JP5928705B2 - Method for producing polyimide precursor solution, polyimide precursor solution using the same, and porous polyimide - Google Patents

Description

  The present invention relates to a polyimide precursor solution capable of forming a porous polyimide having a low dielectric constant, and a method for producing the same, and further relates to a composition for synthesizing a polyimide precursor, a porous polyimide, and a method for producing a porous polyimide.

  Polyimide resin has high heat resistance, insulation, mechanical strength, solvent resistance, dimensional stability, and other properties, so it is widely used as an insulating film for electronic parts and for semiconductor devices. ing. In recent years, with the increase in functionality and integration of electronic components, it has been required to increase the signal transfer speed of devices, and the peripheral members of the wiring are also required to support high speed. A polyimide resin used as an insulating film is also required to have a low dielectric constant and a low dielectric loss tangent as electrical characteristics corresponding to high speed.

  As a method for reducing the dielectric of the polyimide resin film, it is conceivable to make the film porous. As a method for obtaining a porous polyimide resin film, for example, in JP-A 2000-44719 (Patent Document 1), a raw material solution in which a polyimide precursor soluble in an organic solvent and a hydrophilic polymer are dissolved is prepared, There has been proposed a method for producing a porous polyimide by decomposing and removing the hydrophilic polymer by firing a precursor obtained by drying the raw material liquid. Here, by using the hydrophilic polymer, a fine dispersed phase of the hydrophilic polymer can be easily formed in the polyimide, and fine pores can be formed by burning off the hydrophilic polymer. Specifically, an alkylene glycol such as polyethylene glycol having a molecular weight of 2 to 4 million is used as a hydrophilic polymer, and a solvent of polyimide is 1,2-dichloroethane, N-methylpyrrolidone, γ-butyrolactone, methyl ethyl ketone. And polar solvents such as dimethylacetamide (paragraph 0018).

  Moreover, in Unexamined-Japanese-Patent No. 2003-26850 (patent document 2), a film is produced from the resin solution containing the dispersible compound and solvent which can be disperse | distributed with respect to a polyimide resin precursor as a raw material, From the obtained film It has been proposed to extract and remove the dispersible compound with an extraction solvent. Here, as the dispersible compound, polyethylene glycol, polypropylene glycol, and one or both end methyl-blocked products thereof are used. In Examples, a resin solution obtained by blending polyethylene glycol dimethyl ether having a weight average molecular weight of 500 with a polyimide precursor solution was used to form a polyimide precursor film, and then carbon dioxide was injected under pressure, followed by heating. Thus, polyethylene glycol dimethyl ether is extracted and removed (paragraph 0051-paragraph 0055).

  Japanese Patent Application Laid-Open No. 2011-140580 (Patent Document 3) discloses a tetracarboxylic dianhydride and a diamine in the presence of an isocyanate-modified organic polymer obtained by reacting an organic polymer having a thermal decomposition temperature of 350 ° C. or less with a diisocyanate. By carrying out the condensation polymerization, a polyimide precursor having a thermally decomposable polymer group introduced into the molecular chain is obtained, and the resulting thermally decomposable group-containing polyimide precursor film is thermally imidized to thermally decompose. A method for forming a porous polyimide film in which pores based on a functional polymer group are formed has been proposed.

JP 2000-44719 A JP 2003-26850 A JP 2011-140580 A

  However, in the method described in Patent Document 1, as described in paragraph 0005 of JP2003-26850A, when the hydrophilic polymer is directly removed by baking or solvent extraction and then imidized, the pores become flat. Or there is a problem that the porosity corresponding to the amount of the hydrophilic polymer cannot be achieved due to clogging.

  In addition, the method described in Patent Document 2 requires a special device separately in the process of heating imidization, such as using supercritical carbon dioxide for extraction and removal of the organic polymer, and is difficult to apply to mass production. is there.

  The present invention has been made in view of such circumstances, and an object of the present invention is to achieve a low dielectric constant at a level that can be easily applied to mass production without requiring a special apparatus. It is an object of the present invention to provide a method capable of producing a porous polyimide film having suitable fine pores distributed almost uniformly, a polyimide precursor solution used therefor, and a method for producing the same.

