JP2018132387A - Radiation shielding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation shielding material which has an excellent function of shielding radiation and can be easily dealt with.SOLUTION: The radiation shielding material according to an embodiment of the present invention is formed by depositing a plurality of sheets, which are first composite fiber sheets of barium sulfate and fibers.SELECTED DRAWING: None

Description

  The present invention relates to a radiation shielding material.

  The fiber exhibits various properties based on the functional groups on the surface thereof, but the surface may need to be modified depending on the application. So far, techniques for surface modification of fibers have been developed.

  For example, Patent Document 1 describes a composite in which crystalline calcium carbonate is mechanically bonded onto a fiber. Patent Document 2 describes a technique for producing a composite of pulp and calcium carbonate by precipitating calcium carbonate in a pulp suspension by a carbon dioxide method. Patent Document 3 discloses a method for improving the whiteness and cleanliness of waste paper fibers by adding a large amount of filler to the fibers for paper and paperboard, and sending the slurry of waste paper pulp to a gas-liquid contact device. On the other hand, a technique is described in which an alkali salt slurry is contacted in the direction of flow with pulp in the contact zone, and a suitable reactive gas is fed and mixed with the sedimentary filler to adhere the filler to the fiber surface. Patent Documents 4 and 5 disclose a technique for manufacturing a fiber web in which calcium carbonate is efficiently incorporated by precipitating calcium carbonate in a step of forming a fiber web (wet paper).

  By the way, lead is known as a radiation shielding material, but an alternative material is required for its influence on the environment. As alternative materials, tungsten and barium sulfate are known.

Japanese Patent Laid-Open No. 06-158585 US Pat. No. 5,679,220 US Pat. No. 5,665,205 Special table 2013-521417 gazette US Patent Publication No. 2011/000633

  As a product using barium sulfate, a sheet kneaded in a resin is known. However, there is a need for a radiation shielding material that has a good radiation shielding function and is easier to handle.

  One embodiment of the present invention has been made in order to meet such a demand, and provides a radiation shielding material having a good radiation shielding function and easier to handle.

The present invention includes, but is not limited to, the following inventions.
(1) A radiation shielding material, which is a composite fiber of barium sulfate and fiber, in which a plurality of first composite fiber sheets in sheet form are laminated.

  According to one embodiment of the present invention, it is possible to provide a radiation shielding material that has a good radiation shielding function and is easier to handle.

It is a schematic diagram which shows the structure of the outline of the reaction apparatus used for the synthesis | combination of sample 1-6 of experiment 1 (6). It is a figure which shows the observation result by the electron microscope of the composite fiber (sample 1-1) produced in Experiment 1 (left: 3000 time, right: 10000 time). It is a figure which shows the observation result by the electron microscope of the composite fiber (sample 1-2) produced in Experiment 1 (left: 3000 time, right: 10000 time). It is a figure which shows the observation result by the electron microscope of the composite fiber (sample 1-3) produced in Experiment 1 (left: 3000 time, right: 10000 time). It is a figure which shows the observation result by the electron microscope of the composite fiber (sample 1-4) produced in Experiment 1 (left: 3000 times, right: 50000 times). It is a figure which shows the observation result by the electron microscope of the composite fiber (sample 1-5) produced in Experiment 1 (left: 3000 time, right: 10000 time). It is a figure which shows the observation result by the electron microscope of the composite fiber (sample 1-6) produced in Experiment 1 (left: 3000 time, right: 10000 time). It is a figure which shows the observation result by the electron microscope of the composite fiber (sample 1-7) produced in Experiment 1 (left: 3000 time, right: 10000 time). In Experiment 2, it is a figure which shows the observation result by the electron microscope of the composite fiber sheet (sheet 2-1) manufactured from the composite fiber (sample 1-1) (left: 500 time, right: 10000 time). In Experiment 2, it is a figure which shows the observation result by the electron microscope of the composite fiber sheet (sheet 2-2) manufactured from the composite fiber (sample 1-2) (left: 500 time, right: 10000 time). In Experiment 2, it is a figure which shows the observation result by the electron microscope of the composite fiber sheet (sheet 2-4) manufactured from the composite fiber (sample 1-4) (left: 500 times, right: 3000 times). In Experiment 2, it is a figure which shows the observation result by the electron microscope of the composite fiber sheet (sheet | seat 2-5-1) manufactured from the composite fiber (sample 1-5) (left: 500 time, right: 3000 time). In Experiment 2, it is a figure which shows the observation result by the electron microscope of the composite fiber sheet (sheet 2-5-2) manufactured from the composite fiber (sample 1-5) (left: 500 times, right: 3000 times). In Experiment 2, it is a figure which shows the observation result by the electron microscope of the composite fiber sheet (sheet 2-7) manufactured from the composite fiber (sample 1-7) (left: 500 times, right: 3000 times). It is a figure which shows the external appearance of the combustion test apparatus used in the Example. It is a figure which shows the external appearance of the composite board (board A-1) after the fire resistance test of Experiment 3 (left: combustion surface, right: back surface). It is a figure which shows the external appearance of the composite board (board B) after the fire resistance test of Experiment 3 (left: combustion surface, right: back surface). It is a schematic diagram which shows the structure of the outline of the reaction apparatus used for the synthesis | combination of the sample 1-7 of Experiment 1 (7).

(Radiation shielding material)
The radiation shielding material according to one embodiment of the present invention is a composite fiber of barium sulfate and fiber, and a plurality of first composite fiber sheets in a sheet form are stacked.

  The radiation shielding material according to one embodiment of the present invention is composed of fibers. The fiber has properties such as light weight and easy processing. Therefore, handling is easy compared with the conventional radiation shielding material. In addition, barium sulfate has radiation shielding properties, is inexpensive, has a low environmental load, is highly safe for human bodies, and has flame retardancy. Therefore, the radiation shielding material according to one embodiment of the present invention is lightweight, inexpensive, highly safe to the human body, and has flame resistance. Furthermore, the radiation shielding material according to one embodiment of the present invention has a low environmental load when discarded. In addition, since composite fibers of barium sulfate and fibers have good ink and ink adhesion, they have excellent printing characteristics.

[First composite fiber sheet]
The 1st composite fiber sheet which constitutes the radiation shielding material concerning one mode of the present invention is a composite fiber of barium sulfate and a fiber, and is a sheet form.

[Composite fiber]
The composite fiber sheet of barium sulfate and fiber is not just a mixture of fiber and barium sulfate, but the fiber and barium sulfate are bound by hydrogen bonding or the like. Less likely to fall out of the fiber. The binding strength between the fiber and barium sulfate in the composite fiber sheet can be evaluated by, for example, ash yield (%). For example, it can be evaluated by a numerical value such as (sheet ash content / composite fiber ash content before disaggregation) × 100. Specifically, the composite fiber sheet is dispersed in water, adjusted to a solid content concentration of 0.2%, and disaggregated for 5 minutes with a standard disaggregator specified in JIS P 8220-1: 2012, and then JIS P 8222: 1998. The ash yield when formed into a sheet using a 150 mesh wire can be used for evaluation. In a preferred embodiment, the ash yield is 20% by mass or more, and in a more preferred embodiment, the ash yield is 50% by mass or more. It is. In other words, unlike the case where barium sulfate is simply blended into the fiber, when barium sulfate is compounded with the fiber, the barium sulfate is not only easily retained in the composite fiber sheet, but also a composite that is uniformly dispersed without agglomeration. A fiber sheet can be obtained.

  In one preferred embodiment, a composite fiber of fiber and barium sulfate is obtained by a method of synthesizing barium sulfate in a solution containing the fiber. Moreover, it is preferable that 15% or more of the fiber surface in the composite fiber sheet is covered with barium sulfate. When the fiber surface is coated with barium sulfate at such an area ratio, features resulting from barium sulfate are greatly produced, while features resulting from the fiber surface are reduced. In the composite fiber sheet, the fiber coverage (area ratio) by barium sulfate is more preferably 25% or more, and further preferably 40% or more. Moreover, according to the said method, the composite fiber whose coverage is 60% or more and 80% or more can be manufactured suitably. The upper limit of the coverage may be set as appropriate according to the application, but is 100%, 90%, or 80%, for example. Further, the composite fiber sheet obtained by the above method, in a preferred embodiment, shows that barium sulfate is not only fixed on the outer surface of the fiber and the inner side of the lumen, but also generated on the inner side of the microfibril. It is clear.

  The content of the composite fiber of barium sulfate and fibers contained in the first composite fiber sheet is preferably 10% to 100% with respect to the total weight of the first composite fiber sheet, 25 It is more preferable that it is% to 100%. By containing a composite fiber of 5% or more of barium sulfate and fiber with respect to the total weight of the first composite fiber sheet, the first composite fiber sheet can be produced.

[Barium sulfate]
Barium sulfate constituting the first composite fiber sheet is not particularly limited, but can be synthesized by a known method. In some cases, synthesis of barium sulfate is carried out in an aqueous system, and a composite fiber of barium sulfate and fibers is sometimes used in an aqueous system.

Barium sulfate is an ionic crystalline compound composed of barium ions and sulfate ions represented by BaSO ₄ , often in the form of a plate or a column, and is hardly soluble in water. Pure barium sulfate is a colorless crystal, but when it contains impurities such as iron, manganese, strontium and calcium, it becomes yellowish brown or blackish gray and becomes translucent. Although it can be obtained as a natural mineral, it can also be synthesized by chemical reaction. In particular, synthetic products by chemical reaction are used not only for pharmaceuticals (X-ray contrast media) but also widely used in paints, plastics, storage batteries, etc. by applying chemically stable properties.

  Barium sulfate compounded with fibers such as cellulose fibers is not particularly limited, but can be synthesized by a known method. In some cases, synthesis of barium sulfate is carried out in an aqueous system, and a composite fiber of barium sulfate and fibers is sometimes used in an aqueous system.

  As one preferred embodiment, the average primary particle diameter of barium sulfate complexed with fibers in the first composite fiber sheet can be, for example, 1.5 μm or less, but the sulfuric acid having an average primary particle diameter of less than 1200 nm Barium particles and barium sulfate particles having an average primary particle size of less than 900 nm can be used. Furthermore, barium sulfate particles having an average primary particle diameter of 200 nm or less and barium sulfate particles having an average primary particle diameter of 150 nm or less can be used. The average primary particle diameter of the barium sulfate particles can be 10 nm or more. The average primary particle diameter can be calculated from an electron micrograph.

  Further, in the first composite fiber sheet, the barium sulfate may take the form of secondary particles in which fine primary particles are aggregated, and can generate secondary particles according to the application, or aggregate by pulverization. A lump can be made fine. For grinding, ball mill, sand grinder mill, impact mill, high-pressure homogenizer, low-pressure homogenizer, dyno mill, ultrasonic mill, kanda grinder, attritor, stone mill, vibration mill, cutter mill, jet mill, breaker, beater Short shaft extruder, twin screw extruder, ultrasonic stirrer, household juicer mixer and the like.

  The average particle diameter, shape, etc. of the barium sulfate particles constituting the first composite fiber sheet can be confirmed by observation with an electron microscope. Furthermore, barium sulfate having various sizes and shapes can be combined with the fiber by adjusting the synthesis conditions and the like of barium sulfate. For example, a composite fiber in which plate-like barium sulfate is combined with the fiber can be used.

〔fiber〕
Although the fiber which comprises a 1st composite fiber sheet is not restrict | limited in particular, For example, a cellulose fiber, an aramid fiber, etc. are mentioned, A cellulose fiber is preferable. Examples of cellulose fiber raw materials include pulp fibers (wood pulp, non-wood pulp), cellulose nanofibers, bacterial cellulose, cellulose from animals such as sea squirts, and algae. Wood pulp is produced by pulping wood raw materials. That's fine. Wood raw materials include red pine, black pine, todomatsu, spruce, beech pine, larch, fir, tsuga, cedar, hinoki, larch, shirabe, spruce, hiba, douglas fir, hemlock, white fur, spruce, balsam fur, cedar, pine, Coniferous trees such as Merck pine, Radiata pine, etc., and mixed materials thereof, beech, hippopotamus, alder tree, oak, tab, shii, birch, broadleaf tree, poplar, tamo, dragonfly, eucalyptus, mangrove, lawan, acacia, etc. Examples are materials.

