KR102427370B1 - Porous polyimide film and manufacturing method thereof - Google Patents

Abstract

The present invention provides a porous PI film excellent in heat resistance, light weight, and sound quality properties, which can be suitably used for a speaker diaphragm, and a method for producing the same. The present invention provides <1> a porous polyimide (PI) film having a thickness of 30 μm or more and 300 μm or less, a density of 50 kg/m ³ or more, 250 kg/m ³ or less, and an average pore diameter of 0.1 μm or more and 15 μm or less, <2> On a substrate, a solution containing PI or a PI precursor and a solvent is applied to form a coating film, and then phase separation is caused in the coating film by removing the solvent in the coating film to form a porous PI layer wherein, as the solvent of the solution, a solution containing PI or tetraglyme, which is a poor solvent of a PI precursor, 70% by mass or more with respect to the total solvent mass is used, the method for producing the porous PI film, <3 > It relates to the speaker diaphragm which consists of the said porous PI film.

Description

Porous polyimide film and manufacturing method thereof

The present invention relates to a porous polyimide (PI) film that can be suitably used as a speaker diaphragm of a mobile phone or the like, and a method for producing the same.

With the increase in functionality of mobile communication terminals such as cellular phones, reduction in size, weight, and thickness of the speaker used for this is also required. As a speaker used in such a mobile communication terminal, it is known that a polymer foam film having a thickness of about 100 µm to 1000 µm is used as a flat speaker diaphragm.

For example, Patent Document 1 proposes a method in which a foam made of polyester such as polyethylene terephthalate is used as a polymer foam film. Patent Document 2 proposes a method in which a foam composed of a polymer alloy of polystyrene and polyphenylene ether is used as a polymer foam film. Patent Document 3 proposes a method in which a foam made of a poly(meth)acrylimide-based resin is used as a polymer foam film. For such a speaker diaphragm, there is a growing demand for sound quality improvement, particularly, sound quality improvement in a high-temperature environment.

However, since the above-mentioned polymer has a low glass transition temperature, the foam film made of these polymers cannot sufficiently maintain its rigidity (modulus of elasticity) under high temperature, and there is a problem that good sound quality characteristics cannot be obtained. That is, it was difficult to secure a sufficient speed of sound (propagation speed of sound waves) as a diaphragm. Here, the speed of sound (speed of sound = (E/ρ) ^1/2 , E: modulus of elasticity of the film, ρ: density of the film) is a parameter that directly affects the sound quality of the speaker, and the larger this is, the greater the It is known that vibration followability is improved, thereby reducing sound distortion.

As a speaker diaphragm corresponding to such a problem, in patent document 4, the speaker diaphragm using the polyimide (PI) foam which can maintain high rigidity even under high temperature is proposed. Here, a PI foam block having a density of 8 kg/m ³ and a thickness of about 8 mm is used as a speaker diaphragm. However, since the PI foam block proposed in Patent Document 4 has a thickness of 8 mm, it has been difficult to use it as a speaker diaphragm for a mobile phone or the like that requires reduction in size and thickness. In addition, since the density was too low at 8 kg/m ³ , the mechanical strength was not sufficient, for example, it was difficult to slice this PI foam block to obtain those having a thickness of 100 μm to 300 μm.

On the other hand, various methods for obtaining a porous PI film excellent in heat resistance have been proposed. Among them, PI and a solution containing a good solvent and a poor solvent for PI are applied on a substrate to form a coating film, and then the coating film is dried to remove the solvent in the coating film, so that in the coating film A method of causing phase separation to form a porous PI layer is known. For example, Patent Document 5 proposes a method of using a PI solution obtained by blending a specific amount of triglyme as a poor solvent and an amide-based solvent as a good solvent for PI. From this solution, a porous PI film having a density of 200 kg/m ³ or less is obtained. Patent Document 6 proposes a method of using a PI solution containing a specific amount of an amide-based solvent as a good solvent and a mixed solvent consisting of dimethyl succinate, dimethyl glutarate, and dimethyl adipic acid as poor solvents in a specific amount. have.

