JP6046428B2 - Radiation shielding sheet - Google Patents

Description

  The present invention relates to a radiation shielding sheet material comprising at least a fibrous material and a binder resin. More specifically, the present invention relates to a radiation shielding sheet material suitable for a gasket or a sealing material having radiation shielding properties and excellent mechanical strength, flexibility and sealing properties.

  Gaskets are used in a wide range as various sealing materials. Its basic composition consists of a fiber material, a filler, and a binder such as rubber or resin. In particular, gaskets used in industrial plants and the like are required to have extremely high heat resistance, chemical resistance, and sealing properties. Until now, such applications have excellent heat resistance and chemical resistance and are low in cost. Many gaskets using asbestos as a fiber material have been used. However, the development of gaskets that do not use asbestos and are excellent in heat resistance and chemical resistance has been vigorously developed against the background of the recent social impact on asbestos.

  For example, in Japanese Patent Publication No. 4-5053, an aromatic polyamide fiber and / or a fibrillated aromatic polyamide fiber is used as a fiber material instead of asbestos, and a binder component such as a rubber material, a filler, and a polyolefin polymer are used. A joint sheet characterized in that it is included is disclosed.

  On the other hand, as the industrial use and importance of radiation increases, radiation handling facilities and radioactive waste storage facilities are expected to expand in the future. In particular, how to prevent leakage of radiation is a major issue. Especially in plants that handle radiation, such as nuclear power plants, radiation shielding performance is provided in gaskets and sealing materials to prevent leakage of radiation from piping. Is required.

  Examples of gaskets and seals that meet such requirements include metal, but they are poor in flexibility and elasticity, and require high tightening force to improve compatibility with the contact surface. However, there is a problem that a stable sealability cannot be ensured during long-term use, such as biting. Thus, there is a strong demand for the development of gaskets and sealing materials that have radiation shielding properties and have both mechanical strength, flexibility, and sealing properties.

Japanese Patent Publication No. 4-5053

  The present invention is intended to solve the problems of the prior art, and has radiation shielding properties, excellent mechanical strength, flexibility and sealing properties, and suitable for gaskets and sealing materials. A shielding sheet material is provided.

As a result of the study by the present inventors, by using a sheet material skillfully combining a fibrous material and a binder resin, for example, inorganic particles such as tungsten can be blended by 55 % or more by weight, and high radiation shielding is achieved. It has been found that a gasket or sealing material having not only performance but also excellent mechanical strength and flexibility can be obtained.

Thus, according to the present invention, there is provided a sheet material comprising at least a binder resin comprising a fibrous material and a fluororesin, and a flocculant having an action of destabilizing dispersion of the fluororesin powder in water, wood is, at least one inorganic particles atomic number is from a single piece or a compound consisting of 40 or more elements, the total weight of the sheet material contains 55 to 90 percent by weight based, Schopper Riegler filtration of the fibrous material A radiation shielding sheet material having a water degree of 20 to 80 ° SR is provided. Moreover, the gasket or sealing material comprised from said radiation shielding sheet material is provided.

  The sheet material of the present invention is excellent in mechanical strength, flexibility and sealing properties while having high radiation shielding performance, and can be suitably used for a gasket or a sealing material.

  Hereinafter, embodiments of the present invention will be described in detail. The sheet material of the present invention is a sheet material composed of at least a fibrous material and a binder resin, and the sheet material contains at least one kind of inorganic particles composed of a simple substance or a compound composed of an element having an atomic number of 40 or more. It is important to contain 50 to 96% by weight based on the total weight of the material. As a result, the above-mentioned inorganic particles can be firmly held at a high content and have a high radiation shielding property, and at the same time, a sheet material excellent in mechanical properties and flexibility can be obtained.

  Examples of the inorganic particles include barium, zirconium, niobium, silver, copper, indium, tin, lanthanum, cerium, neodymium, tantalum, tungsten, molybdenum, and other simple elements, and oxides, hydroxides, chlorides thereof, Various compounds such as halides and sulfates can be mentioned, and high radiation shielding properties can be realized by including these inorganic particles. In particular, barium sulfate and tungsten are preferable in terms of both safety and radiation shielding.

