JP2009108242A - Method for production of polyimide foam, and polyimide foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyimide foam having such flexibility that the foam generates hardly cracks even upon deformation, and having practical mechanical characteristics such as superior cushioning property as a foamed body, and to provide a method for the production of a polyimide foam having uniform foam cells and a high closed cell rate. <P>SOLUTION: The method for producing a polyimide foam comprises heat treating and expanding a polyimide precursor containing, as essential components, an aromatic tetracarboxylic acid component, an aromatic diamine component and an acidic phosphoric acid ester having a specified structure. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a polyimide foam having practical mechanical properties such as flexibility and excellent cushioning properties that do not easily crack even when deformed, or a foam cell having a uniform and closed cell ratio. The present invention relates to a method for producing a polyimide foam having a high value.

Various studies have been made on polyimide foams because excellent properties such as heat resistance can be expected. Many of them, for example, were obtained by subjecting a polyimide precursor composed of a diamine and a tetracarboxylic acid ester to heat treatment or microwave radiation and polymerizing imidization with foaming to obtain a polyimide foam. .
Patent Document 1 discloses a method for producing a particulate polyimide precursor capable of forming a polyimide foam, in which a solution of a diamine and 3,3 ′, 4,4′-benzophenone tetracarboxylic acid ester is atomized by a spray dryer. Are listed.
Patent Document 2 discloses a liquid resin precursor capable of forming a polyimide foam composed of a diamine and a tetracarboxylic acid ester, or a powdered polyimide precursor capable of forming a polyimide foam obtained by dry-powdering the liquid resin precursor. A method for producing polyimide foam by exposure to wave radiation is disclosed.
Patent Document 3 describes a method for producing a polyimide foam having durability by using an aliphatic diamine as a diamine component, which does not break or break even in a short cycle dynamic fatigue test. With the use of diamine, heat resistance is sacrificed.
Patent Document 4 discloses an amic acid foam characterized by reacting tetracarboxylic acid with an anhydride, a foam stabilizer, water, and a tertiary amino group-containing polyhydric alcohol to form a resin foam having an amic acid bond. A manufacturing method is disclosed. Here, it is described that a phosphate ester is used. However, there is no description about using acidic phosphate ester.

JP-A-57-53533 Japanese Unexamined Patent Publication No. 57-80427 JP-A-61-195126 JP 2005-330392 A

The polyimide constituting the polyimide foam obtained by the production method as described above often has insufficient flexibility. For this reason, there has been a demand for a method for producing a foamed polyimide having improved practical mechanical properties as a foam such as flexibility that does not easily cause cracks even when deformed and excellent cushioning properties. Furthermore, as a foam, the manufacturing method of the polyimide foam which can obtain the polyimide foam with a uniform foam cell and a high closed cell rate easily was desired.
Accordingly, an object of the present invention is to provide a uniform polyimide foam or foam cell having practical mechanical properties as a foam such as flexibility and excellent cushioning properties that do not easily crack even when deformed. And providing a method for producing a polyimide foam having a high closed cell ratio.

  The present invention relates to a polyimide foam characterized by heat-treating a polyimide precursor containing an aromatic tetracarboxylic acid component, an aromatic diamine component, and an acidic phosphate ester of the following chemical formula (1) as essential components. It relates to the manufacturing method.

ここで、（ａ）Ｒ１はＯＨであり、Ｒ２及びＲ３はそれぞれ独立にＯＲである、（ｂ）Ｒ１及びＲ２はＯＨであり、Ｒ３はＯＲである、または（ｃ）Ｒ１はＣＨ２ＣＯＯＹであり、Ｒ２及びＲ３はそれぞれ独立にＯＲである。
なお、Ｒは炭素数が１〜２５のアルキル基又は炭素数が１〜２５のアルケニル基であり、これらの基は更に炭素数が１〜２５のアルコキシ基又は炭素数が１〜５のアルキル基からなる置換基を有してもよい。また、Ｙは水素原子又は炭素数が１〜５のアルキル基である。

Where (a) R1 is OH, R2 and R3 are each independently OR, (b) R1 and R2 are OH, R3 is OR, or (c) R1 is CH2COOY, R2 and R3 are each independently OR.
R is an alkyl group having 1 to 25 carbon atoms or an alkenyl group having 1 to 25 carbon atoms, and these groups are further alkoxy groups having 1 to 25 carbon atoms or alkyl groups having 1 to 5 carbon atoms. You may have a substituent which consists of. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

  The present invention also relates to the method for producing a polyimide foam, wherein the aromatic tetracarboxylic acid component is an aromatic tetracarboxylic acid diester and the aromatic diamine component is an aromatic diamine.

  The present invention also provides the polyimide foam, wherein the amount of the acidic phosphate is 0.1 to 10 parts by mass with respect to the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component. It relates to the manufacturing method.

  In addition, the present invention relates to the method for producing a polyimide foam, wherein the acidic phosphate has a decomposition temperature of 180 ° C. or higher.

