Binder composition for non-woven fabric, and non-woven fabric

Abstract

The present invention addresses the problem of providing a non-woven fabric having excellent dry strength and wet strength. The problem can be solved by means of a binder composition for a non-woven fabric, the composition comprising a chemically modified nanocellulose.

Description

Binder composition for nonwoven fabric, and nonwoven fabric

[0001] The present invention relates to a binder composition for nonwoven fabrics and nonwoven fabrics.

[0002] Nonwoven fabrics are used as wipes or absorbent sheets for household and industrial use, or as components of industrial products, for example, as separators in batteries such as alkaline secondary batteries.

[0003] Among nonwoven fabrics, cellulosic nonwoven fabrics made from cellulosic fibers exhibit excellent absorbency for aqueous liquids, making them suitable for household and industrial wipes or absorbent sheets. While these cellulosic nonwoven fabrics have excellent hydrophilic properties, they suffer from the problem of water easily penetrating between fibers or between the fibers and binder, resulting in reduced strength in a wet state (hereinafter also referred to as wet strength). Therefore, to enhance the strength of cellulosic nonwoven fabrics in a wet state while maintaining their hydrophilic properties, aqueous resin dispersions primarily composed of styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, acrylic copolymers, etc. have traditionally been used as binders (hereinafter also referred to as binders). Patent Document 1 also describes an emulsion obtained by emulsion polymerization of a monomer mixture primarily composed of alkyl acrylate in the presence of a water-soluble polymer having a specific acid value and containing acrylic acid monomer as an essential component.

[0004] Nonwoven fabrics used as battery separators include those primarily composed of polyester fibers, polyolefin fibers, polyvinyl chloride fibers, polyvinyl alcohol fibers, polyacrylonitrile fibers, polyamide fibers, etc. Binders are used to improve the strength of these nonwoven fabrics. For example, Patent Document 2 discloses the use of microfibrillated cellulose, which is a very fine fiber, as a binder during the production of nonwoven fabrics. It is said that the microfibrillated cellulose is very tightly entangled with polyolefin fibers, thereby increasing the strength of the nonwoven fabric.

[0005] JP 2007-138325 JP 10-144282

[0006] For nonwoven fabrics, binders are required that can not only improve the strength in a dry state (hereinafter also referred to as dry strength), but also improve the wet strength.

[0007] The binder in Patent Document 1 can increase the wet strength of nonwoven fabrics, but further improvements in performance are required, and further improvement in wet strength is an issue. The nonwoven fabric in Patent Document 2 contains microfibrillated cellulose, but Patent Document 2 lists microfibrillated cellulose produced by applying mechanical shear force or bacterial cellulose as the microfibrillated cellulose used, and does not disclose the use of chemically modified nanocellulose.

[0008] An object of the present invention is to provide a nonwoven fabric having excellent dry strength and wet strength.

[0009] As a result of extensive research, the inventors have found that nonwoven fabrics obtained using chemically modified nanocellulose have excellent dry strength and wet strength, and have thus completed the present invention.

[0010] That is, the present invention is as follows. [1] A binder composition for nonwoven fabrics comprising chemically modified nanocellulose. [2] The binder composition for nonwoven fabrics according to [1], wherein the chemically modified nanocellulose comprises oxidized nanocellulose. [3] The binder composition for nonwoven fabrics according to [2], wherein the oxidized nanocellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds. [4] The binder composition for nonwoven fabrics according to [2] or [3], wherein the oxidized nanocellulose comprises hydrophobically modified oxidized nanocellulose. [5] The binder composition for nonwoven fabrics according to any of [1] to [4], wherein the nonwoven fabric is a cellulosic nonwoven fabric made from cellulosic fibers. [6] The binder composition for nonwoven fabrics according to any of [1] to [5], further comprising at least one selected from styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, and acrylic copolymer. [7] A nonwoven fabric produced using the nonwoven fabric binder composition according to any one of [1] to [6]. [8] A nonwoven fabric comprising chemically modified nanocellulose. [9] The nonwoven fabric according to [8], wherein the chemically modified nanocellulose comprises oxidized nanocellulose.

[10] The nonwoven fabric according to [9], wherein the oxidized nanocellulose comprises an oxidation product of a cellulose-based raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.

[11] A method for producing a binder composition for nonwoven fabric comprising chemically modified nanocellulose, the method comprising the step of: obtaining the binder composition for nonwoven fabric by defibrating the chemically modified cellulose by stirring a mixture containing chemically modified cellulose and a material of the binder composition for nonwoven fabric other than the chemically modified nanocellulose; the chemically modified cellulose comprises oxidized cellulose; and the oxidized cellulose comprises an oxidation product of a cellulose-based raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.

[12] A method for producing a binder composition for nonwoven fabrics containing chemically modified nanocellulose, comprising the steps of: stirring chemically modified cellulose and continuously adding materials other than the chemically modified nanocellulose to the binder composition for nonwoven fabrics to defibrate the chemically modified cellulose to obtain the binder composition for nonwoven fabrics; wherein the chemically modified cellulose comprises oxidized cellulose; and the oxidized cellulose comprises an oxide of a cellulose-based raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.

[0011] According to the present invention, by using chemically modified nanocellulose, a nonwoven fabric having excellent dry strength and wet strength can be provided.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments. However, the present invention is not limited to the following embodiments and can be practiced in various modified forms within the scope of the present invention.

[0013] [Binder composition for nonwoven fabric] The binder composition for nonwoven fabric of the present invention contains chemically modified nanocellulose. When the chemically modified nanocellulose in the binder composition of the present invention is contained in a nonwoven fabric, the strength of the nonwoven fabric when dry (dry strength) can be improved. In addition, it prevents liquid from penetrating between the fibers of the nonwoven fabric or between the nonwoven fabric and the binder, and suppresses a decrease in strength due to the nonwoven fabric substrate absorbing liquid, i.e., it has excellent wet strength. Therefore, it is believed that the binder composition for nonwoven fabric of the present invention can achieve both dry strength and wet strength. However, the reasons why the present invention is excellent in dry strength and wet strength are not limited to the above.

[0014] The nonwoven fabric binder composition of the present invention is a composition for binding to a nonwoven fabric. The method of use of the nonwoven fabric binder composition of the present invention is not limited as long as it is used to bind and composite the binder component in the composition with the nonwoven fabric. A method for combining the nonwoven fabric binder composition of the present invention with a nonwoven fabric includes, for example, coating the nonwoven fabric with the composition, and this method may be a wet method or a dry method. Another method for combining the nonwoven fabric binder composition of the present invention with a nonwoven fabric includes blending the composition with the raw materials of the nonwoven fabric to composite it, and then forming the nonwoven fabric. One suitable method for using the nonwoven fabric binder composition of the present invention is to apply it to a nonwoven fabric. Here, "applying it to a nonwoven fabric" refers to a procedure in which the binder composition of the present invention is brought into contact with a nonwoven fabric as a substrate, thereby binding the binder component to at least a portion of the nonwoven fabric. The specific operation is not particularly limited, and examples thereof include a method of applying the binder composition of the present invention to the nonwoven fabric by spraying, and a method of impregnating the binder composition into the nonwoven fabric.

[0015] <Nonwoven Fabric> Examples of nonwoven fabrics in the present invention include nonwoven fabrics entangled by needle punching or hydroentanglement, nonwoven fabrics produced by thermal bonding, and nonwoven fabrics produced by spunbonding. The components constituting the fibers of the nonwoven fabric are not particularly limited, and examples include polyester, polyethylene, polypropylene, polyvinyl chloride, polyacrylic acid, polyamide, polyvinyl alcohol, polyurethane, polyvinyl ester, polymethacrylic acid ester, rayon, and acetate. The fibers may contain only one type of resin or multiple types of resins. The fibers may also contain cotton, silk, wool, and the like. Furthermore, the fibers may contain cellulose or viscose fibers. The fibers may be, for example, a blend of polyester and cotton. Among these, cellulosic nonwoven fabrics made from cellulosic fibers are preferred. Here, the term "cellulosic" in cellulosic fibers or cellulosic nonwoven fabrics refers to those containing cellulose as a constituent component. The fiber diameter of the fibers forming the nonwoven fabric is not particularly limited, but is usually 1 μm or more and 1 mm or less.

[0016] <Chemically Modified Nanocellulose> The chemically modified nanocellulose used in the present invention is a nano-sized product of chemically modified cellulose-based raw materials. By using chemically modified nanocellulose, cellulose-based raw materials can be efficiently micronized, and nanocellulose tends to be easily obtained. Chemically modified nanocellulose may also be a product obtained by nano-nizing cellulose-based raw materials and then chemically modifying them. In this specification, chemically modified nanocellulose is also simply referred to as nanocellulose. The main component of plants is cellulose, and bundles of cellulose molecules are called cellulose microfibrils. The cellulose in cellulose-based raw materials is also contained in the form of cellulose microfibrils. In the present invention, nanocellulose is a general term for nano-sized cellulose, and includes fine cellulose fibers, cellulose nanocrystals, etc. Fine cellulose fibers are also called cellulose nanofibers (also referred to as CNF).

[0017] Chemical modification is not particularly limited as long as it partially changes the cellulose structure, and examples include oxidation modification, phosphorylation modification, and carboxymethylation modification. In oxidation modification, carboxy groups are introduced into at least a portion of the cellulose structure by oxidizing a cellulosic raw material. In phosphorylation modification, a compound or a salt thereof containing phosphate groups on at least some of the hydroxyl groups of the glucose units constituting the cellulose undergoes a dehydration reaction to form a phosphate ester, thereby introducing phosphate groups or their salts. In carboxymethylation modification, carboxymethyl groups are ether-linked to at least some of the hydroxyl groups of the glucose units constituting the cellulose, thereby introducing carboxymethyl groups. Among these modifications, oxidation modification is preferred. Therefore, the chemically modified nanocellulose of the present invention is preferably a nano-sized version of oxidized cellulose obtained by oxidizing a cellulosic raw material. In other words, the chemically modified nanocellulose of the present invention preferably includes oxidized nanocellulose. The oxidation method is not particularly limited, but examples include oxidation using an N-oxyl compound such as 2,2,6,6-tetramethylpiperidine 1-oxyl (hereinafter also referred to as TEMPO), and oxidation using hypochlorous acid or a salt thereof. The oxidation using hypochlorous acid or a salt thereof referred to here refers to oxidation that occurs when hypochlorous acid or a salt thereof acts on a cellulosic raw material.

