Water-disintegratable paper and process for producing the same

Abstract

To provide a water-disintegrable paper capable of contributing to reduction of environmental load.SOLUTION: The water-disintegrable paper of the present invention comprises a paper sheet containing cellulose fibers and a food-extraction residue, and has a disintegratability of 1 second or more and 100 seconds or less as defined by JISP4501. The food extraction residue preferably contains particles having an aspect ratio of 10 or less and a median diameter of 10 μm or more and 1000 μm or less. One example of the water-disintegratable paper of the invention further comprises an anionic polymer and a cationic polymer, wherein the anionic polymer comprises carboxymethyl cellulose and the cationic polymer comprises poly (acrylamide-co-diallyldimethylammonium chloride) and / or polymethacryloyloxyethyltrimethylammonium chloride.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to water-disintegrable paper containing food extract residue. [Background technology]

[0002] Conventionally, cleaning products have been used as products for cleaning around toilets or wiping the body, in which water-disintegrable paper holds an aqueous chemical so that it can be flushed down the toilet after use. This type of water-disintegrable paper needs to have sufficient strength for practical use to withstand wiping work, and to ensure this, the water-disintegrable paper has a configuration in which cellulose fibers such as wood pulp are bound with an anionic polymer. Patent Document 1 describes water-disintegrable paper that uses carboxymethyl cellulose as the anionic polymer.

[0003] BACKGROUND ART Conventionally, a technique for blending a tea extract or its extraction residue with a paper product mainly made of cellulose fibers such as wood pulp has been known. Patent Document 2 describes a pulp molded product obtained by molding an aqueous slurry containing pulp fibers, a pyrrolidone-containing polymer, and a tea extract by a wet papermaking method. The tea extract is used to impart antibacterial and antioxidant properties to the pulp molded product, and is tea polyphenols obtained by extraction from tea leaves with water and / or an organic solvent, rather than an extraction residue. Patent Document 3 describes paper obtained by molding a paper pulp slurry containing wet-ground tea leaves by a wet papermaking method. The wet-ground tea leaves are an extraction residue obtained by wet-grounding hydrated tea leaves, which are the residue after extracting tea liquor from tea leaves. The paper described in Patent Document 3 is said to have the antibacterial and deodorizing properties that are favorable due to the wet-ground tea leaves, as well as durability such as being difficult to dissolve in water (paragraph

[0008] of Patent Document 3), but is not water-decomposable. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-41649 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-203577 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-255515 Summary of the Invention [Problem to be solved by the invention]

[0005] Biomass materials, which are organic resources derived from living organisms, are sustainable renewable resources, and their active use is expected to lead to a reduction in CO2 in the atmosphere, thereby contributing to the prevention of global warming and the creation of an environmentally friendly society.

[0006] Large quantities of coffee powder (coffee grounds) are generated after brewing at factories that manufacture coffee products such as canned coffee and instant coffee, as well as at major chain cafes. For example, statistical data shows that the total amount of coffee grounds generated worldwide in 2022 will be approximately 8 million tons. As coffee consumption worldwide is increasing year by year, the amount of coffee grounds generated is expected to increase in the future. Coffee grounds are a relatively inexpensive and easily available biomass material, and their effective use is an important issue from the perspective of environmental issues.

[0007] An object of the present invention is to provide water-disintegrable paper that can contribute to reducing the environmental burden. [Means for solving the problem]

[0008] As a result of extensive research into the effective use of coffee grounds, the inventors have discovered that by using coffee grounds in combination with cellulose fibers such as wood pulp to produce water-disintegratable paper that is water-disintegratable enough to be flushed down the toilet after use, it is possible to obtain water-disintegratable paper with a unique texture not found in conventional water-disintegratable paper while maintaining the water-disintegratability. Furthermore, they have discovered that not only coffee grounds but also tea leaves after extraction (tea residue) are useful raw materials for water-disintegratable paper, and have concluded that food extraction residues such as these are useful raw materials for water-disintegratable paper.

[0009] The present invention was made based on the above findings, and is a water-decomposable paper having a papermaking sheet containing cellulose fibers and food extract residues. In one embodiment of the water-disintegrable paper of the present invention, the ease of disintegration as defined by JIS P 4501 is preferably 1 second or more and 100 seconds or less.

[0010] The present invention has been made based on the above findings, and is a water-disintegrable cleaning article comprising the above-mentioned water-disintegrable paper of the present invention and an aqueous chemical.

[0011] The present invention has been made based on the above findings, and provides a method for producing water-disintegrable paper, which includes a slurry preparation step of preparing a slurry containing cellulose fibers, food extract residue, an anionic polymer, a cationic polymer, and water. In one embodiment of the method for producing water-disintegrable paper of the present invention, it is preferable to further include a sheeting step in which the slurry is sheeted by a wet papermaking method to obtain a wet papersheet, and the papersheet is dried by heating.

[0012] The present invention has been made based on the above findings and provides a method for producing a water-decomposable cleaning article, which includes a slurry preparation step of preparing a slurry containing cellulose fibers, food extract residue, an anionic polymer, a cationic polymer, and water. In one embodiment of the method for producing a water-decomposable cleaning article of the present invention, it is preferable to further include a sheeting step in which the slurry is formed into a sheet by a wet papermaking method to obtain a wet papersheet, and the papersheet is dried by heating. In one embodiment of the method for producing a water-decomposable cleaning article of the present invention, it is preferable to further include a step of retaining an aqueous chemical on the paper sheet that has been subjected to the sheet-forming step. Other features, advantages and embodiments of the present invention are described below. [Effects of the Invention]

[0013] According to the present invention, water-disintegrable paper that can contribute to reducing the environmental load is provided. DETAILED DESCRIPTION OF THE INVENTION

[0014] The water-disintegrable paper of the present invention has a paper sheet containing cellulose fibers and food extract residue. The paper sheet is produced by forming a slurry containing cellulose fibers and food extract residue into a sheet by a wet papermaking method.

