Polyimide foam and method for producing same
View Patent ↗Disclosed is a polyimide foam made of an aromatic polyimide composed of a tetracarboxylic acid component, which is composed of 0 to 90% by mole of a 3,3′,4,4′-biphenyltetracarboxylic acid component and 100 to 10% by mole of a 3,3′,4,4′-benzophenone tetracarboxylic acid component and/or a 2,3,3′,4′-biphenyltetracarboxylic acid component, and a diamine component, which is composed of 50 to 97% by mole of m-phenylenediamine and 50 to 3% by mole of 4,4′-methylenedianiline. The polyimide foam can be produced easily, has uniform and fine cells, and has the mechanical properties required for practical use as a foam, such as flexibility that prevents the foam from cracking easily even when deformed and excellent cushioning properties, as well as heat resistance that can resist use at high temperatures.
1. A polyimide foam made of an aromatic polyimide having a repeating unit represented by chemical formula (1) shown below:
wherein, 40 to 70% by mole of A in the chemical formula (1) is a tetravalent unit based on a biphenyltetracarboxylic acid structure represented by chemical formula (2) shown below, and 60 to 30% by mole of A is a combination of a tetravalent unit based on a benzophenone tetracarboxylic acid structure represented by chemical formula (3) shown below and a tetravalent unit based on a biphenyltetracarboxylic acid structure represented by chemical formula (4) shown below:
and 50 to 97% by mole of B in the chemical formula (1) is a divalent unit based on a m-phenylene structure represented by chemical formula (5) shown below, and 50 to 3% by mole of B is a divalent unit based on a diphenylmethane structure represented by chemical formula (6) shown below:
2. The polyimide foam according to claim 1 , characterized by having at least such flexibility that no cracks appear when a specimen of the polyimide foam with a 1-by-1-cm cross section and a length of 5 cm is deformed until the specimen's opposite ends, in its length direction, come into contact with each other and the specimen is deformed into a ring.
3. The polyimide foam according to claim 1 , characterized by having such cushioning properties that, when a 2-by-2-by-2-cm cubic specimen of the polyimide foam is compressed by applying a load on one surface of the specimen to a thickness of 0.2 cm, held in the compressed state for 30 seconds, and released from the load, the permanent strain in thickness is 30% or less.
4. The polyimide foam according to claim 1 , wherein the aromatic polyimide has a glass transition temperature of at least 300° C.
5. The polyimide foam according to claim 1 , where the polyimide foam has an expansion ratio of at least 75.
6. A method for producing a polyimide foam, comprising:
preparing a polyimide precursor by uniformly dispersing an aromatic tetracarboxylic acid diester component composed of 40 to 40% by mole of a 3,3′,4,4′-biphenyltetracarboxylic acid diester and 30 to 60% by mole of a combination of a 3,3′,4,4′-benzophenone tetracarboxylic acid diester and a 2,3,3′,4′-biphenyltetracarboxylic acid diester, and an aromatic diamine component composed of 50 to 97% by mole of m-phenylenediamine and 50 to 3% by mole of 4,4′-methylenedianiline; and
then heating the polyimide precursor.
7. The polyimide foam production method according to claim 6 , wherein the polyimide precursor contains a polyimidization catalyst.
8. The polyimide foam production method according to claim 6 , wherein the polyimide precursor contains a surfactant.
9. The polyimide foam according to claim 2 , characterized by having such cushioning properties that, when a 2-by-2-by-2-cm cubic specimen of the polyimide foam is compressed by applying a load on one surface of the specimen to a thickness of 0.2 cm, held in the compressed state for 30 seconds, and released from the load, the permanent strain in thickness is 30% or less.
10. The polyimide foam according to claim 2 , wherein the aromatic polyimide has a glass transition temperature of at least 300° C.
11. The polyimide foam according to claim 3 , wherein the aromatic polyimide has a glass transition temperature of at least 300° C.
12. The polyimide foam according to claim 2 , where the polyimide foam has an expansion ratio of at least 75.
13. The polyimide foam according to claim 3 , where the polyimide foam has an expansion ratio of at least 75.
14. The polyimide foam according to claim 4 , where the polyimide foam has an expansion ratio of at least 75.