JP6645232B2 - Method for producing polyimide foam - Google Patents

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 which prevents cracks from occurring in the production process.

  Polyimide foams have better heat resistance and mechanical properties than other polymer foams, and can be expected to be used as heat insulators, sound insulators, sound absorbers, etc. in high-temperature environments. Various studies have been made.

  For example, Patent Document 1 discloses a polyimide foam using 2,3,3 ', 4'-biphenyltetracarboxylic diester as a tetracarboxylic acid component and using an aromatic diamine such as paraphenylenediamine and diaminosiloxane as a diamine component. A method for producing 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. It is described that the material has excellent mechanical properties such as flexibility and excellent cushioning properties that do not easily crack even when deformed, and that it has excellent heat resistance.

JP-A-2002-12688 JP 2010-138392 A

  However, in the production of a polyimide foam, it was not easy to produce a large-sized product having a uniform cell shape such as a cube having a side of 0.5 m or more without generating defects such as cracks. Therefore, an object of the present invention is to provide an improved method for producing a polyimide foam, which can produce a large-sized polyimide foam in a uniform cell state without generating cracks.

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,
Filling the polyimide precursor powder in the mold, including the step of scraping the upper surface, not including the step of increasing the bulk density by applying vibration to the polyimide precursor powder filled in the mold And a method for producing a polyimide foam.
2. The aromatic tetracarboxylic acid diester component is composed of 50 to 70 mol% of 3,3 ′, 4,4′-biphenyltetracarboxylic acid diester and 5 to 15 mol% of 2,3,3 ′, 4′-biphenyltetracarboxylic acid. A carboxylic acid diester and 20 to 40 mol% of 3,3 ′, 4,4′-benzophenonetetracarboxylic acid diester, wherein the aromatic diamine component comprises 70 to 97 mol% of m-phenylenediamine; Item 3. The method for producing a polyimide foam according to Item 1, comprising 3 mol% of 4,4′-methylenedianiline.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to manufacture a large-sized polyimide foam without generating a crack in a uniform cell state, and can manufacture a product with good yield.

The polyimide foam can be manufactured 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 filling a polyimide precursor powder as a raw material in a mold, the upper surface is rubbed flat with a rod or a plate, and then foamed from this state. Further, it is characterized in that an operation of increasing the bulk density by applying vibration to the polyimide precursor powder is not performed.

  The aromatic tetracarboxylic diester component constituting the polyimide precursor used in the present invention is preferably an aromatic tetracarboxylic diester composed of an aromatic tetracarboxylic acid and a lower alcohol. Aromatic tetracarboxylic diester is obtained by reacting an aromatic tetracarboxylic dianhydride with a 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 diester component is not particularly limited, and may be any aromatic tetracarboxylic 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, 3,3 ′, 4,4 ′ -Biphenyltetracarboxylic acid such as -biphenyltetracarboxylic acid, 3,3 ', 4,4'-benzophenonetetracarboxylic acid, 4,4'-oxydiphthalic acid, pyromellitic acid, 3,3', 4,4'-diphenyl Diesters such as sulfonetetracarboxylic acid and 2,2-bis (3,4-dicarboxyphenyl) methane are preferred.

  As the lower alcohol used for the esterification, an alkyl alcohol having 1 to 6 carbon atoms such as methanol, ethanol, propanol, butanol, and pentanol is suitable.

  The aromatic diamine component constituting the polyimide precursor used in the present invention is not particularly limited, and may be any aromatic diamine capable of forming 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'-Diaminodiphenyl sulfone, 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 Fluoropropane, 9,9-bis (4-aminophenyl) fluorene, bis [4- (4-aminophenoxy) phenyl] sulfone, 4,4′-bis (4-aminophenoxy) biphenyl and the like are preferably mentioned. it can.

  In the present invention, particularly, the aromatic tetracarboxylic diester component is 2,3,3 ′, 4′-biphenyltetracarboxylic acid, 2,2 ′, 3,3′-biphenyltetracarboxylic acid, 3,3 ′, Diesters of biphenyltetracarboxylic acid such as 4,4'-biphenyltetracarboxylic acid, 3,3 ', 4,4'-benzophenonetetracarboxylic diester, 4,4'-oxydiphthalic diester, and pyromellitic diester are selected. Preferably, it is a compound. Further, the aromatic diamine component is p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,5-diaminotoluene, m-tolidine, 4,4′-diaminodiphenylmethane, 4,4′-methylene It is preferably a compound selected from dianiline.

