JP2018087256A - Particulate cellulose complex and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particulate cellulose complex that has high affinity with various fibers without using an adhesive by mixing a fiber, which is raw material for paper, with at least one functional material, and a method of producing the same.SOLUTION: The present invention provides a plurality of particulate cellulose complexes which consists of a plurality of cellulose nanofibers bound to each other, the cellulose nanofibers made from wood or non-wood pulp and being 2 nm-10 μm in fiber width, which has the shape with an average circularity of 0.7 or more and less than 1.0, and which includes at least one functional material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a composite in which various functional materials can be firmly imparted without using an adhesive, in which cellulose is mixed with at least one functional material and processed into particles, and a method for producing the same Is.

  Security printed matter such as banknotes, passports, securities, identification cards, cards, and passports that require anti-counterfeiting effects, decorative items that give a visual impression, home appliances and office supplies used in ordinary households In addition, various functional materials are used in various fields such as sanitary products such as disposable diapers, filters, pet discharge sheets, food additives, daily products, etc. with deodorant, antibacterial and fragrance effects. .

  These functional materials are materials that produce an effect only under conditions suitable for the intended purpose of use, such as magnetic materials, infrared absorbing materials, colored pigments, dyes, fluorescent light emitting materials, and various malodorous components. A considerable number of known materials alone are known, such as a deodorant having a function of decomposing water.

  In order to apply such a functional material to printed matter and products, it is necessary to apply the functional material using an adhesive (fixing agent, binder, adhesive resin, etc.) (hereinafter referred to as “adhesive”). In particular, the object to be applied is often made of various fibers such as natural fibers, synthetic fibers, or chemical fibers.

  A representative article using fibers is paper. Adding a processing or functional material to the paper is a forgery prevention technique. As one of the anti-counterfeiting techniques, there is a so-called penetration technique in which a pattern is formed according to the density or thinness of a sheet and visually recognized under transmitted light. This plowing technique is a classic technique that has existed for a long time because it is possible to determine authenticity in any environment as long as a certain amount of light is present. Nevertheless, it is still used on banknotes around the world.

  Since the plowing technology is given in the paper manufacturing process, a very large manufacturing device like a paper machine is actually required, and it is used as a useful technology to prevent counterfeiting. . As described above, since the anti-counterfeiting technology applied to the paper is not limited to the squeeze technology, it still requires a great investment in manufacturing. It is coming.

  As anti-counterfeiting technology formed on the paper itself, a technology is disclosed in which various functional materials, for example, magnetic powder, fluorescent material, infrared absorbing material, and the like are applied on a paper machine. For example, the present applicant nozzles a substance having a spectral reflectance that is substantially the same as the spectral reflectance of the paper in the visible light region, but is different from the spectral reflectance of the paper in a specific wavelength region in the ultraviolet region or the near infrared region. We are developing a technique for spraying materials suitable for machine reading (for example, ultraviolet absorbing materials, infrared absorbing materials, fluorescent light emitting materials, etc.) on a paper machine by a spray method.

  However, the technology for imparting these functionalities has the problem that, even if functional materials are available, several sheets can be manufactured using a simple device unless mass production is required. there were. Therefore, forgery prevention technology in which the functional material is not applied separately but applied to the fiber itself has been effective.

  As one of the anti-counterfeiting techniques applied to the fiber, the present applicant fixed an intermediate color dye such as brown or purple to cellulosic fiber with sodium sulfate, and processed with a fixing agent containing a polyamine condensate as a component. And a colored fiber mixed paper for copy prevention is disclosed in which a colored fiber sheet formed by a paper machine is mixed with a normal paper stock at the paper making stage (see, for example, Patent Document 1).

  In addition, the present applicant uses a nanofiber that has been attracting attention in recent years, and has a technology that uses the fineness of the fiber. The nanofiber thus suspended is used as an ink to print on paper regardless of wet paper or dry paper ( (Patent Document 2), for example.

  The techniques described in Patent Documents 1 and 2 are also anti-counterfeiting techniques using a paper manufacturing technique that cannot be manufactured unless a large investment is made, and both are techniques for processing fibers constituting the paper. As a technology for processing this fiber, it is excellent in water-based dispersibility and can be used in various applications. Therefore, a suspension in which an appropriate amount of cationic resin is mixed with fine cellulose particles obtained by pulverizing wood pulp is sprayed with a spray dryer. A cellulose fine particle aggregate that has been dried and granulated is disclosed (for example, see Patent Document 3).