[0018] The chemically modified nanocellulose in the present invention can be commercially available chemically modified nanocellulose, or can be prepared from a cellulosic raw material such as softwood pulp. When preparing chemically modified nanocellulose, for example, Cellulose Commun., 14(2), 62(2007) and WO 2018 / 230354 pamphlet can be referenced.

[0019] From the viewpoint of further improving the dry strength and wet strength of the nonwoven fabric, the chemically modified nanocellulose of the present invention is preferably a nano-sized version of oxidized cellulose obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof. Here, the oxidized cellulose can also be referred to as an oxide of the cellulosic raw material. The chemically modified nanocellulose of the present invention preferably includes an oxide of the cellulosic raw material with hypochlorous acid or a salt thereof.

[0020] The chemically modified nanocellulose of the present invention is obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof, and it is preferable not to use N-oxyl compounds such as TEMPO in this oxidation. For this reason, it is preferable that the chemically modified nanocellulose of the present invention is substantially free of N-oxyl compounds. Such nanocellulose has a high level of safety, as the impact of N-oxyl compounds on the environment and human body is sufficiently reduced. Here, in this specification, the chemically modified nanocellulose "substantially free of N-oxyl compounds" means that the chemically modified nanocellulose does not contain any N-oxyl compounds, or the content of N-oxyl compounds is 2.0 ppm by mass or less, preferably 1.0 ppm by mass or less, relative to the total amount of chemically modified nanocellulose. Furthermore, when the content of N-oxyl compounds is increased from the cellulosic raw material, preferably 2.0 ppm by mass or less, more preferably 1.0 ppm by mass or less, it also means that the chemically modified nanocellulose is "substantially free of N-oxyl compounds." The content of N-oxyl compounds can be measured by known means. Known means include a method using a trace total nitrogen analyzer. The content of the N-oxyl compound can be specifically measured by the method described in the Examples.

[0021] When the chemically modified nanocellulose of the present invention contains oxidized nanocellulose, it contains a carboxyl group, and the carboxyl group may be in the H type (-COOH) or in the salt type (-COO － X ＋ :X ＋is an anion forming a salt form), or the carboxy group may be modified by reacting with another compound to form a covalent bond. The type of salt is not particularly limited, and examples include alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as calcium salts and barium salts; other metal salts such as magnesium salts and aluminum salts; ammonium salts, and organic amine salts. When the carboxy group is modified by a covalent bond, the other compound is not particularly limited as long as it reacts with carboxylic acid.

[0022] The carboxy group includes salt forms as described above, but is not limited to -COO － Oxidized nanocellulose can be hydrophobically modified by appropriately selecting the type of counter anion or by reacting the carboxyl group with another compound to form a covalent bond and modify it. By controlling the hydrophobicity or hydrophilicity of the oxidized cellulose, the dispersibility of the binder component in the binder composition of the present invention can be adjusted. By controlling the dispersibility, the binder component tends to be applied uniformly to the nonwoven fabric substrate, further improving the dry strength and wet strength of the nonwoven fabric. Furthermore, by controlling the hydrophobicity or hydrophilicity of the binder component, the affinity of the binder component with the nonwoven fabric can be adjusted, further improving the dry strength and wet strength.

[0023] The compound that hydrophobically modifies oxidized nanocellulose is not particularly limited, but examples thereof include metal soaps, amines, and quaternary ammonium salt compounds.

[0024] The metal soap is not particularly limited and includes, for example, metal salts of long-chain fatty acids such as magnesium salts, calcium salts, and zinc salts of long-chain fatty acids; mixtures of calcium salts and zinc salts of long-chain fatty acids; and lead-based metal soaps. Among these, metal salts of long-chain fatty acids are preferred. Furthermore, as metal salts of long-chain fatty acids, polyvalent metal salts of long-chain fatty acids are preferred. Examples of long-chain fatty acids include butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, isostearic acid, stearic acid, oleic acid, linoleic acid, ricinoleic acid, octylic acid, arachidic acid, arachidonic acid, behenic acid, lignoceric acid, and montanic acid. More preferred metal soaps include magnesium stearate, mixtures of calcium stearate and zinc stearate, and lead-based thermal metal soaps. These metal soaps may be used alone or in combination of two or more. As the metal soap, commercially available products containing the above-mentioned metal soaps may be used, and examples of commercially available products include RZ-161, RZ-162, MDZ-CP-102, FTZ-111, SCI-HSA-M1, SAK-CS-P, SAK-CS-G, SAK-CS-P-1 / USP, SAK-CS-PPT, SAK-CS-GPT-1, SAK-CS-POF, SAK-CS-PLB, SAK-CS-PC, SAK-ZS-P, SAK-ZS-TB, SAK-ZS-PLB500, SAK-ZS-TPS, and SAK-CS-GPT-1 manufactured by San-Ace. Examples include AK-ZS-TBPS, SAK-MS-P, SAK-MS-P / USP, SCI-HCS, SCI-HCS-SG, SCI-HCS-AB, SCI-HZS, SCI-HMS, SCI-ZNB, SAK-NAS-P, SAK-KS-CP, SAK-ZL-P, SCI-LIS, FerricStearate 83X, Sakai Chemical Industry's LHR-200 series, LHR-300 series, LHR-400 series, and Nitto Kasei Kogyo's HT-series, PSL series, SR series, and TR series.

[0025] The amine is not particularly limited and may be primary, secondary, or tertiary. The number of carbon atoms in the hydrocarbon group or aromatic group bonded to the nitrogen atom of the amine or quaternary ammonium salt compound (when two or more hydrocarbon groups or aromatic groups are bonded to the nitrogen atom, the total carbon number) is not particularly limited and may be selected from between 1 and 100 carbon atoms. As the amine, one having a polyalkylene oxide structure such as an ethylene oxide / propylene oxide (EO / PO) copolymer may also be used. From the viewpoint of imparting sufficient hydrophobicity to the oxidized nanocellulose, the number of carbon atoms is preferably 3 or more, more preferably 5 or more.

[0026] The quaternary ammonium salt compound is not particularly limited, and specific examples of the quaternary ammonium salt compound include quaternary ammonium hydroxides such as tetrapropylammonium hydroxide and tetrabutylammonium hydroxide, quaternary ammonium chlorides such as tetrabutylammonium chloride, quaternary ammonium bromides such as tetrabutylammonium bromide, and quaternary ammonium iodides such as tetrabutylammonium iodide.

[0027] The cellulosic raw material in the present invention is not particularly limited as long as it is a material primarily composed of cellulose, and examples thereof include pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by depolymerizing a cellulose raw material through mechanical treatment. Commercially available products such as crystalline cellulose derived from pulp can be used as is as the cellulosic raw material. Alternatively, unused biomass containing a large amount of cellulose components, such as soybean pulp refuse or soybean hulls, may also be used as the raw material. When oxidizing the cellulosic raw material, the cellulosic raw material may be treated with an alkali of an appropriate concentration to facilitate penetration of the oxidizing agent into the raw pulp.

[0028] (Carboxy Group Amount) The carboxy group amount of the oxidized nanocellulose and oxidized cellulose of the present invention is preferably 0.20 to 2.0 mmol / g. A carboxy group amount of 0.20 mmol / g or more can impart sufficient defibration properties to the oxidized cellulose. This is believed to enable a binder composition with stable dispersion to be obtained even when defibration treatment is performed under mild conditions, further improving coatability. On the other hand, a carboxy group amount of 2.0 mmol / g or less can enable the production of oxidized nanocellulose with a low proportion of particulate cellulose and uniform quality. This is believed to improve the dispersibility of the oxidized nanocellulose and further enhance its binding to nonwoven fabrics. From this perspective, the carboxy group amount of the oxidized nanocellulose and oxidized cellulose of the present invention is more preferably 0.35 mmol / g or more, even more preferably 0.40 mmol / g or more, even more preferably 0.42 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably greater than 0.50 mmol / g, and even more preferably 0.55 mmol / g or more. The upper limit of the carboxyl group content may be 1.5 mmol / g or less, 1.2 mmol / g or less, 1.0 mmol / g or less, or 0.9 mmol / g or less. A preferred range of the carboxyl group content can be determined by appropriately combining the above-mentioned upper and lower limits. The carboxyl group content of oxidized nanocellulose and oxidized cellulose is more preferably 0.35 to 2.0 mmol / g, even more preferably 0.35 to 1.5 mmol / g, still more preferably 0.40 to 1.5 mmol / g, even more preferably 0.50 to 1.2 mmol / g, even more preferably more than 0.50 to 1.2 mmol / g, and even more preferably 0.55 to 1.0 mmol / g.

[0029] The amount of carboxyl groups (mmol / g) was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of weak acid, where the change in electrical conductivity is gradual, after adding 0.1 M aqueous hydrochloric acid to an aqueous solution of oxidized cellulose mixed with water to adjust the pH to 2.5, and then adding 0.05 N aqueous sodium hydroxide dropwise and measuring the electrical conductivity until the pH reaches 11.0. Details follow the method described in the Examples below. The amount of carboxyl groups can be adjusted by changing the reaction time, reaction temperature, pH of the reaction solution, etc. of the oxidation reaction. Amount of carboxyl groups = a (ml) x 0.05 / mass of oxidized cellulose (g)

[0030] The oxidized cellulose can be obtained, for example, by oxidizing a cellulosic raw material under conditions in which the available chlorine concentration of hypochlorous acid or a salt thereof in the reaction system is relatively high (e.g., 6% to 43% by mass). The oxidized cellulose can also be produced by appropriately controlling reaction conditions such as the available chlorine concentration, the pH during the reaction, and the reaction temperature. The oxidized cellulose thus obtained preferably has a structure in which at least two of the hydroxyl groups on the glucopyranose ring constituting the cellulose are oxidized, and more specifically, preferably has a structure in which the hydroxyl groups at the second and third positions on the glucopyranose ring are oxidized and carboxyl groups are introduced. Furthermore, the hydroxyl group at the sixth position on the glucopyranose ring in this oxidized cellulose is preferably not oxidized and remains as a hydroxyl group. The position of the carboxyl group on the glucopyranose ring of oxidized cellulose is determined by the oxidization of the hydroxyl group at the sixth position. 13 It can be analyzed by C-NMR spectrum.

