JP2000154273A - Porous body and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a porous body excellent in heat insulation and dielectric properties by preparing a wet polyimide gel from a polyimide precursor as the starting material and drying the wet gel to obtain a dry polyimide gel. SOLUTION: This porous body comprises a dry gel of a polyimide resin and has an apparent density of 800 kg/m3 and an average pore size of 1 μm or lower. The polyimide resin preferably has a three-dimensional crosslinked structure. The porous body is produced e.g. by preparing a polyimide precursor, imidizing the precursor by a thermal or chemical treatment to give a polyimide resin, dissolving or swelling the polyimide resin in or with a solvent, preparing a wet gel from the resultant solution or swelled resin, and drying the wet gel to obtain a dry gel. Preferably, the drying step is done by supercritical drying since the gel is thereby prevented from shrinking in the step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous body having excellent heat resistance and used for a building material, a heat insulating material, an insulating material, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Polyimide resins have excellent heat resistance and insulation properties, and have been widely applied to liquid crystal alignment films, interlayer insulating films for semiconductor circuits, and the like. Taking advantage of such characteristics of the polyimide resin, it has been studied to improve the performance of the product by using the polyimide resin as a substitute for the conventional general-purpose resin. Further, it has been studied to add a new function to the polyimide resin so as to further increase the value added to the polyimide resin. As an example of the technology development of such a polyimide resin, there is an attempt to lower the dielectric constant or the thermal conductivity by making the polyimide resin porous. For example, JP-A-5-205526 and Thermal Conductivity Magazine, Vol. 18, pp. 437-443, 198
In 5 years (author DD Burley, title Thermal Conductivity of a Polyimide Foam), a technique for making a polyimide resin porous is disclosed.

The above publication discloses a method in which a block copolymer of a polyimide matrix and a thermally decomposable polymer matrix is formed, and heat treatment is performed after film formation to remove the thermally decomposable polymer and make the porous material porous. . Further, the above-mentioned article discloses a method of foaming a polyimide by foaming it with a foaming agent. Since the polyimide resin itself has high chemical resistance and a glass transition point of 300 ° C. or higher, it is a material that is difficult to mold. Accordingly, the method for making the resin porous also has advantages and disadvantages. For example, consider the case where it is used as a heat insulating material. According to the method described in the above publication, a fine porous body having a pore diameter of 1 μm or less can be obtained. However, since there is a heating step for thermal decomposition, there is a problem that it cannot be applied to a substrate having low heat resistance. Further, in the technique described in the above-mentioned paper, air bubbles of the order of several 100 μm are generated. Therefore, in order to further improve the heat insulating property, it is necessary to make the air bubbles finer. In addition to the above methods, various techniques for making a polyimide resin porous have been attempted. However, a technique for obtaining a porous body from a polyimide-based resin has not yet been established, and research is being conducted each time according to the required use. That is, a method for obtaining a porous body having a low density and a small average pore diameter from a polyimide resin is desired.

[0004]

In view of the above problems, an object of the present invention is to provide a porous body having a low density and a small average pore diameter. Another object is to provide a method for producing such a porous body. Furthermore, the present invention
An object of the present invention is to provide a semiconductor circuit having a heat insulator having excellent heat insulation properties and an insulator having excellent dielectric performance.

[0005]

In view of the above-mentioned object, the porous body of the present invention is made of a dried gel of a polyimide resin, has an apparent density of 800 kg / m ³ or less, and has an average pore size of 1 or less.
μm or less. It is made of a carbon material obtained by firing a polyimide-based dry gel and has an apparent density of 80.
0 kg / m ³ or less and an average pore diameter of 1 μm or less. Further, the present invention provides a method for producing a porous body, which comprises a gelation step of obtaining a wet gel of a polyimide resin, and a drying step of removing a solvent of the wet gel to obtain a dry gel of a polyimide resin. In addition, the method for producing a porous body according to the present invention includes a step of obtaining a solution or a swollen body of the polyimide precursor, and a step of cross-linking the solution or the swollen body of the polyimide precursor to obtain a wet gel of the polyimide precursor. A gelling step, a drying step of removing the solvent of the wet gel of the polyimide precursor to form a dry gel of the polyimide precursor, and an imidization treatment of the dry gel of the polyimide precursor to form a dry gel of the polyimide resin. Is obtained. In the method for producing a porous body of the present invention, the dried gel of the polyimide-based resin obtained in the above-described step is heated to 500 ° C. under an inert gas atmosphere.
As described above, the method includes a baking treatment step of performing a heat treatment to obtain a porous body made of a carbon material. Further, the heat insulator according to the present invention is characterized in that the porous body produced by any of the above methods is filled in a container. Here, it is preferable that the container is a gas-shielding container, and the pressure in the container is reduced. Further, in the semiconductor circuit according to the present invention, an interlayer insulating film that insulates between a plurality of electrode lines disposed on a substrate is formed using the porous body manufactured by any of the above methods. Features.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A porous body according to the present invention is a structure having continuous fine pores and made of a dried gel having a fine gel skeleton. By having such a structure,
Excellent heat insulation performance can be exhibited. Further, since the porosity is high, the insulator can have a low dielectric constant. The dry gel is obtained by drying a wet gel in which a resin containing a solvent forms a gel skeleton.
Air is present in the space (hole) from which the solvent in the dried gel has escaped, and is in a solid state. When the dry gel is an aerogel obtained by supercritically drying a wet gel, the heat insulation performance and the dielectric performance are improved, which is convenient.

