Porous polyamide-imide film

Abstract

To provide a porous polyamide imide film which is useful for an antenna film such as a millimeter wave and secures a low dielectric tangent and a high specific tensile modulus.SOLUTION: There is provided a porous PAI film having the following characteristics. 1) The dissipation factor (Df) is 0.0050 or less. 2) The specific tensile modulus is 1000 m / sec or more. For example, by using "a dry phase-separation method" in which a solution containing PAI and a solvent is applied on a base material to form a coating film and then the coating film is dried at a temperature of 100°C or more and 300°C or less to form a PAI coating film on the base material, followed by peeling the porous PAI coating film from the base material, a porous pAI coating film can be obtained by selecting this condition setting.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a porous low-dielectric polyamideimide (PAI) film. In particular, the present invention relates to a low-dielectric porous PAI film useful as an antenna film for millimeter waves and the like.

Background Art

[0002] High frequencies with frequencies of 1 GHz to 300 GHz, such as millimeter waves, can transmit a large amount of data at once due to their short wavelengths. Therefore, high frequencies such as millimeter waves are expected to be used for short-range wireless communication applications and in-vehicle radars such as those in automobiles. In order to increase the gain of a millimeter-wave antenna and extend the communication distance of millimeter waves as long as possible, it is effective to reduce the dielectric loss tangent (Df) of the substrate material. On the other hand, in general, polyimide-based films are widely used as substrate materials for antennas and the like from the viewpoints of heat resistance, dimensional stability, mechanical properties, and the like. Among them, polyamideimide (PAI) films are advantageous materials from the perspective of process cost because, unlike ordinary polyimide films produced via polyamic acid, they do not require a high temperature of 300 °C or higher during film formation. Therefore, various methods for improving the dielectric properties of this PAI film have been proposed. Among them, a method has been proposed in which the film is made porous to improve dielectric properties, that is, to reduce Df. For example, Patent Document 1 describes a porous PAI film (film) "made of a polyamideimide resin having a glass transition temperature of 200 °C or higher and a logarithmic viscosity of 0.5 dl / g or higher, having a dielectric loss tangent of 0.02 or less when measured at a frequency of 1 GHz, and having a film thickness of 5 to 200 μm".

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] However, the Df of the porous PAI film actually obtained in the example of Patent Document 1 was approximately 0.006 to 0.007, and moreover, this Df was measured at a frequency of 1 GHz. Considering that Df tends to gradually increase as the measurement frequency increases, this Df was not low enough and needed to be reduced further. Furthermore, while it is already known that increasing porosity is effective in reducing Df in porous films, there was a problem in porous PAI films where increasing porosity and thereby lowering Df resulted in a decrease in mechanical properties, particularly the specific tensile modulus of the film. [Means for solving the problem]

[0005] As a result of diligent research to solve the aforementioned problems, we discovered that the problems can be solved by specifying the properties of a porous PAI film, and thus the present invention was completed.

[0006] The present invention relates to a porous PAI film characterized by the following: 1) The Df at 10GHz is 0.0050 or less. 2) The specific tensile modulus is 1000 m / sec or more. [Effects of the Invention]

[0007] The porous PAI film of the present invention has a low Df value of 0.0050 or less, ensuring good dielectric properties as a PAI substrate, and also has good mechanical properties with a specific tensile modulus of 1000 m / sec, making it suitable for use as a substrate for high-frequency applications. [Modes for carrying out the invention]

[0008] The present invention will be described in detail below.

[0009] The PAI constituting the porous PAI of the present invention is a general term for polymers having imide bonds and amide bonds in their main chain, and is usually obtained by a condensation reaction between tricarboxylic acid and diisocyanate.

[0010] The porous PAI film of the present invention must have a Df of 0.0050 or less at 10 GHz. Df is preferably 0.0045 or less, and more preferably 0.0040 or less. Here, Df is an indicator of the energy required for polarization of electrons in a dielectric material. The smaller Df, the less likely it is that the energy of electromagnetic waves will be converted into heat, thus suppressing signal attenuation. Therefore, by setting Df to 0.0050 or less, the dielectric loss of the substrate material can be reduced. Df can be confirmed by measuring it at 10 GHz using the resonance method with a network analyzer.

