JP2541666B2 - Air carrier for irradiation - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to polyethylene-2,6-
The present invention relates to a naphthalenecarboxylate air carrier. More specifically, for irradiation of various substances, it can be put as it is in the case of solid substances, and enclosed in glass or plastic ampoules in the case of liquid or gaseous substances or mixtures thereof. A container (air carrier) necessary for studying physical changes in radiation resistance and chemical reaction area of irradiated material
It is about.

Conventional technology and its problems Conventionally, polyethylene has been used as a material for a pneumatic carrier made of plastic. In the case of polyethylene containers, this polymer is relatively vulnerable to radiation, and upon irradiation it deteriorates and becomes brittle in a relatively short time, making it unusable in a short time, especially under high dose irradiation conditions such as reactor irradiation. There was a problem.

And ones that can withstand high dose radiation for a long time,
Alternatively or additionally, there is a need for an air carrier made of a material that withstands repeated use and does not denature.

Further, when a material containing an air carrier is irradiated with a neutron beam in a nuclear reactor, for example, an element contained in the air carrier may be activated. In order to avoid this phenomenon, it is very inconvenient as a real problem when the irradiated substance is immediately taken out from the air carrier after irradiation and used for other tests, and the air carrier itself is not activated or emitted. Even if it is made into a material, there is a long-felt need for a material whose radioactivity decays in a short time.

Means for Solving the Problems The present inventor has conducted research to provide an irradiation carrier which does not have the above-mentioned drawbacks, and has made polyethylene-2,6-naphthalenedicarboxylate (hereinafter referred to as PEN) having specific characteristics.
The present invention has been accomplished by finding that an air carrier made of (abbreviated as -2, 6) is extremely suitable as an irradiation container.

That is, the present invention has an intrinsic viscosity of 0.45 to 0.90 polyethylene-2,6-naphthalenedicarboxylate,
It is an air carrier for irradiation which has a density of 1.345 g / cm ³ or less, contains titanium as a catalyst residue or an additive at a concentration of 50 ppm or less, and is substantially free of other metal impurities.

The polymer, which is the material constituting the pneumatic carrier of the invention, may be any polymer whose structural unit is substantially composed of ethylene-2,6-naphthalene dicarboxylate, and PEN
Not only -2,6 but also a small amount, for example, 10 mol% or less, preferably 5 mol% or less, of an ethylene-2,6-naphthalenecarboxylate-modified polymer modified with a third component are included. PEN-2,6 is generally synthesized by combining naphthalene-2,6-dicarboxylic acid or its functional derivative and ethylene glycol or its functional derivative in the presence of a catalyst under suitable reaction conditions. It In addition, as a modified polymer, it is necessary to prepare a suitable polymer before completion of the polymerization of PEN-2,6.
One or two or more types of third component modifiers are added to form a copolymerized or mixed polyester.

Suitable third component is a compound having a divalent ester-forming functional group such as oxalic acid, adipic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalene-2,7-
Dicarboxylic acids such as dicarboxylic acids and diphenyl ether carboxylic acids or lower alkyl esters thereof: oxycarboxylic acids such as P-oxybenzoic acid and P-oxyethoxybenzoic acid or lower alkyl esters thereof: propylene glycol, trimethylene glycol, tetra Examples thereof include compounds such as dihydric alcohols such as methylene glycol, hexamethylene glycol and neopentyl glycol.

Further, PEN-2,6 or a modified polymer thereof may be, for example, benzoic acid, a monofunctional compound such as methoxypolyalkylene glycol in which a terminal hydroxyl group and / or a carboxyl group is blocked, or For example, it may be modified with a very small amount of a trifunctional or higher-functional polyfunctional ester-forming compound such as glycerin or pentaerythritol within the range where a substantially linear copolymer is obtained. The base polymer in the present invention has an intrinsic viscosity of 0.45 to 0.90 measured at 35 ° C. in a tetrachloroethane / phenol [6/4 (polymerization ratio)] mixed solvent. Particularly, those having an intrinsic viscosity of 0.55 to 0.70 are preferable because they have excellent physical properties.

PEN-2,6 in the present invention can be synthesized, for example, as follows.

Dimethyl-2,6-naphthalenedicarboxylate and ethylene glycol were used in a reaction vessel with a titanium compound as a catalyst to carry out a transesterification reaction under a conventional method or under pressure, and then a polycondensation reaction under reduced pressure to perform PEN-2,6. To obtain PEN-2,6 by subjecting 2,6-naphthalenedicarboxylic acid and ethylene glycol to a titanium compound as a catalyst for a direct esterification reaction under a conventional method or under pressure, and further performing a polycondensation reaction under reduced pressure. How to get.

Examples of the titanium compound include tetrabutyl titanate, trimellitic acid, hemimellitic acid, and titanium carboxylate which is a reaction product of titanium tetrabutoxide and the like.

The present invention is a pneumatic carrier molded from the polymer as described above.

A conventionally known melt injection molding method can be used to form the pneumatic carrier in the present invention from the polymer.

That is, PEN-2,6 consisting of a homopolymer or a modified polymer
Is melted at a temperature of 280 ° C. to 310 ° C., injected into a mold, solidified by cooling, and molded to have a density of 1.345 g / cm ³ or less.

In this way, crystallization during molding is suppressed and irradiation resistance is increased, with an outer diameter of 15 to 20 mm, a length of about 60 mm to 80 mm, and a thickness of about 1.5 to 2
A cylindrical container having a size of about m is formed.

