JP4338264B2 - Method for producing porous body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous body having excellent heat resistance used for building materials, heat insulating materials, insulating materials, and the like, and a method for producing the same.
[0002]
[Prior art]
Polyimide resins are excellent in heat resistance and insulation, and have a wide range of applications such as liquid crystal alignment films and interlayer insulation films for semiconductor circuits. Taking advantage of the characteristics of such polyimide resins, it has been studied to improve the performance of products using polyimide resins as an alternative to conventional general-purpose resins. In addition, a new function is added to the polyimide resin to further increase the value added to the polyimide resin.
As an example of the technical 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, in Japanese Patent Laid-Open No. 5-205526 and Thermal Conductivity magazine Vol. 18, pages 437-443, 1985 (Author DD Burley, title Thermal Conductivity of a Polyimide Foam), a porous polyimide resin is used. Techniques for quality improvement are disclosed.
[0003]
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 the film formation to remove the thermally decomposable polymer to make it porous. The paper also discloses a method of forming a foam by foaming polyimide with a foaming agent.
The polyimide resin itself has a high chemical resistance and has a glass transition point of 300 ° C. or higher, so that it is a difficult material to mold. Therefore, there are advantages and disadvantages in the method of making the resin porous. 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 paper, bubbles of the order of several hundreds of μm are generated. Therefore, in order to further improve the heat insulation, it is necessary to make the bubbles fine. In addition to the methods described above, various techniques for making a polyimide resin porous have been tried.
However, a technique for obtaining a porous body from a polyimide 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]
[Problems to be solved by the invention]
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. Moreover, it aims at providing the method of manufacturing such a porous body. Furthermore, an object of the present invention is to provide a semiconductor circuit having a heat insulator excellent in heat insulation and an insulator excellent in dielectric performance.
[0005]
[Means for Solving the Problems]
  In view of the above-mentioned object, the porous body of the present inventionManufacturing methodIsThe average pore diameter is in the range of 1 nm to 100 nm, and the apparent density is 50 kg / m. ^Three 500 kg / m or more ^Three In the following rangeFrom a dry gel of polyimide resinA method for producing a porous body comprising:
(I) Imidizing a polyimide precursor that is a polyamide solution to obtain the polyimide resin, an polyimide resin obtained in the imidization process, a solvent in which the polyimide resin is dissolved, From the dissolution or swelling step of obtaining the polyimide resin solution or swelling body, and adding the crosslinking agent to the polyimide resin solution or swelling body obtained in the dissolution or swelling step and heating, Drying to obtain a dried gel of the polyimide resin by crosslinking and gelling, drying the gelled step of obtaining the polyimide resin wet gel, and drying the polyimide resin wet gel obtained in the gelation step Including a process,
(Ii) It is obtained by a dissolution or swelling step of obtaining a solution or swelling body of the polyimide precursor from a polyimide precursor that is a polyamide solution and a solvent in which the polyimide resin is dissolved, and the dissolution or swelling step. The polyimide precursor solution or swollen body was added with a cross-linking material and heated to perform cross-linking and gelation to obtain a wet gel of the polyimide precursor, and obtained in the gelation step Imidizing the polyimide precursor wet gel to obtain the polyimide resin wet gel, and drying the polyimide resin wet gel obtained in the imidization step, the polyimide resin Or a drying step to obtain a dry gel of
(Iii) It is obtained by a dissolution or swelling step of obtaining a solution or swelling body of the polyimide precursor from a polyimide precursor that is a polyamide solution and a solvent in which the polyimide resin is dissolved, and the dissolution or swelling step. The polyimide precursor solution or swollen body was added with a cross-linking material and heated to perform cross-linking and gelation to obtain a wet gel of the polyimide precursor, and obtained in the gelation step Drying the polyimide resin by drying the polyimide precursor wet gel to obtain the polyimide precursor dry gel and imidizing the polyimide precursor dry gel obtained in the drying step. Imidization step to obtain a gel,It is characterized by that.
  The method for producing a porous body according to the present invention is a method for obtaining a porous body made of a carbon material by heat-treating the dried gel of the polyimide resin obtained in the above step at 500 ° C. or higher in an inert gas atmosphere. It includes a processing step.
  In addition, the heat insulator according to the present invention is characterized in that the container is filled with the porous body produced by any one of the methods described above.
  Here, it is preferable that the container is a gas shielding container and the inside of the container is decompressed.
  Furthermore, in the semiconductor circuit according to the present invention, an interlayer insulating film that insulates a plurality of electrode lines arranged on the substrate is formed using the porous body manufactured by any of the above methods. Features.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The porous body according to the present invention is a structure having a continuous fine pore and comprising a dry gel having a fine gel skeleton. By having such a structure, excellent heat insulation performance can be exhibited. Further, since the porosity is high, an insulator having a low dielectric constant can be obtained.