International Publication No. 2003/073787 Japanese Patent Laid-Open No. 2009-35709 International Publication 2014/017528 Japanese Patent Laid-Open No. 2002-374593 Japanese Patent Laid-Open No. 2007-211136 Japanese Patent Laid-Open No. 2018-53099

However, in Patent Document 5, a porous PI film having a density of 200 kg/m ³ or less was obtained, but the thickness was about 400 μm (Examples 1-4) and was thick. In addition, in the porous PI film obtained from the solution disclosed in Patent Document 5, even if process conditions such as the blending amount of triglyme are changed, only those having a large average pore diameter can be obtained. did.

For the solution used in Patent Document 6, only those having a density of 260 kg/m ³ are obtained, and a porous PI film having a low density (light weight) and good mechanical properties (rigidity) having a density of 250 kg/m ³ or less. was not obtained.

As described above, in the field of speaker diaphragms in which further miniaturization, weight reduction and thinning are required, a porous PI film capable of serving as a diaphragm having a sufficient sound velocity has not been known.

Then, this invention solves the said subject, and aims at provision of the porous PI film which is excellent in heat resistance and light weight, and has favorable mechanical properties (rigidity).

MEANS TO SOLVE THE PROBLEM The present inventors discovered that the said subject was solved by making an average pore diameter into a specific thing in a porous PI film which has a specific density and thickness, and came to completion of this invention.

The present invention has the following object.

<1> A porous polyimide (PI) film having a thickness of 30 μm or more and 300 μm or less, a density of 50 kg/m ³ or more and 250 kg/m ³ or less, and an average pore diameter of 0.1 μm or more and 15 μm or less.

<2> On a substrate, a solution containing PI or a PI precursor and a solvent is applied to form a coating film, and then phase separation is caused in the coating film by removing the solvent in the coating film to form a porous PI layer The method for producing the porous PI film according to claim , wherein as the solvent of the solution, a solution containing PI or tetraglyme, which is a poor solvent of a PI precursor, 70% by mass or more with respect to the total solvent mass is used.

<3> The speaker diaphragm which consists of the said porous PI film.

The porous PI film of the present invention is lightweight and thin, has excellent heat resistance and mechanical properties (rigidity), and also has excellent sound quality characteristics when used as a speaker diaphragm, so that it can be used suitably for mobile communication terminals such as mobile phones. can

PI forming the porous PI film of the present invention is a heat-resistant polymer having an imide bond in the main chain, and is a polyamic acid obtained by reacting tetracarboxylic dianhydride and diamine in a solvent (a PI precursor, hereinafter abbreviated as "PAA") In some cases), a solution can be used to make PI. That is, PI can be obtained by applying and drying a soluble PI solution obtained by thermally or chemically imidizing PAA in solution on a substrate. Moreover, it can be set as PI by apply|coating, drying, and thermally imidating the PAA solution which is a PI precursor on a base material. In this invention, PI obtained by apply|coating a PAA film on a base material, drying, and thermal imidation is used preferably.

These PIs also include polyamideimide (PAI), polyesterimide (PEI), and the like, which are PI-modified substances.

These PIs may be thermoplastic or non-thermoplastic.

It is preferable that the glass transition temperature (Tg) based on DSC is 200 degreeC or more, and, as for these PI, it is more preferable that it is 250 degreeC or more.

The porous PI film of the present invention needs to have a density of 50 kg/m ³ or more and 250 kg/m ³ or less, and preferably 100 kg/m ³ or more and 250 kg/m ³ or less. Moreover, the thickness of the porous PI film of this invention needs to be set to 30 micrometers or more and 300 micrometers or less, and it is preferable to set it as 100 micrometers or more and 300 micrometers or less. In addition, the average pore diameter of the porous PI film is required to be 0.1 µm or more and 15 µm or less, and preferably more than 1 µm and less than 10 µm. By doing in this way, for example, when it uses as a speaker diaphragm, favorable sound velocity (sound quality), and rigidity and heat resistance as a speaker diaphragm can be ensured. Here, thickness can be calculated|required by measuring at 25 degreeC based on JISK7130 and the prescription|regulation of JIS Z8807. An average pore diameter can be confirmed by acquiring the SEM (scanning electron microscope) image of the cross section of a porous PI film at 5000-10000 times magnification, and analyzing with image processing software.

