JP6713891B2 - Composite of barium sulfate and fiber and method for producing the same - Google Patents

Description

TECHNICAL FIELD 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 a radiation shielding ability and a method for producing the same.

Fibers exhibit various properties based on the functional groups on the surface thereof, but in some cases it may be necessary to modify the surface depending on the application, and so far, techniques for modifying the surface of fibers have been developed. There is.

For example, regarding a technique of depositing inorganic particles on fibers such as cellulose fibers, Patent Document 1 describes a composite in which crystalline calcium carbonate is mechanically bonded to the 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 gas method. Patent Document 3 describes 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 to flow. In contrast to this, there is described a technique of adhering the filler to the surface of the fiber by adsorbing the slurry of the alkali salt in the flow direction in the admixing region and admixing a suitable reactive gas with the sedimentable filler.

Further, Patent Documents 4 and 5 disclose a technique for producing a fiber web in which calcium carbonate is efficiently taken in by precipitating calcium carbonate in the step of forming the fiber web (wet paper).

JP, 06-158585, A US Pat. No. 5,679,220 US Patent No. 5665205 Japanese Patent Publication No. 2013-521417 US Patent Publication No. 2011/0000633

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

The present invention includes, but is not limited to, the following inventions.
(1) A composite of barium sulfate and fibers.
(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 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), which comprises a step of synthesizing barium sulfate in a solution in the presence of fibers.
(7) A radiation shielding material containing 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, it is possible to provide a fiber whose surface is coated with barium sulfate. Particularly, according to the present invention, it is possible to obtain a fiber-inorganic particle composite body in which 15% or more of the fiber surface is coated with barium sulfate.

That is, by coating many parts of the fiber surface with barium sulfate, it is possible to obtain a unique composite having the characteristics of both the fiber and barium sulfate. In particular, by coating the surface of the fiber with barium sulfate, it becomes possible to obtain a composite having a radiation shielding property. Further, since barium sulfate is attached to the fibers, it is possible to obtain a radiation shielding material having a high ash yield. Further, it can be dehydrated and dried to be in a form that is 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 manufactured 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 manufactured from the composite (Sample 4) (left: 500 times, right: 3000 times).

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

Further, in the composite of the present invention, not only the fibers and barium sulfate are mixed, but the fibers and barium sulfate are bound by hydrogen bonding or the like, so that barium sulfate is also dropped from the fibers by disaggregation treatment. Rarely. The binding strength between the fiber and barium sulfate in the composite can be evaluated by a numerical value such as ash yield (%, that is, ash content of the sheet/ash content of the composite before disaggregation×100). Specifically, the complex is dispersed in water to adjust the solid content concentration to 0.2%, and after defibration for 5 minutes with a standard defibration machine defined in JIS P 8220-1:2012, according to JIS P 8222:1998. The ash yield when formed into a sheet using a wire of 150 mesh can be used for evaluation, and in a preferred embodiment, the ash yield is 20 mass% or more, and in a more preferred embodiment, the ash yield is 50 mass% or more. is there.

Fiber In the present invention, a fiber such as a cellulose fiber or an aramid fiber is combined with barium sulfate. The fibers constituting the composite are preferably cellulose fibers, but for example, not only 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 the raw material of the cellulose fiber include pulp fiber (wood pulp or non-wood pulp), cellulose nanofiber, bacterial cellulose, animal-derived cellulose such as ascidian, algae, etc. The wood pulp is produced by pulping the wood raw material. Good. As the wood raw material, red pine, black pine, todo pine, ezo pine, black pine, larch, fir, hemlock, cedar, cypress, larch, silabe, spruce, hiba, douglas fir, hemlock, white fir, spruce, balsam fir, cedar, pine, pine, Softwood such as mercantia pine and radiata pine, and mixed materials thereof, beech, birch, alder, oak, oak, tab, shii, birch, cottonwood, poplar, tamo, droyagi, eucalyptus, mangrove, lauan, acacia, etc., and mixtures thereof The material is illustrated.

The method for pulping a natural material such as a wood raw material (woody raw material) is not particularly limited, and a pulping method generally used in the paper manufacturing industry is exemplified. Wood pulp can be classified by a pulping method, for example, a chemical pulp cooked by a method such as a Kraft method, a sulfite method, a soda method, and a polysulfide method; a mechanical pulp obtained by pulping with a mechanical force such as a refiner or a grinder; a chemical. Examples include semi-chemical pulp, waste paper pulp, deinked pulp and the like, which are obtained by performing pulping by mechanical force after pretreatment with. The wood pulp may be unbleached (before bleaching) or bleached (after bleaching).

Examples of the pulp derived from non-wood include cotton, hemp, sisal, Manila hemp, flax, straw, bamboo, bagasse, kenaf, sugar cane, corn, rice straw, kozo, mitsumata and the like.

The pulp fiber may be unbeaten or beaten, and may be selected according to the physical properties of the composite sheet, but beating is preferable. This can be expected to improve the sheet strength and accelerate the fixing of the inorganic particles.

Composite fibers of synthetic fibers and cellulose fibers can also be used in the present invention, for example, composite fibers of cellulose fibers with polyester, polyamide, polyolefin, acrylic fibers, glass fibers, carbon fibers, various metal fibers and the like. be able to.