[0031] Rayon has the same chemical structure as cellulose, and its oxide (rayon oxide) is water-soluble. １３By performing C-NMR measurement, a carbon peak assigned to the carboxy group is observed at 165 to 185 ppm. In one embodiment of the oxidized cellulose or nanocellulose used in the present invention, obtained by oxidizing raw cellulose with hypochlorous acid or its salt, two signals appear in this chemical shift range. Furthermore, by solution two-dimensional NMR measurement, it can be determined that the carboxy groups are introduced at the 2- and 3-positions.

[0032] Oxidized cellulose or nanocellulose solid obtained by oxidizing raw cellulose with hypochlorous acid or its salts １３ In C-NMR, when the amount of carboxyl groups introduced is large, two signals appear at 165 to 185 ppm, and when the amount of carboxyl groups introduced is small, a very broad signal may appear. As can be seen from the results for oxidized rayon, the signals of the carboxyl group carbons introduced at the 2nd and 3rd positions are close to each other, and the signals are not clearly visible in solid state analysis with low resolution. １３ In C-NMR, the separation of the two signals is insufficient. Therefore, when the amount of carboxyl group introduced is small, a broad signal is observed. １３ In the C-NMR spectrum, the introduction of carboxy groups at the 2nd and 3rd positions can be confirmed by evaluating the broadening of the peak appearing at 165 to 185 ppm. １３A baseline is drawn around the peak in the range of 165 ppm to 185 ppm in a C-NMR spectrum to determine the overall area value, and then the area value is vertically divided at the peak top to determine the ratio of the two peak area values ​​(larger area value / smaller area value). If this peak area value ratio is 1.2 or greater, the peak is considered to be broad. The presence or absence of a broad peak can be determined by the ratio of the length L of the baseline in the range of 165 ppm to 185 ppm to the length L' of the perpendicular line from the peak top to the baseline. That is, if the ratio L' / L is 0.1 or greater, it can be determined that a broad peak is present. The ratio L' / L may be 0.2 or greater, 0.3 or greater, 0.4 or greater, or 0.5 or greater. The upper limit of the ratio L' / L is not particularly limited, but it is usually 3.0 or less, or may be 2.0 or less, or 1.0 or less. The structure of the glucopyranose ring can also be determined by analysis according to the method described in Sustainable Chem. Eng. 2020, 8, 48, 17800-17806.

[0033] The chemically modified nanocellulose of the present invention is an aggregate of individual fibers. The chemically modified nanocellulose of the present invention is sufficient as long as it contains at least one chemically modified nanocellulose, and it is preferable that the chemically modified nanocellulose is the main component. Here, chemically modified nanocellulose being the main component means that the proportion of chemically modified nanocellulose in the total amount of nanocellulose exceeds 50% by mass, preferably exceeds 70% by mass, and more preferably exceeds 80% by mass. The upper limit of the above proportion is 100% by mass, but it may also be 98% by mass or 95% by mass.

[0034] The average fiber length of the chemically modified nanocellulose in the present invention is preferably 50 to 2000 nm. If the average fiber length exceeds 2000 nm, the slurry containing the chemically modified nanocellulose tends to thicken. Furthermore, if the average fiber length is less than 50 nm, the viscosity characteristic of chemically modified nanocellulose is less likely to be exhibited and the binding ability tends to decrease. Furthermore, it is believed that an average fiber length of 50 to 2000 nm can suppress an increase in the viscosity of the binder composition, further improving the coatability and imparting good binding ability. The average fiber length is more preferably 100 to 1000 nm, even more preferably 100 to 500 nm, and even more preferably 100 to 400 nm.

[0035] The average fiber width of the chemically modified nanocellulose in the present invention is not particularly limited, but is preferably 1 to 200 nm. It is believed that an average fiber width of 1 to 200 nm can suppress an increase in the viscosity of the binder composition and further improve coatability. The average fiber width is more preferably 1 to 10 nm, and even more preferably 1 to 5 nm.

[0036] In the chemically modified nanocellulose of the present invention, the aspect ratio (average fiber length / average fiber width), which is the ratio of the average fiber width to the average fiber length, is preferably 20 or more and 200 or less. It is believed that an aspect ratio of 200 or less can further enhance binding properties. From this perspective, the aspect ratio is more preferably 145 or less, even more preferably 130 or less, even more preferably 120 or less, and even more preferably 100 or less. On the other hand, if the aspect ratio is too low, that is, if the shape of the nanocellulose is a thick rod rather than a long, thin fiber, aggregation occurs due to uneven distribution, and dispersibility tends to decrease. Therefore, the aspect ratio is preferably 20 or more, more preferably 30 or more, even more preferably 35 or more, and even more preferably 40 or more.

[0037] The average fiber width and average fiber length were calculated by mixing nanocellulose with water to a nanocellulose concentration of approximately 1 to 10 ppm, air-drying the resulting sufficiently diluted cellulose aqueous dispersion on a mica substrate, observing the shape of the nanocellulose using a scanning probe microscope, randomly selecting any number of fibers from the obtained image, and calculating the cross-sectional height of the shape image = fiber width and the perimeter divided by 2 = fiber length. Image processing software can be used to calculate these average fiber widths and lengths. While the image processing conditions are arbitrary, differences in calculated values ​​may occur even for the same image depending on the conditions. The range of difference in values ​​depending on the conditions is preferably within ±100 nm for average fiber length. The range of difference in values ​​depending on the conditions is preferably within ±10 nm for average fiber width. More detailed measurement methods follow the methods described in the Examples below.

[0038] Chemically modified cellulose and chemically modified nanocellulose are usually obtained in a state containing a dispersion medium due to their manufacturing method, but they may also be in the form of a dried product. The dried product form provides excellent handleability. The shape of the dried product is not particularly limited, and examples include lumps, granules, cotton, powder, and flakes.

[0039] The drying method is not particularly limited, and examples thereof include heat drying and freeze drying. The drying method may be used alone or in combination of two or more.

[0040] The moisture content of the dried product of chemically modified cellulose and chemically modified nanocellulose is not particularly limited, but is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less. A moisture content of 30% by mass or less can suppress increases in storage space, storage and transportation costs, and improve handleability. When the dried product is a dried product of chemically modified cellulose, the moisture content is more preferably 9% by mass or less, even more preferably 8% by mass or less, and particularly preferably 5.5% by mass or less, from the viewpoint of further improving the defibration properties of the chemically modified cellulose. The lower limit of the moisture content is ideally 0% by mass from the viewpoint of improving handleability, but may be greater than 0% by mass, 0.5% by mass or more, or 1% by mass or more, from the viewpoint of drying efficiency. The moisture content of the dried product can be measured using a heat-drying moisture meter.

[0041] (Method for producing oxidized nanocellulose) The oxidized nanocellulose used in the present invention may be a commercially available product or may be prepared by the user. A method for producing the oxidized nanocellulose will now be described. The oxidized nanocellulose used in the present invention can be produced, for example, by a method comprising step A of oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof to obtain oxidized cellulose, and, if necessary, step B of defibrating the oxidized cellulose.

[0042] (Step A: Production of oxidized cellulose) Examples of hypochlorous acid or a salt thereof used in the oxidation of a cellulosic raw material include hypochlorous acid water, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite. Among these, sodium hypochlorite is preferred from the viewpoint of ease of handling.

[0043] Methods for producing oxidized cellulose by oxidation of a cellulosic raw material include mixing the cellulosic raw material with a reaction solution containing hypochlorous acid or a salt thereof. Water is preferred as the solvent contained in the reaction solution, as it is easy to handle and unlikely to cause side reactions. The available chlorine concentration of hypochlorous acid or a salt thereof in the reaction solution is preferably 6 to 43% by mass, more preferably 7 to 43% by mass, and even more preferably 8 to 43% by mass. When the available chlorine concentration of the reaction solution is within the above range, the amount of carboxy groups in the oxidized cellulose can be sufficiently increased, making it easy to defibrate the oxidized cellulose.

[0044] From the viewpoint of sufficiently increasing the amount of carboxy groups in the oxidized cellulose, the available chlorine concentration of the reaction solution is more preferably 14% by mass or more, even more preferably 18% by mass or more, and even more preferably 20% by mass or more. Furthermore, from the viewpoint of suppressing excessive decomposition of cellulose during defibration, the available chlorine concentration of the reaction solution is more preferably 40% by mass or less, and even more preferably 38% by mass or less. The range of the available chlorine concentration of the reaction solution can be an appropriate combination of the above-mentioned lower and upper limits. The range of the available chlorine concentration is more preferably 16 to 43% by mass, and even more preferably 18 to 40% by mass.

[0045] From the viewpoints of reducing the cost of producing oxidized cellulose and improving productivity, such as by facilitating the availability and handling of hypochlorous acid or its salts, it is preferable to keep the effective chlorine concentration low. From this viewpoint, the upper limit of the effective chlorine concentration is preferably less than 14% by mass, more preferably 13% by mass or less, even more preferably 12% by mass or less, and still more preferably 11% by mass or less. From the viewpoints of more smoothly proceeding with the micronization of oxidized cellulose and improving productivity, the range of the effective chlorine concentration is preferably from 6% by mass to less than 14% by mass, more preferably from 7% by mass to less than 14% by mass, even more preferably from 7% by mass to 13% by mass, and still more preferably from 8% by mass to 13% by mass.

[0046] The effective chlorine concentration of hypochlorous acid or its salt is defined as follows: Hypochlorous acid is a weak acid that exists as an aqueous solution, and hypochlorite is a compound in which the hydrogen of hypochlorous acid is replaced by another cation. For example, sodium hypochlorite, which is a hypochlorite, exists in a solvent (preferably in an aqueous solution), so the concentration is measured as the effective chlorine amount in the solution, not the concentration of sodium hypochlorite. Here, regarding the effective chlorine of sodium hypochlorite, the oxidizing power of the divalent oxygen atom generated by the decomposition of sodium hypochlorite is equivalent to two atomic equivalents of monovalent chlorine, so the bonded chlorine atoms of sodium hypochlorite (NaClO) are equivalent to the unbonded chlorine (Cl ２ ), so available chlorine = 2 x (chlorine in NaClO). The specific measurement procedure is to first accurately weigh the sample, add water, potassium iodide, and acetic acid, and leave it to stand. The liberated iodine is then titrated with a sodium thiosulfate solution using an aqueous starch solution as an indicator to measure the available chlorine concentration.

