JPH04366139A - Cryogenic material made of fiber-reinforced resin - Google Patents

Abstract

PURPOSE:To provide a cryogenic FRP which exhibits scarcely any shrinkage due to temp. fall and hardly any magnetization and is light in wt. CONSTITUTION:A fiber-reinforced resin comprising an org. reinforcing fiber (e.g. a high-strength polyethylene fiber) and a matrix resin (e.g. an epoxy resin with an alicyclic acid anhydride as a curative) is used as a cryogenic material.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fiber-reinforced plastic composite materials used as various parts in extremely low-temperature environments.

0002

[Background Art] In recent years, research and development using liquid helium in cryogenic environments has become active in the field of superconductivity, etc., and materials for cryogenic temperatures have been developed such as stainless steel, titanium alloys, aluminum alloys, etc. progress is being made on metal materials such as 100% and non-metallic materials such as fiber-reinforced plastics. The application fields of materials under such extremely low temperatures are wide-ranging, so
There are many requirements for performance, and they differ for each field. For example, in the medical field where it is applied to skid magnetometers or MRI, the cryostat has magnetic susceptibility, conductivity, vibration damping properties, and liquid helium (hereinafter referred to as H).
(abbreviated as "e") are important in terms of leakage properties, and as a support material, dimensional stability, low thermal conductivity, etc. are important. On the other hand, in transportation fields such as linear motor cars and aerospace, lightness will be an important required characteristic, and mechanical properties, workability, etc. are also required performances in any field.

[0003] Metal materials, which have traditionally been widely used as cryogenic materials, have excellent mechanical properties, workability, and He leak resistance, but because of their high thermal conductivity, they are difficult to use as heat-insulating support materials. Naturally, it cannot be used in heat transfer parts such as cryostat or dewar, and furthermore, it has disadvantages such as high coefficient of thermal expansion and poor dimensional stability, which makes it even more difficult to apply it to support materials. Also,
Metal materials have high conductivity and magnetic susceptibility, so when applied to a skid magnetometer, a high S/N ratio cannot be obtained, and MR
When used in a cryostat for AC equipment such as I, SMES, etc., the amount of He evaporation increases due to heat generation caused by eddy currents, causing problems in terms of thermal efficiency and economy. Furthermore, in the cutting-edge transportation field, including linear motor cars,
There is a strong demand for weight reduction in order to increase speed and save energy, and even light alloys such as aluminum are now too heavy.

[0004] In the cryogenic field where metal materials such as those mentioned above cannot be used, composite materials (sometimes abbreviated as FRP) consisting of fibers such as glass fibers and matrix resin are used. Although these composite materials are superior to metal materials in terms of electrical conductivity, magnetic susceptibility, and heat insulation, they are still not satisfactory in terms of overall properties including other properties.

For example, glass fiber composite material (sometimes abbreviated as GFRP) is a material in which both the general matrix resin and glass fibers have a positive expansion coefficient, and the ambient temperature changes from room temperature to extremely low temperature. Although volumetric shrinkage is unavoidable when the volume decreases, the microcracks that occur at this time cause He leakage, which impedes application to cryostat and DUA.Furthermore, due to poor dimensional stability due to this shrinkage, various It is often difficult to use it as a member for cryogenic temperatures. In addition, although the magnetic susceptibility of the above composite materials is considerably smaller than that of metals, it is still not sufficient for applications such as skid magnetometers that aim for high sensitivity, and there is still room for further improvements in weight reduction. be.

[0006]

[Problems to be Solved by the Invention] The present invention was made in consideration of the above-mentioned drawbacks of FRP as a material for cryogenic use, and its first objective is to make it lightweight and to have almost no volume shrinkage due to temperature drop. It is an object of the present invention to provide a high-performance FRP for cryogenic use, which has good dimensional stability, excellent micro-crack resistance at cryogenic temperatures, and has substantially zero magnetic susceptibility.

[0007]

[Means for Solving the Problems] The gist of the present invention is to use a fiber-reinforced resin composite material using organic fibers as reinforcing fibers as a cryogenic material.

[0008]

[Function] The organic fibers used in the present invention include:
PBZ polymers such as high strength polyethylene, aramid, polyarylate, polybenzbisoxazole, polybenzbisthiazole, polyethylene terephthalate, polyphenylene sulfide, polyethylene naphthalate,
Examples include fibers such as polyamideimide, polyetheretherketone, and polyetherketoneketone. These fibers have a much lower specific gravity than glass fibers, making it possible to obtain reinforcing fibers with high strength, high modulus, and light weight.They are also superior in terms of magnetic susceptibility compared to inorganic fibers and metal materials. ing. Furthermore, all of these fibers are unique substances that have a negative coefficient of expansion, and their volume increases as the temperature is lowered from room temperature. Generally, matrix resin has a positive expansion coefficient, so by combining the above fibers, it is possible to obtain FRP with little change in volume due to temperature. Among the above-mentioned fibers, high-strength polyethylene fibers are preferred because they exhibit the best performance in terms of magnetic susceptibility, specific gravity, and strength. Such polyethylene fibers are disclosed in, for example, JP-A-55-107506 and JP-A-56-15408.
It can be obtained using a manufacturing method as disclosed in the above publication.

[0009] As for the form of the above-mentioned fibers, various types of yarns such as short fiber filaments, twisted yarns, and spun yarns, or known forms of woven fabrics such as plain weave, twill weave, satin weave, bag weave, and basket weave can be used. In addition, in order to satisfy all of the many characteristics, 2
It is also possible to use more than one kind of organic fiber or a mixture of organic fiber and inorganic fiber. Inorganic fibers include glass,
Examples include ceramic fibers such as alumina, silica, zirconia, titania, silicon nitride, and silicon carbide, and fibers of metals such as aluminum and steel or their alloys.