[0015] As the cellulose fiber, any fiber applicable to a wet papermaking process can be used without particular limitation. Examples include bleached wood pulp such as softwood bleached kraft pulp (NBKP), softwood bleached sulfite pulp, and hardwood bleached kraft pulp; unbleached wood pulp such as softwood unbleached kraft pulp, softwood unbleached sulfite pulp, and hardwood unbleached kraft pulp; non-wood pulp such as cotton, straw, kenaf, and hemp; and regenerated cellulose fibers such as rayon, lyocell, and cupra. These fibers can be used alone or in combination. From the viewpoint of ensuring that the physical properties of the water-disintegrable paper, such as strength, are practically sufficient, bleached or unbleached wood pulp is preferred as the cellulose fiber, and NBKP is particularly preferred. Furthermore, cellulose fibers derived from recycled paper can also be used, but from the same viewpoint, virgin cellulose fibers such as virgin pulp are preferred.

[0016] Cellulose fiber is typically the main component of the papermaking sheet, accounting for 50% by mass, preferably 60% by mass or more of the total mass of the papermaking sheet. On the other hand, the upper limit of the cellulose fiber content in the papermaking sheet is preferably 90% by mass or less, more preferably 85% by mass or less, based on the total mass of the papermaking sheet, in order to ensure room for the inclusion of other components such as food extract residues.

[0017] The papermaking sheet according to the present invention includes those having a single layer structure and those having a laminated structure in which multiple layers are laminated in the thickness direction. When the papermaking sheet has such a laminated structure, the "content of cellulose fiber in the papermaking sheet" refers to the content of cellulose fiber in each of the multiple layers constituting the laminated structure. Unless otherwise specified, the same applies to other components (food extract residue, anionic polymer, etc.) other than cellulose fiber in the papermaking sheet.

[0018] The food extraction residue used in this invention is the substance remaining after extracting a specific target component from food. The term "food" as used herein refers to any substance in an edible or drinkable state that can be consumed by humans, including ingredients such as vegetables, fruits, fresh fish, and meat, as well as cooked products made from such ingredients. The method for "extracting the target component" is not particularly limited, but is typically a solvent extraction method in which the target component is eluted from the food by contacting the food with a solvent (e.g., hot water or an organic solvent).

[0019] Conventionally, food extract residues have been discarded, but in the present invention, by using them as a raw material for water-disintegrable paper, the cellulose fiber content in the water-disintegrable paper is reduced, thereby reducing the amount of cellulose fiber used and thereby reducing the environmental burden. The water-disintegrable paper of the present invention may contain one type of food extract residue, or two or more types of food extract residues.

[0020] The food extract residue may contain plant-derived substances, animal-derived substances, or both. The food extract residue is typically composed of plant-derived substances. The plant source of the plant-derived substances is not particularly limited, and may be a woody plant or a herbaceous plant. Furthermore, the part of the plant source of the plant-derived substances is not particularly limited, and may be leaves, stems, roots, or fruits.

[0021] Specific examples of food extraction residues suitable for use in the present invention include plant-derived substances such as coffee grounds, tea grounds, beer grounds, rice husks, and vegetable or fruit pulp. Coffee grounds are coffee powder after extraction. Tea grounds are tea leaves after extraction, including green tea leaves and black tea leaves. Beer grounds are malt dregs generated after beer production. By incorporating the above food extraction residues made from plant-derived substances into water-disintegrable paper, it is possible to obtain water-disintegrable paper with a unique texture not found in conventional water-disintegrable paper.

[0022] From the viewpoint of improving the unique texture of the water-disintegrable paper, the food extract residue preferably contains particles with an aspect ratio of 10 or less and a median diameter of 10 μm or more and 1000 μm or less (hereinafter also referred to as "specific particles"). One embodiment of water-disintegrable paper with a good unique texture is one in which relatively small food extract residues are uniformly dispersed throughout the water-disintegrable paper, and when the food extract residue contained in the water-disintegrable paper contains specific particles, it becomes easier to obtain water-disintegrable paper in this form. Food extract residues with an aspect ratio of 10 or less are not fibrous but particulate, and by dispersing the particulate food extract residues uniformly throughout the water-disintegrable paper, it becomes easier to impart a desirable and unique texture to the water-disintegrable paper. The median diameter of the specific particles is preferably 100 μm or more and 500 μm or less, more preferably 300 μm or less. Incidentally, the median diameter of coffee powder, which is the source of typical coffee beverages, is approximately 0.5 to 1 mm. The median diameter of the food extract residue (specific particles) can be adjusted by pulverizing the food extract residue to reduce the particle size using a commercially available grinder (e.g., a household multi-blender or an industrial hammer mill).

[0023] The aspect ratio is defined as the ratio between the maximum diameter of the food extract residue and the length of the portion of the food extract residue having the maximum diameter in the direction perpendicular to the extending direction. The aspect ratio can be measured, for example, by imaging the food extract residue with an electron microscope and using the image data. Specifically, for water-disintegrable paper (paper containing food extract residue), images with 10 or more food extract residue particles per field of view are taken with a scanning electron microscope, and the average value of 10 randomly selected food residue particles is used as the aspect ratio.

[0024] The median diameter refers to the particle size D50 at 50% cumulative volume measured using a particle size distribution measurement method based on laser diffraction and scattering for food extract residue with a moisture content of 10% by mass or less. An example of a device for measuring the median diameter is the "LA-960" manufactured by Horiba, Ltd. If the moisture content of the food extract residue to be measured exceeds 10% by mass, the food extract residue is dried, for example by heating, to adjust the moisture content to 10% by mass or less before measuring the median size.

[0025] The moisture content of the food extract residue is measured by the loss on drying method. A sample whose mass has been measured in advance is heated and dried at 105°C until it reaches a constant weight. The loss in mass after drying is taken as the moisture content (unit: g) of the food extract residue, and the remaining mass is taken as the solid content (unit: g) of the food extract residue. The moisture content of the food extract residue is calculated using the following formula: Moisture content of food extract residue (mass%) = (moisture content / solid content) x 100

[0026] The specific particles are typically in the form of particles at room temperature and pressure, and are not in the form of fibers like cellulose fibers. The particle shape of the specific particles may be spherical, lumpy, bale-like, or irregular.

[0027] The proportion of the mass of the specific particles to the total mass of the food extract residue in the papermaking sheet (specific particle occupancy) is preferably as high as possible from the viewpoint of improving the unique texture of the water-disintegrable paper. Specifically, it is preferably 5% by mass or more, more preferably 15% by mass or more, and most preferably 100% by mass, i.e., the entire food extract residue in the papermaking sheet is made up of specific particles.