A polyimide resin can be obtained by obtaining a precursor polyamic acid (hereinafter referred to as “polyimide precursor”) from a raw material and then imidizing the precursor. The polyimide resin in the present invention widely includes synthetic polymers having an imide ring structure in the main chain skeleton, such as polyamide imide and polyether imide, in addition to those generally classified as polyimide.
Each of them is excellent in heat resistance, insulation, chemical resistance and environmental resistance.

Hereinafter, the porous body of the present invention will be described. The porous body of the present invention is a dried gel made of a polyimide resin, and the polyimide resin forms a matrix skeleton of the gel, and air exists in pores. In particular, when the apparent density of the dried gel is 800 kg / m ³ or less and the average pore size is 1 μm or less, the porous body is excellent in heat insulation performance as heat insulation and dielectric performance as electric insulation. Here, the thermal conductivity of the porous body is obtained from the sum of the thermal conductivity of the skeleton of the porous body, the thermal conductivity of the gas in the pores, and the thermal conductivity due to radiation convection. The heat insulation performance can be improved by lowering the value. In the porous body of the present invention, since the skeleton of the gel blocks the flow of air, the thermal conductivity due to radiant convection is much smaller than the other two thermal conductivity. Therefore, the thermal conductivity of the gas in the holes also decreases.

In particular, the average pore diameter of the porous body of the present invention is 10
It is preferably 0 nm or less. In this case, the average pore diameter becomes equal to or less than the mean free path of the molecules in the air, the thermal conductivity of the gas in the pores sharply decreases, and the heat insulating performance of the porous body improves. The lower limit of the average pore diameter of the porous body is preferably as small as possible, but in the present invention, it may be about 1 nm. Apparent density is 500kg
/ M ³ or less. In this case, the volume of the skeleton is reduced, and the thermal conductivity of the skeleton of the porous body can be reduced. The lower limit of the apparent density of the porous body is preferably as small as possible, but in the present invention, it may be about 50 kg / m ³ . Further, the shape of the porous body of the present invention may be any shape such as a block shape, a sheet shape, a plate shape, and a powder shape.

Next, the porous body of the present invention may be made of a carbon material obtained by firing the above-mentioned dried gel of the polyimide resin. The porous body made of the carbon material retains the shape of the dried gel and has an apparent density of 80.
Particularly excellent performance is obtained when the weight is 0 kg / m ³ or less and the average pore diameter is 1 μm or less. In general, a resin obtained by carbonizing a polyimide resin by a baking treatment is used as an electrode material, activated carbon, or the like. Since the porous body made of the carbon material of the present invention is made of a low-density carbon material, it has a large specific surface area and excellent performance as a carbon material. In particular, those having a specific surface area of 400 m ² / g or more measured by the Brunauer-Emmett-Teller (BET) method have excellent performance as a carbon material. Therefore, when used as a carbon material, it is preferable that the dried gel of the polyimide resin before firing also has a BET specific surface area of 400 m ² / g or more.

Here, FIG. 1 shows a cross-sectional view of a heat insulator manufactured using the porous body of the present invention. The porous body 1 according to the present invention is used as a core material and inserted into a gas-shielding container 2. Next, after the container 2 is evacuated, the container is sealed to produce a heat insulator. By evacuating the inside of the container 2, a vacuum heat insulator having higher performance is obtained. When used for this heat insulator, the average pore diameter of the porous body is preferably 100 nm or less. Because, in this case, the heat conductivity obtained when the inside of the container filled with the conventional vacuum insulating material made of powder is evacuated to a degree of vacuum of about 0.01 Torr is the same as that obtained when the inside of the container is 10 to 10 Torr. This is because it can be obtained only by evacuating to a degree of vacuum of about 100 Torr. Such an effect is obtained depending on the shape of the porous body of the present invention. The porous body of the present invention exhibiting such excellent performance can be suitably used as an interlayer insulating film of a semiconductor circuit. FIG. 2 is a schematic cross-sectional view of one embodiment of a semiconductor circuit having an interlayer insulating film made of a porous body according to the present invention. As shown in FIG. 2, electrodes 4 made of metal or the like are wired on a semiconductor substrate 3, and an interlayer insulating layer 5 made of a porous material of the present invention is formed so as to bury the electrodes. Further, a protective layer 6 is formed on the interlayer insulating layer 5. Instead of forming the protective layer 6, an element may be further formed on an upper layer to form a multilayer circuit.

The porous body of the present invention can maintain excellent strength because the volume occupied by air is larger than the volume of the skeleton of the gel and the pores are small and dense. Therefore, in the semiconductor circuit, it can be suitably used as a dielectric having a low dielectric constant for maintaining structural strength. Therefore, when the porous body of the present invention is used for a semiconductor circuit, a printed circuit board, or the like, the dielectric loss of the insulator can be reduced, and the signal propagation speed can be increased. Further, high-frequency power loss of electric / electronic devices can be reduced. Further, when applied to a rotating machine such as a motor, power leakage at high frequencies can be reduced, and energy saving of equipment can be achieved. Next, a method for producing a porous body of the present invention will be described. The method for producing a porous body of the present invention can be roughly classified into two types. The order of the steps in each manufacturing method will be described with reference to FIG.