The dry gel is obtained by drying a wet gel in which a resin containing a solvent forms a gel skeleton. And air exists in the space (hole) from which the solvent in the dried gel was removed, and it is in a solid state. Moreover, when the dried gel is an airgel obtained by supercritically drying a wet gel, it is advantageous in that the heat insulating performance and the dielectric performance are improved.
[0007]
The polyimide resin can be obtained by obtaining a polyamic acid as a precursor (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 polyamideimide and polyetherimide, in addition to those generally classified as polyimide. And all are excellent in heat resistance, insulation, chemical resistance, and environmental resistance.
[0008]
Below, the porous body of this invention is demonstrated.
The porous body of the present invention is a dry gel made of a polyimide resin, and the polyimide resin forms a matrix skeleton of the gel, and air exists in the pores. In particular, the apparent density of the dried gel is 800 kg / m^ThreeHereinafter, when the average pore diameter is 1 μm or less, the porous body is excellent in heat insulation performance that is heat insulation and dielectric performance that is electrical 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 radiant convection. It is possible to improve the heat insulation performance by lowering. In the porous body of the present invention, since the gel skeleton blocks the air flow, the thermal conductivity by radiant convection is extremely small compared to the other two thermal conductivities. Therefore, the thermal conductivity of the gas in the holes is also reduced.
[0009]
In particular, the average pore size of the porous body of the present invention is preferably 100 nm or less. In this case, the average pore diameter becomes equal to or less than the average free path of the molecules in the air, the thermal conductivity of the gas in the pores rapidly decreases, and the heat insulating performance of the porous body is improved. In addition, although the minimum of the average hole diameter of a porous body is so preferable that it is small, in this invention, what is necessary is just about 1 nm.
Apparent density is 500kg / m^ThreeIt is preferable that: In this case, the volume of the skeleton is reduced, and the thermal conductivity of the skeleton portion of the porous body can be reduced. In addition, although the lower limit of the apparent density of the porous body is preferably as small as possible, in the present invention, 50 kg / m^ThreeAny degree is acceptable.
In addition, 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.
[0010]
Next, the porous body of the present invention may be made of a carbon material obtained by firing the above-described polyimide resin dry gel. The porous body made of this carbon material retains the shape of the dried gel and has an apparent density of 800 kg / m.^ThreeHereinafter, when the average pore diameter is 1 μm or less, particularly excellent performance is obtained.
In general, a carbonized polyimide resin is used for electrode materials, activated carbon, and the like. Since the porous body made of the carbon material of the present invention is composed of a low-density carbon material, the specific surface area is large and the performance as a carbon material is also excellent.
In particular, the specific surface area measured by Brunauer Emmett Teller (BET) method is 400 m.²/ G or more has excellent performance as a carbon material. Therefore, when used as a carbon material, the dry gel of the polyimide resin before firing also has a BET specific surface area of 400 m.²/ G or more is preferable.
[0011]
Here, in FIG. 1, sectional drawing of the heat insulating body produced using the porous body of this invention is shown. The porous body 1 according to the present invention is used as a core material and is 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 higher performance vacuum insulator is obtained.
When used for this heat insulator, the average pore diameter of the porous body is preferably 100 nm or less. This is because, in this case, a thermal conductivity comparable to that obtained when the inside of a container filled with a vacuum heat insulating material made of conventional powder is exhausted to a degree of vacuum of about 0.01 Torr, This is because it can be obtained only by exhausting to a vacuum degree 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 that exhibits such excellent performance can be suitably used as an interlayer insulating film of a semiconductor circuit. FIG. 2 shows a schematic cross-sectional view of an embodiment of a semiconductor circuit having an interlayer insulating film made of a porous body of the present invention. As shown in FIG. 2, an electrode 4 made of metal or the like is wired on a semiconductor substrate 3, and an interlayer insulating layer 5 made of a porous body of the present invention is formed so as to embed between the electrodes. Further, a protective layer 6 is formed on the interlayer insulating layer 5. A circuit having a multilayer structure may be formed by forming an element in an upper layer without forming the protective layer 6.
[0012]
Since the porous body of the present invention has a large volume occupied by air with respect to the volume of the skeleton of the gel, and the pores are small and dense, it can maintain excellent strength. Therefore, in the semiconductor circuit, it can be suitably used as a dielectric having a low dielectric constant that maintains the structural strength.
Therefore, when the porous body of the present invention is used for a semiconductor circuit, a printed board or the like, the dielectric loss of the insulator can be reduced, and the signal propagation speed can be increased. Moreover, the high frequency power loss of an electric / electronic device can be reduced. Furthermore, when applied to a rotating machine such as a motor, power leakage at a high frequency can be reduced, and energy saving of the device can be achieved.