[0047] The oxidation reaction of the cellulosic raw material with hypochlorous acid or a salt thereof is preferably carried out while adjusting the pH to the range of 5.0 to 14.0. Within this range, the oxidation reaction of the cellulosic raw material can be sufficiently progressed, and the amount of carboxy groups in the oxidized cellulose can be sufficiently increased. This facilitates defibration of the oxidized cellulose. The pH of the reaction system is more preferably 7.0 or higher, even more preferably 8.0 or higher, even more preferably 8.5 or higher, even more preferably 9.0 or higher, and even more preferably 9.5 or higher. There is no particular upper limit to the pH of the reaction system, but it is preferably 14.5 or lower, more preferably 14.0 or lower, even more preferably 13.0 or lower, even more preferably 12.5 or lower, even more preferably 12.0 or lower, and even more preferably 11.5 or lower. The pH range of the reaction system is more preferably 7.0 to 14.0, even more preferably 8.0 to 13.5, and even more preferably 8.5 to 13.0.

[0048] Hereinafter, the method for producing oxidized cellulose will be further explained using as an example the case where sodium hypochlorite is used as hypochlorous acid or a salt thereof.

[0049] When oxidizing a cellulosic raw material using sodium hypochlorite, the reaction liquid is preferably a sodium hypochlorite aqueous solution. Methods for adjusting the effective chlorine concentration of a sodium hypochlorite aqueous solution to a target concentration (for example, target concentration: 6% by mass to 43% by mass) include concentrating a sodium hypochlorite aqueous solution having a lower effective chlorine concentration than the target concentration, diluting a sodium hypochlorite aqueous solution having a higher effective chlorine concentration than the target concentration, and dissolving sodium hypochlorite crystals (for example, sodium hypochlorite pentahydrate) in a solvent. Among these, adjusting the effective chlorine concentration as an oxidizing agent by diluting a sodium hypochlorite aqueous solution or dissolving sodium hypochlorite crystals in a solvent is preferred because it causes less self-decomposition (i.e., less reduction in effective chlorine concentration) and makes it easy to adjust the effective chlorine concentration.

[0050] In order to efficiently proceed with the oxidation reaction of the cellulosic raw material, it is preferable to carry out the oxidation reaction while stirring the mixture of the cellulosic raw material and the aqueous sodium hypochlorite solution. Examples of stirring methods include a magnetic stirrer, a stirring rod, a stirrer with stirring blades (three-one motor), a homomixer, a disperser-type mixer, a homogenizer, and external circulation stirring. Among these, methods using one or more of shear-type stirrers such as homomixers and homogenizers, stirrers with stirring blades, and disperser-type mixers are preferred, as they facilitate smooth progression of the oxidation reaction of the cellulosic raw material, and methods using a stirrer with stirring blades are particularly preferred. When a stirrer with stirring blades is used, devices equipped with known stirring blades such as propeller blades, paddle blades, and turbine blades can be used as the stirrer. Furthermore, when a stirrer with stirring blades is used, stirring is preferably carried out at a rotation speed of 50 to 300 rpm.

[0051] The reaction temperature in the oxidation reaction is preferably 15°C to 100°C, and more preferably 20°C to 90°C. During the reaction, the pH of the reaction system decreases as carboxyl groups are generated in the cellulosic raw material by the oxidation reaction. Therefore, from the viewpoint of efficiently progressing the oxidation reaction, it is preferable to add an alkaline agent (e.g., sodium hydroxide) or an acid (e.g., hydrochloric acid) to the reaction system to adjust the pH of the reaction system to the above-mentioned preferred range. The reaction time of the oxidation reaction can be set according to the degree of progress of the oxidation, but is preferably about 15 minutes to 50 hours. When the pH of the reaction system is to be 10 or higher, it is preferable to set the reaction temperature to 30°C or higher and / or the reaction time to 30 minutes or longer.

[0052] The solution containing oxidized cellulose obtained by the above reaction can be subjected to known isolation treatments such as filtration, and further purified as necessary to obtain oxidized cellulose as an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof. The solution containing oxidized cellulose obtained by the above reaction may also be subjected to defibration treatment as is.

[0053] (Step B: Defibration Treatment) The oxidized nanocellulose of the present invention can be obtained by defibrating the oxidized cellulose obtained above into nano-sized particles. Methods for defibrating oxidized cellulose include weak stirring using a magnetic stirrer or the like, and mechanical defibration. Mechanical defibration is preferred for oxidized cellulose, as this allows for sufficient defibration of the oxidized cellulose and shortens the defibration time.

[0054] Examples of mechanical defibration methods include methods using various mixing and stirring devices such as a screw mixer, paddle mixer, disperser mixer, turbine mixer, homomixer under high-speed rotation, high-pressure homogenizer, ultra-high-pressure homogenizer, double-cylinder homogenizer, ultrasonic homogenizer, water current opposing collision type disperser, beater, disk refiner, conical refiner, double-disc refiner, grinder, single-shaft or multi-shaft kneader, planetary stirrer, vibration stirrer, etc. These devices can be used alone or in combination of two or more types to treat oxidized cellulose, preferably in a dispersion medium, to nanosize the oxidized cellulose and produce nanocellulose.

[0055] For defibration of oxidized cellulose, a method using an ultra-high-pressure homogenizer is preferably used, since it allows the production of nanocellulose with a more advanced defibration. When defibration treatment using an ultra-high-pressure homogenizer is applied, the pressure during the defibration treatment is preferably 100 MPa or more, more preferably 120 MPa or more, and even more preferably 150 MPa or more. The number of defibration treatments is not particularly limited, but from the viewpoint of sufficiently progressing defibration, it is preferably two or more, more preferably three or more. Furthermore, the above-mentioned oxidized cellulose can be sufficiently defibrated by mild stirring using a planetary stirrer or a vibration stirrer. Examples of vibration stirrers include a vortex mixer (touch mixer). In other words, with the above-mentioned oxidized cellulose, homogenized nanocellulose can be obtained even when the defibration treatment is performed under mild defibration conditions.

[0056] The defibration treatment is preferably carried out in a state where the oxidized cellulose is mixed with a dispersion medium. There are no particular restrictions on the dispersion medium, and it can be selected appropriately depending on the purpose. Specific examples of dispersion mediums include water, alcohols, ethers, ketones, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. As the solvent, one of these may be used alone, or two or more may be used in combination.

[0057] Among the above dispersion media, examples of alcohols include methanol, ethanol, isopropanol, isobutanol, sec-butyl alcohol, tert-butyl alcohol, methyl cellosolve, ethylene glycol, and glycerin. Examples of ethers include ethylene glycol dimethyl ether, 1,4-dioxane, and tetrahydrofuran. Examples of ketones include acetone and methyl ethyl ketone. Using an organic solvent as a dispersion medium during the defibration treatment facilitates the isolation of oxidized cellulose and the nanocellulose obtained by defibrating it.

[0058] The chemically modified nanocellulose of the present invention preferably satisfies the following zeta potential and light transmittance.

[0059] (Zeta potential) The chemically modified nanocellulose of the present invention preferably has a zeta potential of -30 mV or less. When the zeta potential is -30 mV or less (i.e., an absolute value of 30 mV or more), sufficient repulsion between microfibrils is obtained, making it easier to produce chemically modified nanocellulose with a high surface charge density during mechanical defibration. This improves the dispersibility of the chemically modified nanocellulose, tends to have excellent viscosity stability when made into a slurry, and tends to achieve a better balance between dry strength and wet strength. When the zeta potential is -100 mV or more (i.e., an absolute value of 100 mV or less), oxidative scission in the fiber direction as oxidation progresses tends to be suppressed, making it possible to obtain chemically modified nanocellulose of uniform size, and the binding property tends to be improved.

[0060] The zeta potential of the chemically modified nanocellulose of the present invention is preferably -35 mV or less, more preferably -40 mV or less, and even more preferably -50 mV or less. Furthermore, the lower limit of the zeta potential is preferably -90 mV or more, more preferably -85 mV or more, even more preferably -80 mV or more, even more preferably -77 mV or more, even more preferably -70 mV or more, and even more preferably -65 mV or more. The range of the zeta potential can be appropriately combined with the above-mentioned lower and upper limits. The zeta potential is preferably -90 mV or more to -30 mV or less, more preferably -85 mV or more to -30 mV or less, even more preferably -80 mV or more to -30 mV or less, even more preferably -77 mV or more to -30 mV or less, even more preferably -70 mV or more to -30 mV or less, even more preferably -65 mV or more to -35 mV or less. In this specification, the zeta potential is a value measured at pH 8.0 and 20 ° C. for a cellulose aqueous dispersion obtained by mixing chemically modified nanocellulose and water to a concentration of chemically modified nanocellulose of 0.1% by mass. Specifically, it can be measured according to the following method. Pure water is added to the aqueous dispersion of chemically modified nanocellulose to dilute it so that the concentration of chemically modified nanocellulose is 0.1%. After dilution, a 0.05 mol / L aqueous sodium hydroxide solution is added to the aqueous dispersion of chemically modified nanocellulose, and the pH is adjusted to 8.0. The zeta potential is measured at 20 ° C. using a zeta potential measuring device such as a zeta potential meter (ELSZ-1000) manufactured by Otsuka Electronics Co., Ltd.

[0061] (Light transmittance) The chemically modified nanocellulose of the present invention has few aggregates, and the chemically modified nanocellulose dispersion dispersed in a dispersion medium has little light scattering of fine cellulose fibers and tends to exhibit high light transmittance. Specifically, the chemically modified nanocellulose of the present invention preferably has a light transmittance of 95% or more in a mixed solution mixed with water to a solids concentration of 0.1% by mass. The light transmittance is more preferably 96% or more, even more preferably 97% or more, and even more preferably 99% or more. The light transmittance is a value at a wavelength of 660 nm measured using a spectrophotometer. Light transmittance can also be measured using an aqueous dispersion containing chemically modified nanocellulose. Specifically, it can be measured according to the following method. The aqueous dispersion of chemically modified nanocellulose is placed in a 10 mm thick quartz cell, and the light transmittance at a wavelength of 660 nm is measured using a spectrophotometer such as a JASCO V-550.

[0062] When the chemically modified nanocellulose is, for example, oxidized nanocellulose, the zeta potential and light transmittance can be controlled by oxidation using hypochlorous acid or a salt thereof, particularly by adjusting the reaction time, reaction temperature, stirring conditions, etc. of the oxidation reaction. Specifically, as the reaction time and / or reaction temperature is increased, oxidation of the cellulose microfibril surface in the cellulosic raw material progresses, and the repulsion between fibrils due to electrostatic repulsion and osmotic pressure increases, resulting in a smaller average fiber width. Furthermore, the zeta potential tends to be increased by setting one or more of the oxidation reaction time, reaction temperature, and stirring conditions (e.g., by increasing the reaction time) to further promote oxidation (i.e., to increase the degree of oxidation).