  Spray drying by this spray dryer method is utilized in various technical fields, and is a well-known technique as a method for granulating materials. In addition to the technique described in Patent Document 3 described above, for example, a magnetic powder used as a raw material for colored magnetic materials such as magnetic color toner and magnetic color ink is provided with a bright white color or a desired color. Disclosed is a colored magnetic powder in which an inorganic pigment is adhered around the magnetic powder by mixing a magnetic powder, an inorganic pigment, an organic solvent and a surface treatment agent into a slurry, and spraying the slurry by a spray dryer method. (For example, see Patent Document 4).

  Moreover, there is an article using a deodorant as another functional material. For example, a liquid-permeable surface sheet, a liquid-impermeable sheet, an absorbent body interposed therebetween, and a deodorizing sheet disposed on the side opposite to the absorbent body with respect to the liquid-impermeable sheet The deodorant sheet is disposed in the body having at least a post-treatment tape among the front body and the back body, and has a smaller area than the body in which the deodorizing sheet is disposed. There is a disposable diaper characterized in that is disposed so as to overlap the absorbent body (see, for example, Patent Document 5).

  The deodorant sheet in this disposable diaper preferably has a three-dimensional structure, a layered structure or a porous structure capable of physically adsorbing odors, and deodorant particles such as activated carbon and zinc oxide are applied to the sheet base material by an adhesive resin. Glued.

JP 08-144195 A Japanese Patent No. 5652797 JP 2013-173861 A Japanese Patent No. 5604694 JP 2010-125127 A

  The technique described in Patent Document 1 is a technique applied to the paper itself, and is difficult to manufacture unless a large investment is made, and also requires a fixing agent to integrate the dye with the fiber. It was. In addition, it is a true / false discrimination element with the naked eye, and it is not a machine reading technique. Furthermore, since more than 20 years have passed since its development, a new anti-counterfeiting technique using fibers. The development of was demanded.

  In addition, nanofibers have recently attracted attention as a technology that can be effectively used in various fields by miniaturizing the fibers. Among them, the technology described in Patent Document 2 is a technique for preventing forgery using nanofibers. Pioneering. However, although the technique of Patent Document 2 is an epoch-making technique in which fibers are applied by a printing method, if the fibers can be made into nanofibers, it can be implemented relatively easily, and the effect of preventing forgery is further increased. Improvement is desired.

  Therefore, as another technique for finely processing the fiber, the technique that the applicant has focused on is spray drying using a spray dryer. By utilizing the spray drying of this technique, as in the technique of Patent Document 2 described above, it is possible to apply the particulate microfibers not only in the papermaking process but also in the printing process.

  As described above, this spray drying technique has already been used in various fields. However, the technique described in Patent Document 3 is a technique aimed at improving aqueous dispersibility in the same papermaking field. Therefore, it could not be used as anti-counterfeiting technology.

  Further, although the technique described in Patent Document 4 is a kind of functional material called magnetism, it is a technique for the purpose of improving the color of toner and ink, and the functionality as anti-counterfeiting technique was also sought. It was not a thing.

  In the technique described in Patent Document 5, as described above, deodorant particles are used as the functional material, but in order to adhere to the sheet base material, it must be adhered by an adhesive resin. It is said that urethane resin is suitable for this adhesive resin, but in order to manufacture urethane resin, organic diisocyanate compound and polymer diol compound are reacted to synthesize urethane prepolymer, and further chain extension It is necessary to react an agent and a reaction terminator. As described above, in order to bond the deodorant particles, an adhesive resin is required, and in order to manufacture the adhesive resin, another process and material are required.

  Temporarily, when applying a deodorant to discharge sheets such as paper diapers and pets, it may be performed by spraying, dripping or transferring without using an adhesive, Since it has not been firmly fixed, a functional material that has been removed by the time it is actually used may be generated, and the desired function may not be exhibited.

  The present invention is intended to solve the above-described problems, and does not simply apply a functional material to an article such as paper made of various fibers, but at least a functional material is applied to a fiber that is a raw material of paper. By mixing one or more, a particulate cellulose composite having a high affinity with various fibrous articles without using an adhesive and a method for producing the same are provided.