  In particular, the aromatic tetracarboxylic acid diester component is composed of 50-70 mol% of 3,3 ′, 4,4′-biphenyltetracarboxylic diester and 5-15 mol% of 2,3,3 ′, 4′- Biphenyltetracarboxylic diester and 20 to 40 mol% of 3,3 ′, 4,4′-benzophenonetetracarboxylic diester, wherein the aromatic diamine component is 70 to 97 mol% of m-phenylenediamine; From 30 to 3 mol% of 4,4′-methylene dianiline is preferable from the viewpoint of mechanical properties and heat resistance of the obtained 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 preferably added to the polyimide precursor powder used in the present invention, if necessary. Can be added. As the surfactant (foam stabilizer), a surfactant suitably used as a foam stabilizer for a polyurethane foam can be suitably used. Above all, a graft copolymer in which a part of the methyl group of polydimethylsiloxane is substituted by a polyalkylene oxide group such as a polyethylene oxide group, a poly (ethylene-propylene) oxide group or a propylene oxide group (the substituted polyalkylene oxide group The terminal is a hydroxyl group or an alkyl ether group such as methyl ether or an alkyl ester group such as acetyl group).

  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 (all manufactured by Dow Corning Toray Silicone), L-5340, SZ-1666, SZ-1668 (all manufactured by Nippon 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 (above, 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 pyridines 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 obtained by uniformly evaporating a solvent from a so-called molecular-dispersed polyimide precursor solution of a raw material mainly containing the polyimide precursor and drying the solvent to obtain a dried product (solid). Can be manufactured by pulverizing the solvent or simultaneously evaporating and pulverizing the solvent using a spray drier or the like. When evaporating the solvent, it is preferable to perform the heat treatment within a low temperature range where foaming does not occur. Here, it is sufficient that the raw material can be powdered, and it is preferable that the solvent remains at about 0.1 to 15% by mass. Usually, for example, even when methanol, which is a low boiling point solvent, is used, 0.1 to 10% by mass, preferably 0.5 to 5% by mass of (free) methanol remains. The polyimide precursor powder obtained by evaporating at a temperature higher than the above-mentioned temperature has significantly reduced foaming properties. 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 at least an aromatic tetracarboxylic acid diester component and an aromatic amine component, and if necessary, additives such as a surfactant (foam stabilizer), a catalyst, and a flame retardant. Add the components of the body, mix and stir at preferably 60 ° C. or lower (usually room temperature, for example, 24 ° C.), preferably for about 0.1 to 6 hours (usually 1 to 2 hours), and dissolve uniformly. Can be manufactured by
In particular, first, an aromatic tetracarboxylic dianhydride and, if necessary, an esterification catalyst are added and reacted in a lower alcohol to prepare a lower alcohol solution of an aromatic tetracarboxylic ester component, and the reaction solution is prepared. A method in which another component such as an aromatic amine component is added, uniformly dissolved and mixed is preferable.
Here, the aromatic tetracarboxylic acid ester component and the aromatic amine component have a substantially equivalent number, specifically, the ratio of the equivalent number (aromatic tetracarboxylic acid component / aromatic diamine component) is 0.95 to 1. In the case of the aromatic tetracarboxylic acid ester component and the aromatic diamine component, the molar ratio (aromatic tetracarboxylic acid component / aromatic diamine component) is 0.95 to 1 It is preferable to use in the range of 0.05.

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, but when powdered to obtain a polyimide precursor, a low-boiling solvent is suitably used.
In addition, additives such as a surfactant, a catalyst, and a flame retardant, which are added as necessary to the polyimide precursor, 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 into a mold and heating 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 above the edge of the mold is flattened by scraping with a rod or a plate, and then foamed from this state. The shape and size of the mold are not particularly limited.

  Further, the production method of the present invention does not include a step of increasing the bulk density by applying vibration to the polyimide precursor powder filled in the mold. It is preferable that the polyimide precursor powder be scraped off without being compressed even in the above-mentioned grinding step.

  The heat treatment in the foaming step is not limited as long as heating for foaming can be performed, but can be suitably performed using, for example, 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 according to the type and processing amount of the polyimide precursor.

  In the case of heating in an oven, it is necessary to perform heat treatment at a temperature range of preferably 80 to 200 ° C, more preferably 100 to 180 ° C, 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 above-mentioned heating temperature, a long time is required for foaming, which is not preferable. If the heating temperature is higher than the above-mentioned heating temperature, it becomes difficult to make the foam cells of the polyimide foam uniform, which is not preferable.

  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 larger output. For example, an output of 1 to 25 kW is suitably employed for a few tens to a few thousand grams of the 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, at the stage where foaming is completed, the obtained polyimide foam does not have sufficient mechanical strength. Therefore, it is preferable to further heat the obtained polyimide foam using a heating device such as an oven.