Below, the manufacturing method of the porous body of this invention is demonstrated. The method for producing the porous body of the present invention can be roughly classified into two types. The order of steps in each manufacturing method will be described with reference to FIG.
[0013]
The method A to method C in FIG. 3 is a method of obtaining a polyimide wet gel and then drying it to obtain a polyimide-based resin dry gel, which is shown separately depending on the process for producing the polyimide wet gel.
In the method A, a polyimide resin is formed by imidizing a polyimide precursor, and the polyimide resin is dissolved in a solvent to form a solution, or the polyimide resin that has wettability with affinity is given. After making it into a swollen body, it is gelled by a crosslinking treatment or the like to obtain a polyimide wet gel.
In the method B, after obtaining a polyimide precursor solution or a polyimide precursor swollen body, the solution or swollen body is gelled, and the resulting polyimide precursor wet gel is imidized in a wet state. A polyimide wet gel is obtained. When imidizing by heat treatment in a wet state, a solvent having a high boiling point is selected. Alternatively, it is imidized by chemical treatment.
In the method C, after obtaining a polyimide precursor solution or a polyimide precursor swollen body, the solution or swollen body is subjected to a gelation treatment, and a heat treatment for promoting gelation is performed in combination. The treatment is performed simultaneously to obtain a polyimide wet gel.
Comparing these methods, the method A has the advantage that, unlike the methods B and C, there is no process in which gel shrinkage occurs during imidization, and therefore the dimensional design by the construction method is easy. However, there is a limitation that a polyimide molecular structure that is soluble or wettable in the solvent must be selected.
[0014]
In the method D, a polyimide precursor solution or a polyimide precursor swell is obtained, and then the solution or swell is gelled to obtain a polyimide precursor wet gel. Subsequently, the wet gel of the polyimide precursor is converted into a dry gel by a drying process and imidized to obtain a dry gel of a polyimide resin.
This method D is characterized in that the manufacturing process is easy because the skeleton of the porous body can be formed by a polyimide precursor that is easily dissolved in a solvent. In particular, it is effective when obtaining a polyimide resin that is hardly soluble in a solvent. In this case, in order to prevent rewetting of the obtained dried gel, it is suitable that the final imidization is performed by a dry process of heat treatment.
Moreover, when obtaining the porous body which consists of carbon materials, the process of heating and carbonizing the dry gel of the polyimide-type resin obtained as mentioned above is included. The carbonization treatment is performed in a vacuum or in an inert gas in order to avoid burning the dry gel during the treatment.
As a particularly simple method, it is preferable to perform firing in an inert atmosphere such as nitrogen or argon in a temperature atmosphere of 500 ° C. or higher. If it is 500 degreeC or more, carbonization of a dry gel will advance. In order to completely carbonize, the heating temperature is 800 ° C. or higher, preferably 1000 ° C. or higher. Moreover, the upper limit of temperature should just be about 1500 degreeC from the reason that carbonization advances efficiently.
[0015]
Furthermore, when using the obtained porous body as activated carbon, in addition to this carbonization treatment, activation treatment with water vapor or inorganic salt may be performed.
Next, the manufacturing method of the porous body of this invention is demonstrated in detail, referring FIG.
[0016]
(1) About Method A
(i) Process 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 referred to as “compound a”) and an aromatic or aliphatic diamine compound (hereinafter referred to as “compound b”). It is synthesized by the condensation reaction. Therefore, here, the compound a and the compound b are condensed to produce a polyamic acid which is a polyimide precursor. Since this polyimide precursor is soluble in an organic solvent, it can be processed into a sheet-like shape.
In order to increase the solubility of the polyimide precursor and the polyimide resin obtained in Step A-2 in an organic solvent, the molecular structures of the compound a and the compound 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 the side chain is easily dissolved in the solvent.
Moreover, the solubility and wettability of a polyimide precursor and a polyimide-type resin can be improved by introduce | transducing a hydroxyl group, a sulfo group, a carboxyl group, an amino group etc. as a substituent. Furthermore, these substituents serve as a crosslinking moiety when gelling.
[0017]
Examples of the compound a include pyromellitic anhydride, bisphenyltetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4′-hexafluoroisopropylidenebis (phthalic anhydride), cyclobutanetetracarboxylic acid Anhydrides, 2,3,5-tricarboxycyclopentyl acetic acid dianhydride, and the like. These may be used alone or in any combination as long as the effects of the present invention are not impaired.
As compound b, 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, etc. These may be used alone or in any combination as long as the effects of the present invention are not impaired.
The raw material compound a and compound b are not limited to these as long as a polyimide resin can be formed.
