JP3425183B2 - Method for producing prepolymer for polyimide foam, polyimide foam and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a prepolymer for a polyimide foam, a polyimide foam and a method for producing the same, and particularly to a polyimide foam having a large expansion ratio without lowering heat resistance and mechanical performance. And a method for economically producing the polyimide foam, and a prepolymer capable of providing the polyimide foam.

[0002]

2. Description of the Related Art As a method for producing a polyimide foam having excellent heat resistance and flame resistance, there are known methods using various diamines as described below. For example, (1) two types of diamines containing not only aromatic diamine but also aliphatic diamine and a foaming agent are used to improve the elasticity of the foam (Japanese Patent Laid-Open No. 61-195126), (2) ) A thermoplastic polyimide foam produced by using an aromatic ether diamine as the diamine (JP-A-2-255).
841), and (3) two kinds of diamines of aromatic diamine and heterocyclic diamine, or a prepolymer obtained by using one kind of diamine is heated by microwave irradiation or the like to be foamed to be wholly aromatic. Manufactured polyimide-based polyimide (JP-A-2-41332, US Pat. Nos. 4,332,656 and 4,816,493)
No. 4,305,796, No. 4,822,53
No. 7, No. 4,897, 432, No. 4,900, 7
No. 61) etc.

[0003]

However, since the molecular structure of the wholly aromatic polyimide is quite rigid, it is difficult to perform molding processing, and the melt viscosity of this polyimide prepolymer is too high, which causes problems such as a low expansion ratio. is there. Therefore, in order to improve the rigidity and the expansion ratio, a copolymerization prepolymer produced by introducing two or more diamines is used. However, this copolymerized polyimide generally has a tendency of lowering heat resistance and mechanical performance, and the diamine thereof is relatively expensive, which is economically problematic. In particular, when an aliphatic diamine is used, the heat resistance and the mechanical performance are greatly reduced.
From the above, there has been a demand for a method capable of increasing the expansion ratio without lowering the heat resistance and mechanical performance of the polyimide foam, and producing the polyimide foam by using an inexpensive and easily available diamine.

The present invention overcomes the above problems.
Using a diamine that is inexpensive and easily available, a prepolymer capable of producing a polyimide foam having a large expansion ratio without deteriorating heat resistance and mechanical performance, and a polyimide foam produced using the prepolymer having excellent performance. An object is to provide a body and a method for producing the body.

[0005]

The method for producing a prepolymer for a polyimide foam (hereinafter, simply referred to as "prepolymer") of the first invention is an aromatic dianhydride as an esterifying agent and a foaming agent. It is esterified with a functional solvent and then the esterified product is combined with aniline and formaldehyde.
The condensate of hydr [represented by the general formula (1) of Chemical formula 1]
It is characterized by responding . The method for producing a polyimide foam according to the second aspect of the present invention comprises esterifying an aromatic dianhydride with a solvent that functions as an esterifying agent and a foaming agent, and then,
This esterified product , aniline and formaldehyde
With a condensate (represented by the general formula (1) in the above chemical formula 1)
It is characterized in that the prepolymer for a polyimide foam is obtained by reacting it , then the prepolymer is dried and, if necessary, crushed to obtain a prepolymer powder, and the prepolymer powder is heated to foam.

Examples of the above-mentioned "aromatic acid dianhydride" include 4,4'-oxaisophthalic anhydride shown in Chemical formula 3,
3,3 ', 4,4'-diphenylsulfone tetracarboxylic dianhydride shown in Chemical formula 4, 3,3', 4 shown in Chemical formula 5
4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, or acid dianhydride having a biphenyl structure in which an ether bond is eliminated in Chemical formula 3, or an anthracene structure in which a benzene ring is condensed, and the like Can be used.

[0007]

[Chemical 3]

[Chemical 4]

[Chemical 5]

As the above-mentioned "solvent", methanol, ethanol, isopropyl alcohol or the like can be used. In addition, as the above-mentioned “ester compound”, usually 1 mol of alcohol is reacted with the acid anhydride part [C- (COO
R) -C (COOH)] structure is applied. The foaming-causing substance in this case is water and alcohol, but the foaming-causing substance in the case where both acid groups are completely esterified is alcohol. The above-mentioned "aniline" means not only aniline but also a compound having a predetermined substituent by reacting (substituting) with formaldehyde and having an amino group (-N
It may be a compound having H ₂ ). In addition, the above
The n number of the “condensate” represented by is usually 0 to 4 (preferably 0 to 2). When it exceeds 4, unreacted amino groups increase, and the heat resistance of the foam deteriorates, which is not preferable. When it is 2 or less, the amino group can be completely reacted, which is more preferable.