[0063] The chemically modified nanocellulose of the present invention is obtained by nanoparticle-forming chemically modified cellulose (hereinafter also referred to as chemically modified cellulose). That is, the chemically modified nanocellulose of the present invention is obtained via chemically modified cellulose. Here, the degree of polymerization of the chemically modified cellulose used in the present invention is preferably 600 or less. When the degree of polymerization of chemically modified cellulose exceeds 600, it tends to require a large amount of energy for defibration, and sufficient defibration properties cannot be exhibited, which tends to result in a decrease in the dispersibility of the chemically modified nanocellulose and ultimately a decrease in binding properties. Furthermore, when the degree of polymerization of chemically modified cellulose exceeds 600, there is a large amount of chemically modified cellulose that is not sufficiently defibrated. Therefore, when this is finely defibrated and nanocellulose is dispersed in a dispersion medium, light scattering and the like increase, and transparency may decrease. From the viewpoint of easy defibration, there is no particular lower limit for the degree of polymerization of chemically modified cellulose. However, if the degree of polymerization of chemically modified cellulose is less than 50, the proportion of particulate cellulose rather than fibrous cellulose increases, which may reduce the effect of nanocellulose. From the above viewpoint, the degree of polymerization of chemically modified cellulose is preferably in the range of 50 to 600.

[0064] The degree of polymerization of the chemically modified cellulose is more preferably 580 or less, even more preferably 560 or less, even more preferably 550 or less, even more preferably 500 or less, even more preferably 450 or less, and even more preferably 400 or less. From the viewpoint of improving the viscosity stability and coatability of the slurry, the lower limit of the degree of polymerization is more preferably 60 or more, even more preferably 70 or more, even more preferably 80 or more, even more preferably 90 or more, even more preferably 100 or more, even more preferably 110 or more, and particularly preferably 120 or more. A preferred range of the degree of polymerization can be determined by appropriately combining the above-mentioned upper and lower limits. The degree of polymerization of the chemically modified cellulose is more preferably 60 to 600, even more preferably 70 to 600, even more preferably 80 to 600, even more preferably 80 to 550, even more preferably 80 to 500, even more preferably 80 to 450, and particularly preferably 80 to 400. The degree of polymerization of chemically modified cellulose is the average degree of polymerization (viscosity-average degree of polymerization) measured by viscosity method. Details are as follows: Chemically modified cellulose is added to an aqueous sodium borohydride solution adjusted to pH 10, and reduction treatment is performed at 25°C for 5 hours. The amount of sodium borohydride is 0.1 g per 1 g of chemically modified cellulose. After reduction treatment, solid-liquid separation is performed by suction filtration, followed by washing with water, and the resulting chemically modified cellulose is freeze-dried. 0.04 g of dried chemically modified cellulose is added to 10 ml of pure water and stirred for 2 minutes, after which 10 ml of 1 M copper ethylenediamine solution is added to dissolve it. Then, the flow time of the blank solution and the flow time of the cellulose solution are measured at 25°C using a capillary viscometer. The relative viscosity (η) is calculated from the flow time of the blank solution (t0), the flow time of the cellulose solution (t), and the concentration of chemically modified cellulose (c [g / ml]) using the following formula: r ), specific viscosity (η sp ), and intrinsic viscosity ([η]) are measured in turn, and the degree of polymerization (DP) of the chemically modified cellulose is calculated using the viscosity measurement formula. r =η / η0=t / t0 η sp =η r -1 [η] = η sp / (100 × c(1 + 0.28η sp )) DP=175×[η]

[0065] When the chemically modified cellulose is oxidized cellulose, the degree of polymerization of the oxidized cellulose can be controlled by oxidation using hypochlorous acid or a salt thereof. This can be adjusted, in particular, by changing the reaction time, reaction temperature, pH, and effective chlorine concentration of hypochlorous acid or a salt thereof during the oxidation reaction. Specifically, since increasing the degree of oxidation tends to decrease the degree of polymerization, methods for decreasing the degree of polymerization include, for example, increasing the reaction time and / or reaction temperature. Alternatively, the degree of polymerization of the oxidized cellulose can be adjusted by changing the stirring conditions of the reaction system during the oxidation reaction. For example, under conditions where the reaction system is sufficiently homogenized using a stirring blade or the like, the oxidation reaction proceeds smoothly, and the degree of polymerization tends to decrease. On the other hand, under conditions where the reaction system is likely to be insufficiently stirred, such as stirring with a stirrer, the reaction tends to become non-uniform, making it difficult to sufficiently reduce the degree of polymerization of the oxidized cellulose. Furthermore, the degree of polymerization of oxidized cellulose tends to vary depending on the selection of the raw cellulose. Therefore, the degree of polymerization of oxidized cellulose can also be adjusted by selecting the cellulosic raw material.

[0066] <Other binder components> The binder composition of the present invention may contain other binder components other than the above-mentioned chemically modified nanocellulose. The other binder components are not particularly limited as long as they are generally used in nonwoven fabrics. In addition, the other binder components may be appropriately selected depending on the type of material of the nonwoven fabric, and commercially available products can be used.

[0067] Examples of other binder components include styrene-butadiene copolymers, ethylene-vinyl acetate copolymers, acrylic copolymers, and the like, as well as aqueous resin dispersions containing these resins as the main component. These may be used alone or in combination of two or more. Here, "containing" as the main component means that the proportion of the styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, or acrylic copolymer relative to the total amount of resin constituting the aqueous resin dispersion is usually 50% or more, preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, still more preferably 90% or more, even more preferably 95% or more, and particularly preferably 98% or more.

[0068] Aqueous resin dispersions primarily composed of acrylic copolymers are described in JP 2007-138325 A, specifically, emulsions for nonwoven fabrics having a glass transition temperature of 80°C or less, which are obtained by emulsion polymerization of a monomer mixture containing an alkyl acrylate as an essential component in the presence of a neutralized product of a water-soluble polymer having acrylic acid as an essential monomer component and an acid value of 200 mgKOH / g or more. These emulsions for nonwoven fabrics are commercially available. The water-soluble polymer is a homopolymer of acrylic acid as an essential monomer, or a copolymer of acrylic acid and other monomers. Other copolymers include, for example, alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, lauryl acrylate, and stearyl acrylate; (meth)acrylamides such as acrylamide and methacrylamide (acrylamides and methacrylamides are collectively referred to as (meth)acrylamides); acrylamidoalkanesulfonic acids such as 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamidoethanesulfonic acid, 2-acrylamidopropanesulfonic acid, and 2-acrylamidobutanesulfonic acid (which may be salts thereof. When used as a salt, sodium salts, potassium salts, etc. are exemplified, and sodium Acrylamide alkanesulfonic acid and its salts are hereinafter collectively referred to as acrylamidoalkanesulfonic acid (salts). Examples of such monomers include alkyl acrylates, alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate, styrenes such as styrene, α-methylstyrene, and vinyltoluene, functional group-containing monomers such as allyl glycidyl ether, glycidyl (meth)acrylate, and hydroxyethyl (meth)acrylate, vinyl carboxylates such as vinyl acetate and vinyl propionate, olefins such as ethylene and propylene, and halogenated olefins such as vinyl chloride and vinylidene chloride (note that acrylic acid esters and methacrylic acid esters are collectively referred to as (meth)acrylic acid esters). As the other monomer, it is preferable to use at least one of alkyl acrylates, (meth)acrylamides, and acrylamidoalkanesulfonic acids (salts).As the alkyl acrylate used in the monomer mixture, the monomers exemplified for the water-soluble polymer can be used.

[0069] <Dispersion medium> The binder composition for nonwoven fabric of the present invention may contain a dispersion medium for dispersing the chemically modified nanocellulose. The dispersion medium used in the binder composition for nonwoven fabric of the present invention is not particularly limited as long as it can disperse nanocellulose.

[0070] Examples of dispersion media include water, alcohols, ethers, ketones, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. These may be used alone or in combination of two or more. Examples of the alcohols include methanol, ethanol, isopropanol, isobutanol, sec-butyl alcohol, tert-butyl alcohol, methyl cellosolve, ethylene glycol, and glycerin. Examples of the ethers include ethylene glycol dimethyl ether, 1,4-dioxane, and tetrahydrofuran. Examples of the ketones include acetone and methyl ethyl ketone.

[0071] In the nonwoven fabric binder composition of the present invention, when a dispersion medium is included, the content of chemically modified nanocellulose may be adjusted appropriately depending on the type of nonwoven fabric, etc., but is typically 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, based on the total amount of the composition. A nanocellulose content of 0.01% by mass or more allows the binder component to be efficiently bound to the nonwoven fabric, tending to increase dry strength and wet strength. The upper limit of the nanocellulose content is not particularly limited, but is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. A nanocellulose content of 10% by mass or less tends to improve coatability on nonwoven fabrics. The preferred range of the nanocellulose content can be determined by appropriately combining the above-mentioned upper and lower limits, and is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and even more preferably 0.5 to 3% by mass or more.

[0072] When the binder composition for nonwoven fabrics of the present invention contains a dispersion medium, the solids concentration is usually in the range of 1% by mass to 99% by mass, and from the viewpoint of improving coatability, it is preferably 1% by mass to 50% by mass, more preferably 1% by mass to 30% by mass.

[0073] The amount of chemically modified nanocellulose is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the solid content of the nonwoven fabric binder composition. The upper limit of the amount of chemically modified nanocellulose relative to the solid content is not particularly limited, but may be, for example, 100% by mass, 98% by mass, 96% by mass, or 94% by mass. The range of the amount of chemically modified nanocellulose can be determined by appropriately combining the above-mentioned upper and lower limits, and may be, for example, 60 to 100% by mass, 70 to 98% by mass, 80 to 96% by mass, or 90 to 94% by mass.

[0074] [Method for producing binder composition for nonwoven fabric] The binder composition for nonwoven fabric of the present invention can be produced by blending chemically modified nanocellulose and, if necessary, other binder components. The chemically modified nanocellulose is preferably a dispersion containing a dispersant such as water. In the method for producing the binder composition for nonwoven fabric, the solid content may be appropriately adjusted by adding a dispersant.

