JPH0532498A - Organic whisker - Google Patents

Abstract

PURPOSE:To improve heat resistance by using an aromatic polyimide having specific fiber length. CONSTITUTION:An aromatic tetracarboxylic acid shown by formula I and aromatic diamines shown by formula II and formula III are dissolved in a heated solvent for recrystallization, insoluble substances are removed and the solution is gradually cooled to precipitate needle-like crystal. The needle-like crystal is gradually cooled under 0.1-1 Torr vacuum degree at 350-450 deg.C for 5-30 hours to give organic whiskers comprising an aromatic polyimide having <=1 mm average fiber length.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an organic whisker having excellent heat resistance.

[0002]

2. Description of the Related Art Whiskers are extremely thin linear crystal bodies, also called whiskers, and are characterized by extremely high tensile strength of about 1000 kg / mm ² . However, it is known that the tensile strength of whiskers decreases as the thickness increases, and finally approaches the value of the normal structure. Also, it is known that the tensile strength decreases as the length increases. ing.
Therefore, when whiskers are used as a reinforcing material, efforts are being made to add whiskers that are relatively thin and short to other materials such as metals, ceramics and polymers.

Conventionally, generally known whiskers are carbon whiskers or metal whiskers. However, recently, ceramic whiskers such as alumina whiskers and silicon carbide whiskers have been developed. Further, as organic whiskers, silver, lead azide, silver halide on an alginic acid film, and the like are known, and, for example, polyoxymethylene whiskers are known as whiskers consisting essentially of organic substances.

Polyoxymethylene whiskers are produced by cationic polymerization in a solution of trioxane and have been improved to an industrially usable level, but they have a problem in heat resistance. Further, JP-A-61-28528 discloses a method for producing an organic whisker by irradiating a polymerizable organic low molecular compound or a composition thereof with an energy ray. According to this method, whiskers made of an epoxy resin, a polyester resin, a polyurethane resin, etc. are provided, but the organic whiskers made of these resins have the same problem of heat resistance as described above.

By the way, the polyimide resin is excellent in heat resistance and mechanical properties, and is widely used as a super engineering plastic in the fields of aircraft, automobiles, construction machinery, or electric / electronic industries. Also,
Polyimide resin is being compounded with carbon fiber or Kevlar fiber, and its application is being developed as a functional component requiring high strength and high elasticity. And whiskers made of an organic material having extremely excellent heat resistance such as polyimide resin have not been known.

[0006]

Most of the conventionally known heat-resistant whiskers are inorganic whiskers, and organic whiskers are not known. Therefore,
If an organic whisker with heat resistance is developed, it can be made lighter in weight than an inorganic whisker, so that new fields of application can be developed. Then, the subject of this invention is
To provide organic whiskers with excellent heat resistance.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that an aromatic polyimide having excellent heat resistance becomes a whisker, and arrived at the present invention. That is,
The gist of the present invention consists of an aromatic polyimide and has a fiber length of 1
It is an organic whisker characterized by being below mm.

Next, the present invention will be described in more detail. The organic whisker of the present invention is made of aromatic polyimide and has a fiber length of 1 mm or less. If the fiber length exceeds 1 mm, the tensile strength will decrease. The diameter is preferably 10 μm. If it exceeds 10 μm, the tensile strength tends to decrease.

This organic whisker was prepared by preparing needle crystals of a salt from an aromatic tetracarboxylic acid compound and an aromatic diamine compound as described below, and then heating the needle crystals of the salt under vacuum to dehydrate them. It is manufactured by converting it to an aromatic polyimide. The aromatic polyimide obtained by this method maintains the acicular crystal state of the salt as the precursor and becomes an organic whisker. In the present invention, the aromatic tetracarboxylic acid is a tetravalent carboxylic acid containing at least one carbon 6-membered ring, of which divalent groups form pairs.
Characterized by bonding to adjacent carbon atoms in a member ring, specifically, those represented by the following formulas can be mentioned.

[0010]

[Chemical 1]

In the present invention, the aromatic diamine compound is a diamine containing 1 to 4 carbon 6-membered rings, and examples thereof include those represented by the following formula.

[0012]

[Chemical 2]

[0013]

[Chemical 3]

Among the above-mentioned aromatic tetracarboxylic acids, the following are particularly preferable.

[0015]

[Chemical 4]

Among the aromatic diamines, the followings are particularly preferable.

[0017]

[Chemical 5]

The needle-like crystals of the salt prepared by the present invention are usually
It can be obtained by a method called recrystallization. That is, aromatic tetracarboxylic acid and aromatic diamine,
It dissolves in the heated recrystallization solvent, and if there are insolubles, remove them by filtration and slowly cool the solution to obtain needle-shaped crystals. The recrystallization solvent may be of any type as long as it can dissolve the aromatic tetracarboxylic acid and the aromatic diamine during heating, but water is preferred from the viewpoint of operability and economy. The molar ratio of aromatic tetracarboxylic acid to aromatic diamine is preferably in the range of 0.5 to 1.5, 0.9 to
The range of 1.1 is more preferable. If it is less than 0.5 or exceeds 1.5, the organic whiskers tend to be easily broken.

When the needle-like crystals of the salt thus obtained are heated under vacuum, they are dehydrated while maintaining the shape of the salt to become organic whiskers made of polyimide. The heating conditions under vacuum may be those for producing ordinary polyimide moldings. For example, after heating under vacuum of 0.1 to 1 torr at 350 to 450 ° C. for 5 to 30 hours,
Slowly cool to obtain organic whiskers made of polyimide. (When the organic whiskers made of the polyimide thus obtained were measured by an X-ray diffractometer, the diffraction curve showed a typical crystalline pattern. From this, the polyimide single molecules were arranged in an orderly manner and crystallized. It is clear that the polyimide is a whisker).

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 5.1 g of pyromellitic acid and 4.0 g of diaminodiphenyl ether were put in 900 ml of water and heated and boiled. After the trace amount of insoluble matter was filtered off, the solution was cooled slowly. The precipitated needle crystals were collected, washed with cold water, and vacuum dried at 35 ° C. to obtain 7.4 g of needle crystals. Furthermore, 4.0 g of needle crystals was heated to 400 ° C. in vacuum over 100 hours and maintained at 400 ° C. for 10 hours, then returned to room temperature over 25 hours, average fiber length 100 μm, average fiber diameter 5 μm.
m of an organic whisker (3.2 g) was obtained.

Example 2 2.5 g of pyromellitic acid and 2.0 g of diaminodiphenylmethane were placed in 750 ml of water and heated to boiling. After the trace amount of insoluble matter was filtered off, the solution was cooled slowly, the precipitated needle crystals were collected, washed with cold water, and vacuum dried at 35 ° C. 3.5 g of needle crystals were obtained. Furthermore, 2.0 g of needle crystals were heated to 400 ° C. under vacuum for 100 hours,
After maintaining at 400 ° C. for 10 hours, the temperature was returned to room temperature over 25 hours to obtain 1.4 g of an organic whisker having an average fiber length of 150 μm and an average fiber diameter of 3 μm.

[0022]

Since the organic whiskers of the present invention are made of polyimide, they are excellent in heat resistance.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoshiaki Echigo 23 Uji Kozakura, Uji City, Kyoto Prefecture Unitika Ltd. Central Research Laboratory

Claims (1)

Claims: 1. An aromatic polyimide, fiber length of 1 m.
An organic whisker characterized by being m or less.