  The present invention also relates to a method for producing the polyimide foam, wherein the green body made of a polyimide precursor powder is heat-treated and foamed.

  In addition, the present invention provides a method for producing a polyimide foam, comprising subjecting a mixture of a polyimide precursor and at least one compound selected from water, alcohol, and ether to a liquid compound at room temperature to heat treatment to cause foaming. About.

  The present invention also relates to a method for producing the polyimide foam, wherein the heat treatment is performed by microwave heating.

  Furthermore, this invention relates to the manufacturing method of the said polyimide foam characterized by heat-processing at the temperature higher than the glass transition temperature of the polyimide which comprises the further foamed polyimide, after making it foam by heat processing.

  Moreover, this invention relates to the polyimide foam manufactured by one of the said polyimide foam manufacturing methods.

  According to the present invention, a polyimide foam having a practical mechanical property as a foam such as flexibility and excellent cushioning property that does not easily crack even if deformed, or a foam cell is uniform and has a closed cell ratio The manufacturing method of a polyimide foam with high can be provided.

  In the method for producing a polyimide foam of the present invention, a polyimide precursor containing an aromatic tetracarboxylic acid component, an aromatic diamine component, and an acidic phosphate of the following chemical formula (1) as essential components is heat-treated and foamed. Is a method for producing a polyimide foam.

ここで、（ａ）Ｒ１はＯＨであり、Ｒ２及びＲ３はそれぞれ独立にＯＲである、（ｂ）Ｒ１及びＲ２はＯＨであり、Ｒ３はＯＲである、または（ｃ）Ｒ１はＣＨ２ＣＯＯＹであり、Ｒ２及びＲ３はそれぞれ独立にＯＲである。
なお、Ｒは炭素数が１〜２５のアルキル基又は炭素数が１〜２５のアルケニル基であり、これらの基は更に炭素数が１〜２５のアルコキシ基又は炭素数が１〜５のアルキル基からなる置換基を有してもよい。また、Ｙは水素原子又は炭素数が１〜５のアルキル基である。

Where (a) R1 is OH, R2 and R3 are each independently OR, (b) R1 and R2 are OH, R3 is OR, or (c) R1 is CH2COOY, R2 and R3 are each independently OR.
R is an alkyl group having 1 to 25 carbon atoms or an alkenyl group having 1 to 25 carbon atoms, and these groups are further alkoxy groups having 1 to 25 carbon atoms or alkyl groups having 1 to 5 carbon atoms. You may have a substituent which consists of. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

The aromatic tetracarboxylic acid component is not particularly limited, but for example, 3,3 ′, 4,4′-biphenyltetracarboxylic acid component, 2,3,3 ′, 4′-biphenyltetracarboxylic acid component 2,2 ′, 3,3′-biphenyltetracarboxylic acid component, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid component, pyromellitic acid component, 4,4′-oxydiphthalic acid component, 3,3 ', 4,4'-diphenylsulfonetetracarboxylic acid component, 2,2-bis (4-phenoxyphenyl) propanetetracarboxylic acid component, 2,3,6,7-naphthalenetetracarboxylic acid component, 1,4,5 , 8-naphthalenetetracarboxylic acid component. These may be used alone or as a mixture of plural kinds. Here, the tetracarboxylic acid component means tetracarboxylic acids that can form a polyimide, such as tetracarboxylic acid, acid anhydrides or esterified derivatives thereof.
In the present invention, an esterified derivative of a lower (alkyl) alcohol having 1 to 6 carbon atoms, particularly an aromatic tetracarboxylic diester (aromatic tetracarboxylic diester dicarboxylic acid) of a lower alcohol having 1 to 6 carbon atoms is used. It can be used suitably. The aromatic tetracarboxylic acid diester is obtained by adding aromatic tetracarboxylic dianhydride to a lower alcohol having 1 to 6 carbon atoms at a temperature of 120 ° C. or lower for 0.1 to 24 hours, preferably about 1 to 12 hours. It can be easily obtained by reacting. Specifically, the lower alcohol having 1 to 6 carbon atoms is preferably methanol, ethanol, propanol, butanol, or a mixture thereof.
Furthermore, in the present invention, biphenyl tetracarboxylic acid diester, benzophenone tetracarboxylic acid diester, or a mixture thereof can be particularly preferably used.