In the porous PI film of the present invention, for example, a solution containing PAA and a solvent is applied on a substrate to form a coating film, and then, phase separation is caused in the coating film by removing the solvent in the coating film. In forming the porous PAA layer, a solution containing PAA as a solute and containing tetraglyme, which is a poor solvent of PAA, is 70 mass % or more, preferably 80 mass % with respect to the total solvent mass, using a solution, It can obtain by apply|coating this on a base material, forming a coating film, and performing thermosetting (thermal imidation) at 200-400 degreeC after drying this at 100-200 degreeC.

Here, during drying of the coating film, phase separation is induced, and a low-density porous PI structure is formed. On the other hand, in drying, as described in Unexamined-Japanese-Patent No. 2015-136633, it is preferable to fill the space in a drying furnace with the solvent volatilized from the coating-film surface, and to heat.

In order to melt|dissolve PI and set it as an optically uniform solution in PAA solution, it is preferable to contain the solvent for dissolving PAA, ie, a good solvent with respect to PAA.

As such a solvent, an amide-based solvent and a urea-based solvent, which are nitrogen-containing polar solvents, are preferable. Examples of the amide solvent include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide, and N,N-dimethylacetamide (DMAc). Examples of the urea solvent include tetramethyl urea and dimethyl ethylene urea. A nitrogen-containing polar solvent may be used individually by these, and may be used in combination of 2 or more type. Among them, DMAc and NMP are preferred.

As described above, the PAA solution used in the present invention consists of a mixed solvent (hereinafter, sometimes abbreviated as "mixed solvent") in which the solvent contains 70 mass % or more of tetraglyme with respect to the total solvent mass. It is preferable that the solution is uniform and optically uniform.

The PAA solution mix|blends so that the sum total of tetracarboxylic dianhydride and the sum total of diamine may become substantially equimolar, and the solution obtained by making this polymerize-react at 10-70 degreeC in the said mixed solvent can be used.

Specific examples of tetracarboxylic dianhydride include pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride Aromatic tetracarboxylic dianhydride, such as these, is mentioned. These may be used independently and may be used in combination of 2 or more type. Among these, PMDA, BPDA, and BTDA are preferable.

It is preferable to use 0.1-10 mol% of the said aromatic tetracarboxylic dianhydride by substituting with the tetracarboxylic dianhydride which has an oxyalkylene unit and/or tetracarboxylic dianhydride which has a siloxane unit as shown below.

Specific examples of the tetracarboxylic dianhydride having an oxyalkylene unit include ethylene glycol bisanhydrotrimellitate, diethylene glycol bisanhydrotrimellitate, triethylene glycol bisanhydrotrimellitate, and tetraethylene. Glycol bisanhydrotrimellitate, polyethylene glycol bisanhydrotrimellitate, etc. are mentioned. These may be used independently and may be used in combination of 2 or more type.

Specific examples of the tetracarboxylic dianhydride having a siloxane unit include bis(3,4-dicarboxyphenyl)tetramethylsiloxane dianhydride, bis(3,4-dicarboxyphenyl)tetraethylsiloxane dianhydride, and an acid at both terminals. The siloxane oligomer etc. which have an anhydride group are mentioned. These may be used independently and may be used in combination of 2 or more type. As a siloxane oligomer having acid anhydride groups at both terminals, "X22-168AS" (number average molecular weight 1000), copper "X22-168A" (number average molecular weight 2000), copper "X22-168B" (number average molecular weight 2000), manufactured by Shin-Etsu Chemical Co., Ltd. Average molecular weight 3200), copper "X22-168-P5-8" (number average molecular weight 4200), the Gelest company make, commercial items, such as "DMS-Z21" (number average molecular weight 600-800), can be used. Among the tetracarboxylic dianhydrides which have these siloxane units, the siloxane oligomer which has acid anhydride groups at both terminals is preferable, and it is preferable that the number average molecular weights are 500-3000.

