Water-disintegrable sheet

Abstract

To provide a water-disintegrable sheet that contains fibers derived from recycled paper and offers both sheet strength and water solubility.SOLUTION: A water-disintegrable sheet of the present invention includes a water-disintegrable sheet-like base material containing fibers and a water-disintegrable binder, and a liquid composition retained on the sheet-like base material. The fibers contain fibers derived from recycled paper, and the liquid composition contains organic acids. Preferably, the fibers derived from recycled paper contain trivalent or higher metal ions (e.g., aluminum ions). Preferably, the organic acid contains one or more selected from malic acid, citric acid, and lactic acid. Preferably, pH of the liquid composition is 3.2 or higher and 4.5 or lower.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a hydrolyzable sheet using waste paper as a fiber raw material.

Background Art

[0002] There is known a hydrolyzable sheet in which fibers such as wood pulp are bound with a binder and impregnated with a liquid composition, which can be discarded by flowing it into water after use as a wiping material. Patent Document 1 describes using, as the liquid composition, one containing a pH buffer adjusted to an acidic-side pH with an organic acid such as succinic acid, whereby a low-irritation, non-sticky, and refreshing wiping feeling wiping material for human use can be obtained. Patent Document 2 describes using, as the liquid composition, one containing specific amounts of an organic acid, a surfactant, and a metal ion compound, whereby a wiping material having both bactericidal properties and strength can be obtained. Patent Document 3 describes using, as the liquid composition, one containing an organic acid such as citric acid, whereby a deodorizing effect on bad odors such as ammonia odor can be imparted to the wiping material. Patent Documents 1 to 3 do not describe using waste paper as the fiber raw material of the wiping material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] For a hydrolyzable sheet, it is required to balance sheet strength and hydrolyzability. Specifically, it is a balance between sheet strength that is not easily torn even when used for wiping work in a wet state impregnated with a liquid, and hydrolyzability that can be quickly disintegrated and dispersed when put into a large amount of water. On the other hand, in recent years, from the perspective of global environmental conservation, the protection of forest resources has been promoted, and as part of this, the recycling of waste paper has been promoted in various fields. For hydrolyzable sheets as well, it is required to use waste paper as a fiber raw material. There is still no hydrolyzable sheet that can achieve a high level of balance between sheet strength and hydrolyzability while using waste paper as a fiber raw material, that is, while containing waste paper-derived fibers.

[0005] An object of the present invention relates to providing a hydrolyzable sheet that contains waste paper-derived fibers and achieves a balance between sheet strength and hydrolyzability.

Means for Solving the Problems

[0006] As a result of various studies to solve the above problems, the present inventors found that in a conventionally known hydrolyzable sheet using virgin pulp as a fiber and containing a water-soluble binder, simply using waste paper-derived fibers instead of virgin pulp may significantly reduce hydrolyzability. The present inventors also found that such a decrease in hydrolyzability is due to the formation of an insoluble salt by trivalent or higher metal ions contained in waste paper-derived fibers and the water-soluble binder. As a result of further studies based on these findings, the present inventors found that by using waste paper-derived fibers as the constituent fibers of the sheet and containing an organic acid in the liquid composition held by the sheet, the formation of the insoluble salt is suppressed, and a hydrolyzable sheet that solves the above problems can be obtained.

[0007] The present invention is based on the above findings, and is a hydrolyzable sheet having a hydrolyzable sheet-like base material containing fibers and a water-soluble binder, and a liquid composition held by the sheet-like base material, wherein the fibers contain waste paper-derived fibers, and the liquid composition contains an organic acid.

Effects of the Invention

[0008] According to the present invention, there is provided a hydrolyzable sheet containing fibers derived from waste paper, which achieves both sheet strength and hydrolyzability.

Brief Description of the Drawings

[0009]

Figure 1

Mode for Carrying Out the Invention

[0010] The hydrolyzable sheet of the present invention has a sheet-like base material and a liquid composition held on the sheet-like base material. Since the liquid composition is held on the sheet-like base material, the hydrolyzable sheet of the present invention is in a wet state at normal temperature and pressure. Therefore, the hydrolyzable sheet of the present invention can be used as a cleaning material as it is without separately using a cleaning agent in combination.

[0011] The sheet-like base material contains fibers. The fiber content in the sheet-like base material is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, and preferably 10.0% by mass or less, more preferably 7.0% by mass or less, based on the total mass of the sheet-like base material, from the viewpoint of imparting the functions necessary for the hydrolyzable sheet as a cleaning material and from the viewpoint of containing a necessary amount of components other than fibers such as a water-soluble binder in the hydrolyzable sheet.