The aromatic diamine component is not particularly limited as long as it is a diamine capable of forming a polyimide such as an aromatic diamine or a derivative obtained by modifying the amino group thereof to an isocyanate group, but for example, 3,4'-oxy Dianiline, 4,4′-oxydianiline, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4- Aminophenoxy) benzene, 3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfone, bis (4- (4-aminophenoxy) phenyl) sulfone, bis (4- (3-aminophenoxy) phenyl) sulfone 4,4′-bis (3-aminophenoxy) biphenyl, 4,4′-bis (4-aminophenoxy) Phenyl, 2,2-bis (4- (4-aminophenoxy) phenyl) propane, 4,4'-methylenedianiline, and aromatic diamine or its derivatives such as 2,6-diaminotoluene. These may be used alone or as a mixture of plural kinds.
In the present invention, it is preferable to use an aromatic diamine as the aromatic diamine component, among which m-phenylenediamine, 3,4′-oxydianiline, 2,4-diaminotoluene, 4,4′-methylenedi. Any of aniline or a mixture thereof can be used particularly preferably.
In the present invention, a small amount (5 mol% or less, particularly 3 mol% or less in the diamine component) of diaminosiloxane such as 1,3-bis (3-aminopropyl) tetramethylsilane may be used. Absent.

The acidic phosphate used in the present invention is a compound represented by the chemical formula (1). That is, the acidic phosphate ester also means a pentavalent phosphorus compound having at least one hydroxyl group in the molecule, or a pentavalent phosphorus compound having at least one CH ₂ COOY group in the molecule. Specifically, for example, monomethyl phosphate, dimethyl phosphate, monoethyl phosphate, diethyl phosphate, monobutyl phosphate, dibutyl phosphate, mono (2-ethylhexyl) phosphate, di (2-ethylhexyl) phosphate, monooleyl phosphate, dioleyl phosphate Suitable examples include monoisopropyl phosphate, diisopropyl phosphate, monostearyl phosphate, distearyl phosphate, and ethyl diethylphosphonoacetate.
These include monoesters such as ethyl acid phosphate JP-502, butyl acid phosphate JP-504, 2-ethylhexyl acid phosphate JP-508, oleyl acid phosphate JP-518-0 (above, manufactured by Johoku Chemical Co., Ltd.) As a mixture of diesters, and as a monoester such as ethyl acid phosphate JUMP-18-0 and stearyl acid phosphate JUMP-18 (above, manufactured by Johoku Chemical Industry Co., Ltd.), dibutyl phosphate DBP, bis (2- It can be suitably obtained as a diester such as ethylhexyl) phosphate LB-58 (manufactured by Johoku Chemical Industry Co., Ltd.). Moreover, it can obtain suitably as ethyl diethyl phosphono acetate JC-224 (made by Johoku Chemical Industry Co., Ltd.).
In the present invention, it is preferable that the acidic phosphate has a decomposition (start) temperature of 180 ° C. or higher. In the production of the polyimide foam, the heat treatment is usually performed to a high temperature of 180 ° C. or higher as described below. In the case where the acidic phosphate ester decomposes at less than 180 ° C., the effect of the acidic phosphate ester cannot be obtained particularly in the process of greatly affecting the mechanical properties in the production process of the polyimide foam. More preferably, the decomposition temperature of the acidic phosphate is less than 300 ° C, particularly less than 290 ° C. The maximum heat treatment temperature of the polyimide foam is usually 300 ° C. or higher. In order to improve the mechanical properties such as cushioning properties, the acidic phosphate ester is not decomposed during the heat treatment and remains in the polyimide foam. Is preferred.

The method for producing a polyimide foam of the present invention can be obtained by uniformly dissolving at least the aromatic tetracarboxylic acid component, the aromatic diamine component, and the acidic phosphate ester, for example, in a solvent. When foaming using a polyimide precursor that is molecularly dispersed (they are uniformly dispersed at the molecular level, the aromatic tetracarboxylic acid component and the aromatic diamine may form a salt) There are features.
That is, the polyimide precursor is obtained by adding an aromatic diamine component and an acidic phosphate ester to a solution of an aromatic tetracarboxylic acid component (for example, aromatic tetracarboxylic acid diester), and preferably 60 ° C. or less (usually room temperature, for example, 24 ℃), preferably by mixing and stirring for about 0.1 to 6 hours (usually 1 to 2 hours).
Here, the aromatic tetracarboxylic acid component and the aromatic diamine component are approximately equimolar, specifically, the molar ratio (aromatic tetracarboxylic acid component / aromatic diamine component) is in the range of 0.95 to 1.05. It is preferable to use it. Moreover, the addition amount of acidic phosphate ester can be used suitably in the range which becomes a uniform solution, However, Preferably it is 0.00 with respect to a total of 100 mass parts of an aromatic tetracarboxylic acid component and an aromatic diamine component. 1 to 10 parts by mass, more preferably 1 to 5 parts by mass, especially 2 to 3 parts by mass.

The solvent used for preparing the polyimide precursor is not particularly limited as long as it can dissolve the aromatic tetracarboxylic acid component, the aromatic diamine component, and the acidic phosphate ester. Alcohols, ethers, ketones, or other organic solvents can be suitably used, but when a polyimide precursor is pulverized to obtain a powdered polyimide precursor, a low boiling point solvent is preferably employed.
The polyimide precursor is prepared by reacting an aromatic tetracarboxylic dianhydride in a lower alcohol to form an aromatic tetracarboxylic diester, and then adding an aromatic diamine component and an acidic phosphate to the reaction solution. It doesn't matter how.