[0018]
As a solvent used for the synthesis of the polyimide precursor, N-methylpyrrolidone, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide and the like are often used. In addition, cresol, tetrahydrofuran, dioxane, methanol and the like are used depending on the molecular structure of the obtained polyimide. These can be used alone or in any desired mixture.
Furthermore, in the above, the high boiling point solvent having a boiling point of 100 ° C. or more 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 the step A-2.
[0019]
(ii) Step A-2
Furthermore, this polyimide precursor can be imidized by a heat treatment or a chemical treatment using a dehydrated solvent such as acetic anhydride or pyridine to obtain a polyimide resin. The obtained polyimide resin has a high solvent resistance, and many of them are hardly soluble in the solvent.
The imidation process from polyimide precursor to polyimide is roughly classified into heat treatment and chemical treatment.
Imidization by heat treatment is performed by heating at about 50 to 400 ° C. Heating is preferably performed at a temperature in the range of 100 to 300 ° C. Since imidation is a reaction in which an imide ring is formed by dehydrating from polyamic acid, for example, 100 ° C. for 1 hour, 200 ° C. for 1 hour, and 300 ° C. for 1 hour without rapidly increasing the heating temperature. It is better to increase the temperature stepwise. In addition to air, the atmosphere is preferably an inert atmosphere such as nitrogen or argon. Further, heat treatment in a vacuum may be used.
As 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. In addition, since this method is wet, it is not suitable for utilizing for imidation of the dry gel of a polyimide precursor like the D method.
[0020]
(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 synthesis solvent, polar solvents and nonpolar solvents such as xylene, toluene, hexane, cyclohexane, 2-butanone, methanol, ethanol, 2-methoxyethanol, dichloromethane, dichloroethane and the like are used. These can be used alone or in any mixture. Moreover, water can be added to these to wet them. Furthermore, when the resin skeleton has a hydrophilic group such as a hydroxyl group, 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 resin component weight and the solvent volume so that the apparent density of the dried gel to be finally obtained is obtained.
The swelling body of the polyimide resin is also prepared by selecting the 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 dry gel to be finally obtained is obtained. To do.
The solvent at this time may be not only a single solvent but also a mixed solvent. In the case of a single solvent, those that have high affinity with the resin component but do not dissolve are preferred. For example, in the case of a resin component having a hydroxyl group, water or an alcohol solvent is suitable.
In the case of a mixed solvent, those in which the resin component is dissolved and those 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.
[0021]
(iv) Step A-4
Next, a gelation method for obtaining a wet gel from a polyimide resin solution or swollen body will be described.
In the case of a swollen body, depending on the type of solvent, it may gel in that state. In order to increase the strength of the gel, it is effective to perform crosslinking. A hydroxyl group, a carboxyl group, a sulfo group, an amino group or the like is introduced into the resin component, and a crosslinking agent that reacts with the hydroxyl group, carboxyl group, sulfo group or amino group 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. As such a functional group, for example, 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, an alkoxysilyl group, and the like can be used. The crosslinking agent having these functional groups preferably has two or more functional groups in order to maintain strength. In addition, an acid, a base, an acid anhydride, or the like can be added as a curing agent in order to crosslink these.
[0022]
Specific examples of the crosslinking agent include diols such as ethylene glycol, 1,4-butanediol, and cyclopentane-1,2-diol, polyhydric alcohols such as glycerin and pentaerythritol, phenol resins, and melamine resins. Methylol group-containing resins, amines such as ammonia and methylamine, polyvalent amines such as ethylenediamine, hexamethylenediamine, phenylenediamine and diethylenetriamine, isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and hexamethylene diisocyanate, phenylglycidyl ether , Epoxy resins such as ethylene glycol diglycidyl ether, bisphenol A diglycidyl ether, novolak diglycidyl ether, formaldehyde Aldehydes such as acetaldehyde, furfural and benzaldehyde, dialdehydes such as glyoxal, succindialdehyde, glutardialdehyde and phthalaldehyde, dicarboxylic acids such as maleic acid, oxalic acid, adipic acid, suberic acid, sebacic acid and phthalic acid And acid chloride compounds thereof, acid anhydrides such as phthalic anhydride and maleic anhydride, silane compounds such as tetrachlorosilane, trichlorosilane, tetramethoxysilane and tetraethoxysilane, and silane oligomers condensed with them be able to. Of course, the crosslinking agent that can be used in the present invention is not limited to these.
[0023]
(v) Step A-5
Next, a drying process for obtaining a dried gel from the wet gel will be described. For the drying treatment, a normal drying method such as natural drying, heat drying or reduced pressure drying, a supercritical drying method, or a freeze drying method can be used.