The methods A to C in FIG. 3 are methods for obtaining a polyimide wet gel and then drying the same to obtain a dry gel of a polyimide resin. I have. In the method A, a polyimide precursor is formed by imidizing a polyimide precursor to form a polyimide resin, and the polyimide resin is dissolved in a solvent to form a solution, or a polyimide resin having affinity and imparting wettability. After forming the swelled body, it is gelled by a crosslinking treatment or the like to obtain a polyimide wet gel. In the method B, after obtaining a solution of the polyimide precursor or a swelled body of the polyimide precursor, the solution or the swelled body is gelled, and the wet gel of the obtained polyimide precursor is imidized in a wet state. Obtain a polyimide wet gel. When imidation is performed by heat treatment in a wet state, a solvent having a high boiling point is selected. Alternatively, it is imidized by a chemical treatment. In the method C, after obtaining a solution of the polyimide precursor or a swelled body of the polyimide precursor, the solution or the swelled body is subjected to a gelling treatment, and a heat treatment for accelerating gelation is also performed. The treatment is performed simultaneously to obtain a polyimide wet gel. Comparing these methods, the method A has an advantage that the dimensional design by the method is easy because the method A does not have a process of causing gel shrinkage at the time of imidization, unlike the methods B and C. However, there is a limitation that a polyimide molecular structure that is soluble or wettable with respect to the solvent must be selected.

In the method D, a solution of the polyimide precursor or a swollen body of the polyimide precursor is obtained, and then the solution or the swollen body is gelled to obtain a wet gel of the polyimide precursor. Subsequently, the wet gel of the polyimide precursor is converted into a dry gel by a drying step and imidized to obtain a dry gel of a polyimide resin. This D method is
Since the skeleton of the porous body can be formed by the polyimide precursor which is easily soluble in the solvent, the manufacturing operation is easy. In particular, it is effective for obtaining a polyimide resin that is hardly soluble in a solvent. In this case, in order to prevent re-wetting of the obtained dried gel, the final imidization is suitably performed by a dry process of heat treatment.
When a porous body made of a carbon material is obtained, a step of heating the dried gel of the polyimide resin obtained as described above and carbonizing the dried gel is included. The carbonization process is performed in a vacuum to avoid burning the dried gel during the process.
Alternatively, the reaction is performed in an inert gas. As a particularly simple method,
The firing is preferably performed in an atmosphere of inert gas such as nitrogen or argon and in a temperature atmosphere of 500 ° C. or higher. If the temperature is 500 ° C. or higher, carbonization of the dried gel proceeds. For complete carbonization, the heating temperature is 800 ° C. or higher, preferably 1000 ° C.
It is good to be above. Further, the upper limit of the temperature may be about 1500 ° C. for the reason that the carbonization proceeds efficiently.

Further, when the obtained porous body is used as activated carbon, an activation treatment with water vapor or an inorganic salt may be performed in addition to the carbonization treatment. Next, the method for producing a porous body of the present invention will be described in detail with reference to FIG.

(1) Method A (i) Step A-1 In step A-1, first, a polyimide precursor is synthesized. The polyimide resin is usually an aromatic or aliphatic tetracarboxylic dianhydride compound (hereinafter, “compound a”).
That. ) And an aromatic or aliphatic diamine compound (hereinafter, referred to as “compound b”). Therefore, here, the compound a and the compound b are condensed to produce polyamic acid, which is a precursor of polyimide. Since this polyimide precursor is soluble in an organic solvent, it can be processed into a sheet shape or the like. In order to increase the solubility of the polyimide precursor and the polyimide resin obtained in the step A-2 in an organic solvent, the molecular structures of the compounds a and b may be selected. A compound having an ether group or a ketone group in the main chain, a compound having a bulky group such as a phenyl group, an alkyl group, or a trifluoromethyl group in a side chain, or the like is easily dissolved in a solvent. Further, by introducing a hydroxyl group, a sulfo group, a carboxyl group, an amino group, or the like as a substituent, the solubility and wettability of the polyimide precursor and the polyimide resin can be improved. Furthermore, these substituents serve as a cross-linking part when gelling.

The compound a includes, for example, pyromellitic anhydride, bisphenyltetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, 4,4'-hexafluoroisopropylidenebis (phthalic anhydride), cyclobutanetetra Examples thereof include carboxylic acid dianhydride and 2,3,5-tricarboxycyclopentylacetic acid dianhydride. These can be used alone or in any combination as long as the effects of the present invention are not impaired. Compound b includes paraphenylenediamine, metaphenylenediamine, bis (4-aminophenyl) ether, 4,4′-diaminotriphenylmethane, 2,2-bis (4-aminophenyl) -hexafluoropropane, 4,4'-diamino-4 "-hydroxytriphenylmethane, 3,3'-dihydroxy-4,
4'-diaminobiphenyl, 2,2-bis (3-amino-4-hydroxyphenyl) -hexafluoropropane, 3,5-diaminobenzoic acid and the like. These can be used alone or in any combination as long as the effects of the present invention are not impaired. In addition,
The compounds a and b as raw materials are not limited to these as long as a resin having a polyimide structure can be formed.

