Method for producing regenerated cellulose-derived cellulose dispersion, method for producing regenerated cellulose-derived cellulose molded body, regenerated cellulose-derived cellulose beads, and cosmetic material

Abstract

[Problem] Provided are: a method for producing a regenerated cellulose-derived cellulose dispersion or a regenerated cellulose-derived cellulose molded body capable of suppressing swelling in alkali and deterioration of whiteness over time; regenerated cellulose-derived cellulose beads; and a cosmetic material. [Solution] This method comprises: a pulverization step in which a regenerated cellulose is used as a dispersion raw material and the dispersion raw material is pulverized; a depolymerization step in which sodium hypochlorite is added to the pulverized raw material obtained in the pulverization step to reduce a degree of polymerization of the pulverized raw material; a pH adjustment step in which a pH-adjusted cellulose is obtained through a first pH adjustment operation for adjusting the pH of the depolymerized cellulose obtained in the depolymerization step to an alkaline pH of at least 9, a second pH adjustment operation for adjusting the pH of the depolymerized cellulose to an acidic pH of at most 6, and a neutralization operation for neutralizing the depolymerized cellulose; a washing step in which the pH-adjusted cellulose is washed; and a micronization step in which the pH-adjusted cellulose after the washing step is micronized to obtain a cellulose dispersion.

Description

Method for producing a cellulose dispersion derived from regenerated cellulose, method for producing a cellulose molded body derived from regenerated cellulose, cellulose beads derived from regenerated cellulose, and cosmetics

[0001] The present invention relates to a method for producing a cellulose dispersion, a method for producing a cellulose molded body, cellulose beads, and cosmetics containing the same, and particularly to a method for producing a cellulose dispersion derived from regenerated cellulose using regenerated cellulose as a raw material, a method for producing a cellulose molded body derived from regenerated cellulose, cellulose beads derived from regenerated cellulose, and cosmetics.

[0002] Generally, regenerated cellulose is produced by a viscose method or the like in which cellulose fibers contained in raw materials such as pulp are derivatized with chemicals, dissolved in a solvent to form viscose, and then coagulated. The regenerated cellulose thus obtained is derived from natural materials and has properties such as biodegradability, and thus the demand as a product is increasing. It is formed into an appropriate molded body such as a fibrous, film-like, or spherical shape and processed into various products such as paper products, clothing, and sanitary products.

[0003] In recent years, due to problems such as environmental burdens related to waste liquid treatment of chemicals used in the viscose method and exhaust gas treatment generated during the manufacturing process, a method has been proposed in which an ionic liquid is used without performing the viscose method to directly dissolve a cellulose material to produce regenerated cellulose (see, for example, Patent Document 1). This method for producing regenerated cellulose has fewer steps than the viscose method, improves work efficiency, and does not require exhaust gas treatment performed in the viscose method, thereby reducing the environmental burden.

[0004] By the way, with the promotion of sustainable development goals (SDGs), efforts are being actively made to realize a circular society that takes environmental considerations into account in various fields. Recycling, which reuses products and the like discarded after use as resources, is well known as an environmentally considerate effort. Therefore, in products made of regenerated cellulose, utilization as a recycling raw material is also required.

[0005] However, recycled cellulose is difficult to recycle because it does not possess thermoplastic properties and there are limited methods for dissolving it. In particular, cellophane, a film product made from recycled cellulose, sometimes contains softeners such as glycerin as additives. Therefore, when recycling cellophane as a raw material for recycled cellulose using ionic liquids as solvents, the softeners in the cellophane may remain in the ionic liquid, causing process abnormalities. For this reason, cellophane has been disposed of as waste without being recycled.

[0006] Special table 2016-537461 publication

[0007] Therefore, the inventors have found a method for producing a cellulose dispersion or molded article that can use regenerated cellulose, including cellophane and other materials that are difficult to recycle, as a raw material, by including a step of depolymerizing the regenerated cellulose with sodium hypochlorite.

[0008] However, cellulose beads obtained through the depolymerization process with sodium hypochlorite sometimes swell and lose their shape when exposed to alkaline solutions, or their whiteness decreases and they turn yellow over time. Therefore, we discovered that they are difficult to use in applications requiring solvent resistance or in cosmetics where the beads need to retain their color.

[0009] The present invention has been made in view of the above points, and provides a method for producing a cellulose dispersion or molded article derived from regenerated cellulose that can suppress swelling in alkali and decrease in whiteness over time, as well as cellulose beads derived from regenerated cellulose and cosmetics.

[0010] In other words, the first invention relates to a method for producing a cellulose dispersion derived from regenerated cellulose, comprising: a grinding step of grinding the dispersion raw material using regenerated cellulose as the dispersion raw material; a depolymerization step of adding sodium hypochlorite to the grinding raw material obtained in the grinding step to reduce the degree of polymerization of the grinding raw material; a pH adjustment step of obtaining pH-adjusted cellulose by adjusting the pH of the depolymerized cellulose obtained in the depolymerization step to an alkaline state of 9 or higher; a second pH adjustment step of adjusting the pH to an acidic state of 6 or lower after the first pH adjustment step; and a neutralization step of neutralizing the pH-adjusted cellulose after the second pH adjustment step; a washing step of washing the pH-adjusted cellulose; and a micronization step of micronizing the pH-adjusted cellulose after the washing step to obtain a cellulose dispersion.

[0011] The second invention relates to a method for producing a cellulose dispersion derived from regenerated cellulose, wherein, in the depolymerization step, the degree of polymerization of the pulverized raw material is reduced by sodium hypochlorite with an effective chlorine concentration of 0.50 to 0.85%.

[0012] The third invention relates to a method for producing a cellulose dispersion derived from regenerated cellulose, wherein, in the first or second invention, the first pH adjustment operation includes adding sodium borohydride in an amount of 2% or less relative to the pulverized raw material.