If the amount of the solid component in the wet gel is reduced in order to reduce the density of the dry gel, the gel strength is lowered. In general, in a drying method in which the gel is simply dried, the gel contracts due to stress during evaporation of the solvent. The aforementioned crosslinking treatment is also effective in suppressing this drying shrinkage. Moreover, the shrinkage | contraction of the gel at the time of drying can be prevented by using supercritical drying or freeze-drying as a drying method.
In the supercritical drying method or freeze-drying method, by changing the phase of the solvent from the liquid state, the gas-liquid interface can be eliminated and the gel skeleton can be dried without stress on the surface of the gel. This is a method suitable for obtaining a porous body of a low density dry gel. In particular, a dry gel made by a supercritical drying method is called an aerogel.
[0024]
The solvent used for the supercritical drying can be a wet gel solvent, but is preferably replaced with a solvent that is easy to handle in the supercritical drying.
Examples of the solvent to be substituted include methanol, ethanol such as ethanol and isopropanol, and carbon dioxide which directly make the solvent a supercritical fluid. Furthermore, it may be replaced with a common organic solvent such as acetone, isoamyl acetate or hexane which is easily eluted with these supercritical fluids.
Supercritical drying conditions are carried out in a pressure vessel such as an autoclave. For example, in methanol, the critical conditions are a critical pressure of 8.09 MPa and a critical temperature of 239.4 ° C. or higher, and the pressure is gradually released at a constant temperature. And dry. In the case of carbon dioxide, the critical pressure is 7.38 MPa and the critical temperature is 31.1 ° C. or higher. Similarly, the pressure is released from the supercritical state at a constant temperature, and the gas is dried.
[0025]
(2) About Method B
(i) Process B-1
In Method B, a polyimide precursor is first prepared in the same manner as in Step A-1. (ii) Step B-2
Next, a solution or swollen polyimide precursor is obtained in the same manner as in Step A-3. In this case, the same solvent as the solvent used to obtain a polyimide resin solution or swollen body can be used.
Here, by forming a tertiary amine such as triethylamine in the carboxylic acid portion of the polyamic acid, which is a polyimide precursor, the affinity with water can be increased and swollen. That is, in order to dissolve or swell the polyimide precursor, a tertiary amine such as triethylamine is preferably reacted with the carboxylic acid portion of the polyamic acid as a precursor to form a salt structure. This is because the affinity of the polyimide precursor to the organic solvent or water can be controlled to control the dissolved and swollen state.
The solution of the polyimide precursor is prepared by selecting a solvent in which the resin component is dissolved and adjusting the resin component weight and the solvent volume so that the apparent density of the dried gel to be finally obtained is obtained. Also, for the swollen body of the polyimide precursor, select the solvent in which the resin component swells as described above, and adjust the resin component weight and solvent volume so that the apparent density of the dry gel to be finally obtained is adjusted. To make.
[0026]
The solvent at this time may be not only a single solvent but also a mixed solvent. In the case of a single solvent, those that have high affinity with the resin component but do not dissolve are preferred. For example, in the case of a resin component having a hydroxyl group, water or an alcohol solvent is suitable. Furthermore, in the case of a polyimide precursor, the affinity with water can be increased and swollen by forming a tertiary amine such as triethylamine in the carboxylic acid portion of the polyamic acid that is the resin skeleton.
In the case of a mixed solvent, those in which the resin component is dissolved and those 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.
[0027]
(iii) Step B-3
Next, the solution or swollen body of the polyimide precursor is gelled in the same manner as in Step A-4 to obtain a wet polyimide gel precursor.
(iv) Step B-4 and Step B-5
Next, the polyimide precursor wet gel 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 the steps A-2 and A-5.
[0028]
(3) About Method C and Method D
Method C is the same as Method B except that imidization and gelation are simultaneously performed in Step C-3.
In step C-3, the polyimide precursor may be imidized by heating in a wet state. That is, when the polyimide precursor becomes polyimide, it is insolubilized or incompatible 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.
As described above, the polyimide dry gel obtained in any one of the methods A to D can be used as a porous material as it is, but it can be further carbonized to obtain 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 atmospheric furnace, or a carbonization furnace and heating it. In particular, the heat treatment may be performed by heat treatment at 500 ° C. or more which is a general upper limit of heat resistance of a polyimide resin in an inert atmosphere such as nitrogen or argon. Above this temperature, the polyimide resin self-condenses and carbonizes.
[0029]
Next, the characteristics 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.^ThreeHereinafter, a porous body of a dry gel made of a polyimide resin having an average pore diameter of 1 μm or less can be obtained.