In the present invention, additives such as a surfactant, a catalyst, and a flame retardant can be suitably added to the polyimide precursor as necessary. These additives are preferably added prior to the aromatic diamine when the aromatic diamine and acidic phosphate are added to the aromatic tetracarboxylic acid diester solution to obtain a uniform solution. It may be added after the group diamine.
As the surfactant (foam stabilizer), a surfactant suitably used as a foam stabilizer for polyurethane foam can be preferably used. Among them, a graft copolymer in which a part of the methyl group of polydimethylsiloxane is substituted with a polyalkylene oxide group such as a polyethylene oxide group, a poly (ethylene-propylene) oxide group or a propylene oxide group (of a substituted polyalkylene oxide group). A polyether-modified silicone oil such as a hydroxyl group or an alkyl ether group such as methyl ether or an alkyl ester group such as acetyl group is particularly suitable.
Specific examples of the polyether-modified silicone oil include SH-193, SH-192, SH-194, SH-190, SF-2937, SF-2908, SF-2904, SF-2964, SRX-298, and SRX-2908. , SRX-274C, SRX-295, SRX-294A, SRX-280A (above, manufactured by Toray Dow Corning Silicone), L-5340, SZ-1666, SZ-1668 (above, manufactured by Nihon Unicar), TFA4205 (GE) Toshiba Silicone Co., Ltd.), X-20-5148 (Shin-Etsu Chemical Co., Ltd.) and the like.
As the catalyst, in order to promote polymerization imidization, imidazoles such as 1,2-dimethylimidazole and benzimidazole, quinolines such as isoquinoline, pyridines such as pyridine and the like may be added.
Moreover, although the polyimide foam of this invention has high flame retardance, in order to make it flame-retardant further, you may use phosphorus compounds, such as a trivalent phosphite.

  The polyimide foam of the present invention is obtained, for example, by adding an aromatic diamine component and an acidic phosphate ester to a solution of a tetracarboxylic acid component (for example, an aromatic tetracarboxylic acid diester) as described in Patent Document 2. The obtained polyimide precursor can be suitably obtained by heat-treating the solution as it is. In addition, the polyimide foam of the present invention is obtained by using a powdery polyimide precursor that can be easily obtained by removing a solvent (for example, alcohol) from a solution of the polyimide precursor, for example, the powdery polyimide precursor. The green body obtained by compressing can be suitably obtained by heat treatment. Moreover, the polyimide foam of this invention can be suitably obtained by heat-processing the mixture (solution or slurry) which mixed the said powdery polyimide precursor with the suitable solvent again. As the solvent at that time, a solvent having a low boiling point (preferably having a boiling point of 150 ° C. or lower, more preferably 100 ° C. or lower) such as water, alcohol (particularly a lower (alkyl) alcohol having 1 to 6 carbon atoms) or ether is suitable. Can be listed.

  The polyimide precursor is powdered by evaporating the solvent from the polyimide precursor solution to dryness, and pulverizing the resulting dried product (solid material) or using a spray dryer as described in Patent Document 1. Thus, it can be suitably carried out by a method of simultaneously evaporating and pulverizing the solvent. In the evaporation of the solvent, it is preferable to perform the heat treatment within a low temperature range where foaming does not occur, preferably 100 ° C. or less, more preferably 50 ° C. or more. The polyimide precursor powder obtained by performing the evaporation at a temperature higher than the above temperature has a marked decrease in foamability. The evaporation of the solvent and the drying of the powder may be performed under normal pressure, under pressure, or under reduced pressure.

  The green body can be suitably obtained, for example, by filling a mold with a polyimide precursor powder at room temperature and compressing it. The green body can also be obtained by casting a polyimide precursor solution dissolved in an appropriate solvent such as a lower alcohol into a mold and evaporating the solvent as it is to dry.

  When the polyimide precursor powder is mixed with the solvent again, the polyimide precursor powder and an appropriate amount of solvent, preferably a lower alcohol, are mixed to obtain a mixture (dissolved or slurried). Although heating may be performed at the time of mixing for obtaining this mixture, it is preferably 100 ° C. or lower, more preferably 60 ° C. or lower, and further preferably performed at room temperature to room temperature or lower without heating.

  The heat treatment for obtaining a polyimide foam by foaming a polyimide precursor is not limited as long as heating for foaming can be performed. For example, an oven or a microwave device described in Patent Document 2 It can carry out suitably using a heating apparatus. The heat treatment conditions (heating temperature, time, etc.) at this time can be appropriately selected in accordance with the type of polyimide precursor and the amount of treatment.