In the method for producing a polyimide precursor solution of the present invention, a pyrolysis organic compound having a pyrolysis temperature of 350 ° C. or lower and comprising a diamine compound having amines bonded to both ends of a polyether , and a boiling point of 150 to 210 at normal pressure. Tetracarboxylic dianhydride in the presence of a mixed solvent containing an aprotic polar solvent at ℃ and an ether solvent having a boiling point of 200 to 300 ℃ at normal pressure in a mass ratio of 40:60 to 60:40 A step of reacting the product with diamine.

The ether solvent may, Ri triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether der, the protic polar solvent is N- methyl-2-pyrrolidone, dimethyl sulfoxide or γ- butyrolactone der Rukoto, is preferred.

  The manufacturing method of the porous polyimide of this invention includes the process of imidating by heating the polyimide precursor solution manufactured by the manufacturing method of the said invention to 350 degreeC or more.

Another aspect of the present invention relates to a thermally decomposable organic compound having a pyrolysis temperature of 350 ° C. or lower, comprising a diamine compound having amines bonded to both ends of tetracarboxylic dianhydride, diamine, and polyether , and atmospheric pressure. Polyimide precursor containing a mixed solvent in which an aprotic polar solvent having a boiling point of 150 to 210 ° C. and an ether solvent having a boiling point of 200 to 300 ° C. at normal pressure are contained in a mass ratio of 40:60 to 60:40 Composition for body synthesis: containing an aprotic polar solvent having a boiling point of 150 to 210 ° C at normal pressure and an ether solvent having a boiling point of 200 to 300 ° C at normal pressure in a mass ratio of 40:60 to 60:40 in a mixed solvent is, tetracarboxylic dianhydride, diamine, and a thermal decomposition temperature 350 ° C. or less of the thermally decomposable organic compound amine at both ends of the polyether is composed of a diamine compound bound Polyimide precursor comprising reaction with the polyimide precursor solution is dissolved; and a polyimide precursor solution is heated at 350 ° C. or higher, an average pore diameter 0.001~0.5μm obtained by cyclodehydration Of porous polyimide.

  Here, the “polyimide precursor” refers to a polymer (polyamic acid) that can be imidized by heat treatment to form a polyimide.

  Furthermore, the “thermal decomposition temperature” in the present invention refers to a temperature at which the mass reduction rate is 50% when the temperature is increased from room temperature to 10 ° C./min in a nitrogen atmosphere. For example, it can be measured by measuring thermogravimetry using TG / DTA (simultaneous differential thermothermal gravimetric measuring device) manufactured by SII Nanotechnology Corporation.

  According to the method for producing a polyimide precursor of the present invention, since a polyimide precursor solution in which a thermally decomposable organic compound is finely dispersed can be obtained, a porous polyimide in which micropores are distributed substantially evenly by heating is obtained. Can be manufactured.

Porous polyimide no. It is a scanning microscope (SEM) photograph (50000 times) which imaged 2 cut surfaces. Porous polyimide no. It is a scanning microscope (SEM) photograph (1000 times) which imaged the section of No. 5.

[Composition for polyimide precursor synthesis: Raw material for polyimide precursor solution]
First, the raw material (composition for polyimide precursor synthesis) of the polyimide precursor solution of the present invention will be described.
The composition for synthesizing a polyimide precursor includes a monomer (tetracarboxylic dianhydride and diamine compound) that is a raw material of the polyimide precursor, a thermally decomposable organic compound that plays a role of forming pores, and an organic solvent that dissolves these. contains. Hereinafter, each will be described in order.

