JPH06211993A - Fiber-reinforced plastic material for cryogenic temperature - Google Patents

Abstract

PURPOSE:To obtain the subject material which is lightweight, has a susceptibility of substantially zero, does not cause He leak even when used at a cryogenic temp., and exhibits little change due to thermal shrinkage by integrally molding a resin and an org. fiber each having a specified coefficient of linear thermal expansion at the liq.-nitrogen temp. CONSTITUTION:This plastic material is obtd. by integrally molding a resin (e.g. an epoxy resin) and an org. fiber (e.g. a polyethylene fiber) each having a coefficient of linear thermaml expansion at the liq-nitrogen temp. satisfying the relation: alpham-alphaf<=62X10<-6> [1/K] (wherein alpham is the coefficient of linear thermal expansion of the resin [1/K]; and alphaf is that of the fiber [1/K]). Thus is provided the material which is lightweight, has a susceptibility of substantially zero and an excellent dimensional stability, and does not cause He leak even when used at a cryogenic temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber reinforced plastic material used as various members in an environment of extremely low temperature.

[0002]

2. Description of the Related Art Conventionally, members used in an extremely low temperature environment are made of metal such as stainless steel or aluminum alloy, or reinforced plastic material (GFRP) made of glass fiber. On the other hand, there are various fields of application under cryogenic temperatures, and the required performance varies from field to field. For example, when applied to a skit magnetometer for medical use, MRI, etc., it is important for the cryostat to have magnetic susceptibility, conductivity, vibration damping, and He leakage, and for the support material to have dimensional stability and heat conduction. is there. In addition, lightness is particularly important in the transportation fields such as linear motor cars and aerospace, and mechanical properties and workability are necessary for all applications. On the other hand, metal has great reliability in mechanical properties, workability, and He leak property, but has high thermal conductivity, and aluminum alloy is particularly remarkable. Therefore, it cannot be used for a heat transfer part of a cryostat or a dewar as well as a heat insulating support material. In addition, it has the drawbacks of a high coefficient of thermal expansion and poor dimensional stability, which makes its application to a support member even more difficult. In addition, since the conductivity and magnetic susceptibility are high and the vibration damping property is poor, a high S / N cannot be obtained with the skid magnetometer, and the He evaporation amount due to the heat generated by the eddy current in the MRI, SMES and other cryostats for AC devices. Increase, causing thermal efficiency and economic problems. Furthermore, in the transportation field, there is a strong demand for weight reduction with the aim of speeding up and energy saving. In that respect, stainless steel is extremely heavy, and many developments cannot be expected. Aluminum alloys are heavily used to make up for the drawbacks, but they have the drawback that they are still heavier and have a much higher thermal conductivity than fiber-reinforced plastics. Fiber-reinforced plastics made of glass fibers are used in such fields where metallic materials having many drawbacks cannot be used. For example, in terms of electrical conductivity, thermal susceptibility, and heat insulation, a great improvement was seen compared to metal-based materials. On the other hand, this GFRP also has various problems, and it is the current situation that it cannot be developed in many fields.

[0003]

As a main application in the cryogenic field, there are cryostats or dewars.
In this case, GFRP inevitably causes He leakage due to microcracks at extremely low temperatures, and this is the biggest problem in that the replacement of metal cryostats with FRP cannot proceed. Next is the issue of dimensional stability. In general, matrix resins and glass fibers are materials having a positive coefficient of expansion, and have the drawback of showing a large dimensional change from extremely low temperature to room temperature. That is, the GFRP used as a member tends to gradually shrink in the process of lowering the temperature, and even if the GFRP is positioned in the normal temperature state, the GFRP shrinks as the temperature lowers, resulting in positional displacement. There is a problem. Further, the magnetic susceptibility also has a value significantly smaller than that of metal, but it is the current situation that it cannot be coped with by increasing the sensitivity of the skid magnetometer expected in the future. Regarding the lightness, GFRP is lighter than metal, but in reality, it is heavier than reinforced plastic using organic fibers instead of glass. The present invention has been made in view of the above problems, and an object thereof is to prevent He leakage even when used at an extremely low temperature, a small change due to thermal contraction, a magnetic susceptibility substantially close to 0, and a light weight. To provide excellent fiber reinforced plastics.