[0013] The fourth invention relates to a method for producing a cellulose dispersion derived from regenerated cellulose, comprising a separation step in the first or second invention, in which coarse particles with a particle size of 10 μm or more are removed from the cellulose dispersion, wherein the solid content yield of the finely milled cellulose after the separation step is 80% or more compared to the cellulose before the separation step.

[0014] The fifth invention relates to a method for producing a regenerated cellulose-derived cellulose molded article, which includes a molding step of drying and molding the cellulose dispersion obtained by the manufacturing method of the first invention to obtain a regenerated cellulose-derived cellulose molded article.

[0015] The sixth invention relates to a method for producing a cellulose molded article derived from regenerated cellulose, wherein, in the fifth invention, the degree of polymerization of the pulverized raw material is reduced by sodium hypochlorite with an effective chlorine concentration of 0.50 to 0.85% in the depolymerization step.

[0016] The seventh invention relates to a cellulose molded article obtained by the manufacturing method described in the fifth or sixth invention, wherein the cellulose molded article is a cellulose bead, and the cellulose bead is a regenerated cellulose-derived cellulose bead having a swelling rate of 200% or less when immersed in a 3% by weight sodium hydroxide aqueous solution for 24 hours.

[0017] The eighth invention relates to a cellulose molded article obtained by the manufacturing method described in the sixth invention, wherein the cellulose molded article is a cellulose bead, and the cellulose bead has a whiteness of 80% or more after being heated at 80°C for 15 hours, and is derived from regenerated cellulose.

[0018] The ninth invention relates to regenerated cellulose-derived cellulose beads of the seventh invention, wherein the surface of the regenerated cellulose-derived cellulose beads is coated with a surface treatment agent.

[0019] The tenth invention relates to regenerated cellulose-derived cellulose beads of the eighth invention, wherein the surface of the regenerated cellulose-derived cellulose beads is coated with a surface treatment agent.

[0020] The eleventh invention relates to cellulose beads derived from regenerated cellulose, wherein the surface treatment agent in the ninth invention consists of at least one of the following: a wax-based treatment agent, a synthetic resin-based treatment agent, a chromium complex salt-based treatment agent, a fluorine-based treatment agent, a metal soap-based treatment agent, a cationic surfactant, a silicone-based treatment agent, or an amino acid-based treatment agent.

[0021] The twelfth invention relates to cellulose beads derived from regenerated cellulose, wherein the surface treatment agent in the tenth invention consists of at least one of the following: a wax-based treatment agent, a synthetic resin-based treatment agent, a chromium complex salt-based treatment agent, a fluorine-based treatment agent, a metal soap-based treatment agent, a cationic surfactant, a silicone-based treatment agent, or an amino acid-based treatment agent.

[0022] The thirteenth invention relates to a cosmetic composition containing cellulose beads of the seventh invention.

[0023] The fourteenth invention relates to a cosmetic composition containing cellulose beads according to the ninth invention.

[0024] The 15th invention relates to a cosmetic composition containing cellulose beads of the 11th invention.

[0025] The sixteenth invention relates to a cosmetic composition containing cellulose beads according to the eighth, tenth, or twelfth invention.

[0026] The method for producing a cellulose dispersion derived from regenerated cellulose according to the first invention includes: a grinding step of grinding the dispersion raw material using regenerated cellulose as the dispersion raw material; a depolymerization step of adding sodium hypochlorite to the grinding raw material obtained in the grinding step to reduce the degree of polymerization of the grinding raw material; a pH adjustment step of obtaining pH-adjusted cellulose by adjusting the pH of the depolymerized cellulose obtained in the depolymerization step to an alkaline pH of 9 or higher; a second pH adjustment step of adjusting the pH to an acidic pH of 6 or lower after the first pH adjustment step; and a neutralization step of neutralizing the pH after the second pH adjustment step; a washing step of washing the pH-adjusted cellulose; and a micronization step of micronizing the pH-adjusted cellulose after the washing step to obtain a cellulose dispersion. As a result, a cellulose dispersion using regenerated cellulose as the raw material can be obtained, and furthermore, swelling of the (micronized) cellulose in the cellulose dispersion due to alkaline solutions and a decrease in whiteness over time can be suppressed.

[0027] According to the method for producing a cellulose dispersion derived from regenerated cellulose in the second invention, in the first invention, the degree of polymerization of the pulverized raw material is reduced by sodium hypochlorite with an effective chlorine concentration of 0.50 to 0.85% in the depolymerization step, so that the yield can be improved while maintaining good moldability, and swelling of the (finely ground) cellulose in the cellulose dispersion due to the alkaline solution and the decrease in whiteness over time can be further suppressed.

[0028] According to the method for producing a cellulose dispersion derived from regenerated cellulose according to the third invention, in the first or second invention, the first pH adjustment operation includes adding sodium borohydride in an amount of 2% or less relative to the pulverized raw material, thereby more effectively suppressing swelling of the (finely ground) cellulose in the cellulose dispersion due to the alkaline solvent and the decrease in whiteness over time.

[0029] According to the method for producing a cellulose dispersion derived from regenerated cellulose according to the fourth invention, the first or second invention includes a separation step of removing coarse particles with a particle size of 10 μm or more from the cellulose dispersion, and since the solid content yield of the finely milled cellulose after the separation step is 80% or more compared to before the separation step, the production efficiency is improved and it is economically superior.

[0030] The method for producing a molded cellulose article derived from regenerated cellulose according to the fifth invention includes a molding step of drying and molding the cellulose dispersion obtained by the production method of the first invention to obtain a molded cellulose article derived from regenerated cellulose. Therefore, it is possible to obtain a molded cellulose article derived from regenerated cellulose in which swelling due to alkaline solutions and a decrease in whiteness over time are suppressed.

[0031] According to the method for producing a cellulose molded article derived from regenerated cellulose in the sixth invention, in the fifth invention, the degree of polymerization of the pulverized raw material is reduced by sodium hypochlorite with an effective chlorine concentration of 0.50 to 0.85% in the depolymerization step, so that a cellulose molded article derived from regenerated cellulose can be obtained in which swelling due to alkaline solutions and the decrease in whiteness over time are further suppressed.