  When heating in an oven, it is necessary to heat-treat in the temperature range of preferably 80 to 200 ° C, more preferably 100 to 180 ° C, and particularly preferably 130 to 150 ° C for foaming. The time is preferably about 5 to 60 minutes, more preferably about 10 to 30 minutes. If the temperature is lower than the heating temperature, a long time is required for foaming, which is not preferable. Moreover, since it becomes difficult to make the foam cell of the polyimide foam obtained uniform when temperature becomes higher than the said heating temperature, it is not suitable.

When using a microwave heating apparatus in Japan, it is usually performed at a frequency of 2.45 GHz based on the Radio Law. Increasing the throughput of the polyimide precursor requires greater output. For example, an output of 1 to 5 kw is suitably employed for several tens to thousands of grams of polyimide precursor powder. When the microwave is irradiated, foaming usually starts in about 1 to 2 minutes, and the foaming converges in 5 to 10 minutes.
In either case of oven heating or microwave irradiation, the obtained polyimide foam does not have sufficient mechanical strength when foaming is completed. Therefore, it is preferable that the obtained polyimide foam is further post-heated by a heating device such as an oven.

  The post-heating depends on the size of the obtained polyimide foam, but is in a temperature range of 200 ° C. or more and [glass transition temperature + 10 ° C.] or less, preferably from the glass transition temperature to [glass transition temperature + 10 ° C. ], Usually 200 to 400 ° C., preferably 280 to 370 ° C., for 5 minutes to 24 hours. The post-heating is, for example, a temperature profile that gradually increases from a relatively low temperature of about 200 ° C. at a temperature increase rate of 10 ° C./min, and finally heat-treated at a high temperature of about 300 ° C. or higher. Therefore, a method of changing the heating temperature may be used.

  The expansion ratio and the apparent density (density) are the amount of volatile components at the time of foaming (alcohol and water generated during polymerization imidization, further solvent and other volatile additives, etc.), and the heat treatment method. Moreover, it can control suitably according to various conditions, such as a temperature profile at the time of a heating.

In the present invention, the acidic phosphate ester represented by the chemical formula (1) makes an aromatic tetracarboxylic acid ester derivative and an aromatic diamine, which are inherently poor in solubility, into a uniform solution, and further, at some molecular level by some action. It seems to have a role of interacting to form a so-called molecularly dispersed polyimide precursor. Furthermore, it is considered that the acidic phosphate ester represented by the chemical formula (1) has an action of promoting polymerization imidization when the polyimide precursor is heat-treated and polymerized imidized while foaming. In addition, the action of promoting the polymerization imidation works particularly effectively in the post-heating step. As a result, it is considered that the polyimide foam obtained in the present invention is formed by a polyimide having a higher molecular weight than the conventional one.
That is, the polyimide foam of the present invention has a uniform and fine structure in the foaming process because the foam cell is formed by a polyimide having a sufficiently large molecular weight in addition to using a uniformly dispersed polyimide precursor. A foam cell can be formed, and has practical mechanical properties as a foam, such as flexibility and excellent cushioning properties that do not easily crack even when further deformed.

  The polyimide foam of the present invention preferably has a uniform and fine foam cell. The foam cell may be a closed cell or an open cell, but means a bubble that is considered to be foamed as one cell in the foaming process for forming the foam. Therefore, each cell is regarded as one foam cell even if the cells are open-celled after foaming. In the polyimide foam of the present invention, the diameter of the foam cell is approximately 5000 μm or less, preferably 3000 μm or less, more preferably 0.1 to 2000 μm, particularly 1 to 1000 μm. Here, “substantially” means that the area of 80% or more, particularly 90% or more of the cross-sectional area is composed of the foam cell, and the diameter of the foam cell means each foam in the cross section of the polyimide foam. It means the maximum inner diameter of the cell.

That is, the polyimide foam of the present invention has a uniform and fine foam cell. Particularly preferably, the area of 80% or more, preferably 90% or more of the cross-sectional area is in the range of 1 to 1000 μm in diameter. It is composed of foam cells.
The expansion ratio of the polyimide foam of the present invention is preferably 50 times or more (apparent density is 0.0272 g / cm ³ or less), more preferably 100 times or more (apparent density is 0.0136 g / cm ³ or less). Yes, preferably 500 times or less (apparent density is 0.0027 g / cm ³ or more), more preferably 400 times or less (apparent density is 0.0034 g / cm ³ or more). If the foaming ratio is less than 50 times, not only becomes rigid and it becomes impossible to obtain flexibility and cushioning properties, but also characteristics and features normally expected as a foam such as weight reduction cannot be obtained. On the other hand, if the expansion ratio exceeds 500 times, the foam cell wall becomes thin and the mechanical properties are lowered, and cracking is likely to occur due to deformation. Therefore, as a foam such as flexibility and excellent cushioning properties It becomes difficult to obtain a polyimide foam having practical mechanical properties.