EFFECTS OF THE INVENTION When the pneumatic carrier made of PEN-2,6 of the present invention is used for irradiation, it has the following advantages.

1. Since it is remarkably less deteriorated than an air carrier made of polyethylene, it can be used under irradiation with a high dose rate. In particular, it is suitable as a pneumatic carrier for nuclear reactor irradiation.

2. The air carrier according to the present invention has an extremely large attenuation of radioactivity when irradiated, and therefore has an advantage of facilitating handling after irradiation of the irradiated object.

3. It can be used at low temperature because it does not become brittle even under low temperature, for example, dry ice methanol temperature conditions.

4. Since the glass transition temperature is high, it can be used at a relatively high temperature of about 100 ° C.

EXAMPLES Hereinafter, the present invention will be further described with reference to examples. In addition,
The characteristics in the present invention are measured as follows.

(A) Intrinsic viscosity number In the present invention, the intrinsic viscosity number is calculated from the value measured at 35 ° C. in a mixed solvent of tetrachloroethane / phenol in a weight ratio of 6: 4.

(B) Density A small piece was cut from the molded product and used as a sample for density measurement. The density was measured at 25 ° C. with a density gradient tube of carbon tetrachloride to n-heptane system.

(C) Radiation resistance test PEN-2, 6 and a test piece or pneumatic element made of other comparative materials were prepared and the neutron flux of the irradiation hole was 5.5 × 10 ¹³ using the JRR-2 pneumatic tube of the Japan Atomic Energy Research Institute. ~ 8.0 × 10 ¹³ n / cm ²・ s
irradiated with ec. The radioactivity of the neutron-irradiated test piece was measured by an ionization chamber type dose rate meter (IC-247) or a GM dose rate meter.

(D) Impact test A test piece was prepared according to JIS K-7111 and an impact test was performed.

At that time, a Charpy / impact tester manufactured by Toyo Seisakusho was used as a test device.

Examples and Comparative Examples Polyethylene-2,6-naphthalenedicarboxylate containing 15 ppm of titanium as an impurity content and substantially free of other impurities was synthesized. In addition, polyethylene-2,6-naphthalenedicarboxylate containing 55 ppm of zinc as an impurity content and substantially free of other impurities was synthesized. Furthermore, as an impurity content, antimony 302 ppm,
Polyethylene-2,6-naphthalenedicarboxylate containing 49ppm cobalt and 83ppm phosphorus was synthesized. These PEN−
In addition to 2,6, polyethylene Marlex 50 was used. PEN-2, 6 to 3
It is melted at 00 ℃ and extruded into a mold kept at a predetermined temperature.
A test piece with a thickness of 3.2 mm, a width of 13 mm, a length of 64 mm, and a notch was made.

On the other hand, commercially available polyethylene Malex50 (melting index about 5)
Was melted at 190 ° C., and a pneumatic tube of the same shape was made by the same method as above.

These molded products were sent to a reactor irradiation part and irradiated with a predetermined dose for a predetermined time, and then subjected to various tests.

The results are shown in Table 1. The pneumatic carrier of the present invention shown in Example 1 showed a small decrease in the impact test value even at a high irradiation dose, a large attenuation of the radiation dose rate, and was sufficiently durable for practical use. Comparative Example 1 uses PEN-2,6 having the same composition as that of Example 1, but the impact test value was significantly lowered because the density of the test piece was large (because crystallization progressed).

In Comparative Example 2, the impact test value does not decrease much, but the radiation dose rate is less likely to be attenuated, so that the object of the present invention cannot be achieved. In Comparative Example 3, the radiation dose rate was too high to handle, and the impact test was stopped. Comparative Example 4 is a conventionally used polyethylene. Although the radiation dose rate is greatly attenuated, there is a drawback that the material becomes brittle in an extremely short time.

In addition, by creating an air carrier having the characteristics shown in Example 1,
The reactor was irradiated with neutrons at 2.6 × 10 ¹⁸ , but it did not become brittle, and it was found that it could be put to practical use. As described above, the pneumatic carrier for irradiation of the present invention is extremely useful.

Front Page Continuation (72) Inventor Kenji Arikane 2 Shirane, Shikata, Tokai-mura, Naka-gun, Ibaraki Prefecture 4 Inside the Tokai Research Institute, Japan Atomic Energy Research Institute (72) Shigeo Shinda Shirahone, Shikata-kata, Naka-gun, Ibaraki Prefecture No. 2 4 Inside the Japan Atomic Energy Research Institute Tokai Research Institute (72) Inventor Hyota Waraya, Shirahane, Shirahane, Tokai-mura, Naka-gun, Ibaraki Prefecture 4 No. 4 Inside the Japan Atomic Energy Research Institute Tokai Research Institute (72) Inventor Tadao Seguchi Takasaki Gunma Prefecture 1233, Watanuki-cho, Japan Inside the Takasaki Research Institute, Japan Atomic Energy Research Institute (72) Inventor Isao Aoyama 4 Shirane, Shirahane, Tokai-mura, Naka-gun, Ibaraki Prefecture 4 Inside the Tokai Research Institute, Japan Atomic Energy Research Institute (56) -278200 (JP, A) JP-A-3-188399 (JP, A)

Claims (1)

(57) [Claims] 1. A molded article made of polyethylene-2,6-naphthalene dicarboxylate having an intrinsic viscosity of 0.45.
A gas atomizer for irradiation, which has a density of up to 0.90 and a density of 1.345 g / cm ³ or less, contains titanium as a catalyst residue or an additive at a concentration of 50 ppm or less, and is substantially free of other metal impurities.