JPH07216122A - Porous polyimide and its production - Google Patents

Abstract

PURPOSE:To produce a porous polyimide with high strengths and elongation by a simple process by pressing a pile of sheets of wet paper comprising a specific polyimide precursor at normal temp. to remove water from the wet paper and simultaneously to unite the pile into a board and heating the board to subject the precursor to cyclodehydration. CONSTITUTION:A porous polyimide comprising poly(4,4- oxydiphenylenepyromellitimide) and having a porosity of 20-50%, a tensile strength of 3kg/mm<2> or higher, and an elongation of 10% or higher is produced by a simple process without using a blowing agent by dispersing, in an aq. medium. fibrids comprising a polyimide precursor which is cyclized poly(4,4'-- oxydiphenylenepyromellitimide), forming the dispersion into paper. piling sheets of the resulting wet paper, pressing the piled wet paper at noraml temp. to remove water from the paper and to unite the pile into a board, heating the board at 100-200 deg.C to cyclize 50-90% of the precursor, thermally pressing the board at 100-300 deg.C under 1-1,000kg/cm<2>, and heating the board at 300 deg.C or higher under normal pressure to complete the cyclization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyimide porous body and a method for producing the same.

[0002]

2. Description of the Related Art Polyimide has excellent heat resistance, mechanical properties, electrical properties, weather resistance and the like, and is known to be useful as a raw material for films and molded products. For example,
From polyimides produced from 4,4′-diaminodiphenyl ether and pyromellitic dianhydride, films and molded products having excellent heat resistance are obtained, and these are widely used for electrical insulation applications and the like.

Conventionally, a thick molded article of a non-thermoplastic polyimide has a polyimide powder of about 700 to 7,000 kg / cm ² as described in JP-B-49-5737.
Compressed at a molding pressure of
It was obtained by heating at a temperature of ℃ or more and sintering.
However, since polyimide powder does not have heat-melting property and deformability, extremely high pressure as described above is required for molding, and it is difficult to obtain a preform that can be handled at a lower pressure. Therefore, it is difficult to obtain a porous molded product having uniform pores by such a method.

Further, Japanese Patent Publication No. 57-49056 discloses that
A method of press-molding a polyimide powder and a granular polymer of formaldehyde and sintering to obtain a porous polyimide molding is disclosed. However, this method has a problem that toxic formaldehyde gas is generated in the heating step. In addition, a method of mixing a polyimide powder with a sublimable substance or the like, a method of molding after foaming a polyimide precursor solution, etc. have been devised,
All of them had problems such as complicated operation and low strength of the product.

[0005]

In view of such circumstances, an object of the present invention is to provide a polyimide porous body having high strength and a simple method for producing the same.

[0006]

Means for Solving the Problems As a result of intensive investigations, the present inventors will be described later using a fibrid composed of a polyimide precursor which is ring-closed to form poly (4,4'-oxydiphenylenepyromellitimide). It was found that a polyimide porous body having high strength can be easily manufactured by manufacturing the polyimide porous body by such a method, and thus the present invention has been accomplished.

That is, the gist of the present invention is poly (4,
4′-oxydiphenylenepyromellitimide), having a porosity of 20 to 50% and a tensile strength of 3 kg / mm ^2.
As described above, the polyimide precursor has an elongation of 10% or more, and the polyimide porous body is a polyimide precursor that forms a poly (4,4′-oxydiphenylenepyromellitimide) by ring closure. The fibrid consisting of is dispersed in an aqueous medium for papermaking, the wet paper thus obtained is laminated in a wet state, and the laminated wet paper is dehydrated by a room temperature press and integrated to form a board, which is heated at 100 to 200 ° C. 50 to 50 of the polyimide precursor constituting the fibrids
After 90% ring closure, 100 ~ 300 ℃, 1 ~ 1000
Heat press at kg / cm ² and 300 at normal pressure
It is obtained by terminating the ring-closing reaction by heating to ℃ or higher.

The present invention will be described in detail below. Fibrids of the polyimide precursor used in the present invention,
When closed, it forms poly (4,4'-oxydiphenylenepyromellitimide), which is produced by polymerizing pyromellitic dianhydride and diaminodiphenyl ether.

The polyimide precursor has an intrinsic viscosity [η] of 0.
It is preferably 1 or more, and particularly preferably 0.5 or more. If [η] is less than 0.1, it tends to be difficult to obtain a product having high strength. [Η] is a value directly related to the molecular weight of the polymer measured by gel permeation chromatography (GPC) or the like, and the polyimide precursor concentration is 0.5% by weight in an N, N-dimethylacetamide solvent. Measure at 30 ° C. To calculate [η], the time required for the polymer solution to flow through a capillary tube having a fixed volume of a standard viscometer and the time for which only a solvent flows can be measured, and can be calculated using the following equation.