  The content of the inorganic particles is 50 to 96% by weight based on the total weight of the sheet material, preferably 55 to 90% by weight, more preferably 60 to 85% by weight, and still more preferably 65 to 85% by weight. 85% by weight. When the content is more than 50% by weight, sufficient radiation shielding properties cannot be exhibited. On the other hand, when the content exceeds 96% by weight, the inorganic particles easily fall off from the sheet material, which is not preferable.

  The primary particle diameter of the inorganic particles is preferably 0.1 to 10.0 μm, more preferably 0.5 to 5.0 μm. Specific examples of the inorganic particles used in the present invention include W-1kD, W-3kD, and W-4kD (primary particle diameter: 0.6 to 0.9 μm, 1.5 to 2. 0 μm, 2.0 to 4.0 μm).

  In addition, it is preferable that the inorganic particles are uniformly dispersed in a base material composed of a fibrous material and a binder resin. If the inorganic particles are partially aggregated or unevenly distributed, sufficient radiation The shielding may not be obtained.

  In addition, in this invention, fillers (filler etc.) other than the said inorganic particle can be contained in the range which does not impair a physical property. Examples of the filler include non-fibrous fillers such as plates, scales, granules, irregular shapes, and crushed products. Specifically, for example, carbon, potassium titanate, barium titanate, aluminum borate, nitriding Silicon, mica, layered clay mineral, talc, kaolin, silica, calcium carbonate, glass beads, glass flake, glass microballoon, clay, molybdenum disulfide, graphite, expanded graphite, wollastonite, titanium dioxide, zinc oxide, calcium polyphosphate Generally, known fillers such as metal powder, metal flakes, metal ribbons and metal oxides can be used singly or in combination, and the type, particle size, shape, combination, blending ratio, etc. are particularly limited. It is not a thing. In addition, an appropriate amount of various pigments can be appropriately added for the purpose of coloring the sheet.

  Examples of the fibrous material used in the present invention include inorganic fibers such as glass fibers, ceramic fibers, alumina fibers, potassium titanate fibers, rock wool, carbon fibers, and steel fibers, aromatic polyamide fibers (aramid fibers), acrylic fibers, Cellulose fibers, polypropylene fibers, polyethylene fibers, polyparaphenylene benzobisoxazole fibers, wholly aromatic polyester fibers, organic fibers such as polyphenylene sulfide fibers, etc., preferably these short fibers, more preferably fibrils and fibrillation described later Pulp. In particular, aromatic polyamide (aramid) fibrils, fibrillated aromatic polyamide (aramid) pulps, para-type aromatic polyamide fibrils, and fibrillated para-type aromatic polyamide pulps are particularly mentioned. The fibers can be used singly or in combination, and the type, combination, blending ratio, etc. are not particularly limited.

  In the present invention, it is particularly desirable that the fibrous material has fibrils, and fibrils obtained by introducing a polymer solution into an aqueous coagulation liquid are preferable. Examples thereof include fibrils manufactured by WO2004 / 099476A1. can do. Moreover, the pulp fibrillated using a disaggregator (pulper), a beater, a refiner, a mixer, etc. can be illustrated.

  In particular, we dry and heat press the above-mentioned fibrils and fibrillated pulps, especially the fibrils containing many fine fibrils of 1 micron or less, dispersed in water and made into paper. In doing so, it was noted that paper with very high strength and smoothness could be obtained. It is considered that physically fine fibrils are entangled with each other to develop strength, and the entanglement is considered to be further strengthened by shrinkage during drying. Therefore, when used as a fibrous material for the sheet material, it serves as a reinforcing material for the sheet material, and a sheet material having excellent mechanical strength can be obtained.

