JP2017066578A - Composite of barium sulfate and fiber and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inorganic/filament composite in which, a filament surface is coated with barium sulfate.SOLUTION: According to the invention, a composite of barium sulfate and a filament can be acquired. The composite is excellent in radiation shield performance, and is useful as a radiation shield material.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a composite of barium sulfate and fiber and a method for producing the same. In particular, the present invention relates to a barium sulfate / fiber composite having radiation shielding ability and a method for producing the same.

  Fibers exhibit various properties based on functional groups on the surface, etc., but depending on the application, the surface may need to be modified. So far, techniques for surface modification of fibers have been developed. Yes.

  For example, regarding a technique for depositing inorganic particles on fibers such as cellulose fibers, Patent Document 1 describes a composite in which crystalline calcium carbonate is mechanically bonded onto fibers. 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).

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

  An object of the present invention is to provide a barium sulfate / fiber composite in which barium sulfate is fixed to a fiber.

The present invention includes, but is not limited to, the following inventions.
(1) A composite of barium sulfate and fiber.
(2) The composite according to (1), wherein the fibers are cellulose fibers.
(3) The composite according to (1) or (2), wherein 15% or more of the fiber surface is covered with barium sulfate.
(4) The composite according to any one of (1) to (3), wherein the average primary particle diameter of barium sulfate is 1.5 μm or less.
(5) The composite according to any one of (1) to (4), wherein the weight ratio of the fiber to barium sulfate is 5/95 to 95/5.
(6) The method for producing a composite according to any one of (1) to (5), comprising a step of synthesizing barium sulfate in a solution in the presence of fibers.
(7) A radiation shielding material comprising the composite according to any one of (1) to (5).
(8) The radiation shielding material according to (7), which is in the form of a sheet.

  According to the present invention, a fiber whose surface is coated with barium sulfate can be provided. In particular, according to the present invention, a fiber / inorganic particle composite in which 15% or more of the fiber surface is coated with barium sulfate can be obtained.

  That is, by coating many portions of the fiber surface with barium sulfate, a unique composite having both the characteristics of the fiber and barium sulfate can be obtained. In particular, by coating the surface of the fiber with barium sulfate, it is possible to obtain a composite having radiation shielding properties. Moreover, since barium sulfate adheres to the fiber, a radiation shielding material with a good ash yield can be obtained. Moreover, it can be dehydrated and dried to make it easy to handle.

FIG. 1 is a schematic diagram of the reaction apparatus used for the synthesis of Experiment 1 (5). FIG. 2 is an electron micrograph of Sample 1 (left: 3000 times, right: 10,000 times). FIG. 3 is an electron micrograph of Sample 2 (left: 3000 times, right: 10000 times). FIG. 4 is an electron micrograph of Sample 3 (left: 3000 times, right: 10,000 times). FIG. 5 is an electron micrograph of sample 4 (left: 3000 times, right: 50000 times). FIG. 6 is an electron micrograph of Sample 5 (left: 3000 times, right: 10,000 times). FIG. 7 is an electron micrograph of a sheet produced from the composite (Sample 1) (left: 500 times, right: 10,000 times). FIG. 8 is an electron micrograph of a sheet produced from the composite (Sample 2) (left: 500 times, right: 10,000 times). FIG. 9 is an electron micrograph of a sheet produced from the composite (Sample 4) (left: 500 times, right: 3000 times).

  The present invention relates to a fiber whose surface is coated with barium sulfate. In particular, according to the present invention, in a preferred embodiment, a fiber / inorganic composite in which 15% or more of the fiber surface is coated with barium sulfate can be obtained.

  Further, in the composite of the present invention, the fiber and barium sulfate are not simply mixed, but the fiber and barium sulfate are bound by hydrogen bonding or the like, so that the barium sulfate is dropped from the fiber even by the disaggregation treatment. There are few things. The strength of binding between fibers and barium sulfate in the composite can be evaluated by, for example, a numerical value such as ash yield (%, that is, ash content of the sheet ÷ ash content of the composite before disaggregation × 100). Specifically, the composite is dispersed in water, adjusted to a solid content concentration of 0.2%, and disaggregated for 5 minutes with a standard disintegrator specified in JIS P 8220-1: 2012, and then in accordance with JIS P 8222: 1998. The ash yield when sheeted 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. is there.