As the solvent used for synthesizing the polyimide precursor, N-methylpyrrolidone, N, N-dimethylacetamide, dimethylsulfoxide, hexamethylphosphoramide and the like are often used. In addition, cresol, tetrahydrofuran, dioxane, methanol, or the like is used depending on the molecular structure of the obtained polyimide. These can be used alone or arbitrarily mixed. Further, among the above, the high-boiling solvent having a boiling point of 100 ° C. or higher can be used not only for the synthesis of the polyimide precursor but also for the synthesis of the polyimide resin accompanied by the heat treatment in Step A-2.

(Ii) Step A-2 Further, the polyimide precursor can be imidized by heat treatment or chemical treatment using a dehydrated solvent such as acetic anhydride or pyridine to obtain a polyimide resin. The resulting polyimide resin has high solvent resistance,
Many solvents are hardly soluble. The imidization treatment for converting a polyimide precursor into a polyimide is roughly classified into a heat treatment and a chemical treatment. Imidation by heat treatment is 50-400 ° C
This is done by moderate heating. Preferably 100-300 ° C
Heating is performed at a temperature in the range of Since imidization is a reaction to form an imide ring by dehydration from a polyamic acid, for example, at 100 ° C. for 1 hour without rapidly increasing the heating temperature,
It is preferable to increase the temperature stepwise, for example, at 200 ° C. for 1 hour and at 300 ° C. for 1 hour. The atmosphere is preferably performed in an inert atmosphere such as nitrogen or argon in addition to air. Further, heat treatment in a vacuum may be used. For imidization by chemical treatment, for example, a polyimide precursor is immersed in a dehydrating solvent such as acetic anhydride or pyridine to form an imide ring. Since this method is a wet method, it is not suitable for use in imidizing a dried gel of a polyimide precursor as in Method D.

(Iii) Step A-3 Next, a polyimide resin solution or a swollen body is obtained. As the solvent used at this time, in addition to the above-mentioned solvent for synthesis,
Xylene, toluene, hexane, cyclohexane, 2-
Polar solvents and non-polar solvents such as butanone, methanol, ethanol, 2-methoxyethanol, dichloromethane and dichloroethane can be used alone or in any mixture. In addition, water can be added to these materials to make them wet. Furthermore, hydroxyl group in the skeleton of the resin,
When it has a hydrophilic group such as a carboxyl group or a sulfo group, only water can be used. The solution of the polyimide resin is prepared by selecting a solvent in which the resin component is dissolved and adjusting the weight of the resin component and the volume of the solvent such that the apparent density of the dried gel to be finally obtained is attained. A swelled polyimide resin is also prepared by selecting a solvent in which the resin component swells as described above, and adjusting the resin component weight and solvent volume so that the apparent density of the dried gel finally obtained is attained. I do.
The solvent at this time may be a single solvent or a mixed solvent. In the case of a single solvent, those having high affinity for the resin component but not dissolving are preferred. For example, in the case of a resin component having a hydroxyl group, water and alcohol solvents are suitable. In the case of a mixed solvent, one in which the resin component is soluble and one in which the resin component is insoluble, for example, N-methylpyrrolidone and methanol can be selected. Further, when the solvents to be mixed are not compatible with each other, an emulsion in a compatible-incompatible state may be formed when mixed with the resin component.

(Iv) Step A-4 Next, a gelation method for obtaining a wet gel from a solution or a swollen body of the polyimide resin will be described. In the case of a swollen body, gelation may occur in that state depending on the type of the solvent. In order to increase the strength of the gel, it is effective to perform crosslinking. Hydroxyl group, carboxyl group, sulfo group, amino group, etc. are introduced into the resin component,
A crosslinking agent which reacts with this is added to cause crosslinking. Any crosslinking agent may be used as long as it has a functional group that reacts with a functional group in the resin component. Examples of such a functional group include a hydroxyl group, a methylol group, an amino group, an isocyanate group, an epoxy group, an aldehyde group, a carboxyl group, a chloroformyl group, a chlorosilyl group, and an alkoxysilyl group. It is preferable that the crosslinking agent having these functional groups has two or more functional groups in order to maintain strength. Further, an acid, a base, an acid anhydride or the like can be added as a curing agent to crosslink these.

Specific crosslinking agents include, for example, diols such as ethylene glycol, 1,4-butanediol and cyclopentane-1,2-diol, polyhydric alcohols such as glycerin and pentaerythritol, phenol resins, melamine Methylol group-containing resins such as resins,
Ammonia, amines such as methylamine, polyamines such as ethylenediamine, hexamethylenediamine, phenylenediamine, diethylenetriamine, isocyanates such as tolylenediisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, phenylglycidyl ether, ethylene glycol diglycidyl ether Epoxy resins such as bisphenol A diglycidyl ether, novolak diglycidyl ether, aldehydes such as formaldehyde, acetaldehyde, furfural, benzaldehyde, glyoxal, succindialdehyde, glutardialdehyde, dialdehydes such as phthalaldehyde, maleic acid, Oxalic acid, adipic acid, suberic acid,
Secarboxylic acid, dicarboxylic acids such as phthalic acid and acid chloride compounds thereof, phthalic anhydride, acid anhydrides such as maleic anhydride, silane compounds such as tetrachlorosilane, trichlorosilane, tetramethoxysilane, tetraethoxysilane and the like Can be used. Of course, the crosslinking agent that can be used in the present invention is not limited to these.

