JP2017141355A - Method for producing polyimide foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an improved polyimide foam capable of producing a large-sized polyimide foam in a state of homogeneous cells without causing cracking.SOLUTION: There is provided a method for producing a polyimide foam which comprises a step of heating and foaming a polyimide precursor powder composed of an aromatic tetracarboxylic acid diester component and an aromatic diamine component, where the method comprises a step of filling the polyimide precursor powder into a molding frame and rubbing and cutting the top surface and does not comprise a step of vibrating the polyimide precursor powder filled into the molding frame to increase the bulk density.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a polyimide foam made of an aromatic polyimide. In particular, the present invention relates to a method for producing a polyimide foam that prevents the occurrence of cracks in the production process.

  Polyimide foam is superior to other polymer foams in heat resistance, mechanical properties, etc., and can be expected to be used as a heat insulating material, sound insulating material, sound absorbing material, etc. in a high temperature environment. Various studies have been made.

  For example, Patent Document 1 discloses a polyimide foam using a 2,3,3 ′, 4′-biphenyltetracarboxylic acid diester as a tetracarboxylic acid component, and an aromatic diamine such as paraphenylenediamine and diaminosiloxane as a diamine component. A manufacturing method of a body is described, and it is described that this polyimide foam has a high glass transition temperature (Tg) and a sufficient expansion ratio.

  Patent Document 2 describes a method for producing a polyimide foam using 3,3 ′, 4,4′-biphenyltetracarboxylic acid diester as a tetracarboxylic acid component, and the resulting polyimide foam is: It describes that it is excellent in mechanical properties such as flexibility, excellent cushioning properties, and heat resistance, which do not easily crack even when deformed.

JP 2002-12688 A JP 2010-138392 A

  However, in the production of polyimide foam, it has not been easy to produce a large-sized product, for example, a cube having a side of 0.5 m or more and a uniform cell without causing defects such as cracks. Then, an object of this invention is to provide the manufacturing method of the improved polyimide foam which can manufacture a large sized polyimide foam in a state with a uniform cell, without generating a crack.

The present invention relates to the following items.
1. A method for producing a polyimide foam comprising a step of heating and foaming a polyimide precursor powder comprising an aromatic tetracarboxylic acid diester component and an aromatic diamine component,
The method includes the step of filling the polyimide precursor powder into the mold and scraping the upper surface, and does not include the step of increasing the bulk density by applying vibration to the polyimide precursor powder filled in the mold. The manufacturing method of a polyimide foam.
2. The aromatic tetracarboxylic acid diester component is 50 to 70 mol% 3,3 ', 4,4'-biphenyltetracarboxylic acid diester and 5 to 15 mol% 2,3,3', 4'-biphenyltetra. It consists of carboxylic acid diester and 20 to 40 mol% of 3,3 ′, 4,4′-benzophenone tetracarboxylic acid diester, and the aromatic diamine component is 70 to 97 mol% of m-phenylenediamine and 30 to Item 2. The method for producing a polyimide foam according to Item 1, comprising 3 mol% of 4,4'-methylenedianiline.

  According to the present invention, a large-sized polyimide foam can be produced without causing cracks in a uniform cell state, and a product can be produced with good yield.

The polyimide foam can be produced by heating and foaming and imidizing a polyimide precursor powder containing a polyimide precursor composed of an aromatic tetracarboxylic acid diester component and an aromatic diamine component. The present invention is characterized in that after the polyimide precursor powder as a raw material is filled in a mold, the upper surface is scraped and flattened with a bar or plate, and foamed from this state. In addition, the polyimide precursor powder is not subjected to an operation of increasing the bulk density by applying vibration.

  The aromatic tetracarboxylic acid diester component constituting the polyimide precursor used in the present invention is preferably an aromatic tetracarboxylic acid diester composed of an aromatic tetracarboxylic acid and a lower alcohol. Aromatic tetracarboxylic acid diester is esterified by reacting aromatic tetracarboxylic dianhydride with lower alcohol at a temperature of 200 ° C. or lower, preferably 120 ° C. or lower for 0.1 to 48 hours, preferably 1 to 24 hours. Can be easily obtained. In this reaction, an esterification catalyst may be added as necessary.