Specific examples of the diamine include 4,4'-diaminodiphenyl ether (ODA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane, p-phenylenediamine, m-phenylene Diamine, 2,4-diaminotoluene, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 3,3'-diphenyl Aminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy) ) benzene, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2 and aromatic diamines such as ,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane.

These may be used independently and may be used in combination of 2 or more type. Among these, ODA is preferable.

It is preferable to substitute 0.1-10 mol% of the said aromatic diamine with the diamine which has an oxyalkylene unit and/or a diamine which has a siloxane unit as shown below.

Specific examples of the diamine having an oxyalkylene unit include ethylene glycol bis(2-aminoethyl) ether, diethylene glycol bis(2-aminoethyl) ether, and triethylene glycol bis(2-aminoethyl) ether. Ether, tetraethylene glycol bis(2-aminoethyl) ether, polyethylene glycol bis(2-aminoethyl) ether, propylene glycol bis(2-aminoethyl) ether, dipropylene glycol bis(2) -aminoethyl) ether, tripropylene glycol bis(2-aminoethyl) ether, tetrapropylene glycol bis(2-aminoethyl) ether, polypropylene glycol bis(2-aminoethyl) ether, etc. can These may be used independently and may be used in combination of 2 or more type. Among these, polyethylene glycol bis(2-aminoethyl) ether and polypropylene glycol bis(2-aminoethyl) ether are preferable. A commercial item can be used for these compounds, and it is preferable that it is 500-3000 as the number average molecular weight.

Specific examples of the diamine having a siloxane unit include 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, 1,3-bis(4-aminobutyl)-1, 1,3,3-tetramethyldisiloxane, bis(4-aminophenoxy)dimethylsilane, 1,3-bis(4-aminophenoxy)-1,1,3,3-tetramethyldisilox Sein, a siloxane oligomer having diamine groups at both terminals, and the like. These may be used independently and may be used in combination of 2 or more type. As the siloxane oligomer having diamine groups at both terminals, Shin-Etsu Chemical Co., Ltd. KF-8010 (number average molecular weight 860), Copper X22-161A (number average molecular weight 1600), Copper X22-161B (number average molecular weight 3000), Copper Commercially available products such as KF-8012 (number average molecular weight 4400), Dow Corning Toray, BY16-835U (number average molecular weight 900), Chisso Corporation, and Cylaplane FM3311 (number average molecular weight 1000) can be used. Among the diamines having these siloxane units, siloxane oligomers having diamine groups at both terminals are preferable, and the number average molecular weight thereof is preferably 500 to 3000.

1-15 mass % is preferable and, as for the solid content concentration of PAA in a PAA solution, 5-10 mass % is more preferable. By setting the solid content concentration in this way, a porous PI film having a low density of 50 kg/m ³ or more and 250 kg/m ³ or less is easily obtained. Moreover, 0.5-50 Pa*s is preferable and, as for the viscosity in 30 degreeC of PAA solution, 1-10 Pa*s are more preferable.

A mold release agent can be mix|blended with a PAA solution in order to improve mold release property with a base material.

As a mold release agent, higher fatty acids, such as stearic acid and palmitic acid, which are disclosed in Unexamined-Japanese-Patent No. 5283408, its amide, a metal salt, etc. are preferable. As a compounding quantity of a mold release agent, it is preferable to set it as 0.01-2 mass parts with respect to 100 mass parts of PI solid content.

You may add well-known additives, such as a leveling agent, a silane coupler, and an imidation accelerator, to PAA solution as needed in the range which does not impair the effect of this invention. Moreover, you may add polymers other than PI as needed in the range which does not impair the effect of this invention.

The porous PI film of the present invention can be obtained by, for example, applying a PAA solution to the surface of a substrate, drying and thermosetting, and then peeling the porous PI film from the substrate. On the other hand, the porous PI film formed on the base material may be used without peeling from the base material, and may be used by laminating and integrating with the base material.

The said drying process WHEREIN: Phase separation is induced by volatilizing the solvent contained in a coating film, and a porous crude PAA film|membrane is formed. As a drying temperature, it is preferable to set it as 100-200 degreeC. Moreover, as a temperature for thermosetting PAA to set it as PI, it is preferable to set it as 250-400 degreeC.