[0010]

[Equation 1]

In the present invention, the polyimide precursor fibrids refer to fibrous or film-like particles of the polyimide precursor, and the size of the fibrids is such that two of the three dimensions are on the order of microns. The polyimide precursor fibrids that can be used in the present invention can be any as long as the above conditions are satisfied, but in order to obtain a polyimide porous body having high strength, it was produced as follows. It is preferable to use the polyimide precursor fibrids.

That is, in order to obtain the preferred polyimide precursor fibrids, a solution of the polyimide precursor is obtained, and the polyimide precursor solution is poured into the coagulation bath under shearing action to precipitate the solution. As a device for that, a mixer,
A Waring mixer, a flow path agitator combining a rotor and a stator, and the like are used.

As the coagulation bath, any solvent may be used as long as it is a poor solvent for the polyimide precursor. Usually, water which is a typical poor solvent for the polyimide precursor, or
A mixed solvent containing 70% by weight or more of water is used. As the solvent in the mixed solvent containing water, any solvent having water solubility may be used, but water-soluble ethers, water-soluble alcohols, and water-soluble ketones are preferably used. The volume ratio of the coagulation bath to the polyimide precursor solution is preferably 5 to 100. The appropriate temperature for fibrid formation is 10 to 60 ° C, and the time for exerting shearing action is 5
Seconds to 10 minutes are suitable.

In the present invention, there is no limitation on the polyimide precursor solution for producing the polyimide precursor fibrids, but a solvent consisting of a mixed solvent of a solvent which does not strongly solvate the polyimide precursor and the solvent alone or a solvent consisting of a single solvent. Among them, those obtained by polymerizing pyromellitic dianhydride and diaminodiphenyl ether are preferable. The polymerization reaction temperature is −30 to 60 to obtain a polyimide precursor solution in a solvent that is not strongly solvated with the polyimide precursor.
C is preferable, and -20 to 40 C is more preferable. The polymerization reaction time is preferably 1 to 200 minutes, more preferably 5 to 100 minutes. Further, the polyimide precursor solution may be manufactured by dissolving a polyimide precursor manufactured by another method in these solvents. The concentration of the polyimide precursor in the polyimide precursor solution is preferably 0.1 to 60% by weight, and 1
-25% by weight is more preferred.

As the mixed solvent of the polyimide precursor and the solvent which is strongly unsolvated, a mixed solvent selected from water-soluble ether compounds, water-soluble alcohol compounds, water-soluble ketone compounds and water is preferably used. As the sole solvent, a water-soluble compound having an ether group and an alcoholic hydroxyl group in the same molecule is preferably used.

Examples of the water-soluble ether compounds include tetrahydrofuran (THF), dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether and the like. Particularly preferred is THF.

As the water-soluble alcohol compound, for example, methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol,
Ethylene glycol, 1,2-propanediol, 1,
3-propanediol, 1,3-butanediol, 1,
4-butanediol, 2,3-butanediol, 1,5
-Pentanediol, 2-butene-1,4-diol,
2-methyl-2,4-pentanediol, glycerin,
2-ethyl-2- (hydroxymethyl) -1,3-propanediol, 1,2,6-hexatriol and the like can be mentioned. Particularly preferred are methanol, ethanol and ethylene glycol.

As the water-soluble ketone compound, for example,
Acetone, methyl ethyl ketone, etc. are mentioned. Particularly preferred is acetone. In the case of the mixed solvent, the combination of the water-soluble ether compound and water, the combination of the water-soluble ether compound and the water-soluble alcohol compound, and the combination of the water-soluble ketone compound and water are particularly preferable.

The mixing ratio of the solvent in the mixed solvent is, by weight, 9 in the case of the water-soluble ether compound and water.
6: 4 to 79:21, 90:10 to 56:44 for water-soluble ether compounds and water-soluble alcohol compounds,
In the case of water-soluble ketone compound and water, 90:10 to 65:
35 is preferred.

In the case of a single solvent, a water-soluble compound having an ether group and an alcoholic hydroxyl group in the same molecule is used. Examples of such a solvent include 2-methoxyethanol, 2-ethoxyethanol and 2- (methoxymethoxy). ) Ethoxyethanol, 2-isopropoxyethanol, 2-butoxyethanol, tetrahydrofurfuryl alcohol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monoethyl ether, tetraethylene glycol, 1-
Methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, polyethylene glycol, polypropylene glycol and the like can be mentioned. Particularly preferred are 2-methoxyethanol, diethylene glycol monomethyl ether, and tetrahydrofurfuryl alcohol. Further, a water-soluble compound having an ether group and an alcoholic hydroxyl group in the same molecule and a poor solvent can be used in combination.