  The method for pulping natural materials such as wood raw materials (woody raw materials) is not particularly limited, and examples thereof include pulping methods generally used in the paper industry. Wood pulp can be classified by pulping method, for example, chemical pulp digested by methods such as kraft method, sulfite method, soda method, polysulfide method; mechanical pulp obtained by pulping by mechanical force such as refiner, grinder; Semi-chemical pulp obtained by carrying out pulping by mechanical force after pretreatment by; waste paper pulp; deinked pulp and the like. Wood pulp may be unbleached (before bleaching) or bleached (after bleaching).

  Examples of the non-wood-derived pulp include cotton, hemp, sisal hemp, manila hemp, flax, straw, bamboo, bagasse, kenaf, sugar cane, corn, rice straw, straw, honey and so on.

  The pulp fiber may be either unbeaten or beaten, and may be selected according to the physical properties of the first composite fiber sheet, but it is preferable to beaten. Thereby, improvement in sheet strength of the first composite fiber sheet and promotion of fixing barium sulfate can be expected.

  A composite fiber of synthetic fiber and cellulose fiber can also be used as a fiber constituting the first composite fiber sheet. For example, polyester, polyamide, polyolefin, acrylic fiber, glass fiber, carbon fiber, various metal fibers, etc. and cellulose Composite fibers with fibers can also be used.

  Further, these cellulose raw materials are further processed to give finely pulverized cellulose, chemically modified cellulose such as oxidized cellulose, and cellulose nanofiber: CNF (microfibrillated cellulose: MFC, TEMPO oxidized CNF, phosphate esterified CNF, carboxymethyl) CNF, mechanically pulverized CNF, etc.). The finely pulverized cellulose includes both what is generally called powdered cellulose and the above mechanically pulverized CNF. The powdered cellulose is produced, for example, by a method in which finely selected pulp is mechanically pulverized without treatment, or an undegraded residue obtained after acid hydrolysis is purified, dried, pulverized and sieved. Crystalline cellulose powder having a certain particle size distribution in the form of a rod axis may be used, or commercially available products such as KC Flock (manufactured by Nippon Paper Industries), Theolas (manufactured by Asahi Kasei Chemicals), Avicel (manufactured by FMC), etc. May be. The degree of polymerization of cellulose in the powdered cellulose is preferably about 100 to 1500, the degree of crystallinity of the powdered cellulose by X-ray diffraction is preferably 70% to 90%, and the volume average particle by a laser diffraction type particle size distribution measuring device. The diameter is preferably 1 μm to 100 μm. Oxidized cellulose can be obtained, for example, by oxidizing in water using an oxidizing agent in the presence of a compound selected from the group consisting of N-oxyl compounds and bromides, iodides or mixtures thereof. As the cellulose nanofiber, a method of defibrating the cellulose raw material is used. As the defibrating method, for example, an aqueous suspension of chemically modified cellulose such as cellulose or oxidized cellulose is mechanically ground or beaten with a refiner, a high-pressure homogenizer, a grinder, a uniaxial or multiaxial kneader, a bead mill or the like. A method of defibration can be used. Cellulose nanofibers may be produced by combining one or more of the above methods. The fiber diameter of the produced cellulose nanofiber can be confirmed by observation with an electron microscope or the like, and is, for example, in the range of 5 nm to 1000 nm, preferably 5 nm to 500 nm, more preferably 5 nm to 300 nm. When producing the cellulose nanofiber, before and / or after the cellulose is defibrated and / or refined, an arbitrary compound may be further added and reacted with the cellulose nanofiber to modify the hydroxyl group. it can. As functional groups to be modified, acetyl group, ester group, ether group, ketone group, formyl group, benzoyl group, acetal, hemiacetal, oxime, isonitrile, allene, thiol group, urea group, cyano group, nitro group, azo group , Aryl group, aralkyl group, amino group, amide group, imide group, acryloyl group, methacryloyl group, propionyl group, propioyl group, butyryl group, 2-butyryl group, pentanoyl group, hexanoyl group, heptanoyl group, octanoyl group, nonanoyl group , Decanoyl group, undecanoyl group, dodecanoyl group, myristoyl group, palmitoyl group, stearoyl group, pivaloyl group, benzoyl group, naphthoyl group, nicotinoyl group, isonicotinoyl group, furoyl group, cinnamoyl group and other acyl groups, 2-methacryloyl Isocyanate groups such as oxyethylisocyanoyl group, methyl group, ethyl group, propyl group, 2-propyl group, butyl group, 2-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl Group, decyl group, undecyl group, dodecyl group, myristyl group, palmityl group, stearyl group and other alkyl groups, oxirane group, oxetane group, oxyl group, thiirane group, thietane group and the like. Hydrogen in these substituents may be substituted with a functional group such as a hydroxyl group or a carboxy group. Further, a part of the alkyl group may be an unsaturated bond. The compound used for introducing these functional groups is not particularly limited. For example, a compound having a phosphoric acid-derived group, a compound having a carboxylic acid-derived group, a compound having a sulfuric acid-derived group, or a sulfonic acid-derived compound And the like, compounds having an alkyl group, compounds having an amine-derived group, and the like. Although it does not specifically limit as a compound which has a phosphoric acid group, Lithium dihydrogen phosphate which is phosphoric acid and the lithium salt of phosphoric acid, Dilithium hydrogen phosphate, Trilithium phosphate, Lithium pyrophosphate, Lithium polyphosphate is mentioned. . Furthermore, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate and sodium polyphosphate which are sodium salts of phosphoric acid are mentioned. Furthermore, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate which are potassium salts of phosphoric acid are mentioned. Further examples include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate, which are ammonium salts of phosphoric acid. Of these, phosphoric acid, sodium phosphate, phosphoric acid potassium salt, and phosphoric acid ammonium salt are preferred from the viewpoint of high efficiency in introducing a phosphate group and easy industrial application. Sodium dihydrogen phosphate Although disodium hydrogen phosphate is more preferable, it is not particularly limited. The compound having a carboxyl group is not particularly limited, and examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. . The acid anhydride of the compound having a carboxyl group is not particularly limited, but examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. It is done. Although it does not specifically limit as a derivative of the compound which has a carboxyl group, The derivative of the acid anhydride of the compound which has a carboxyl group and the acid anhydride imidation of a compound which has a carboxyl group are mentioned. Although it does not specifically limit as an acid anhydride imidation thing of a compound which has a carboxyl group, Imidation thing of dicarboxylic acid compounds, such as maleimide, succinic acid imide, and phthalic acid imide, is mentioned. The acid anhydride derivative of the compound having a carboxyl group is not particularly limited. For example, at least some of the hydrogen atoms of the acid anhydride of the compound having a carboxyl group, such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. are substituted (for example, alkyl group, phenyl group, etc. ) Are substituted. Among the compounds having a group derived from a carboxylic acid, maleic anhydride, succinic anhydride, and phthalic anhydride are preferred because they are easily applied industrially and easily gasified, but are not particularly limited. Further, the cellulose nanofiber may be modified in such a manner that the compound to be modified is physically adsorbed on the cellulose nanofiber without being chemically bonded. Examples of the physically adsorbing compound include surfactants, and any of anionic, cationic, and nonionic may be used. When the above-described modification is performed before cellulose is defibrated and / or pulverized, these functional groups can be removed after defibrating and / or pulverization to return to the original hydroxyl group. By performing the modification as described above, it is possible to promote the defibration of the cellulose nanofiber or to easily mix it with various substances when the cellulose nanofiber is used.

  In addition to cellulose fibers, various natural fibers, synthetic fibers, semi-synthetic fibers, and inorganic fibers can be used. Examples of natural fibers include protein fibers such as wool, silk thread and collagen fibers, and complex sugar chain fibers such as chitin / chitosan fibers and alginic acid fibers. Examples of synthetic fibers include polyester, polyamide, polyolefin, acrylic fiber, and semi-synthetic fibers such as rayon, lyocell, and acetate. Examples of the inorganic fiber include glass fiber, carbon fiber, and various metal fibers.

  In addition, composite fibers of synthetic fibers and cellulose fibers can also be used. For example, composite fibers of polyester fibers, polyamides, polyolefins, acrylic fibers, glass fibers, carbon fibers, various metal fibers, etc. and cellulose fibers should also be used. Can do.

  Among the examples shown above, it is preferable to include wood pulp or to include a combination of wood pulp and non-wood pulp and / or synthetic fiber, and more preferably only wood pulp.

  In a preferred embodiment, the fibers constituting the first composite fiber sheet are pulp fibers. Further, for example, a fibrous substance recovered from the wastewater of a paper mill may be supplied to the complexing reaction with barium sulfate of the present invention. By supplying such a substance to a composite reaction tank with barium sulfate, various composite particles can be synthesized, and fibrous particles and the like can be synthesized in terms of shape.

  In addition to the fibers, a substance that does not directly participate in the barium sulfate synthesis reaction but is taken into the product barium sulfate particles to form composite particles can be used. For example, in a mode in which fibers such as pulp fibers are used, composite particles in which these substances are further incorporated are produced by synthesizing barium sulfate in a solution containing inorganic particles, organic particles, polymers, etc. Is possible.

  About the fiber illustrated above, you may use individually or in combination of 2 or more types.

  Moreover, the fiber length of the fiber to be combined is not particularly limited. For example, the average fiber length may be about 0.1 μm to 15 mm, and may be 1 μm to 12 mm, 100 μm to 10 mm, 500 μm to 8 mm, and the like.

  The amount of fibers to be combined is preferably such that 15% or more of the fiber surface is covered with barium sulfate. For example, the weight ratio of fiber to barium sulfate can be 5/95 to 95/5, 10/90 to 90/10, 20/80 to 80/20, 30/70 to 70/30, 40 It is good also as / 60-60 / 40. As will be described later, flame retardants other than barium sulfate may be combined with the fiber. In this case, “weight ratio of fiber to barium sulfate” is read as “weight ratio of fiber to barium sulfate and flame retardant”.

〔Flame retardants〕
As one preferred embodiment, the first composite fiber sheet may contain a flame retardant. Thereby, stronger flame retardancy can be easily imparted to the first composite fiber sheet. Flame retardants include flame retardant inorganic particles such as magnesium carbonate, aluminum compounds and hydrotalcite, and tetrabromobisphenol A, decabromobiphenyl, pentabromodiphenyl ether, chlorinated paraffin, chlorinated polyethylene, phosphate ester, polyphosphoric acid It may be at least one selected from the group consisting of ammonium, sodium polyborate, borax, zinc borate, silicone resin, ammonium phosphate, guanidine compound, and organic flame retardant such as melamine compound. It is preferable that the 1st composite fiber sheet contains the aluminum compound as a flame retardant. A detailed description of the flame retardant will be described later. An example of the aluminum compound is aluminum hydroxide.

  In the case where the first composite fiber sheet contains a flame retardant, a mode in which the flame retardant forms a composite fiber with the fibers constituting the first composite fiber sheet is more preferable. That is, in this aspect, in the first composite fiber sheet, the barium sulfate, the flame retardant and the fiber form a composite fiber. By combining the flame retardant with the fiber, the fiber and the flame retardant are not simply mixed, but the fiber and the flame retardant are bound by hydrogen bonding or the like. Less likely to drop off.