[0032] The cellulose beads derived from regenerated cellulose according to the seventh invention are a cellulose molded body obtained by the manufacturing method described in the fifth or sixth invention, wherein the cellulose molded body is a cellulose bead, and the swelling rate of the cellulose beads when immersed in a 3% by weight sodium hydroxide aqueous solution for 24 hours is 200% or less, thus suppressing the swelling of the cellulose beads derived from regenerated cellulose by alkaline solutions.

[0033] The cellulose beads derived from regenerated cellulose according to the eighth invention are a cellulose molded body obtained by the manufacturing method described in the sixth invention, wherein the cellulose molded body is a cellulose bead, and the whiteness of the cellulose beads after heating at 80°C for 15 hours is 80% or more, thus suppressing the decrease in the whiteness of the cellulose beads derived from regenerated cellulose.

[0034] The cellulose beads derived from regenerated cellulose according to the ninth invention have their surfaces coated with a surface treatment agent, allowing them to possess physical properties suitable for their intended use. Furthermore, by treating the surface of the cellulose beads, good dispersibility can be imparted not only to hydrophilic materials but also to hydrophobic dispersion media and hydrophobic resins.

[0035] The cellulose beads derived from regenerated cellulose according to the tenth invention are made possible because the surface of the cellulose beads derived from regenerated cellulose according to the eighth invention is coated with a surface treatment agent, thereby providing physical properties suitable for the application. Furthermore, by treating the surface of the cellulose beads, good dispersibility can be imparted not only to hydrophilic materials but also to hydrophobic dispersion media and hydrophobic resins.

[0036] The cellulose beads derived from regenerated cellulose according to the 11th invention, in the 9th invention, have a surface treatment agent consisting of at least one of the following: a wax-based treatment agent, a synthetic resin-based treatment agent, a chromium complex salt-based treatment agent, a fluorine-based treatment agent, a metal soap-based treatment agent, a cationic surfactant, a silicone-based treatment agent, or an amino acid-based treatment agent, thus allowing them to possess physical properties suitable for their intended use. Furthermore, by treating the surface of the cellulose beads, good dispersibility can be imparted not only to hydrophilic materials but also to hydrophobic dispersion media and hydrophobic resins.

[0037] The cellulose beads derived from regenerated cellulose according to the 12th invention, in the 10th invention, have a surface treatment agent consisting of at least one of the following: a wax-based treatment agent, a synthetic resin-based treatment agent, a chromium complex salt-based treatment agent, a fluorine-based treatment agent, a metal soap-based treatment agent, a cationic surfactant, a silicone-based treatment agent, or an amino acid-based treatment agent, so that they can be made to have physical properties according to their intended use. Furthermore, by treating the surface of the cellulose beads, good dispersibility can be imparted not only to hydrophilic materials but also to hydrophobic dispersion media and hydrophobic resins.

[0038] The cosmetic composition according to the 13th invention contains cellulose beads according to the 7th invention, and can therefore be used as a substitute for microplastics, thus contributing to addressing environmental issues.

[0039] The cosmetic composition according to the 14th invention contains cellulose beads according to the 9th invention, and can therefore be used as a substitute for microplastics, thus contributing to addressing environmental issues.

[0040] The cosmetic composition according to the 15th invention contains cellulose beads according to the 11th invention, and can therefore be used as a substitute for microplastics, thus contributing to addressing environmental issues.

[0041] The cosmetic composition according to the 16th invention contains cellulose beads according to the 8th, 10th, and 12th inventions, and can therefore be used as a substitute for microplastics, thus contributing to environmental protection.

[0042] This is a schematic process diagram of a method for producing a molded cellulose article derived from regenerated cellulose according to one embodiment of the present invention.

[0043] The method for producing a cellulose molded article derived from regenerated cellulose, as shown in the schematic process diagram of Figure 1, is a method for producing a cellulose molded article using regenerated cellulose as a raw material via a cellulose dispersion. This method for producing a cellulose molded article includes a grinding step (S1), a depolymerization step (S2), a pH adjustment step (S3), a washing step (S4), a micronization step (S5), a separation step (S6), a molding step (S7), and a collection step (S8).

[0044] Regenerated cellulose is the main raw material (molded body raw material) for cellulose dispersions or molded bodies produced by the manufacturing method of the present invention. The lower the degree of polymerization of the regenerated cellulose, the easier it is to defibrillate the cellulose and process it, thereby improving production efficiency. If the degree of polymerization of the regenerated cellulose is too high, the cellulose becomes difficult to defibrillate, which may make it difficult to manufacture cellulose molded bodies. For this reason, it is desirable that the degree of polymerization of the regenerated cellulose used as a molded body raw material be 600 or less. Generally, the degree of polymerization of regenerated cellulose produced by the viscose method is about 200 to 300, so it is suitable for use as a raw material in the manufacturing method of the present invention. Furthermore, the degree of polymerization of regenerated cellulose obtained by a manufacturing method using a cellulose solvent such as an ionic liquid is about 600, so it is also suitable as a raw material in the manufacturing method of the present invention.

[0045] As the raw material for the dispersion or the molded body, regenerated cellulose can be a material in an appropriate form such as fibrous, film-like, spherical, etc. manufactured by a known production method, or a regenerated cellulose product obtained by processing the manufactured regenerated cellulose. These regenerated celluloses are type II celluloses having a type II crystal structure.

[0046] Examples of the production method of regenerated cellulose include, for example, a method of chemically derivatizing cellulose fibers such as the viscose method and then dissolving them with a solvent or the like, and a method of dissolving cellulose fibers with an ionic liquid. Examples of regenerated cellulose products include paper products, clothing products, sanitary products, etc. processed from molded bodies such as rayon, cellophane, and cellulose beads.