[0012] The fibers contained in the sheet-like base material contain at least fibers derived from waste paper. Fibers derived from waste paper are fibers recovered from waste paper and are not so-called virgin pulp that has not been used. The use of fibers derived from waste paper leads to the reuse of resources and has the merit of relatively low environmental impact. Also, generally, fibers derived from waste paper are inexpensive and can be procured, so the use of these can be expected to reduce the manufacturing cost of the hydrolyzable sheet.

[0013] The fibers derived from waste paper are typically cellulose fibers. The fibers derived from waste paper may be natural cellulose fibers or non-natural cellulose fibers. Examples of natural cellulose fibers include wood pulps such as softwood kraft pulp (NBKP) represented by softwood-derived pulp and hardwood kraft pulp (LBKP) represented by hardwood-derived pulp; and non-wood pulps such as cotton pulp and hemp pulp. Examples of non-natural cellulose fibers include modified pulps such as cationized pulp and mercerized pulp; and regenerated cellulose fibers such as cupra and rayon. The fibers derived from waste paper are typically wood pulps (NBKP, LBKP, etc.).

[0014] As the waste paper that is the source of the fibers derived from waste paper, those recovered as papermaking raw materials can be used. In Japan, in the operation guidelines of the Law for the Promotion of Effective Utilization of Resources (enacted on October 25, 1991), waste paper is defined as follows. In the present invention, waste paper that conforms to the following definition can be used. Definition of waste paper: An article such as paper, paper products, books, etc., all or part of which is paper, that has been used once, or collected without being used, or discarded, and is useful and can be used as a raw material for paper (including those imported after being collected) or has the potential to be so. However, it excludes those generated in the papermaking process at the factory or workplace of a paper manufacturer (hereinafter referred to as "factory, etc.") and those generated when processing, etc. is carried out at the factory, etc. of a paper manufacturer (including the case where the paper manufacturer entrusts another operator to perform processing before shipping the product) and that are not shipped as a product but are used as a raw material for paper by the paper manufacturer.

[0015] Examples of waste paper that can be used in the present invention include newspapers, magazines, cardboard, "super white paper · cards" (e.g., super white, cream super white, ruled white), extra white, medium white, "imitation · colored paper" (e.g., imitation, colored, Kent, white art, leaflets, beverage packs, office paper), "ticket · second-hand antique" (e.g., special upper ticket, separate upper ticket, second-hand antique), tea imitation paper (e.g., cut tea · plain tea, miscellaneous bags, kraft cardboard), "mounting paper · land deeds · balls" (e.g., one-ply, upper mounting paper, mounting paper, miscellaneous paper), etc. One of these can be used alone or in combination of two or more.

[0016] The waste paper-derived fibers preferably contain metal ions of trivalent or higher. Examples of the metal ions of trivalent or higher include aluminum ions and iron ions. The waste paper-derived fibers may contain one type or two or more types of metal ions of trivalent or higher. According to the findings of the present inventors, when the waste paper-derived fibers, which are the constituent fibers of the sheet-like substrate, contain metal ions of trivalent or higher, the strength uniformity of the sheet-like substrate (hydrolyzable sheet) can be further improved. That is, in order to enhance the strength uniformity of the sheet-like substrate so that the entire sheet-like substrate has practically sufficient strength, it is important that water-soluble binders such as carboxymethyl cellulose contained in the sheet-like substrate are immobilized throughout the sheet-like substrate. For this purpose, it is effective that the water-soluble binder and the metal ions bind firmly. Since the binding force of metal ions of trivalent or higher with the water-soluble binder is greater than that of divalent metal ions, when the waste paper-derived fibers, which are the constituent fibers of the sheet-like substrate, contain metal ions of trivalent or higher, it becomes easier to obtain a sheet-like substrate with high strength uniformity that can exhibit a certain strength regardless of which part is sampled. In particular, it is preferable that the waste paper-derived fibers contain aluminum ions as the metal ions of trivalent or higher because such an effect can be more surely achieved. The content of metal ions of trivalent or higher in the sheet-like substrate is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and preferably 0.01% by mass or less, more preferably 0.006% by mass or less, based on the total mass of the sheet-like substrate.