  When aluminum sulfate is used as a raw material for synthesizing barium sulfate, it is possible to synthesize not only barium sulfate but also aluminum compounds such as aluminum hydroxide. If it is this method, since both barium sulfate and an aluminum compound can be synthesize | combined, the flame retardance of a 1st composite fiber sheet can be improved more easily.

  Of course, it is also possible to produce a first composite fiber sheet containing a flame retardant by a method of adding a flame retardant to a solution of the composite fiber after synthesizing the composite fiber of barium sulfate and fiber.

  When the first composite fiber sheet contains a flame retardant, the weight ratio between the synthesized barium sulfate and the flame retardant may be set as appropriate, and is preferably 2/1 to 6/1, for example. When the first composite fiber sheet contains the flame retardant within the above range, the flame retardance can be enhanced without impairing the radiation shielding property of the first composite fiber sheet. Details of the flame retardant will be described later.

[Synthesis of composite fiber of barium sulfate and fiber]
In one preferred embodiment, the composite fiber of barium sulfate and fiber can be obtained by synthesizing barium sulfate in the presence of fibers such as cellulose fibers. This is because the fiber surface is a suitable place for precipitation of barium sulfate, and it is easy to synthesize a composite fiber of barium sulfate and fiber.

  Examples of the method for synthesizing barium sulfate in the presence of fibers include a method for synthesizing barium sulfate in a solution of fibers such as cellulose fibers. For example, a composite fiber of barium sulfate and fiber is obtained by a method of reacting an acid (such as sulfuric acid) with a base by neutralization, reacting an inorganic salt with an acid or base, or reacting an inorganic salt with each other. be able to. For example, barium hydroxide can be reacted with sulfuric acid or aluminum sulfate to obtain barium sulfate, or barium chloride can be added to an aqueous solution containing sulfate to precipitate barium sulfate. When aluminum sulfate is used as a raw material for synthesizing barium sulfate, it is possible to synthesize not only barium sulfate but also aluminum compounds such as aluminum hydroxide. With this method, it is possible to synthesize composite fibers of barium sulfate and aluminum compounds and fibers.

  In addition, when an alkaline barium sulfate precursor typified by barium hydroxide is used as a raw material, the fiber can be swollen by dispersing the fiber in a barium sulfate precursor solution in advance, so that sulfuric acid can be efficiently used. A composite fiber of barium and fiber can be obtained. The reaction can be started after promoting the swelling of the fibers by stirring them for 15 minutes or more after mixing, but the reaction may be started immediately after mixing. There is no particular limitation on the form of the reaction tank and the stirring conditions for obtaining the composite fiber of barium sulfate and fiber. For example, the solution containing the fiber and the barium sulfate precursor is stirred and mixed in an open reaction tank. The composite fiber may be synthesized or may be synthesized by injecting an aqueous suspension containing the fiber and a barium sulfate precursor into the reaction vessel. As will be described later, when an aqueous suspension of a barium sulfate precursor is injected into the reaction vessel, cavitation bubbles may be generated and barium sulfate may be synthesized in the presence thereof.

  Further, the liquid may be ejected under conditions that cause cavitation bubbles in the reaction vessel, or may be ejected under conditions that do not cause cavitation bubbles. The reaction vessel is preferably a pressure vessel in any case. In addition, the pressure vessel in this invention is a container which can apply the pressure of 0.005 Mpa or more. In the condition that does not generate cavitation bubbles, the pressure in the pressure vessel is preferably 0.005 MPa or more and 0.9 MPa or less in static pressure.

(Cavitation bubbles)
When a composite fiber of barium sulfate and fiber is synthesized, barium sulfate can be precipitated in the presence of cavitation bubbles. Cavitation is a physical phenomenon in which bubbles are generated and disappeared in a short time due to a pressure difference in a fluid flow, and is also called a cavity phenomenon. Bubbles generated by cavitation (cavitation bubbles) are generated with very small “bubble nuclei” of 100 microns or less existing in the liquid as the nucleus when the pressure in the fluid becomes lower than the saturated vapor pressure for a very short time.

  Cavitation bubbles can be generated in the reaction vessel by a known method. For example, cavitation bubbles are generated by jetting fluid at high pressure, cavitation is generated by stirring at high speed in the fluid, cavitation is generated by causing explosion in the fluid, ultrasonic vibration It can be considered that cavitation is generated by a child (vibratory cavitation).

  Further, since the generation and control of cavitation bubbles are easy, it is particularly preferable to generate cavitation bubbles by jetting a fluid at a high pressure. In this aspect, by compressing the jet liquid using a pump or the like and jetting it through a nozzle or the like at high speed, cavitation bubbles are generated at the same time as the liquid itself expands due to extremely high shearing force near the nozzle and sudden pressure reduction . The method using a fluid jet has high generation efficiency of cavitation bubbles, and can generate cavitation bubbles having a stronger collapse impact force. In the present invention, controlled cavitation bubbles are present when synthesizing barium sulfate, which is clearly different from cavitation bubbles that cause uncontrollable harm that naturally occurs in fluid machinery.

  Cavitation can be generated by using a reaction solution such as a raw material as an injection liquid as it is, or cavitation bubbles can be generated by injecting some fluid into the reaction vessel. The fluid in which the liquid jet forms a jet may be any liquid, gas, solid such as powder or pulp, or a mixture thereof as long as it is in a fluid state. Furthermore, if necessary, another fluid such as carbon dioxide can be added to the above fluid as a new fluid. The fluid and the new fluid may be uniformly mixed and ejected, but may be ejected separately.

  The liquid jet is a jet of a fluid in which solid particles or gas are dispersed or mixed in the liquid or a liquid, and refers to a liquid jet containing pulp, barium sulfate raw material slurry or bubbles. The gas referred to here may include bubbles due to cavitation.

  In addition, when the injection liquid is injected through the nozzle or the orifice pipe to generate cavitation, the pressure of the injection liquid (upstream pressure) is desirably 0.01 MPa to 30 MPa, and 0.7 MPa to 20 MPa. Is preferable, and 2 MPa to 15 MPa is more preferable. If the upstream pressure is 0.01 MPa or more, it is easy to obtain a pressure difference from the downstream pressure, and the effect is large. Moreover, if it is 30 Mpa or less, since a consumed energy can be suppressed without requiring a special pump and a pressure vessel, it is advantageous in cost. On the other hand, the pressure in the container (downstream pressure) is preferably 0.005 MPa to 0.9 MPa in static pressure. Moreover, the ratio of the pressure in the container and the pressure of the jet liquid is preferably in the range of 0.001 to 0.5.

  Further, the inorganic particles can be synthesized by spraying the spray liquid under the condition that cavitation bubbles are not generated. Specifically, it is more preferable that the pressure of the spray liquid (upstream pressure) is 2 MPa or less, preferably 1 MPa or less, and the pressure of the spray liquid (downstream pressure) is released to 0.05 MPa or less.

  The jet velocity of the jet liquid is desirably in the range of 1 m / sec to 200 m / sec, and preferably in the range of 20 m / sec to 100 m / sec. If the jet velocity is 1 m / sec or more, the pressure is sufficiently lowered and cavitation is likely to occur. On the other hand, if it is 200 m / sec or less, a necessary pressure can be obtained without requiring a special device, which is advantageous in terms of cost.

  Cavitation may be generated in a reaction vessel in which barium sulfate is deposited. Moreover, although it is possible to process by one pass, it can also circulate as many times as necessary. Furthermore, it can be processed in parallel or in permutation using a plurality of generating means.

  The liquid injection for generating cavitation may be performed in a container open to the atmosphere, but is preferably performed in a pressure container in order to control cavitation.

  When cavitation is generated by liquid injection, the solid content concentration of the reaction solution is preferably 30% by weight or less, and more preferably 20% by weight or less. This is because the cavitation bubbles easily act on the reaction system uniformly at such a concentration. In addition, the aqueous suspension of slaked lime that is the reaction solution preferably has a solid concentration of 0.1% by weight or more from the viewpoint of reaction efficiency.

  When synthesizing a composite fiber of barium sulfate and fiber, the reaction can be controlled by monitoring the pH of the reaction solution as long as the pH of the reaction solution changes as the reaction proceeds.

  Further, by increasing the liquid injection pressure, the flow rate of the injection liquid increases, and the pressure decreases accordingly, and stronger cavitation can be generated. Further, by pressurizing the pressure in the reaction vessel, the pressure in the region where the cavitation bubbles collapse is increased and the pressure difference between the bubbles and the surroundings increases, so that the bubbles collapse violently and the impact force can be increased. The reaction temperature is preferably 0 ° C to 90 ° C, and particularly preferably 10 ° C to 60 ° C. In general, the impact force is considered to be the maximum at the midpoint between the melting point and the boiling point. Therefore, in the case of an aqueous solution, a temperature around 50 ° C. is suitable, but even below that temperature is affected by the vapor pressure. Therefore, a high effect can be obtained within the above range.

  By adding a surfactant, the energy required to generate cavitation can be reduced. As the surfactant to be used, known or novel surfactants, for example, nonionic surfactants such as fatty acid salts, higher alkyl sulfates, alkylbenzene sulfonates, higher alcohols, alkylphenols, alkylene oxide adducts such as fatty acids, etc. , Anionic surfactants, cationic surfactants, amphoteric surfactants and the like. These may consist of a single component or a mixture of two or more components. The addition amount may be an amount necessary for reducing the surface tension of the jet liquid and / or the liquid to be jetted.

  The method for synthesizing barium sulfate employed when synthesizing barium sulfate in a solution containing fibers can be performed by a known method.

  In addition, water is used for the preparation of the suspension, and as this water, normal tap water, industrial water, ground water, well water, etc. can be used, ion-exchanged water, distilled water, ultrapure water, Industrial wastewater and water obtained when separating and dehydrating the reaction liquid can be suitably used.

  Moreover, the reaction liquid of a reaction tank can be circulated and used. By circulating the reaction liquid in this way and urging the solution to be stirred, the reaction efficiency is increased and it becomes easy to obtain a desired composite fiber.

  Moreover, when manufacturing a 1st composite fiber sheet, various well-known auxiliary | assistant can be added with respect to the composite fiber of barium sulfate and a fiber. For example, chelating agents can be added. Specifically, polyhydroxycarboxylic acids such as citric acid, malic acid and tartaric acid, dicarboxylic acids such as oxalic acid, sugar acids such as gluconic acid, iminodiacetic acid, ethylenediaminetetra Aminopolycarboxylic acids such as acetic acid and alkali metal salts thereof, alkali metal salts of polyphosphoric acid such as hexametaphosphoric acid and tripolyphosphoric acid, amino acids such as glutamic acid and aspartic acid and alkali metal salts thereof, acetylacetone, methyl acetoacetate, acetoacetic acid Examples include ketones such as allyl, saccharides such as sucrose, and polyols such as sorbitol. Further, as a surface treatment agent, saturated fatty acids such as palmitic acid and stearic acid, unsaturated fatty acids such as oleic acid and linoleic acid, resin acids such as alicyclic carboxylic acid and abietic acid, salts, esters and ethers thereof, alcohols Activators, sorbitan fatty acid esters, amide or amine surfactants, polyoxyalkylene alkyl ethers, polyoxyethylene nonyl phenyl ether, sodium alpha olefin sulfonate, long chain alkyl amino acids, amine oxides, alkyl amines, fourth A quaternary ammonium salt, aminocarboxylic acid, phosphonic acid, polyvalent carboxylic acid, condensed phosphoric acid and the like can be added. Moreover, a dispersing agent can also be used as needed. Examples of the dispersant include sodium polyacrylate, sucrose fatty acid ester, glycerin fatty acid ester, acrylic acid-maleic acid copolymer ammonium salt, methacrylic acid-naphthoxypolyethylene glycol acrylate copolymer, methacrylic acid-polyethylene glycol. Examples include monomethacrylate copolymer ammonium salts and polyethylene glycol monoacrylate. These can be used alone or in combination. The timing of addition may be before or after the synthesis reaction. Various auxiliaries can be added in an amount of preferably 0.001 to 20%, more preferably 0.1 to 10% with respect to the amount of barium sulfate to be synthesized.