As mentioned above, the example of PI using the PAA solution which is a PI precursor has been described, but also for PI such as soluble PI or modified PI such as PAI and PEI, by the same method as the above method, the porous PI film of the present invention can do. That is, a solution containing PI and a solvent is applied on a substrate to form a coating film, and then, by removing the solvent in the coating film, phase separation occurs in the coating film to form a porous PI layer, the solute A homogeneous solution containing PI as the PI and containing tetraglyme, which is a poor solvent of PI, is 70% by mass or more, preferably 80% by mass, based on the total solvent mass, and this is applied on a substrate to form a coating film and drying this at 100 to 200°C, the porous PI film of the present invention can be obtained. As soluble PI or modified PI, a commercial item can be used. As a commercial item, the product made by Savik, Ultem (soluble PI), the Solvay Advanced Polymers company, Toron (PAI), etc. are mentioned.

Application of the PAA solution or the PI solution to the substrate can be performed using an arbitrary coating machine. Examples of the coating machine include a die coater, a lip coater, a gravure coater, a bar coater, a doctor blade coater, a comma coater, a reverse roll coater, and a bar reverse roll coater. In addition, multilayer application|coating is also possible, and the PAA solution or PI solution of each layer may be the same or different in that case.

As the base material, metal foil (copper, aluminum, iron, silver, palladium, nickel, chromium, molybdenum, tungsten or alloys thereof, etc.), polyester film (polyethylene terephthalate, polyethylene naphthalate, etc.), aromatic polyimide film , a fluororesin film (such as polytetrafluoroethylene).

Among these, a polyethylene terephthalate film or aluminum foil is preferable. It is preferable that these base materials have a smooth surface.

Moreover, the metal foil or plastic film for mold release in which the heat-resistant mold release layer was formed in the surface can also be used preferably.

A commercial item can be used for these metal foil for mold release or a plastic film.

The porous PI film obtained in this way has “30 μm or more and 300 μm or less” as a thickness, “50 kg/m ³ or more and 250 kg/m ³ or less” as a density, and “0.1 μm or more and 15 μm or less” as an average pore diameter, A porous PI film having such characteristics is effective as the porous PI film of the present invention.

The use of a porous PI film having the above characteristics as a speaker diaphragm has not been known conventionally. Since the porous PI film of the present invention has a sufficiently small average pore diameter, for example, when used as a speaker diaphragm, even when the weight is reduced, a sufficient sound velocity can be ensured.

As a sound speed of a diaphragm, it is preferable to set it as 900 m/sec or more, and it is more preferable to set it as 1000 m/sec or more. Here, the speed of sound is a value obtained by measuring the elastic modulus in the tensile mode based on JIS K7161, then dividing the elastic modulus by the density to calculate the specific elastic modulus and finding the square root thereof.

By making the thickness and density of the porous PI film as described above and the average pore diameter as described above, when the porous PI film is used as a speaker diaphragm, it is possible to reduce the weight and secure the good sound quality.

When the porous PI film of the present invention is used as a speaker diaphragm, an adhesive layer is interposed on both surfaces of the porous PI film, and aluminum foil can be laminated for use. By doing in this way, the sound quality characteristic when it is set as a speaker diaphragm can be improved more. It is preferable that thickness shall be 5 micrometers - 200 micrometers, and, as for aluminum foil, it is more preferable to set it as 10 micrometers - 150 micrometers.

The adhesive is preferably an adhesive having heat resistance, and specific examples thereof include an epoxy-based adhesive, an acrylic adhesive, a cyanoacrylate-based adhesive, a urethane-based adhesive, a polyester-based adhesive, and a polyimide-based adhesive.

Example

Hereinafter, the present invention will be described in more detail by way of Examples. In addition, the present invention is not limited by the Examples.

<Example 1>

In a glass reaction vessel, in a nitrogen gas atmosphere, ODA: 0.6 mol as the diamine component, PMDA: 0.6 mol as the tetracarboxylic acid component, and a mixed solvent consisting of DMAc and tetraglyme as the solvent (the mixing ratio of DMAc/tetraglyme is the mass ratio furnace 25/75), and by making it react at 40 degreeC for 10 hours under stirring, the copolymerization PAA solution whose solid content concentration is 9.5 mass % was obtained.