(V) Step A-5 Next, a drying step for obtaining a dry gel from a wet gel will be described. For the drying treatment, an ordinary drying method of natural drying, heat drying, and reduced pressure drying, a supercritical drying method, and a freeze drying method can be used. If the amount of the solid component in the wet gel is reduced to reduce the density of the dry gel, the gel strength decreases. Also,
Usually, in the drying method in which the gel is simply dried, the gel shrinks due to the stress at the time of evaporation of the solvent. The crosslinking treatment described above is also effective in suppressing the drying shrinkage.
Further, by using supercritical drying or freeze drying as a drying method, it is possible to prevent gel shrinkage during drying.
In the supercritical drying method and freeze-drying method, by changing the phase state of the solvent from the liquid state, the gas-liquid interface can be eliminated and the gel can be dried without stress on the gel skeleton due to surface tension. Can prevent shrinkage of
This is a method suitable for obtaining a low-density dry gel porous material. In particular, a dried gel produced by the supercritical drying method is called aerogel.

As the solvent used for the supercritical drying, a solvent for a wet gel can be used, but it is preferable to replace the solvent with a solvent which is easy to handle in the supercritical drying. Examples of the solvent to be replaced include alcohols such as methanol, ethanol and isopropanol, which directly make the solvent a supercritical fluid, and carbon dioxide. Furthermore, the organic solvent may be replaced with a general easy-to-handle organic solvent such as acetone, isoamyl acetate or hexane which is easily eluted with these supercritical fluids. The supercritical drying conditions are performed in a pressure vessel such as an autoclave. For example, for methanol, the critical conditions are a critical pressure of 8.09 MPa and a critical temperature of 239.
The temperature is kept at 4 ° C. or higher, and the pressure is gradually released while the temperature is kept constant to perform drying. In the case of carbon dioxide, the critical pressure is set to 7.38 MPa and the critical temperature is set to 31.1 ° C. or higher. Similarly, the pressure is released from the supercritical state at a constant temperature, and drying is performed in a gas state.

(2) Method B (i) Step B-1 In the method B, first, a polyimide precursor is prepared in the same manner as in the step A-1. (ii) Step B-2 Next, a solution or a swollen body of the polyimide precursor is obtained in the same manner as in Step A-3. In this case, the same solvent as that used for obtaining the polyimide resin solution or the swollen body can be used. Here, by forming a tertiary amine such as triethylamine on the carboxylic acid portion of the polyamic acid, which is a polyimide precursor, swelling can be achieved by increasing the affinity with water. That is, in order to dissolve or swell the polyimide precursor, it is preferable to react a tertiary amine such as triethylamine with the carboxylic acid portion of the precursor polyamic acid to form a salt structure. This is because the dissolution and swelling state can be controlled by controlling the affinity of the polyimide precursor for the organic solvent or water. The solution of the polyimide precursor is prepared by selecting a solvent in which the resin component is dissolved and adjusting the weight of the resin component and the volume of the solvent such that the apparent density of the dried gel to be finally obtained is attained. In addition, the swelled polyimide precursor is also selected from the solvent in which the resin component swells as described above, and the resin component weight and the solvent volume are adjusted so that the apparent density of the dried gel finally obtained is attained. To make.

The solvent at this time may be a single solvent or a mixed solvent. In the case of a single solvent, those having high affinity for the resin component but not dissolving are preferred. For example, in the case of a resin component having a hydroxyl group, water and alcohol solvents are suitable. Furthermore, in the case of a polyimide precursor,
By forming a tertiary amine such as triethylamine on the carboxylic acid portion of the polyamic acid as the resin skeleton, the affinity with water can be increased to swell. In the case of a mixed solvent, one in which the resin component is soluble and one in which the resin component is insoluble, for example, N-methylpyrrolidone and methanol can be selected. Further, when the solvents to be mixed are not compatible with each other, an emulsion in a compatible-incompatible state may be formed when mixed with the resin component.

(Iii) Step B-3 Next, the polyimide precursor solution or swelled body is gelled in the same manner as in Step A-4 to obtain a wet gel of the polyimide precursor. (iv) Step B-4 and Step B-5 Next, the wet gel of the polyimide precursor is imidized to obtain a polyimide wet gel, and dried to obtain a polyimide dry gel. This step may be performed in the same manner as in steps A-2 and A-5.

(3) Method C and Method D The method C is the same as the method B except that imidization and gelation are simultaneously performed in the step C-3. Step C-3
In the above, the polyimide precursor may be heated in a wet state to be imidized. That is, when the polyimide precursor becomes polyimide, the polyimide precursor is insolubilized or immiscible with the solvent to form a gel. Also in this case, the strength of the gel can be reinforced by performing the crosslinking treatment. The method D is the same as the method B except that the order of the imidization step and the drying step is reversed. The dried polyimide gel obtained by any one of the methods A to D can be used as a porous body as it is, but can be further carbonized to be a carbon material. And this carbon material can also be used as a porous body. This carbonization treatment is performed by placing the dried gel in a heating furnace such as an electric furnace, an atmosphere furnace, or a dry distillation furnace and heating it. In particular, the heat treatment may be performed by heat treatment under an inert atmosphere such as nitrogen or argon at 500 ° C. or higher, which is a general upper limit of heat resistance of a polyimide resin. Above this temperature, the polyimide resin self-condenses and carbonizes.