[0047] When using regenerated cellulose as the raw material for the dispersion or the molded body, from the perspective of reducing the environmental load, it is preferable to use products of regenerated cellulose as the recycling raw material. The recycling raw material of regenerated cellulose includes waste materials generated in the manufacturing process of molded bodies and products of regenerated cellulose. Since products and waste materials of regenerated cellulose were materials that were conventionally difficult to recycle and were disposed of as waste, using them as recycling raw materials can greatly contribute to reducing the environmental load.

[0048] The pulverization step (S1) is a step of pulverizing regenerated cellulose, which is the raw material for the dispersion or the molded body, to obtain a pulverized raw material. This pulverization step aims to improve the reactivity of the regenerated cellulose (pulverized raw material) in the subsequent depolymerization step (S2) by pulverizing and making the regenerated cellulose of the molded body raw material finer. The pulverized raw material obtained in the pulverization step is preferably pulverized so that the regenerated cellulose has a size of 500 μm or less. The size of the regenerated cellulose is measured according to JIS Z 8825 (2013) by a laser diffraction / scattering type particle size distribution measuring device. If the pulverized regenerated cellulose is too large, the reactivity in the subsequent depolymerization step (S2) may be insufficient, resulting in a decrease in productivity. In this pulverization step, known pulverization methods such as dry pulverization and wet pulverization can be appropriately used.

[0049] The depolymerization step (S2) is a step in which the pulverized raw material obtained in the pulverization step is depolymerized to obtain depolymerized cellulose with a reduced degree of polymerization. This depolymerization step weakens the structure of the pulverized regenerated cellulose by depolymerizing the pulverized raw material, making the cellulose more easily defibrillated (depolymerized cellulose). The degree of polymerization of the depolymerized cellulose obtained in the depolymerization step is adjusted using sodium hypochlorite. If the degree of polymerization of the depolymerized cellulose is too high, the defibrillability in the finer processing step (S5) described later may be insufficient, potentially reducing productivity.

[0050] In the depolymerization process, sodium hypochlorite is used to depolymerize the pulverized raw material. Sodium hypochlorite oxidizes the hydroxyl groups at positions 2 and 3 of cellulose, causing a β-alkoxy elimination reaction due to the carbonyl group, which depolymerizes the cellulose. Sodium hypochlorite is suitable for use because it is easy to handle and the degree of polymerization of regenerated cellulose can be efficiently reduced by controlling the pH and temperature.

[0051] For the pH adjustment process described later, the amount of sodium hypochlorite added should be adjusted so that the effective chlorine concentration is 0.50 to 0.90%, more preferably 0.50 to 0.85%. By adjusting the effective chlorine concentration to this range, the yield of finely milled cellulose is improved, finely milled cellulose suitable for molding can be obtained, and it is effective in suppressing swelling of the cellulose molded body by alkaline solution and suppressing the decrease in whiteness over time.

[0052] The pH adjustment step (S3) is a step in which the pH of the depolymerized cellulose obtained in the depolymerization step is adjusted to obtain pH-adjusted cellulose. In this pH adjustment step, the pH of the depolymerized cellulose is adjusted by first making it alkaline, then acidic, and finally neutral. The depolymerized cellulose that has gone through the depolymerization step is weakly acidic, and the first pH adjustment operation makes it alkaline depolymerized cellulose with a pH of 9 or higher. In the first pH adjustment operation, alkali is added, and if necessary, a reducing agent is added.

[0053] The alkali used in the first pH adjustment step is, for example, an alkali metal hydroxide such as sodium hydroxide. When depolymerized cellulose is washed with alkali, it is thought that the defibrillation of cellulose progresses, and trace amounts of chlorine bound to the cellulose molecules are removed. At this stage, the alkaline depolymerized cellulose is in a viscous, gel-like state. The pH is preferably made strongly alkaline in the first pH adjustment step, and a pH of 9 or higher, preferably 10 or higher, can be expected to lead to a more stable reaction.

[0054] The reducing agent used in the first pH adjustment step is sodium borohydride. Depolymerized cellulose, after undergoing the depolymerization process, has unsaturated carbonyl groups. By adding sodium borohydride to the depolymerized cellulose, the unsaturated carbonyl groups of the depolymerized cellulose can be reduced and removed. Generally, adding an excess amount of reducing agent allows the oxidation-reduction reaction to proceed smoothly. However, if the amount of reducing agent added is too excessive, a large amount of reducing agent will remain. For these reasons, it is preferable that the amount of sodium borohydride added is 2% or less of the amount of the pulverized raw material.

[0055] The alkaline depolymerized cellulose, adjusted to an alkaline state by the first pH adjustment operation, is then converted to acidic depolymerized cellulose with a pH of 6 or lower by the second pH adjustment operation. The acid used in the second pH adjustment operation is, for example, an inorganic acid such as sulfuric acid or an organic acid such as acetic acid. When alkaline depolymerized cellulose is acid-washed, it is thought that the washing of the cellulose becomes easier compared to the alkaline state, and metal ions bonded to the carboxyl groups present in trace amounts on the cellulose molecules are removed. At this point, the acidic depolymerized cellulose becomes a lumpy, semi-solid gel-like substance, making washing for neutralization easier. It is preferable to make the pH strongly acidic in the second pH adjustment operation, and a more stable reaction can be expected if the pH is 6 or lower, preferably 2 or lower.

[0056] The acid-depolymerized cellulose, which has been adjusted to an acidic state by the second pH adjustment operation, is neutralized by a neutralization operation to obtain pH-adjusted cellulose. For the neutralization operation, an alkali metal hydroxide such as sodium hydroxide is used, for example. It is preferable that the neutralization operation proceeds slowly so that the acid-depolymerized cellulose does not become alkaline.

[0057] The washing step (S4) is a step in which the pH-adjusted cellulose obtained in the pH adjustment step is washed as appropriate. The washing method for the pH-adjusted cellulose is not particularly limited, but for example, it may be washed with running water in a centrifugal washing machine, a ceramic rotary filter, or a packed column.

