JPH059312A - Prepreg for fiber-reinforced composite material - Google Patents

Abstract

PURPOSE:To provide a prepreg having good varnish storage stability and used for fiber-reinforced composite materials by employing a PMR type polyimide comprising a specific terminal-sealing agent, a dialkyl tetracarboxylate ester and a diamine as an impregnating agent. CONSTITUTION:A prepreg for fiber-reinforced composite materials having excellent mechanical properties is impregnated with a PMR type polyimide produced from (A) a nadic imide type end-sealing agent of formula I, (B) a dialkyl tetracarboxylate ester of formula II [R1 is CH2, O, SO2, CO, S, C(CH3)2; X is 1-4C alkyl], and (C) a diamine of formula III [R2 is CH2, 0, CO, SO2, S C(CH3)2; X is 1-4C alkyl].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prepreg for a fiber reinforced composite material. More specifically, the present invention relates to a prepreg for a fiber reinforced composite material using PMR type polyimide, which is suitable as a matrix resin having good storage stability of varnish and high mechanical properties of the fiber reinforced composite material.

[0002]

BACKGROUND OF THE INVENTION Condensation-polymerization type polyimides become insoluble in organic solvents as the degree of polymerization increases, so when used as matrix resins for composite materials, so-called amic acid prepolymers before dehydration ring closure are used. It has been used in a state where it is dissolved in a high boiling point solvent such as NMP or DMF and impregnated into the reinforcing fiber.

However, in this method, it is difficult to remove condensed water and high-boiling point solvent generated by ring closure during molding, so that these volatile components remain in the molded product and voids are formed, resulting in physical properties. There was a problem such as a decrease.

In order to solve this problem, addition-curable polyimide has been developed. Addition curing type polyimide
It is a thermosetting resin which is an oligomer having a molecular weight of about 1500 and which has an addition-reactive nadic acid at the terminal, becomes a polyimide polymer through an amic acid prepolymer, and is then crosslinked by a ring-opening addition reaction of the terminal nadic acid.

However, the addition-curable polyimide is also NMP,
It has a problem that it is soluble only in a high boiling point solvent such as DMF.

Therefore, as a result of researches to improve the solubility, PMR type polyimide (in-situ Polymerizat) in which a carboxylic acid anhydride type monomer is esterified with an alcohol and the alcohol is used as a solvent.
ion of Monomeric Reactant
s) is a US WR Systems (TR)
Developed by W Systems, Inc. [Journal of Applied Polymer Science (J. Appl.
Polym. Sci. ). 16, (1972), 90
5]. That is, the PMR-type polyimide is characterized in that a conventional polyimide is a method of dissolving amic acid prepolymer in a high-boiling point solvent to prepare a varnish, whereas a monomer is dissolved in a low-boiling point solvent to prepare a varnish. ..

For example, PMR-15, which is a typical resin among PMR-type polyimides, has 3,3'4 as a monomer.
4'-benzophenone tetracarboxylic acid dimethyl ester (BTDE), nadic acid monomethyl ester (N
E) and 4,4'-diaminodiphenylmethane (DD
M) is directly dissolved in methanol to prepare a varnish, and this varnish is used to produce a prepreg by a wet method.

However, NE has a higher reactivity with diamines such as DDM than aromatic tetracarboxylic acid diesters such as BTDE, and therefore, the reaction between NE and DDM preferentially proceeds during the storage of the varnish. Had a problem that low molecular weight bisdiimide (BNI) was produced [ACS Organic Coatings and Plastics (ACS Organic
Coating and Plastics), 4
0, (1979), 935; Journal of Applied Polymer Science (J. Appl. Poly).
m. Sci. ), 27 (1982), 4295]. Thus, since the monomer composition in the adjusted resin solution changes during storage, it was extremely difficult to produce a prepreg with stable quality.

When a large amount of BNI is produced, the remaining monomer forms a high molecular weight oligomer, which changes the molecular weight distribution of the entire resin and deteriorates the moldability such as a decrease in fluidity during molding. In addition, the composite material thus obtained deteriorates mechanical properties such as interlaminar shear strength and bending strength, and also has a bad influence on heat resistance such as a decrease in thermal decomposition temperature [National Sampe Symposium (N
nationalSAMPE Symposium), 2
6, (1981), 89].