[0017] As a preferable example of the fibers derived from waste paper, fibers derived from paper containers with aluminum can be mentioned. The fibers derived from paper containers with aluminum are the fibers recovered from paper containers with aluminum. A paper container with aluminum is a container using aluminum foil composite laminated paper which is a laminate of an aluminum foil and a fiber sheet, and in waste paper statistics, it is classified as "imitation / colored" as a "pack for beverages" such as milk, juice, and liquor. The fibers derived from paper containers with aluminum usually contain aluminum ions and are the above-mentioned "fibers derived from waste paper containing metal ions of trivalent or higher".

[0018] The ratio of the mass of the fibers derived from waste paper to the mass of all the fibers in the sheet-like base material (waste paper-derived fiber occupancy rate) is preferably as large as possible from the viewpoint of enhancing the significance of using the fibers derived from waste paper, preferably 70% by mass or more, more preferably 80% by mass or more, and most preferably 100% by mass, that is, all the constituent fibers of the sheet-like base material are fibers derived from waste paper.

[0019] The sheet-like base material may contain other fibers other than the fibers derived from waste paper. Examples of the other fibers include, for example, cellulose fibers not derived from waste paper; biodegradable fibers made of polylactic acid or the like; synthetic fibers such as polypropylene fibers, polyvinyl alcohol fibers, polyester fibers, and polyacrylonitrile fibers, and one of these can be used alone or in combination of two or more. The ratio of the mass of the other fibers other than the fibers derived from waste paper to the mass of all the fibers in the sheet-like base material is preferably 30% by mass or less, more preferably 20% by mass or less.

[0020] The sheet-like substrate contains, in addition to fibers, a water-soluble binder. As the water-soluble binder, when the sheet-like substrate holds the liquid composition and is in a wet state, the binder temporarily becomes insoluble, thereby functioning as a binder that maintains the bonding between the constituent fibers of the sheet-like substrate and playing a role in maintaining the strength during the use of the hydrolyzable sheet. Examples of such water-soluble binders include natural polysaccharides, polysaccharide derivatives, and synthetic polymers. Note that the above-mentioned "temporary insolubilization of the water-soluble binder" typically occurs by the action of a binder-insolubilizing component (e.g., a cross-linking agent for the binder) in the liquid composition held by the sheet-like substrate.

[0021] Examples of natural polysaccharides include sodium alginate, tragacanth gum, guar gum, xanthan gum, gum arabic, carrageenan, galactomannan, gelatin, casein, albumin, and pullulan. Examples of polysaccharide derivatives include carboxymethyl cellulose, carboxyethyl cellulose, carboxymethylated starch or its salts, starch, methyl cellulose, and ethyl cellulose. Examples of synthetic polymers 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 unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic anhydride, maleic acid, and fumaric acid.

[0022] Among the above-mentioned water-soluble binders, water-soluble binders having a carboxyl group are preferred because of their good performance as binders and good affinity with cross-linking agents described later. Examples of water-soluble binders having a carboxyl group include carboxymethyl cellulose (CMC), carboxyethyl cellulose, or their salts.

[0023] The content of the water-soluble binder in the sheet-like substrate is preferably 2% by mass or more, more preferably 5% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, from the viewpoint of balancing the wet strength and hydrolyzability of the sheet-like substrate while suppressing the content of the binder to the minimum necessary. Here, the "content of the water-soluble binder in the sheet-like substrate" refers to the content of the water-soluble binder in each of the plurality of layers constituting the laminated structure when the sheet-like substrate has a laminated structure such as the sheet-like substrate 1 shown in FIG. 1.

[0024] The sheet-like substrate is hydrolyzable. A hydrolyzable sheet-like substrate does not disintegrate to the extent that it holds the liquid composition and can maintain a predetermined shape in a wet state, but disintegrates rapidly when discarded in a large amount of water. Therefore, the hydrolyzable sheet of the present invention in which the liquid composition is held in the hydrolyzable sheet-like substrate can be discarded by simply flowing it into water after use, and by doing so, it disintegrates rapidly and does not clog the drain pipe. The hydrolyzability of the sheet-like substrate can be evaluated by the hydrolysis time measured by the following method. The shorter the hydrolysis time, the better the hydrolyzability of the measurement target (sheet-like substrate) is evaluated to be, and it is easily disintegrated and dispersed in water. The hydrolysis time of the sheet-like substrate measured by the following method is preferably 110 seconds or less, more preferably 100 seconds or less, and even more preferably 90 seconds or less, from the viewpoint of imparting practically sufficient hydrolyzability to the sheet-like substrate.