Further, by further treating these cellulose raw materials, powdered cellulose, chemically modified cellulose such as oxidized cellulose, and cellulose nanofiber: CNF (microfibrillated cellulose: MFC, TEMPO oxidized CNF, phosphate esterified CNF, carboxymethylated). CNF, mechanically ground CNF, etc.). As the powdered cellulose used in the present invention, for example, a non-decomposed residue obtained after acid hydrolysis of a selected pulp is purified/dried, crushed/sieved by a method such as a constant particle size produced by sieving. A crystalline cellulose powder having a distribution may be used, or a commercially available product such as KC Flock (manufactured by Nippon Paper Industries), Theolus (manufactured by Asahi Kasei Chemicals), or Avicel (manufactured by FMC) may be used. The degree of polymerization of cellulose in the powdered cellulose is preferably about 100 to 1500, the crystallinity of the powdered cellulose by the X-ray diffraction method is preferably 70 to 90%, and the volume average particle diameter by a laser diffraction type particle size distribution measuring device is measured. 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 with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide or a mixture thereof. it can. As the cellulose nanofiber, a method of defibrating the above cellulose raw material is used. As the defibration method, for example, an aqueous suspension of chemically modified cellulose such as cellulose or oxidized cellulose is mechanically ground or refined by a refiner, a high pressure homogenizer, a grinder, a uniaxial or multiaxial kneader, a bead mill, etc. A method of defibrating can be used. One or more of the above methods may be combined to produce cellulose nanofibers. The fiber diameter of the produced cellulose nanofibers can be confirmed by electron microscope observation or the like, and is in the range of, for example, 5 nm to 1000 nm, preferably 5 nm to 500 nm, more preferably 5 nm to 300 nm. At the time of producing this cellulose nanofiber, before and/or after defibrating and/or refining the cellulose, an arbitrary compound may be further added to react with the cellulose nanofiber to give a hydroxyl group-modified product. it can. As the functional group to be modified, an acetyl group, an ester group, an ether group, a ketone group, a formyl group, a benzoyl group, an acetal, a hemiacetal, an oxime, an isonitrile, an allene, a thiol group, a urea group, a cyano group, a nitro group, an azo group. , Aryl group, aralkyl group, amino group, amide group, imide group, acryloyl group, methacryloyl group, propionyl group, propioroyl 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-methacryloyloxyethyl isocyanate Isocyanate group such as noyl 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 Examples thereof include an alkyl group such as a group, an undecyl group, a dodecyl group, a myristyl group, a palmityl group, and a stearyl group, an oxirane group, an oxetane group, an oxyl group, a thiirane group, and a thietane group. Hydrogen in these substituents may be replaced with a functional group such as a hydroxyl group or a carboxy group. Further, part of the alkyl group may be an unsaturated bond. The compound used for introducing these functional groups is not particularly limited, and examples thereof include a compound having a group derived from phosphoric acid, a compound having a group derived from carboxylic acid, a compound having a group derived from sulfuric acid, and a sulfonic acid derived group. And a compound having an alkyl group, a compound having an amine-derived group, and the like. The compound having a phosphoric acid group is not particularly limited, and examples thereof include phosphoric acid, lithium dihydrogen phosphate that is a lithium salt of phosphoric acid, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, and lithium polyphosphate. .. Further, sodium dihydrogenphosphate, disodium hydrogenphosphate, trisodium phosphate, sodium pyrophosphate, and sodium polyphosphate, which are sodium salts of phosphoric acid, can be mentioned. Furthermore, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate, which are potassium salts of phosphoric acid, may be mentioned. Further, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate and the like, which are ammonium salts of phosphoric acid, can be mentioned. Of these, phosphoric acid, sodium phosphate, phosphoric acid potassium salt, phosphoric acid ammonium salt, and phosphoric acid ammonium salt are preferable from the viewpoint of high efficiency of phosphoric acid group introduction and easy industrial application, and sodium dihydrogen phosphate is preferred. , Disodium hydrogen phosphate is more preferable, but 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, and examples thereof include maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic acid anhydride, and acid anhydrides of dicarboxylic acid compounds such as itaconic anhydride. To be The derivative of the compound having a carboxyl group is not particularly limited, and examples thereof include an imidized product of an acid anhydride of a compound having a carboxyl group and a derivative of an acid anhydride of a compound having a carboxyl group. The imidized product of an acid anhydride of a compound having a carboxyl group is not particularly limited, and examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide. The derivative of the acid anhydride of the compound having a carboxyl group is not particularly limited. For example, at least a part of hydrogen atoms of an acid anhydride of a compound having a carboxyl group such as dimethylmaleic anhydride, diethylmaleic anhydride and diphenylmaleic anhydride is a substituent (for example, an alkyl group, a phenyl group, etc.). ) Is substituted. Of the above-mentioned compounds having a group derived from a carboxylic acid, maleic anhydride, succinic anhydride, and phthalic anhydride are preferable because they are industrially applicable and easily gasified, but are not particularly limited. Further, the cellulose nanofibers may be modified in such a manner that the compound to be modified is physically adsorbed on the cellulose nanofibers without being chemically bound. Examples of the physically adsorbing compound include a surfactant, and any of anionic, cationic and nonionic compounds may be used. When the above modification is performed before defibrating and/or crushing cellulose, these functional groups can be eliminated after the defibrating and/or crushing to restore the original hydroxyl groups. By performing the above-mentioned modifications, it is possible to promote the defibration of the cellulose nanofibers or to facilitate the mixing with various substances when the cellulose nanofibers are used.