In particular, as a porous body excellent in heat insulation performance and dielectric performance, the apparent density is 800 kg / m.^ThreeHereinafter, a porous body having an average pore diameter of 1 μm or less can be provided. Furthermore, the apparent density with excellent heat insulation performance at atmospheric pressure is 500 kg / m^ThreeHereinafter, a porous body having an average pore diameter of 100 nm or less can be provided. The specific surface area is 400 m as measured by the BET method.²/ G or more can be provided.
Generally, since a thermoplastic resin melts and softens at 200 ° C. or lower, the heat resistant temperature is 200 ° C. or lower. Further, even with a thermosetting resin, thermal decomposition starts to proceed at 200 ° C. or higher, but the heat resistant temperature is about 250 ° C.
On the other hand, the bulk polyimide resin has a continuous use durability temperature of 250 ° C. or higher, and is said to have heat resistance up to 400 ° C. unsteadyly.
Since the porous body of the present invention has a heat resistance comparable to that of a bulk polyimide resin that is not a porous body, it can provide a porous body having excellent heat resistance.
[0030]
In addition, a porous body having a thermal conductivity at an average temperature of 24 ° C. under atmospheric pressure of 0.025 W / mK or lower and a value lower than a general glass wool thermal conductivity of 0.035 W / mK is provided. it can. When the average pore diameter is 100 nm or less, a porous body having a lower thermal conductivity (0.017 W / mK or less) can be provided.
Furthermore, when a porous film of the present invention is filled in an aluminum or stainless steel laminate film container and vacuum sealed, a heat insulator having excellent heat insulation performance with a thermal conductivity of 0.012 W / mK or less can be obtained. .
In addition, a porous body having a relative dielectric constant of about 2 or less at a frequency of 1 MHz can be provided. Since the relative dielectric constant of bulk polyimide resin at a frequency of 1 MHz is about 3.3, a value lower than the relative dielectric constant of about 2 of tetrafluoroethylene having the lowest relative dielectric constant can be obtained in the bulk material. It can be said that the porous body of the present invention has excellent high-frequency characteristics.
[0031]
【Example】
Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.
Example 1
In this example, the porous body of the present invention was produced according to Method A.
4,4′-hexafluoroisopropylidenebis (phthalic anhydride) is used as compound a, and 2,2-bis (3-amino-4-hydroxyphenyl) -hexafluoropropane is used as compound b. A polyimide precursor was synthesized by mixing in N, N′-dimethylacetamide (hereinafter referred to as “DMAc”) so that the ratio was 1: 1.
This solution was reprecipitated with methanol and dried. The obtained polyimide precursor in a solid state was heat-treated at 100 ° C. for 1 hour and at 200 ° C. for 2 hours in a nitrogen stream to obtain a polyimide resin.
10 g of the obtained polyimide was dissolved in 50 cc of tetrahydrofuran (hereinafter referred to as “THF”) to obtain a polyimide solution. To this solution, 3 g of hexamethylene diisocyanate was added as a crosslinking agent and 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 supercritically dried at 50 ° C. and 9 MPa using carbon dioxide to obtain an airgel of polyimide dry gel.
As described above, the apparent density of the dried gel prepared according to the method A is about 300 kg / m.^ThreeThe average pore size is 40 nm and the BET specific surface area is 600 m.²/ G. Moreover, even if it was left in a thermostat bath at 300 ° C. for 2 hours, the apparent density was not changed, and it had excellent heat resistance.
The obtained porous body had a thermal conductivity of about 0.020 W / mK at an average temperature of 24 ° C. In addition, the thermal conductivity of the heat insulator manufactured by inserting the porous body into an aluminum laminate film container and setting the container internal pressure to 0.01 Torr and then sealing it is about 0.008 W / mK at an average temperature of 24 ° C. It showed excellent heat insulation performance.
[0032]
Example 2
In this example, the porous body of the present invention was produced according to Method B.
A polyimide precursor was prepared in the same manner as in Example 1, using pyromellitic anhydride as the compound a, 3,3′-dihydroxy-4,4′-diaminobiphenyl as the compound b, and N-methylpyrrolidone (hereinafter referred to as NMP) as the solvent. The body was synthesized. This solution was diluted with NMP to obtain a solution having a polyimide precursor concentration of 0.10 g / cc.
To this solution, p-phthalic acid chloride as a crosslinking agent was added in an amount to a concentration of 0.04 g / cc, and heated and cross-linked at 80 ° C. to obtain a polyimide precursor wet gel.
This wet gel was heat-treated at 160 ° C. for 5 hours to obtain a polyimide wet gel. This treatment did not cause significant wet gel shrinkage.