[0025] <Method for Measuring Hydrolysis Time> Place a 300-ml beaker containing 300 ml of water (water temperature: 20 ± 5°C) and a rotor (disc-shaped, 35 mm in diameter and 12 mm in thickness) on a magnetic stirrer, and set the rotation speed of the rotor to 600 ± 5 revolutions per minute. Place a test piece (sheet-like substrate) in the shape of a square with a side length of 80 mm in plan view into this beaker, and press the stopwatch. The rotation speed of the rotor will initially decrease to approximately 500 revolutions due to the resistance of the test piece present in the water, but will increase as the disintegration and dispersion of the test piece progresses. Stop the stopwatch when the rotation speed of the rotor has recovered to 540 revolutions, and measure the time in 1-second units. Perform the above measurement three times for one type of measurement target (sheet-like substrate), and take the average of these measurement values as the hydrolysis time of the measurement target.

[0026] From the viewpoint that the sheet-like substrate can be used as a cleaning wipe in a wet state holding the liquid composition (and is difficult to tear in normal use methods), it is preferable that the wet tensile strength measured by the following method is preferably 300 cN / 25 mm or more, more preferably 400 cN / 25 mm or more.

[0027] <Method for Measuring Wet Tensile Strength> Based on JIS P8113, measure the wet tensile strength in the machine direction (MD) during the production of the measurement target (sheet-like substrate). Cut out a rectangular shape with a length of 70 mm in the MD and a width of 25 mm in the direction perpendicular to the MD (CD) from the measurement target to obtain a test piece. Pipette 50 μL of water onto the center of the test piece in plan view, leave it for 30 seconds, and then attach the test piece to the chuck of a tensile testing machine (Autograph AG-1kN manufactured by Shimadzu Corporation) without tension so that the MD of the test piece becomes the tensile direction. The distance between the chucks is 50 mm. Pull the test piece attached to the chuck in the MD at a tensile speed of 300 mm / min, and measure the maximum strength (unit: cN / 25 mm) until the test piece breaks. Perform the above measurement three times for one type of measurement target (sheet-like substrate), and take the average of these measurement values as the wet tensile strength of the measurement target.

[0028] Factors affecting the hydrolyzability (hydrolysis time) and wet tensile strength of the sheet-like substrate include the type and content of the water-soluble binder and the beating degree of the fibers. Therefore, the hydrolyzability and wet tensile strength of the sheet-like substrate can be adjusted by appropriately adjusting these factors. The beating degree of the fibers can be indicated by the Canadian standard freeness defined in JIS P8121. The smaller the value of this freeness, the higher the beating degree of the fibers, and it is evaluated that the entanglement of the fibers is progressing. Usually, the lower the content of the water-soluble binder, or the lower the beating degree of the fibers (the larger the value of the freeness), the more the hydrolyzability of the sheet-like substrate is improved (the hydrolysis time is reduced), and the wet tensile strength is decreased. Also, the higher the content of the water-soluble binder, or the higher the beating degree of the fibers (the smaller the value of the freeness), the more the hydrolyzability of the sheet-like substrate is decreased (the hydrolysis time is increased), and the wet tensile strength is improved.

[0029] The sheet-like substrate can be manufactured by various methods. For example, a water-soluble binder and, if necessary, a fixing agent for the binder to the fibers are added to a dispersion containing fibers (fibers containing fibers derived from waste paper) to obtain a papermaking raw material, and the sheet-like substrate can be manufactured by performing a known wet papermaking method using the papermaking raw material. This manufacturing method is a method of internally adding a water-soluble binder. Also, for example, a wet sheet is manufactured from a dispersion containing fibers (fibers containing fibers derived from waste paper) by a known wet papermaking method, and after subjecting the sheet to a pressing and dewatering treatment and / or a heat treatment such as hot air spraying to make it in a dry or semi-dry state, a water-soluble binder is applied by spraying or coating on one side of the sheet, and further dried, whereby the sheet-like substrate can be manufactured. This manufacturing method is a method of externally adding a water-soluble binder. The sheet-like substrate manufactured by such a wet papermaking method (internal addition method, external addition method) is paper.

[0030] For example, it is also possible to manufacture the sheet-like base material by a method other than the above-described wet papermaking method (internal addition method, external addition method). Specifically, for example, after defibering fibers (fibers containing fibers derived from waste paper) dry without water to form a web, a water-soluble binder is sprayed onto the web and the like, and then dried to manufacture a sheet-like base material. This manufacturing method is the airlaid method. The sheet-like base material manufactured by the airlaid method is a nonwoven fabric.