[0058] The micronization step (S5) is a step in which the washed pH-adjusted cellulose is defibrated and micronized to obtain a cellulose dispersion containing the micronized cellulose. Defibration of the pH-adjusted cellulose is performed by mechanical (physical) defibration. Mechanical (physical) defibration is performed by known methods such as homogenizers and water jets. The micronized cellulose obtained in this way is in the form of a dispersion of unmodified cellulose fine particles because it is not defibrated using chemicals (chemical defibration).

[0059] Here, since the regenerated cellulose, which is the dispersion or molded product raw material, has its degree of polymerization reduced by the depolymerization process, it can be easily defibrated and micronized even without applying high pressure. Thus, because pH-adjusted cellulose can be easily micronized, it is also advantageous in terms of equipment for the micronization process.

[0060] The micronization of pH-adjusted cellulose may be carried out in multiple stages. For example, by performing preliminary defibration using a mixer followed by main defibration using a homogenizer, uniformly micronized cellulose with small particle sizes can be obtained. Furthermore, preliminary defibration reduces problems such as the pH-adjusted cellulose clogging the defibration equipment, which is significant from the standpoint of equipment protection. Preliminary defibration is carried out using a mixer, refiner, etc., by known methods. The micronization of pH-adjusted cellulose only needs to be reduced to an average particle size of several hundred nanometers, and the processability of the resulting cellulose molded article is excellent when the particle size is around 100 nm to 3 μm, more preferably 1200 nm or less.

[0061] The separation step (S6) is a step in which coarse particles are removed from the cellulose dispersion obtained in the micronization step. Coarse particles refer to cellulose aggregates and other component residues with a particle size of 10 μm or more. Removing coarse particles improves the transparency of the cellulose dispersion and allows for the production of a uniform, highly white cellulose molded product from the cellulose dispersion.

[0062] The finely ground cellulose obtained through the separation process has a solid content yield of 80% or more relative to the amount of cellulose contained in the cellulose dispersion before the separation process, resulting in a very high yield and excellent economic efficiency.

[0063] The molding process (S7) is a process in which the finely milled cellulose obtained in the separation or milling process is dried to obtain a molded body. The finely milled cellulose, which is in the form of a dispersion, is dried by spray drying and aggregated to form a granular (bead) molded body. Since this molded body is molded using regenerated cellulose as the raw material for the molded body, it is a cellulose molded body derived from regenerated cellulose. In the molding process, the viscosity of the finely milled cellulose dispersion, measured using a B-type viscometer under the condition of a shear rate of 4.0 / sec according to JIS Z 8803 (2011), is preferably 15,000 mPa·s or less. If the viscosity of the finely milled cellulose dispersion is higher than 15,000 mPa·s, the fluidity of the solution will decrease, and there is a risk that the liquid supply piping to the spray drying device and the spray drying nozzles will become clogged.

[0064] Furthermore, the conditions for spray drying are an air pressure of 0.025 to 0.6 MPa. If the air pressure for spray drying is insufficient, the cellulose particles will not be properly atomized, resulting in larger particle sizes and a deterioration of physical properties and texture. Also, if the air pressure is higher than 0.6 MPa, the air generator will become excessively large and impractical.

[0065] In the present invention's method for producing a cellulose molded article derived from regenerated cellulose, a collection step (S8) is performed after the molding step (S7) as needed. The collection step is a process of removing unwanted particles from the granular cellulose molded article (cellulose beads) formed in the molding step and recovering a cellulose molded article with suitable particles. The collection means is not particularly limited as long as it is possible to recover the appropriate particles, but collection can be done using known collection means such as a bag filter or a cyclone dust collector.

[0066] Thus, in the manufacturing method of the present invention, the regenerated cellulose used as a raw material for a molded body is ground to an appropriate particle size, for example, 500 μm or less, in a grinding step (S1), the degree of polymerization of the obtained ground raw material is adjusted to an arbitrary degree of polymerization in a depolymerization step (S2), the pH of the depolymerized cellulose is adjusted in a pH adjustment step (S3), the material is washed in a washing step (S4), and a cellulose dispersion is obtained through a micronization step (S5) to further refine the cellulose. If necessary, a separation step (S6) is performed, followed by a molding step (S7) to obtain a cellulose molded body. Therefore, a cellulose dispersion or molded body can be obtained by using regenerated cellulose as a dispersion or raw material for a molded body.

[0067] In particular, since it becomes possible to use cellophane and other materials that were previously considered difficult to recycle as recycled raw materials for molded products, it can significantly contribute to reducing the environmental burden. Furthermore, since this regenerated cellulose-derived cellulose dispersion or molded product is a molded product of unmodified cellulose that has not undergone chemical defibration, it is possible to reduce the amount of environmentally harmful chemicals used compared to conventional cellulose molded products. Moreover, the resulting cellulose dispersion or molded product exhibits suppressed swelling due to alkaline solvents and a decrease in whiteness over time, making it easy to handle and resulting in a cellulose dispersion or molded product with excellent appearance.

[0068] The swelling of the regenerated cellulose-derived cellulose molded article (cellulose beads) of the present invention in an alkaline solvent is defined as follows. When the cellulose beads are immersed in a 3% by weight sodium hydroxide aqueous solution for 24 hours, if the swelling rate is 250% or less, it can be said that the swelling is sufficiently suppressed, and preferably it is 200% or less. If the swelling rate of the cellulose beads in an alkaline solvent is 250% or less, they have excellent processing suitability and are easy to handle without limitations on their applications. A lower swelling rate is more preferable, so if the swelling rate of the cellulose beads in an alkaline solvent is 200% or less, they become even easier to handle and are more suitable as a substitute for existing plastic beads.

[0069] Furthermore, the whiteness of the regenerated cellulose-derived cellulose molded article (cellulose beads) of the present invention over time is defined as follows. After heating the cellulose beads at 80°C for 15 hours, if the whiteness is 75% or higher, it can be said that the decrease in whiteness is sufficiently suppressed, and preferably it is 80% or higher. If the decrease in whiteness of the cellulose beads over time is less than 25%, that is, if the whiteness of the cellulose beads after the change over time is 75% or higher, the change in appearance over time (yellowing) is suppressed, resulting in excellent appearance, and it can be widely used in cosmetics, mixing with resins, and other applications. Furthermore, if the decrease in whiteness of the cellulose beads over time is less than 20%, that is, if the whiteness of the cellulose beads after the change over time is 80% or higher, the appearance is further improved.