  Further, the first composite fiber sheet may contain particles generally called inorganic fillers and organic fillers, and various fibers (hereinafter referred to as “fillers”). For example, as inorganic filler, calcium carbonate (light calcium carbonate, heavy calcium carbonate), magnesium carbonate, barium carbonate, aluminum compound, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay (kaolin, calcined kaolin, deramikaolin) , Talc, zinc oxide, zinc stearate, titanium dioxide, silica produced from sodium silicate and mineral acid (white carbon, silica / calcium carbonate composite fiber, silica / titanium dioxide composite fiber), white clay, bentonite, diatomaceous earth, sulfuric acid Examples include inorganic fillers that regenerate and use calcium, zeolite, ash obtained from the deinking process, and inorganic fillers that form composite fibers with silica or calcium carbonate in the process of regeneration. As the calcium carbonate silica composite, amorphous silica such as white carbon may be used together with calcium carbonate and / or light calcium carbonate silica composite. Organic fillers include urea-formalin resin, polystyrene resin, phenol resin, fine hollow particles, acrylamide composite fiber, wood-derived substances (fine fiber, microfibril fiber, powder kenaf), modified insolubilized starch, ungelatinized starch, etc. Is mentioned. As fibers, natural fibers such as cellulose, synthetic fibers that are artificially synthesized from raw materials such as petroleum, regenerated fibers (semi-synthetic fibers) such as rayon and lyocell, and inorganic fibers are not limited. Can be used. The filler and the like can be added in an amount of preferably 1 to 80%, more preferably 5 to 50%, based on the amount of barium sulfate to be synthesized.

  The reaction conditions for synthesizing the composite fiber of barium sulfate and fiber are not particularly limited, and can be set as appropriate according to the application. For example, the temperature of the synthesis reaction is, for example, 0 ° C. to 90 ° C., and preferably 10 ° C. to 70 ° C. The reaction temperature can be controlled by a temperature control device. If it is 0 degreeC or more, sufficient reaction efficiency is obtained and it is advantageous in terms of cost, and if it is 90 degrees C or less, it can prevent that barium sulfate particle increases.

  The reaction when synthesizing the composite fiber of barium sulfate and fiber can be a batch reaction or a continuous reaction. In general, it is preferable to perform a batch reaction step for the convenience of discharging the residue after the reaction. The scale of the reaction is not particularly limited, but the reaction may be performed on a scale of 100 L or less, or may be performed on a scale of more than 100 L. The size of the reaction vessel can be, for example, about 10 L to 100 L, or about 100 L to 50000 L.

  In addition, the reaction can be controlled by the electric conductivity of the reaction solution and / or the reaction time, and specifically, the time during which the reaction product stays in the reaction vessel can be adjusted and controlled. In addition, the reaction can also be controlled by stirring the reaction solution in the reaction tank or making the reaction a multistage reaction.

  In the method of synthesizing barium sulfate in a solution containing fibers, a composite fiber that is a reaction product is obtained as a suspension. Therefore, if necessary, it can be stored in a storage tank, concentrated, dehydrated, ground, Processing such as classification, aging, and dispersion can be performed. These can be performed by known processes, and may be appropriately determined in consideration of the application, energy efficiency, and the like. For example, the concentration / dehydration treatment is performed using a centrifugal dehydrator, a sedimentation concentrator, or the like. Examples of the centrifugal dehydrator include a decanter and a screw decanter. When using a filter or a dehydrator, the type is not particularly limited, and a general one can be used. For example, a pressure dehydrator such as a filter press, a drum filter, a belt press, a tube press, A barium sulfate cake can be obtained by suitably using a vacuum drum dehydrator such as an Oliver filter. For grinding, ball mill, sand grinder mill, impact mill, high-pressure homogenizer, low-pressure homogenizer, dyno mill, ultrasonic mill, kanda grinder, attritor, stone mill, vibration mill, cutter mill, jet mill, breaker, beater Short shaft extruder, twin screw extruder, ultrasonic stirrer, household juicer mixer and the like. Examples of the classification method include a sieve such as a mesh, an outward type or inward type slit or round hole screen, a vibrating screen, a heavy foreign matter cleaner, a lighter foreign matter cleaner, a reverse cleaner, and a sieving tester. Examples of the dispersion method include a high-speed disperser and a low-speed kneader.

  The composite fiber obtained by the method of synthesizing barium sulfate in the fiber-containing solution can be blended into the filler or pigment in the suspension state without completely dehydrating, You can also Although there is no restriction | limiting in particular also about the dryer in this case, For example, an airflow dryer, a band dryer, a spray dryer etc. can be used conveniently.

  The composite fiber of barium sulfate and fiber can be modified by a known method. For example, in some embodiments, the surface can be hydrophobized to improve miscibility with a resin or the like.

[Manufacture of composite fiber sheet]
The composite fiber of barium sulfate and fiber may be formed into a sheet shape by a conventionally known method. Examples of paper machines used for producing sheets from composite fibers of barium sulfate and fibers include long net paper machines, round net paper machines, gap formers, hybrid formers, multilayer paper machines, and these devices. The well-known papermaking machine etc. which combined these papermaking systems are mentioned. The press linear pressure in the paper machine and the calendar linear pressure in the case where the calendar process is performed in the latter stage can be determined within a range that does not hinder the operability and the performance of the composite fiber sheet. Further, starch, various polymers, pigments, and mixtures thereof may be applied to the formed sheet by impregnation or coating.

  When forming into a sheet, a wet and / or dry paper strength agent (paper strength enhancer) can be added. Thereby, the intensity | strength of a composite fiber sheet can be improved. Examples of paper strength agents include urea formaldehyde resin, melamine formaldehyde resin, polyamide, polyamine, epichlorohydrin resin, vegetable gum, latex, polyethyleneimine, glyoxal, gum, mannogalactan polyethyleneimine, polyacrylamide resin, polyvinylamine. And a resin such as polyvinyl alcohol; a composite polymer or copolymer composed of two or more selected from the above resins; starch and processed starch; carboxymethylcellulose, guar gum, urea resin, and the like. The addition amount of the paper strength agent is not particularly limited.

  In order to promote the fixing of the filler to the fiber or to improve the yield of the filler and the fiber, a high molecular weight polymer or an inorganic substance can be added. For example, as coagulants, polyethyleneimine and modified polyethyleneimines containing tertiary and / or quaternary ammonium groups, polyalkyleneimines, dicyandiamide polymers, polyamines, polyamine / epichlorohydrin polymers, and dialkyldiallyl quaternary ammonium monomers, dialkyls Cations such as aminoalkyl acrylate, dialkylaminoalkyl methacrylate, dialkylaminoalkyl acrylamide, polymers of dialkylaminoalkyl methacrylamide and acrylamide, polymers of monoamines and epihalohydrin, polymers having polyvinylamine and vinylamine moieties, and mixtures thereof In addition to the functional polymer, a cation ligand obtained by copolymerizing an anionic group such as a carboxyl group or a sulfone group in the molecule of the polymer. Zwitterionic polymers, can be used mixtures of a cationic polymer and an anionic or zwitterionic polymer. As a retention agent, a cationic, anionic, or amphoteric polyacrylamide-based material can be used. In addition to these, a retention system called a so-called dual polymer that uses at least one kind of cation or anionic polymer can also be applied, and at least one kind of anionic bentonite, colloidal silica, polysilicic acid, It is a multi-component yield system using one or more inorganic fine particles such as polysilicic acid or polysilicate microgel and modified aluminum thereof, or organic fine particles having a particle diameter of 100 μm or less, which is called a micropolymer obtained by crosslinking polymerization of acrylamide. Also good. In particular, when the polyacrylamide material used alone or in combination has a weight average molecular weight of 2 million daltons or more by the intrinsic viscosity method, a good yield can be obtained, preferably 5 million daltons or more, and more preferably Can obtain a very high yield in the case of the above acrylamide-based material of 10 million daltons or more and less than 30 million daltons. The form of the polyacrylamide-based material may be an emulsion type or a solution type. The specific composition is not particularly limited as long as the substance contains an acrylamide monomer unit as a structural unit. For example, a copolymer of quaternary ammonium salt of acrylate ester and acrylamide, or acrylamide And a quaternized ammonium salt after copolymerization of acrylate and acrylate. The cationic charge density of the cationic polyacrylamide material is not particularly limited.

  In addition, according to the purpose, inorganic particles such as drainage improver, internal sizing agent, pH adjuster, antifoaming agent, pitch control agent, slime control agent, bulking agent, calcium carbonate, kaolin, talc, silica (so-called Etc.). The amount of each additive used is not particularly limited.

The basis weight of the sheet, may be appropriately adjusted depending on the purpose, high radiation blocking effect when a ^{40g / m 2 ~1200g / m 2} , also is good for drying load during production is low. The basis weight of the ^sheet, it ^is also possible to ^{60g / m 2 ~1000g / m 2} , it is also possible to ^{100g / m 2 ~600g / m 2} .

  It is also possible to apply or impregnate the first composite fiber sheet with a material containing a flame retardant. Moreover, it is also possible to coat | cover the 1st composite fiber sheet with the material containing a flame retardant. Thereby, the flame retardance of a 1st composite fiber sheet can be improved more.

[Manufacture of radiation shielding materials]
A radiation shielding material can be produced by stacking a plurality of first composite fiber sheets to form a laminate (multilayer sheet or multilayer board). When the first composite fiber sheet is used by being laminated, for example, 2 to 50 sheets can be used, 3 to 30 sheets are preferably used, and 4 to 20 sheets are preferably used. More preferably, it is used. Thus, by setting it as the laminated body which piled up the 1st composite fiber sheet, radiation shielding property improves greatly. When laminating sheets, a binder or the like may be used as appropriate. The kind of binder is not specifically limited. For example, the binder normally used for bonding of sheets, such as a vinyl acetate binder, is mentioned.

  Here, in the present specification, the “radiation shielding property” refers to a property of preventing the transmission of X-rays and γ-rays or reducing the amount of transmission of X-rays and γ-rays. Specifically, the X-ray dose reduction rate (%) of the radiation shielding material measured by the method described in the examples described later is preferably 25% or more, more preferably 40% or more, and even more preferably 50% or more. Most preferably 60% or more, or the dose reduction rate (%) of γ rays is preferably 2% or more, more preferably 5% or more, still more preferably 10% or more, and most preferably 15% or more. The radiation shielding material is said to have radiation shielding properties. In the present specification, the “radiation shielding” may be referred to as “radiation shielding”.

  Furthermore, the laminated body of the first composite fiber sheet is coated or impregnated with a material containing a flame retardant. The laminated body of the first composite fiber sheet is coated with a material containing a flame retardant, or described later. A flame retardant sheet may be bonded to one or both sides of the first composite fiber sheet laminate to form a flame retardant composite board. The flame retardant sheet to be bonded may be one sheet or plural sheets. However, when a plurality of flame retardant sheets are bonded to each other, for example, 2 to 20 sheets can be used. It is preferable to use one sheet, and it is more preferable to use 2 to 10 sheets.

  Further, various organic substances such as polymers and various inorganic substances such as pigments may be added to the composite fiber molding later. For example, it is possible to laminate a desired substance on the surface by applying (applying) a sheet (including laminated ones and board-like ones). For example, a binder such as starch and PVA, a hydrophobizing agent such as a sizing agent, an organic or inorganic flame retardant, and the like can be applied. Furthermore, it is possible to further enhance the function by impregnating sheets (including laminated ones and board-like ones) with various substances.

  These sheets, laminates, and boards can be further processed into a three-dimensional structure such as a honeycomb structure.