[0075] When the nonwoven fabric binder composition of the present invention contains oxidized nanocellulose that contains an oxidation product of a cellulosic raw material with hypochlorous acid or its salt and is substantially free of N-oxyl compounds, the binder composition can also be produced using oxidized cellulose before defibration. As described above, when a cellulosic raw material is oxidized with hypochlorous acid or its salt, oxidized cellulose with excellent defibration properties can be obtained. During production, the oxidized cellulose is defibrated in the composition by a dispersion or kneading operation to form nanocellulose. Specifically, nanocellulose can be produced by blending the oxidized cellulose with materials other than the oxidized cellulose of the nonwoven fabric binder composition, and defibrating the mixture by agitation such as dispersion or kneading, or by the user defibrating the oxidized cellulose themselves to form nanocellulose. The agitation can be performed as described above (Step B: Defibration Treatment).

[0076] One aspect of the present invention is a method for producing a binder composition for nonwoven fabrics using oxidized cellulose, which contains an oxide of a cellulose-based raw material produced by hypochlorous acid or a salt thereof and is substantially free of N-oxyl compounds. Specifically, the method is a method for producing a binder composition for nonwoven fabrics containing chemically modified nanocellulose, comprising a step of stirring a mixture containing the chemically modified cellulose (oxidized cellulose) and a material other than the chemically modified nanocellulose of the binder composition for nonwoven fabrics to defibrate the chemically modified cellulose, thereby obtaining the binder composition for nonwoven fabrics. Another aspect of the present invention is a method for producing a binder composition for nonwoven fabrics containing chemically modified nanocellulose, comprising a step of stirring the chemically modified cellulose (oxidized cellulose) and subsequently adding a material other than the chemically modified nanocellulose of the binder composition for nonwoven fabrics to defibrate the chemically modified cellulose, thereby obtaining the binder composition for nonwoven fabrics. Examples of the chemically modified nanocellulose, oxidized cellulose, and binder composition for nonwoven fabrics are as described above. The material other than chemically modified nanocellulose in the nonwoven fabric binder composition refers to any material other than chemically modified nanocellulose that can be contained in the nonwoven fabric binder composition, including, but not limited to, the other binder components and dispersion media described above. Furthermore, as used herein, "continuously adding materials" means that the oxidized cellulose is refined by stirring and the materials are added in a continuous sequence. Specific examples of sequentially performing stirring and addition include, but are not limited to, a one-pot operation in which the oxidized cellulose is stirred to refine it and the materials are added; and a method in which the oxidized cellulose is stirred while the materials are added simultaneously.

[0077] [Nonwoven Fabric] The nonwoven fabric of the present invention is a nonwoven fabric produced using the nonwoven fabric binder composition of the present invention, or a nonwoven fabric containing the chemically modified nanocellulose of the present invention. The nonwoven fabric of the present invention can be produced, for example, by diluting the nonwoven fabric binder composition or chemically modified nanocellulose of the present invention with a dispersion medium as necessary, applying it to a nonwoven fabric, and drying it at any temperature. Application methods include, but are not limited to, spraying the binder composition onto the nonwoven fabric or impregnating the nonwoven fabric with the binder composition. The nonwoven fabric of the present invention can also be produced by combining the nonwoven fabric binder composition or chemically modified nanocellulose with the nonwoven fabric. Examples of the combination method include producing a nonwoven fabric using (e.g., spinning) a mixture of the nonwoven fabric binder composition or chemically modified nanocellulose and the raw materials for the nonwoven fabric (substrate).

[0078] The amount of solids attached to the nonwoven fabric of the present invention derived from the binder composition for nonwoven fabrics can be adjusted appropriately depending on the type of nonwoven fabric, but is usually 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 1.0% by mass or more, based on the fiber basis weight. A ratio of 0.1% by mass or more tends to increase dry strength and wet strength. The upper limit of the ratio of the attached amount is not particularly limited, but is usually 50% by mass or less, and may be 40% by mass or less, 30% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, or 5% by mass or less. A preferred range of the amount of solids attached can be determined by appropriately combining the above-mentioned upper and lower limits, and is preferably 0.1 to 50 mass%, more preferably 0.1 to 40 mass%, even more preferably 0.5 to 30 mass%, still more preferably 0.5 to 20 mass%, even more preferably 1.0 to 15 mass%, and more preferably 1.0 to 10 mass%.

[0079] Further, as one aspect of the present invention, when chemically modified nanocellulose is used as the main binder component of the binder composition for nonwoven fabric, or when chemically modified nanocellulose itself is used, the adhesion amount is preferably 0.1% by mass to 15% by mass, more preferably 0.5% by mass to 15% by mass, and even more preferably 0.5% by mass to 10% by mass. Here, "chemically modified nanocellulose as the main binder component of the binder composition for nonwoven fabric" means that when the binder component is 100 parts by mass, the chemically modified nanocellulose is more than 50 parts by mass, preferably 60 parts by mass or more, more preferably 80 parts by mass or more, even more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, even more preferably 98 parts by mass or more, and particularly preferably 100 parts by mass.

[0080] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0081] The physical properties of nanocellulose in this example were measured by the following methods.

[0082] (Method for measuring average fiber length and average fiber width of CNF) The obtained CNF dispersion was diluted 1,000 to 1,000,000 times with pure water and allowed to air dry on a mica substrate. The CNF shape was observed in AC mode using an Oxford Asylum scanning probe microscope "MFP-3D infinity." The obtained images were binarized and analyzed using the image processing software "ImageJ." For 100 or more fibers, the average fiber length was calculated as fiber length = "perimeter" ÷ 2. For 50 or more fibers, the average fiber width was calculated using the software provided with the "MFP-3D infinity" by calculating the cross-sectional height of the shape image = fiber width.

[0083] (Method for measuring the amount of carboxy groups) To 60 ml of an oxidized cellulose aqueous dispersion in which the concentration of oxidized cellulose fibers had been adjusted to 0.5% by mass, 0.1 M aqueous hydrochloric acid was added to adjust the pH to 2.5, and then 0.05 N aqueous sodium hydroxide solution was added dropwise, and the electrical conductivity was measured until the pH reached 11.0. The amount of carboxy groups (mmol / g) was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid, where the change in electrical conductivity was gradual: amount of carboxy groups = a (ml) × 0.05 / mass of oxidized cellulose fibers (g).

[0084] [Production Example 1: Production of nanocellulose including a hypooxidation process] As a cellulose-based raw material, softwood pulp (SIGMA-ALDRICH NIST RM 8495, bleached kraft pulp) was cut with scissors into 5 mm squares and processed in a "Wonder Blender WB-1" manufactured by Osaka Chemical Co., Ltd. at 25,000 rpm for 1 minute to mechanically defibrate it into a cotton-like state. 350 g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass were placed in a beaker, and pure water was added and stirred to adjust the effective chlorine concentration to 21% by mass. 35% by mass of hydrochloric acid was added and stirred to obtain a sodium hypochlorite aqueous solution with a pH of 11. The sodium hypochlorite aqueous solution was heated to 30°C in a thermostatic water bath while stirring at 200 rpm using a propeller-type stirring blade in a stirrer (Three-One Motor, BL600) manufactured by Shinto Scientific Co., Ltd., and 50 g of the above-mentioned cellulose-based raw material was then added. After the cellulose-based raw material was added, the mixture was kept at 30°C in the same thermostatic water bath, and the pH during the reaction was adjusted to 11 by adding 48% by mass of sodium hydroxide. The mixture was then stirred for 30 minutes under the same conditions using the stirrer. After the reaction was completed, the product was subjected to solid-liquid separation by suction filtration using a PTFE mesh filter with a mesh size of 134 μm, and the resulting oxidized cellulose was washed with pure water. The carboxyl group content of the filtered product (oxidized cellulose) after washing was measured and found to be 0.45 mmol / g. The average fiber length was 553 nm, and the average fiber width was 4.5 nm. Purified water was added to oxidized cellulose to prepare a 5% dispersion, which was then processed at 200 MPa for 10 passes in a Sugino Machine Corporation ultra-high-pressure homogenizer called "Starburst Lab" (hereinafter referred to as "Starburst Lab") to obtain a nanocellulose aqueous dispersion. In the ultra-high-pressure homogenizer, the oxidized cellulose aqueous dispersion is circulated through the built-in ultra-high-pressure defibration section to advance defibration. One pass through the defibration section is referred to as one pass. The residual nitrogen content of the nanocellulose derived from N-oxyl compounds was 1.0 ppm or less. The residual nitrogen content was measured as the amount of nitrogen using a trace total nitrogen analyzer (manufactured by Nitto Seiko Analytech Co., Ltd., device name: TN-2100H) and calculated as the increase from the raw pulp. The nanocellulose obtained in Production Example 1 is also referred to as CNF-2.

[0085] The effective chlorine concentration in the sodium hypochlorite aqueous solution was measured by the following method. (Measurement of effective chlorine concentration in sodium hypochlorite aqueous solution) 0.582 g of an aqueous solution prepared by adding sodium hypochlorite pentahydrate crystals to pure water was precisely weighed, 50 ml of pure water was added, 2 g of potassium iodide and 10 ml of acetic acid were added, and the container was immediately sealed and left in the dark for 15 minutes. After leaving the container for 15 minutes, the liberated iodine was titrated with 0.1 mol / L sodium thiosulfate solution (indicator: starch test solution), and the titration amount was 34.55 ml. A blank test was separately performed to correct for this, and 1 ml of 0.1 mol / L sodium thiosulfate solution corresponded to 3.545 mg Cl, so the effective chlorine concentration in the sodium hypochlorite aqueous solution was 21% by mass.

[0086] In addition, the solid state of the sample obtained by freeze-drying the oxidized cellulose and then leaving it at 23°C and 50% RH for 24 hours or more was １３ As a result of measuring C-NMR, it was confirmed that both compounds had a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring were oxidized to introduce carboxyl groups. １３ The C-NMR measurement conditions are as follows: (1) Sample tube: Zirconia tube (4 mm diameter) (2) Magnetic field strength: 9.4 T (1H resonance frequency: 400 MHz) (3) MAS rotation speed: 15 kHz (4) Pulse sequence: CPMAS method (5) Contact time: 3 ms (6) Waiting time: 5 seconds (7) Number of accumulations: 10,000 to 15,000 (8) Measuring device: JNM ECA-400 (manufactured by JEOL Ltd.) The fact that the oxidized cellulose obtained in each production example has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring have been oxidized and carboxyl groups have been introduced was also confirmed by the results of two-dimensional NMR measurement using a model molecule of the oxidized cellulose as a sample. Furthermore, the solid state of the cellulose-based raw material related to item 6 was analyzed. １３ C-NMR and solid oxidized cellulose １３ Since no change in the spectral data was observed with C-NMR, it was determined that the hydroxyl group at position 6 was not oxidized and remained as a hydroxyl group in the oxidized cellulose.