The polyimide porous body of the present invention is prepared by dispersing the above-mentioned polyimide precursor fibrids in an aqueous medium for papermaking,
The obtained wet papers are laminated in a wet state, and the laminated wet papers are dehydrated by a normal temperature press and integrated to form a board.
After heating at 00 to 200 ° C. to cyclize 50 to 90% of the polyimide precursor constituting the fibrids, 100 to
It is obtained by hot pressing at 300 ° C. and 1 to 1000 kg / cm ² , and further heating at 300 ° C. or higher under normal pressure to terminate the ring-closing reaction.

That is, the polyimide precursor fibrids are uniformly dispersed in an aqueous medium such as water by a method such as stirring, and a Fourdrinier or cylinder type papermaking machine is used as in the case of the conventionally known papermaking of natural pulp. Papermaking, and then squeezing and dehydrating at 1 to 10 kg / cm ² at room temperature to obtain a polyimide precursor wet paper. Laminate any number of the obtained polyimide precursor wet paper, and at room temperature, 1 to 200 kg / cm
^{In 2} , further dehydration and integration of the laminated layers.
Pressing in a wet state forms a polyimide precursor board in which the fibrids of each layer are strongly bonded to each other.

Dry the resulting polyimide precursor board
The board is heated to obtain a board in which a part of the polyimide precursor constituting the fibrids is closed. That is, a sufficiently dried polyimide precursor board is heated at 100 to 200 ° C., particularly 160 to 190 ° C., and 50 to 90%, particularly 60 to 8% of the polyimide precursor constituting the fibrids.
Close 0%. If the temperature is higher than 200 ° C., the ring-closing reaction proceeds in a short time, so that it is difficult to control the ring-closing rate, and it tends to be difficult to obtain a product having high strength. When hot pressing is performed without partial ring closure, abrupt ring closure reaction easily causes foaming, cracking, etc., and a high-strength polyimide porous body cannot be obtained.

Next, hot pressing is performed. The conditions of the hot press are 100 to 300 ° C. and 1 to 1000 kg / c.
m ² , especially 200 to 300 ° C., 1 to 200 kg / cm ²
Is suitable, and the effect of the present invention cannot be obtained unless it is within this range. That is, at a temperature lower than this condition and a low pressure, a product having a tensile strength of 3 kg / mm ² or more cannot be obtained. At a temperature higher than this condition and a high pressure, the porosity is 20% or more and the elongation is 1
0% or more of products cannot be obtained. Finally, it is heated to 300 ° C. or higher to terminate the ring-closing reaction.

In this way, a polyimide porous body is obtained.
The porosity of the polyimide porous body can be controlled by the pressure of the laminating press and / or the heating press, and the porosity can be adjusted to 2
0 to 50%. When the porosity is within this range, a polyimide porous body having a tensile strength of 3 kg / mm ² or more and an elongation of 10% or more can be obtained. The porosity is calculated from the following formula, where the theoretical density of polyimide is Ag / cm ³ and the apparent density of the porous polyimide body is Bg / cm ³ .

[0026]

[Equation 2]

Additives such as short fibers can be added to the polyimide porous body within a range that does not impair the effects of the present invention. In this case, when the polyimide precursor fibrids are added to the aqueous slurry when making a paper, a product in which the additives are uniformly dispersed can be obtained.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Each characteristic value was obtained as follows. Water retention: JAPAN TAPPI Paper pulp test method N
o. 26-78. Elongation rate: Measured according to JIS K6911. Tensile strength: Measured based on JIS K6911.

Example 1 4.00 g of diaminodiphenyl ether was dissolved in a mixed solvent of 59.6 g of THF and 15.9 g of methanol,
It was kept at 3.8 ° C. To this solution, 4.40 g of pyromellitic dianhydride was added all at once and stirring was continued for 1 hour to obtain a polyamic acid solution having a polyamic acid [η] of 1.0.
A mixed solvent of THF and methanol (weight ratio 4/1) was added to this polyamic acid solution so that the solid content concentration became 7.5%.
Diluted with. The rotational viscosity at this time was 74 cps. Diluted polyamic acid solution at 24 ml / min,
Continuous continuous homomixer (capacity 500 ml, turbine speed 8500 rp.
m) to obtain a fibrid slurry, and the fibrid slurry was continuously taken out from the discharge port. Polyamic acid fibrids were separated from the fibrid slurry by filtration, 1 liter of water was added, and the mixture was stirred and filtered three times. The obtained polyamic acid fibrid had an [η] of 0.8 and a water retention of 460.