  The present invention relates to a cellulose nanofiber having a fiber width of 2 nm to 10 μm produced from wood or non-wood pulp, and having an average circularity of 0.7 or more and less than 1.0, and at least one functional material Is a particulate cellulose composite.

  In addition, the particulate cellulose composite of the present invention is characterized in that the average particle size is 0.1 μm to 30 μm.

  The present invention is also characterized in that it is a paper containing the particulate cellulose composite of the present invention.

  The present invention also includes a suspension containing cellulose nanofibers prepared in advance, a functional material mixing step of mixing a predetermined amount of at least one functional material, and a suspension in which the functional material is mixed. It is a manufacturing method of the particulate cellulose composite provided with the powdering process processed into a particle form by the spray-drying method.

  The method for producing a particulate cellulose composite of the present invention can integrate various functional materials and cellulose nanofibers without requiring an adhesive.

  The particulate cellulose composite of the present invention has high hydrophilicity because cellulose having a large number of hydroxyl groups is a main material, and thus has good dispersibility in water, and is compatible with various articles composed of natural fibers and chemical fibers. High nature.

  Moreover, since the particulate cellulose composite of the present invention is an aggregate in which a plurality of cellulose nanofibers are hydrogen-bonded, it is not defibrated even when immersed in water or the like.

  Further, since the particulate cellulose composite of the present invention has a spherical shape, it has good fluidity as a powder and can be easily distinguished from fibers when applied to paper.

  Moreover, since the particulate cellulose composite of the present invention uses cellulose nanofibers prepared from natural fibers, it becomes an environment-friendly type.

Illustration of particulate cellulose composite Electron micrograph of particulate cellulose composite Diagram of fiber morphology by manufacturing method of particulate cellulose composite Flow chart of manufacturing process of particulate cellulose composite Electron micrograph of particulate cellulose composite Particle size distribution chart of particulate cellulose composite Area circularity distribution map of particulate cellulose composite Electron micrograph of particulate cellulose composite

  DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below, and includes various other embodiments within the scope of the technical idea described in the scope of claims.

  FIG. 1 is a schematic diagram showing an example of a particulate cellulose composite (hereinafter referred to as “composite”) (1) according to the first embodiment of the present invention. The composite (1) is composed of one or more cellulose nanofibers (2) and one or more functional materials (3), and has a spherical shape.

  The cellulose nanofibers (2) in the composite (1) are integrated with each other by hydrogen bonding. Moreover, the functional material (3) is embraced by the cellulose nanofiber (2) and integrated.

  This composite (1) has a particle size (volume basis) of generally 0.1 μm to 30 μm and an area circularity of 0.7 to 1.0. The aspect ratio has a distribution of 0.3 to 1.0. However, the particle size is left to the size of the functional material to be used, and the fiber width of the cellulose nanofiber is 2 nm to 10 μm as will be described later. Will not be able to. The lower limit is about 0.1 μm in the present specification because the pigment is used. However, depending on the type of the functional material, a smaller particle size can be obtained. The lower limit is not particularly limited as long as it can contain a functional material, not limited to 1 μm.

  Here, the area circularity is a ratio of the circumference of a circle having the same area as the projected object and the square of the perimeter of the object, and the true circle is 1, and the value is increased when moving away from the circle. Get smaller. The aspect ratio is the ratio of the minor axis diameter to the major axis diameter of the particle, and is an equation for calculating the aspect ratio = minor axis diameter / major axis diameter. The value of the aspect ratio is 0 to 1, the perfect circle is 1, and the value becomes lower as it is elongated.

  The composite (1) is a dry powder, and the moisture content of the composite (1) conditioned at room temperature of 23 ° C. and relative humidity of 50% for 4 hours or more is about 10% or less. This water | moisture content is what the cellulose of the composite (1) absorbed.

  FIG. 2A is an overall photograph of the composite (1) observed with a scanning electron microscope. FIG. 2 (b) is an enlarged photograph of the single composite (1) in FIG. 2 (a) observed with a scanning electron microscope. When observing FIG. 2 (a), it is possible to observe fibers in a fiber shape that is not spherical in part, but it can be confirmed that most of the fibers are spherical (particulate) masses. As described above, the composite (1) in the present invention is a spherical (particulate) mass. FIG.2 (b) is an enlarged photograph figure of a particulate cellulose composite (1), and it can observe a mode that a fine fiber is integrated in the state of a string.