[0010]

The present invention has the following constitution in order to solve the above problems. That is, the formula [I]

[0011]

[Chemical 4] And a general formula [II]

[0012]

[Chemical 5] And a tetracarboxylic acid dialkyl ester represented by the general formula [III]

[0013]

[Chemical 6] A fiber-reinforced composite material prepreg, which is obtained by impregnating a PMR-type polyimide composed of a diamine represented by

Of course, the polyimide end-capping agent used in the present invention can be used in addition to the PMR type. However, the effect of the present invention is greatest in the case of the PMR type as described below.

Nadiic acid monoalkyl ester (NE), which is a conventional nadic acid type end-capping agent, is stored in BNI during storage.
As a result of research on the cause of the formation of the following, the following conclusions were reached. That is, BTDE, which is a monomer constituting the main chain of PMR-type polyimide, is an aromatic tetracarboxylic acid dialkyl ester, while NE is an alicyclic dicarboxylic acid monoalkyl ester, which has a difference in chemical structure. There was a root cause. The reaction between the aromatic disulphonic acid monoalkyl ester and the aromatic amine begins at 100 ° C or higher, whereas the alicyclic dicarboxylic acid monoalkyl ester has high reactivity, so that the reaction with the aromatic amine is easy even at room temperature. proceed. Therefore, in order to solve this problem, reduce the reactivity of the endcapping agent,
It is necessary to make it as reactive as the other monomers that make up the main chain of the PMR-type polyimide.

Therefore, as a result of intensive investigations by the present inventors on a reactively controlled end-capping agent, as a result, a nadiimide-type end-capping agent having an aromatic amine as a reaction moiety as represented by the above-mentioned formula [I] is obtained. It has been found that the agent meets this requirement. That is, by introducing an aromatic amine in place of using a highly reactive alicyclic dicarboxylic acid monoester as a reactive part of the terminal blocking agent,
It was possible to give the same reactivity as other monomers.

The end-capping agent according to the present invention is prepared by reacting nadic acid anhydride and nitroaniline in an acetamide solution to synthesize nadiimidonitrobenzene as an intermediate, which is then reacted with stannous chloride. It can be synthesized by the method shown in the following reaction formula [IV] for reduction.

[0018]

[Chemical 7] In addition to this, there is also a method shown in the following reaction formula [V] in which maleimidonitrobenzene is synthesized in advance, cyclopentadiene is added, and finally the nitro group is reduced. Therefore, the synthesis method is limited to the above reaction formula [IV]. It is not something that will be done.

[0019]

[Chemical 8] Next, the PMR-type polyimide varnish is prepared by dissolving the terminal blocking agent represented by the formula [I], the tetracarboxylic acid dialkyl ester represented by the general formula [II], and the diamine represented by the general formula [III] in alcohol. It can be adjusted by The polyimide oligomer obtained from this varnish has a molar ratio of diamine: tetracarboxylic acid dialkyl ester: terminal blocking agent of n: (n +), where n is the number of repeating units when oligomerized.
By adjusting so that 1): 2, an arbitrary average molecular weight can be provided.

In the PMR-type polyimide varnish used in the present invention, heat resistance, physical properties, and moldability can be obtained by controlling the chemical structure of the diamine type monomer and the tetracarboxylic acid dialkyl ester type monomer and the average molecular weight when they are oligomerized. Etc. different resins are obtained.

The resin obtained from the PMR-type polyimide varnish has improved mechanical properties as the average molecular weight when oligomerized is increased, but the heat resistance and moldability are lowered.
Therefore, the average number of repeating units n when oligomerized is preferably in the range of 0 to 10, and particularly in the range of 0.4 to 2 where n is well-balanced in terms of heat resistance, moldability and physical properties.
It is suitable as an MR type polyimide varnish.

The PMR type polyimide varnish used in the present invention has good tackiness and drape of the prepreg when impregnated into the reinforcing fiber and has excellent moldability, and the resin obtained by curing the prepreg has excellent heat resistance. It has excellent mechanical properties and is excellent as a matrix resin for fiber-reinforced composite materials. In addition, it is also suitable as an adhesive or a molding material.

When the PMR-type polyimide varnish used in the present invention is used for a fiber-reinforced composite material, the most excellent curing is obtained when carbon fibers are used as the reinforcing fibers, especially when the carbon fibers have high strength. In addition to carbon fibers, glass fibers may be used as the reinforcing fibers, and fibers of different types may be mixed and used.
The fiber may be in any form such as long fiber, woven fabric, knitted fabric, matte or cut fiber.