[0087] [Production Example 2: Production of Tetrapropylammonium-Modified Nanocellulose] The oxidation reaction was carried out under the same conditions as in Production Example 1, except that the stirring time (i.e., reaction time) after supplying the cellulose-based raw material was 120 minutes. After completion of the reaction, the excess sodium hypochlorite was quenched by adding aqueous sodium sulfite solution. Subsequently, hydrochloric acid was added to adjust the pH to 2.5, converting the carboxyl groups to the -COOH type (H type). The resulting oxidized cellulose aqueous dispersion was subjected to solid-liquid separation and washing. Specifically, the process consisted of centrifugation (1000 G, 10 minutes), removal of the supernatant by decantation, addition of an amount of pure water equivalent to the amount removed, thorough stirring with a spoon to homogenize, and re-centrifugation. This process was repeated six times to recover purified oxidized cellulose. Subsequently, tetrapropylammonium hydroxide was added in an amount approximately equivalent to the amount of carboxyl groups introduced, modifying the carboxyl groups to the tetrapropylammonium type. The oxidized cellulose aqueous dispersion was adjusted to 1% by mass by adding pure water, and then defibrated in a homomixer (10,000 rpm, 10 minutes) to obtain nanocellulose as an aqueous dispersion. The nanocellulose obtained in Production Example 2 is also referred to as CNF-3.

[0088] Production Example 3: Dried oxidized cellulose product (thin flakes) 500 g of an aqueous sodium hypochlorite solution with a pH of 12.8 and an available chlorine concentration of 21% by mass was placed in a jacketed glass vessel, and the mixture was heated to 30°C while being stirred at 200 rpm using a mixer (Three-One Motor, BL600) manufactured by Shinto Scientific Co., Ltd. using three swept-back blades, and then 25 g of powdered pulp (KC Flock W-100GK) manufactured by Nippon Paper Industries Co., Ltd. was added as the cellulosic raw material. After supplying the cellulosic raw material, the mixture was stirred while maintaining the temperature at 30°C until the pH dropped to 11.3, and then the pH during the reaction was adjusted to 11.3 by adding a 25% by mass aqueous sodium hydroxide solution, and the mixture was stirred for a total of 6 hours under the same conditions after the addition of the cellulosic raw material. After the reaction was completed, the remaining sodium hypochlorite was inactivated by adding aqueous sodium sulfite solution, and then hydrochloric acid was added to convert the carboxyl groups of the oxidized cellulose from the salt form (-COO-Na+) to the proton form (-COO-H+), yielding an aqueous dispersion with a pH of 2.5. Solid-liquid separation was performed by pressure filtration at 0.2 MPa, followed by washing with aqueous hydrochloric acid at a pH of 2.5. Sodium hydroxide was added to the resulting proton-form oxidized cellulose to convert the carboxylic acid groups from the proton form (-COO-H+) back to the salt form (-COO-Na+), yielding an aqueous dispersion of salt-form oxidized cellulose with a pH of 6.8. The amount of carboxyl groups was measured to be 0.73 mmol / g, and the degree of polymerization was 100. Furthermore, the nitrogen component derived from N-oxyl compounds in the oxidized cellulose was measured as the amount of nitrogen using a trace total nitrogen analyzer (manufactured by Mitsubishi Chemical Analytech Co., Ltd., model number: TN-2100H). The increase from the raw pulp was calculated to be less than 1 ppm. The oxidized cellulose aqueous dispersion obtained in Production Example 3 (oxidized cellulose concentration 12% by mass, 1000 g) was dried in a drum dryer. The drying conditions were reduced pressure (100 torr), a drum temperature of 80°C, a drum rotation speed of 0.5 rpm, and a clearance between the drums of 0.6 mm. A dried oxidized cellulose product (in the form of thin flakes) of Production Example 3 was obtained.

[0089] [Production Example 4: Dried oxidized cellulose (powder form)] 5 g of the dried oxidized cellulose (thin flakes) obtained in Production Example 3 was placed in a Wonder Blender WB-1 manufactured by Osaka Chemical Co., Ltd. and processed at 25,000 rpm for 5 seconds to obtain the dried oxidized cellulose (powder form) of Production Example 4. The dried oxidized cellulose (powder form) obtained in Production Example 4 is also referred to as OC-P.

[0090] [Production Example 5: Nanocellulose production from oxidized cellulose (thin flakes) (Homomixer)] Pure water was added to 1 g of the dried oxidized cellulose (thin flakes) obtained in Production Example 3 to adjust the concentration to 2.5% by mass, and the mixture was then defibrated in a homomixer (10,000 rpm, 10 minutes) to obtain a nanocellulose aqueous dispersion. The nanocellulose obtained in Production Example 5 is also referred to as CNF-4. The average fiber length of the nanocellulose produced from the dried oxidized cellulose (thin flakes) was 170 nm, and the average fiber width was 3.6 nm.

[0091] [Production Example 6: Nanocelluloseization of Oxidized Cellulose (Flakes) (Manual Shaking)] Pure water was added to 1 g of the dried oxidized cellulose (flakes) obtained in Production Example 3 to adjust the concentration to 2.5% by mass, and the entire amount was then placed in a glass tube. The lid was then tightened and the tube was shaken by hand at a speed of 120 times per minute (amplitude: approximately 50 cm) to obtain a nanocellulose aqueous dispersion. The nanocellulose obtained in Production Example 6 is also referred to as CNF-5. The average fiber length of the nanocellulose produced from the dried oxidized cellulose (flakes) was 190 nm and the average fiber width was 4.5 nm.

[0092] [Production Example 7: Nanocelluloseization of oxidized cellulose (powdered) (Homomixer)] Pure water was added to 1 g of the dried oxidized cellulose (powdered) obtained in Production Example 4 to adjust the concentration to 2.5% by mass, and the mixture was then defibrated in a homomixer (10,000 rpm, 10 minutes) to obtain a nanocellulose aqueous dispersion. The nanocellulose obtained in Production Example 7 is also referred to as CNF-6. The average fiber length of the nanocellulose produced from the dried oxidized cellulose (powdered) was 160 nm, and the average fiber width was 3.5 nm.

[0093] [Production Example 8: Nanocelluloseization of Oxidized Cellulose (Powdered) (Manual Shaking)] Pure water was added to 1 g of the dried oxidized cellulose (powdered) obtained in Production Example 4 to adjust the concentration to 2.5% by mass, and the entire amount was then placed in a glass tube. The lid was then tightened and the tube was shaken by hand at a speed of 120 times per minute (amplitude: approximately 50 cm) to obtain a nanocellulose aqueous dispersion. The nanocellulose obtained in Production Example 8 is also referred to as CNF-7. The average fiber length of the nanocellulose produced from the dried oxidized cellulose (powdered) was 180 nm, and the average fiber width was 4.2 nm.

[0094] [Examples 1 to 6] <Preparation of binder composition for nonwoven fabric> 100 parts by mass of acrylic binder "Aron NW-7090" manufactured by Toagosei Co., Ltd. (referred to as NW-7090 in Table 1) and a nanocellulose aqueous dispersion were adjusted to the ratio shown in Table 1, and mixed and stirred to prepare a binder composition for nonwoven fabric. The following nanocellulose was used as the nanocellulose for the nanocellulose aqueous dispersion. Note that CNF-1, 2, and 3 in Table 1 are as follows. CNF-1: Leocrysta (registered trademark) I-2S (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) CNF-2: Nanocellulose of Production Example 1 CNF-3: Nanocellulose of Production Example 2 <Preparation of nonwoven fabric> The binder composition for nonwoven fabric was diluted with distilled water to a solids concentration of 20% to obtain a diluted solution. Pulp web (NBKP pulp, fiber basis weight: 45 g / m) prepared using a roller card ２ The diluted solution was uniformly sprayed onto a nonwoven fabric (10 cm x 10 cm) so that the amount of solids in the composition adhered was 15% by mass relative to the fiber basis weight. The nonwoven fabric was then dried at 155°C for 7 minutes to obtain a nonwoven fabric.

[0095] [Comparative Example 1] A nonwoven fabric was obtained in the same manner as in Example 1, except that a binder composition for nonwoven fabrics not containing nanocellulose (a nonwoven fabric composition containing no nanocellulose and NW-7090) was used.

[0096] The nonwoven fabrics obtained in Examples 1 to 6 and Comparative Example 1 were evaluated by the following methods.

[0097] (Evaluation of dry strength) The pulp nonwoven fabric for evaluation was cut into a rectangle with a width of 2.5 cm and a length of 10 cm to prepare a test piece for measuring dry strength. Next, the breaking strength of the obtained test piece when dry was measured using a tensile tester under conditions of a chuck distance of 5 cm and a tensile speed of 200 mm / min. In the examples and comparative examples, the breaking strength was measured for eight samples per type of sample, and the dry strength was determined by averaging the measurement results. The dry strength of Comparative Example 1, which is a sample without added nanocellulose, was set to 100 as the standard, and the strength of the examples was expressed.

[0098] (Evaluation of Wet Strength) The entire central 1 cm width of the above test piece for measuring dry strength was wetted with water, and after 5 seconds, a tensile test was performed under the same conditions as for the dry strength to determine the wet strength. The wet strength of Comparative Example 1, a sample without added nanocellulose, was set to 100, and the strength of the examples was expressed.

[0099] The physical properties of the nonwoven fabrics obtained in the examples and comparative examples are shown in Table 1.

[0100]

[0101] From the results in Table 1, Examples 1 to 6, in which a binder composition for nonwoven fabric containing nanocellulose was applied, had better dry strength and wet strength than Comparative Example 1, in which a binder composition for nonwoven fabric not containing nanocellulose was applied.

[0102] [Examples 7 to 11] <Preparation of binder composition for nonwoven fabric> Pure water was added to the nanocellulose CNF-2 obtained in Production Example 1 to adjust the concentration to 2.5%, and the resulting nanocellulose aqueous dispersion was used as a binder composition for nonwoven fabric. <Preparation of nonwoven fabric> The binder composition for nonwoven fabric was applied to a pulp web (NBKP pulp, fiber basis weight: 45 g / m) prepared using a roller card. ２The composition was uniformly sprayed onto a pulp web (10 cm x 10 cm) so that the amount of solids in the composition adhered to the fiber basis weight was the amount (% by mass) shown in Table 2. The nonwoven fabric was then dried at 155°C for 7 minutes to obtain a nonwoven fabric. The values ​​in Table 2 represent the amount of solids adhered per 100 parts by mass of the pulp web. The dry strength, wet strength, dry elongation, and bending resistance of the obtained nonwoven fabric were measured.