  In the present invention, not only a low foaming ratio (high density) polyimide foam in which uniform and fine foam cells are composed of polyimide having a sufficiently large molecular weight, but also a high foaming ratio (low density). In addition, a polyimide foam having excellent flexibility and cushioning properties can be suitably obtained. That is, although not limited, the polyimide foam of the present invention preferably has a foaming ratio of 50 to 500 times and does not easily crack even when deformed, such as flexibility and cushioning properties. It is a polyimide foam excellent in practical mechanical properties as a foam.

  Next, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

In the following examples, each abbreviation means the following compound.
s-BPDA: 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride a-BPDA: 2,3 ′, 3,4′-biphenyltetracarboxylic dianhydride MPD: m-phenylenediamine 3, 4′-ODA: 3,4′-oxydianiline 2,4-DAT: 2,4-diaminotoluene MDA: 4,4′-methylenedianiline MeOH: methanol (acidic phosphate ester)
JP-502: Ethyl acid phosphate JP-502 (manufactured by Johoku Chemical Industry Co., Ltd.), mixture of monoethyl ester and diethyl ester, decomposition temperature: 200 ° C.
JP-508: 2-ethylhexyl acid phosphate JP-508 (manufactured by Johoku Chemical Co., Ltd.), mixture of mono (ethylhexyl) ester and di (ethylhexyl) ester, decomposition temperature: 198 ° C
JC-224: ethyl diethylphosphonoacetate JC-224 (manufactured by Johoku Chemical Industry Co., Ltd.), ethyl diethylphosphonoacetate, decomposition temperature: 240 ° C
JP-518-0: Oleyl acid phosphate JP-518-0 (manufactured by Johoku Chemical Industry Co., Ltd.), mixture of monooleyl ester and dioleyl ester, decomposition temperature: 200 ° C.

The measurement method used in the present invention will be described. Note that matters not specifically described were in accordance with JIS K-6400.
[Apparent density (Polyimide foam density)]
The apparent density was calculated by cutting the polyimide foam into a 50 mm × 50 mm × 50 mm cube and measuring its weight.
The measurement was carried out under the same conditions for a sample held at 25 ° C. and 50% RH for 24 hours.

[Foaming ratio]
A polyimide film composed of the same tetracarboxylic acid component and diamine component as those constituting the polyimide foam was prepared with the maximum heating temperature equal to the heating temperature of the polyimide foam. The density (true density) of the polyimide film was measured using a density gradient tube and a pycnometer.
The expansion ratio was calculated by dividing the true density of the obtained polyimide film by the apparent density of the polyimide foam.
The measurement was carried out under the same conditions for a sample held at 25 ° C. and 50% RH for 24 hours.

[Observation of foam cells (uniformity)]
A sample of dimensions: 2 cm × 2 cm × 2 cm was cut out from the polyimide foam so as not to be loaded with a microtome. Each cross section of the sample was taken with a scanning electron microscope (SEM) at a magnification of 20 times. The SEM measurement was carried out under the same conditions for a foam sample that was held for 24 hours at 25 ° C. and 50% RH.
The cross-sectional photograph by the SEM was analyzed using image processing software (“Scion Image” manufactured by Scion Corporation). That is, the inner diameter of the foam cell was calculated by clicking one end of a specific foam cell in the cross-sectional photograph by SEM and dragging it to the other end. Moreover, the area was calculated by surrounding the specific foam cell while dragging. And the area ratio with respect to the total cross-sectional area of a specific foam cell was computed by remove | dividing the sum of the area of a specific foam cell by a total cross-sectional area.
In the present invention, according to the above method, each cross-sectional area of the sample was measured and the average value was obtained. The uniformity of the foam cell is such that the sum of the cross-sectional areas of the foam cells having a diameter in the range of 1 to 1000 μm is 80% or more with respect to the total cross-sectional area (particularly in the range of 1 to 500 μm in diameter). The sum of the cross-sectional areas of the foam cells was evaluated as 80) or more with respect to the total cross-sectional area, and less than 80% was evaluated as 50% or more as Δ and less than 50% as x.
In the above method, the closed cell ratio (%) was calculated by dividing the sum of the areas of the foam cells of the closed pores by the total cross-sectional area.

[Flexibility]
A polyimide foam having a cross section of 1 cm × 1 cm and a length of 5 cm was cut out and used as a sample. The both ends of the sample in the longitudinal direction were deformed in about 5 seconds until both ends contacted to form a ring shape. Check the presence or absence of cracks by visual observation, × if the crack was broken and the sample was broken in two, Δ if the crack was broken but the sample was not broken in two, and ○ if the crack did not occur evaluated.
The measurement was carried out under the same conditions for a sample held at 25 ° C. and 50% RH for 24 hours.