  The aromatic tetracarboxylic acid diester component is not particularly limited as long as it is an aromatic tetracarboxylic acid diester capable of forming a polyimide foam. Examples of the aromatic tetracarboxylic acid diester include 2,3,3 ′, 4′-biphenyltetracarboxylic acid, 2,2 ′, 3,3′-biphenyltetracarboxylic acid, and 3,3 ′, 4,4 ′. -Biphenyltetracarboxylic acid such as biphenyltetracarboxylic acid, 3,3 ', 4,4'-benzophenone tetracarboxylic acid, 4,4'-oxydiphthalic acid, pyromellitic acid, 3,3', 4,4'-diphenyl Preferable examples include diesters such as sulfonetetracarboxylic acid and 2,2-bis (3,4-dicarboxyphenyl) methane.

  As the lower alcohol used for esterification, alkyl alcohols having 1 to 6 carbon atoms such as methanol, ethanol, propanol, butanol, pentanol and the like are preferable.

  The aromatic diamine component which comprises the polyimide precursor used by this invention does not have limitation in particular, What is necessary is just an aromatic diamine which can form a polyimide foam. Examples of the aromatic diamine include diaminobenzene such as 1,4-diaminobenzene, 1,3-diaminobenzene, and 1,2-diaminobenzene, diaminotoluene such as 2,4-diaminotoluene and 2,6-diaminotoluene, 2,6-diethyl-1,3-diaminobenzene, 4,6-diethyl-2-methyl-1,3-diaminobenzene, 3,5-diethyltoluene-2,6-diamine, 4,4′-diaminodiphenyl ether 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 4, , 4′-diaminodiphenylsulfone, bis (2,6-diethyl-4 Aminophenyl) methane, 4,4′-methylene-bis (2,6-diethylaniline), bis (2-ethyl-6-methyl-4-aminophenyl) methane, 4,4′-methylene-bis (2- Ethyl-6-methylaniline), 2,2-bis (3-aminophenyl) propane, 2,2-bis (4-aminophenyl) propane, 1,3-bis (4-aminophenoxy) benzene, 1,3 -Bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, benzidine, 3,3'-dimethylbenzidine, 2,2- Bis (4-aminophenoxy) propane, 2,2-bis (3-aminophenoxy) propane, 2,2-bis [4 ′-(4 ″ -aminophenoxy) phenyl] hex Preferred examples include fluoropropane, 9,9-bis (4-aminophenyl) fluorene, bis [4- (4-aminophenoxy) phenyl] sulfone, 4,4′-bis (4-aminophenoxy) biphenyl, and the like. it can.

  In the present invention, in particular, the aromatic tetracarboxylic acid diester component is 2,3,3 ′, 4′-biphenyltetracarboxylic acid, 2,2 ′, 3,3′-biphenyltetracarboxylic acid, 3,3 ′, It is selected from diesters of biphenyltetracarboxylic acid such as 4,4′-biphenyltetracarboxylic acid, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid diester, 4,4′-oxydiphthalic acid diester, and pyromellitic acid diester A compound is preferred. In addition, the aromatic diamine component is p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,5-diaminotoluene, m-tolidine, 4,4′-diaminodiphenylmethane, 4,4′-methylene. A compound selected from dianiline is preferred.

  In particular, the aromatic tetracarboxylic acid diester component is 50 to 70 mol% 3,3 ′, 4,4′-biphenyltetracarboxylic acid diester and 5 to 15 mol% 2,3,3 ′, 4′-. Biphenyltetracarboxylic acid diester and 20 to 40 mol% 3,3 ', 4,4'-benzophenone tetracarboxylic acid diester, wherein the aromatic diamine component is 70 to 97 mol% m-phenylenediamine; It is preferable from 30 to 3 mol% of 4,4′-methylenedianiline from the viewpoint of mechanical properties and heat resistance of the resulting polyimide foam.