[Flame Retardant Sheet]
A flame-retardant sheet can be further laminated on the radiation shielding material according to one embodiment of the present invention. A flame-retardant sheet | seat contains a flame retardant and is a sheet | seat of a sheet form. By further laminating the flame retardant sheets, the flame retardance of the radiation shielding material can be further improved. The flame retardant sheet may be in the form of a sheet containing a conventionally known flame retardant material, but is preferably a composite fiber sheet (second composite fiber sheet) of a flame retardant and a fiber.

[Composite fiber]
The description of the composite fiber of the flame retardant and the fiber can be incorporated by replacing “barium sulfate” with “flame retardant” in the description of “composite fiber” in the section of “first composite fiber sheet” above. .

  The composite fiber content of the flame retardant and fiber contained in the second composite fiber sheet is preferably 10% or more and 100% or less with respect to the total weight of the second composite fiber sheet. 25% or more and 100% or less is more preferable. By containing 5% or more of the composite fiber of the flame retardant and the fiber with respect to the total weight of the second composite fiber sheet, excellent flame retardancy can be obtained.

〔Flame retardants〕
As the flame retardant, a flame retardant other than barium sulfate may be used, and examples thereof include magnesium carbonate, aluminum compound, hydrotalcite, magnesium hydroxide, calcium carbonate, calcium phosphate, and silica. Particularly preferably, magnesium carbonate, Flame retardant inorganic particles such as aluminum compounds, barium sulfate, hydrotalcite, and tetrabromobisphenol A, decabromobiphenyl, pentabromodiphenyl ether, chlorinated paraffin, chlorinated polyethylene, phosphate ester, ammonium polyphosphate, polyboric acid It may be at least one selected from the group consisting of sodium, borax, zinc borate, silicone resin, ammonium phosphate, guanidine compound, organic flame retardant such as melamine compound. Among these, magnesium carbonate, an aluminum compound, and hydrotalcite are more preferable, and magnesium carbonate is more preferable.

  Moreover, it is preferable that a 1st composite fiber contains an aluminum compound, and the said flame-retardant sheet | seat contains magnesium carbonate and / or an aluminum compound, and / or a hydrotalcite. When producing a barium sulfate, employing a synthesis method that also produces an aluminum compound can easily impart stronger flame retardancy to the first composite fiber. The flame retardance of the radiation shielding material can be further improved by imparting strong flame retardancy to the second composite fiber to the magnesium carbonate and / or aluminum compound and / or hydrotalcite.

[Magnesium carbonate]
One of the preferable embodiments of the second composite fiber sheet is a composite fiber sheet of magnesium carbonate and fibers. The average primary particle size of the magnesium carbonate fine particles is preferably less than 50 μm, but may be magnesium carbonate having an average primary particle size of 30 μm or less. In a preferred embodiment, the average primary particle diameter of the magnesium carbonate fine particles can be about 10 nm to 3 μm.

  Magnesium carbonate may take the form of secondary particles in which fine primary particles are aggregated, and secondary particles can be generated according to the application, and the agglomerates can be made fine by pulverization. For grinding, ball mill, sand grinder mill, impact mill, high-pressure homogenizer, low-pressure homogenizer, dyno mill, ultrasonic mill, kanda grinder, attritor, stone mill, vibration mill, cutter mill, jet mill, breaker, beater Short shaft extruder, twin screw extruder, ultrasonic stirrer, household juicer mixer and the like.

  Magnesium carbonate can be synthesized, for example, from a raw material selected from the group consisting of magnesium oxide, magnesite, dolomite, huntite, magnesium carbonate, magnesium hydroxide, brucite, and mixtures thereof. Among these, it is more preferable to synthesize from magnesium hydroxide.

  As a manufacturing method of the composite fiber sheet of magnesium carbonate and a fiber, the method of synthesize | combining magnesium carbonate in the solution containing a fiber is mentioned, for example. At the time of obtaining magnesium hydroxide from a magnesium hydroxide precursor typified by magnesium oxide or the like, the fibers can be dispersed in the reaction solution. Further, the fiber can be dispersed in the step of obtaining magnesium carbonate from magnesium hydroxide. In any case, since the reaction solution is alkaline, the fibers can be swollen by being immersed in the reaction solution, and a composite fiber of magnesium carbonate and fibers can be obtained efficiently. The carbonation reaction can be started immediately after the fibers are dispersed, or the carbonation reaction can be started after the fiber is further swollen by stirring for 15 minutes or more. For example, magnesium carbonate may be synthesized by injecting an aqueous suspension containing magnesium hydroxide into a reaction vessel. As will be described later, when jetting an aqueous suspension of magnesium hydroxide into the reaction vessel, it is a preferred embodiment to generate cavitation bubbles and synthesize magnesium carbonate in the presence thereof.

  In the method for synthesizing the magnesium carbonate fine particles in the solution containing the fibers, the magnesium carbonate can be synthesized by a known method. For example, magnesium bicarbonate can be synthesized from magnesium hydroxide and carbon dioxide, and basic magnesium carbonate can be synthesized from magnesium bicarbonate via normal magnesium carbonate. Magnesium bicarbonate, normal magnesium carbonate, basic magnesium carbonate, and the like can be obtained by a magnesium carbonate synthesis method, but basic magnesium carbonate is particularly preferable. This is because basic magnesium carbonate is relatively stable compared to other magnesium carbonates and is more easily fixed to fibers than normal magnesium carbonate which is a columnar (needle-like) crystal. On the other hand, by carrying out a chemical reaction to basic magnesium carbonate in the presence of fibers, a composite fiber of magnesium carbonate and fibers with the fiber surface coated in a scale or the like can be obtained.

  As a preferable aspect of the second composite fiber sheet, there is an aspect in which 15% or more of the fiber surface in the composite fiber sheet is coated with magnesium carbonate. Further, in the composite fiber sheet, the coverage (area ratio) of the fiber with magnesium carbonate is more preferably 25% or more, and further preferably 40% or more. Moreover, according to the method of synthesizing magnesium carbonate in a solution containing fibers, a composite fiber having a coverage of 60% or more and 80% or more can be suitably produced. The upper limit of the coverage may be set as appropriate according to the application, but is 100%, 90%, or 80%, for example.

  When magnesium carbonate and fiber are made into composite fiber, magnesium carbonate is not only easy to yield in the product compared to the case where magnesium carbonate is mixed with fiber, but also a product in which the product is uniformly dispersed without agglomeration is obtained. Can do. In other words, the yield of the composite fiber of magnesium carbonate and fiber to the product (weight ratio of the magnesium carbonate that remains in the product) can be 60% or more, and 70% or more or 90% or more. You can also.

  Further, it is preferable that cavitation bubbles exist when the magnesium carbonate is synthesized. In this case, cavitation bubbles do not need to exist in all of the synthesis routes of magnesium carbonate, and cavitation bubbles may exist in at least one stage.

For example, when producing basic magnesium carbonate, magnesium oxide MgO is used as a magnesium source, and carbon dioxide gas CO ₂ is blown into magnesium hydroxide Mg (OH) ₂ obtained from magnesium oxide to produce magnesium bicarbonate Mg (HCO _{3 2} ) and basic magnesium carbonate is obtained from magnesium bicarbonate through normal magnesium carbonate MgCO ₃ .3H ₂ O. When the magnesium carbonate is synthesized, the basic magnesium carbonate can be synthesized on the fiber by allowing the fiber to be present. Cavitation bubbles are preferably present at any stage of the synthesis of magnesium carbonate, and more preferably, cavitation bubbles are present when synthesizing magnesium carbonate. In a preferred embodiment, cavitation bubbles can be present in the step of synthesizing magnesium bicarbonate from magnesium hydroxide. In another embodiment, cavitation bubbles can be present in the step of synthesizing basic magnesium carbonate from magnesium bicarbonate or normal carbonate. In yet another embodiment, basic magnesium carbonate can be present when synthesized and then aged.

  Generally, a gas blowing type carbonator and a mechanical stirring type carbonator are known as a reaction vessel (carbonation reactor: carbonator) for producing magnesium carbonate by the carbon dioxide method. Among these, a mechanical stirring type carbonator is more preferable. The mechanical stirring type carbonator is provided with a stirrer inside the carbonator, and introduces carbon dioxide gas near the stirrer to make carbon dioxide into fine bubbles. This mechanism makes it easy to control the size of bubbles uniformly and finely. This improves the reaction efficiency in synthesis using carbon dioxide gas (“Cement, Gypsum, Lime Handbook”, Gihodo Publishing, 1995, p. 495). In the gas blowing type carbonator, carbon dioxide gas is blown into a carbonation reaction tank containing slaked lime suspension (lime milk), and slaked lime and carbon dioxide gas are reacted.

  It is more preferable to synthesize magnesium carbonate in the presence of cavitation bubbles. This is because even if the concentration of the reaction solution is high or the carbonation reaction proceeds and the resistance of the reaction solution increases, the carbon dioxide gas can be refined by sufficient stirring. Therefore, the carbonation reaction can be accurately controlled, and energy loss can be prevented. In addition, the magnesium hydroxide residue having low solubility is likely to stay at the bottom because it settles quickly, but if it is synthesized in the presence of cavitation bubbles, the gas inlet can be prevented from being blocked.

  Therefore, it is possible to efficiently promote the carbonation reaction and produce uniform magnesium carbonate fine particles. In particular, by using jet cavitation, sufficient stirring can be performed without a mechanical stirrer such as a blade. In addition, conventionally known reaction vessels can be used, and of course, the above-described gas blowing type carbonator and mechanical stirring type carbonator can be used without any problem, and jet cavitation using nozzles or the like in these vessels. May be combined.

  When synthesizing magnesium carbonate, the solid content concentration of the aqueous magnesium hydroxide suspension is preferably 0.1% by weight or more from the viewpoint of achieving better reaction efficiency and suppressing the production cost. Preferably it is 0.5 weight% or more, More preferably, it is 1 weight% or more. Further, the solid content concentration is preferably 40% by weight or less, more preferably 30% by weight or less, and still more preferably 20% by weight from the viewpoint of achieving better reaction efficiency by reacting in a state where fluidity is good. % Or less. In the embodiment in which magnesium carbonate is synthesized in the presence of cavitation bubbles, the reaction solution and carbon dioxide can be more suitably mixed even when a suspension (slurry) having a high solid content is used.

  As an aqueous suspension containing magnesium hydroxide, a commonly used one can be used. For example, it can be prepared by mixing magnesium hydroxide with water or by adding magnesium oxide to water. . The conditions for preparing the magnesium hydroxide slurry from magnesium oxide are not particularly limited. For example, the MgO concentration is 0.1 wt% or more, preferably 1 wt% or more, and the temperature is 20 to 100 ° C., preferably 30 It can be set to -100 degreeC. The reaction time is preferably 5 minutes to 5 hours (preferably within 2 hours), for example. The apparatus may be a batch type or a continuous type. Note that the preparation of the magnesium hydroxide slurry and the carbonation reaction may be performed using separate apparatuses or in one reaction tank.

[Aluminum compound]
It is also preferable that the second composite fiber sheet is a composite fiber sheet of an aluminum compound and fibers. There are various methods for synthesizing aluminum compounds, and they can be synthesized by adding an alkaline solution to a substance containing an aluminum salt. For example, it can be obtained by adding sodium hydroxide to aluminum sulfate. Further, when aluminum sulfate is used as a raw material for synthesizing barium sulfate, not only barium sulfate but also an aluminum compound such as aluminum hydroxide can be synthesized at the same time. With this method, since both barium sulfate and aluminum compound can be synthesized simultaneously, the flame retardancy of the composite fiber sheet can be easily improved. Note that as one embodiment of the present invention, the first composite fiber sheet is manufactured by a method of simultaneously synthesizing both barium sulfate and an aluminum compound, and a form obtained by further laminating sheets obtained by the same method is used as barium sulfate and aluminum. Since the composite fiber sheets of the compound are laminated, it can be said that the compound fiber sheets correspond to those obtained by laminating the first composite fiber sheets.