[0024]

The present invention will be described in more detail by the following examples. (Example 1) <Synthesis of 1-amino-4-nadiimidobenzene> a. 1-nitro-4-nadiimidobenzene 1-amino-4-nitrobenzene 138 g was dissolved in dimethylacetamide 500 ml, and a solution of 164 g of nadic acid anhydride dissolved in 500 ml of dimethylacetamide was added dropwise while stirring at room temperature. did. After completion of dropping, the mixture was stirred at room temperature for 1 hour, 150 ml of triethylamine and 150 ml of benzene were added, and the mixture was stirred at 140 ° C for 3 hours.
Reacted for hours. After completion of the reaction, the mixture was left standing overnight at room temperature.
It was poured into water and the orange precipitate was filtered, washed with water and dried in vacuo.

Yield 236 g (83%) Elemental analysis result (calculated value) C: 63.98 (63.38); H: 4.11 (4.2)
3); N: 10.02 (9.86) b. 1-Amino-4-nadimidobenzene 200 g of 1-nitro-4-nadimidobenzene was dissolved in acetonitrile, 850 g of stannic chloride dihydrate was added, and the mixture was reacted at 60 ° C for 2 hours. After cooling to room temperature, the reaction solution was poured into water and neutralized with sodium carbonate. The precipitate was filtered, vacuum dried, and Soxhlet extracted with acetonitrile. Acetonitrile was distilled off under reduced pressure to obtain a white solid.

Yield 130 g (75%) Elemental analysis result (calculated value) C: 70.32 (70.87); H: 5.68 (5.5)
1); N: 10.87 (11.02) (Example 2) Ethanol was added to 3,3 ', 4,4'-benzophenonetetracarboxylic acid and the mixture was refluxed for 3 hours to completely dissolve the diester. Compound (BTD
A solution of E) was obtained. Next, 1-
Amino-4-nadiimidobenzene (ANB) and 4,4 '
Dissolve diaminodiphenylmethane (DDM). At this time, the molar ratio of ANB: BTDE: DDM is 2 :.
Added at 3: 2. Excess ethanol was distilled off from this solution under reduced pressure to obtain a PMR-type polyimide varnish.

When this varnish was stored at 20 ° C. and analyzed by high performance liquid chromatography over time, 6
The composition did not change even after 0 day, and the storage stability was good.

A prepreg was prepared by the hot melt method using a varnish stored at 20 ° C. for 60 days and “Torayca” T400 manufactured by Toh & Les Co., Ltd. The resin content of the obtained prepreg was 39.6%. The prepreg thus obtained was cut into a piece having a length of 30 cm and a width of 20 cm, laminated with each other, pressurized to 14 kg / cm ² at 160 ° C. in an autoclave, heated to 290 ° C., held for 2 hours, and then allowed to reach room temperature. After cooling, the molded product was taken out from the autoclave.
The obtained molded product was after-cured at 316 ° C. for 6 hours to obtain a molded product. It was found that the obtained molded product had a volume content of carbon fiber of 60.2% and a glass transition temperature of 332 ° C. measured by a DSC method and had good heat resistance.

Next, from the obtained molded product, ASTM, D-7
A test piece was cut out in accordance with 90 and the bending characteristics were measured. The bending strength was 190 kg / mm ² , the bending elastic modulus was 1
It had excellent mechanical properties at 3.8 t / mm ² . Comparative Example P was prepared in the same manner as in Example 2 except that nadic acid monomethyl ester (NE) was used as the end-capping agent and the molar ratio of NE: BTDE: DDM was 2: 2: 3.
An MR type polyimide varnish was prepared.

When this varnish was stored at 20 ° C. and analyzed by high performance liquid chromatography over time, 6
After 0 days, 13% of bisnadiimide was produced, and the composition of the varnish was changed. Using this varnish, a prepreg was prepared in the same manner as in Example 2 and molded, and the bending characteristics of the composite material were measured.
It had a low physical property of 62 kg / mm ² and a flexural modulus of 13.6 t / mm ² .

[0031]

INDUSTRIAL APPLICABILITY The prepreg for a fiber-reinforced composite material of the present invention has a good storage stability of varnish, and the fiber-reinforced composite material obtained thereby has excellent mechanical properties.

[Chemical 9]

[Chemical 10]

[Chemical 11]

Claims (1)

Claims: [Claim 1] Formula [I] An end-capping agent represented by the general formula [II] And a tetracarboxylic acid dialkyl ester represented by the formula [III] A fiber-reinforced composite material prepreg, which is impregnated with a PMR-type polyimide composed of a diamine represented by: