JPH0521928B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polyimide prepolymer with excellent moldability. More specifically, the present invention relates to an addition polymerizable polyimide prepolymer with good heat resistance and suitable as a matrix resin for fiber-reinforced composite materials.

(Prior Art) Polyimide resin has excellent heat resistance and is therefore used as a matrix resin for molded products and fiber-reinforced composite materials. However, many polyimide resins have extremely poor fluidity even when heated to high temperatures, so addition polymerization type polyimide prepolymers are widely used as the matrix resin for fiber-reinforced composite materials. . A typical example of such a polyimide prepolymer is PMR-15 manufactured by TRW in the United States. PMR-15 is a polyimide polymer represented by the general formula (A). ,5
- Due to the ring-opening addition reaction of endomethylene-1,2,5,6-tetrahydrophthalic anhydride (commonly known as nadzic acid, hereinafter referred to as nadzic acid), volatile matter is not generated during the reaction, and polyimide pre Since the molecular weight of the polymer is small, the resin flows sufficiently during molding, so it has favorable characteristics as a matrix resin for fiber-reinforced composite materials, and is therefore widely used.

However, since the polyimide prepolymer represented by general formula (A) does not have a sufficiently satisfactory level of solubility in solvents and fluidity at high temperatures, when used as a matrix resin for fiber reinforced composite materials, polyamic acid prepolymers are usually used. The polyimide prepolymer of general formula (A) is obtained by impregnating it into reinforcing fibers in a state where it is heated and causing an imidization reaction on the fiber to form a polyimide prepolymer of general formula (A), or by causing an imidization reaction to occur during molding. Methods such as making molded products by carrying out an addition reaction at the rear end have been used.

Various improvements have been made to improve the moldability of such polyimide resins, particularly of fiber-reinforced composite materials, but the biggest problem in molding polyimide resins is the high molding temperature. Although the molding temperature of polyimide resin has been improved with the development of addition polymerization type polyimide resin as shown in general formula (A), the molding temperature is still 300℃.
A higher temperature than that is required. From the fluidity point of view of the polyimide prepolymer, it is possible to lower the molding temperature of the polyimide resin to below 300°C, but in the case of polyimide prepolymers with nadzic acid terminals, addition reactions will occur unless heated above 300°C. The molding temperature must be 300°C or higher to prevent the process from progressing. However, TTSerafini et al. (36th Annual
Conference, Reinforced Plastics／Composites
Institute, The Society of the Plastics
Industries, Inc.February 16−20, 1981,
Section 17-F) discovered the possibility of significantly lowering molding temperatures with the development of vinyl-terminated polyimide prepolymers using m-aminostyrene.

That is, since the addition reaction of a polyimide prepolymer having m-aminostyrene at both ends proceeds at 200°C to 300°C, it can be seen that such a polyimide prepolymer is a polyimide resin that can be molded at 250°C. However, when both ends of the polyimide prepolymer represented by the general formula (A) are changed from nadic acid to a vinyl-terminated compound, good molded products cannot be obtained because the prepolymer has poor fluidity. In other words, while the temperature at which the prepolymer flows is around 210°C, the addition reaction of vinyl groups proceeds at temperatures above 200°C, so before the prepolymer has sufficient fluidity, the addition reaction at the terminals progresses and the viscosity rapidly increases. It was found that this was because the resin was hardened before it was fully impregnated with the resin.

(Problems to be Solved by the Invention) From these facts, it has been found that improving the fluidity of the prepolymer without impairing the heat resistance is an essential condition for improving the moldability of polyimide resin. .

(Means for Solving the Problems) Therefore, the present inventors conducted intensive research on improving the fluidity of polyimide prepolymers, and as a result, they arrived at the present invention.

That is, the present invention has the following configuration.

(1) Tetracarboxylic acid anhydride represented by general formula (), (), amine component represented by general formula () and m-aminostyrene represented by general formula (), or tetracarboxylic acid anhydride represented by general formula () styrene
A method for producing a polyimide prepolymer, characterized in that it is synthesized from 3,4-dicarboxylic acid anhydride.

However, in the formula, Z represents -CH= _CH2 , R is CO,
It represents CH ₂ and O, and the value of n is 1 or more and 5 or less on average.

Note that the average number of repeating units of the prepolymer formed at this time is preferably 10 or less from the viewpoint of fluidity.

Generally used polyimide resins are synthesized from aromatic diamine and aromatic tetracarboxylic acid from the viewpoint of heat resistance, but such polyimide prepolymers have poor fluidity even in the form of polyamic acid prepolymers, and are used in fiber-reinforced composite materials. In order to provide the fluidity necessary for molding, the temperature should be 200℃ or higher, preferably 250℃.
It is necessary to heat it above ℃. However, the present inventors have improved the heat resistance of polyimide by replacing a part of the aromatic tetracarboxylic acid compound () with compound () and using a polyamine represented by the general formula () as the amine component. They succeeded in lowering the fluidity of the prepolymer to below 160°C without impairing its properties.

By the way, in the polyamine (compound []) used in the present invention, from the viewpoint of the fluidity of the prepolymer, if the value of n is too large, the fluidity of the polymer will deteriorate.
The average value shall be 1 or more and 5 or less. Next, regarding the ratio of compound [] and compound [], the fluidity of the prepolymer improves as the ratio of compound [] increases, but on the other hand, the heat resistance decreases, so the number of moles is determined by M() and M(), respectively. Then,
It is preferable that the value of M()/M() is within the range of 0.15 or more and 0.50 or less. If the value of M()/M() is less than 0.15, moldability will be poor due to insufficient fluidity, while if it exceeds 0.50, heat resistance will decrease, which is not preferable. More preferably, when the value of M()/M() is within the range of 0.20 or more and 0.40 or less, a polyimide with the best moldability and heat resistance can be obtained.

It goes without saying that the prepolymer of the present invention can be obtained from tetracarboxylic acid esters thereof as well as the acid anhydrides of general formulas () and (). Note that m-aminostyrene or styrene-3,4-dicarboxylic acid anhydride is used as the vinyl group-containing compound.

Next, in carrying out the present invention, the form of the polyimide prepolymer can be arbitrarily selected depending on the shape of the molded product, the molding method, etc. That is, when making a molded article by using polyimide resin alone or by filling it with powder filler, chopped fiber, etc., it is desirable to use the polyimide prepolymer in the form of polyimide prepolymer. However, when used as a matrix resin for fiber-reinforced composite materials, it can be used in the form of a polyimide prepolymer, but from the viewpoint of impregnation of the resin into fiber bundles, it is difficult to use polyamide, which is a precursor of the polyimide prepolymer. It is more advantageous to split the fibers in the acid state. Furthermore, in terms of impregnating properties, compared to the method of using polyamic acid in the form of polyamic acid, it is possible to convert the tetracarboxylic acid among the raw material monomers into dialkyl esters, dissolve the raw material monomers in a low boiling point solvent such as alcohol, and form the fibers in the monomer state. It is very effective to adopt a method of impregnating the fibers to form polyamic acid on the fibers. Which method to adopt can be arbitrarily selected according to the molding method of the intermediate material and the required specifications for the intermediate material, and the state of the resin on the reinforcing fibers also depends on the intermediate material regardless of the impregnation method. The state of the polyimide prepolymer, the state of the polyamic acid, etc. can be arbitrarily selected according to the required specifications, and these methods are not particularly limited in carrying out the present invention.

Next, the fiber-reinforced composite material according to the present invention can use any of the reinforcing fibers used as reinforcing fibers in ordinary fiber-reinforced composite materials, such as carbon fibers, glass fibers, and organic fibers. , the fibers are aligned in one direction,
It may be in any form such as woven fabrics or knitted fabrics, and it is also possible to use a combination of different types of fibers such as carbon fibers and organic fibers, and is not particularly limited.

Hereinafter, the content of the present invention will be explained in more detail with reference to Examples.

(Example) Example 1 2.00 mol of m-aminostyrene, 4,4'-diaminodiphenylmethane (n in compound ())
= 0), 2.40 moles of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (compound ()), and 5-(2,5-dioxotetrahydrofuryl). After dissolving -3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (compound ()) in NMP at a ratio of 0.72 mol,
Stirring was continued for about 3 hours at room temperature to synthesize polyamic acid, and then the mixture was poured into a large amount of acetone/ether mixed solvent, and the resulting precipitate was filtered and dried under vacuum. The obtained polyamic acid was reacted at 160°C for 3 hours, placed in a polyimide prepolymer mold, heated to 200°C, pressurized to 30Kg/cm ² , and further heated to 250°C while being pressurized. After being heated for 2 hours, the molded product was cooled to room temperature and taken out.
After curing the obtained molded product for 4 hours in an oven at 300°C, the Tg was measured using the DSC method and found to be 328°C, and as a result of thermogravimetric analysis, no thermal decomposition was observed up to 420°C. First, the heat resistance was good.