  Next, how this complex (1) is produced will be described with reference to FIG.

  FIG. 3 is a schematic view showing a fiber form by the method for producing the composite (1). FIG. 3A shows one plant-derived natural fiber (4). The natural fiber of FIG. 3 (a) is defibrated into the cellulose nanofiber (2) shown in FIG. 3 (b), and as shown in FIG. 3 (c), the cellulose nanofiber (2), water and one or more types After preparing the composite material suspension (5) in which the functional material (3) is mixed, it is processed using a spray-drying method using a known spray-drying device, so that the cellulose nanofiber (2) itself is processed before processing. However, after processing, as shown in FIG. 3 (d), several cellulose nanofibers (5) became a string-like lump, and the functional material (3) It becomes the particulate cellulose composite (1) in which is entrained. In addition, the method of fibrillating the natural fiber (4) into the cellulose nanofiber (2) will be described later.

  The cellulose nanofiber (2) in the composite (1) is a fiber mainly composed of cellulose, and the natural fiber (4) is fibrillated to a fiber width of 2 nm to 10 μm, preferably 2 nm to 1 μm. Natural fibers (4) are made from various wood-based raw materials such as LBKP, NBKP, SP, LUKP, NUKP, and other chemical pulps, GP, TMP, CTMP, and other mechanical pulps, recycled paper, etc., rice straw, straw, abaca, Non-wood pulp made by cooking non-wood fibers such as cotton, kenaf, honey or bamboo, bagasse, hemp, etc., if necessary, bleaching treatment, selective processing, etc. Even if these fibers are used alone It may be used as a mixture. The fiber forms such as fiber length and fiber width of the natural fiber (4) are not particularly limited.

  The fiber length of the cellulose nanofiber (2) is not particularly limited, but the fiber length is preferably shorter. When the fiber length is long, even if it is processed by spray drying, it does not become a lump-like lump, maintains the fibrous form as it is, and cannot incorporate the functional material (3). Therefore, the fiber length of the cellulose nanofiber (2) is preferably less than 500 μm.

  Here, defibration means unraveling the natural fiber (4) mainly composed of cellulose up to several micro or nanofibril units. Usually, the plant-derived natural fiber (4) is an aggregate of cellulose nanofibrils composed of 30 to 50 cellulose molecules and having a fiber width of about 2 nm to 5 nm. Cellulose microfibrils are firmly bonded by an infinite number of hydrogen bonds. However, by performing physical or chemical treatment, cellulose microfibrils can be unraveled into several units of cellulose micro or nanofibrils in the form of fibers.

  As a method of defibration from natural fiber (4) to cellulose nanofiber (2), in the physical method, defibration by mechanical force using a grinder, refiner, high-pressure homogenizer, microfluidizer (opposing jet collision method), etc. In addition, there is a method of atomizing by adding an organic solvent to mechanical grinding by a dry ball mill. As chemical methods, there are a method of removing non-crystalline portions of cellulose fibers by sulfuric acid treatment, a method of introducing a carboxyl group only on the surface of crystalline cellulose nanofibrils by oxidation treatment, and highly dispersing by molecular chain repulsion. These methods are all known, and in the present invention, the cellulose nanofiber (2) can be produced by these known methods.

  The functional material (3) in the composite (1) is a material other than cellulose, and is an inorganic material or an organic material. By integrating with materials other than cellulose, it can have functions and effects that cellulose does not have. As the functional material (3), one kind may be used alone, or two or more kinds of functional materials (3) may be mixed and used.