Next, the features of the porous body of the present invention obtained by the above method will be described. According to the production method of the present invention, the apparent density is 1000 kg / m ³ or less, and the average pore diameter is 1 μm.
m or less can be obtained as a dried gel porous body made of a polyimide resin. In particular, as a porous body excellent in heat insulation performance and dielectric performance, the apparent density is 800 kg / m ^3.
Hereinafter, a porous body having an average pore diameter of 1 μm or less can be provided. Furthermore, it has excellent heat insulation performance at atmospheric pressure, an apparent density of 500 kg / m ³ or less, and an average pore diameter of 100 n.
m or less can be provided. In addition, a material having a specific surface area of 400 m ² / g or more as measured by the BET method can be provided. Generally, the thermoplastic resin has 2
Melts and softens below 00 ° C, heat resistant temperature is 200 ° C
It is as follows. Further, even with a thermosetting resin, thermal decomposition starts to progress at 200 ° C. or higher, but the heat-resistant temperature is 250 ° C.
It is about. On the other hand, it is said that the bulk polyimide resin has a continuous use durability temperature of 250 ° C. or higher, and has a heat resistance up to 400 ° C. in an unsteady state. Since the porous body of the present invention has the same heat resistance as the bulk polyimide resin that is not a porous body,
A porous body having excellent heat resistance can be provided.

A porous material having a thermal conductivity of 0.025 W / mK or less at atmospheric pressure and an average temperature of 24 ° C., which is lower than a general glass wool thermal conductivity of 0.035 W / mK. Can provide body. If the average pore diameter is 100 nm or less, a lower thermal conductivity (0.017 W / mK)
The following porous body can be provided. Further, when the porous body of the present invention is filled in a laminate film container of aluminum or stainless steel and vacuum-sealed, a heat conductivity of 0.01
A heat insulator having excellent heat insulation performance of 2 W / mK or less can be obtained. Further, a porous body having a relative dielectric constant at a frequency of 1 MHz of about 2 or less can be provided. The relative dielectric constant of the bulk polyimide resin at a frequency of 1 MHz is about 3.3, which is lower than the relative dielectric constant of tetrafluoroethylene, which has the lowest relative dielectric constant of about 2 in the bulk state. It can be said that the porous body of the present invention has excellent high-frequency characteristics.

[0031]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 In this example, the porous body of the present invention was manufactured according to Method A. 4,4′- as compound a
Hexafluoroisopropylidenebis (phthalic anhydride), compound b as 2,2-bis (3-amino-4-
(Hydroxyphenyl) -hexafluoropropane, and at room temperature, N,
A polyimide precursor was synthesized by mixing in N'-dimethylacetamide (hereinafter, referred to as "DMAc"). The solution was reprecipitated using methanol and dried.
Under a nitrogen stream of the obtained solid-state polyimide precursor,
Heat treatment was performed at 100 ° C. for 1 hour and at 200 ° C. for 2 hours to obtain imidation, thereby obtaining a polyimide resin. 10 g of the obtained polyimide is mixed with 50 cc of tetrahydrofuran (hereinafter referred to as “T
HF ". ) To obtain a polyimide solution. To this solution, 3 g of hexamethylene diisocyanate was added as a crosslinking agent, and the mixture was heated at 55 ° C. for 3 days to obtain a polyimide wet gel. This polyimide wet gel was placed in a stainless steel autoclave, and carbon dioxide was used at 50 ° C. for 9 hours.
Supercritical drying was performed at MPa to obtain an airgel of a dried polyimide gel. As described above, the apparent density of the dried gel prepared according to Method A was about 300 kg / m ³ , the average pore diameter was 40 nm, and the BET specific surface area was 600 m ² / g.
Further, even when left in a constant temperature bath at 300 ° C. for 2 hours, the apparent density and the like did not change, and the sample had excellent heat resistance. The thermal conductivity of the obtained porous body was about 0.020 W / mK at an average temperature of 24 ° C. After the porous body was inserted into an aluminum laminate film container, the internal pressure of the container was adjusted to 0.01 Torr, and then the heat insulation of the hermetically sealed heat insulator had an average temperature of about 0.008 at 24 ° C.
W / mK, indicating excellent heat insulation performance.