Fiber In the present invention, a fiber such as cellulose fiber or aramid fiber and barium sulfate are combined. The fibers constituting the composite are preferably cellulose fibers. For example, natural cellulose fibers, but also regenerated fibers (semi-synthetic fibers) such as rayon and lyocell, and synthetic fibers can be used without limitation. . Examples of cellulose fiber raw materials include pulp fibers (wood pulp and non-wood pulp), cellulose nanofibers, bacterial cellulose, animal-derived cellulose 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 kraft method, sulfite method, soda method, polysulfide method, etc .; 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 composite sheet, but it is preferable to beaten. Thereby, improvement of sheet strength and promotion of fixing of inorganic particles can be expected.

  A composite fiber of a synthetic fiber and a cellulose fiber can also be used in the present invention. For example, a composite fiber of a polyester fiber, a polyamide, a polyolefin, an acrylic fiber, a glass fiber, a carbon fiber, various metal fibers, etc. and a cellulose fiber is also used. be able to.

  Further, these cellulose raw materials are further processed to give powdery cellulose, chemically modified cellulose such as oxidized cellulose, and cellulose nanofiber: CNF (microfibrillated cellulose: MFC, TEMPO oxidized CNF, phosphate esterified CNF, carboxymethylated). CNF, machine pulverized CNF, etc.) can also be used. As the powdered cellulose used in the present invention, for example, a fixed particle size in the form of a rod shaft produced by a method of purifying and drying an undegraded residue obtained after acid hydrolysis of a selected pulp, pulverizing and sieving. A crystalline cellulose powder having a distribution may be used, or commercially available products such as KC Flock (manufactured by Nippon Paper Industries), Theolas (manufactured by Asahi Kasei Chemicals), and Avicel (manufactured by FMC) may be used. The degree of polymerization of cellulose in powdered cellulose is preferably about 100 to 1500, the degree of crystallinity of powdered cellulose by X-ray diffraction is preferably 70 to 90%, and the volume average particle size by a laser diffraction type particle size distribution analyzer. Is preferably 1 μm or more and 100 μm or less. The oxidized cellulose used in the present invention 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. it can. 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 single or multi-screw 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, 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, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate which are ammonium salts of phosphoric acid are included. 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.

  The fibers shown above may be used alone or in combination. Especially, it is preferable that wood pulp is included or the combination of wood pulp, non-wood pulp, and / or synthetic fiber is included, and it is more preferable that it is only wood pulp.

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

  In the present invention, in addition to the fiber, a substance that is incorporated into the product inorganic particles to form composite particles can be used. In the present invention, fibers such as pulp fibers are used, but these substances are further incorporated by synthesizing barium sulfate in a solution containing inorganic particles, organic particles, polymers and the like. Composite particles can be produced.

  The fiber length of the fibers 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 fiber to be combined is preferably used in such an amount that 15% or more of the fiber surface is covered with barium sulfate. For example, the weight ratio of the fiber to barium sulfate is 5/95 to 95/5. 10/90 to 90/10, 20/80 to 80/20, 30/70 to 70/30, or 40/60 to 60/40.

  In the composite according to the present invention, 15% or more of the fiber surface is coated with barium sulfate, and if the surface of the cellulose fiber is coated with such an area ratio, a characteristic due to barium sulfate is greatly generated. On the other hand, the characteristics resulting from the fiber surface are reduced.

Barium sulfate In the present invention, barium sulfate complexed with fibers such as cellulose fibers is not particularly limited, but can be synthesized by a known method. In some cases, barium sulfate is synthesized in an aqueous system, and the composite is used in an aqueous system.

It is an ionic crystalline compound composed of barium ions and sulfate ions represented by barium sulfate (BaSO ₄ ), and is often in the form of a plate or 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.