(1) Tetracarboxylic dianhydride Tetracarboxylic dianhydride includes aliphatic groups having 2 to 27 carbon atoms, cyclic aliphatic groups having 4 to 10 carbon atoms, monocyclic aromatic groups, condensed poly Tetracarboxylic dianhydrides bonded to cyclic aromatic groups can be used. Specifically, 3,4,3 ′, 4′-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride (a-BPDA), pyro Mellitic acid dianhydride (PMDA), 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-diphenylsulfone Tetracarboxylic dianhydride, bicyclo (2,2,2) -oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid Anhydride, 2,2-bis (3,4-dicarboxyxyphenyl) hexafluoropropane dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic Examples include acid dianhydrides Is, it may be used alone or in combination. Of these, aromatic tetracarboxylic dianhydrides are preferably used.

(2) Diamine Compound The diamine compound may be a compound in which an amino group is bonded to an aromatic group, an aliphatic group, or an aromatic group linked by a cross-linking member, but an aromatic diamine is preferably used.

  Examples of the aromatic diamine include 2,2′-dimethyl 4,4′-diaminobiphenyl (mTBHG), 2,2′-bis (trifluoromethyl) 4,4′-diaminobiphenyl (TFMB), and 2,2 ′. -Bis (4-aminophenyl) hexafluoropropane (Bis-A-AF) paraphenylenediamine (PPD), metaphenylenediamine, 4,4'-diaminodiphenyl ether (ODA), 3,4'-diaminodiphenyl ether, 3, 3'-dihydroxy 4,4'-diaminobiphenyl, 4,4'-dihydroxy 3,3'-diaminobiphenyl, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,2'-bis (4-aminophenoxyphenyl) propane and the like, and these may be used alone or in combination of two or more. It may be used Te.

  The diamine compound is a compound that forms a polyimide precursor by condensation polymerization with tetracarboxylic dianhydride, and is blended so as to have a substantially equimolar ratio with tetracarboxylic dianhydride. However, when an amine-modified compound is used as a thermally decomposable organic compound to be described later, the amine-modified compound can participate in a polymerization reaction with tetracarboxylic dianhydride as a diamine compound. What is necessary is just to mix | blend the quantity from which the total amount of a thermally decomposable organic compound and a diamine compound becomes equimolar with tetracarboxylic dianhydride.

(3) Thermally decomposable organic compound The thermally decomposable organic compound used in the present invention is an organic compound having a half-temperature of 350 ° C. or lower. Here, the half temperature of 350 ° C. or lower means that the temperature when the mass reduction rate when the temperature is raised at 10 ° C./min in a nitrogen atmosphere is 50% is 350 ° C. or lower. For example, it can be measured by measuring thermogravimetry using TG / DTA (simultaneous differential thermogravimetric measuring device) manufactured by SII Nanotechnology. When the thermal decomposition temperature of the organic compound that generates pores exceeds 350 ° C., thermal decomposition in the imidization process becomes insufficient, and as a result, it becomes difficult to form sufficient pores in the polyimide resin.

  The thermal decomposable organic compound is a weight at the time of the synthesis of the polyimide precursor, that is, the solvent for the polycondensation reaction between the tetracarboxylic dianhydride and the diamine compound, and the compatibility with the polyimide precursor raw material. The average molecular weight is preferably 10,000 or less, more preferably 1000 to 8000, and still more preferably 2000 to 5000. When the weight average molecular weight is less than 1000, the polyimide precursor film has excellent compatibility with the skeleton or solvent. However, in the polyimide precursor film, the agglomerated portion of the thermally decomposable organic compound becomes too small, and the pores are decomposed. Is difficult to form. On the other hand, when the weight average molecular weight exceeds 10,000, the compatibility of the polyimide precursor with the raw material monomer is lowered, and it is difficult to obtain a desired pore size.

  Examples of such thermally decomposable organic compounds include polyethers such as polyethylene oxide and polypropylene oxide; compounds obtained by amine-modifying one or both ends of the polyether; isocyanate or epoxy at one or both ends of the polyether Examples thereof include modified compounds, and these can be used alone or in combination of two or more.

  A commercially available amine-modified product can be used as the compound in which one or both ends of the polyether are amine-modified. For example, Jeffamine D2000, D4000 manufactured by Mitsui Chemical Fine Co., Ltd. can be used.