Example 2 In this example, the porous body of the present invention was manufactured according to Method B. Using pyromellitic anhydride as compound a, 3,3′-dihydroxy-4,4′-diaminobiphenyl as compound b, and N-methylpyrrolidone (hereinafter referred to as NMP) as a solvent,
A polyimide precursor was synthesized in the same manner as in Example 1. This solution was diluted with NMP to obtain a solution having a polyimide precursor concentration of 0.10 g / cc. To this solution was added p-phthalic chloride as a crosslinking agent in an amount to give a concentration of 0.04 g / cc, and the mixture was heated and crosslinked at 80 ° C. to obtain a wet gel of a polyimide precursor. This wet gel was heated at 160 ° C. for 5 hours to obtain a polyimide wet gel. This treatment did not show any noticeable shrinkage of the wet gel. The polyimide wet gel was immersed in an aqueous formaldehyde solution, and then diluted hydrochloric acid was added thereto to further perform a crosslinking treatment at 80 ° C. for 2 days. This crosslinked polyimide wet gel was solvent-substituted with acetone, and then dried at 50 ° C. under reduced pressure to obtain a polyimide dry gel. As described above, the apparent density of the dried gel prepared according to the method B is about 180 kg.
/ M ³ , the average pore size was about 100 nm, and the BET specific surface area was about 800 m ² / g. Further, even when left in a constant temperature bath at 300 ° C. for 2 hours, the apparent density and the like did not change, and the sample had excellent heat resistance.

Example 3 The dried gel prepared in Example 2 was carbonized by heating at 1000 ° C. for 1 hour in a nitrogen atmosphere to obtain a porous body made of a carbon material. The apparent density of carbon material from this dried gel is about 200 kg /
m ³ , average pore size about 90 nm, BET specific surface area about 80
It was 0 m ² / g. Despite some shrinkage, a low density porous structure was maintained. In addition, when the electric resistivity was measured by a tester, the electric resistivity was lower than that of the porous body before the carbonization treatment due to carbonization.

Example 4 In this example, a porous body of the present invention was obtained according to Method C. 4,4′-hexafluoroisopropylidenebis (phthalic anhydride) as compound a, and 4,4′-diamino- as compound b
4 " -hydroxytriphenylmethane, DM as solvent
A polyimide precursor was synthesized in the same manner as in Example 1 using Ac. The solution was reprecipitated in methanol and then dried to obtain a solid-state polyimide precursor. 8 g of this polyimide precursor was dissolved in 50 cc of m-cresol to obtain a polyimide precursor solution. To this solution was added 4 g of succindialdehyde as a crosslinking agent, and the mixture was heated at 160 ° C. for 1 day to simultaneously perform a crosslinking treatment and an imidization treatment to obtain a polyimide wet gel. After the solvent of the wet gel was replaced with methanol from m-cresol, it was placed in a stainless steel autoclave and supercritically dried at 250 ° C. and 10 MPa to obtain an aerogel of a polyimide dry gel. As described above, the apparent density of the dried gel prepared according to the method C is about 250 kg / m ³ , the average pore size is about 80 nm, and the BE
The T specific surface area was about 800 m ² / g. Also, 300
Even when left in a thermostat at 2 ° C. for 2 hours, the apparent density and the like were not changed, and the sample had excellent heat resistance. The thermal conductivity of the obtained porous body was about 0.3 at an average temperature of 24 ° C.
018 W / mK. Also, the porous body is inserted into a container made of an aluminum laminated film, and the pressure inside the container is set to 10 To.
The thermal conductivity of the heat-insulated body which was hermetically sealed at rr was about 0.0108 W / mK at an average temperature of 24 ° C., and had excellent heat-insulating performance.

Example 5 In this example, the porous body of the present invention was manufactured according to Method A. Pyromellitic anhydride as compound a, 3,3′-dihydroxy-4,4′-diaminobiphenyl and 4,
4′-diaminodiphenyl ether is used in a molar ratio of 1:
The mixture was mixed with NMP so that the ratio became 0.5: 0.5, and a polyimide precursor was synthesized at room temperature. The solution was reprecipitated using methanol and dried. This was dissolved again in NMP, processed into a sheet by a casting method, dried, and then subjected to an imidization treatment at 200 ° C. for 3 hours in a nitrogen atmosphere to obtain a polyimide resin sheet. This polyimide sheet is immersed in a mixed solvent of methanol / water at 50 ° C.
For 1 day to obtain a polyimide swollen body. In this state, gelation was achieved by continuing to heat for 7 days. And
The polyimide wet gel was supercritically dried using carbon dioxide to obtain a polyimide dry gel. As described above, the apparent density of the dried gel prepared according to Method A is about 500
kg / m ³ , the average pore size was about 700 nm, and the BET specific surface area was about 450 m ² / g. Next, this polyimide dry gel was carbonized in a nitrogen atmosphere at 800 ° C. to obtain a porous body made of a carbon material. The apparent density of the porous body made of this carbon material is about 800 kg / m ³ , and the average pore size is about 6
00 nm, the BET specific surface area is about 500 m ² / g,
A tester was used to confirm a decrease in electrical resistivity.

Example 6 In this example, the porous body of the present invention was manufactured according to Method D. A polyimide precursor was synthesized in the same manner as in Example 5, except that Compound a and Compound b used in Example 5 and THF / methanol as a solvent were used. Methanol was mixed with this solution, and novolak polyglycidyl ether and phthalic anhydride were added as crosslinking agents to obtain a polyimide precursor wet gel. The wet gel was dried at 60 ° C. for 3 days under a nitrogen atmosphere to obtain a dry gel of a polyimide precursor. Further, under a nitrogen atmosphere, at 150 ° C. for 1 hour, at 200 ° C. for 1 hour, 25
An imidation treatment was performed at 0 ° C. for 1 hour to obtain a dried polyimide gel. As described above, the apparent density of the dried gel prepared according to Method D was about 250 kg / m ³ , the average pore diameter was about 80 nm, and the BET specific surface area was about 600 m ² / g.