  In the present invention, a composite of barium sulfate and fibers can be produced by synthesizing barium sulfate in a solution in the presence of fibers. For example, a method of reacting an acid (such as sulfuric acid) and a base by neutralization, reacting an inorganic salt with an acid or a base, or reacting inorganic salts with each other can be mentioned. 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.

  In one preferred embodiment, the composite of the present invention 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, so that it is easy to synthesize a composite of barium sulfate and cellulose fiber.

  As one preferred embodiment, the average primary particle diameter of barium sulfate in the composite of the present invention can be, for example, 1.5 μm or less, but the average primary particle diameter can be 1200 nm or less or 900 nm or less, Furthermore, the average primary particle diameter can be 200 nm or less or 150 nm or less. Moreover, the average primary particle diameter of barium sulfate can be 10 nm or more. The average primary particle diameter can be measured with an electron micrograph.

  Further, the barium sulfate in the composite of the present invention may take the form of secondary particles in which fine primary particles are aggregated, and can generate secondary particles according to the application by an aging process, or by pulverization. Agglomerates can also 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 composite obtained by the present invention can be used in various shapes, for example, powders, pellets, molds, aqueous suspensions, pastes, sheets, and other shapes. Moreover, it can also be set as molded objects, such as a mold, particle | grains, and a pellet, with a composite as a main component and other materials. There is no particular limitation on the dryer in the case of drying into a powder, but for example, an air dryer, a band dryer, a spray dryer or the like can be preferably used.

The composite obtained by the present invention can be used for various applications, for example, paper, fiber, cellulosic composite material, filter material, paint, plastic and other resins, rubber, elastomer, ceramic, glass, tire. , Building materials (asphalt, asbestos, cement, board, concrete, brick, tile, plywood, fiberboard, etc.), various carriers (catalyst carrier, pharmaceutical carrier, agricultural chemical carrier, microbial carrier, etc.), adsorbent (impurity removal, deodorization) , Dehumidifier, etc.), anti-wrinkle agent, clay, abrasive, modifier, repair material, heat insulating material, heat resistant material, heat radiating material, moisture proof material, water repellent material, water resistant material, light shielding material, sealant, shield material, insect repellent , Adhesives, inks, cosmetics, medical materials, paste materials, anti-discoloring agents, food additives, tablet excipients, dispersants, shape retention agents, water retention agents, filter aids, essential oil materials, oil treatment agents, Modifiers, radio wave absorbers, insulation materials, sound insulation materials, vibration insulation materials, semiconductor sealing materials, radiation shielding materials, cosmetics, fertilizers, feeds, fragrances, additives for paints and adhesives, flame retardant materials, sanitary goods ( It can be widely used for all uses such as 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, a radiation shielding material is preferable.
The composite of the present invention may be applied to papermaking applications, for example, printing paper, newspaper, ink jet paper, PPC paper, kraft paper, fine paper, coated paper, fine coated paper, wrapping paper, thin paper, and color fine paper. Paper, cast coated paper, non-carbon paper, label paper, thermal paper, various fancy papers, water-soluble paper, release paper, process paper, base paper for wallpaper, non-combustible paper, flame retardant paper, laminated base paper, printed electronics paper, battery Separator, cushion paper, tracing paper, impregnated paper, ODP paper, building paper, decorative paper, envelope paper, tape paper, heat exchange paper, synthetic fiber paper, sterilized paper, water resistant paper, oil resistant paper, heat resistant paper, photocatalyst Paper, decorative paper (grease paper, etc.), various sanitary paper (toilet paper, tissue paper, wipers, diapers, sanitary products, etc.), tobacco paper, paperboard (liner, Corrugating, etc. white paperboard), paper plates base paper cup base paper, baking paper, abrasive paper, and synthetic paper. That is, according to the present invention, a composite of inorganic particles and fibers having a small primary particle size and a narrow particle size distribution can be obtained, which is different from the conventional inorganic filler having a particle size of more than 2 μm. Can exhibit its characteristics. Furthermore, unlike the case where the inorganic particles are simply blended with the fibers, if the inorganic particles are combined with the fibers, the inorganic particles are not only easily retained on the sheet, but also a sheet in which the particles are uniformly dispersed without agglomeration. Can be obtained. In the preferred embodiment, the inorganic particles in the present invention are not only fixed on the outer surface of the fiber and the inner side of the lumen, but are also generated on the inner side of the microfibril.