  In the case of a compound in which one or both ends of the polyether is modified, it is incorporated into the polyimide precursor as a part of the raw material monomer. For example, in the case of an amine-modified compound, it reacts with tetracarboxylic dianhydride as an alternative to a part of the diamine that is a raw material monomer, so that it is incorporated into the molecular chain of the polyimide precursor. In the case of an isocyanate or epoxy-modified compound, the isocyanate group or epoxy group reacts with an acid anhydride or diamine and is incorporated into the molecular chain of the polyimide precursor.

  The thermally decomposable organic compound as described above is preferably 10 to 60 parts by mass, more preferably 20 to 100 parts by mass of the polyimide precursor raw material (acid anhydride, diamine, thermally decomposable organic compound). -50 mass parts. Since the thermally decomposable organic compound burns out to form pores, when it exceeds 60 parts by mass, the porosity becomes too high and the polyimide resin film tends to be reduced in strength. On the other hand, if it is less than 10 parts by mass, the porosity tends to be small, and it tends to be difficult to sufficiently reduce the dielectric constant. When an amine-modified thermally decomposable organic compound is used, it is used as a substitute for the diamine compound as a part of the polyimide precursor raw material, so that the total amount of the raw material diamine and the carboxylic dianhydride is 1: The amount is preferably 1.

(4) Organic solvent The organic solvent contained in the composition for synthesizing the polyimide precursor of the present invention is an organic solvent used as a reaction solvent for the polyimide precursor raw material, and has a boiling point of 150 to 210 ° C. at normal pressure. It is a mixed solvent of a protic polar solvent and an ether solvent having a boiling point of 200 to 300 ° C. at normal pressure.

  Conventionally, for the synthesis of a polyimide precursor (polyamic acid), a raw material monomer (diamine, acid anhydride) and a polar solvent capable of dissolving the polyamic acid are generally used. However, the thermally decomposable organic compound used for pore formation as described above has low solubility in a polar solvent when the molecular weight is increased, and the formation of a fine phase separation structure is insufficient. The pores of the resulting porous polyimide have a large pore size and nonuniform pore distribution. In addition, too large vacancies may be crushed and a predetermined porosity may not be achieved. In this regard, a porous medium in which minute pores are uniformly distributed by using a mixed solvent of an aprotic polar solvent at 150 to 210 ° C. and an ether solvent having a boiling point at normal pressure of 200 to 300 ° C. The body is obtained. On the other hand, in the case of an ether solvent alone, since the raw material monomer does not dissolve, the polymerization reaction itself does not proceed.

  As said aprotic polar solvent, the polar solvent conventionally used in the case of the synthesis | combination of a polyimide precursor can be used. Specifically, N, N dimethylacetamide (DMAc: boiling point 165 ° C.), N-methyl-2-pyrrolidone (NMP: boiling point 202 ° C.), N, N dimethylformamide (boiling point 153 ° C.), dimethyl sulfoxide (boiling point 189 ° C.) ), Γ-butyrolactone and the like are preferably used. If the boiling point is less than 150 ° C., no suitable solvent for dissolving the polyimide precursor can be found at present. On the other hand, if it exceeds 210 ° C., the solvent is difficult to volatilize and a fine phase separation structure cannot be obtained.

  Examples of the ether solvent include triethylene glycol dimethyl ether (boiling point: 216 ° C.), tetraethylene glycol dimethyl ether (boiling point: 275 ° C.), and the like. Such an ether solvent is excellent as a solvent for the thermally decomposable organic compound used in the present invention, particularly a polyether organic compound. Further, in the case of ether having a boiling point of 200 ° C. or higher, it is easy to handle because it has low volatility and has a low risk of ignition. On the other hand, in the case of an ether having a boiling point higher than 300 ° C., it is not sufficiently evaporated at the start of the imidation reaction and may remain while the polyimide resin film is formed, thereby inhibiting the formation of a fine porous structure.