  In addition to the aromatic tetracarboxylic acid ester component and the aromatic amine component, additives such as a surfactant (foam stabilizer), a catalyst, and a flame retardant are suitably used for the polyimide precursor powder used in the present invention. Can be added. 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, 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)), X-20-5148, X-20-8046, X-20-8047, X-20-8048, X-20-8049, F-518, F-348, F-395, F -506, F-317M, KF-351A, KF-353A, KF-354L, KP-101 (Shin-Etsu Made Gakusha), L6100J, L6100, L6884, L6887, L6900, L6970, L5420 (manufactured by Momentive Performance Materials, Inc.), and is commercially available, such as.

  Further, the catalyst is for accelerating imidization, and includes imidazoles such as 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole and benzimidazole, quinolines such as isoquinoline, and pyridine such as pyridine. And amines such as 1,8-diaza-bicyclo (5,4,0) undecene-7 are preferred.

  The polyimide precursor powder used in the present invention is a solid product obtained by evaporating a solvent from a polyimide precursor solution in which a raw material mainly containing a polyimide precursor is uniformly dispersed in a so-called molecule and evaporating the solvent. Or by evaporating the solvent and pulverizing at the same time using a spray dryer or the like. When evaporating the solvent, it is preferable to perform heat treatment within a low temperature range in which foaming does not occur, preferably 100 ° C. or less, more preferably 70 ° C. or less. Here, it is sufficient that the raw material can be powdered, and it is preferable that the solvent remains about 0.1 to 15% by mass. Usually, even when methanol which is a low-boiling solvent is used, for example, 0.1 to 10% by mass, more preferably 0.5 to 5% by mass (free) methanol remains. The polyimide precursor powder obtained by performing the evaporation at a temperature higher than the above temperature has a marked decrease in foamability. Note that evaporation of the solvent and drying of the powder may be performed under normal pressure, under pressure, or under reduced pressure.

The polyimide precursor solution is a polyimide precursor comprising, in a solvent, at least an aromatic tetracarboxylic acid diester component and an aromatic amine component, and optionally additives such as a surfactant (foam stabilizer), a catalyst, and a flame retardant. Add each component of the body, preferably at 60 ° C. or lower (usually room temperature, for example, 24 ° C.), preferably 0.1 to 6 hours (usually 1 to 2 hours) for mixing and stirring to dissolve uniformly. Can be manufactured.
In particular, first, a lower alcohol solution of an aromatic tetracarboxylic acid ester component is prepared by adding an aromatic tetracarboxylic dianhydride and, if necessary, an esterification catalyst to the lower alcohol and reacting, and the reaction solution is used as the reaction solution. A method in which other components such as an aromatic amine component are added and uniformly dissolved and mixed is suitable.
Here, the aromatic tetracarboxylic acid ester component and the aromatic amine component have approximately the same number of equivalents, specifically, the ratio of the number of equivalents (aromatic tetracarboxylic acid component / aromatic diamine component) is 0.95 to 1. In the range of 05, in the case of an aromatic tetracarboxylic acid ester component and an aromatic diamine component, substantially equimolar, specifically, a molar ratio (aromatic tetracarboxylic acid component / aromatic diamine component) is 0.95-1. It is preferable to use within the range of .05.

The solvent used for preparing the polyimide precursor solution is not particularly limited as long as it can dissolve the aromatic tetracarboxylic acid diester component, the aromatic amine component, and other components. Alcohols, ethers, ketones, or other organic solvents can be suitably used. However, when powdered to obtain a polyimide precursor, a low boiling point solvent is preferably employed.
Additives such as surfactants, catalysts, and flame retardants that are added to the polyimide precursor as needed are added to the solution of the aromatic tetracarboxylic acid ester component when the aromatic diamine is added to make a uniform solution. Is preferably added prior to the aromatic diamine, but may be added after the aromatic diamine.

  In the foaming step, the polyimide precursor powder obtained as described above is heated and foamed. The production method of the present invention includes a step of filling the polyimide precursor powder in a mold and scuffing the upper surface before heating the polyimide precursor powder. That is, an excessive amount of the polyimide precursor powder is put into the mold, and the polyimide precursor powder located above the edge of the mold is flattened by scraping with a stick or a plate, and foamed from this state. The shape and size of the mold are not particularly limited.