  Moreover, when using the composite_body | complex obtained by this invention, the particle | grains generally called an inorganic filler and an organic filler, and various fibers can be used together. For example, as inorganic filler, calcium carbonate (light calcium carbonate, heavy calcium carbonate), magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay (kaolin, calcined kaolin, deramikaolin) ), Talc, zinc oxide, zinc stearate, titanium dioxide, silica made from sodium silicate and mineral acid (white carbon, silica / calcium carbonate composite, silica / titanium dioxide composite), white clay, bentonite, diatomaceous earth, Examples thereof include calcium sulfate, zeolite, an inorganic filler that regenerates and uses the ash obtained from the deinking process, and an inorganic filler that forms a complex 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 composites, wood-derived substances (fine fibers, microfibril fibers, powder kenaf), modified insolubilized starch, ungelatinized starch, etc. Is mentioned. Fibers include 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. Can be used. In addition to the above, the 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 the cellulose-based raw material include pulp fibers (wood pulp and non-wood pulp), animal-derived cellulose such as bacterial cellulose and sea squirt, and algae. The wood pulp may be produced by pulping the wood raw material. Wood materials include red pine, black pine, todomatsu, spruce, beech pine, larch, fir, tsuga, cedar, hinoki, larch, syrup, 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 the wood raw material is not particularly limited, and examples thereof include a pulping method generally used in the paper industry. Wood pulp can be classified by pulping method, for example, chemical pulp digested by kraft method, sulfite method, soda method, polysulfide method, etc .; 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. Wood pulp and non-wood pulp may be either unbeaten or beaten. Further, these cellulose raw materials are further processed to give powdery cellulose, chemically modified cellulose such as oxidized cellulose, and cellulose nanofiber: CNF (microfibrillated cellulose: MFC, TEMPO oxidized CNF, phosphate esterified CNF, carboxymethylated). CNF, mechanically pulverized CNF). Synthetic fibers include polyester, polyamide, polyolefin, acrylic fiber, semi-spun fibers include rayon and acetate, and inorganic fibers include glass fiber, carbon fiber, and various metal fibers. About these, these may be used alone or in combination of two or more.

  The average particle diameter, shape, and the like of barium sulfate constituting the composite of the present invention can be confirmed by observation with an electron microscope. Furthermore, barium sulfate having various sizes and shapes can be combined with fibers by adjusting the conditions for synthesizing barium sulfate.

  The manufacturing method of the composite based on this invention makes it essential to synthesize | combine barium sulfate in the solution containing a fiber. For example, 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 barium sulfate can be efficiently used. And a fiber composite 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 are no particular restrictions on the form of the reaction tank and the stirring conditions for obtaining this composite. For example, a composite containing a fiber and a barium sulfate precursor is stirred and mixed in an open reaction tank to synthesize the composite. Alternatively, it may be synthesized by injecting an aqueous suspension containing fibers and a barium sulfate precursor into a reaction vessel. As will be described later, when an aqueous suspension of a barium sulfate precursor is injected into a reaction vessel, cavitation bubbles may be generated and barium sulfate may be synthesized in the presence of the bubbles.

  In the present invention, 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 to 0.9 MPa in static pressure.

(Cavitation bubbles)
When the composite according to the present invention is synthesized, barium sulfate can be precipitated in the presence of cavitation bubbles. In the present invention, cavitation is a physical phenomenon in which bubbles are generated and disappear in a short time due to a pressure difference in a fluid flow, and is also referred to as 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.

  In the present invention, 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).

  In particular, in the present invention, since cavitation bubbles are easily generated and controlled, it is preferable to generate cavitation bubbles by ejecting 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.

  In the present invention, 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. Further, 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 or a fluid in which solid particles or gas are dispersed or mixed in the liquid, and refers to a liquid jet containing raw slurry or bubbles of pulp or inorganic particles. The gas referred to here may include bubbles due to cavitation.