This polyimide wet gel was soaked in an aqueous formaldehyde solution, and then diluted hydrochloric acid was added, followed by further crosslinking treatment at 80 ° C. for 2 days. The 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.^ThreeThe average pore diameter is about 100 nm and the BET specific surface area is about 800 m.²/ G. Moreover, even if it was left in a thermostat bath at 300 ° C. for 2 hours, the apparent density was not changed, and it had excellent heat resistance.
[0033]
Example 3
The polyimide dry gel prepared in Example 2 was heated at 1000 ° C. for 1 hour in a nitrogen atmosphere to perform carbonization treatment to obtain a porous body made of a carbon material.
The apparent density of the carbon material from this dried gel is about 200 kg / m.^ThreeThe average pore diameter is about 90 nm and the BET specific surface area is about 800 m.²/ G. Although it contracted slightly, it maintained a low-density porous structure. Moreover, when the electrical resistivity was measured with a tester, it was carbonized, and thus the electrical resistivity was lower than that of the porous body before carbonization.
[0034]
Example 4
In this example, the porous body of the present invention was obtained according to the C method.
4,4'-hexafluoroisopropylidenebis (phthalic anhydride) as compound a, 4,4'-diamino- as compound b4 "A polyimide precursor was synthesized in the same manner as in Example 1, using -hydroxytriphenylmethane and DMAc as the solvent. This 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, 4 g of succindialdehyde was added as a cross-linking agent and heated at 160 ° C. for 1 day to perform cross-linking treatment and imidization treatment simultaneously 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 a polyimide dry gel airgel.
As described above, the apparent density of the dried gel prepared according to the C method is about 250 kg / m.^ThreeThe average pore diameter is about 80 nm and the BET specific surface area is about 800 m.²/ G. Moreover, even if it was left in a thermostat bath at 300 ° C. for 2 hours, the apparent density was not changed, and it had excellent heat resistance.
The obtained porous body had a thermal conductivity of about 0.018 W / mK at an average temperature of 24 ° C. In addition, the thermal conductivity of a heat insulating body produced by inserting a porous body into an aluminum laminate film container and sealing the container with an internal pressure of 10 Torr is about 0.0108 W / mK at an average temperature of 24 ° C., which is excellent. It had a good thermal insulation performance.
[0035]
《Reference example》
  BookreferenceIn the example, method ALikeA porous body was produced.
  Pyromellitic anhydride as compound a and 3,3′-dihydroxy-4,4′-diaminobiphenyl and 4,4′-diaminodiphenyl ether as compound b so that the molar ratio is 1: 0.5: 0.5 The polyimide precursor was synthesized at room temperature. This solution was reprecipitated with methanol and dried. This was dissolved again in NMP, processed into a sheet by a casting method, dried, and then imidized at 200 ° C. for 3 hours in a nitrogen atmosphere to obtain a polyimide resin sheet.
  This polyimide sheet was immersed in a mixed solvent of methanol / water and heated at 50 ° C. for 1 day to obtain a polyimide swollen body. In this state, gelation occurred by further heating for 7 days. The polyimide wet gel was supercritically dried using carbon dioxide to obtain a polyimide dry gel.
  As mentioned above, method ALikeThe apparent density of the prepared dried gel is about 500 kg / m.^ThreeThe average pore diameter is about 700 nm and the BET specific surface area is 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.^ThreeThe average pore size is about 600 nm and the BET specific surface area is about 500 m.²/ G, and a decrease in electrical resistivity was confirmed by a tester.
[0036]
Example 6
In this example, the porous body of the present invention was produced according to the D method.
A polyimide precursor was synthesized in the same manner as in Example 5 using Compound a and Compound b used in Example 5 and THF / methanol as a solvent. Methanol was mixed with this solution, and novolak polyglycidyl ether and phthalic anhydride were added as a crosslinking agent 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 polyimide precursor dry gel. Furthermore, imidation treatment was performed at 150 ° C. for 1 hour, 200 ° C. for 1 hour, and 250 ° C. for 1 hour in a nitrogen atmosphere to obtain a polyimide dry gel.
As described above, the apparent density of the dried gel prepared according to the D method is about 250 kg / m.^ThreeThe average pore diameter is about 80 nm and the BET specific surface area is about 600 m.²/ G.
[0037]
Example 7
Bisphenyltetracarboxylic anhydride as compound a and 3,3′-dihydroxy-4,4′-diaminobiphenyl as compound b are mixed in DMAc so as to have a molar ratio of 1: 1 at room temperature. The body was synthesized. This solution was diluted with an aqueous triethylamine solution to form a polyimide precursor triethylamine salt. This 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 crosslinking agent to obtain an emulsion in which the triethylamine salt of the polyimide precursor was swollen.