  The mixing ratio of the aprotic polar solvent and the ether solvent is preferably 30:70 to 70:30, more preferably 40:60 to 60: polar solvent: ether solvent (mass ratio). 40, more preferably 50:50. If the balance of these mixing ratios is too biased, either the raw material monomer of the polyimide precursor, the thermally decomposable organic compound, or the generated polyimide precursor cannot be dissolved, the synthesis reaction does not proceed, or the thermally decomposable organic The compound is not uniformly dispersed and incorporated in the polyimide precursor, and the resulting porous polyimide film has large pores and is inhomogeneous.

The mixed solvent as described above can dissolve not only the polyimide precursor raw material monomer and the thermally decomposable compound but also the synthesized polyimide precursor, so that it is necessary to dissolve the raw material monomer so that the synthesis reaction can proceed. Although it should just contain, when forming as a polyimide resin film, when using as a coating liquid to a base material, you may use the quantity which can be diluted to the viscosity which does not have trouble in coating workability | operativity.
Specifically, it is preferable to set the amount of the resulting polyimide precursor solution so that the resulting polyimide precursor has a solid content concentration of about 10 to 30% by mass.

[Polyimide precursor solution and production method thereof]
The polyimide precursor solution of the present invention can be obtained by reacting the polyimide precursor synthesis composition of the present invention.
That is, the method for producing a polyimide precursor solution of the present invention comprises a pyrolyzable organic compound having a pyrolysis temperature of 350 ° C. or less, an aprotic polar solvent having a boiling point of 150 to 210 ° C. at normal pressure, and normal pressure. A step of reacting a tetracarboxylic dianhydride and a diamine in the presence of a mixed solvent with an ether solvent having a boiling point of 200 to 300 ° C.

The reaction step is usually carried out by dissolving the diamine compound in the mixed solvent and then adding tetracarboxylic dianhydride while stirring at room temperature.
A ring-opening polyaddition reaction proceeds and a polyamic acid is synthesized. At this time, when a modified organic compound is used as the thermally decomposable organic compound, it is incorporated in the molecular chain of the synthesized polyamic acid. When the thermally decomposable organic compound does not have a reactive group with the raw material monomer, a polyamic acid is synthesized from the raw material monomer.

  The composition having undergone the reaction in this manner is a solution in which a polyimide precursor in which a thermally decomposable organic compound is incorporated is dissolved in a mixed solvent, or a solution in which a polyimide precursor and a thermally decomposable organic compound are substantially uniformly dissolved. It has become. The polyimide precursor solution of the present invention is thus obtained. Preferably, it is a solution in which a polyimide precursor incorporating a thermally decomposable organic compound is dissolved in a mixed solvent.

  In addition, for example, various surfactants such as an antifoaming agent and a leveling agent, a photopolymerizable monomer, and the like may be added to the polyimide precursor solution of the present invention. These additives can be added at appropriate stages before blending the polyimide precursor raw material, at the blending stage, and after blending (after the polyimide precursor synthesis), but are preferably added after the polyimide precursor synthesis.

  The polyimide precursor solution obtained as described above undergoes an imidization reaction of the polyimide precursor by heat curing, and the thermally decomposable organic compound is thermally decomposed, volatilized, and burned out. As a result, it is possible to obtain a porous polyimide in which portions where the thermally decomposable organic compound existed (portions where the thermally decomposable organic compound was incorporated) became pores.

[Porous polyimide]
The porous polyimide of the present invention can be obtained by heat-treating the polyimide precursor solution of the present invention.
Specifically, a polyimide precursor film is formed by applying a polyimide precursor solution to a substrate and drying the solvent. Next, when heat treatment is performed, imidization of the polyimide precursor occurs, and the thermally decomposable organic compound (existing as a thermally decomposable organic compound residue) contained in the polyimide precursor molecular chain is thermally decomposed and burned down, and is fine. A porous polyimide having pores is formed.