  In addition, when the inorganic particles and the filler are simultaneously engraved, the fine fibril fibers of the fibril or fibrillated pulp retain the inorganic particles and the like, and the inorganic particles are mixed at a high mixing ratio and uniformly. can do. This is considered that not only the inorganic particles and the like are physically adsorbed on the fine fibrils but also the fibrils are entangled with each other at the time of drying and the binder performance is exhibited, whereby the inorganic particles and the like are held. In addition, when the sheet material is used, it is possible to uniformly disperse the inorganic particles and the like without selecting a direction such as a surface direction or a thickness direction of the sheet material.

  In the present invention, the shopper leaguer freeness of the fibrous material is preferably 20 to 80 ° SR, more preferably 25 to 80 ° SR, and further preferably 40 to 80 ° SR. If the freeness is too small, it is difficult to keep the inorganic material at a high content. If the freeness is too high, the drainage time becomes long and the productivity is poor.

  Further, the moisture content of the fibrous material is preferably 10 to 99%, more preferably 20 to 99%. Due to the presence of a large amount of moisture in the fiber, shrinkage when water is removed during drying. It is thought that the entanglement between fibers and fibrils is strengthened. Accordingly, a sheet material having excellent mechanical strength and high sealing properties can be obtained.

  From the viewpoint of the shopper ligler freeness and moisture content of the above fibrous material, fibrillated or fibrillated pulp, especially fibrillated aromatic polyamide pulp or aromatic polyamide fibril, particularly aromatic polyamide fibril It is preferable to use it.

As the binder resin in the present invention, for example, nitrile butadiene rubber, styrene butadiene rubber, butadiene rubber, butyl rubber, silicon rubber, ethylene propylene rubber, fluorine rubber, isoprene rubber, natural rubber, and the like, a latex of a generally known rubber is used. Alternatively, a plurality of combinations can be used as appropriate. Further, in order to vulcanize such rubber, an appropriate amount of a vulcanizing agent such as sulfur, isocyanate, or peroxide can be used. Moreover, resin emulsions, such as a fluororesin, a urethane resin, an epoxy resin, a phenol resin, a melanin resin, a urea resin, can also be used. In particular, a fluororesin is preferable because of its excellent heat resistance and chemical resistance, and it is used in combination with the above-mentioned fibril or fibrillated pulp, particularly fibrillated aromatic polyamide pulp or aromatic polyamide fibril, especially aromatic polyamide fibril. It was found that, in addition to heat resistance and chemical resistance, the inorganic particles can be retained at the above-described high content, and a sheet material exhibiting high radiation shielding performance can be obtained.

  Examples of the fluororesin include, for example, tetrafluoroethylene resin (PTFE), perfluoroalkoxy resin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), and tetrafluoroethylene-ethylene copolymer. Resin (ETFE), vinylidene fluoride resin (PVDF), trifluoroethylene chloride resin (PCTFE), and the like are mentioned. Among these, tetrafluoroethylene resin (PTFE) is preferable.

  In the present invention, the weight ratio of fibrous material: binder resin is preferably in the range of 10:90 to 80:20. If the amount of the fibrous material is too small, the mechanical strength tends to decrease, and if the amount of the binder resin is too small, it is difficult to sufficiently bond and hold the fibrous material and the inorganic particles.

  As a manufacturing method of the sheet material of the present invention described above, for example, a conventionally used method for making wood pulp can be applied as it is. At that time, various dispersers (pulpers), various beaters such as a Niagara beater, or various refiners such as a single disc refiner may be used.

  Hereinafter, a method of using a binder resin dispersion (sometimes called a dispersion or an emulsion) will be described. The binder resin dispersion is prepared by stably dispersing the binder resin powder in water containing an anionic, cationic, or nonionic surfactant. In general, a similar binder resin powder dispersion can be prepared by aqueous polymerization of a binder resin raw material monomer in the presence of one or more surfactants. It is also possible to use a commercially available binder resin dispersion as it is. For example, as an aqueous dispersion of fluororesin powder, dispersion of fluororesin commercially available from Asahi Glass Co., Ltd., Daikin Industries, Ltd. and the like can be mentioned.