[Hydrotalcite]
Generally, ^{_{hydrotalcite, [M 2+ 1-x M}} 3+ x (OH) 2] [A n- x / n · mH 2 O] ( ^{wherein, M 2+} is a divalent metal ^{ion, M 3+} is It represents a trivalent metal ion, and A ⁿ⁻ _x / n represents an interlayer anion, and 0 <x <1, where n is the valence of A, and 0 ≦ m <1. It is. Here, M ²⁺ that is a divalent metal ion is a trivalent metal ion such as Mg ²⁺ , Co ²⁺ , Ni ²⁺ , Zn ²⁺ , Fe ²⁺ , Ca ²⁺ , Ba ²⁺ , Cu ²⁺ , Mn ^{2+, and the} like. there ^{M 3+} are, for ^{example, Al 3+, Fe 3+, Cr} 3+, Ga 3+ , etc., ^{a n-} is an interlayer anion, for ^{_{example, OH -, Cl -, CO}} 3 -, SO 4 - the n-valent, etc. Anions can be mentioned, and x is generally in the range of 0.2 to 0.33. The crystal structure has a laminated structure composed of a two-dimensional basic layer in which octahedral brucite units having a positive charge are arranged and an intermediate layer having a negative charge.

  Hydrotalcite has been used for various applications utilizing its anion exchange function, such as ion exchange materials, adsorbents, deodorants and the like. In addition, by utilizing the combination of constituent metal ions, hydrotalcite in which each constituent metal ion is in a good mixed state is heated and dehydrated, or further heated and fired to easily produce a complex oxide with a uniform composition. Examples of use in catalyst applications and the like are also found.

  The ratio of hydrotalcite in the second composite fiber sheet can be 10% by weight or more, can be 20% by weight or more, and preferably 40% by weight or more. The ash content of the composite fiber of hydrotalcite and fiber can be measured according to JIS P 8251: 2003. The ash content of the composite fiber sheet of hydrotalcite and fibers can be 10% by weight or more, can be 20% by weight or more, and preferably 40% by weight or more. Alternatively, the composite fiber sheet of idrotalcite and fibers preferably contains 10% by weight or more of magnesium or zinc in the ash, and more preferably contains 40% or more. The magnesium or zinc content in the ash can be quantified by fluorescent X-ray analysis.

  As a preferable aspect of the second composite fiber sheet, there is an aspect in which 15% or more of the fiber surface in the composite fiber sheet is covered with hydrotalcite. In the composite fiber sheet, the fiber coverage (area ratio) by hydrotalcite is more preferably 25% or more, and further preferably 40% or more. Moreover, according to the method of synthesizing hydrotalcite in a solution containing fibers, it is possible to suitably produce a composite fiber having a coverage of 60% or more and 80% or more. The upper limit of the coverage may be set as appropriate according to the application, but is 100%, 90%, or 80%, for example. Further, in a preferred embodiment, the composite fiber sheet of hydrotalcite and fiber provided in the radiation shielding material according to one embodiment of the present invention is not limited to the hydrotalcite fixing on the outer surface of the fiber or the inside of the lumen, but also microfibrils. It is clear from the result of electron microscopic observation that it is also generated inside.

  When hydrotalcite and fiber are made into composite fiber, compared with the case where hydrotalcite is simply mixed with fiber, not only the hydrotalcite is easy to yield in the product, but also a product that is uniformly dispersed without agglomeration. Can be obtained. That is, according to the second composite fiber sheet, the yield of hydrotalcite and fiber composite fiber to the product (weight ratio in which the hydrotalcite that is input remains in the product) can be 65% or more. 70% or more or 85% or more.

  Examples of a method for forming a composite fiber of hydrotalcite and fiber include a method of producing a composite fiber of hydrotalcite and fiber by synthesizing hydrotalcite in a solution in the presence of the fiber.

  The synthesis method of hydrotalcite can be based on a known method. For example, the fibers are immersed in an aqueous carbonate solution containing carbonate ions constituting the intermediate layer and an alkaline solution (such as sodium hydroxide) in the reaction vessel, and then an acid solution (divalent metal ions and trivalent ions constituting the basic layer). Hydrotalcite is synthesized by adding a metal salt aqueous solution containing metal ions) and controlling the temperature, pH, etc. and coprecipitation reaction. Further, in the reaction vessel, the fiber is immersed in an acid solution (metal salt aqueous solution containing divalent metal ions and trivalent metal ions constituting the basic layer), and then carbonate aqueous solution containing carbonate ions constituting the intermediate layer. Hydrotalcite can also be synthesized by dropwise addition of an alkaline solution (such as sodium hydroxide) and controlling the temperature, pH, etc. and coprecipitation reaction. Although the reaction at normal pressure is common, there is also a method obtained by a hydrothermal reaction using an autoclave or the like (JP-A-60-6619).

  As a supply source of divalent metal ions constituting the basic layer, various chlorides, sulfides, nitrates, and sulfates of magnesium, zinc, barium, calcium, iron, copper, cobalt, nickel, and manganese can be used. In addition, various chlorides, sulfides, nitrates, and sulfates of aluminum, iron, chromium, and gallium can be used as a supply source of trivalent metal ions constituting the basic layer.

  In addition, water is used for the preparation of the suspension, and as this water, normal tap water, industrial water, ground water, well water, etc. can be used, ion-exchanged water, distilled water, ultrapure water, Industrial wastewater and water obtained during the production process can be suitably used.

  As the interlayer anion, carbonate ion, nitrate ion, chloride ion, sulfate ion, phosphate ion, or the like can be used as the anion. When carbonate ions are used as interlayer anions, sodium carbonate is used as the source. However, sodium carbonate can be replaced with a gas containing carbon dioxide (carbon dioxide gas), and may be a substantially pure carbon dioxide gas or a mixture with other gases. For example, exhaust gas discharged from an incinerator, a coal boiler, a heavy oil boiler or the like of a paper mill can be suitably used as the carbon dioxide-containing gas. In addition, a carbonation reaction can also be performed using carbon dioxide generated from the lime baking step.

[Synthesis of composite fiber of flame retardant and fiber]
When using an inorganic substance as a flame retardant, the composite fiber of a flame retardant and a fiber can be obtained by synthesizing a flame retardant in the presence of fibers such as cellulose fibers in one preferred embodiment. This is because the fiber surface is a suitable place for precipitation of the flame retardant, and it is easy to synthesize a composite fiber of fiber and flame retardant.

  As one preferable aspect, when the flame retardant compounded with fibers in the second composite fiber sheet is in the form of particles, the average primary particle diameter of the flame retardant particles is, for example, 1.5 μm or less. However, the average primary particle diameter can be 1200 nm or less or 900 nm or less, and the average primary particle diameter can be 200 nm or less or 150 nm or less. The average primary particle size of the flame retardant can be 10 nm or more. The average primary particle diameter can be measured with an electron micrograph.

  In addition, the flame retardant in the second composite fiber sheet may take the form of secondary particles in which fine primary particles are aggregated, and can generate secondary particles according to the application by the aging process, and pulverization The agglomerates can also be made finer. For grinding, ball mill, sand grinder mill, impact mill, high-pressure homogenizer, low-pressure homogenizer, dyno mill, ultrasonic mill, kanda grinder, attritor, stone mill, vibration mill, cutter mill, jet mill, breaker, beater Short shaft extruder, twin screw extruder, ultrasonic stirrer, household juicer mixer and the like.

  When the flame retardant constituting the second composite fiber sheet is in the form of particles, the average particle diameter, shape, etc. of the flame retardant particles can be confirmed by observation with an electron microscope. Furthermore, the flame retardant which has various magnitude | sizes and shapes can be compounded with a fiber by adjusting the synthetic | combination conditions etc. of a flame retardant.

  Moreover, what is necessary is just to make the composite fiber of a fiber and a flame retardant into a sheet shape by a conventionally well-known method.

  Moreover, the additive and filler mentioned above can be added to a 2nd composite fiber sheet similarly to a 1st composite fiber sheet.

  As a manufacturing method of a 2nd composite fiber sheet, the method of synthesize | combining a flame retardant in the solution containing a fiber is mentioned, for example. For example, when using a precursor of an alkaline flame retardant as a raw material, the fiber can be swollen by dispersing the fiber in the precursor solution in advance, so that a composite fiber of the flame retardant and the fiber is efficiently obtained. be able to. The reaction can be started after promoting the swelling of the fibers by stirring them for 15 minutes or more after mixing, but the reaction may be started immediately after mixing. There are no particular restrictions on the form of the reaction tank and the stirring conditions for obtaining the composite fiber. For example, a composite fiber may be synthesized by stirring and mixing a solution containing the fiber and the precursor in an open reaction tank. Alternatively, the aqueous suspension containing the fiber and the precursor may be injected into the reaction vessel. As will be described later, when the aqueous suspension of the precursor is injected into the reaction vessel, cavitation bubbles may be generated and the flame retardant may be synthesized in the presence thereof.

  Further, the liquid may be ejected under conditions that cause cavitation bubbles in the reaction vessel, or may be ejected under conditions that do not cause cavitation bubbles. The reaction vessel is preferably a pressure vessel in any case. In addition, the pressure vessel in this invention is a container which can apply the pressure of 0.005 Mpa or more. In the condition that does not generate cavitation bubbles, the pressure in the pressure vessel is preferably 0.005 MPa or more and 0.9 MPa or less in static pressure. Since “cavitation bubbles” are as described in the section “First composite fiber sheet”, description thereof is omitted.

[Production of second composite fiber sheet]
The method for producing the second composite fiber sheet from the composite fiber of the fiber and the flame retardant is as described above in the section “First composite fiber sheet”.

The basis weight of the sheet, may be appropriately adjusted depending on the ^purpose, flame retardancy When 40g / ^{m 2} ~1200g / m 2 is high, also is good for drying load during production is low. The basis weight of the ^sheet, it ^is also possible to ^{60g / m 2 ~1000g / m 2} , it is also possible to ^{100g / m 2 ~600g / m 2} .

  Further, in the blending / drying / molding described above, only one type of conjugate fiber can be used, or two or more types of conjugate fibers can be mixed and used. When two or more types of composite fibers are used, those obtained by mixing them in advance can be used, or those obtained by blending, drying and molding each can be mixed later.

  The laminate obtained by the present invention can be used for various applications utilizing its radiation shielding properties, such as paper, fiber, cellulosic composite material, filter material, paint, plastic and other resins, rubber, Elastomer, ceramic, glass, tire, building material (asphalt, asbestos, cement, board, concrete, brick, tile, plywood, fiberboard, wall material, ceiling material, partition board, wallpaper, etc.), various carriers (catalyst carrier, pharmaceuticals) Carrier, agricultural chemical carrier, microbial carrier, etc.), adsorbent (impurity removal, deodorization, dehumidification, etc.), wrinkle prevention agent, clay, abrasive, modifier, repair material, heat insulating material, heat-resistant material, heat dissipation material, moisture-proof material Water repellent material, water resistant material, light shielding material, sealant, shielding material, insect repellent, adhesive, ink, cosmetics, medical materials, paste material, anti-discoloration agent, food additives , Tablet excipients, dispersants, shape retention agents, water retention agents, filter aids, essential oil materials, oil treatment agents, oil modifiers, radio wave absorbers, insulation materials, sound insulation materials, vibration insulation materials, semiconductor encapsulants It can be widely used for radiation shielding materials, cosmetics, fertilizers, feeds, fragrances, additives for paints / adhesives, sanitary products (disposable diapers, sanitary napkins, incontinence pads, breast milk pads, etc.). Moreover, it can be used for various fillers and coating agents in the above applications. Among these, it can be suitably used particularly for building materials (wall materials, ceiling materials, partition boards, wallpaper, etc.) from the viewpoint of excellent flame retardancy and material adsorption / desorption performance.