This emulsion was coated on a silicon substrate wired with a copper electrode. This substrate was heated at 70 ° C. for 1 hour, 90 ° C. for 1 hour, and 110 ° C. for 1 hour to crosslink to gel, and then dried. Furthermore, imidation was performed by drying at 200 ° C. for 2 hours in a vacuum to form an interlayer insulating layer of polyimide dry gel. Further, a silica protective layer was formed thereon by a chemical vapor deposition method to obtain a semiconductor circuit.
The apparent density of the interlayer insulating layer of this semiconductor circuit is about 400 kg / m^ThreeThe 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, and a low value was obtained with respect to the bulk relative dielectric constant of about 3.3 of this polyimide resin. As a result, power leakage at high frequencies can be reduced by about half, and the signal propagation delay has been improved by a factor of 1.5.
[0038]
【The invention's effect】
As described above, according to the present invention, a porous body having excellent heat resistance, low density and a small average pore diameter can be provided. Moreover, when the porous body of the present invention is used, it is possible to provide a heat insulator having low heat conductivity and excellent heat insulating performance. Furthermore, an insulator having a low dielectric constant and excellent dielectric performance in a high frequency region can be provided, and a semiconductor circuit using the insulator 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 production process of a porous body of the present invention.
[Explanation of symbols]
1 Porous material
2 Gas shielding container
3 Substrate
4 Interlayer insulation film
5 Protective film

Claims (10)

The average pore diameter is in the range of 1 nm to 100 nm, and the apparent density is 50 kg / m. ^Three 500 kg / m or more ^Three A method for producing a porous body comprising a dry gel of a polyimide resin in the following range,
An imidization step of obtaining the polyimide resin by imidizing a polyimide precursor which is a polyamide solution;
From the polyimide resin obtained in the imidization step and the solvent in which the polyimide resin is dissolved, a solution or swelling step of obtaining a solution or swelling body of the polyimide resin,
A gelling step of adding a cross-linking material to the solution or swollen body of the polyimide resin obtained in the dissolving or swelling step and heating to obtain a wet gel of the polyimide resin; ,
A drying step of drying the wet gel of the polyimide resin obtained in the gelation step to obtain a dry gel of the polyimide resin. The average pore diameter is in the range of 1 nm to 100 nm, and the apparent density is 50 kg / m. ^Three 500 kg / m or more ^Three A method for producing a porous body comprising a dry gel of a polyimide resin in the following range,
A dissolving or swelling step of obtaining a solution or swelling body of the polyimide precursor from a polyimide precursor that is a polyamide solution and a solvent in which the polyimide resin is dissolved;
A gelling step of adding a cross-linking material to the solution or swollen body of the polyimide precursor obtained in the dissolving or swelling step and heating to cross-link and gelate to obtain a wet gel of the polyimide precursor; ,
An imidization step of obtaining a wet gel of the polyimide resin by imidizing a wet gel of the polyimide precursor obtained in the gelation step;
A drying step of drying the polyimide resin wet gel obtained in the imidization step to obtain a dry gel of the polyimide resin. The manufacturing method of the porous body of Claim 2 which performs the said gelatinization process and the said imidation process simultaneously. The average pore diameter is in the range of 1 nm to 100 nm, and the apparent density is 50 kg / m. ^Three 500 kg / m or more ^Three A method for producing a porous body comprising a dry gel of a polyimide resin in the following range,
A dissolving or swelling step of obtaining a solution or swelling body of the polyimide precursor from a polyimide precursor that is a polyamide solution and a solvent in which the polyimide resin is dissolved;
A gelling step of adding a cross-linking material to the solution or swollen body of the polyimide precursor obtained in the dissolving or swelling step and heating to cross-link and gelate to obtain a wet gel of the polyimide precursor; ,
Drying the polyimide precursor wet gel obtained in the gelation step to obtain the polyimide precursor dry gel; and
The imidization process of obtaining the dry gel of the said polyimide-type resin by imidating the dry gel of the polyimide precursor obtained at the said drying process. The method for producing a porous body according to any one of claims 1 to 4, wherein the dry gel is an airgel. The method for producing a porous body according to any one of claims 1 to 4 , wherein the drying step is a supercritical drying treatment, and the obtained dried gel is an airgel. The production of the porous body according to any one of claims 1 to 6 , further comprising a baking treatment step of obtaining a porous body made of a carbon material by heat-treating the dried gel of the polyimide resin in an inert atmosphere of 500 ° C or higher. Method. A heat insulator formed by filling a porous body produced by the method for producing a porous body according to any one of claims 1 to 7 in a container. The heat insulator according to claim 8, wherein the container is a gas shielding container, and the inside of the container is depressurized. A semiconductor circuit in which an interlayer insulating film that insulates between a plurality of electrode lines arranged on a substrate is formed using the porous body manufactured by the method for manufacturing a porous body according to any one of claims 1 to 7. .

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