  In the present invention, it is preferable to use an aggregating agent having an action of destabilizing the dispersion of the binder resin powder in water, thereby playing a role of depositing the binder resin on the surface of the fibrous material. The type of flocculant to be applied and the amount added are determined by the type of surfactant used to disperse the binder resin powder and the specific surface area of the fibrous material. In addition, using a condensate of polyhydroxy aromatic carboxylic acid and glucose and a polyvalent metal salt as a binder resin, particularly a fluororesin flocculant, regardless of the type of surfactant used, It is particularly effective. Examples of condensates include tannic acid and gallic acid. Examples of metal salts include aluminum sulfate and calcium chloride. At this time, adding alkaline components such as calcium hydroxide and ammonia to the system to adjust the pH of the system to the range of 3.5 to 6.0 causes the binder resin powder to be deposited on the fibrous material. This is effective.

As a method of depositing the binder resin and the inorganic particles on the surface of the fibrous material, a dispersion in which the fibrous material, the inorganic particles, and the binder resin powder are dispersed in water is prepared, and an aggregating agent is added to the dispersion. be able to. However, it is preferable to add a flocculant in advance to a dispersion in which the fibrous material is dispersed in water, and then add a dispersion in which the binder resin powder and inorganic particles are dispersed in water. The fibrous material on which the binder resin powder and the inorganic particles are deposited is made according to a conventional method, then dehydrated as necessary, and then dried to obtain a sheet material.

  In the present invention, papermaking can be carried out by applying a commonly used long net type or round net type paper machine. The sheet thus produced may contain a surfactant used to disperse the binder resin powder and inorganic particles in water and a chemical used during aggregation. Since these components may be gasified during firing of the preform and cause defects such as cracking and swelling, it is necessary to remove these components from the sheet material. The removal method varies depending on the type of the binder resin, the surfactant, and the flocculant. When the binder resin is a fluororesin, the temperature is from 200 ° C. to less than the melting point of the fluororesin, more preferably from 220 ° C. to the fluororesin. It is preferable to heat within a range of 20 ° C. below the melting point.

The sheet made of the fibrous material, the binder resin, and the inorganic particles obtained as described above can be used as a sheet material as it is.
In the case where the binder resin is a fluororesin, it is loaded into a mold in a state of being laminated as necessary, and then pressed to produce a sheet material preform. Furthermore, this preform can be fired by holding it at 350 to 400 ° C. in nitrogen for 0.5 to 1.5 hours, for example, to produce a sheet material. At this time, in order to make a gasket or a sealing material made of the sheet material, a preform is prepared by arbitrarily adjusting the size and the number of laminated sheets of the paper sheet, and further subjected to firing under the above-described conditions. And a gasket or a sealing material may be formed.

(1) Shopper leaguer freeness of fibrous material It measured by the method based on JISP8121.
(2) Moisture content of fibrous material Measured according to JIS L 1013 and calculated by the following formula.
Moisture content of fibrous material = (W ₀ −W) / W ₀ × 100
Here, W ₀ represents the weight before drying of the fibrous material, and W represents the weight after drying of the fibrous material.
(3) Thickness and basis weight of sheet material Measurement was performed by a method based on JIS L 1096. The thickness was measured with a load for fabric measurement (240 g / m ² ) using a digimatic thickness tester.
(4) Tensile strength of sheet material Measurement was performed by a method based on JIS K 7137.
(5) Radiation shielding performance of sheet material The lead equivalent in the thickness direction of the sheet material was measured according to JIS Z 4501.

[Example 1]
As a fiber material, a fibrid of poly-p-phenylene terephthalamide was prepared in accordance with Example 1 of WO2004 / 099476A1. Using this fibrid, dispersion of PTFE powder as a binder resin (trade name “Fluon Dispersion AD911E”, manufactured by Asahi Glass Co., Ltd.), and tungsten particles having a primary particle diameter of 2.5 μm (trade name “W” -4 kD "(manufactured by Nippon Shin Metals Co., Ltd.) with the compositions shown in Table 1, respectively, to prepare sheet materials.
First, aramid fibrite, PTFE dispersion, and tungsten particles are dispersed in water, and a fixing agent (trade name “Gragin CF”, manufactured by Matsumoto Yushi Co., Ltd., tannic acid / aluminum sulfate = 60/40 (weight ratio)) Then, an aqueous solution of sodium aluminate was added to adjust the pH, and the mixture was stirred for 10 minutes to fix PTFE and inorganic particles to the fibrid. And after making with a paper machine, making it spin-dry | dehydrated and drying, it was made to dry at 260 degreeC for 8 hours, and the volatile component contained in a sheet | seat was removed. Next, a predetermined number of the obtained sheets were stacked and pressed at a surface pressure of 100 kgf / cm ² to obtain a preform. This preform was baked by holding at 380 ° C. for 1 hour in nitrogen to prepare a sheet material.