[Cushioning]
A polyimide foam of 2 cm × 2 cm × 2 cm was cut out and used as a sample. By applying a load from the upper surface of the sample, the upper surface and the bottom surface are separated by a tensile compression tester (ORIENTEC TENSILON RPA-500 manufactured by Orientec Corp.) until the thickness becomes 0.2 cm (one tenth of the thickness before compression). Compression was performed while maintaining parallelism, the load was removed after being held for 30 seconds in this state, and permanent set (thickness that could not be recovered) was measured when the thickness after 30 seconds was recovered. The cushioning property was evaluated by the ratio of the permanent strain to the thickness before compression.
Permanent distortion was evaluated as 0 to 10% as ◯, 11 to 20% as Δ, and 20% or more as ×.
In addition, when the sample has anisotropy, the average value of the measured values in the three directions was used.
The measurement was performed under the same conditions for 24 hours under conditions of 25 ° C. and 50% RH.

[Example 1]
A 1000 ml eggplant-shaped flask was charged with 50 g (0.1699 mol) of s-BPDA and 94.5823 g of MeOH, and heated and stirred for 120 minutes while refluxing in an oil bath at 80 ° C. A reaction solution was obtained. After cooling the obtained reaction solution to room temperature, acid phosphate 2-ethylhexyl acid phosphate JP-508 (manufactured by Johoku Chemical Industry Co., Ltd.) 2.8375 g, MPD of aromatic diamine component 18.3730 g (0 1699 mol), 0.958 g of silicone surfactant X-20-5148 (manufactured by Shin-Etsu Silicone) was added and stirred to obtain a uniform solution without causing precipitation. The solution was concentrated by removing MeOH as a solvent with an evaporator, and dried at room temperature using a vacuum dryer to obtain a solid. The obtained solid was finely pulverized using a mortar to obtain a polyimide precursor powder. Next, the polyimide precursor powder is spread on a 100 mm × 100 mm × 10 mm metal frame, and compressed at room temperature by using a compression molding machine (S-37.5, manufactured by Kondo Metal Industry Co., Ltd.). Molded. The obtained molded body was foamed by microwave heating treatment at 1120 W for 5 minutes using a microwave oven (RE-6200 manufactured by Sharp Corporation) to obtain a polyimide foam. This foam was put into a hot air oven (High Temp Oven HTO-9B manufactured by Koyo Thermo System Co., Ltd.) set at 200 ° C., and post-heat treatment was performed at a maximum temperature of 360 ° C. The obtained polyimide foam had a fine foam cell, was uniform, and had excellent flexibility and cushioning properties. The results are shown in Table 1.

[Example 2]
Implemented except that ethyl acid phosphate JP-502 (manufactured by Johoku Chemical Industry Co., Ltd.) was used as the acidic phosphate ester, 3,4'-ODA was used as the aromatic diamine component, and the maximum temperature of the post-heating treatment was performed at 260 ° C. A polyimide foam was obtained according to Example 1. The obtained polyimide foam had a fine foam cell, was uniform, and had excellent flexibility and cushioning properties. The results are shown in Table 1.

Example 3
Except that ethyl diethylphosphonoacetate JC-224 (manufactured by Johoku Chemical Co., Ltd.) was used as the acidic phosphate ester, 2,4-DAT was used as the aromatic diamine component, and the maximum temperature of the post-heating treatment was 370 ° C. A polyimide foam was obtained according to Example 1. The obtained polyimide foam had a fine foam cell, was uniform, and had excellent flexibility and cushioning properties. The results are shown in Table 1.

Example 4
A polyimide precursor powder was obtained according to Example 1 except that oleyl acid phosphate JP-518-0 (manufactured by Johoku Chemical Industry Co., Ltd.) was used as the acidic phosphate ester. 100 g of the obtained polyimide precursor powder was uniformly redissolved in 10 g of isopropyl alcohol. Using the solution, a polyimide foam was obtained according to the microwave heating conditions and post-heating treatment conditions of Example 1. The obtained polyimide foam had a fine foam cell, was uniform, and had excellent flexibility and cushioning properties. The results are shown in Table 1.

Example 5
A 1000-ml eggplant-shaped flask was charged with 50 g (0.1699 mol) of a-BPDA and 94.5823 g of MeOH, and heated and stirred for 120 minutes while refluxing in an oil bath at 80 ° C. to esterify a-BPDA and uniformly A reaction solution was obtained. After cooling the obtained reaction solution to room temperature, acid phosphate 2-ethylhexyl acid phosphate JP-508 (manufactured by Johoku Chemical Industry Co., Ltd.) 2.8375 g, aromatic diamine component MDA 33.6925 g (0 1699 mol), 0.958 g of silicone surfactant X-20-5148 (manufactured by Shin-Etsu Silicone) was added and stirred to obtain a uniform solution without causing precipitation. The solution was concentrated by removing MeOH as a solvent with an evaporator, and dried at room temperature using a vacuum dryer to obtain a solid. The obtained solid was finely pulverized using a mortar to obtain a polyimide precursor powder. Next, the polyimide precursor powder is spread on a 100 mm × 100 mm × 10 mm metal frame, and compressed at room temperature by using a compression molding machine (S-37.5, manufactured by Kondo Metal Industry Co., Ltd.). Molded. The obtained molded body was foamed by microwave heating treatment at 1120 W for 5 minutes using a microwave oven (RE-6200 manufactured by Sharp Corporation) to obtain a polyimide foam. This foam was put into a hot air oven (High Temp Oven HTO-9B manufactured by Koyo Thermo System Co., Ltd.) set at 200 ° C., and post-heat treatment was performed at a maximum temperature of 300 ° C. The obtained polyimide foam had a fine foam cell, was uniform, and had excellent flexibility and cushioning properties. The results are shown in Table 1.