[0031] The configuration of the sheet-like base material is not particularly limited, and it may have a single-layer structure or a laminated structure in which a plurality of layers are laminated in the thickness direction. Regardless of whether it is a single-layer structure or a laminated structure, the fiber layer constituting the sheet-like base material may contain only fibers derived from waste paper as fibers, may contain only other fibers other than fibers derived from waste paper, or may contain both fibers derived from waste paper and other fibers other than those.

[0032] FIG. 1 shows a sheet-like base material 1 which is an embodiment of the sheet-like base material according to the present invention. The sheet-like base material 1 has a laminated structure of a first layer 2 mainly composed of fibers derived from waste paper and a second layer 3 composed of a fiber layer not containing fibers derived from waste paper. Here, the term "mainly composed of" means that the content of the component (specifically, fibers derived from waste paper) in the layer (specifically, the first layer) is 50% by mass or more based on the total mass of the layer. More specifically, the sheet-like base material 1 has a first layer 2, a pair of second layers 3, 3 arranged so as to be in contact with the first layer 2 on both sides in the thickness direction of the first layer 2, and a binder layer 4 interposed between the two layers 2, 3. The binder layer 4 is a layer formed by applying a water-soluble binder. The ratio of the mass of fibers derived from waste paper to the mass of all fibers in the first layer 2 is preferably 80% by mass or more, and may be 100% by mass, that is, all of the constituent fibers of the first layer 2 may be fibers derived from waste paper. The constituent fibers of the second layer 3 are not particularly limited on the premise that they are fibers other than fibers derived from waste paper, that is, unused (virgin) fibers, and examples thereof include virgin wood pulp (NBKP, LBKP, etc.). Note that the sheet-shaped base material according to the present invention is not limited to the configuration shown in FIG. 1. For example, the first layer 2 and the second layer 3 may be interchanged in the configuration shown in FIG. 1. That is, the sheet-shaped base material according to the present invention may have a configuration including a second layer 3, a pair of first layers 2, 2 arranged so as to be in contact with the second layer 3 on both sides in the thickness direction of the second layer 3, and a binder layer 4 interposed between the two layers 2, 3.

[0033] The sheet-shaped base material may be a flat sheet having a substantially uneven-free surface, or may be a concavo-convex sheet having concavo-convexities formed on the surface (one side or both sides). The formation of concavo-convexities on the surface of the sheet-shaped base material can be carried out, for example, by performing embossing with or without heat on the sheet-shaped base material. The "surface of the sheet-shaped base material" referred to here is the surface that can come into contact with the object to be wiped (e.g., a toilet bowl) when the sheet-shaped base material (hydrolyzable sheet) is used as a wiping material. As an example of the sheet-shaped base material having concavo-convexities formed on the surface, the fiber sheet 2 illustrated in Japanese Unexamined Patent Application Publication No. 2021-65488 can be mentioned. Regarding the sheet-shaped base material, on the premise of not departing from the gist of the present invention, the contents described for the fiber sheet in Japanese Unexamined Patent Application Publication No. 2021-65488 can be appropriately applied.

[0034] The basis weight of the sheet-shaped base material is preferably 20 g / m 2 or more, more preferably 25 g / m 2 or more, and preferably 50 g / m 2 or less, more preferably 40 g / m 2 or less from the viewpoint of the balance between softness and sufficient wet strength. Note that the "basis weight of the sheet-shaped base material" referred to here, when the sheet-shaped base material has a laminated structure such as the sheet-shaped base material 1 shown in FIG. 1, refers to the basis weight of each of the plurality of layers constituting the laminated structure.

[0035] In the hydrolyzable sheet of the present invention, the sheet-shaped base material holds a liquid composition. The liquid composition is typically liquid at normal temperature and normal pressure and is held by being impregnated into the sheet-shaped base material.

[0036] The hydrolyzable sheet of the present invention is characterized in that the constituent fibers of the sheet-like substrate contain fibers derived from waste paper, and the liquid composition held on the sheet-like substrate contains an organic acid. The former (sheet-like substrate) is as described above. In the present invention, one of the main reasons for including an organic acid in the liquid composition is to suppress the formation of insoluble salts due to trivalent or higher metal ions contained in the waste paper-derived fibers and the water-soluble binder described above, and to impart practically sufficient hydrolyzability to the hydrolyzable sheet using waste paper-derived fibers. The reason why the formation of the insoluble salt is suppressed by including an organic acid in the liquid composition is not clear, but it is presumed that the organic acid functions as a chelating agent for trivalent or higher metal ions contained in the waste paper-derived fibers and suppresses the insolubilization of the water-soluble binder.