Using a doctor blade coater, this PAA solution was apply|coated on the 100-micrometer-thick mold release layer addition polyester film (base material), and it dried at 130 degreeC for 30 minutes, and formed the porous PAA coating film. In drying, the solvent volatilized was made to fill the space in a drying furnace, and it was made to heat. Then, this coating film is separated from the polyester film, heated at 200 ° C. for 30 minutes, 320 ° C. for 90 minutes, and thermally cured, whereby a porous PI film having a DSC-based glass transition temperature of 400 ° C. or higher (A- 1) was obtained. Table 1 shows the properties of this PI film.

<Example 2>

As a diamine component, ODA:0.58 mol and Shin-Etsu Chemical Co., Ltd. KF-8010 (number average molecular weight 860): Except having used 0.02 mol, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the copolymerization PAA solution was obtained. This PAA solution was carried out similarly to Example 1, and the porous PI film (A-2) was obtained. Table 1 shows the characteristics of A-2.

<Example 3>

As the diamine component, ODA: 0.59 mol and Huntsman Co., Ltd. "Jepamine" D2000 (diamine having an oxyalkylene unit, number average molecular weight 2000) 0.01 mol, except having used 0.01 mol, it carried out similarly to Example 1, and copolymerized PAA A solution was obtained. This PAA solution was carried out similarly to Example 1, and the porous PI film (A-3) was obtained. Table 1 shows the characteristics of A-3.

<Example 4>

As the mixed solvent, a copolymerized PAA solution was obtained in the same manner as in Example 1, except that a mixture ratio of DMAc/tetraglyme was used in a mass ratio of 20/80. This PAA solution was carried out similarly to Example 1, and the porous PI film (A-4) was obtained. Table 1 shows the characteristics of A-4.

<Example 5>

As the mixed solvent, a copolymerized PAA solution was obtained in the same manner as in Example 1, except that a mixture ratio of DMAc/tetraglyme was used in a mass ratio of 15/85. This PAA solution was carried out similarly to Example 1, and the porous PI film (A-5) was obtained. Table 1 shows the characteristics of A-5.

<Example 6>

Except having used BPDA as a tetracarboxylic-acid component, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (A-6) was obtained. Table 1 shows the characteristics of A-6. On the other hand, the glass transition temperature of A-6 was 285 degreeC.

<Example 7>

Except having used BTDA as a tetracarboxylic-acid component, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (A-7) was obtained. Table 1 shows the characteristics of A-7. On the other hand, the glass transition temperature of A-7 was 285 degreeC.

<Example 8>

A porous PI film (A-8) was obtained in the same manner as in Example 1 except that a porous PI film having a thickness of 210 μm was prepared by adjusting the gap between the doctor blade and the substrate. Table 1 shows the characteristics of A-8.

<Example 9>

A copolymerized PAA solution was obtained in the same manner as in Example 1 except that a porous PI film having a thickness of 150 μm was prepared by adjusting the gap between the doctor blade and the substrate. This PAA solution was carried out similarly to Example 1, and the porous PI film (A-9) was obtained. Table 1 shows the characteristics of A-9.

<Example 10>

As PI, PAI powder (Thon 4000T-HV manufactured by Solvay Advanced Polymers) having a glass transition temperature of 280°C was prepared. This was uniformly dissolved in a mixed solvent of NMP and tetraglyme (the mixing ratio of NMP/tetraglyme was 15/85 in mass ratio) to obtain a PAI solution having a solid content concentration of 9.5% by mass.

Using a doctor blade coater, this PAI solution was apply|coated on the polyester film (base material) with a release layer addition of thickness 100 micrometers, and it dried at 140 degreeC for 30 minutes, and formed the porous PAI coating film. In drying, the solvent volatilized was made to fill the space in a drying furnace, and it was made to heat. By peeling this coating film from a base material, the porous PI film (A-10) was obtained. Table 1 shows the properties of this PI film.