[0011] The porous PAI film of the present invention must have a specific tensile modulus of 1000 m / sec or more. The specific tensile modulus is preferably 1400 m / sec or higher, and more preferably 1500 m / sec or higher. By adjusting the specific tensile modulus in this way, high rigidity can be obtained, making the material less prone to fracture, and ensuring good operability and reliability when used as a substrate material for millimeter-wave antennas and the like. The specific tensile modulus is a value obtained by measuring the modulus in tensile mode according to JIS K7161, dividing this modulus by the density, and then calculating the square root of the result.

[0012] There are no restrictions on the thickness of the porous PI-based film of the present invention, but it is usually between 10 μm and 300 μm, and preferably between 20 μm and 200 μm.

[0013] There is no limitation on the apparent density of the porous PAI film of the present invention, but the apparent density is preferably 0.15 to 0.45 g / cm 3 and more preferably 0.20 to 0.35 g / cm 3 . By setting the apparent density in this way, the porosity of the porous PAI film can be controlled, and the Df and specific tensile modulus of the porous PAI film of the present invention can be within a predetermined range.

[0014] The porous PAI film of the present invention can be obtained, for example, by the following method. That is, after applying a solution containing PAI and a solvent on a substrate to form a coating film, drying is performed at a temperature of 80°C or higher and 300°C or lower to form a porous PAI film on the substrate, and then the porous PAI film is peeled off from the substrate. By using the "dry phase separation method" and selecting this condition setting, the porous PAI film of the present invention can be obtained. In the "dry phase separation method", phase separation is induced during the drying of the coating film, and a low-density porous PAI structure is formed.

[0015] The PAI solution for obtaining the porous PAI film of the present invention can be obtained, for example, by the following method. That is, first, a PAI solution is obtained by subjecting substantially equimolar trimellitic acid (TMA) and diisocyanate to a polymerization reaction in a nitrogen-containing polar solvent (a good solvent for PAI), and then a poor solvent for PAI is added thereto to obtain an optically uniform PAI solution for forming a porous film for forming a porous PAI film. Since this PAI solution contains a poor solvent for PAI, phase separation is induced in the coating film when the coating film is dried due to the action of this poor solvent. Here, the "good solvent for PAI" refers to a solvent having a solubility in PAI of 1% by mass or more at 25°C, and the "poor solvent for PAI" refers to a solvent having a solubility in PAI of less than 1% by mass at 25°C.

[0016] Examples of the diisocyanate include o-tolidine diisocyanate (TODI), 4,4'-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), xylylene diisocyanate, 3,3'-diphenylmethane diisocyanate, paraphenylene diisocyanate, hexamethylene diisocyanate, naphthalene diisocyanate, isophorone diisocyanate, and the like. These may be used alone or in combination of two or more. Among these, TODI is preferable from the viewpoint of ensuring a high specific tensile modulus of the obtained porous PAI film. Here, since a homopolymer composed only of TMA and TODI tends to be insoluble in the reaction solvent, it is preferable to substitute 10 to 50 mol% of TODI with MDI and / or TDI.

[0017] As the tolylene diisocyanate (TDI), 2,4-TDI, 2,6-TDI or a mixture thereof can be used. As the mixture, for example, a mixture having a molar ratio of 2,4-TDI / 2,6-TDI = 70 to 100 / 0 to 30 can be used.

[0018] From the viewpoint of further reducing Df of the porous PAI film of the present invention, it is preferable to substitute 0.5 to 20 mol% of TMA with dimer acid (DA). Here, DA is a fatty acid mainly composed of a dibasic acid of C36 dicarboxylic acid produced by dimerization of C18 unsaturated fatty acids using vegetable oils and fats as raw materials, and can be obtained as a commercial product from companies such as Croda Japan and Tsukino Food Industry Co., Ltd. Note that a part of TMA may be substituted with a tetracarboxylic acid component. Specifically, if it is 10 mol% or less of TMA, it may be substituted with pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, or the like.

[0019] Preferred nitrogen-containing polar solvents include amide solvents and urea solvents. Examples of amide solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, and N,N-dimethylacetamide (DMAc). Examples of urea solvents include tetramethylurea and dimethylethyleneurea. These may be used individually or in combination of two or more. Among these, NMP and DMAc are preferred. Furthermore, it is preferable that these polymerization solvents are dehydrated to have a water content of 100 ppm or less.