  The heat treatment is performed by heating at 300 to 500 ° C. for 1 to 24 hours. The heat treatment conditions for thermal decomposition, volatilization, and burning (porosification) of the thermally decomposable organic compound are selected according to the thermal decomposition temperature of the thermally decomposable organic compound. The heating time may be appropriately set according to the heat treatment temperature. However, when heated for a long time at a high temperature exceeding 400 ° C., the polyimide deteriorates. Therefore, it is usually preferable to heat at 200 to 400 ° C. for about 2 to 10 hours.

  As the coating film is thermally cured by imidization, the thermally decomposable organic compound is thermally decomposed and burned out, so that the portion where the thermally decomposable organic compound was present becomes pores. That is, in the obtained porous polyimide, since the pores are caused by the thermally decomposable organic compound, there is little variation in the pore size, and the pore distribution is based on a homogeneous dissolved state, and the uniformity of the distribution is also high. . Accordingly, a porous polyimide in which fine pores are uniformly distributed is obtained, and the porous polyimide has a low dielectric constant based on pores.

  The porous polyimide obtained as described above has an average pore diameter of usually from 0.001 μm to 1 μm, preferably from 0.005 μm to 0.5 μm, and has mechanical strength, heat resistance, resistance to resistance. Low dielectric constant can be achieved with a porous body that retains the excellent properties inherent in polyimide resins such as solvent properties.

  The porosity of the porous polyimide is not particularly limited, but is preferably 10 to 60%, more preferably 20 to 50%. By using the polyimide precursor solution of the present invention, a porous body having a porosity of about 60% can be formed, and a necessary and sufficient strength can be secured even with a porosity of about 60%. On the other hand, even if the content of the thermally decomposable organic compound is increased too much, a part of the pyrolyzable organic compound remains without being burned out, and it tends to be difficult to produce a porous body exceeding 60%. In addition, if it is the porosity in the said range, it can control by content of the thermally decomposable organic compound contained in a polyimide precursor.

The porous polyimide as described above can achieve a low dielectric constant of 3.2 or less, preferably 3.0 or less at 1 GHz, and has excellent properties, mechanical strength, heat resistance, and solvent resistance. Sex can be maintained.
Specifically, the linear thermal expansion coefficient (CTE) can be reduced to 30 ppm / K or less by introducing a rigid structure into the molecular skeleton of the polyimide precursor. By adjusting the linear thermal expansion coefficient of the resin within the above range, it becomes possible to reduce the difference in thermal expansion coefficient between the base material and the conductor layer made of metal or silicon, and between the polyimide layer and the metal layer. Problems such as cracks and delamination caused by accumulation of residual stress can be solved.

Applications of porous polyimide are also within the scope of the present invention.
As an application product of porous polyimide, for example, one side of a polyimide base material having a conductor wiring made of a metal such as copper, and having a porous polyimide film as a coverlay film (protective film) on the conductor wiring A flexible printed wiring board can be illustrated.
In addition, an insulating layer such as polyimide is provided on a metal foil base material such as stainless steel, and a conductor wiring (circuit) made of a metal such as copper is provided thereon, and a porous polyimide film is provided on the conductor wiring as a protective film. A suspension board with a circuit as shown in FIG.
Further, in the printed wiring board and suspension board, the porous polyimide of the present invention may be used for a polyimide base material or a polyimide film as an insulating layer.

  The form for implementing this invention is demonstrated by an Example. The following examples are not intended to limit the scope of the invention.

[Measurement evaluation method]
(1) Average pore diameter (μm)
The cut surface of the produced polyimide resin film was observed with a scanning electron microscope (SEM), and the average pore diameter was calculated.

(2) Porosity (%)
The thickness and weight of the produced polyimide resin film were measured, and the porosity was calculated from the following formula. In the formula, S represents the area of the resin film sample, T represents the film thickness, W represents the weight of the measured resin, and D represents the density of the polyimide. The density of the polyimide was calculated from a polyimide film having no pores.
Porosity (%) = 100-100 × (W / D) / (S × T)

(3) Dielectric constant The dielectric constant was measured at a measurement frequency of 1 GHz by the capacitance method of an impedance analyzer. The low dielectric constant film is desired to have a dielectric constant of 3.2 or less.