Further, when the cavitation is generated by injecting the injection liquid through the nozzle or the orifice pipe, the pressure of the injection liquid (upstream pressure) is desirably 0.01 MPa or more and 30 MPa or less, and 0.7 MPa or more and 20 MPa or less. It is preferable that it is 2 MPa or more and 15 MPa or less. When the upstream pressure is less than 0.01 MPa, it is difficult to produce a pressure difference with the downstream pressure, and the effect is small. On the other hand, when the pressure is higher than 30 MPa, a special pump and a pressure vessel are required, and energy consumption increases, which is disadvantageous in terms of 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.

  In the present invention, the inorganic particles can also be synthesized by spraying the spray liquid under conditions that do not generate cavitation bubbles. 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 / second to 200 m / second, and preferably in the range of 20 m / second to 100 m / second. When the jet velocity is less than 1 m / sec, the effect is weak because the pressure drop is low and cavitation hardly occurs. On the other hand, when it is higher than 200 m / sec, a high pressure is required and a special device is required, which is disadvantageous in terms of cost.

  What is necessary is just to generate | occur | produce the cavitation generation | occurrence | production place in this invention in the reaction container which synthesize | combines barium sulfate. 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 complex in the present invention, 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.

  In the present invention, by increasing the jetting pressure of the liquid, the flow velocity of the jetting liquid is increased, and accordingly, the pressure is lowered, 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. or higher and 90 ° C. or lower, and particularly preferably 10 ° C. or higher and 60 ° C. or lower. 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.

  In the present invention, the energy necessary for generating cavitation can be reduced by adding a surfactant. 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.

Synthesis of Barium Sulfate and Fiber Composite In one embodiment of the present invention, a composite can be synthesized by synthesizing barium sulfate in a solution containing fibers. Can depend on the method.

  In the present invention, water is used for the preparation of the suspension. As this water, normal tap water, industrial water, ground water, well water, etc. can be used, ion-exchanged water, distilled water, Pure water, industrial waste water, and water obtained when separating and dehydrating the reaction liquid can be suitably used.

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

  When producing the composite of the present invention, various known auxiliaries can be further added. 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 their alkali metal salts, alkali metal salts of polyphosphoric acid such as hexametaphosphoric acid and tripolyphosphoric acid, amino acids such as glutamic acid and aspartic acid and their alkali metal salts, acetylacetone, methyl acetoacetate, acetoacetic acid Examples include ketones such as allyl, saccharides such as sucrose, and polyols such as sorbitol. In addition, as surface treatment agents, 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. Such an additive can be added in an amount of preferably 0.001 to 20%, more preferably 0.1 to 10% with respect to the inorganic particles.

  When synthesizing the complex in the present invention, the reaction conditions are not particularly limited, and can be appropriately set according to the application. For example, the temperature of the synthesis reaction can be 0 to 90 ° C, preferably 10 to 70 ° C. The reaction temperature can be controlled by a temperature controller, and if the temperature is low, the reaction efficiency decreases and the cost increases. On the other hand, if it exceeds 90 ° C., there is a tendency for coarse barium sulfate to increase.

  In the present invention, the reaction 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 1000 L.

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

  In the present invention, since the complex which is a reaction product is obtained as a suspension, it can be stored in a storage tank or subjected to processing such as concentration, dehydration, pulverization, classification, aging, and dispersion as necessary. Can do. These can be performed by known processes, and may be appropriately determined in consideration of the application and energy efficiency. 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-type dehydrator such as a filter press, a drum filter, a belt press, a tube press, A calcium carbonate 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 lightweight foreign matter cleaner, a reverse cleaner, a sieving tester, and the like. Examples of the dispersion method include a high-speed disperser and a low-speed kneader.

  The composite obtained by the present invention can be blended in a filler or pigment in a suspension state without being completely dehydrated, but can also be dried to form a powder. 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 obtained by the present invention can be modified by a known method. For example, in an embodiment, the surface can be hydrophobized to improve miscibility with a resin or the like.