[0020] As a poor solvent for PAI, ether-based solvents are preferred. Preferably, triglyme and tetraglyme are used as ether-based solvents, and these may be used individually or in combination of two or more. The boiling point of the poor solvent is preferably 5°C or more higher than the boiling point of the good solvent, more preferably 20°C or higher, and even more preferably 30°C or higher. The proportion of the poor solvent is preferably 40% by mass or more and 90% by mass or less, and more preferably 40% by mass or more and 70% by mass or less, relative to the total mass of the solvent. The solid content concentration of PAI in the PAI solution is preferably 5% by mass or more and 16% by mass or less, and more preferably 8% by mass or more and 14% by mass or less.

[0021] The polymerization of the PAI can be carried out, for example, as follows. Specifically, approximately equimolar amounts of TMA and diisocyanate are polymerized in a nitrogen-containing polar solvent at a temperature of 100 to 200°C, preferably 120 to 180°C. In this reaction, there are no particular restrictions on the order in which the monomers and solvent are added; any order is acceptable. Furthermore, the molar ratio of TMA to the diisocyanate component is preferably 1 / 1.01 to 1.05. Thus, it is preferable to use a PAI solution in which the diisocyanate component is used in a small excess relative to TMA. During the polymerization reaction, it is preferable to add basic compounds such as 1,8-diazabicyclo[5.4.0]undecene-7 (DBU) and triethylenediamine (DABCO) in an amount of 0.01 to 1 mol% relative to TMA. By using these polymerization conditions, a high-viscosity PAI solution can be obtained. The viscosity of the PAI solution after polymerization (before the addition of the poor solvent) is preferably 50 Pa·s or higher, and more preferably 80 Pa·s or higher, at 30°C when the PAI concentration is 20% by mass. By using such a high-viscosity PAI solution, it is possible to ensure a low Df of the resulting porous PAI film while also achieving a high specific tensile modulus.

[0022] The PAI solution can be applied to the substrate using any application machine. Examples of application machines include die coaters, lip coaters, gravure coaters, bar coaters, doctor blade coaters, comma coaters, reverse roll coaters, and bar reverse roll coaters. Multilayer coating is also possible, in which case the composition of the PAI solution in each layer may be the same or different.

[0023] Examples of substrates include metal foils (copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, or alloys thereof), polyester films (polyethylene terephthalate, polyethylene naphthalate, etc.), aromatic polyimide films, and fluororesin films (polytetrafluoroethylene, etc.). Among these, polyethylene terephthalate film or aluminum foil is preferred. These substrates are preferably smooth in surface. Furthermore, release metal foils or plastic films with a heat-resistant release layer formed on their surface can also be preferably used. These release metal foils or plastic films can be commercially available. [Examples]

[0024] The present invention will be described in detail below based on examples, but is not limited to these examples.

[0025] The apparent density, dielectric loss tangent, and specific tensile modulus of the porous PAI film were measured by the method described above.

[0026] Furthermore, the material failure of the porous PAI film when a load was applied was evaluated as follows: The obtained porous PAI film was cut into strips 2 cm wide and 5 cm long, and bent to a 90° angle. Those that did not break were marked with ○, and those that broke were marked with ×.

[0027] <Example 1> In a glass reaction vessel, under a nitrogen atmosphere, 1.00 mol of TMA, 0.82 mol of TODI, 0.20 mol of MDI, and 0.0005 mol of DABCO were charged together with dehydrated NMP (moisture content 80 ppm) to a solid content concentration of 20% by mass. The mixture was heated to 150°C while stirring and reacted for 5 hours to obtain a PAI solution with a viscosity of 152 Pa·s at 30°C and a PAI solid content concentration of 20% by mass. For drying, 100 parts by mass of tetraglyme was added to 100 parts by mass of this PAI solution to obtain a porous film-forming PAI solution with a solid content concentration of 10.0% by mass. Next, the obtained PAI solution was applied to a polyester film and dried at 80°C for 10 minutes and then at 160°C for 8 minutes, after which the coating was peeled off the polyester film. Subsequently, this coating was sandwiched between metal frames, and the temperature was gradually increased under a nitrogen gas atmosphere, and finally dried at 250°C for 60 minutes to obtain a PAI film (A-1) with a thickness of 40 μm.

[0028] <Example 2> A porous PAI film (A-2) was obtained in the same manner as in Example 1, except that the amount of tetraglyme after polymerization was 120 parts by mass and a PAI solution with a solid content concentration of 9.1% by mass was used.

[0029] <Example 3> A porous PAI film (A-3) was obtained in the same manner as in Example 1, except that the PAI solution was prepared by changing "TMA: 1.00 mol" to "TMA: 0.94 mol, DA: 0.06 mol".