Example 6
A polyimide foam was obtained according to Example 5 except that ethyl diethylphosphonoacetate JC-224 (manufactured by Johoku Chemical Co., Ltd.) was used as the acidic phosphate ester. The obtained polyimide foam had a fine foam cell, was uniform, and had excellent flexibility and cushioning properties. The results are shown in Table 1.

Example 7
A polyimide precursor powder was obtained according to Example 5. 100 g of the obtained polyimide precursor powder was uniformly dissolved in 12 g of MeOH. Using the solution, a polyimide foam was obtained according to the microwave heating conditions and post-heating treatment conditions of Example 5. The obtained polyimide foam had a fine foam cell, was uniform, and had excellent flexibility and cushioning properties. The results are shown in Table 1.

[Comparative Example 1]
According to Example 1 except that acid phosphate is not added, 50 g (0.1699 mol) of s-BPDA and 94.5823 g of MeOH are charged into a 1000 ml eggplant-shaped flask and refluxed in an oil bath at 80 ° C. The mixture was heated and stirred for 120 minutes, and s-BPDA was esterified to obtain a uniform reaction solution. After cooling the obtained reaction liquid to room temperature, MPD 18.3730 g (0.1699 mol) of aromatic diamine component and 0.9458 g of silicone surfactant X-20-5148 (manufactured by Shin-Etsu Silicone) were added. Upon stirring, a precipitate was formed. The mixed solution was concentrated and dried according to Example 1, and the obtained solid powder was heat-treated. Foaming occurred only very unevenly. Further, the obtained polyimide foam is completely different from the polyimide foam of the present invention, and the foam cells have extremely rough and non-uniform eyes, and are not cushioning and flexible (brittle). there were. The results are shown in Table 1.

[Comparative Example 2]
A polyimide foam was obtained according to Example 5 except that the acidic phosphate was not added. The obtained polyimide foam was not good in flexibility and cushioning properties. The results are shown in Table 1.

[Comparative Example 3]
Except for using tributyl phosphate in place of the acidic phosphate ester, an attempt was made to produce a polyimide foam according to Example 5, but a uniform polyimide foam could not be obtained. The results are shown in Table 1.

  According to the present invention, a polyimide foam having a practical mechanical property as a foam such as flexibility and excellent cushioning property that does not easily crack even if deformed, or a foam cell is uniform and has a closed cell ratio The manufacturing method of a polyimide foam with high can be obtained.

Claims (9)

A method for producing a polyimide foam, characterized by heat-treating a polyimide precursor containing an aromatic tetracarboxylic acid component, an aromatic diamine component, and an acidic phosphate ester of the following chemical formula (1) as essential components.

Where (a) R1 is OH, R2 and R3 are each independently OR, (b) R1 and R2 are OH, R3 is OR, or (c) R1 is CH2COOY, R2 and R3 are each independently OR.
R is an alkyl group having 1 to 25 carbon atoms or an alkenyl group having 1 to 25 carbon atoms, and these groups are further alkoxy groups having 1 to 25 carbon atoms or alkyl groups having 1 to 5 carbon atoms. You may have a substituent which consists of. Y is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.   2. The method for producing a polyimide foam according to claim 1, wherein the aromatic tetracarboxylic acid component comprises an aromatic tetracarboxylic acid diester, and the aromatic diamine component comprises an aromatic diamine.   The amount of the acidic phosphate is 0.1 to 10 parts by mass with respect to the total amount of the aromatic tetracarboxylic acid component and the aromatic diamine component. Manufacturing method of polyimide foam.   The method for producing a polyimide foam according to any one of claims 1 to 3, wherein the acidic phosphate has a decomposition temperature of 180 ° C or higher.   The method for producing a polyimide foam according to any one of claims 1 to 4, wherein the green body made of a polyimide precursor powder is heated to cause foaming.   5. The polyimide foam according to claim 1, wherein the polyimide precursor is foamed by heat treatment of a mixture of a polyimide precursor and at least one compound selected from water, alcohol, and ether at room temperature. Production method.   The method for producing a polyimide foam according to any one of claims 1 to 6, wherein the heat treatment is performed by microwave heating.   The method for producing a polyimide foam according to any one of claims 1 to 7, wherein after the foaming is performed by the heat treatment, the heat treatment is performed at a temperature higher than the glass transition temperature of the polyimide constituting the further foamed polyimide. .   The polyimide foam manufactured by the manufacturing method in any one of Claims 1-8.