[0037] As a result of various studies by the present inventors on a sheet containing waste paper-derived fibers and a water-soluble binder, it has been clarified that the presence of trivalent or higher metal ions typified by aluminum ions contained in the waste paper-derived fibers is a causative substance that reduces the hydrolyzability of the sheet. For example, when a predetermined amount of zinc ions is added as metal ions to a colorless and transparent CMC aqueous solution containing 1% by mass of CMC as a water-soluble binder, no insoluble salt precipitates and the CMC aqueous solution remains colorless and transparent, or even if an insoluble salt precipitates and the CMC aqueous solution becomes cloudy, it becomes colorless and transparent by diluting it about 2.0 times. On the other hand, the present inventors have confirmed that when aluminum ions are added as metal ions to the CMC aqueous solution, an insoluble salt precipitates and the CMC aqueous solution becomes cloudy, and it does not become colorless and transparent even when diluted 2.0 times. This is presumably because, when aluminum ions are added, relatively strong ionic crosslinking occurs between and / or within the molecules of CMC as compared with the case when zinc ions are added. Here, when an organic acid was further added to the CMC aqueous solution in addition to aluminum ions, no insoluble salt precipitated and the CMC aqueous solution remained colorless and transparent. From this, by using a liquid composition containing an organic acid as the liquid composition to be held on the sheet-like substrate containing the water-soluble binder, even when the sheet-like substrate contains trivalent or higher metal ions derived from waste paper-derived fibers, a hydrolyzable sheet with a good balance between sheet strength and hydrolyzability can be obtained.

[0038] Examples of the organic acid to be contained in the liquid composition include malic acid, citric acid, lactic acid, acetic acid, oxalic acid, succinic acid, tartaric acid, and fumaric acid, and one of these can be used alone or in combination of two or more. Among these organic acids, malic acid, citric acid, lactic acid, and acetic acid are particularly preferable.

[0039] According to the findings of the present inventors, the hydrolyzability of the hydrolyzable sheet is significantly affected by the pH of the liquid composition. From the viewpoint of improving the hydrolyzability of the hydrolyzable sheet, the pH of the liquid composition is preferably 3.2 or higher, more preferably 3.5 or higher, and preferably 4.5 or lower, more preferably 3.8 or lower. The "pH of the liquid composition" referred to here is the pH when the temperature of the liquid composition is 25°C. The pH of the liquid composition can be measured according to a conventional method using a known pH measuring device. The pH of the liquid composition can be adjusted using an acid agent and / or an alkali agent. The organic acid, which is an essential component of the liquid composition according to the present invention, can function as the acid agent. As the alkali agent, for example, sodium hydroxide, sodium carbonate, calcium hydroxide, and calcium carbonate can be used.

[0040] The preferable range of the pH of the liquid composition varies depending on the type of the organic acid contained in the liquid composition. Specifically, it is as follows. When the organic acid contained in the liquid composition is malic acid, the pH of the liquid composition is preferably 3.2 or higher and 4.2 or lower, more preferably 3.5 or higher and 4.1 or lower. When the organic acid contained in the liquid composition is citric acid, the pH of the liquid composition is preferably 3.2 or higher and 4.2 or lower, more preferably 3.5 or higher and 4.0 or lower. When the organic acid contained in the liquid composition is lactic acid, the pH of the liquid composition is preferably 3.2 or higher and 4.0 or lower, more preferably 3.5 or higher and 3.8 or lower. When the organic acid contained in the liquid composition is acetic acid, the pH of the liquid composition is preferably 3.2 or higher and 4.5 or lower, more preferably 3.2 or higher and 4.2 or lower.

[0041] The content of the organic acid in the liquid composition is preferably 0.4% by mass or more, more preferably 0.5% by mass or more, and preferably 2.0% by mass or less, more preferably 1.2% by mass or less, based on the total mass of the liquid composition. When the content of the organic acid is within the above range, the above-described effects can be more surely achieved with a necessary and sufficient amount of the organic acid.

[0042] The preferred content of the organic acid in the liquid composition varies depending on the type of the organic acid contained in the liquid composition. Specifically, it is as follows. When the organic acid contained in the liquid composition is malic acid, the content of malic acid in the liquid composition is preferably 0.4% by mass or more, more preferably 0.5% by mass or more, and preferably 1.5% by mass or less, more preferably 1.2% by mass or less, based on the total mass of the liquid composition. When the organic acid contained in the liquid composition is citric acid, the content of citric acid in the liquid composition is preferably 0.4% by mass or more, more preferably 0.5% by mass or more, and preferably 1.5% by mass or less, more preferably 1.2% by mass or less, based on the total mass of the liquid composition. When the organic acid contained in the liquid composition is lactic acid, the content of lactic acid in the liquid composition is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and preferably 2.0% by mass or less, more preferably 1.5% by mass or less, based on the total mass of the liquid composition. When the organic acid contained in the liquid composition is acetic acid, the content of acetic acid in the liquid composition is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and preferably 2.0% by mass or less, more preferably 1.5% by mass or less, based on the total mass of the liquid composition.