Example 2 NMP of polyamic acid was prepared in the same manner as in Example 1.
A solution was prepared. Next, the carbon fibers were impregnated with the polyamic acid solution using the Torayka T300 carbon fiber manufactured by Toray Industries, Inc., and dried on the drum at about 60°C for 2 hours, and then the prepreg was removed from the drum. I took it out. The obtained prepreg was further heated at 160°C for 3 hours to completely imidize it, and then cut into pieces of 30 cm long and 20 cm wide.
Laminated in the mold. Note that the resin content in the obtained prepreg was 32% by weight.

Next, the mold laminated with prepreg was inserted into a press heated to 200℃, held at contact pressure for 10 minutes, and kept under pressure of 30Kg/ ^cm2 , then heated to 250℃, and then heated to 250℃. After holding for 2 hours, the mold was cooled and the molded product was taken out. After curing the molded product in an oven for 4 hours at 300℃, test pieces were cut according to the ASTM method and physical properties were evaluated.The bending strength was 195Kg/mm ² .
Flexural modulus 14.0×10 ³ Kg/mm ² , interlaminar shear strength 10.3
It was Kg/ ^mm2 . Note that there were no voids in the molded product, and the volume content of carbon fiber was 60.8%, indicating that it was a good molded product.

Example 3 2.00 mol of m-aminostyrene, 1.81 mol of polyamine (n=0.37 in compound ())
mol, 2.40 mol of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 5-(2,
The procedure was exactly the same as in Example 2, except that polyamic acid was synthesized by dissolving 5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride in NMP at a ratio of 0.72 mol. The prepreg prepared by this method was used to perform press molding. First, a mold laminated with prepreg was inserted into a press heated to 160℃, held at contact pressure for 10 minutes, and then 30Kg/
The molded product was pressurized to cm ² , then heated to 250° C. while being pressurized, kept heated for 2 hours, cooled to room temperature, and the molded product was taken out. The obtained molded product was subjected to after-cure at 300°C for 4 hours. As a result of measuring the physical properties in the same manner as in Example 2, the bending strength was 192
It had good physical properties such as Kg/mm ² , flexural modulus of 13.8×10 ³ Kg/mm ² , and interlaminar shear strength of 10.5 Kg/mm ² . Moreover, no voids were observed when the cross section of the molded product was observed under a microscope, and it was confirmed that the molded product had good moldability.

Comparative example: 2.0 mol of m-aminostyrene, 2. mol of 4,4'-diaminodiphenylmethane, and 3,3',4,
4′-benzophenonetetracarboxylic dianhydride
A prepreg was prepared in exactly the same manner as in Example 2, except that polyamic acid was synthesized by dissolving it in NMP at a ratio of 3.0 mol. Using the obtained prepreg, press molding was performed. The molded product was first heated at 200° C. and then raised to 250° C. in the same manner as in Example 2, but the molded product had a significant number of voids. Therefore, we investigated the molding temperature, inserted the mold into a heated press at 250℃, preheated it for 5 minutes, then pressurized it to 50Kg/cm ² , raised the temperature to 300℃ while pressurized, held it for 1 hour, and then cooled it. Then I took out the molded product. The obtained molded article was placed in an oven at 300° C. and after-cured for 3 hours, and then its physical properties were evaluated in the same manner as in Example 2. As a result, the bending strength was 163Kg/mm ² ,
Flexural modulus 14.1×10 ³ Kg/mm ² , interlaminar shear strength 8.6
The physical properties were lower in terms of Kg/mm ² than in Example 2, and there were so many voids in the molded product that they were clearly visible to the naked eye.

(Effects of the Invention) The fluidity of polyimide prepolymers can be significantly improved without impairing heat resistance.

Claims (1)

[Scope of Claims] 1 General formula (), tetracarboxylic acid anhydride represented by (), amine component represented by general formula (), and m-aminostyrene represented by general formula () or general formula ( ) Styrene-3,4
- A method for producing a polyimide prepolymer, characterized in that it is synthesized from a dicarboxylic acid anhydride. However, in the formula, Z represents -CH= _CH2 , R is CO,
It represents CH ₂ and O, and the value of n is 1 or more and 5 or less on average.