  Functional materials (3) include, for example, papermaking fillers, colored pigments, white pigments, inorganic pigments, organic pigments, extender pigments, pearl pigments, fluorescent pigments, colorless fluorescent pigments, phosphorescent materials, magnetic materials, and infrared transmitting materials , Infrared absorbing materials, conductive materials, resin bead pigments, colored dyes, fluorescent dyes, UV shielding materials, paper making chemicals, dry paper strength agents, wet paper strength agents, sizing agents, aluminum sulfate, bulking agents, antiseptics There are agents. Also, deodorizing ingredients such as catechin, tannin, flavonoid, polyphenol, cationic surfactants such as benzalkonium chloride, dialkyldimethylammonium chloride, alkyltrimethylammonium chloride, alkyldimethylamine oxide, alkyldiaminoethylglycine hydrochloride, alkyl There are deodorants having antibacterial components such as amphoteric surfactants such as dimethylaminoacetic acid betaine and fragrances having a predetermined fragrance. Therefore, the functional material in the present invention is not particularly limited as long as it is a material that exhibits a predetermined function in accordance with the intended use.

  The size of the functional material (3) is preferably smaller than the particle size of the composite (1). For example, since the particle diameter (volume basis) of the composite (1) is a distribution of 0.1 μm to 30 μm, a size of less than 30 μm is preferable. The shape of the functional material (3) is not particularly limited, and may be any shape such as a particle shape, a rod shape, a needle shape, a spindle shape, and a thin plate shape.

  The composite (1) in the present invention is formed by a spray drying method using a spray drying apparatus which is a known technique in the state of FIG.

  In general, the spray drying method using a spray drying apparatus is a drying method capable of instantly drying a liquid raw material such as a solution or a slurry into particles. This is a method of drying in a short time by spraying a liquid raw material in a drying chamber with a atomizer, increasing the surface area by atomizing the liquid material, and continuously contacting with hot air. Spherical particles can be formed under the influence of the surface tension of the solvent of the liquid raw material. Since spherical dry particles can be obtained, the particles have good fluidity. The spraying method mainly includes a rotary atomizer method and a nozzle method, but in order to produce the composite (1) of the present invention, a nozzle method suitable for granulation with a particle diameter of 30 μm or less is more desirable. .

(Production method)
Next, the manufacturing method of the composite_body | complex (1) of this invention is demonstrated based on the flowchart of the manufacturing process of FIG.

  First, as Step 1, a fiber suspension is prepared by mixing a predetermined amount of natural fiber (4) and a predetermined amount of water in order to convert natural fiber (4) into cellulose nanofiber (2). About the ratio of the natural fiber (4) and water in this process, it is about 0.1%-4% as solid content concentration of a natural fiber (4).

  Next, cellulose nanofiber (2) is produced using Step 2 as the fiber suspension produced in Step 1. As described above, the specific production method may be defibrated by a physical method or a chemical method.

  Next, as Step 3, a composite material suspension (5) is prepared by mixing the cellulose nanofibers (2) prepared in Step 2, water, and a predetermined functional material (3) to be used. About each compounding ratio here, the solid content concentration of cellulose nanofiber (2) is preferably about 0.1% to 4%, and the functional material (3) is solid content of cellulose nanofiber (2). It is in the range of 0.01% to 50% with respect to the weight.

  Finally, as Step 4, the composite material suspension (5) prepared in Step 3 is formed into particles by a known spray drying method.

  Since the produced composite (1) is mostly formed of fibers, it has a strong affinity for paper using natural fibers, products using chemical fibers, and the like, and particularly uses an adhesive. Even if it does not exist, it becomes possible to provide a functional material.

  As described above, since the functional material in the present invention includes all materials that exhibit a predetermined function in accordance with the intended use, the composite produced by using such a production method includes various fibers and Utilizing strong fixation by hydrogen bonding, diapers, antibacterial sheets and other sanitary goods, filters with deodorant, antibacterial and aroma functions, paper, non-woven fabric, rubber, plastic fillers, food additives, cosmetics Furthermore, it is also effective in pharmaceuticals, and functional materials can be firmly established in various fields regardless of the field.

  Hereinafter, the composite (1) in the present invention will be described in detail using examples, but is not limited to the following examples, and any technical category described in the scope of claims. Needless to say, it can be changed as appropriate.

  For natural fiber (4), LBKP, which is wood fiber, is used. A fiber suspension with a solid content concentration of 2% in which natural fiber (4) is mixed with water is used to obtain a fiber width of about 2%. Cellulose nanofibers (2) of 2 nm to 1 μm were produced. As the grinder device, a super mas colloider, manufactured by Masuko Sangyo Co., Ltd., was used, and the pass treatment was performed 6 times with this device. The grindstone used in the grinder apparatus was a standard grindstone for soft raw materials (model: MKE, 46 mesh). The produced cellulose nanofiber (2) is in a state of an aqueous suspension, and the solid content concentration is 2%. The average fiber length of the cellulose nanofiber (2) was about 200 μm, and the fiber width was a distribution of 18 nm to 0.3 μm.