In the case of obtaining the prepolymer powder in the above-mentioned second invention, not only the case where the powder is obtained only by drying, but also the case where the powder becomes a lump substance after drying, pulverization is necessary. The polyimide foam of the third aspect of the present invention has a unit in which an aromatic acid dianhydride and a diamine consisting of a condensate of aniline and formaldehyde [represented by the general formula (1) of the above chemical formula 1] are condensed. It has a repeated structure and is characterized by having bubbles inside. The aromatic dianhydride may be a compound represented by the general formula of Chemical formula 2, as shown in the fourth invention. The apparent density of this foam can be about 8.0 kg / m ^{3 to} 10 kg / m ³ . The reason why the density is within this range is that the melt viscosity of the prepolymer during foaming is adapted.

[0010]

The diamine used in the prepolymer of the present invention is a condensate of aniline and formaldehyde. Both anilines and formaldehyde are inexpensive and easily available, and can be easily condensed to synthesize them, which is economical. Also, since one kind of diamine is used, 2
Compared with the case of using a kind of diamine, it does not reduce the rigidity and mechanical strength of the polyimide foam produced, and since it is an aromatic diamine, the rigidity and mechanical strength can be maintained from this point as well. .

According to the production method of the present invention, since the above-mentioned prepolymer is used, a polyimide foam having a repeating unit represented by the above general formula (2) can be produced.
As described above, it has excellent balance characteristics. Since the methylene group was randomly linked to the benzene ring of aniline, the polyimide synthesized from this condensate had weakened rigidity,
Excellent workability. In addition, since the melting temperature of this prepolymer is relatively low, the viscosity of the melt is low, so that the expansion ratio of the foam can be increased. Furthermore, since a prepolymer obtained by reacting an esterified product (particularly a half-esterified product) with a diamine is used, alcohol and water are easily vaporized by heating, and a foam can be easily manufactured.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 155.1 g (0.5 mol) of 4,4'-oxa-bis-isophthalic acid dianhydride (abbreviated as ODPA) shown in Chemical formula 3
A suspension of 100 ml of anhydrous methanol was heated to 65 ° C., refluxed until the solution became transparent and dissolved, and then further refluxed for 1 hour. After cooling the solution to below 40 ° C,
Condensate of aniline and formaldehyde shown in Chemical formula 1 (1)
100.38 g (contains 1 equivalent of amine groups.
And n = 0.6. ) Was added. This mixture was heated at about 40 ° C., and after becoming a transparent solution, the mixture was further reacted at the same temperature for about 1 hour to synthesize a prepolymer solution. To this solution, the surfactant "SH193" (trade name,
3 g of Toray Dow Corning Co., Ltd.) was added and stirred for 5 minutes to form a uniform solution.

Next, excess methanol of this solution was removed by a rotary drying method, a vacuum evaporation method, a spray drying method or the like. The powder obtained by drying is sieved through a 125 μm sieve, and 12
Powder of 5 μm pass (melting temperature 123 ° C., foaming temperature 132
C) was obtained. This powder can be stored for a long time as a foam prepolymer.

120 g of this dry powder was placed in a microwave oven kept at 140 ° C. in a container, melted at the same temperature, and irradiated with a 2 kw microwave to start the condensation reaction. Since this prepolymer melts immediately after entering the microwave oven, the hot air temperature of the oven was set in advance to 140 ° C., which is higher than the melting temperature. The molten prepolymer swelled due to vaporization of water and alcohol produced in this reaction. As a result, a pale yellow foam was obtained. The density of this foam is about 8 kg
/ M ² (0.008 g / cm ³ ). The density was measured according to JIS K6401.

Further, the foam immediately after foaming is heated at 200 ° C. to 2 ° C.
When it was subjected to a stepwise heat treatment up to 50 ° C. (post-cure, total heating time; about 120 minutes), it became an elastic pale yellow foam. When this post-cure was performed, the foamed sample shrank, so that the density was 9 kg / m ³ (9 g / cm ^3
3 ) became. The physical properties of the foam are as shown in Table 1 below. In addition, this physical property was measured by the following methods. Tensile strength is measured according to JIS K6301,
Thermal loss analysis (TGA) is performed by SEIKO SSC / 5200.
Temperature rising rate 10 ° C / min, nitrogen atmosphere 10 by thermal analysis device
It is performed at 0 ml / min, and the thermal conductivity is "Au" manufactured by Eiko Seiki
to- [Lambda] HC-072 "thermal conductivity coefficient measuring device was used. The measurement conditions are as follows: environmental temperature 22.5 ° C, high temperature 4
0 ℃, low temperature 10 ℃, sample size 150mm
It is × 150 mm × 20 mm. In addition, flame retardancy is UL-
The standard was 94.

[0016]

[Table 1] Table 1 −−−−−−−−−−−−−−−−−−−−−− 1− 1 2 3 Comparative Example ------------------------------------ density (kg / m ³⁾ 9. 0 10 10> 20 Tensile strength (kg / cm ² ) 1.4 1.2 1.0 −204 ° C. Thermal loss (TGA) (%) 0.8 0.8 0.8 − Thermal decomposition start temperature (TGA) (5% heat loss) (° C) 506 452 455-Heat aging (250 ° C, 1,000 hours) Tensile strength preservation rate (%)>60>60> 60 -Flame retardancy (UL-94) V-0 V- 0 V-0-Thermal conductivity (Kcal / mh ° C.) 0.034 0.034 0.034 −−−−−−−−−−−−−−−−−−−−−−−−−−−− −−−−−−−−−−

Example 2 3,3 ', 4,4'-diphenylsulfone tetracarboxylic acid dianhydride (abbreviated as DSDA) 179.
3 g (0.5 mol) was dissolved in 320 ml absolute ethanol. A prepolymer and a foam were produced in the same manner as in Example 1 except for the above. The melting temperature of this prepolymer is 135 ° C., the foaming temperature is 145 ° C., and the oven temperature is 150 ° C. The density of the foam after this post-cure was 10 kg / m ³ . Other physical properties are shown in Table 1.

Example 3 161.1 g of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (abbreviated as BTDA) shown in Chemical formula 5
(0.5 mol) was dissolved in 200 ml of isopropyl alcohol in the same manner as in Example 1. Then, this solvent was distilled off at 40 ° C. under reduced pressure, and then vacuum drying was performed at 40 ° C., and as a result, about 210 g of BTDE esterified powder was obtained. 320 ml of this powder 176.9 g (0.4 mol)
Was dissolved in methanol to obtain an esterification solution. Then, the condensate (diamine) 8 used in Example 1 was added to this solution.
0.3 g (containing 0.8 equivalents of amine groups) was added. After that, a prepolymer and a foam were produced in the same manner as in Example 1. The melting temperature of this prepolymer was 150 ° C, the foaming temperature was 161 ° C, and the temperature of the oven was 170 ° C. The density of the foam after this post-cure was 10 kg / m ³ . Other physical properties are shown in Table 1.

Comparative Example BTDA shown in Chemical formula 5 was heated under reflux in an excess of ethyl alcohol to obtain a half-esterified product (6) shown in Chemical formula 6. The half-esterified product (6) was converted to the diamine shown in Chemical formula 7. By reacting (7), a prepolymer (8) shown in Chemical formula 8 was obtained. This prepolymer was foamed at 150 ° C. to produce a foam. The density of this foam is also shown in Table 1.

[0020]

[Chemical 6]

[Chemical 7]

[Chemical 8]

Effects of Examples The prepolymers used in each example are easily melted at 140 to 170 ° C. to show excellent fluidity, and water and a predetermined alcohol are vaporized, so that they can be easily foamed. I was able to. Further, the foaming start temperature varies depending on the type of alcohol, and the melt viscosity of the prepolymer at the foaming start temperature affects the properties of the foam, so in order to obtain the desired foaming start temperature and melt viscosity, Various kinds of esterifying agents were selected and used according to the kind of acid dianhydride.
That is, since the viscosity of the prepolymer at the same temperature increases in the order of Example 1, Example 2, and Example 3, the melt viscosity at the time of foaming can be reduced by increasing the foaming start temperature. Furthermore, the density of the foam of each example is much smaller than that of the comparative example (> 20 kg / m ³ ), showing that the expansion ratio is large, and the tensile strength and heat resistance are also excellent. In the present invention, various changes can be made within the scope of the present invention depending on the purpose and application.

[0022]

EFFECT OF THE INVENTION If a polyimide foam is produced using the prepolymer produced by the present invention, a polyimide foam having a large expansion ratio can be produced inexpensively and easily without lowering the heat resistance and mechanical performance of the foam. Can be manufactured. Further, since the foaming start temperature can be adjusted by changing the type of the esterifying agent, the melt viscosity at the time of foaming can be adjusted, and therefore the foaming ratio can be appropriately adjusted.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takao Hitai 3-12 Kobayashi, Shinome-cho, Anjo City, Aichi Prefecture (56) Reference JP-A-57-53533 (JP, A) US Patent 3554939 (US, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) C08G 73/00-73/26

Claims (4)

(57) [Claims] 1. An aromatic dianhydride is esterified with a solvent that functions as an esterifying agent and a foaming agent, and then the esterified product is condensed with aniline and formaldehyde.
A method for producing a prepolymer for a polyimide foam , comprising reacting a compound [represented by the general formula (1) of Chemical formula 1] . [Chemical 1] 2. An aromatic acid dianhydride is esterified with a solvent that functions as an esterifying agent and a foaming agent, and then the esterified product is condensed with anilines and formaldehyde.
Compound (represented by the general formula (1) in the above chemical formula 1)
To obtain a prepolymer for a polyimide foam, then dry the prepolymer for a polyimide foam, and pulverize as necessary to obtain a prepolymer powder, and heat the prepolymer powder to foam. And a method for producing a polyimide foam. 3. A structure in which a unit obtained by condensing an aromatic dianhydride and a condensate of aniline and formaldehyde [represented by the general formula (1) of the above chemical formula 1] is repeated,
A polyimide foam having air bubbles inside. 4. The polyimide foam according to claim 3, wherein the aromatic dianhydride is a compound represented by the general formula of Chemical formula 2. [Chemical 2]