  The post-heating depends on the size of the obtained polyimide foam, but a temperature range of 200 ° C. or more and a glass transition temperature of the polyimide foam + 10 ° C. or less, usually 200 to 500 ° C., preferably 200 to 400 ° C. The heating can be suitably performed by heating in a temperature range for 5 minutes to 24 hours, preferably 1 to 15 hours. The post-heating is performed, for example, by gradually increasing the temperature from a relatively low temperature of about 200 ° C. at a rate of 10 ° C./min, and finally heating at a high temperature of about 350 ° C. according to a predetermined temperature profile. The method may be changed.

  The expansion ratio and apparent density (density) are calculated based on the amount of volatile components (such as alcohol and water generated during polymerization imidization, a solvent and other volatile additives) during foaming, and the method of heat treatment. Alternatively, the temperature can be appropriately controlled by various conditions such as a temperature profile at the time of 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 formed in a fine and uniform cell state without cracks by a simple operation and a simple process. Good (yield) production is possible.

Next, the present invention will be described in more detail by way of examples. Note that the present invention is not limited to the following embodiments.
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 '4,4'-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 × 1.2 m formwork, 7 × 7 points (49 points) with equal vertical and horizontal intervals are specified, and the thickness of the powder is measured with a gold scale to measure 49 points. The average value was taken as the average thickness. The standard deviation (δ) was determined for these measured values.
<Bulk density and bulk density distribution>
A cylinder having a fixed area was inserted into 49 places where the thickness was measured, and the polyimide precursor powder was sampled and weighed.
The bulk density was calculated by the following formula.
Bulk density (g / cc) = weight (g) / recovered area (cm ² ) × thickness (cm)
The standard deviation (δ) was determined for these measured values.
<Void number>
Using a digital camera having 40 million pixels or more, an image was taken so that a cut surface of a 1.05 mx 1.15 m polyimide foam and a scale showing dimensions could be seen.
Using an image processing software ImageJ, it 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)
After charging 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 in a 3 m ³ SUS reactor, the temperature was raised. Then, while refluxing, the mixture was heated and stirred for 2 hours to esterify s-BPDA, a-BPDA, and BTDA, respectively, to obtain a uniform solution.

  After cooling the obtained solution to room temperature, 156 kg (1,440 mol) of MPD of an aromatic diamine component, 32 kg (160 mol) of MDA, and L6100J (manufactured by Momentive Performance Materials) of a silicone-based surfactant were added. 16 kg was added and stirred to obtain a homogeneous solution without generating a precipitate.

  This solution was sprayed into a spray drier and dried at a drying air temperature of 65 ° C. while removing methanol as a solvent 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 charging 17.0 kg of the polyimide precursor powder into a mold having a bottom surface size of 1.2 × 1.2 m and a height of 0.025 m, the square bar is moved along the top surface of the mold, The top surface of the polyimide precursor powder was scraped off and flattened. The amount of 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 Denki Koki) and irradiated with microwaves for 15 kW × 17 minutes and 32 kW × 15 minutes to foam while rotating the turntable at a rotation speed of 3 rpm. This was put into a hot air oven (manufactured by Noritake Co., Ltd.) heated to 200 ° C., and heated stepwise to a maximum temperature of 330 ° C. to perform a 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 pouring 20.0 kg of polyimide precursor powder into a mold frame with a bottom size of 1.2 m x 1.2 m and a height of 0.030 m, level it with a flat plate to make it uniform, and place the flat plate on top. And vibrated for 5 minutes on a vibration table (manufactured by Exen). Then, the square bar was moved along the upper surface of the mold to scrape and flatten the upper surface of the polyimide precursor powder. The amount of 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 the polyimide precursor powder was charged into a mold having a bottom surface 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 maximum height of the obtained polyimide foam was 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, and is leveled with a flat plate so as to be uniform, and a flat plate is placed on top. The sample was placed on a vibrating table (manufactured by Exen) and vibrated for 5 minutes. 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 maximum height of the obtained polyimide foam was 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,
Filling the polyimide precursor powder in the mold, including the step of scraping the upper surface, not including the step of increasing the bulk density by applying vibration to the polyimide precursor powder filled in the mold And a method for producing a polyimide foam. The aromatic tetracarboxylic acid diester component is composed of 50 to 70 mol% of 3,3 ′, 4,4′-biphenyltetracarboxylic acid diester and 5 to 15 mol% of 2,3,3 ′, 4′-biphenyltetracarboxylic acid. A carboxylic acid diester and 20 to 40 mol% of 3,3 ′, 4,4′-benzophenonetetracarboxylic acid diester, wherein the aromatic diamine component comprises 70 to 97 mol% of m-phenylenediamine; The method for producing a polyimide foam according to claim 1, comprising 3 mol% of 4,4'-methylenedianiline.