[0070] Furthermore, the surface of the regenerated cellulose-derived cellulose molded body (cellulose beads) of the present invention can be coated with a surface treatment agent. The surface treatment agent is selected from at least one of the following: wax-based treatment agents, synthetic resin-based treatment agents, chromium complex salt-based treatment agents, fluorine-based treatment agents, metal soap-based treatment agents, cationic surfactants, silicone-based treatment agents, or amino acid-based treatment agents, and a mixture of several of these may be used. By coating the surface of the cellulose beads with a surface treatment agent, they can be adapted to various dispersion media and can be widely used not only in oil-in-water type liquid foundations but also in water-in-oil type liquid foundations.

[0071] Thus, the cellulose-derived molded articles (cellulose beads) of the present invention exhibit suppressed swelling in alkaline solvents, making them easy to handle and providing stable properties. Furthermore, the decrease in whiteness over time is suppressed, resulting in excellent appearance, making them suitable for use in cosmetics. By being included in cosmetics as a substitute for plastic beads, it becomes possible to reduce the use of microplastics, thereby significantly contributing to the reduction of environmental impact.

[0072] [Preparation of Cellulose Molded Articles Derived from Regenerated Cellulose] The regenerated cellulose molded articles for each of the prototype examples and comparative examples below were prepared under the following conditions according to the process diagram in Figure 1.

[0073] The following raw materials were used as regenerated cellulose: Cellophane film manufactured by the viscose process (manufactured by Futamura Chemical Co., Ltd., "NPU") was used as regenerated cellulose 1 (C1).

[0074] <Prototype Example 1> Regenerated cellulose 1 (C1) was pulverized to 359 μm using a pulverizer (manufactured by Horai Co., Ltd.) (pulverization step). 40 g of the pulverized raw material was mixed with 355 ml of sodium hypochlorite (6.3% solution, effective chlorine concentration 0.58%) and reacted in a 60°C water bath for 50 minutes (depolymerization step). Sodium hydroxide was added to the resulting depolymerized cellulose to adjust the pH to 10.9 (first pH adjustment operation). Then sulfuric acid was added to further adjust the pH to 1.5 (second pH adjustment operation). Sodium hydroxide was added again to neutralize and adjust the pH to 7.0 (neutralization operation) to obtain pH-adjusted cellulose (pH adjustment step). The pH-adjusted cellulose was washed by displacement with deionized water (washing step). After that, 600 ml of deionized water was added to form a dispersion, which was then homogenized under a pressure of 70 MPa using a homogenizer (manufactured by SMT Co., Ltd.) to obtain finely milled cellulose (milling step). The finely ground cellulose was processed in a centrifuge (manufactured by Kokusan Co., Ltd.) at 3200 rpm for 8 minutes to remove the settled coarse particles (separation step). The separated cellulose dispersion was spray-dried using a spray dryer (manufactured by Tokyo Rikakikai Co., Ltd.) at an air pressure of 0.2 MPa (processing volume of 300 ml / hr) (molding step) to obtain the regenerated cellulose-derived cellulose beads of prototype example 1.

[0075] <Prototype Example 2> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used was 7.5% with an effective chlorine concentration of 0.69%, the pH of the first pH adjustment operation was set to 10.5, the pH of the second pH operation to 1.1, and the pH of the neutralization operation to 7.1, and a cellulose molded article derived from regenerated cellulose of Prototype Example 2 was obtained.

[0076] <Prototype Example 3> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used was 8.6% with an effective chlorine concentration of 0.80%, the pH of the first pH adjustment operation was set to 10.7, the pH of the second pH operation to 1.6, and the pH of the neutralization operation to 6.9, to obtain the regenerated cellulose-derived cellulose molded article of Prototype Example 3.

[0077] <Prototype Example 4> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used was 7.5% with an effective chlorine concentration of 0.69%, the pH of the first pH adjustment operation was set to 9.1, the pH of the second pH operation to 5.8, and the pH of the neutralization operation to 6.9, to obtain the regenerated cellulose-derived cellulose molded article of Prototype Example 4.

[0078] <Prototype Example 5> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used was 9.8% with an effective chlorine concentration of 0.90%, the pH of the first pH adjustment operation was set to 10.6, the pH of the second pH operation to 1.5, and the pH of the neutralization operation to 6.9, to obtain the regenerated cellulose-derived cellulose molded article of Prototype Example 5.

[0079] <Prototype Example 6> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used was 5.1% and the effective chlorine concentration was 0.47%, the pH of the first pH adjustment operation was set to 10.9, the pH of the second pH operation was set to 1.6, and the pH of the neutralization operation was set to 7.0, to obtain the regenerated cellulose-derived cellulose molded article of Prototype Example 6.

[0080] <Prototype Example 7> In the depolymerization step, a 7.5% sodium hypochlorite solution was used, with an effective chlorine concentration of 0.69%. In the first pH adjustment operation, sodium hydroxide was added to the obtained depolymerized cellulose to adjust the pH to 11.7, and then 381 mg of sodium borohydride (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and reacted for 30 minutes. The pH in the second pH operation was set to 5.2, and the pH in the neutralization operation was set to 7.1. Except for these points, the procedure was the same as in Prototype Example 1, and the regenerated cellulose-derived molded article of Prototype Example 7 was obtained.

[0081] <Comparative Example 1> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used in the depolymerization step was 7.5%, the effective chlorine concentration was 0.69%, the pH of the first pH adjustment operation was set to 10.8, the pH of the second pH operation was set to 1.36, and the neutralization operation was omitted, to obtain the regenerated cellulose-derived cellulose molded article of Comparative Example 1.

[0082] <Comparative Example 2> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used in the depolymerization step was a 7.5% solution with an effective chlorine concentration of 0.69%, and the pH adjustment step was omitted, to obtain the regenerated cellulose-derived cellulose molded article of Comparative Example 2.

[0083] <Comparative Example 3> The depolymerization step was carried out in the same manner as in Prototype Example 1, except that the sodium hypochlorite solution used in the depolymerization step was a 15.0% solution with an effective chlorine concentration of 1.31%, and the pH adjustment step was omitted, to obtain the regenerated cellulose-derived cellulose molded article of Comparative Example 3.

[0084] For the performance evaluation of each prototype example 1-7 and comparative example 1-3, the amount of cellulose after the separation process was calculated as the solid content yield (%) relative to the amount of cellulose after the micronization process. In addition, the swelling rate (%) with an alkaline solvent was calculated, and the whiteness (%) after heat treatment, the average particle size (nm) of the micronized cellulose, and the average particle size (μm) of the cellulose molded product were measured. The results are shown in Tables 1-2. Examples where measurements were not taken are indicated with "-".

[0085] [Solid Content Yield (%)] The solid content yield was calculated as follows. First, for the prototype and comparative examples, 1.0 g of the dispersion liquid before the separation process was taken into a weighing bottle whose weight had been measured in advance, and dried in a convection dryer heated to 100°C for 2 hours. After drying, it was allowed to cool in a desiccator for 15 minutes, and the weight of the weighing bottle was measured using an electronic balance (Shimadzu Corporation, "AUX220"), and the weight after subtracting the value of the empty bottle was taken as W1. The same process was performed on the dispersion liquid after the separation process, and the weight was taken as W2, and the solid content yield was calculated from the following formula: Solid Content Yield (%) = (W2 / W1) × 100

[0086] [Swelling Rate (%)]. The swelling rate was calculated as follows. First, 0.1 g of cellulose samples from the prototype and comparative examples were immersed in 9.9 g of a 3 wt% sodium hydroxide aqueous solution for 24 hours, and the average particle size (D50) was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac-Bell Co., Ltd., "MT3200II"). Similarly, the average particle size (D50) was measured for cellulose samples dispersed in deionized water at arbitrary concentrations, and the swelling rate was calculated from the following formula. The average particle size (D50) after immersion in sodium hydroxide aqueous solution for 24 hours was defined as P1, and the average particle size (D50) in deionized water was defined as P0. The value of P0 was defined as the average particle size (μm) of the cellulose in the molded product. Swelling Rate (%) = (P1 / P0) × 100

[0087] [Whiteness (%)] Whiteness was measured by placing 10 g of cellulose sample from the prototype and comparative examples into a 500 ml beaker and covering it with a watch glass. The beaker was placed in a convection dryer heated to 80°C and maintained for 15 hours, after which it was removed and the whiteness was measured. Whiteness was measured using a powder whiteness clock (C-130, manufactured by Kett Scientific Research Institute Co., Ltd.) and the whiteness was measured by comparison with a whiteness standard plate using the reflectance measurement method.

[0088] [Average Particle Size] The average particle size (nm) of the micronized cellulose was measured by diluting the cellulose dispersion 100 times with deionized water and using a dynamic light scattering particle size analyzer (Otsuka Electronics Co., Ltd., "nanoSAQLA"). The measurement was performed 150 times, and the average value is recorded. The average particle size (μm) of the cellulose molded product is P0, which was measured for use in calculating the swelling rate (%) mentioned above.

[0089]

[0090]

[0091] [Results and Discussion] When comparing prototypes 1-5 and 7, whose swelling rate and whiteness were measured, with Comparative Example 3, the swelling rate was smaller in all cases, and the whiteness after heating was also higher. From this, it can be understood that the pH adjustment process makes it possible to suppress swelling of the cellulose molded body (beads) due to alkaline solutions and the decrease in whiteness over time. In particular, while the swelling of Comparative Example 3 due to the alkaline solvent exceeded 400%, prototypes 1-5 and 7 all swelled to 200% or less, indicating that the pH adjustment process is very effective in suppressing swelling due to alkaline solvents when forming the cellulose molded body.

[0092] Furthermore, according to prototype example 4, regarding the pH adjustment process, it was shown that if the pH of the depolymerized cellulose in the first pH adjustment operation is acidic at 6 or less, and the pH in the second pH adjustment operation is 9 or higher, it is effective in suppressing swelling due to alkaline solvents and the decrease in whiteness over time.

[0093] Next, examining the solid content yields of prototype examples 1-5 and 7, all were good, exceeding 90%. The solid content yield of Comparative Example 1, in which the neutralization step was omitted, was remarkably low at approximately 25%. This result indicates that the neutralization step improves the yield of cellulose solids. Furthermore, it was shown that going through a pH adjustment step after the depolymerization step facilitates and improves the defibration of cellulose in the defibration step. Since the yield improves due to the reduction in coarse particles separated by the separation step, it is considered that the effective utilization of cellulose becomes possible, especially when the amount of sodium hypochlorite added in the defibration step is small, i.e., when the effective chlorine concentration is low, by going through the pH adjustment step.

[0094] Observing the average particle size of the finely milled cellulose in Prototype Examples 1-6 and Comparative Example 3, it can be seen that the average particle size of the finely milled cellulose decreases as the effective chlorine concentration increases. In Prototype Example 6, because the effective chlorine concentration is low, the average particle size of the finely milled cellulose is large, and it is thought that the amount of cellulose separated and removed in the separation process is large, resulting in a decrease in the solid content yield. In Comparative Example 3, the effective chlorine concentration is high, and the average particle size of the finely milled cellulose is the smallest, but the cellulose molded article obtained from the excessively dispersed finely milled cellulose has a high swelling rate. Of Prototype Examples 1-5, Prototype Example 1 has the largest average particle size of the finely milled cellulose, but the average particle size of the cellulose molded article is about the same, and the moldability is good. It was shown that when the amount of sodium hypochlorite added in the depolymerization process is adjusted to an effective chlorine concentration in the range of 0.50-0.90%, finely milled cellulose with excellent processing suitability for cellulose molded articles can be prepared, and the yield is improved.

[0095] Next, when examining the whiteness of prototypes 1 to 5, prototype 5 was found to have a whiteness of less than 80% compared to the other prototypes. This indicates that adjusting the amount of sodium hypochlorite added in the depolymerization process to an effective chlorine concentration of less than 0.9, preferably 0.85 or less, further suppresses the decrease in whiteness of the cellulose molded article over time.

[0096] Unlike prototypes 1-6, prototype example 7 had sodium borohydride added during the first pH adjustment step. Prototype example 7 had the smallest swelling rate and the highest whiteness among the prototypes. This indicates that adding sodium borohydride during the first pH adjustment step more effectively suppresses swelling due to the alkaline solvent and the decrease in whiteness over time.

[0097] Sodium borohydride acts as a reducing agent, reducing and removing the unsaturated carbonyl groups from depolymerized cellulose. Generally, adding an excess amount of reducing agent facilitates the redox reaction. However, if the amount of reducing agent added is too excessive, a large amount of reducing agent will remain. In prototype example 7, 381 mg of sodium borohydride was added to 40 g of pulverized raw material. From these results, it is considered that the redox reaction proceeds smoothly if the amount of sodium borohydride added is 2% or less of the pulverized raw material.

[0098] The present invention's method for producing cellulose dispersions or molded articles allows for the production of cellulose dispersions or molded articles using regenerated cellulose, including cellophane and other materials that are difficult to recycle, as a raw material. This significantly contributes to reducing environmental impact. Furthermore, the resulting cellulose dispersions or molded articles exhibit stable properties, excellent appearance, and good yield because swelling due to alkaline solvents and a decrease in whiteness over time are suppressed. Therefore, they are promising as alternatives to microplastics and chemically modified cellulose beads used in conventional cosmetics, and can contribute to reducing environmental impact.

Claims

1. A method for producing a cellulose dispersion derived from regenerated cellulose, comprising: a grinding step of grinding the dispersion raw material using regenerated cellulose as the dispersion raw material; a depolymerization step of adding sodium hypochlorite to the grinding raw material obtained in the grinding step to reduce the degree of polymerization of the grinding raw material; a pH adjustment step of obtaining pH-adjusted cellulose by adjusting the pH of the depolymerized cellulose obtained in the depolymerization step to an alkaline pH of 9 or higher; a second pH adjustment step of adjusting the pH to an acidic pH of 6 or lower after the first pH adjustment step; and a neutralization step of neutralizing the pH-adjusted cellulose after the second pH adjustment step; a washing step of washing the pH-adjusted cellulose; and a micronization step of micronizing the pH-adjusted cellulose after the washing step to obtain a cellulose dispersion.

2. The method for producing a cellulose dispersion derived from regenerated cellulose according to claim 1, wherein in the depolymerization step, the degree of polymerization of the pulverized raw material is reduced by sodium hypochlorite with an effective chlorine concentration of 0.50 to 0.85%.

3. The method for producing a cellulose dispersion derived from regenerated cellulose according to claim 1 or claim 2, wherein the first pH adjustment operation includes adding sodium borohydride in an amount of 2% or less relative to the pulverized raw material.

4. A method for producing a cellulose dispersion derived from regenerated cellulose according to claim 1 or 2, comprising a separation step of removing coarse particles with a particle size of 10 μm or more from the cellulose dispersion, wherein the solid content yield of the finely milled cellulose after the separation step is 80% or more compared to before the separation step.

5. A method for producing a molded article of regenerated cellulose, comprising a molding step of drying and molding the cellulose dispersion obtained by the manufacturing method described in claim 1 to obtain a molded article of regenerated cellulose.

6. The method for producing a cellulose molded article derived from regenerated cellulose according to claim 5, wherein in the depolymerization step, the degree of polymerization of the pulverized raw material is reduced by sodium hypochlorite with an effective chlorine concentration of 0.50 to 0.85%.

7. A cellulose molded article obtained by the manufacturing method described in claim 5 or 6, wherein the cellulose molded article is a cellulose bead, and the cellulose bead is a regenerated cellulose-derived cellulose bead having a swelling rate of 200% or less when immersed in a 3% by weight sodium hydroxide aqueous solution for 24 hours.

8. A cellulose molded article obtained by the manufacturing method described in claim 6, wherein the cellulose molded article is a cellulose bead, and the cellulose bead has a whiteness of 80% or more after being heated at 80°C for 15 hours.

9. Regenerated cellulose-derived cellulose beads as described in claim 7, wherein the surface of the regenerated cellulose-derived cellulose beads is coated with a surface treatment agent.

10. Regenerated cellulose-derived cellulose beads as described in claim 8, wherein the surface of the regenerated cellulose-derived cellulose beads is coated with a surface treatment agent.

11. The regenerated cellulose-derived cellulose beads according to claim 9, wherein the surface treatment agent comprises at least one of the following: a wax-based treatment agent, a synthetic resin-based treatment agent, a chromium complex salt-based treatment agent, a fluorine-based treatment agent, a metal soap-based treatment agent, a cationic surfactant, a silicone-based treatment agent, or an amino acid-based treatment agent.

12. Cellulose beads derived from regenerated cellulose according to claim 10, wherein the surface treatment agent comprises at least one of the following: a wax-based treatment agent, a synthetic resin-based treatment agent, a chromium complex salt-based treatment agent, a fluorine-based treatment agent, a metal soap-based treatment agent, a cationic surfactant, a silicone-based treatment agent, or an amino acid-based treatment agent.

13. A cosmetic composition comprising cellulose beads as described in claim 7.

14. A cosmetic composition comprising cellulose beads as described in claim 9.

15. A cosmetic composition comprising cellulose beads as described in claim 11.

16. A cosmetic composition comprising cellulose beads according to claim 8, 10, or 12.

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