[Summary]
The present invention includes, but is not limited to, the following inventions.
(1) A radiation shielding material, which is a composite fiber of barium sulfate and fiber, in which a plurality of first composite fiber sheets in sheet form are laminated.
(2) The radiation shielding material according to (1), wherein 15% or more of the surface of the fiber is covered with barium sulfate.
(3) The radiation shielding material according to (1) or (2), wherein an average primary particle diameter of the barium sulfate is 1.5 μm or less.
(4) The radiation shielding material according to any one of (1) to (3), wherein the fibers of the first composite fiber sheet are cellulose fibers.
(5) The radiation shielding material according to any one of (1) to (4), wherein a weight ratio of the fibers of the first composite fiber sheet to the barium sulfate is 5/95 to 95/5. .
(6) The radiation shielding material according to any one of (1) to (5), wherein the first composite fiber sheet includes a flame retardant.
(7) The radiation shielding material according to (6), wherein the material containing the flame retardant is applied or impregnated.
(8) The radiation shielding material according to (6), which is coated with a material containing the flame retardant.
(9) The radiation shielding material according to any one of (1) to (8), further comprising a flame retardant sheet that includes a flame retardant and has a sheet form.
(10) The radiation shielding material according to (9), wherein the flame retardant sheet is laminated as at least one of the outermost layers.
(11) The radiation shielding material according to any one of (6) to (10), wherein the flame retardant is at least one selected from the group consisting of magnesium carbonate, an aluminum compound, and hydrotalcite.
(12) The radiation blocking material according to any one of (6) to (11), wherein the flame retardant is particulate and an average primary particle size of the particles is 1.5 μm or less.
(13) The radiation shielding material according to (9), wherein the flame retardant sheet is a second composite fiber sheet of the flame retardant and fiber.
(14) The radiation shielding material according to (13), wherein 15% or more of the surface of the second composite fiber sheet is covered with the flame retardant.
(15) The radiation shielding material according to (13) or (14), wherein the fibers of the second composite fiber sheet are cellulose fibers.
(16) The radiation shielding material according to any one of (13) to (15), wherein a weight ratio of the fibers of the second composite fiber sheet to the flame retardant is 5/95 to 95/5. .
(17) The radiation shielding material according to any one of (13) to (16), wherein the first composite fiber sheet includes an aluminum compound and the second composite fiber sheet includes magnesium carbonate.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention will be described more specifically with specific experimental examples, but the present invention is not limited to the following specific examples. Unless otherwise specified in the present specification, concentrations, parts, and the like are based on weight, and numerical ranges are described as including the end points.

[Experiment 1: Synthesis and evaluation of composite fiber of barium sulfate and fiber]
(1) Sample 1-1: Composite fiber of barium sulfate and pulp fiber 1% pulp slurry (hardwood bleached kraft pulp / softwood bleached kraft pulp = 8/2, Canadian standard freeness CSF = about 80 mL, average fiber length : About 1.2 mm, slurry weight 500 g) and barium hydroxide octahydrate (Wako Pure Chemical, 5.82 g) were mixed with stirring by a three-one motor (1000 rpm), and then sulfuric acid (Wako Pure Chemical, 2% aqueous solution) 88 g) was added dropwise at 8 g / min with a peristaltic pump. After completion of dropping, stirring was continued for 30 minutes to obtain Sample 1-1. It was. In this example, the above-mentioned “hardwood bleached kraft pulp” is hereinafter abbreviated as “LBKP”. In addition, the above “conifer bleached kraft pulp” is abbreviated as “NBKP”. Both LBKP and NBKP were made from Nippon Paper Industries. The “Canadian Standard Freeness” was prepared using a single disc refiner (SDR). Moreover, the average fiber length of the pulp in the used pulp slurry was measured with a fiber tester (Lorentzen & Wettre).

(2) Sample 1-2: Composite fiber of barium sulfate and aramid fiber A slurry of 0.8% aramid fiber (Twaron RD-1094, Teijin, average fiber length: about 1.3 mm, slurry weight 625 g) as the fiber content A sample 1-2 was obtained by synthesizing in the same manner as in the sample 1-1 except that was used.

(3) Sample 1-3: Composite fiber of barium sulfate and aluminum hydroxide and fiber 1% pulp slurry (LBKP, CSF = 500 mL, average fiber length: about 0.7 mm, slurry weight 1300 g) and barium hydroxide eight Hydrate (Wako Pure Chemical, 57 g) was mixed with stirring with a three-one motor (800 rpm), and aluminum sulfate (sulfuric acid band, 77 g) was added dropwise at 2 g / min with a peristaltic pump. After completion of the dropwise addition, stirring was continued for 30 minutes to obtain Sample 1-3.

(4) Sample 1-4: Composite fiber of barium sulfate and aluminum hydroxide and fiber 2% pulp slurry (LBKP / NBKP = 8/2, CSF = 390 mL, average in container (machine chest, volume: 4 m ³ ) Fiber length: about 1.3 mm, solid content 25 kg) and barium hydroxide octahydrate (Nippon Chemical Industry, 75 kg) are added and mixed, and then aluminum sulfate (sulfate band, 98 kg) is added using a peristaltic pump. It was dripped at about 500 g / min. After completion of the dropwise addition, stirring was continued for 30 minutes to obtain Sample 1-4.

(5) Sample 1-5: Composite fiber of barium sulfate / aluminum hydroxide and fiber 1.5% pulp slurry (LBKP / NBKP = 8/2, CSF = 416 mL) in a container (machine chest, volume: 30 m ³ ) , Average fiber length: about 1.3 mm, solid content 300 kg) and barium hydroxide octahydrate (Nippon Chemical Industry, 1250 kg) were mixed and mixed, and then aluminum sulfate (8% alumina sulfate band, alumina, 1752 kg) was added dropwise at about 34 kg / min. After completion of dropping, stirring was continued for 30 minutes to obtain Sample 1-5.

(6) Sample 1-6: Composite fiber of barium sulfate and fiber 1% pulp slurry (LBKP, CSF = 490 mL, average fiber length: about 0.7 mm, solid content 140 g) and barium hydroxide octahydrate (sum) An aqueous suspension containing optically pure drug, 140 g) was prepared. 14 L of this aqueous suspension was put into a 45 L cavitation apparatus, and while circulating the reaction solution, sulfuric acid (Wako Pure Chemicals, 1280 g of 2% aqueous solution) was dropped into the reaction vessel at 50 g / min with a peristaltic pump. .

  In the synthesis of the composite fiber, cavitation bubbles were generated in the reaction vessel by circulating the reaction solution and injecting it into the reaction vessel as shown in FIG. Specifically, the reaction solution was injected at high pressure through a nozzle (nozzle diameter: 1.5 mm) to generate cavitation bubbles. The jet velocity was about 70 m / s, and the inlet pressure (upstream pressure) was The outlet pressure (downstream pressure) was 7 MPa and 0.3 MPa.

  After completion of the sulfuric acid dropping, the pressure in the reaction vessel was released to stop the generation of cavitation, and the reaction solution was circulated in the apparatus for 30 minutes to obtain Sample 1-6.

(7) Sample 1-7: Composite fiber of magnesium carbonate and fiber 5250 g of magnesium hydroxide (Ube Materials, UD653) and 3500 g of kraft pulp (LBKP (CSF = 500 mL, average fiber length = 0.76 mm)) in water To prepare an aqueous suspension (170 L).

As shown in FIG. 18, this aqueous suspension is put into a cavitation apparatus (500 L volume), and while the reaction solution is circulated, carbon dioxide gas is blown into the reaction vessel, and the composite of magnesium carbonate fine particles and fibers is obtained by the carbon dioxide method. Fiber was synthesized. The reaction start temperature was about 40 ° C., the carbon dioxide gas was supplied with a commercially available liquefied gas, and the amount of carbon dioxide blown was 20 L / min. When the pH of the reaction solution reached about 7.8, the introduction of CO ₂ was stopped (pH before the reaction was 10.3), and then the cavitation generation and the circulation of the slurry in the apparatus were continued for 30 minutes, A composite fiber of magnesium carbonate fine particles and pulp fiber was obtained (Sample 1-7).

  In the synthesis of the composite fiber, cavitation bubbles were generated in the reaction vessel by circulating the reaction solution and injecting it into the reaction vessel as shown in FIG. Specifically, the reaction solution was injected at high pressure through a nozzle (nozzle diameter: 1.5 mm) to generate cavitation bubbles. The jet velocity was about 70 m / s, and the inlet pressure (upstream pressure) was The outlet pressure (downstream pressure) was 7 MPa and 0.3 MPa.

<Evaluation of composite fiber>
The weight ratio (ash content) of the fiber of the obtained composite fiber: inorganic particles was obtained by suction-filtering the composite fiber slurry (3 g in terms of solid content) using filter paper, and then drying the residue in an oven (105 ° C., 2 hours) The organic content was further burned at 525 ° C., and the weight was calculated from the weight before and after the burning.

  In addition, about the samples 1-3, 1-4, and 1-5 in which the composite fiber contains multiple types of inorganic particles, the total weight ratio of fiber: multiple types of inorganic particles is represented.

Each composite fiber sample was washed with ethanol and then observed with an electron microscope (FIGS. 2 to 8). As a result, in each sample, it was observed that the fiber surface was covered with an inorganic substance and self-fixed. Most of the inorganic particles fixed on the fiber were plate-like, and those having a small size were observed as amorphous particles. The primary particle size of the inorganic particles of each composite fiber sample estimated as a result of the observation was as shown in the following table (Table 1).

[Experiment 2: Production and evaluation of composite fiber sheet]
(1) Sheet 2-1 and sheet 2-2: sheet of first composite fiber (first composite fiber)
A slurry obtained by sucking and filtering the composite fibers (Sample 1-1 and Sample 1-2) obtained in Experiment 1 (1) and Experiment 1 (2) with a filter paper is a slurry having a concentration of about 0.2% using tap water. Prepared. After this slurry was disaggregated for 5 minutes with a standard disintegrator specified in JIS P 8220-1: 2012, a handsheet having a basis weight of 60 g / m ² was prepared using a 150 mesh wire in accordance with JIS P 8222: 1998. Produced.

  The obtained handsheet was observed with an electron microscope and ash content was measured. The results are shown in FIG. 9 (Sample 2-1) and FIG. 10 (Sample 2-2). When the surface of the handsheet was observed with an electron microscope, the inorganic substance was firmly fixed on the fiber surface. I was observed.

(2) Sheet 2-3: Sheet of kraft pulp (KP) only (Comparative example of 2-4)
A cationic retention agent (ND300, Hymo) and anionic retention agent in a slurry (LBKP / NBKP = 8/2, CSF = 390 mL, average fiber length: 1.3 mm) in which only KP is dispersed (FA230, Hymo) was added at 100 ppm each as a solid content, and a sheet was produced using a long net paper machine.

(3) Sheet 2-4: Sheet of composite fiber of barium sulfate and aluminum hydroxide and fiber The composite fiber (sample 1-4, concentration: 1%) obtained in Experiment 1 (4) is a cationic step. A stock slurry was prepared by adding 100 ppm each of a retention agent (ND300, Hymo) and an anionic retention agent (FA230, Hymo) as solids. Next, a sheet was produced from this stock slurry using a long paper machine at a speed of 10 m / min.

  The obtained composite fiber sheet was observed using an electron microscope. In the composite sheet of Sample 2-4, it was confirmed that the surface and inside of the paper were densely covered and filled with barium sulfate and aluminum hydroxide (FIG. 11).