Example 7 Bisphenyltetracarboxylic anhydride as compound a and 3,3′-dihydroxy-4,4′-diaminobiphenyl as compound b at room temperature in a molar ratio of 1: 1. The mixture was mixed in DMAc to synthesize a polyimide precursor. This solution was diluted with an aqueous triethylamine solution to form a polyimide precursor triethylamine salt. The mixed solution was reprecipitated in methanol to obtain a solid polyimide precursor triethylamine salt. This polyimide precursor triethylamine salt was added to a water / ethanol solution containing tetraethoxysilane as a cross-linking agent to obtain an emulsion in which the triethylamine salt of the polyimide precursor was swollen. The emulsion was coated on a silicon substrate with copper electrode wiring. This substrate was heated at 70 ° C. for 1 hour, at 90 ° C. for 1 hour, and at 110 ° C. for 1 hour to cause crosslinking and gelation, followed by drying treatment.
Further, imidization was performed by drying at 200 ° C. for 2 hours in a vacuum to form an interlayer insulating layer of a dried polyimide gel. Further, a silica protective layer was formed thereon by a chemical vapor method to obtain a semiconductor circuit. The apparent density of the interlayer insulating layer of this semiconductor circuit was about 400 kg / m ³ , and the average pore diameter was about 100 nm. The relative dielectric constant between the electrodes of the interlayer insulating layer was about 1.4 at a frequency of 1 MHz, which was lower than the relative dielectric constant of the bulk of this polyimide resin of about 3.3. This reduced power leakage at high frequencies by about half and improved signal propagation delay by a factor of 1.5.

[0038]

As described above, according to the present invention, a porous body having excellent heat resistance, low density, and small average pore diameter can be provided. In addition, when the porous body of the present invention is used, a heat insulator having low heat conductivity and excellent heat insulation performance can be provided. Further, an insulator having a low dielectric constant and excellent in dielectric performance in a high frequency region can be provided, and a semiconductor circuit using the same can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a heat insulator using a porous body of the present invention.

FIG. 2 is a schematic cross-sectional view of a semiconductor circuit using the porous body of the present invention as an interlayer insulating film.

FIG. 3 is a diagram showing a process for producing a porous body of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Porous body 2 Gas shielding container 3 Substrate 4 Interlayer insulating film 5 Protective film

Claims (15)

[Claims] 1. A dry gel of a polyimide resin,
Apparent density is 800 kg / m ³ or less, average pore size is 1 μm
The following porous body. 2. The porous body according to claim 1, wherein the polyimide resin has a three-dimensional crosslinked structure. 3. The porous body according to claim 1, wherein the dried gel is an airgel. 4. A porous material according to claim 1, wherein the porous material is calcined and has an apparent density of 800 kg.
/ M ³ or less, and a porous body having an average pore size of 1 μm or less. 5. A method for producing a porous body, comprising: a gelation step of obtaining a wet gel of a polyimide resin; and a drying step of removing a solvent of the wet gel to obtain a dry gel of a polyimide resin. 6. The porous body according to claim 5, wherein the gelling step includes a step of obtaining a solution or a swollen body of the polyimide precursor, and a step of imidizing the polyimide precursor in the solution or the swollen body. Manufacturing method. 7. The gelling step comprises a step of imidizing a polyimide precursor to obtain a polyimide resin, a step of obtaining a solution or a swelled body of the polyimide resin, and a step of obtaining a polyimide resin in the solution or the swelled body. The method for producing a porous body according to claim 5, comprising a step of performing a crosslinking treatment. 8. The gelling step is a step of obtaining a solution or swelling of the polyimide precursor, a step of crosslinking the solution or swelling of the polyimide precursor to obtain a wet gel of the polyimide precursor, and The method for producing a porous body according to claim 5, comprising a step of imidizing a polyimide precursor in the wet gel. 9. A step of obtaining a solution or swelling of the polyimide precursor, a step of gelling the polyimide precursor to obtain a wet gel of the polyimide precursor by crosslinking the solution or swelling of the polyimide precursor, Removing the solvent of the wet gel of the body to form a dried gel of the polyimide precursor, and comprising imidizing the dried gel of the polyimide precursor to obtain a dried gel of the polyimide resin. A method for producing a porous body. 10. The drying step is a supercritical drying treatment, and the obtained dried gel is aerogel.
10. The method for producing a porous body according to any one of 9 above. 11. The dried gel of the polyimide-based resin is
The method for producing a porous body according to any one of claims 5 to 10, further comprising a baking treatment step of performing a heat treatment in an inert atmosphere at a temperature of 00C or higher to obtain a porous body made of a carbon material. 12. The apparent density of the obtained porous body is 80.
The method for producing a porous body according to claim 5, wherein the porous body has an average pore diameter of 1 μm or less and 0 kg / m ³ or less. 13. A heat insulator obtained by filling the porous body according to claim 1 in a container. 14. The container is a gas shielding container,
14. The heat insulator according to claim 13, wherein the pressure in the container is reduced. 15. A semiconductor circuit using the porous body according to claim 1 to form an interlayer insulating film for insulating between a plurality of electrode lines disposed on a substrate.