  Moreover, in the manufacturing method of this invention, the process which gives a vibration to the polyimide precursor powder with which the mold was filled and enlarges a bulk density is not included. Also in the above-mentioned scraping process, it is preferable to scrape the polyimide precursor powder without compressing it.

  The heat treatment in the foaming step is not limited as long as heating for foaming can be performed, but for example, it can be suitably performed using a heating device such as an oven or a microwave device. 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 heating with microwaves, it is usually performed at a frequency of 2.45 GHz based on the Radio Law. Increasing the throughput of the polyimide precursor powder requires a greater output. For example, an output of 1 to 25 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 20 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 a temperature range of 200 ° C. or higher and a glass transition temperature of the polyimide foam + 10 ° C. or lower, usually 200 to 500 ° C., preferably 200 to 400 ° C. It can be suitably carried out by heating in the temperature range for 5 minutes to 24 hours, preferably 1 to 15 hours. The post-heating is carried out according to a predetermined temperature profile in which, for example, the temperature is gradually raised from a relatively low temperature of about 200 ° C. at a rate of 10 ° C./min, and finally heated at a high temperature of about 350 ° C. You may change the method.

  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. In addition, it can be appropriately controlled according to various conditions such as a temperature profile during heating.

  According to the method for producing a polyimide foam according to the present invention, a large-sized polyimide foam can be easily and reproducibly produced in a thin and uniform cell state without cracks by simple operations and simple steps. It is possible to manufacture well (with good yield).

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 BTDA: 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride a-BPDA: 2,3,3 ′ , 4′-biphenyltetracarboxylic dianhydride MPD: m-phenylenediamine MDA: 4,4′-methylenedianiline 1,2-DMz: 1,2-dimethylimidazole

The evaluation method of each characteristic is as follows.
<Thickness distribution>
For polyimide precursor powder filled in a 1.2 m x 1.2 m mold, specify 7 x 7 points (49 points) at equal intervals in the vertical and horizontal directions, measure the thickness of the powder with a metal ruler, and measure 49 points. The average value was defined as the average thickness. Further, a standard deviation (δ) was obtained for these measured values.
<Bulk density and bulk density distribution>
A cylinder with a certain area was inserted into 49 places where the thickness was measured, and polyimide precursor powder was collected and weighed.
The bulk density was calculated by the following formula.
Bulk density (g / cc) = weight (g) / recovered area (cm ² ) × thickness (cm)
Further, a standard deviation (δ) was obtained for these measured values.
<Number of voids>
The image was taken with a digital camera having 40 million pixels or more so that a scale showing a cut surface and dimensions of a 1.05 m × 1.15 m polyimide foam was captured.
Using an image processing software ImageJ, recognizes a cell having an area of 0.79mm ² ~314mm ² as a void, indicated in the void number per unit area (m ^2).

(Reference example)
A 3 m ³ SUS reactor was charged with 954 kg of methanol, 282 kg (960 mol) of s-BPDA, 47 kg (160 mol) of a-BPDA, 155 kg (480 mol) of BTDA, and 7 kg of 1,2-DMz, and then heated. The mixture was heated and stirred for 2 hours while refluxing to esterify s-BPDA, a-BPDA, and BTDA, respectively, to obtain uniform solutions.

  After cooling the resulting solution to room temperature, MPD of aromatic diamine component was 156 kg (1,440 mol), MDA was 32 kg (160 mol), and silicone surfactant L6100J (made by Momentive Performance Materials) was used. 16 kg was added and stirred to obtain a uniform solution without causing precipitation.

  This solution was sprayed into a spray dryer and dried while removing methanol as a solvent at a dry air temperature of 65 ° C. to obtain a polyimide precursor powder. The average particle size of the obtained powder was 47 μm, and the bulk density was 0.35 g / cc. In the following examples, this polyimide precursor powder was used.