[0028] The presence or absence of specific particles in water-disintegrable paper such as the papermaking sheet can be confirmed by the following method. Specifically, water-disintegrable paper is first immersed in water to disintegrate it, obtaining a dispersion in which the components contained in the water-disintegrable paper form the dispersoid. Next, food extract residue is extracted from the dispersion. Specifically, "substances that may be food extract residue" are extracted from the dispersion, and the substances are qualitatively analyzed using known chemical substance identification methods such as FT-IR to confirm whether or not the substances are food extract residue. Details of the method for extracting food extract residue from the dispersion are described below. Next, the food extract residue extracted from the dispersion is subjected to image analysis using an image analysis particle size distribution analyzer (Valmet FS5, manufactured by Valmet Automation Co., Ltd.) according to the manual, and food extract residue with an aspect ratio of 10 or less is extracted from the food extract residue subjected to image analysis based on the results of the image analysis. The median diameter of the food extract residue thus extracted, which has an aspect ratio of 10 or less, is measured using the above-mentioned method. If the measured value is 10 μm or more and 1000 μm or less, the food extract residue is determined to be a specific particle (particulate food extract residue with an aspect ratio of 10 or less and a median diameter of 10 μm or more and 1000 μm or less). The specific particle occupancy rate is calculated as a percentage of the value obtained by measuring the total mass (dry mass) of the specific particles in the papermaking sheet using the method described above and dividing the measured value by the total mass (dry mass) of the food extract residue in the papermaking sheet.

[0029] A method for extracting food extract residue from the dispersion (a dispersion containing components of water-disintegrable paper as dispersoids) is described below. Food extract residue is typically a colored substance that has a different color from the cellulose fiber, the main component of water-disintegrable paper, and this can be utilized to extract food extract residue. Cellulose fiber is usually white or off-white, whereas food extract residue is often a color other than white, such as black, brown, or gray. Specifically, for example, the colored substance can be separated and recovered from the dispersion by filtering the dispersion using a filter or centrifuging the dispersion, and the colored particles can be qualitatively analyzed using a chemical identification method to confirm whether the colored particles are food extract residue. When the food extract residue and cellulose fiber are the same color and cannot be distinguished by color, differences in particle size and / or specific gravity can be utilized to separate and recover substances other than cellulose fiber from the dispersion by filtration and / or centrifugation, and the substances can be qualitatively analyzed using a chemical identification method to confirm whether the substances are food extract residue.

[0030] The higher the content of food extract residues in the papermaking sheet, the better from the viewpoint of providing water-disintegrable paper that can contribute to reducing the environmental burden, but if the content is too high, the content of other components of the papermaking sheet, including cellulose fiber, will decrease, and as a result, the basic performance of the water-disintegrable paper, such as water-decomposability and strength, may decrease. Taking the above into consideration, the content of food extract residues in the papermaking sheet is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 25% by mass or less, based on the total mass of the papermaking sheet.

[0031] The content of food extract residue in the papermaking sheet can be measured by the following method. First, the papermaking sheet is immersed in water to disintegrate it, and a dispersion liquid containing the components of the papermaking sheet as dispersoids is obtained. Next, food extract residue is extracted from the dispersion liquid. This method of extracting food extract residue is as described above. The total mass (dry mass) of the food extract residue (colored substances) extracted from the dispersion liquid is measured, and the measured value is divided by the total mass (dry mass) of the papermaking sheet to obtain a percentage, thereby calculating the content of food extract residue in the papermaking sheet.

[0032] The papermaking sheet preferably further contains an anionic polymer in addition to cellulose fibers and food extract residue. The anionic polymer functions as a binder that maintains the bonds between cellulose fibers in the papermaking sheet, and can improve the wet strength of the papermaking sheet. In particular, in a water-disintegrable cleaning article containing water-disintegrable paper and an aqueous chemical, the water-disintegrable paper is in a wet state retaining the aqueous chemical. In the wet state of the water-disintegrable paper, the anionic polymer contained in the water-disintegrable paper binds to a polymer-insolubilizing component (e.g., a metal ion) contained in the aqueous chemical and is temporarily insolubilized, thereby ensuring the strength required for use of the water-disintegrable paper.

[0033] The anionic polymer contained in the papermaking sheet is preferably a water-soluble anionic polymer, specific examples of which include natural polysaccharides, polysaccharide derivatives, and synthetic polymers. The papermaking sheet may contain one type of anionic polymer or two or more types of anionic polymers. Examples of the natural polysaccharides include sodium alginate, tolanthus gum, guar gum, xanthan gum, gum arabic, carrageenan, galactomannan, gelatin, casein, albumin, and purpuran. Examples of the polysaccharide derivatives include carboxymethyl cellulose, carboxyethyl cellulose, carboxymethylated starch or a salt thereof, starch, methyl cellulose, and ethyl cellulose. Examples of the synthetic polymer include polyvinyl alcohol, polyvinyl alcohol derivatives, salts of polymers or copolymers of unsaturated carboxylic acids, and salts of copolymers of unsaturated carboxylic acids and monomers copolymerizable with the unsaturated carboxylic acids. Examples of the unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic anhydride, maleic acid, and fumaric acid. Among the water-soluble anionic polymers, those having carboxyl groups are preferred as anionic polymers to be contained in the papermaking sheet because of their excellent binder properties. A preferred example of a water-soluble anionic polymer having carboxyl groups is carboxymethyl cellulose (CMC). In this specification, "CMC" includes CMC and its salts.

[0034] Whether or not water-disintegrable paper such as the paper sheet contains CMC can be confirmed by the following method. That is, first, the water-disintegrable paper is immersed in an aqueous solution containing zinc sulfate, for example, to impregnate the water-disintegrable paper with the aqueous solution, and then the water-disintegrable paper is squeezed to recover the eluate from the water-disintegrable paper, which is then dried to obtain a dried product. Next, the dried product is analyzed by FT-IR, and in the IR spectrum obtained by the analysis (horizontal axis: wave number, vertical axis: transmittance or absorbance), a peak at 1647 cm -1 If a peak derived from the carboxylate salt of carboxymethyl cellulose is observed nearby, the water-disintegrable paper is determined to contain CMC. Anionic polymers other than CMC are also analyzed by FT-IR in the same way, and whether or not the water-disintegrable paper contains anionic polymers can be determined by whether or not the IR spectrum derived from the functional groups specific to the anionic polymer (typically carboxylate salts) is recognized.

[0035] The content of the anionic polymer in the papermaking sheet is preferably 0.5% by mass or more, more preferably 1.5% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, based on the total mass of the papermaking sheet, from the viewpoint of balancing the wet strength and water disintegrability of the papermaking sheet while keeping the content of the anionic polymer to the minimum necessary.

[0036] The content of CMC as an anionic polymer in the paper sheet can be measured by the naphthalenediol method described in JIS K 3362. The paper sheet confirmed to contain CMC by this method is used as the measurement target. The paper sheet to be measured is dispersed and stirred in 6% sodium hydroxide for 6 hours, and then filtered to obtain a CMC extract. A naphthalenediol solution is added to the CMC extract and kept at 100°C for 6 hours. The extract is then analyzed by ultraviolet-visible spectroscopy, and the CMC content is calculated from the absorbance at 530 nm.

[0037] The papermaking sheet preferably further contains a cationic polymer in addition to the cellulose fibers and the food extract residue, which functions as a retention improver for the food extract residue in the papermaking sheet. The "food extract residue yield" refers to the ratio of the mass of food extract residue actually used (mass of food extract residue contained in the papermaking sheet) to the total mass of food extract residue used in the production of the papermaking sheet, and the numerical value representing this food extract residue yield as a percentage is called the "food extract residue yield rate" (unit: mass%). The method for calculating the food extract residue yield rate will be described later. By using a combination of food extract residue and cationic polymer during the production of the papermaking sheet (during wet papermaking), the probability that the added food extract residue will remain in the papermaking sheet increases, reducing waste of food extract residue and lowering production costs, and effectively preventing problems such as contamination of production equipment due to the outflow of food extract residue.The papermaking sheet may contain one type of cationic polymer, or two or more types of cationic polymers. In the slurry during wet papermaking, cellulose fibers are negatively charged, and coffee grounds, a typical food extraction residue, are also negatively charged. However, by applying electrostatic attraction with a cationic polymer, the yield can be improved. In particular, the yield improvement effect of cationic polymers is achieved for specific particles with small median diameters, which generally tend to have low yields.

[0038] The cationic polymer to be contained in the papermaking sheet is preferably one or more selected from the group consisting of poly(acrylamide-co-diallyldimethylammonium chloride) and polymethacryloyloxyethyltrimethylammonium chloride (hereinafter also referred to as "specific cationic polymer"). As mentioned above, one of the purposes of incorporating a cationic polymer into the papermaking sheet is to improve the yield of food extract residue. A person skilled in the art would expect that a cationic polymer that can be used to achieve this purpose would be one that has traditionally been used as a paper strength agent in ordinary paper other than water-disintegrable paper (e.g., polyacrylamide, polyamidoamine epichlorohydrin). However, as a result of the inventor's investigations, it was found that when a papermaking sheet containing cellulose fibers and food extract residue is incorporated with polyacrylamide or polyamidoamine epichlorohydrin in an amount sufficient to improve the yield, the water-disintegrability of the papermaking sheet decreases (see Comparative Examples 2 and 3 described below). Therefore, after extensive investigations into cationic polymers optimal for the papermaking sheet, the inventors discovered the two specific cationic polymers mentioned above.

[0039] The presence of poly(acrylamide-co-diallyldimethylammonium chloride) or polymethacryloyloxyethyltrimethylammonium chloride in the papermaking sheet can be confirmed by the following method. First, the papermaking sheet is impregnated with an aqueous solution containing zinc sulfate, for example by immersing the papermaking sheet in the aqueous solution. The papermaking sheet is then squeezed to recover the eluate from the papermaking sheet, and the eluate is dried to obtain a dried product. Next, the dried product is dissolved in water or methanol, and the supernatant is recovered by centrifugation. The supernatant is separated into components by molecular weight using gel permeation chromatography. Each separated component is analyzed by nuclear magnetic resonance spectroscopy. If the spectrum matches that of poly(acrylamide-co-diallyldimethylammonium chloride) or polymethacryloyloxyethyltrimethylammonium chloride, the papermaking sheet is determined to contain a specific cationic polymer.

[0040] When the papermaking sheet contains a specific cationic polymer, it is preferable that the papermaking sheet contains CMC as the anionic polymer. That is, it is preferable that the papermaking sheet contains CMC as the anionic polymer and further contains one or more specific cationic polymers as the cationic polymer. This makes it possible to obtain water-disintegrable paper that is excellent in water-disintegrability, wet strength, and food extraction residue retention.

[0041] The general formula of poly(acrylamide-co-diallyldimethylammonium chloride) is as follows: In the formula, x represents the degree of polymerization of acrylamide, and y represents the degree of polymerization of diallyldimethylammonium chloride. As poly(acrylamide-co-diallyldimethylammonium chloride), a commercially available product, "Unisense ZCA1002L" manufactured by Senka Corporation, can be used.

[0042] [ka]

[0043] The general formula of polymethacryloyloxyethyltrimethylammonium chloride is as follows: In the formula, m represents the degree of polymerization.

[0044] [ka]

[0045] The content of the cationic polymer in the papermaking sheet is preferably 0.5% by mass or more, more preferably 1.5% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, relative to the total mass of the papermaking sheet, from the viewpoint of improving the yield of food extraction residue while keeping the content of the cationic polymer to the minimum necessary.

[0046] The basis weight of the papermaking sheet may be appropriately selected depending on the use of the water-disintegrable paper containing the papermaking sheet, and is not particularly limited. For example, when the water-disintegrable paper is used for wiping and cleaning, it is preferably 10 g / m 2 More than 100g / m 2 Less than 20 g / m, more preferably 2 More than 50g / m 2 The basis weight of a paper sheet is measured in the dry state.

[0047] The water-disintegrable paper of the present invention may consist of only the papermaking sheet, or may contain sheets other than the papermaking sheet. The former form, i.e., the exposed water-disintegrable paper in which the papermaking sheet containing the food extract residue is exposed, may have a single-layer structure consisting of one papermaking sheet, or a layered structure in which multiple papermaking sheets are layered in the thickness direction. An example of the latter form is a laminated structure comprising an inner layer made of the papermaking sheet and outer layers arranged on both sides of the inner layer in the thickness direction, the outer layers containing cellulose fibers and a water-soluble binder and substantially free of food extraction residue (hereinafter also referred to as "non-exposed water-disintegrable paper"). In the non-exposed water-disintegrable paper, both sides of the inner layer containing food extraction residue are covered with outer layers that are substantially free of food extraction residue. Therefore, even if food extraction residue is detached from the inner layer, the detached food extraction residue is retained in the outer layers, effectively preventing the problem of food extraction residue leaking out of the water-disintegrable paper.

[0048] The non-exposed water-disintegrable paper will now be described. The outer layer is bonded to the surface of the inner layer. The method for bonding the outer layer and the inner layer is not particularly limited as long as the desired effects of the present invention are achieved, and although they may be bonded using an adhesive, typically, they are bonded only by hydrogen bonds between the cellulose fibers of both layers. The outer layer is not particularly limited in its configuration, provided that it is a sheet that can be integrated with the papermaking sheet (the inner layer) and has the same degree of water decomposability as the papermaking sheet. A preferred example of the outer layer is a papermaking sheet that contains cellulose fiber and a water-soluble binder and is substantially free of food extract residues. The term "substantially free of food extract residue" refers to both a case in which the content of food extract residue in the outer layer is zero and a case in which the content is not zero but can be considered to be substantially zero. The latter case is, for example, a case in which food extract residue is contained but the content is so small that no food extract residue can be detected by visually observing the appearance of the outer layer. In the latter case, the content of food extract residue in the outer layer is preferably 1% by mass or less, more preferably 0.5% by mass or less, based on the total mass of the outer layer. As the cellulose fibers for the outer layer, those that can be used for the papermaking sheet (the inner layer) can be used. The water-soluble binder in the outer layer can be any material that can be used as a water-soluble anionic polymer in the papermaking sheet. CMC is particularly preferred. The content of the water-soluble binder in the outer layer can be adjusted to the same level as the content of the anionic polymer in the papermaking sheet. The basis weight of the outer layer may be appropriately selected depending on the intended use of the non-exposed water-disintegrable paper including the outer layer, and is not particularly limited. For example, when the water-disintegrable paper is used as a cleaning product for wiping off dirt from an object to be cleaned, the basis weight is preferably 10 g / m 2 More than 100g / m 2 Less than 20 g / m, more preferably 2 More than 50g / m 2 The following is the result.

[0049] The water-disintegrable paper of the present invention has a disintegration time as specified by JIS P 4501 of 1 second to 100 seconds, preferably 1 second to 80 seconds, more preferably 30 seconds or less. The ease of disintegration is the time (disintegration time) required for the water-disintegrable paper to disintegrate in water in a specified disintegration test, and the shorter this disintegration time, the easier the water-disintegrable paper is to disintegrate and the higher its water-disintegrability is evaluated to be. When the ease of disintegration (disintegration time) is within the above range, the water-disintegrable paper has water-disintegrability that allows it to be flushed down the toilet and practically sufficient strength to withstand the task of wiping off dirt, making it suitable as a cleaning article that can be disposed of by flushing down the toilet after wiping. As mentioned above, the water-disintegrable paper of the present invention includes both paper made only of the papermaking sheet (exposed water-disintegrable paper) and paper having sheets other than the papermaking sheet (e.g., the outer layer) (e.g., non-exposed water-disintegrable paper), and it is preferable that the ease of disintegration of the water-disintegrable paper as a whole is within the above range. That is, for example, in the case of non-exposed water-disintegrable paper, it is preferable that the ease of disintegration of the papermaking sheet (the inner layer) and the outer layer that constitute it are each within the above range. The ease of disintegration, i.e., the water-disintegrability of water-disintegrable paper, is affected by the type and content of the anionic polymer (binder), the beating degree of the cellulose fibers (Canadian standard freeness as defined in JIS P8121), etc., and can be adjusted by appropriately adjusting these.

[0050] The water-disintegrable paper of the present invention may be a flat sheet with a substantially smooth surface, or a textured sheet with texture formed on one or both sides. Texture can be formed on the surface of the water-disintegrable paper, for example, by embossing the water-disintegrable paper (e.g., the papermaking sheet or the outer layer) with or without heat. The "surface of the water-disintegrable paper" referred to here is the surface that can come into contact with the object to be cleaned (e.g., a toilet bowl) when the water-disintegrable paper is used as a cleaning article. An example of a sheet-like substrate with texture formed on its surface is the fiber sheet 2 illustrated in JP 2021-97733 A.

[0051] The water-disintegrable paper of the present invention can be produced by known wet papermaking methods. Wet papermaking methods include an external addition method in which additives such as paper strength agents and retention aids are added to a sheet produced by the wet papermaking method, and an internal addition method in which a sheet containing fibers and the additives is produced by the wet papermaking method. The water-disintegrable paper of the present invention can be produced by either method, and the anionic polymer and cationic polymer described above are examples of the additives. When the papermaking sheet is produced by the external addition method, typically, a slurry containing cellulose fibers, food extract residue, and water is formed into a sheet by a wet papermaking method to obtain a wet sheet, and the wet sheet is subjected to a press dehydration treatment and / or a heat treatment to dry or semi-dry the sheet. After that, an anionic polymer and / or a cationic polymer is applied to one or both sides of the dry or semi-dry sheet by spraying or coating, and the sheet is further dried to obtain the desired papermaking sheet. When the papermaking sheet is produced by the internal addition method, typically, a slurry containing cellulose fibers, food extract residue, water, and anionic polymer and / or cationic polymer is prepared, the slurry is formed into a sheet by a wet papermaking method to obtain a wet sheet, and the wet sheet is dried by a known method to obtain the desired papermaking sheet. In the internal addition method, the anionic polymer and / or cationic polymer may be added (externally added) to the wet sheet or a sheet obtained by drying the wet sheet. When the water-disintegrable paper to be produced comprises the papermaking sheet and other sheets (e.g., the outer layer), such as non-exposed water-disintegrable paper, the papermaking sheet and other sheets are each produced by a wet papermaking method, and then the two sheets are stacked to obtain a laminated sheet, which is then embossed with or without heat to integrate the two sheets, thereby obtaining the desired water-disintegrable paper. Each sheet constituting the laminated sheet may be in a wet or dry state.

[0052] A preferred example of the method for producing water-disintegrable paper of the present invention (hereinafter also referred to as "production method α") will be described below. For points not specifically explained in production method α, the above explanation of the water-disintegrable paper of the present invention will be applied as appropriate.

[0053] The manufacturing method α is a type of internal addition method, and includes a slurry preparation step of preparing a slurry, a sheeting step of forming the slurry into a wet paper sheet by a wet papermaking method, and a sheeting step of heating and drying the paper sheet. In the manufacturing method α, the paper sheet is typically dried only once. Production method α can be carried out in a conventional manner using a known wet paper machine such as a Fourdrinier paper machine or a cylinder paper machine. A wet paper machine typically includes a slurry preparation part for preparing a fiber-containing slurry, a forming part for continuously forming a wet sheet from the slurry using a papermaking wire, a drying part for drying the wet sheet using a drying means, and a winder part for winding the heated and dried paper into a roll. The drying means is not particularly limited, and a Yankee dryer or an air-through dryer can be used, for example. The slurry preparation step is carried out in the slurry preparation part, and the sheeting step is carried out in the forming part and the drying part.

[0054] In the slurry preparation step, a slurry containing cellulose fibers, food extract residue, an anionic polymer, a cationic polymer, and water is prepared. The components of the slurry are as described above. A preferred embodiment of the slurry is one in which the anionic polymer contains CMC and the cationic polymer contains one or more of the specific cationic polymers. By adding a cationic polymer to a slurry containing cellulose fibers, food extract residue, and water, an electrostatic attraction is imparted to the cellulose fibers and food extract residue, which are negatively charged, thereby improving the yield of the food extract residue. The yield of the food extract residue can be calculated using the following method. When CMC is used as the anionic polymer, the electrostatic aggregation of the cationic polymer and CMC in water can be utilized to improve sheet yield. Therefore, in the slurry preparation process, it is preferable to prepare a slurry containing cellulose fibers, food extract residue, and water, and then sequentially add CMC and cationic polymer to the slurry. Furthermore, it is preferable to add CMC and cationic polymer to the slurry in amounts that equalize their charge amounts, which is the condition under which both components are most likely to aggregate. The charge amounts of CMC and cationic polymer can be measured using a particle charge analyzer (PCD-06, Phyto Turbo Co., Ltd.).

[0055] <Calculation method for food extract residue yield rate> First, slurry A containing cellulose fiber, food extract residue, and water, and slurry B containing cellulose fiber and water but no food extract residue are prepared. A specific example of slurry A is a slurry containing cellulose fiber, food extract residue, anionic polymer (e.g., CMC), cationic polymer (e.g., the specific cationic polymer), and water. In this case, slurry B is prepared without food extract residue and with the same content of components other than water as the specific example of slurry A. Next, a wet sheet is formed using the slurry A by a wet papermaking method, and the resulting filtrate (the liquid component in the slurry that passes through the papermaking mesh when the slurry is passed through the papermaking mesh) is collected, and the collected filtrate is dried to measure the solid mass (M1). Similarly, a wet sheet is formed using the slurry B by a wet papermaking method, and the solid mass (M2) of the filtrate is measured. The yield rate of the target food extract residue is then calculated using the following formula. In the formula below, "M0" refers to the total mass of the food extract residue in a dry state (water content of 10% by mass or less) used to prepare the slurry A. Food extraction residue yield rate (mass%) = {1-(M1-M2) / M0} x 100

[0056] The manufacturing method α may include a step of adjusting the median diameter of the food extract residue to 10 μm or more and 1000 μm or less before the slurry preparation step. That is, the food extract residue contained in the slurry preferably has a median diameter of 10 μm or more and 1000 μm or less, more preferably in the same range as the preferred median diameter of the specific particles described above. The adjustment of the median diameter of the food extract residue can be carried out according to a conventional method using a commercially available grinder.

[0057] The food extract residue used in the slurry preparation step preferably has a moisture content of 10% by mass or less, from the viewpoints of excellent antiseptic properties and transportation efficiency and low adhesion to manufacturing equipment. If the moisture content of the food extract residue exceeds 10% by mass, the food extract residue is subjected to a drying treatment, such as by heating, to adjust the moisture content to 10% by mass or less.

[0058] In the slurry preparation step, the order of adding the components to be contained in the slurry is not particularly limited, but typically, food extract residue, preferably adjusted to a moisture content of 10% by mass or less, is added to a slurry containing cellulose fiber and water, and then anionic polymer and cationic polymer are added. The amount of food extract residue added to such a slurry is typically 1 part by mass to 50 parts by mass per 100 parts by mass of cellulose fiber in the slurry.

[0059] The water-disintegrable paper of the present invention can be used as a cleaning article for wiping dirt from an object to be cleaned, and can be disposed of by flushing it down the toilet after use. The object to be cleaned with the water-disintegrable paper of the present invention is not particularly limited and may be the human body or an object other than the human body, and specific examples of objects other than the human body include toilet equipment (toilet bowls, floors, etc.).

[0060] The water-disintegrable cleaning article of the present invention will be described below. The differences between the water-disintegrable cleaning article of the present invention and the water-disintegrable paper of the present invention will be described. For the points not specifically described in the water-disintegrable cleaning article of the present invention, the explanation for the water-disintegrable paper of the present invention will be applied as appropriate.

[0061] The water-disintegrable cleaning article of the present invention comprises the water-disintegrable paper of the present invention and an aqueous chemical. The aqueous chemical preferably contains at least a water-soluble organic solvent, an electrolyte containing a divalent metal ion, and water.

[0062] In the aqueous chemical, the water-soluble organic solvent has the function of removing dirt from the object to be cleaned, and also has the function of improving the dispersibility of other components (such as the electrolyte) in the aqueous chemical. Examples of the water-soluble organic solvent include alcohols, polyols, and glycol ethers, and these can be used alone or in combination of two or more. Examples of the alcohols include lower alcohols such as methanol, ethanol, and isopropyl alcohol. Examples of the polyols include alkylene glycols such as ethylene glycol, propylene glycol, methylpropylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,3-butanediol; polyalkylene glycols such as diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and sorbitol; and glycerins such as glycerin, diglycerin, and triglycerin. Examples of the glycol ether include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and ethylene glycol monophenyl ether. The water-soluble organic solvent is preferably at least one selected from the group consisting of 1,2-propanediol and propylene glycol monoethyl ether, from the viewpoint of suppressing stickiness and increasing the drying rate.

[0063] The content of the water-soluble organic solvent in the aqueous agent is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 25% by mass or less, based on the total mass of the aqueous agent.

[0064] In the aqueous chemical, the electrolyte containing the divalent metal ion has the function of improving the wet strength of the water-disintegrable paper. As mentioned above, the water-disintegrable paper typically contains an anionic polymer such as CMC. By retaining the aqueous chemical in the water-disintegrable paper, a crosslinked structure is formed between the anionic functional groups of the anionic polymer and the divalent metal ions derived from the electrolyte in the aqueous chemical, and this crosslinked structure contributes to improving the wet strength of the water-disintegrable paper. In other words, the electrolyte containing the divalent metal ion functions as a crosslinker for the anionic polymer. Examples of the electrolyte containing a divalent metal ion include water-soluble metal salts (hydroxides, chlorides, sulfates, nitrates, carbonates, formates, acetates, etc.) containing divalent metal ions such as alkaline earth metals (magnesium, calcium, strontium, barium), manganese, zinc, cobalt, nickel, etc., and these can be used alone or in combination of two or more. The divalent metal ion is preferably at least one selected from the group consisting of calcium and zinc, from the viewpoint of increasing the wet strength of the paper sheet and improving its water disintegrability.

[0065] The content of the divalent metal ion-containing electrolyte in the aqueous agent is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 5% by mass or less, based on the total mass of the aqueous agent.

[0066] When a fiber-based sheet such as water-disintegrable paper holds a liquid, whether or not the liquid contains the above-mentioned "water-soluble organic solvent" and "electrolyte containing divalent metal ions" can be confirmed, for example, by the following method: The sheet to be confirmed is squeezed to recover the liquid held in the sheet, and the liquid is subjected to known inorganic ion analysis (e.g., analysis by ion chromatography) and organic analysis (e.g., analysis by NMR) to identify the contained components, thereby confirming the presence or absence of the above-mentioned two components in the liquid.

[0067] The content of water in the aqueous agent is preferably 50% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 80% by mass or less, based on the total mass of the aqueous agent.

[0068] The aqueous agent may contain other components in addition to the above-mentioned components (water-soluble organic solvent, electrolyte containing divalent metal ions, and water). Examples of the other components include surfactants, antibacterial agents, disinfectants, deodorants, and fragrances, and these can be used alone or in combination of two or more. The content of the other components in the aqueous agent is preferably 5% by mass or less based on the total mass of the aqueous agent.

[0069] The water-disintegrable cleaning article of the present invention can be obtained by retaining, specifically impregnating, the aqueous chemical in the water-disintegrable paper of the present invention. The amount of the aqueous chemical retained in the water-disintegrable paper is preferably 100% by mass or more and 500% by mass or less, based on the total mass of the water-disintegrable paper in a dry state. There are no particular limitations on the method for retaining the aqueous chemical in the water-disintegrable paper, and examples include a method of immersing the water-disintegrable paper in the aqueous chemical, or a method of applying or spraying the aqueous chemical onto the water-disintegrable paper.

[0070] An example of the method for producing a water-disintegrable cleaning article of the present invention is the method for producing water-disintegrable paper of the present invention, which includes, after the sheet-forming step, a step of retaining an aqueous chemical in the paper sheet that has been subjected to the sheet-forming step in the production method α.

[0071] The water-disintegratable cleaning article of the present invention can be used as a cleaning article for wiping dirt from an object to be cleaned, similar to the water-disintegratable paper of the present invention described above, and can be disposed of by flushing down the toilet after use. Because the water-disintegratable cleaning article of the present invention retains an aqueous chemical, it has a higher cleaning effect on water-soluble dirt than the water-disintegratable paper of the present invention, which does not retain an aqueous chemical. [Example]

[0072] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0073] [Examples 1 to 12 and Comparative Examples 1 to 3: Production of Paper Sheets] Paper sheets were produced having the compositions shown in the "Paper sheet composition" column in Table 1 below. Specifically, a slurry containing the raw materials shown in the column and water and having a cellulose fiber concentration of 0.35% by mass was prepared, and the slurry was formed into a sheet by a wet papermaking method to give a sheet having a basis weight of 40 g / m. 2 The resulting paper sheet had a unique texture derived from food extract residue. NBKP was used as the cellulose fiber. When food extract residue and anionic polymer and / or cationic polymer were used as raw materials (except for Comparative Example 1), the slurry was prepared by adding the food extract residue and the anionic polymer and / or cationic polymer in this order to a slurry containing cellulose fiber and water. The food extract residue used had a moisture content of 10% by mass or less, and the median diameter was adjusted by grinding using a grinder as necessary. In other words, all of the food extract residue was in the form of specific particles. The aspect ratio was 10 or less. Table 1 below shows the aspect ratio, median diameter, and yield rate of the food extract residue used.

[0074] The paper sheets of each Example and Comparative Example were evaluated for ease of disintegration (water disintegration time) by the above method, and the number of lumps was evaluated by the following method. The results are shown in Table 1 below.

[0075] <Method for evaluating the number of lumps> A square area measuring 50 mm on each side in plan view was cut out from the center of the paper sheet to be evaluated to prepare an evaluation sample. One side of the evaluation sample was visually observed, and the number of colored particles (particulate matter with a color different from the color of the water-disintegrable paper) with a maximum diameter of 1 mm or more was counted, and this number was used as the number of agglomerates (unit: pieces / 25 cm) of the paper sheet. 2 The smaller the number of lumps, the better the appearance of the paper sheet, with the food extract residue evenly dispersed, in addition to the unique texture derived from the food extract residue.

[0076] [Table 1]

[0077] As shown in Table 1, the paper sheets of each Example contained food extract residue and could contribute to reducing the environmental impact, but the ease of disintegration as specified in JIS P 4501 was 1 second or more and 100 seconds or less, and they were water-disintegrable papers that could be flushed down the toilet. Example 1 does not contain a cationic polymer, whereas Example 2 does. Example 2 has a higher food extract residue yield rate and is comparable in ease of disintegration to Example 1, demonstrating that cationic polymers are effective in improving the food extract residue yield rate. Comparing Examples 6 to 10, it can be seen that the smaller the median diameter of the food extract residue, the fewer the number of lumps. In general, the smaller the median diameter of the food extract residue, the lower the yield rate, but it can be seen that the use of cationic polymers makes it possible to maintain a high yield rate.

[0078] Examples 13 and 14, Comparative Example 4: Production of Cleaning Articles A three-layer papermaking sheet including an inner layer and a pair of outer layers disposed on both sides of the inner layer in the thickness direction was produced, and the papermaking sheet was immersed in an aqueous chemical to retain the aqueous chemical, thereby producing the cleaning articles of Examples 13 and 14. The three-layer paper sheet was produced by laminating the outer layers in a dry state on both sides of the inner layer in the thickness direction to obtain a three-layer laminated sheet, and then embossing the laminated sheet in the thickness direction. The combinations of the inner and outer layers are as shown in Table 2 below. The cleaning products of Examples 13 and 14 were the non-exposed water-disintegrable paper. Comparative Example 4 is a laminated sheet having a two-layer structure in which two sheets of paper body 1 are stacked, and was produced by carrying out embossing in the same manner as in Examples 13 and 14. "Paper body 1" in Table 2 below is a paper sheet containing cellulose fiber and a water-soluble binder, but not containing food extract residue. Specifically, it contains 95% by mass of NBKP and 5% by mass of CMC (water-soluble binder), and has a basis weight of 30 g / m 2 It is a single-layer papermaking sheet.

[0079] The composition of the aqueous agent is as follows: Propylene glycol monomethyl ether (water-soluble organic solvent): 13% by mass 1,2-propanediol (water-soluble organic solvent): 7% by mass Zinc sulfate (electrolyte containing divalent metal ions): 3% by mass Alkyl glucoside (nonionic surfactant): 0.2% by mass ·Water: 76.8% by mass The paper sheets of the Examples and Comparative Examples were made to retain 200% by mass of the aqueous chemical relative to the total mass of each sheet.

[0080] The cleaning articles of each Example and Comparative Example were evaluated for ease of unraveling by the above method, and also measured for wet tensile strength by the following method. The results are shown in Table 2 below.

[0081] <Wet tensile strength measurement method> Based on JIS P8113, the wet tensile strength of cleaning articles in the machine direction at the time of their manufacture was measured. A rectangular specimen measuring 70 mm in the machine direction and 25 mm in the width direction in plan view was cut out of the cleaning article to prepare a test piece. This test piece was attached to the chuck of a tensile tester (Shimadzu Corporation, Autograph AG-1kN) without tension, with the machine direction of the test piece being the tensile direction. The distance between the chucks was 50 mm. The test piece attached to the chuck was pulled at a tensile speed of 300 mm / min, and the maximum strength (unit: cN / 25 mm) until the test piece broke was measured. The above measurement was performed 10 times for each type of cleaning article, and the average of these measured values ​​was taken as the wet tensile strength of the cleaning article. The higher the wet tensile strength value, the stronger the wet strength and the less likely it was to break under normal use.

[0082] [Table 2]

[0083] As shown in Table 2, the cleaning articles of each Example were configured such that papermaking sheets containing no food extract residue were fixed to both sides of the thickness of water-disintegrable paper (papermaking sheet of Example 2 or 11) that contained food extract residue and had a disintegration rate of 1 to 100 seconds. Therefore, while the cleaning articles had water-disintegratability that allowed them to be flushed down the toilet, they also had a wet tensile strength greater than that of the cleaning article of Comparative Example 4, and were strong enough for wiping tasks.

Claims

1. The water-disintegrable paper has a papermaking sheet containing cellulose fibers and food extract residue, and has a disintegration rate as specified in JIS P 4501 of 1 second or more and 100 seconds or less.

2. 2. The water-disintegrable paper according to claim 1, wherein the food extraction residue contains particles having an aspect ratio of 10 or less and a median diameter of 10 μm or more and 1000 μm or less.

3. The water-disintegrable paper according to claim 1 or 2, which comprises an anionic polymer.

4. the anionic polymer comprises carboxymethyl cellulose; The water-disintegrable paper according to claim 3, further comprising poly(acrylamide-co-diallyldimethylammonium chloride) and / or polymethacryloyloxyethyltrimethylammonium chloride.

5. It has a laminated structure including an inner layer made of the papermaking sheet and outer layers arranged on both sides of the inner layer in the thickness direction, 3. The water-disintegrable paper according to claim 1, wherein the outer layer comprises cellulose fibers and a water-soluble binder, and is substantially free of food extract residues.

6. A water-disintegrable cleaning article comprising the water-disintegrable paper according to claim 1 or 2 and an aqueous chemical.

7. a slurry preparation step of preparing a slurry containing cellulose fibers, food extract residue, an anionic polymer, a cationic polymer, and water; a sheeting step of forming the slurry into a sheet by a wet papermaking method to obtain a wet papersheet, and then heating and drying the papersheet.

8. the anionic polymer comprises carboxymethyl cellulose; The method for producing water-disintegrable paper according to claim 7, wherein the cationic polymer comprises poly(acrylamide-co-diallyldimethylammonium chloride) and / or polymethacryloyloxyethyltrimethylammonium chloride.

9. The method for producing water-disintegrable paper according to claim 7 or 8, further comprising a step of adjusting the median diameter of the food extraction residue to 10 μm or more and 1000 μm or less prior to the slurry preparation step.

10. a slurry preparation step of preparing a slurry containing cellulose fibers, food extract residue, an anionic polymer, a cationic polymer, and water; A sheeting step of forming the slurry into a sheet by a wet papermaking method to obtain a wet papermaking sheet, and heating and drying the papermaking sheet; and a step of retaining an aqueous chemical on the paper sheet that has been subjected to the sheet-forming step.

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