[0030] <Example 4> A porous PAI film (A-4) was obtained in the same manner as in Example 1, except that the PAI solution was prepared by changing "TMA: 1.00 mol" to "TMA: 0.99 mol, DA: 0.01 mol".

[0031] <Example 5> A porous PAI film (A-5) was obtained in the same manner as in Example 1, except that the diisocyanate components were prepared as "TODI: 0.72 mol, TDI: 0.30 mol" in the PAI solution. The TDI used here was a mixture of 2,4-TDI / 2,6-TDI = 80 / 20 (molar ratio). (The same applies to the TDI used below.)

[0032] <Example 6> A PAI solution was obtained using diisocyanate components in the ratios "TODI: 0.87 mol, MDI: 0.15 mol". A porous PAI film (A-6) was then obtained in the same manner as in Example 1, except that the amount of tetraglyme added after polymerization was 80 parts by mass, and a PAI solution with a solid content concentration of 11.1% by mass was used.

[0033] <Example 7> A porous PAI film (A-7) was obtained in the same manner as in Example 1, except that the amount of tetraglyme after polymerization was 55 parts by mass and a PAI solution with a solid content concentration of 12.9% by mass was used.

[0034] <Example 8> A PAI solution was obtained using diisocyanate components in the ratios "TODI: 0.62 mol, MDI: 0.40 mol". A porous PAI film (A-8) was then obtained in the same manner as in Example 1, except that the amount of tetraglyme added after polymerization was 80 parts by mass, and a PAI solution with a solid content concentration of 11.1% by mass was used.

[0035] <Example 9> A porous PAI film (A-9) was obtained in the same manner as in Example 1, except that a PAI solution was obtained by changing "TMA: 1.00 mol" to "TMA: 0.90 mol, DA: 0.1 mol", and then using a PAI solution with a solid content of 11.1% by mass and a tetragly content of 80 parts by mass after polymerization.

[0036] <Comparative Example 1> A porous PAI film (B-1) was obtained in the same manner as in Example 1, except that the diisocyanate component was prepared as "MDI: 1.02 mol" in the PAI solution.

[0037] <Comparative Example 2> A porous PAI film (B-2) was obtained in the same manner as in Example 1, except that the diisocyanate component was prepared as "TDI: 0.41 mol, MDI: 0.61 mol" in the PAI solution.

[0038] <Comparative Example 3> A porous PAI film (B-3) was obtained in the same manner as in Example 1, except that the amount of tetraglyme added after polymerization was 50 parts by mass and a PAI solution with a PAI solid content concentration of 13.3% by mass was used.

[0039] <Comparative Example 4> A porous PAI film (B-4) was obtained in the same manner as in Example 1, except that the diisocyanate components were set to "TODI: 0.72 mol, TDI: 0.30 mol" and the amount of tetraglyme added after polymerization was 50 parts by mass, resulting in a PAI solution with a solid content of 13.3% by mass.

[0040] Table 1 shows the evaluation results of the porous PAI films obtained in the examples and comparative examples.

[0041] [Table 1]

[0042] As shown in the examples, the porous PAI film of the present invention has excellent dielectric properties with a Df of 0.0050 or less, and a high specific tensile modulus of 1000 m / sec or more, and it can be seen that there is no material fracture when a load is applied.

[0043] In contrast, the films of Comparative Examples 1 and 2 had low specific tensile modulus, resulting in material fracture when a load was applied. Furthermore, the films of Comparative Examples 3 and 4 had poor dielectric properties and were unsuitable as substrates for high-frequency applications. [Industrial applicability]

[0044] The porous PAI film of the present invention has good dielectric properties and a high specific tensile modulus, making it suitable for use as a substrate for high-frequency applications.

Claims

1. A porous PAI film made of polyamide-imide (PAI) in which trimellitic anhydride (TMA) is used as the acid component and o-tolidine diisocyanate (TODI) is used as the isocyanate component, and 10 to 50 mol% of TODI is substituted with methylenediphenyl diisocyanate (MDI) and / or toluene diisocyanate (TDI), PAI film with the following characteristics: 1) The dielectric loss tangent (Df) at 10 GHz is 0.0050 or less. 2) The specific tensile modulus is 1000 m / sec or more.

2. A substrate for a millimeter-wave antenna using the porous PAI film described in claim 1.

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