(4) Thermal decomposition temperature of thermally decomposable organic compounds Using TG / DTA (simultaneous differential thermogravimetric measuring device) manufactured by SII NanoTechnology Co., Ltd., the temperature was increased from room temperature to 10 ° C / min in a nitrogen atmosphere. The thermogravimetry was measured. The temperature at which the mass reduction rate was 50% was defined as the thermal decomposition temperature.

[Production of polyimide precursor solution and porous polyimide film]
(1) Polyimide precursor solution No. 1-No. 4
N, N-dimethylacetamide (DMAc: boiling point 165 ° C.) is used as the aprotic polar solvent, and triethylene glycol dimethyl ether (boiling point: 216 ° C.) or tetraethylene glycol dimethyl ether (boiling point: 275 ° C.) is used as the ether solvent. Using. The aprotic polar solvent and the ether solvent were mixed at 1: 1 (mass ratio) to obtain a mixed solvent.

  To the mixed solvent, add 4,4′-diaminodiphenyl ether (ODA) in the amount shown in Table 1 and a thermally decomposable organic compound (diamine-modified polypropylene glycol having a weight average molecular weight of 2000 or 4000) in the amounts shown in Table 1, respectively. The mixture was stirred at 80 ° C. in a nitrogen atmosphere to completely dissolve the mixture. Then, after cooling a reaction liquid to 40 degreeC, pyromellitic dianhydride (PMDA) 100g was added over 5 hours, stirring, and the polyimide precursor solution with a solid content concentration of 23 mass% was obtained.

The thermally decomposable organic compounds used are as follows.
Amine-modified PPG1: Polypropylene glycol modified with diamine at both ends having a weight average molecular weight of 2000, thermal decomposition temperature of 300 ° C.
Amine-modified PPG2: Polypropylene glycol modified with diamine at both ends with a weight average molecular weight of 4000, thermal decomposition temperature of 300 ° C.

The polyimide precursor solution synthesized above was applied onto a copper foil having a thickness of 40 μm by a spin coating method, followed by heating and drying at 90 ° C. for 30 minutes to form a polyimide precursor film having a thickness of 20 μm. Subsequently, heat treatment was performed at 120 ° C. for 1 hour, 250 ° C. for 2 hours, and 370 ° C. for 5 hours in a nitrogen atmosphere to imidize, thereby producing a porous polyimide resin film (porous polyimide).
The cross section of the obtained porous polyimide was observed with a scanning electron microscope SEM, and the average pore diameter was determined. Further, the dielectric constant was measured and calculated according to the above method. The results are shown in Table 1. In addition, the imaged No. A photomicrograph of 2 is shown in FIG. In the photograph, the black portions are pores.

(2) Polyimide precursor solution No. 5
In place of the mixed solvent, only the aprotic polar solvent was used, and the amounts of 4,4′-diaminodiphenyl ether (ODA) and the thermally decomposable organic compound were changed as shown in Table 1. A polyimide resin film (porous polyimide) was prepared using a polyimide precursor solution synthesized in the same manner as in 1. When the cross section of the obtained porous polyimide was observed with a scanning electron microscope (SEM), the average pore diameter was as large as 1 μm to 10 μm, and the pore distribution was uneven. Further, the dielectric constant was measured according to the above method. The results are shown in Table 1. Moreover, the imaged micrograph is shown in FIG.
(3) Polyimide precursor solution No. 6
Instead of the mixed solvent, only tetraethylene glycol dimethyl ether is used, the amount of 4,4′-diaminodiphenyl ether (ODA) and the thermally decomposable organic compound is as shown in Table 1, and pyromellitic dianhydride (PMDA) ) Was dropped, ODA and PMDA did not dissolve, and the polymerization reaction did not proceed.

(4) Reference Example In the presence of an aprotic polar solvent, pyromellitic dianhydride (PMDA) was dropped into 4,4′-diaminodiphenyl ether (ODA) without adding a pyrolytic organic compound and adding a ring. The polyimide addition solution was advanced to synthesize a polyimide precursor solution. The obtained polyimide precursor solution is referred to In the same manner as in Example 1, coating was performed on a copper foil, and the obtained polyimide precursor film was similarly cured by heating to obtain a polyimide resin film having no pores. The results of measuring the dielectric constant of this polyimide resin film are shown in Table 1.