<Example 11>

A porous PI film (A-11) was obtained in the same manner as in Example 10 except that a porous PI film having a thickness of 145 μm was prepared by adjusting the gap between the doctor blade and the substrate. Table 1 shows the characteristics of A-11.

<Comparative Example 1>

A porous PI film with a thickness of 400 μm was used by using a mixed solvent consisting of DMAc and triglyme (the mixing ratio of DMAc/triglyme is 50/50 by mass) as the solvent and adjusting the gap between the doctor blade and the substrate. Except having created, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (B-1) was obtained. Table 1 shows the properties of B-1.

<Comparative Example 2>

A porous PI film having a thickness of 250 μm is used by using a mixed solvent composed of DMAc and triglyme (the mixing ratio of DMAc/triglyme is 50/50 by mass) as the solvent and adjusting the gap between the doctor blade and the substrate. Except having created, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (B-2) was obtained. Table 1 shows the properties of B-2.

<Comparative example 3>

BPDA is used as the acid component, and a mixed solvent consisting of DMAc and triglyme (the mixing ratio of DMAc/triglyme is 50/50 by mass ratio) is used as the solvent, and the gap between the doctor blade and the substrate is adjusted. Thereby, except having created the 250-micrometer-thick porous PI film, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (B-3) was obtained. Table 1 shows the properties of B-3.

<Comparative example 4>

A porous PI film having a thickness of 250 μm was used by using a mixed solvent composed of DMAc and triglyme (the mixing ratio of DMAc/triglyme is 30/70 by mass) as the solvent and adjusting the gap between the doctor blade and the substrate. Except having created, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (B-4) was obtained. Table 1 shows the properties of B-4.

<Comparative Example 5>

A porous PI film having a thickness of 250 μm is used by using a mixed solvent of DMAc and tetraglyme (the mixing ratio of DMAc/tetraglyme is 50/50 by mass) as the solvent and adjusting the gap between the doctor blade and the substrate. Except having created, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (B-5) was obtained. Table 1 shows the properties of B-5.

<Example 12>

Except having made solid content concentration into 18 mass %, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and the porous PI film (B-6) was obtained. Table 1 shows the properties of B-6.

<Comparative Example 7>

A porous PI film having a thickness of 250 μm was used by using a mixed solvent of DMAc and diglyme (the mixing ratio of DMAc/diglyme is 30/70 by mass) as the solvent and adjusting the gap between the doctor blade and the substrate. Except having created, it carried out similarly to Example 1, and obtained the copolymerization PAA solution. This PAA solution was carried out similarly to Example 1, and although it was going to obtain a porous PI film, almost no pores were formed in this film.

<Comparative Example 8>

An attempt was made to obtain a porous PI film with a thickness of 300 μm by slicing a commercially available polyimide foam block with a density of 7 kg/m ³ , but since this block is fragile, the film breaks during slicing, and the porous PI film cannot be collected. there was no

It turns out that the porous PI film obtained in the Example can ensure sufficient sound velocity in spite of the thickness and density falling sufficiently. This shows that the porous PI film of the present invention is suitably used as a speaker diaphragm which is lightweight and excellent in sound quality.

The porous PI film of the present invention is excellent in heat resistance, lightness, rigidity, and sound velocity characteristics. Therefore, the speaker using the speaker diaphragm which consists of a porous PI film of this invention can be used suitably for mobile communication terminals, such as a cellular phone, which require size reduction, thickness reduction, and weight reduction.

Claims (3)

A speaker diaphragm made of a porous polyamideimide (PAI) film having a thickness of 30 μm or more and 300 μm or less, an average pore diameter of 0.1 μm or more and 15 μm or less, and a speed of sound (propagation speed of sound waves) of 900 m/sec or more. A solution containing PAI and a solvent is applied on a substrate to form a coating film, and then phase separation is caused in the coating film by removing the solvent in the coating film to form a porous PAI layer, the solvent of the solution The method for producing a speaker diaphragm according to claim 1, wherein a solution containing tetraglyme, which is a poor solvent for PAI, of 70% by mass or more with respect to the total solvent mass is used.
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