Example 1
After placing 17.0 kg of polyimide precursor powder into a mold having a bottom size of 1.2 × 1.2 m and a height of 0.025 m, the square bar is moved along the upper surface of the mold, The upper surface of the polyimide precursor powder was scraped and flattened. The polyimide precursor powder remaining in the mold was 15.6 kg, the average thickness was 27.2 mm, and the standard deviation (σ) was 1.3. The average bulk density was 0.412 g / cc. This was placed on a turntable of a microwave oven (manufactured by Fuji Electric Koki Co., Ltd.) and foamed by microwave irradiation for 15 kW × 17 minutes and 32 kW × 15 minutes while rotating the turntable at a rotation speed of 3 rpm. This was put into a hot air oven (manufactured by Noritake Co., Ltd.) that had been heated to 200 ° C., and was heated stepwise to a maximum temperature of 330 ° C., followed by post-heating treatment. The obtained polyimide foam had a maximum height of 1.15 m, the cells were uniform and no cracks were observed. The density of the polyimide foam was 7.5 kg / m ³ .

(Comparative Example 1)
After 20.0 kg of the polyimide precursor powder was put into a mold having a bottom size of 1.2 m × 1.2 m and a height of 0.030 m, it was leveled with a flat plate so as to be uniform. Then, it was vibrated for 5 minutes on a vibration table (Exsen). Then, the upper surface of the polyimide precursor powder was scraped and flattened by moving the square bar along the upper surface of the mold. The polyimide precursor powder remaining in the mold was 17.1 kg, the average thickness was 27.8 mm, the standard deviation (σ) was 1.2, and the average bulk density was 0.474 g / cc. This was foamed under the same conditions as in Example 1 to obtain a polyimide foam. The obtained polyimide foam had a maximum height of 1.2 m, and the cells were uneven and large cracks were observed. The density of the polyimide foam was 7.5 kg / m ³ .

(Comparative Example 2)
15.0 kg of polyimide precursor powder was put into a mold having a bottom size of 1.2 m × 1.2 m and a height of 0.030 m, and the powder surface was leveled with a flat plate. The average thickness of the polyimide precursor powder was 25.8 mm, the standard deviation (σ) was 4.6, and the average bulk density was 0.405 g / cc. This was foamed under the same conditions as in Example 1 to obtain a polyimide foam. The obtained polyimide foam had a maximum height of 1.1 m, and the cells were uneven and large cracks were observed. The density of the polyimide foam was 6.8 kg / m ³ .

(Comparative Example 3)
15.0 kg of the polyimide precursor powder is put into a mold having a bottom size of 1.2 m × 1.2 m and a height of 0.025 m, leveled with a flat plate so as to be uniform, and a flat plate is placed on top. Then, it was vibrated for 5 minutes on a vibration table (Exsen). The average thickness of the polyimide precursor powder was 22.2 mm, the standard deviation (σ) was 3.0, and the average bulk density was 0.496 g / cc. This was foamed under the same conditions as in Example 1 to obtain a polyimide foam. The obtained polyimide foam had a maximum height of 1.1 m, and the cells were uneven and large cracks were observed. The density of the polyimide foam was 7.2 kg / m ³ .

Claims (2)

A method for producing a polyimide foam comprising a step of heating and foaming a polyimide precursor powder comprising an aromatic tetracarboxylic acid diester component and an aromatic diamine component,
The method includes the step of filling the polyimide precursor powder into the mold and scraping the upper surface, and does not include the step of increasing the bulk density by applying vibration to the polyimide precursor powder filled in the mold. The manufacturing method of a polyimide foam. The aromatic tetracarboxylic acid diester component is 50 to 70 mol% 3,3 ', 4,4'-biphenyltetracarboxylic acid diester and 5 to 15 mol% 2,3,3', 4'-biphenyltetra. It consists of carboxylic acid diester and 20 to 40 mol% of 3,3 ′, 4,4′-benzophenone tetracarboxylic acid diester, and the aromatic diamine component is 70 to 97 mol% of m-phenylenediamine and 30 to The method for producing a polyimide foam according to claim 1, comprising 3 mol% of 4,4′-methylenedianiline.