[0004]

The present invention is characterized in that an organic fiber is used as a fiber material of a fiber reinforced plastic in order to achieve the above object. The organic fibers mentioned here are fibers having high strength and high elastic modulus, and include polyethylene, aramid, polyarylate (whole aromatic polyester, PB).
Z polymer (polybenzbisoxazole, polybenzbisthiazole, etc.), polyethylene terephthalate,
Polyphenylene sulfide, polyethylene naphthalate, polyamide imide, polyether ether ketone,
Polyether ketone ketone and the like, and polyethylene is particularly preferable. All of them have a smaller specific gravity than glass, and have a high specific strength and a high specific elastic modulus, and a lightweight reinforcing fiber can be obtained. Also, since the magnetic susceptibility does not include an inorganic substance, it shows a much lower value in the inorganic material due to glass fiber having good characteristics.

Next, regarding dimensional stability, all of these fibers have a negative coefficient of expansion (expand when the temperature is lowered from room temperature).
It has the unique property of having. On the other hand, many matrix resins exhibit positive expansion, so in press molding, pultrusion molding, etc., the ratio is changed appropriately, but by selecting the orientation angle appropriately and molding, molding with zero expansion can be achieved with respect to temperature changes. The member can be obtained. Further, at this time, these organic fibers having negative expansion and inorganic fibers having positive expansion can be mixed and used. In that case, examples of the inorganic fibers include glass, alumina, silica, fibers made of ceramics such as titania, zirconia, silicon nitride and silicon carbide, and aluminum, single metals such as steel, and metal fibers made of alloys thereof. However, fibers such as glass, alumina, zirconia, and silica are particularly preferable because they have low thermal conductivity and excellent mechanical properties.

The biggest problem in using GFRP as a cryogenic container (cryostat, dewar) is a problem of cryogen (mainly He) leak. In the present invention,
It is intended to provide a member having a high microcrack resistance at an extremely low temperature by producing a reinforced plastic using a high strength, high elastic modulus, organic fiber such as polyethylene, aramid and polyarylate. As the matrix used here, an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a urethane resin, a urethane acrylate resin or the like can be used, but an epoxy resin is particularly preferable. It is important that the linear expansion coefficient of the matrix resin used here and the organic fiber as the reinforcing fiber satisfy the following relationship. | Αm−αf | ≦ 62 × 10 ⁻⁶ [1 / K] where αm: coefficient of linear expansion of matrix resin at liquid nitrogen temperature [1 / k] αf: 〃 [1 / k] of organic fiber It was found that a molding material having high microcrack resistance at an extremely low temperature can be obtained by producing a fiber-reinforced plastic material satisfying the conditions. As a result, when used as a He container such as a cryostat or Dewar, He
It is possible to obtain the one having excellent leak property, vacuum keeping property and mechanical property. When used as a heat insulating support material,
Even when the temperature is changed repeatedly between room temperature and extremely low temperature, microcracks of the resin do not occur, and because the adhesiveness between the fiber and matrix is high, the dimension retention is also good and the mechanical properties are also good. It has the feature of being excellent.

A filament winding method or a tape winding method of winding a machine fiber in a filament or tape shape around a mandrel while impregnating the matrix resin, a press molding method in which prepregs are laminated and pressed in a mold, and a fiber and a matrix resin are used. Known methods such as a bulging method of integrally extruding under pressure from a die, a vacuum impregnation method of integrally impregnating a fiber and a matrix resin in a vacuum and then molding, an autoclave method and the like can be mentioned. The mixing ratio of the fibers and the matrix resin in the composite material is preferably 35 to 85%, more preferably 40 to 70% as the volume fraction (Vf) of the fibers. If the Vf of the fiber is less than 35%, the reinforcing effect of the fiber is not exhibited, and if it exceeds 85%, it is difficult to impregnate with the matrix resin and the mechanical properties of the composite material deteriorate, which is not preferable.