[0043] In addition to the organic acid, the liquid composition may further contain a surfactant. Thereby, the hydrolyzability of the hydrolyzable sheet (sheet-like substrate that holds the liquid composition) can be further improved. Examples of the surfactant include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants, and one of these can be used alone or in combination of two or more. Preferred surfactants include nonionic surfactants. Specific examples thereof include polyoxyalkylene (number of added moles of alkylene oxide: 1 to 20) alkyl (linear or branched, having 8 to 22 carbon atoms) ethers, alkyl (linear or branched, having 8 to 22 carbon atoms) glycosides (average degree of sugar condensation: 1 to 5), sorbitan fatty acid (linear or branched, having 8 to 22 carbon atoms) esters, and alkyl (linear or branched, having 6 to 22 carbon atoms) glyceryl ethers. Other preferred surfactants include amphoteric surfactants having 8 to 24 carbon atoms in the alkyl group. Specific examples thereof include alkyl carboxybetaines, alkyl sulfobetaines, alkyl hydroxysulfobetaines, alkyl amidocarboxybetaines, alkyl amidosulfobetaines, and alkyl amidohydroxysulfobetaines. In addition, the surfactants (specific acetylene glycols, alkylene oxide adducts of specific acetylene glycols, and specific dialkyl sulfosuccinic acids or their salts) contained in the hydrolyzable sheet described in JP-A-2021-172904 are preferably used in the present invention.

[0044] From the viewpoint of the balance between the hydrolyzability of the hydrolyzable sheet and the feel of the sheet, the content of the surfactant in the liquid composition is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and preferably 2.0% by mass or less, more preferably 1.0% by mass or less, based on the total mass of the liquid composition. If the content of the surfactant is too low, the significance of using it (the further improving effect on the hydrolyzability of the hydrolyzable sheet) is poor, and if the content of the surfactant is too high, there is a risk of deterioration in feel such as stickiness.

[0045] The liquid composition typically contains, in addition to the organic acid, a binder insolubilizing component. The binder insolubilizing component functions as a crosslinking agent for the water-soluble binder contained in the sheet-like substrate. Since the sheet-like substrate is hydrolyzable, if a liquid composition not containing the binder insolubilizing component is held thereon, the sheet-like substrate may disintegrate due to this. By including the binder insolubilizing component in the liquid composition, the shape retention of the sheet-like substrate holding the liquid composition can be improved, and the inconvenience of the sheet-like substrate disintegrating unintentionally can be effectively prevented. As the binder insolubilizing component, an appropriate one may be selected according to the type of the water-soluble binder used, etc., and there is no particular limitation, but a divalent or lower metal ion compound is preferred. Examples of the divalent or lower metal ion compound include metal ion compounds of alkaline earth metals, manganese, zinc, cobalt, and nickel, and one of these may be used alone or two or more thereof may be used in combination. Among the divalent or lower metal ion compounds, in particular, it is preferable to use ion compounds of calcium, strontium, barium, zinc, cobalt, and nickel. The divalent or lower metal ion compound is usually added to the liquid composition in the form of a water-soluble metal salt such as a hydroxide, chloride, sulfate, nitrate, carbonate, formate, or acetate.

[0046] The content of the divalent or lower metal ion compound in the liquid composition may be appropriately adjusted according to the type of the metal ion compound used, etc. For example, when using a divalent metal ion compound, it is preferable that the divalent metal ion is preferably 1 / 4 mol or more, more preferably 1 / 2 mol or more, per 1 mol of the carboxyl group in the water-soluble binder contained in the sheet-like substrate. Adjusting the content of the divalent metal ion compound in the liquid composition in this way is preferable from the viewpoint of causing a sufficient crosslinking reaction.

