Example 1>
A PI film (B-1) was obtained in the same manner as in Example 1, except that only 0.60 mol of ODA was used as the diamine component. The film properties of B-1 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Comparative Example 2>
A PI film (B-2) was obtained in the same manner as in Example 1, except that 0.438 mol of ODA and 0.162 mol of DDA were used as the diamine components. The film properties of B-2 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Comparative Example 3>
A PI film (B-3) was obtained in the same manner as in Example 1, except that 0.576 mol of ODA and 0.024 mol of DDA were used as the diamine components. The film properties of B-3 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

<Comparative Example 4>
A PI film (B-4) was obtained in the same manner as in Example 1, except that 0.558 mol of 2,2'-dimethyl-4,4'-diaminobiphenyl and 0.042 mol of DDA were used as the diamine components. The film properties of B-4 were evaluated in the same manner as in Example 1, and the results are shown in Table 1.

As shown in the examples, the PI film of the present invention has a CTE of more than 30 ppm/K and less than 60 ppm/K, so that the elongation is moderately high and good toughness and rigidity as a PI film are ensured. In addition, the PI of the present invention uses DDA as a diamine component within a specified range, so that a PI film with a low dielectric constant can be obtained while ensuring good mechanical properties.

The PI film of the present invention has excellent dielectric properties, heat resistance and toughness, and can therefore be suitably used as a covering material for electric wires, an insulating material for electronic elements, and the like, and can be particularly suitably used as a covering material for electric wires.

Claims (1)

A polyimide (PI) film having the following characteristics:
1) The PI contains, as diamine components, 10 mol % or more and 25 mol % or less of dimer diamine based on the total diamine components, and 70 mol % or more of 4,4'-oxydianiline based on the total diamine components.
2) The coefficient of linear expansion (CTE) of the PI film is greater than 30 ppm/K and less than or equal to 60 ppm/K.