[Example 2]
The same operation as in Example 1 was performed except that the content of inorganic particles with respect to the total weight of the sheet material was 80%.

[Example 3]
The same operation as in Example 2 was performed except that fibrid having a freeness of 80 ° SR was used as the fibrous material.

[Example 4]
Except for using an aramid pulp (trade name “Twaron 1094”, manufactured by Teijin Aramid BV, length-weighted average fiber length: 0.91 mm) fibrillated with poly-p-phenylene terephthalamide as a fibrous material, The same operation as in Example 1 was performed.

[Example 5]
As the fibrous material, the same procedure as in Example 1 was carried out except that the fibrous material of Example 4 was beaten with a mixer and further fibrillated aramid pulp was used.

[Example 6]
The same procedure as in Example 1 was carried out except that the poly-p-phenylene terephthalamide fibrid produced in the same manner as in Example 1 was appropriately dried to have a moisture content of 24.2%.

[Comparative Example 1]
The same operation as in Example 1 was performed except that inorganic particles were not used.

[Comparative Example 2]
The same operation as in Example 1 was performed except that the content of inorganic particles with respect to the total weight of the sheet material was 40%.

[Comparative Example 3]
The same operation as in Example 1 was performed except that the content of inorganic particles with respect to the total weight of the sheet material was 94%.

[Comparative Example 4]
Except for using aramid pulp (trade name “Twaron 1097”, manufactured by Teijin Aramid BV, length-weighted average fiber length: 1.34 mm) fibrillated with poly-p-phenylene terephthalamide as a fibrous material, The same operation as in Example 1 was performed.
The results are shown in Table 1.

  The sheet material of the present invention is excellent in mechanical strength, flexibility and sealing properties while having high radiation shielding performance, and can be suitably used for a gasket or a sealing material.

Claims (8)

A sheet material comprising at least a binder resin composed of a fibrous material and a fluororesin, and an aggregating agent having an action of destabilizing dispersion of the fluororesin powder in water, the sheet material having an atomic number of 40 Containing at least one kind of inorganic particles composed of the above-described elements alone or a compound based on the total weight of the sheet material in an amount of 55 to 90 % by weight, and the fibrous material has a shopper leaguer freeness of 20 to 80 °. A radiation shielding sheet material characterized by being SR . The fluororesin is tetrafluoroethylene resin (PTFE), perfluoroalkoxy resin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene-ethylene copolymer resin (ETFE). The radiation shielding sheet material according to claim 1, wherein the radiation shielding sheet material is at least one fluororesin selected from the group consisting of vinylidene fluoride resin (PVDF) and ethylene trifluoride chloride resin (PCTFE). The radiation shielding sheet material according to claim 1, wherein the flocculant is a condensate of polyhydroxy aromatic carboxylic acid and glucose. The radiation shielding sheet material according to claim 1, wherein the flocculant is tannic acid or gallic acid. The radiation shielding sheet material according to any one of claims 1 to 4, wherein the fibrous material is made of an aromatic polyamide having fibrils. The radiation shielding sheet according to any one of claims 1 to 5, wherein the fibrous material is a fibrid obtained by introducing an aromatic polyamide solution into an aqueous coagulating liquid, and the moisture content of the fibrid is 10 to 99%. Wood. The gasket comprised from the radiation shielding sheet | seat material in any one of Claims 1-6 . The sealing material comprised from the radiation shielding sheet | seat material in any one of Claims 1-6 .