[0103] Comparative Example 2 Using an uncoated pulp web, the dry strength, wet strength, dry elongation, and bending resistance were measured.

[0104] The dry strength, wet strength, dry elongation, and bending resistance of the nonwoven fabrics of Examples 7 to 11 and Comparative Example 2 were measured as follows.

[0105] (Evaluation of dry strength) The nonwoven fabric for evaluation was cut into a rectangle of 2.5 cm width and 10 cm length to prepare a test piece for measuring dry strength. The obtained test piece was then measured for breaking strength in a dry state using a tensile tester under conditions of a chuck distance of 5 cm and a tensile speed of 200 mm / min. In the examples and comparative examples, the breaking strength was measured for eight samples per type of specimen, and the dry strength was calculated by averaging the measurement results. The dry strength of Comparative Example 2, which is an uncoated sample, was set to 100, and the strength of the examples was expressed.

[0106] (Evaluation of Wet Strength) The test piece for measuring dry strength was wetted with water over a central 1 cm width, and after 5 seconds, a tensile test was carried out under the same conditions as for the dry strength to determine the wet strength. The wet strength of Comparative Example 2, which is an uncoated sample, was set to 100, and the strength of the Examples was expressed.

[0107] (Dry elongation) The distance between chucks was measured when the test piece broke during the dry strength measurement. The dry elongation of Comparative Example 2, which was an uncoated sample, was set to 100, and the elongation of the examples was expressed.

[0108] (Bending resistance) The nonwoven fabric for evaluation was cut into a rectangle having a width of 2.5 cm and a length of 10 cm to prepare a test piece for measuring bending resistance. The short side of the test piece was placed on a smooth horizontal table with a 30° slope at one end, aligning it with the scale baseline. Next, the test piece was gently moved in the direction of the slope, and when the center point of one end of the test piece contacted the slope, the position of the other end was measured with a ruler, and the length (mm) moved by the test piece was measured to determine the bending resistance. The bending resistance of the examples was expressed as 100, with the bending resistance of Comparative Example 2, which was an uncoated sample, being used as the standard.

[0109] The physical properties of the nonwoven fabrics obtained in the examples and comparative examples are shown in Table 2.

[0110]

[0111] From the results in Table 2, Examples 7 to 11, which are nonwoven fabrics coated with nanocellulose, had superior dry strength, wet strength, and bending resistance compared to Comparative Example 2, which is an uncoated sample. Dry elongation was also good.

[0112] [Examples 12 to 15] <Preparation of nonwoven fabric> Spray application A binder composition for nonwoven fabric (nanocellulose) was applied to a pulp web (NBKP pulp, fiber basis weight: 45 g / m) prepared using a roller card. ２ The composition was uniformly sprayed onto a pulp web (10 cm x 10 cm) so that the amount of solids in the composition adhered to the fiber basis weight was the amount (% by mass) shown in Table 3. This was then dried at 155°C for 7 minutes to obtain a nonwoven fabric. The values ​​in Table 3 are the amount of solids adhered when the pulp web is 100 parts by mass. The nonwoven fabric binder compositions (nanocellulose) are as follows: CNF-4: Nanocellulose of Production Example 5 CNF-5: Nanocellulose of Production Example 6 CNF-6: Nanocellulose of Production Example 7 CNF-7: Nanocellulose of Production Example 8 The dry strength, wet strength, dry elongation, and bending resistance of the obtained nonwoven fabric were measured.

[0113] [Example 16] ○ Powder sieving The OC-P obtained in Production Example 4 was sieved into a pulp web (NBKP pulp, fiber basis weight: 45 g / m) prepared using a roller card. ２The pulp web was uniformly sieved and coated onto a 10 cm x 10 cm (10 cm x 10 cm) so that the amount of solids in the composition adhered was the amount (mass %) shown in Table 3 relative to the fiber basis weight, and then pure water was sprayed onto the nonwoven fabric in an amount 20 times the mass of the OC-P adhered. The nonwoven fabric was then dried at 155°C for 7 minutes to obtain a nonwoven fabric. The values ​​in Table 3 represent the amount of solids adhered per 100 parts by mass of the pulp web. The dry strength, wet strength, dry elongation, and bending resistance of the obtained nonwoven fabric were measured.

[0114] Comparative Example 3 Using an uncoated pulp web, the dry strength, wet strength, dry elongation, and bending resistance were measured.

[0115] The dry strength, wet strength, dry elongation, and bending resistance of the nonwoven fabrics of Examples 12 to 16 and Comparative Example 3 were measured as follows.

[0116] (Evaluation of dry strength) The nonwoven fabric for evaluation was cut into a rectangle of 2.5 cm wide and 10 cm long to prepare a test piece for measuring dry strength. The resulting test piece was then measured for breaking strength in a dry state using a tensile tester under conditions of a chuck distance of 5 cm and a tensile speed of 200 mm / min. In the examples and comparative examples, the breaking strength was measured for eight samples per type of specimen, and the dry strength was calculated by averaging the measurement results. The dry strength of Comparative Example 3, which is an uncoated sample, was set to 100, and the strength of the examples was expressed.

[0117] (Evaluation of Wet Strength) The test piece for measuring dry strength was wetted with water over a central 1 cm width, and after 5 seconds, a tensile test was carried out under the same conditions as for the dry strength to determine the wet strength. The wet strength of Comparative Example 3, which is a sample that has not been coated, was set to 100, and the strength of the examples was expressed.

[0118] (Dry elongation) The distance between chucks was measured when the test piece broke during the dry strength measurement. The dry elongation of Comparative Example 3, which was an uncoated sample, was set to 100, and the elongation of the examples was expressed.

[0119] (Bending resistance) The nonwoven fabric for evaluation was cut into a rectangle having a width of 2.5 cm and a length of 10 cm to prepare a test piece for measuring bending resistance. The short side of the test piece was placed on a smooth horizontal table with a 30° inclined surface at one end, aligned with the scale base line. Next, the test piece was gently moved in the direction of the inclined surface, and when the center point of one end of the test piece contacted the inclined surface, the position of the other end was measured with a ruler, and the length (mm) moved by the test piece was measured to determine the bending resistance. The bending resistance of the examples was expressed as 100, with the bending resistance of Comparative Example 3, which was an uncoated sample, being used as the standard.

[0120] The physical properties of the nonwoven fabrics obtained in the examples and comparative examples are shown in Table 3.

[0121]

[0122] From the results in Table 3, Examples 12 to 15, which are nonwoven fabrics spray-coated with nanocellulose, and Example 16, which was dusted with oxidized cellulose (powder), had superior dry strength, wet strength, and bending resistance compared to Comparative Example 3, which was an uncoated sample. Dry elongation was also good.

[0123] The nonwoven fabric binder composition of the present invention has industrial applicability in the field of nonwoven fabrics.

Claims

1. A binder composition for nonwoven fabrics, comprising chemically modified nanocellulose.

2. The chemically modified nanocellulose comprises oxidized nanocellulose; The binder composition for nonwoven fabric according to claim 1 .

3. The oxidized nanocellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds; The binder composition for nonwoven fabric according to claim 2 .

4. The oxidized nanocellulose has a structure in which the second and third hydroxyl groups of the glucopyranose ring are oxidized and carboxyl groups are introduced. The binder composition for nonwoven fabric according to claim 2 .

5. The oxidized nanocellulose comprises hydrophobically modified oxidized nanocellulose; The binder composition for nonwoven fabric according to any one of claims 2 to 4.

6. The nonwoven fabric is a cellulosic nonwoven fabric made from cellulosic fibers. The binder composition for nonwoven fabric according to any one of claims 1 to 5.

7. Further comprising at least one selected from a styrene-butadiene copolymer, an ethylene-vinyl acetate copolymer, and an acrylic copolymer; The binder composition for nonwoven fabric according to any one of claims 1 to 6.

8. A nonwoven fabric produced using the binder composition for nonwoven fabric according to any one of claims 1 to 7.

9. A nonwoven fabric comprising chemically modified nanocellulose.

10. The chemically modified nanocellulose comprises oxidized nanocellulose; The nonwoven fabric of claim 9.

11. The oxidized nanocellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds; The nonwoven fabric of claim 10.

12. The oxidized nanocellulose has a structure in which the second and third hydroxyl groups of the glucopyranose ring are oxidized and carboxyl groups are introduced. The nonwoven fabric of claim 10.

13. A method for producing a binder composition for nonwoven fabrics containing chemically modified nanocellulose, comprising: The method includes a step of defibrating the chemically modified cellulose by stirring a mixture containing the chemically modified cellulose and a material other than the chemically modified nanocellulose of the nonwoven fabric binder composition to obtain the nonwoven fabric binder composition, the chemically modified cellulose comprises oxidized cellulose; The method for producing the oxidized cellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.

14. A method for producing a binder composition for nonwoven fabrics containing chemically modified nanocellulose, comprising: The method includes a step of defibrating the chemically modified cellulose by stirring a mixture containing the chemically modified cellulose and a material other than the chemically modified nanocellulose of the nonwoven fabric binder composition to obtain the nonwoven fabric binder composition, the chemically modified cellulose comprises oxidized cellulose; The oxidized cellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring have been oxidized and carboxyl groups have been introduced.

15. A method for producing a binder composition for nonwoven fabrics containing chemically modified nanocellulose, comprising: The method includes a step of defibrating the chemically modified cellulose by stirring the chemically modified cellulose and continuously adding materials other than the chemically modified nanocellulose of the nonwoven fabric binder composition to obtain the nonwoven fabric binder composition, the chemically modified cellulose comprises oxidized cellulose; The method for producing the oxidized cellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.

16. A method for producing a binder composition for nonwoven fabrics containing chemically modified nanocellulose, comprising: The method includes a step of defibrating the chemically modified cellulose by stirring the chemically modified cellulose and continuously adding materials other than the chemically modified nanocellulose of the nonwoven fabric binder composition to obtain the nonwoven fabric binder composition, the chemically modified cellulose comprises oxidized cellulose; The oxidized cellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring have been oxidized and carboxyl groups have been introduced.