As can be seen from Table 1, all of the porous polyimides (No. 1-4) formed from the polyimide precursor solution synthesized using a mixed solvent of a polar solvent and an ether solvent are as shown in FIG. Fine pores having a pore size of 10 to 200 nm were evenly distributed, and the dielectric constant was 3.1 or less. On the other hand, in the porous polyimide (No. 5) formed from the polyimide precursor solution synthesized using only the polar solvent, as shown in FIG. 2, the pores are large islands and strings. The pore size was 1000 to 10,000 nm, and the pore distribution was sparse and non-uniform, so that the dielectric constant was 3.3. Although the dielectric constant is reduced as compared with non-porous polyimide (reference example), the level of the reduction is not satisfactory.
On the other hand, even if the polyimide raw material monomer and the thermally decomposable organic compound are added and blended in the presence of the thermally decomposable organic compound and the ether solvent, the polyimide raw material monomer does not dissolve, so it becomes a suspension and the polymerization reaction itself proceeds. The polyimide precursor solution could not be synthesized (No. 6).

  By using the method for producing a polyimide precursor solution of the present invention and the polyimide precursor solution of the present invention, fine pores were distributed almost evenly in the same manner as coating, film-forming and firing of non-porous polyimide. Since porous polyimide can be produced, a low-permittivity porous polyimide can be produced with the aid of non-porous polyimide production equipment, which is useful in production.

Claims (7)

Thermally decomposable organic compound comprising a diamine compound having amines bonded to both ends of the polyether and having a pyrolysis temperature of 350 ° C. or lower, an aprotic polar solvent having a boiling point of 150 to 210 ° C. at normal pressure, and normal pressure A polyimide comprising a step of reacting a tetracarboxylic dianhydride and a diamine in the presence of a mixed solvent containing an ether solvent having a boiling point of 200 to 300 ° C. in a mass ratio of 40:60 to 60:40 A method for producing a precursor solution. The ether solvent may, Ri triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether der, the protic polar solvent is N- methyl-2-pyrrolidone, The process according to dimethyl sulfoxide or γ- butyrolactone der Ru claim 1, . The compounding quantity of the said thermally decomposable organic compound with respect to 100 mass parts of total amounts of the said thermally decomposable organic compound, the said tetracarboxylic dianhydride, and the said diamine is 20-50 mass parts. Manufacturing method. The manufacturing method of the porous polyimide including the process of heating the polyimide precursor solution manufactured by the method in any one of Claims 1-3 to 350 degreeC or more, and imidating. Thermally decomposable organic compound having a thermal decomposition temperature of 350 ° C. or lower, composed of a diamine compound in which amines are bonded to both ends of tetracarboxylic dianhydride, diamine, and polyether , and non-boiling point having a boiling point of 150 to 210 ° C. at normal pressure A composition for synthesizing a polyimide precursor containing a mixed solvent in which a protic polar solvent and an ether solvent having a boiling point of 200 to 300 ° C. at normal pressure are contained in a mass ratio of 40:60 to 60:40 . A mixed solvent containing an aprotic polar solvent having a boiling point of 150 to 210 ° C. at normal pressure and an ether solvent having a boiling point of 200 to 300 ° C. at normal pressure in a mass ratio of 40:60 to 60:40 The polyimide precursor formed by the reaction of a thermally decomposable organic compound having a thermal decomposition temperature of 350 ° C. or lower comprising a diamine compound in which amines are bonded to both ends of tetracarboxylic dianhydride, diamine, and polyether is dissolved. The polyimide precursor solution. A method for producing a porous polyimide, wherein the polyimide precursor solution of claim 6 is heated at 350 ° C. or higher to be dehydrated and cyclized to obtain a porous polyimide having an average pore diameter of 0.001 to 0.5 μm .