  To the aqueous suspension of cellulose nanofiber (2) (solid content concentration 2%), two types of functional materials (3), a brown pigment that is an iron oxide pigment and a colorless fluorescent pigment, are added to form a composite A material suspension (5) was prepared. As for the addition rate, 0.5% of the brown pigment and 5% of the colorless fluorescent pigment were added with respect to the solid content weight of the cellulose nanofiber (2). After the addition, the mixture was stirred for about 10 minutes, and the stirring was terminated after confirming that there was no unevenness. The average particle size of the brown pigment is 0.5 μm, and the average particle size of the colorless fluorescent pigment is 1.5 μm.

  Next, the composite material suspension (5) of the cellulose nanofiber (2) to which two kinds of functional materials (3) were added was spray-dried by a spray drying apparatus. As the spray drying apparatus, a turning type spray dryer having a model number TR160 manufactured by Pris Co., Ltd. was used. The spraying method was a two-fluid nozzle method, and two 90-type nozzles were used. The raw material supply rate as the spray drying condition was about 2.8 kg / h, the inlet temperature of the drying air was 150 ° C., the outlet temperature was 75 ° C., and the spray air pressure was 0.5 MPa.

  FIG. 5 shows an electron micrograph of the particulate cellulose composite (1) obtained by spray drying. Fig.5 (a) is one photograph of a composite_body | complex (1), FIG.5 (b) is a photograph which expanded a part of Fig.5 (a). As shown in FIG.5 (b), the mode that the fluorescent pigment which is a functional material (3) adheres to a part of composite_body | complex (1), and is integrated with the cellulose nanofiber (2) is observed.

  FIG. 6 shows a volume-based particle size distribution diagram of the composite (1) obtained by spray drying. The particle size distribution was about 3 μm to about 30 μm, and the particle size (volume basis) D50 was 13.0 μm. D50 is also called a median diameter, and when the particle diameter is divided into two, it means a diameter or a value in which the larger side and the smaller side are equal.

  In FIG. 7, the area circularity distribution map of the composite_body | complex (1) obtained by spray drying is shown. The area circularity was a distribution of about 0.6 to 0.99. The area circularity D50 was 0.88.

  Moreover, the aspect ratio of the composite (1) obtained by spray drying was a distribution of 0.3 to 1.0, and the aspect ratio D50 was 0.76.

  Next, when the composite (1) obtained by spray drying was visually observed, it was confirmed that it was colored with the color of the brown pigment. Moreover, when the ultraviolet lamp was irradiated, it was confirmed that fluorescence was emitted in green.

  Finally, in order to evaluate the fastness of the composite (1), it was immersed in water for 6 months. FIG. 8 is an electron micrograph of the immersed composite (1) taken out and air dried. Even when immersed in water for 6 months, it maintained a spherical shape and did not return to the original cellulose nanofiber (2). Therefore, once the composite (1) is produced, although it is a lump of fibers, it does not separate into each cellulose nanofiber (2) even when immersed in water, and thus is firmly bonded. Can be used.

DESCRIPTION OF SYMBOLS 1 Particulate cellulose composite 2 Cellulose nanofiber 3 Functional material 4 Natural fiber 5 Composite material suspension

Claims (4)

Particles containing a plurality of cellulose nanofibers made of wood or non-wood pulp and having a fiber width of 2 nm to 10 μm and having an average circularity of 0.7 or more and less than 1.0 and containing at least one functional material -Like cellulose composite. The particulate cellulose composite according to claim 1, wherein the particulate cellulose composite has an average particle size of 0.1 to 30 µm. A paper containing the particulate cellulose composite according to claim 1. A suspension containing cellulose nanofibers prepared in advance and a functional material mixing step of mixing a predetermined amount of at least one functional material;
A method for producing a particulate cellulose composite, comprising a pulverization step of processing the suspension mixed with the functional material into particles by a spray drying method.

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