Then, about 6 g of polyamic acid fibrids was dispersed in 3 liters of water, and paper was made into a size of 15 × 15 cm. Five wet papers obtained by pressing and dehydrating at a pressure of 10 kg / cm ² were stacked and further pressed and dehydrated at a pressure of 100 kg / cm ² , and each layer was integrated. After drying at 60 ℃ for 1 hour, heat at 180 ℃ for 10 hours under nitrogen atmosphere to 70%
Partial ring closure was performed. After hot-pressing for 10 minutes at 300 ° C. and 10 kg / cm ² , heat treatment at 300 ° C. for 30 minutes completes the ring closure, and the thickness is 1.26 mm and the porosity is 20.
% Polyimide porous body was obtained. The tensile strength of this polyimide porous body was 5.75 kg / mm ² , and the elongation rate was 20%.

Example 2 A polyimide porous film having a thickness of 1.75 mm and a porosity of 39% was prepared in the same manner as in Example 1 except that 5 wet paper sheets were stacked, squeezed and dehydrated at 10 kg / cm ² and each layer was integrated. Got the body Tensile strength is 3.95 kg / mm ² and elongation is 26.
It was 2%.

Example 3 Five wet paper sheets were stacked and pressed and dehydrated at 20 kg / cm ² , and each layer was integrated, and the pressure of the heating press was 50 kg / cm.
^{The same} procedure as in Example 1 is repeated except that the thickness is changed to 1.38.
A polyimide porous body having a size of mm and a porosity of 36% was obtained. The tensile strength was 4.27 kg / mm ² and the elongation was 26.6%.

Example 4 The same procedure as in Example 1 was carried out except that 5 wet paper sheets were stacked, pressed and dehydrated at 20 kg / cm ² , and the respective layers were integrated, and the pressure of the hot press was set to 2 kg / cm ^2. 1.64m
Thus, a polyimide porous body having m and a porosity of 45% was obtained. The tensile strength was 3.33 kg / mm ² and the elongation was 22.4%.

Example 5 Example 5 except that five wet paper sheets were stacked and squeezed and dehydrated at 20 kg / cm ² and each layer was integrated, and the temperature of the hot press was 200 ° C. and the pressure of the hot press was 50 kg / cm ^2. The same procedure as in 1 was performed to obtain a polyimide porous body having a thickness of 1.42 mm and a porosity of 42%. Tensile strength is 3.48 kg / mm ² ,
The elongation percentage was 27.2%.

Example 6 5.4 g of polyamic acid fibrids and 0.6 g of para-aramid short fibers were dispersed in 3 liters of water to produce paper having a size of 15 × 15 cm. Four wet paper sheets pressed and dehydrated at a pressure of ² kg / cm ² were stacked and further pressed and dehydrated at a pressure of 150 kg / cm ² , and each layer was integrated. After drying at 60 ° C. for 1 hour, it was heated at 180 ° C. for 10 hours in a nitrogen atmosphere to perform 70% ring closure. After hot pressing under conditions of 300 ° C. and 10 kg / cm ² for 10 minutes, heat treatment was performed at 300 ° C. for 30 minutes to complete the ring closure. Thickness 1.00 mm, porosity 3
A 3% polyimide porous body was obtained. Tensile strength is 4.75k
The g / mm ² and the elongation rate were 11.6%.

[0036]

INDUSTRIAL APPLICABILITY As described above, the polyimide porous material of the present invention is characterized by having a porosity of 20 to 50%, excellent strength, and high elongation. Further, according to the production method of the present invention, a polyimide porous body can be obtained by a simple method without using any additive or the like for forming pores.

Claims (2)

[Claims] 1. A poly (4,4′-oxydiphenylenepyromellitimide) having a porosity of 20 to 50%.
A polyimide porous body having a tensile strength of 3 kg / mm ² or more and an elongation of 10% or more. 2. A fibrid comprising a polyimide precursor which forms a poly (4,4′-oxydiphenylenepyromellitimide) by ring closure is dispersed in an aqueous medium for papermaking, and the wet paper obtained is wet. Laminated and laminated wet paper is dehydrated by a normal temperature press and integrated to form a board.
After heating at 0 to 200 ° C. to close 50 to 90% of the polyimide precursor forming the fibrids, 100 to 3
The method for producing a polyimide porous body according to claim 1, wherein hot pressing is carried out at 00 ° C. and 1 to 1000 kg / cm ² and further heated at 300 ° C. or higher under normal pressure to terminate the ring-closing reaction.