[0008]

Example As the organic fiber, polyethylene fiber (Toyobo Dyneema, SK-60), aramid fiber (Japanese aramid fiber, Twaron HM), polyarylate (Kuraray, Vector 32), polybenzobisoxazole, glass fiber were used. .About.4 A total of 7 types of fiber reinforced plastics of Comparative Examples 5 to 7 were prepared by the filament winding method (orientation angle: 55.degree. C.). An epoxy resin was used as a matrix, and Epicoat 827 (oiled shell) and various curing and accelerating agents were added as a main component and uniformly mixed to prepare a resin dope. Next, various organic fibers were impregnated with epoxy resin and wound around a mandrel to form a cylindrical shape.
Next, while holding it on the mandrel, it was cured and molded at 130 ° C. for 5 hours to give a fiber volume content of 65% and an outer diameter of 15%.
A compact having a size of 0 mmφ × 200 mm and a wall thickness of 5 mm was obtained. The results are shown in Table 1. [Crack resistance] Each pipe is placed in liquid He from room temperature for 30 minutes, then pulled up and visually observed. The order of high crack resistance was ◯>△> ×. [He Leakability] First, both ends of each pipe are sealed and evacuated, and then He gas is introduced into the system to obtain a standard leak amount of 5.0.
It was confirmed to be × 10 torr · l / sec. Next, He gas was blown to the pipe outer tube portion to measure the He leak amount, which was shown as a ratio (%) to the standard leak amount. Next, the pipe was previously immersed in liquid He for 30 minutes and then taken out, and the He leak amount was measured in the same manner. [Number of Spins (Ns)] It is generally known that the magnetic susceptibility and the number of spins are proportional. A sample was taken from each molded product, and the ESR was measured while cooling the sample with liquid He to measure the spin number of each sample. [Specific gravity] Each molded product sample was measured with a specific gravity meter. [Bending strength] A sample with a thickness of 5 mm and a width of 5 mm was cut out from each sample pipe, the distance between fulcrums was 25 mm, and the crosshead 1
Bending strength was measured in mm / min at room temperature and liquid helium temperature. [Tensile strength] 1 mm thick and 10 m wide from each sample pipe
m sample cut out, crosshead speed 2 mm / m
Intensity was measured at in and room temperature and liquid helium temperature were measured.

[0009]

[Table 1]

Matrix composition A Epicoat-827 (Oilized shell) 100 HN-2200 (Hitachi Chemical) 80 EM1-24 (Oilized shell) 2 B Epicoat-827 (Oilized shell) 100 HN-5500 (Hitachi Chemical) 105 BM1-12 (Oilized shell) 2 C Epicoat-827 (Oilized shell) 100 Rikashwad DDSA (Nippon Rika) 105 EM1-24 (Oilized shell) 2 D Epicoat-827 (Oilized shell) 100 Epicure YH-300 (〃) 80 EM1-24 (oiled shell) 2 E Epicoat-827 (oiled shell) 100 HN-5500 (Hitachi Kasei) 40 Epicurer YH-300 (oiled shell) 50 EM1-24 (〃) 2 F epicoat -827 (Oilized shell) 100 Epicure 113 (〃) 30 M1-24 (〃) 1

[0011]

EFFECTS OF THE INVENTION According to the present invention, H
e It is possible to provide a lightweight fiber-reinforced plastic having no leakage, excellent dimensional stability, and substantially zero magnetic susceptibility.

Claims (1)

[Claims] 1. A cryogenic fiber reinforced plastic material obtained by integrally molding a resin and an organic fiber, wherein the linear expansion coefficient at a liquid nitrogen temperature of the resin and the organic fiber satisfies the following relationship. Material. | Αm−αf | ≦ 62 × 10 ⁻⁶ [1 / K] where αm: linear expansion coefficient of resin [1 / K] αf: expansion coefficient of organic fiber [1 / K]