[0010] The mixing method in this case is to combine two or more types of organic fibers or organic/inorganic fiber filaments, or to use one fiber filament as a core and cover the surrounding area with the other filament. A method of manufacturing a yarn with a core-sheath structure using organic fibers, a method of manufacturing a mixed fiber yarn using the filaments produced by stacking and converging each filament bundle of both fibers in an opened state, and a method of manufacturing a mixed yarn using organic fibers. Methods include laminating prepregs on each other or prepregs using organic fibers and prepregs using inorganic fibers, but inorganic fibers are significantly inferior to organic fibers in terms of magnetic susceptibility, weight, and coefficient of expansion. The blending amount needs to be considered.

As the matrix resin used in the present invention, epoxy resins, unsaturated polyester resins, vinyl ester resins, urethane resins, urethane acrylate resins, etc. can be used. Among these, the inventors have found that an epoxy resin using an alicyclic acid anhydride as a curing agent has extremely excellent microcrack resistance. As the alicyclic acid anhydride curing agent, methylhexahydrophthalic anhydride and methyltetrahydrophthalic anhydride are preferably selected, and these can be used alone or in mixtures. The epoxy resin is not particularly limited, but general-purpose bisphenol A type and the like can be used.

[0012] Methods for forming the composite material of the present invention into cryogenic members include the filament winding method or tape winding method, in which the thread-like or tape-like organic fibers are impregnated with a matrix resin and wound around a mandrel, and the prepreg method. Press molding method in which the layers are laminated and pressurized in a mold, pultrusion method in which fibers and matrix resin are combined and extruded under pressure from a die,
Known methods include a vacuum impregnation method in which fibers and matrix resin are integrally impregnated in vacuum and then molded, and an autoclave method.

[0013] The mixing ratio of the fibers and matrix resin in the composite material is determined by the volume fraction of the fibers (sometimes abbreviated as Vf).
is preferably 35 to 85%, more preferably 40%.
~70%. If the Vf of the fiber is less than 35%, the reinforcing effect of the fiber will not be exhibited, and if it exceeds 85%, the impregnation with the matrix resin will be insufficient and the mechanical properties of the composite material will deteriorate, which is not preferable.

[0014]

[Examples] The present invention will be specifically explained below using Examples, but the present invention is not limited thereto.

Examples 1 to 3 After mixing matrix resins having the composition shown in Table 1, each organic fiber was impregnated with the filament winding method and wound around a mandrel (orientation angle: 55°) to form a cylindrical shape. Next, while holding this on the mandrel, 1
Cured and molded at 30°C for 3 hours to reduce fiber Vf65% and outer diameter.
A molded body having a diameter of 150 mm×200 mm and a wall thickness of 5 mm was obtained.

Comparative Examples 1 to 4 In Comparative Example 1, glass fibers were impregnated with the vinyl ester resin shown in Table 1 and wound around a mandrel.
C. for 1 hour to form a pipe having the same dimensions as the example. Comparative Example 2 was molded under the same conditions as in Example while impregnating glass fiber with the epoxy resin shown in Table 1. Comparative example 3
The epoxy resin shown in Table 1 was cured at 130° C. for 3 hours and integrally molded into a tube shape. In Comparative Example 4, a pipe of the same dimensions was made of stainless steel (SUS304L).

[0017]

[Table 1]

Each pipe was evaluated by the following method, and the results are shown in Table 2. (1) Crack resistance A sample pipe was placed in liquid He at room temperature, left for 30 minutes, then pulled out and visually observed to see if any cracks had formed. ○; No cracks observed at all. Δ: Some cracks are observed. ×: There are large cracks on the entire surface.

(2) He leakage properties First, seal both ends of each pipe, vacuum the pipes, and then
When e-gas is introduced into the system, the standard leakage amount is 5.0×10-
It was confirmed that the speed was 8 torr·l/sec. Next, He gas was sprayed onto the width of the pipe outer cylinder to measure the He leakage amount, which was expressed as a percentage (%) of the standard leakage amount. Next, the pipe was left in liquid He for 30 minutes, then taken out and the amount of He leakage was measured in the same manner as above.

(3) Spin number (Ns) The spin number was determined by measuring ESR (electron spin resonance) while cooling each sample with liquid He (the spin number is proportional to the magnetic susceptibility).

(4) Shrinkage rate The dimensional change rate of each sample from room temperature to liquid He temperature is TM
The shrinkage rate was calculated using method A (heating rate: 5°C
/min).

(5) Specific gravity Measured with a hydrometer (25°C).

(6) Bending strength A sample with a thickness of 5 mm and a width of 5 mm was cut out from each sample, and the bending strength was measured at room temperature and liquid He temperature with a distance between fulcrums of 25 mm and a crosshead speed of 1 mm/min.

(7) Specific bending strength Specific bending strength was calculated from bending strength and specific gravity.

[0025]

[Table 2]

[0026]

Effects of the Invention: The cryogenic material obtained by the present invention is an FRP that is a composite of organic fibers with a negative expansion coefficient and matrix resin with a positive expansion coefficient, so the shrinkage rate due to temperature drop is almost 0. Therefore, it is possible to obtain an extremely lightweight member with excellent microcrack resistance and dimensional stability even at extremely low temperatures. Furthermore, by using high-strength organic fibers and an epoxy resin blended with a specific curing agent, we were able to provide a cryogenic material with excellent magnetic susceptibility and mechanical properties.

Claims (1)

[Claims] Claim: 1. A cryogenic material made of a fiber-reinforced resin using organic fibers as reinforcing fibers.