  The results of measuring the properties of the composite fiber sheet are shown in the following table (Table 2). By using the composite fiber as a raw material, a sheet having an ash content of about 67% was produced with a paper machine, and the obtained sheet could be continuously wound and rolled. The yield at this time was as high as 96% or more for both the paper yield and the ash yield. Moreover, the obtained composite fiber sheet (sample 2-4) had higher opacity, density, and air resistance than the pulp-only sheet (sample 2-3).

<Measurement method>
-Basis weight: JIS P 8124: 1998
・ Thickness: JIS P 8118: 1998
-Density: Calculated from measured values of thickness and basis weight-Ash content: JIS P 8251: 2003
Whiteness: JIS P 8212: 1998
・ Opacity: JIS P 8149: 2000
Specific scattering coefficient: Calculated by the formula defined in TAPPI T425 (ISO 9416).
-Air permeability resistance: JIS P 8117: 2009
Smoothness: JIS P 8155: 2010
・ L & W bending stiffness: according to ISO 2493, L & W Bending Tester (Lorentzen & Wet
(manufactured by tre) and the bending stiffness with a bending angle of 15 degrees was measured.
-Breaking length: JIS P 8113: 2006

(4) Sheet 2-5-1: Sheet of composite fiber of barium sulfate and aluminum hydroxide and fiber The composite fiber (sample 1-5, concentration: 1%) obtained in Experiment 1 (5) is cationic. A retention slurry (RX5202, Hymo) was added at a solid content of 50 ppm to prepare a paper slurry. Subsequently, a sheet was produced from this stock slurry using a five-layer circular paper machine under conditions of a paper making speed of 20 m / min and a paper making width of 980 mm. A sheet of 107 g / m ² was prepared with one layer of a round net, and 5 layers were laminated to obtain a sheet of 534 g / m ² and an ash content of 45%.

(5) Sheet 2-5-2: Sheet of composite fiber of barium sulfate and aluminum hydroxide and fiber The amount of added retention agent is 150 ppm in terms of solid content, and a sheet of 64 g / m ² per circular mesh layer. A sheet 2-5-2 was obtained in the same manner as the sheet 2-5-1 except that a sheet of 320 g / m ² was obtained by superimposing five layers thereof (sheet ash content 55%).

  The obtained composite fiber sheets (sheet 2-5-1 and sheet 2-5-2) were observed with an electron microscope, and the surface and inside of the paper were densely covered and filled with barium sulfate and aluminum hydroxide. (Figs. 12 and 13).

The results of measuring the properties of the composite fiber sheet by the same method as in Experiment 2 (3) are shown in the following table (Table 3). By using the composite fiber as a raw material, a sheet having an ash content of 45 to 55% was produced by a paper machine, and the obtained sheet could be continuously wound and rolled. Moreover, the obtained composite fiber sheet had high opacity, density, and air resistance.

(6) Sheet 2-7: Sheet of composite fiber of magnesium carbonate and fiber A cationic retention agent (ND300) was added to the composite fiber (Sample 1-7, concentration: 1%) obtained in Experiment 1 (7). , Hymo) and anionic retention agent (FA230, Hymo) were added at 100 ppm each as a solid content to prepare a paper slurry. Next, a sheet was produced from this stock slurry under the conditions of a papermaking speed of 10 m / min using a long paper machine (basis weight: about 190 g / m2, ash content: about 46%). When the obtained composite fiber sheet was observed with an electron microscope, it was confirmed that the surface and the inside of the paper were densely coated and filled with magnesium carbonate (FIG. 14).

[Experiment 3: Preparation of composite fiber board]
(1) Composite board A: Composite board of barium sulfate and aluminum hydroxide composite fiber 10 sheets, 20 sheets, or 40 sheets 2-4 (basis weight: 180 g / m ² ) obtained in Experiment 2 (3) Then, each composite board was produced by bonding with a vinyl acetate binder (composite boards A-1, A-2, A-3).

(2) Composite board B: Composite board of barium sulfate / aluminum hydroxide composite fiber and magnesium carbonate composite fiber Each of the sheets 2-7 (tsubo) obtained in Experiment 2 (6) on the front and back of the board A-1 (Amount: 190 g / m ² ) were bonded to each other to prepare a composite board (basis weight: about 2560 g / m ² ).

(3) Composite board C: Composite board of barium sulfate and aluminum hydroxide composite fiber The sheet 2-5-1 obtained in Experiment 2 (4) was bonded with a sheet bonding machine using a vinyl acetate binder. Each composite board in which three, six, or twelve sheets 2-5-1 were laminated was obtained (composite boards C-1, C-2, C-3).

(4) Composite board D: Composite board of barium sulfate and aluminum hydroxide composite fiber The sheet 2-5-2 obtained in Experiment 2 (5) was bonded with a sheet bonding machine using a vinyl acetate binder, 5, 11, or 22 composite boards were obtained (composite boards D-1, D-2, D-3).

(5) Board E: Filter paper (comparative example)
Filter paper (manufactured by Advantech Co., Ltd., 1.7 mm thick) was bonded using a vinyl acetate binder to obtain two, five, or ten laminated boards (boards E-1, E-). 2, E-3).

(6) Board F: Veneer board (comparative example)
A veneer board (commercial product) was bonded using a vinyl acetate binder to obtain a board in which one, two, or four sheets were laminated (boards F-1, F-2, F-3).

[Experiment 4: Evaluation of flame retardancy of board]
The flammability of the board produced in Experiment 3 was evaluated according to the following procedure based on JIS A 1322 (JIS Z 2150).

  A board cut to a certain size (20 cm × 30 cm) was dried at 50 ° C. for 48 hours, and then left in a desiccator containing drying silica gel for 24 hours to obtain a sample for a combustion test (heating test).

  Attach the sample to the support frame (inner dimensions of the frame 16cm x 25cm), attach it to the heating test device, ignite the gas burner, heat the sample for 2 minutes, and measure the carbonization area, after flame time, and residual time (FIG. 15).

For the combustion test, a 45 ° flammability tester (FL-45M manufactured by Suga Test Instruments Co., Ltd.) was used. For the heating, a Meckel burner (height 160 mm, inner diameter 20 mm) was used, and only the gas was fed and burned without mixing primary air. The fuel was liquefied petroleum gas No. 5 (mainly butane and butylene, JIS K 2240), and the length of the flame was adjusted to 65 mm with no sample attached.
-Carbonization length area: The maximum length and the maximum width were measured and calculated by multiplying the carbonized part of the heated surface of the test specimen (carbonized and apparently changed in strength).
-Residual flame time: The time for which the specimen continued to burn with flames was measured from the end of heating.
-Residual dust: A state in which flameless combustion has occurred since the end of heating.

  Table 4 shows the results of the heating test. Moreover, the external appearance photograph of the sample after a heating test is shown in FIG.

Although the composite board A-1 had a residual flame time of 20 seconds, the residual dust and carbonized area were small. On the other hand, the composite board B in which a composite fiber sheet of magnesium carbonate and fiber is bonded to the front and back has a residual flame time of 10 seconds or less, a residual dust time of 30 seconds or less, and a carbonized area of 50 cm ² or less, and is flameproof. Meets the standards required for goods (plywood) (Reference: Fire and Disaster Management Agency "Knowledge and practice of flameproofing").

[Experiment 5: Evaluation of radiation shielding ability of composite fiber sheet]
About the composite fiber boards A to D manufactured in Experiment 4, the radiation (X-ray) shielding ability was evaluated. Specifically, the transmission X-ray dose rate and the lead equivalent were measured in accordance with JIS Z 4501 “Lead equivalent test method for X-ray protective equipment”.

(Transmission X-Dose Rate) The transmission X-ray dose rate was measured by irradiating X-rays with the quality and arrangement according to the test method of JIS Z 4501. Measurement was performed 5 times for each requested product and each measurement position, and the average value and standard deviation were obtained. From the obtained transmission dose rate, the dose reduction rate was calculated by the following formula.
Dose reduction rate (%) = (transmission dose rate of each sample / transmission dose rate of blank (no sample)) × 100
(Lead equivalent) According to JIS Z 4501, "Lead equivalent test method for X-ray protective article", the transmitted X-ray dose was measured to determine the lead equivalent. The lead equivalent of each sample was determined by preparing an attenuation rate curve from the standard lead plate. The attenuation rate curve was created by quadratic interpolation from the attenuation rates of four standard lead plates with different thicknesses. For the standard lead version, two sheets with a larger attenuation rate than that of each test product and two sheets with a smaller attenuation rate were selected.

(Measurement condition)
-X-ray apparatus: Exlon International MG-452 type (smoothing circuit, focal size 5.5 mm, Be window)
-X-ray tube voltage and tube current: MG-452 type 100 kV 12.5 mA additional filtration plate 0.25 mm Cu
・ X-ray tube focus-sample distance: 1500mm
・ Distance between sample and measuring instrument: 50mm
・ Measurement device: Ionization chamber irradiation dose rate meter Toyo Medic Corporation RAMTEC-1000D type A-4 probe use ・ X dose measurement unit: Air collision kerma ・ X-ray beam: Narrow beam

  As shown in Table 5, the boards A, B, C, and D in which the composite fiber sheets of barium sulfate and aluminum hydroxide and fibers were laminated had an X-ray dose reduction rate of 36.5 to 85.2%, An X-ray shielding effect was confirmed. Similarly, the lead equivalent was 0.05 to 0.31 mm. On the other hand, board E with laminated thick filter paper and board F with laminated veneer, which are comparative examples, have a low X-ray reduction rate of 8% or less, a lead equivalent of 0.05 mm or less, and almost no X-ray shielding effect. I was able to confirm that there was no.

  The radiation shielding material according to one embodiment of the present invention can be used for various applications by taking advantage of its radiation shielding properties.

Claims (17)

  A radiation shielding material, which is a composite fiber of barium sulfate and fibers, and a plurality of first composite fiber sheets in a sheet form are laminated.   The radiation shielding material according to claim 1, wherein 15% or more of the surface of the fiber is covered with barium sulfate.   The radiation shielding material according to claim 1 or 2, wherein the average primary particle diameter of the barium sulfate is 1.5 µm or less.   The radiation shielding material according to any one of claims 1 to 3, wherein the fibers of the first composite fiber sheet are cellulose fibers.   The radiation shielding material according to any one of claims 1 to 4, wherein a weight ratio of the fibers of the first composite fiber sheet to the barium sulfate is 5/95 to 95/5.   The radiation shielding material according to any one of claims 1 to 5, wherein the first composite fiber sheet contains a flame retardant.   The radiation shielding material according to claim 6, wherein the material containing the flame retardant is applied or impregnated.   The radiation shielding material according to claim 6, which is coated with a material containing the flame retardant.   The radiation shielding material according to any one of claims 1 to 8, further comprising a flame retardant sheet containing a flame retardant and having a sheet form.   The radiation shielding material according to claim 9, wherein the flame retardant sheet is laminated as at least one of the outermost layers.   The radiation shielding material according to any one of claims 6 to 10, wherein the flame retardant is at least one selected from the group consisting of magnesium carbonate, an aluminum compound, and hydrotalcite.   The radiation blocking material according to any one of claims 6 to 11, wherein the flame retardant is particulate and an average primary particle size of the particles is 1.5 µm or less.   The radiation shielding material according to claim 9, wherein the flame retardant sheet is a second composite fiber sheet of the flame retardant and fibers.   The radiation shielding material according to claim 13, wherein in the second composite fiber sheet, 15% or more of the surface of the fiber is covered with the flame retardant.   The radiation shielding material according to claim 13 or 14, wherein the fibers of the second composite fiber sheet are cellulose fibers.   The radiation shielding material according to any one of claims 13 to 15, wherein a weight ratio of the fiber and the flame retardant of the second composite fiber sheet is 5/95 to 95/5.   The radiation shielding material according to any one of claims 13 to 16, wherein the first composite fiber sheet contains an aluminum compound, and the second composite fiber sheet contains magnesium carbonate.