Using the complex according to the molding invention conjugates, as appropriate, it is also possible to produce a molded product (the body). For example, when the composite obtained by the present invention is made into a sheet, a high ash content sheet can be easily obtained. Moreover, the obtained sheet | seat can be bonded together and it can also be set as a multilayer sheet. Examples of the paper machine (paper machine) used for sheet production include a long paper machine, a round paper machine, a gap former, a hybrid former, a multilayer paper machine, and a known paper machine that combines the paper making methods of these devices. It is done. The press linear pressure in the paper machine and the calendar linear pressure in the case where the calendar process is performed later can be determined within a range that does not hinder the operability and the performance of the composite sheet. In addition, 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 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.

  Moreover, in order to promote the fixing of the filler to the fiber or to improve the yield of the filler or fiber, a high molecular weight polymer or an inorganic substance can be added. For example, polyethyleneimine and modified polyethyleneimines containing tertiary and / or quaternary ammonium groups, polyalkylenimines, dicyandiamide polymers, polyamines, polyamine / epichlorohydrin polymers, and dialkyldiallyl quaternary ammonium monomers, dialkyls as coagulants Cations such as aminoalkyl acrylate, dialkylaminoalkyl methacrylate, dialkylaminoalkyl acrylamide and polymers of acrylamide and dialkylaminoalkyl methacrylamide, polymers of monoamines and epihalohydrin, polymers with polyvinylamine and vinylamine moieties, and mixtures thereof In addition to the functional polymer, a polymer obtained by copolymerizing an anionic group such as a carboxyl group or a sulfone group in the polymer molecule. Onritchi of zwitterionic polymer, and a mixture of cationic polymer and an anionic or zwitterionic polymers may be used. 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 that uses inorganic fine particles such as polysilicic acid or polysilicate microgels and their modified aluminum products, or one or more organic fine particles having a particle size of 100 μm or less, called so-called micropolymers 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, more preferably Can obtain a very high yield in the case of the above-mentioned 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 can be appropriately adjusted according to the purpose, but when it is 40 to 1200 g / m ² , the shielding effect is high, and the drying load during production is low, which is favorable. The basis weight of the sheet, also can be a 60~1000g / ^{m 2,} may be a 100 to 600 / ^{m 2.}

  It is also possible to use a molding method other than sheeting, for example, a method of pouring raw materials into a mold and drawing it by suction dehydration and drying as called a pulp mold, or spreading and drying on the surface of a molded product such as resin or metal Thereafter, molded articles having various shapes can be obtained by a method of peeling from the substrate. Further, it can be molded into a plastic like by mixing a resin, or it can be shaped like a ceramic by adding a mineral such as silica or alumina and firing. In the blending / drying / molding described above, only one type of composite can be used, or two or more types of composites can be mixed and used. When two or more types of composites 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.

  Further, various organic substances such as polymers and various inorganic substances such as pigments may be added to the composite molded article later.

  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 and parts are based on weight, and numerical ranges are described as including the end points.

Experiment 1: Synthesis of composite of barium sulfate and fiber <Synthesis of composite>
(1) Sample 1
1% pulp slurry (LBKP / NBKP = 8/2, Canadian standard freeness CSF = approx. 80 mL, 500 g) and barium hydroxide octahydrate (Wako Pure Chemicals, 5.82 g) with a three-one motor (1000 rpm) After mixing while stirring, sulfuric acid (Wako Pure Chemical, 88 g of 2% aqueous solution) was added dropwise at 8 g / min with a peristaltic pump. After completion of the dropwise addition, stirring was continued for 30 minutes to obtain Sample 1. In addition, it was 1.21 mm when the average fiber length of the pulp in the used pulp slurry was measured with the fiber tester (Lorentzen & Wettre company).

(2) Sample 2
Sample 2 was synthesized in the same manner as Sample 1 except that a slurry of 0.8% aramid fiber (Twaron RD-1094, Teijin, average fiber length: about 1.3 mm, 625 g) was used as the fiber content. .