The fibers shown above may be used alone or in combination of two or more. Among them, it is preferable to contain wood pulp or a combination of wood pulp and non-wood pulp and/or synthetic fiber, and it is more preferable to use wood pulp alone.

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

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

The fiber length of the fibers to be composited is not particularly limited, but 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.

The fibers to be composited are preferably used in an amount such 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, 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 when the surface area of the cellulose fiber is coated with such an area ratio, the characteristics due to barium sulfate become large. On the other hand, the features attributed to the fiber surface are reduced.

Barium Sulfate In the present invention, barium sulfate to be composited with fibers such as cellulose fibers is not particularly limited, but can be synthesized by a known method. The synthesis of barium sulfate may be carried out in an aqueous system, and the complex may be used in an aqueous system.

It is an ionic crystalline compound composed of barium ion and sulfate ion represented by barium sulfate (BaSO ₄ ), often has a plate-like or columnar form, 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 turns yellowish brown or black gray and becomes translucent. Although it can be obtained as a natural mineral, it can also be synthesized by a chemical reaction. In particular, synthetic products obtained by chemical reaction are used not only for pharmaceuticals (X-ray contrast agents) but also for paints, plastics, storage batteries, etc. by applying their 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) with a base by neutralization, a reaction between an inorganic salt and an acid or a base, or a reaction between inorganic salts can be mentioned. For example, barium sulfate can be obtained by reacting barium hydroxide with sulfuric acid or aluminum sulfate, or barium chloride can be added to an aqueous solution containing a sulfate to precipitate barium sulfate.

The composite of the present invention can be obtained, in one preferred embodiment, 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 thus it is easy to synthesize a composite of barium sulfate and cellulose fibers.

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 also be 1200 nm or less or 900 nm or less, Further, the average primary particle diameter can be 200 nm or less or 150 nm or less. The average primary particle diameter of barium sulfate can be 10 nm or more. The average primary particle diameter can be measured by an electron micrograph.

Further, barium sulfate in the composite of the present invention may take the form of secondary particles in which fine primary particles are aggregated, and it is possible to generate secondary particles according to the application by the aging step, and by pulverization. The agglomerates can also be made finer. As the pulverizing method, a ball mill, a sand grinder mill, an impact mill, a high pressure homogenizer, a low pressure homogenizer, a dyno mill, an ultrasonic mill, a kanda grinder, an attritor, a millstone type mill, a vibration mill, a cutter mill, a jet mill, a disintegrator, and a beater. , A short-screw extruder, a twin-screw extruder, an ultrasonic stirrer, a household juicer mixer and the like.

The composite obtained according to the present invention can be used in various shapes, for example, powder, pellets, molds, aqueous suspensions, pastes, sheets and other shapes. It is also possible to form a molded body such as a mold or particles/pellets with the composite as the main component together with other materials. There are no particular restrictions on the dryer used for drying the powder, but for example, an airflow dryer, a band dryer, a spray dryer and the like can be preferably used.

The composite obtained by the present invention can be used in various applications, for example, paper, fibers, cellulosic composite materials, filter materials, paints, plastics and other resins, rubber, elastomers, ceramics, glass, tires. , Building materials (asphalt, asbestos, cement, board, concrete, brick, tile, plywood, fibreboard, etc.), various carriers (catalyst carrier, pharmaceutical carrier, agricultural chemical carrier, microbial carrier, etc.), adsorbent (impurity removal, deodorant) , Dehumidification, etc.), anti-wrinkle agent, clay, abrasive, modifier, repair material, heat insulating material, heat resistant material, heat radiation material, moistureproof material, water repellent material, water resistant material, light shielding material, sealant, shield material, insect repellent. , Adhesives, inks, cosmetics, medical materials, paste materials, anti-tarnish agents, food additives, tablet excipients, dispersants, shape retention agents, water retention agents, filter aids, essential oils, oil treatment agents, oils Modifiers, radio wave absorbers, insulation materials, sound insulation materials, vibration damping materials, semiconductor encapsulation materials, radiation shielding materials, cosmetics, fertilizers, feeds, fragrances, additives for paints and adhesives, flame retardant materials, hygiene products ( It can be widely used for all purposes such as disposable diapers, sanitary napkins, incontinence pads, breast pads, etc.). Further, it can be used as various fillers and coating agents in the above applications. Of these, the radiation shielding material is preferable.
The composite of the present invention may be applied to papermaking applications, for example, printing paper, newsprint, inkjet paper, PPC paper, kraft paper, fine paper, coated paper, lightly coated paper, wrapping paper, thin paper, high-quality paper. Paper, cast coated paper, non-carbon paper, label paper, thermal paper, various fancy paper, water-soluble paper, release paper, process paper, wallpaper base paper, non-combustible paper, flame retardant paper, laminated board base paper, printed electronics paper, battery Separator, cushion paper, tracing paper, impregnated paper, ODP paper, building material paper, decorative material paper, envelope paper, tape paper, heat exchange paper, synthetic paper, sterile paper, water resistant paper, oil resistant paper, heat resistant paper, photocatalyst Paper, decorative paper (greasing paper, etc.), various sanitary papers (toilet paper, tissue paper, wipers, diapers, sanitary products, etc.), tobacco paper, paperboard (liner, core raw paper, white paperboard, etc.), paper plate raw paper, cups Examples include base paper, baking paper, abrasive paper, and synthetic paper. That is, according to the present invention, it is possible to obtain a composite of inorganic particles and fibers having a small primary particle size and a narrow particle size distribution, and therefore, unlike the conventional inorganic filler having a particle size of more than 2 μm. It is possible to exert excellent characteristics. Furthermore, unlike the case where the inorganic particles are simply mixed with the fibers, when the inorganic particles are complexed with the fibers, not only the inorganic particles are easily retained in the sheet, but also a sheet in which the inorganic particles are uniformly dispersed without agglomeration is formed. Obtainable. It is clear from the results of electron microscope observation that the inorganic particles in the present invention, in a preferred embodiment, are not only fixed on the outer surface/lumen of the fiber but also formed inside the microfibril.

Further, when the composite obtained by the present invention is used, particles generally called an inorganic filler and an organic filler, and various fibers can be used in combination. For example, as inorganic fillers, calcium carbonate (light calcium carbonate, heavy calcium carbonate), magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay (kaolin, calcined kaolin, derami kaolin) ), talc, zinc oxide, zinc stearate, titanium dioxide, silica produced from sodium silicate and mineral acid (white carbon, silica/calcium carbonate complex, silica/titanium dioxide complex), clay, bentonite, diatomaceous earth, Examples thereof include calcium sulfate, zeolite, an inorganic filler that is used by regenerating ash obtained from the deinking step, and an inorganic filler that forms a complex with silica or calcium carbonate during the regeneration process. As the calcium carbonate-silica composite, amorphous silica such as white carbon may be used together with the calcium carbonate and/or the light calcium carbonate-silica composite. As the organic filler, urea-formalin resin, polystyrene resin, phenol resin, micro hollow particles, acrylamide complex, wood-derived substances (fine fibers, microfibril fibers, powder kenaf), modified insolubilized starch, non-gelatinized starch, etc. Are listed. The fibers are not limited to natural fibers such as cellulose, synthetic fibers artificially synthesized from raw materials such as petroleum, regenerated fibers (semi-synthetic fibers) such as rayon and lyocell, and inorganic fibers without limitation. Can be used. In addition to the above, natural fibers include protein fibers such as wool, silk thread, 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), bacterial cellulose, animal-derived cellulose such as squirts, and algae. The wood pulp may be produced by pulping the wood raw material. As the wood raw material, red pine, black pine, todo pine, spruce pine, black pine, larch, fir, hemlock, cedar, cypress, larch, silabe, spruce, hiba, Douglas fir, hemlock, white fir, spruce, balsam fir, cedar, pine, pine, Softwood such as mercantia pine, radiata pine, and their mixed materials, beech, birch, alder, oak, oak, tub, shii, birch, cottonwood, poplar, tamo, droyagi, eucalyptus, mangrove, lauan, acacia, etc., and mixtures thereof A material is illustrated. The method for pulping a wood raw material is not particularly limited, and a pulping method generally used in the paper manufacturing industry is exemplified. Wood pulp can be classified by a pulping method, for example, a chemical pulp cooked by a method such as a Kraft method, a sulfite method, a soda method, and a polysulfide method; a mechanical pulp obtained by pulping with a mechanical force such as a refiner or a grinder; a chemical. Examples include semi-chemical pulp, waste paper pulp, deinked pulp and the like, which are obtained by performing pulping by mechanical force after pretreatment with. The wood pulp may be unbleached (before bleaching) or bleached (after bleaching). Examples of the pulp derived from non-wood include cotton, hemp, sisal, Manila hemp, flax, straw, bamboo, bagasse, kenaf, sugar cane, corn, rice straw, kozo, mitsumata and the like. Wood pulp and non-wood pulp may be unbeaten or beaten. Further, by further treating these cellulose raw materials, powdered cellulose, chemically modified cellulose such as oxidized cellulose, and cellulose nanofiber: CNF (microfibrillated cellulose: MFC, TEMPO oxidized CNF, phosphate esterified CNF, carboxymethylated). It can also be used as CNF, mechanically ground CNF). Examples of the synthetic fiber include polyester, polyamide, polyolefin, acrylic fiber, semi-synthetic fiber such as rayon and acetate, and examples of the inorganic fiber include glass fiber, carbon fiber, various metal fibers and the like. Regarding the above, these may be used alone or in combination of two or more kinds.

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

The method for producing a composite according to the present invention essentially requires synthesizing barium sulfate in a solution containing fibers. For example, when an alkaline barium sulfate precursor typified by barium hydroxide is used as a raw material, it is possible to swell the fiber by dispersing the fiber in a solution of the barium sulfate precursor in advance, so that the 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 these 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 or the stirring conditions for obtaining the present composite, and for example, a solution containing a fiber and a barium sulfate precursor is stirred and mixed in an open reaction tank to synthesize a composite. Alternatively, it may be synthesized by injecting an aqueous suspension containing the fiber and the barium sulfate precursor into the reaction vessel. As described later, cavitation bubbles may be generated when the aqueous suspension of the barium sulfate precursor is injected into the reaction vessel, and barium sulfate may be synthesized in the presence thereof.

In the present invention, the liquid may be ejected under the condition that cavitation bubbles are generated in the reaction vessel, or may be ejected under the condition that cavitation bubbles are not generated. Further, in any case, the reaction vessel is preferably a pressure vessel. The pressure vessel in the present invention is a vessel that can apply a pressure of 0.005 MPa or more. Under the condition that cavitation bubbles are not generated, 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 synthesizing the composite according to the present invention, 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 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) have very small "bubble nuclei" of 100 micron or less existing in the liquid as nuclei 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 injecting 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 is conceivable to cause cavitation by a child (vibratory trellis cavitation).

Particularly in the present invention, it is preferable to generate the cavitation bubbles by injecting a fluid at a high pressure because the generation and control of the cavitation bubbles are easy. In this mode, the jetted liquid is compressed by using a pump or the like and jetted at high speed through a nozzle or the like, so that 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 a high efficiency of generating 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 occurs spontaneously in a fluid machine.

In the present invention, a reaction solution such as a raw material may be used as it is as an injection liquid to generate cavitation, or some kind of fluid may be injected into the reaction container to generate cavitation bubbles. The fluid forming the jet of liquid may be any of liquid, gas, solid such as powder and pulp as long as it is in a fluid state, or may be a mixture thereof. 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, or may be ejected separately.

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

When jetting the jetting liquid through a nozzle or an orifice pipe to generate cavitation, the pressure of the jetting liquid (upstream pressure) is preferably 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. If the upstream pressure is less than 0.01 MPa, a pressure difference is less likely to occur between the upstream pressure and the downstream pressure, and the effect is small. Further, if it is higher than 30 MPa, a special pump and pressure vessel are required, and energy consumption becomes large, which is disadvantageous in terms of cost. On the other hand, the pressure (downstream pressure) in the container is preferably 0.005 MPa or more and 0.9 MPa or less in static pressure.
Further, the ratio of the pressure inside the container and the pressure of the injection liquid is preferably in the range of 0.001 to 0.5.

In the present invention, it is possible to synthesize the inorganic particles by jetting the jetting liquid under the condition that cavitation bubbles are not generated. Specifically, it is more preferable that the pressure of the injection liquid (upstream pressure) is 2 MPa or less, preferably 1 MPa or less, and the pressure of the injection liquid (downstream pressure) is released to 0.05 MPa or less.

The jet velocity of the jet liquid is preferably in the range of 1 m/sec or more and 200 m/sec or less, and more preferably in the range of 20 m/sec or more and 100 m/sec or less. If the jet velocity is less than 1 m/sec, the pressure drop is low and cavitation is unlikely to occur, so the effect is weak. 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 cost.

The cavitation generation place in the present invention may be generated in the reaction vessel for synthesizing barium sulfate. In addition, it is possible to process in one pass, but it is also possible to circulate as many times as necessary. Furthermore, it is possible to process in parallel or in permutation using a plurality of generating means.

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

When cavitation is generated by liquid injection, the solid concentration of the reaction solution is preferably 30% by weight or less, more preferably 20% by weight or less. This is because such a concentration facilitates the uniform action of cavitation bubbles on the reaction system. From the viewpoint of reaction efficiency, the aqueous suspension of slaked lime which is a reaction solution preferably has a solid content concentration of 0.1% by weight or more.

When synthesizing the complex in the present invention, if the pH of the reaction solution changes as the reaction progresses, the reaction can be controlled by monitoring the pH of the reaction solution.

In the present invention, by increasing the injection pressure of the liquid, the flow velocity of the injection liquid is increased, and the pressure is reduced accordingly, and stronger cavitation can be generated. Further, by increasing the pressure in the reaction container, 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, it is considered that the impact force becomes the maximum at the midpoint between the melting point and the boiling point. Therefore, in the case of an aqueous solution, about 50°C is preferable, but even at a temperature lower than that, it is affected by the vapor pressure. Since it does not exist, a high effect can be obtained within the above range.

In the present invention, the energy required to generate cavitation can be reduced by adding a surfactant. As the surfactant to be used, known or new surfactants, for example, nonionic surfactants such as fatty acid salts, higher alkyl sulfates, alkylbenzene sulfonates, higher alcohols, alkylphenols, alkylene oxide adducts of fatty acids and the like. , Anionic surfactants, cationic surfactants, amphoteric surfactants and the like. It may be a single component or a mixture of two or more components. The added amount may be an amount necessary to reduce the surface tension of the jet liquid and/or the jet liquid.

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

In the present invention, water is used for the preparation of a suspension, etc., and as this water, ordinary tap water, industrial water, ground water, well water, etc. can be used, as well as ion exchanged water, distilled water, super water Pure water, industrial waste water, and water obtained when separating and dehydrating the reaction liquid can be preferably used.

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

When manufacturing the composite of the present invention, various known auxiliaries can be added. For example, a chelating agent can be added, and 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 and ethylenediamine tetrachloride. Aminopolycarboxylic acids such as acetic acid and alkali metal salts thereof, hexametaphosphoric acid, alkali metal salts of polyphosphoric acid such as tripolyphosphoric acid, amino acids such as glutamic acid and aspartic acid, and alkali metal salts thereof, acetylacetone, methyl acetoacetate, acetoacetic acid Examples thereof include ketones such as allyl, sugars such as sucrose, and polyols such as sorbitol. Further, as surface treatment agents, saturated fatty acids such as palmitic acid and stearic acid, unsaturated fatty acids such as oleic acid and linoleic acid, alicyclic carboxylic acids, resin acids such as abietic acid, their salts, esters and ethers, alcohols Activators, sorbitan fatty acid esters, amide-based and amine-based 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, etc. can be added. Further, a dispersant can be used if necessary. Examples of the dispersant include sodium polyacrylate, sucrose fatty acid ester, glycerin fatty acid ester, ammonium salt of acrylic acid-maleic acid copolymer, methacrylic acid-naphthoxy polyethylene glycol acrylate copolymer, methacrylic acid-polyethylene glycol. Examples include monomethacrylate copolymer ammonium salt 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 additives can be added to the inorganic particles in an amount of preferably 0.001 to 20%, more preferably 0.1 to 10%.

When synthesizing the complex in the present invention, the reaction conditions are not particularly limited and can be appropriately set depending on the application. For example, the temperature of the synthesis reaction can be 0 to 90°C, preferably 10 to 70°C. Regarding the reaction temperature, the temperature of the reaction solution can be controlled by a temperature control device. When the temperature is low, the reaction efficiency is low and the cost is high, while when it exceeds 90° C., coarse barium sulfate tends to increase.

Further, in the present invention, the reaction may be a batch reaction or a continuous reaction. Generally, it is preferable to carry out the batch reaction step because of the convenience of discharging the residue after the reaction. Although the scale of the reaction is not particularly limited, 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 container may 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 conductivity of the reaction solution and the reaction time, and specifically, the time during which the reactant stays in the reaction tank can be adjusted and controlled. In addition, in the present invention, the reaction can be controlled by stirring the reaction solution in the reaction tank or by making the reaction a multi-step reaction.

In the present invention, since the complex that is the reaction product is obtained as a suspension, it may be stored in a storage tank or subjected to treatments such as concentration, dehydration, pulverization, classification, aging and dispersion, if necessary. You can These can be performed by a known process, and may be appropriately determined in consideration of usage, 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 this 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 prepared by suitably using a vacuum drum dehydrator such as an Oliver filter. As the pulverizing method, a ball mill, a sand grinder mill, an impact mill, a high pressure homogenizer, a low pressure homogenizer, a dyno mill, an ultrasonic mill, a kanda grinder, an attritor, a millstone type mill, a vibration mill, a cutter mill, a jet mill, a disintegrator, and a beater. , A short-screw extruder, a twin-screw extruder, an ultrasonic stirrer, a household juicer mixer and the like. Examples of the classification method include a sieve such as a mesh, an outward or inward type slit or round hole screen, a vibrating screen, a heavy foreign substance cleaner, a lightweight foreign substance cleaner, a reverse cleaner, and a sieving tester. Examples of dispersion methods include a high speed disperser and a low speed kneader.

The composite obtained by the present invention can be blended with a filler or a pigment in a suspension state without being completely dehydrated, or can be dried to give a powder. The dryer in this case is also not particularly limited, but for example, an airflow dryer, a band dryer, a spray dryer and the like can be preferably used.

The composite obtained by the present invention can be modified by a known method. For example, in one embodiment, it is possible to make the surface hydrophobic to improve the miscibility with a resin or the like.

Molded Article of Composite Article A molded article (body) can be appropriately produced using the composite article of the present invention. For example, when the composite obtained by the present invention is formed into a sheet, a sheet with a high ash content can be easily obtained. Also, the obtained sheets can be laminated to form a multilayer sheet. Examples of the paper machine (paper making machine) used for sheet production include a Fourdrinier paper machine, a round net paper machine, a gap former, a hybrid former, a multi-layer paper machine, and a known paper making machine that combines paper making methods of these machines. To be The press linear pressure in the paper machine and the calender linear pressure in the case of performing the calendering treatment in the latter stage can be determined within a range that does not hinder the operability and the performance of the composite sheet. Further, starch, various polymers, pigments and mixtures thereof may be applied to the formed sheet by impregnation or coating.

A wet and/or dry paper-strength agent (paper-strengthening agent) can be added during sheet formation. Thereby, the strength of the composite sheet can be improved. Examples of the paper strength agent include urea formaldehyde resin, melamine formaldehyde resin, polyamide, polyamine, epichlorohydrin resin, vegetable gum, latex, polyethyleneimine, glyoxal, gum, mannogalactan polyethyleneimine, polyacrylamide resin, polyvinylamine. Resins such as polyvinyl alcohol; composite polymers or copolymers of two or more selected from the above resins; starch and modified starch; carboxymethyl cellulose, guar gum, urea resins and the like. The amount of the paper strength agent added is not particularly limited.

Further, in order to promote the fixing of the filler to the fiber and to improve the yield of the filler and the fiber, a high molecular polymer or an inorganic substance can be added. For example, as coagulants polyethyleneimine and modified polyethyleneimine containing tertiary and/or quaternary ammonium groups, polyalkyleneimines, dicyandiamide polymers, polyamines, polyamine/epiclohydrin polymers, and dialkyldiallyl quaternary ammonium monomers, dialkyls. Cation such as aminoalkyl acrylate, dialkylaminoalkyl methacrylate, dialkylaminoalkyl acrylamide, polymer of dialkylaminoalkyl methacrylamide and acrylamide, polymer of monoamines and epihalohydrin, polymer having polyvinylamine and vinylamine moieties, and mixtures thereof. Cation-rich amphoteric polymer obtained by copolymerizing anionic groups such as carboxyl group and sulfone group in the molecule of the polymer, and a mixture of cationic polymer and anionic or zwitterionic polymer. be able to. As the retention agent, a cationic or anionic amphoteric polyacrylamide type substance can be used. Further, in addition to these, in combination with at least one or more cations and anionic polymers, it is also possible to apply a so-called dual polymer retention system, at least one or more anionic bentonite and colloidal silica, polysilicic acid, A multi-component yield system comprising inorganic fine particles such as polysilicic acid or polysilicate microgels and aluminum modified products thereof, and one or more organic fine particles having a particle size of 100 μm or less, which are so-called micropolymers obtained by cross-linking polymerization of acrylamide. Good. In particular, when the polyacrylamide-based substances used alone or in combination have a weight average molecular weight of 2,000,000 daltons or more by an intrinsic viscosity method, a good yield can be obtained, preferably 5,000,000 daltons or more, and more preferably Can obtain a very high yield when the above-mentioned acrylamide-based material has a content of 10 million daltons or more and less than 30 million daltons. The form of this polyacrylamide-based substance 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 acrylic acid ester and acrylamide, or acrylamide Examples of the ammonium salt include a quaternized ammonium salt obtained by copolymerizing an acrylic acid ester with an acrylic acid ester. The cationic charge density of the cationic polyacrylamide-based substance is not particularly limited.

Other inorganic particles such as drainage improver, internally added sizing agent, pH adjuster, defoaming agent, pitch control agent, slime control agent, bulking agent, calcium carbonate, kaolin, talc and silica (so-called) depending on the purpose. Fillers) and the like. 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 manufacturing 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 the raw material into a mold to suck and dehydrate and dry it as is called a pulp mold, or spread it on the surface of a molded product such as resin or metal and dry it. After that, molded articles having various shapes can be obtained by a method such as peeling from the substrate. It is also possible to mix it with a resin to form it into a plastic shape, or to add a mineral such as silica or alumina and fire it to form it into a ceramic shape. In the compounding, drying, and molding described above, only one kind of composite can be used, or two or more kinds of composites can be mixed and used. When two or more kinds of composites are used, it is possible to use a mixture of them in advance, or it is possible to mix the respective components, dry and mold them and mix them later.

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

The present invention will be described more specifically with reference to 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 the numerical range is described as including its endpoints.

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

(2) Sample 2
Sample 2 was prepared 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 Chemical Industries, 57 g) with stirring with a three-one motor (800 rpm) Aluminum sulfate (sulfuric acid band, 77 g) was added dropwise with a perister pump at 2 g/min. After the dropping was completed, stirring was continued for 30 minutes as it was 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 Kagaku Kogyo, 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 perister pump. After the dropping was completed, stirring was continued for 30 minutes as it was 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 Chemical Industries, 140 g) was prepared. 14 L of this aqueous suspension was placed in a cavitation device having a volume of 45 L, and while circulating the reaction solution, sulfuric acid (Wako Pure Chemical Co., Ltd., 1280 g of 2% aqueous solution) was dropped into the reaction vessel at 50 g/min with a perister pump. ..

In the synthesis of the complex, cavitation bubbles were generated in the reaction container by circulating the reaction solution and injecting it into the reaction container 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, but the jet velocity was about 70 m/s, and the inlet pressure (upstream pressure) was The pressure was 7 MPa and the outlet pressure (downstream pressure) was 0.3 MPa.

After the addition of sulfuric acid was completed, 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>
About the obtained composite slurry (3 g in terms of solid content), after suction filtration using filter paper, the residue was dried in an oven (105° C., 2 hours), and the weight ratio of fiber: inorganic particles of the composite was measured. did.

The composite samples were each washed with ethanol and then observed with an electron microscope (FIGS. 2 to 6). As a result, it was observed that in all samples, the fiber surface was covered with the inorganic substance and self-fixed. Most of the barium sulphate fixed to the fibers was plate-like, and those with a small size were observed as amorphous particles. The primary particle diameters of barium sulfate particles estimated as a result of observation are shown in the table below.

Experiment 2: Production and evaluation of composite sheet (1) Sample 1 and Sample 2
The residue obtained by suction-filtering the composites (Sample 1 and Sample 2) obtained in Experiment 1 (1) and Experiment 1 (2) with filter paper was prepared into a slurry having a concentration of about 0.2% using tap water. This slurry was defibrated for 5 minutes by a standard defibration machine defined in JIS P 82220-1:2012, and then a hand-made sheet having a basis weight of 60 g/m 2 was prepared using a 150 mesh wire in accordance with JIS P 8222:1998. did.

The obtained handmade sheet was observed with an electron microscope and measured for ash. The results are shown in Fig. 7 (Sample 1) and Fig. 8 (Sample 2). When the surface of the handmade sheet was observed with an electron microscope, it was observed that the inorganic substance was firmly fixed on the fiber surface. Was done.

(2) Sample 4
A cationic retention agent (ND300, Hymo) and an anionic retention agent (FA230, Hymo) were added to the complex (Sample 4, concentration: 1%) obtained in Experiment 1 (4) in terms of solid content. A paper stock slurry was prepared by adding 100 ppm each. Then, using a Fourdrinier paper machine, a sheet was produced from the stock slurry at a papermaking speed of 10 m/min. As a control, a pulp slurry (LBKP/NBKP=8/2, CSF=390 mL, average fiber length: 1.3 mm) was added to the cationic retention agent (ND300, HYMO) and anionic retention agent (FA230, HYMO). Was added to the solid content by 100 ppm each to produce a sheet using a Fourdrinier paper machine.

When the obtained composite sheet was observed with an electron microscope, it was confirmed that the surface and the inside of the paper were densely covered and filled with barium sulfate (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 papermaking machine, and the obtained sheet could be continuously wound and rolled. The yields at this time were very high at 96% or more for both the stock yield and the ash yield. Further, the obtained composite sheet had higher opacity, density and air permeation resistance than a sheet containing only pulp.

<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 resistance: JIS P 8117:2009
・Smoothness: JIS P 8155:2010
・L&W bending stiffness: In accordance with ISO 2493, L&W Bending Tester (Lorentzen & Wet
Bending stiffness with a bending angle of 15 degrees was measured with a tre company.
・Tear length: JIS P 8113:2006

Experiment 3: Evaluation of radiation shielding ability of the composite sheet The radiation (X-ray) shielding ability of the composite sheet produced in Experiment 2 (2) was evaluated. Specifically, the transmitted X-ray dose rate and the lead equivalent were measured according to JIS Z 4501 "Lead equivalent test method for X-ray protective articles".

(Transmission X-ray dose rate) X-rays were irradiated with a radiation quality and arrangement according to the test method of JIS Z 4501, and the transmission X-ray dose rate was measured. Five measurements were performed for each requested product and each measurement position, and the average value and standard deviation were obtained. From the obtained transmitted dose rate, the dose reduction rate was calculated by the following formula.
Dose reduction rate (%) = (transmitted dose rate of each sample / transmitted dose rate of blank (no sample)) x 100
(Lead Equivalent) According to JIS Z 4501 “Test method for lead equivalent of X-ray protection article”, the transmitted X-ray dose was measured to obtain the lead equivalent. The lead equivalent of each sample was obtained by creating 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 having different thicknesses. As the standard lead plate, two sheets with a larger attenuation rate and two sheets with a smaller attenuation rate than each test product were selected.

(Measurement condition)
・X-ray machine: MG-452 type (smooth circuit, focal point size 5.5 mm, Be window), Exlon International
-X-ray tube voltage and tube current: MG-452 type 100kV 12.5mA additional filtration plate 0.25mmCu
・Focus between X-ray tube and sample: 1500 mm
・Distance between sample and measuring device: 50 mm
・Measuring device: Ionization chamber irradiation dose rate meter RAMTEC-1000D type A-4 probe used by Toyo Medic Co., Ltd. ・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 44.6% when 10 sheets are stacked, 66.3% when 20 sheets are stacked, and 85.2% when 40 sheets are stacked. It was In addition, the lead equivalents when superposed in the same manner were 0.07 mm for 10 sheets, 0.14 mm for 20 sheets, and 0.31 mm for 40 sheets.

Claims (8)

Self fixing, are complex barium sulfate having an average primary particle diameter of 1.5μm or less in the surfaces of cellulose fibers (excluding the case of cellulose fibers is cellulose nanofibers). The composite according to claim 1 , wherein 15% or more of the fiber surface is coated with barium sulfate. The composite according to claim 1 or 2 , wherein the weight ratio of fiber to barium sulfate is 5/95 to 95/5. The composite according to claim 1, wherein the cellulose fiber is pulp fiber. The composite according to any one of claims 1 to 4, wherein the average primary particle diameter of barium sulfate is 10 to 900 nm. A method for producing the composite according to any one of claims 1 to 5, comprising:
A method as described above, comprising synthesizing barium sulphate in solution in the presence of fibers. A radiation shielding material comprising the composite according to claim 1. The radiation shielding material according to claim 7, which is in the form of a sheet.