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

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

(5) Sample 5
An aqueous suspension containing 1% pulp slurry (LBKP, CSF = 490 mL, average fiber length: about 0.7 mm, 1500 g) and barium hydroxide octahydrate (Wako Pure Chemicals, 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 complex, 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 the completion of 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 5.
<Evaluation of complex>
The obtained composite slurry (3 g in terms of solid content) was subjected to suction filtration using filter paper, and then the residue was dried in an oven (105 ° C., 2 hours), and the weight ratio of the composite fiber: inorganic particles was measured. did.

  In addition, each composite sample was washed with ethanol and then observed with an electron microscope (FIGS. 2 to 6). 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 barium sulfate fixed to the fiber was plate-like, and small ones were observed as irregular particles. The primary particle size of the barium sulfate particles estimated as a result of the observation was as shown in the table below.

Experiment 2: Production and evaluation of composite sheet (1) Sample 1 and Sample 2
A residue obtained by suction-filtering the composite (sample 1 and sample 2) obtained in Experiment 1 (1) and Experiment 1 (2) with a filter paper was prepared into a slurry having a concentration of about 0.2% using tap water. After this slurry is disaggregated for 5 minutes with a standard disaggregator specified in JIS P 8220-1: 2012, a handsheet having a basis weight of 60 g / m 2 is prepared using a 150 mesh wire according to JIS P 8222: 1998. did.

  The obtained handsheet was observed with an electron microscope and ash content was measured. The results are shown in FIG. 7 (Sample 1) and FIG. 8 (Sample 2). When the surface of the handsheet is observed with an electron microscope, it is observed that the inorganic substance is firmly fixed on the fiber surface. It was done.

(2) Sample 4
To the composite obtained in Experiment 1 (4) (sample 4, concentration: 1%), a cationic retention agent (ND300, Hymo) and an anionic retention agent (FA230, Hymo) in solid content. A stock slurry was prepared by adding 100 ppm each. Next, a sheet was produced from this stock slurry using a long paper machine at a speed of 10 m / min. In addition, as a control, a pulp slurry (LBKP / NBKP = 8/2, CSF = 390 mL, average fiber length: 1.3 mm), a cationic retention agent (ND300, Hymo) and an anionic retention agent (FA230, Hymo) Was added at a solid content of 100 ppm each, and a sheet was produced using a long paper machine.

When the obtained composite sheet was observed with an electron microscope, it was confirmed that barium sulfate was densely coated and filled on the surface and inside of the paper (FIG. 9).
The results of measuring the properties of the composite sheet are shown in the table below. By using the composite as a raw material, a sheet having an ash content of about 67% was produced by 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. Further, the obtained composite sheet had higher opacity, density, and air resistance than the pulp-only sheet.

<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

Experiment 3: Evaluation of radiation shielding ability of composite sheet The radiation (X-ray) shielding ability of the composite sheet produced in Experiment 2 (2) 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) X-rays were irradiated with the radiation quality and arrangement according to the test method of JIS Z 4501, and the transmission X-ray dose rate was measured. Measurement was performed five times for each requested product and each measurement position, and an average value and a 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 the table, the X-ray dose reduction rate can be reduced to 44.6% by stacking 10 sheets, 66.3% by stacking 20 sheets, and 85.2% by stacking 40 sheets. It was. Similarly, the lead equivalent when superposed was 0.07 mm for 10 sheets, 0.14 mm for 20 sheets, and 0.31 mm for 40 sheets.

Claims (8)

  A composite of barium sulfate and fiber.   The composite according to claim 1, wherein the fibers are cellulose fibers.   The composite according to claim 1 or 2, wherein 15% or more of the fiber surface is coated with barium sulfate.   The composite according to any one of claims 1 to 3, wherein the average primary particle diameter of barium sulfate is 1.5 µm or less.   The composite according to any one of claims 1 to 4, wherein a weight ratio of the fiber to barium sulfate is 5/95 to 95/5. A method for producing the composite according to any one of claims 1 to 5,
The method as described above, comprising the step of synthesizing barium sulfate in solution in the presence of fibers.   The radiation shielding material containing the composite_body | complex in any one of Claims 1-5.   The radiation shielding material according to claim 7, which is in the form of a sheet.