[0047] From the perspective of the balance between the wet strength of the hydrolyzable sheet and the finish of the wiped surface, the content of the metal ion compound with a valence of 2 or less in the liquid composition is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and preferably 10.0% by mass or less, more preferably 4.0% by mass or less, based on the total mass of the liquid composition. If the content of the metal ion compound with a valence of 2 or less is too small, the significance of using it (the further improvement effect of the wet strength of the hydrolyzable sheet) is poor. If the content of the metal ion compound with a valence of 2 or less is too large, there is a risk of deterioration in the finish with residue remaining on the wiped surface.

[0048] In addition to the binder insolubilizing component (metal ion compound with a valence of 2 or less), the liquid composition preferably further contains an organic solvent. Thereby, the formation of the crosslinked complex between the water-soluble binder and the binder insolubilizing component is significantly increased, and since the complex exists in an insoluble state, even if the amount of the aqueous liquid in the liquid composition held by the sheet-like substrate is large, sufficient strength to withstand use can be exhibited. As the organic solvent, water-soluble ones are preferred. For example, monohydric alcohols such as ethanol, methanol, and isopropyl alcohol; glycols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, methylpropylene glycol, dipropylene glycol, butylene glycol, and hexylene glycol; mono- or di-ethers of the above glycols and lower alcohols such as methanol, ethanol, propanol, and butanol; esters of the above glycols and lower fatty acids; polyhydric alcohols such as glycerin and sorbitol, etc. can be mentioned, and one of these can be used alone or in combination of two or more. Among these water-soluble organic solvents, from the perspective of the balance between the hydrolyzability and wet strength of the hydrolyzable sheet, glycol (PG) and methylpropylene glycol (MPG) are preferred.

[0049] From the perspective of the balance between the wet strength and the solvent odor of the hydrolyzable sheet, the content of the organic solvent in the liquid composition is preferably 10.0% by mass or more, more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, based on the total mass of the liquid composition.

[0050] In addition to the aforementioned components (organic acid, surfactant, metal ion compound with a valence of 2 or less, organic solvent), the liquid composition may further contain other components such as water, bactericide, bleaching agent, deodorant, fragrance, etc. for the purpose of improving the cleaning or wiping performance of the liquid composition itself.

[0051] The hydrolyzable sheet of the present invention can be produced by impregnating a sheet-shaped substrate with the liquid composition. Examples of such a method for impregnating the liquid composition include a method of immersing the sheet-shaped substrate in the liquid composition and a method of applying or spraying the liquid composition onto the sheet-shaped substrate.

[0052] In the hydrolyzable sheet of the present invention, the retention amount (impregnation amount) of the liquid composition in the sheet-shaped substrate is preferably 100% by mass or more, more preferably 150% by mass or more, and preferably 500% by mass or less, more preferably 300% by mass or less, based on the dry mass of the sheet-shaped substrate, from the perspective of the balance between the hydrolyzability and the wet strength of the hydrolyzable sheet. When the retention amount of the liquid composition is within such a range, in addition to the aforementioned effects, an improvement effect in cleaning performance due to the liquid slipping effect can be expected.

[0053] The hydrolyzable sheet of the present invention can be used for cleaning articles or wiping the human body. Specific examples of the former include cleaning articles for areas around water such as toilets, washrooms, and kitchens. Specific examples of the latter include buttocks wipes, body wipes for nursing care, and makeup removal sheets.

[0054] As described above, the present invention has been described based on its preferred embodiments. However, the present invention is not limited to the above embodiments and can be appropriately modified without departing from the spirit of the present invention.

Examples

[0055] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to such examples.

[0056] 〔Examples 1 to 20, Comparative Examples 1 to 4〕 First, beverage packs were used as waste paper, and waste paper-derived fibers were prepared. Specifically, the waste paper (beverage pack) was dispersed in water, separated into waste paper-derived fibers and other components, and only the waste paper-derived fibers were collected. The waste paper-derived fibers thus obtained were fibers derived from paper containers with aluminum, and the aluminum ion content was 0.002% by mass. Next, a predetermined amount of CMC was added as a water-soluble binder to a slurry in which the waste paper-derived fibers were dispersed in water (fiber concentration: about 0.3% by mass), and the slurry was wet-laid according to a conventional method to obtain a sheet-like substrate with a basis weight of 30 g / m 2 The obtained sheet-like substrate had a fiber content of 94% by mass, a waste paper-derived fiber occupancy of 100% by mass, and a CMC content of 6.0% by mass in terms of solid content. Next, the sheet-like substrate was immersed in the liquid composition to hold the liquid composition on the sheet-like substrate, thereby producing the target hydrolyzable sheet. The retention amount (impregnation amount) of the liquid composition in the sheet-like substrate was 200% by mass based on the dry mass of the sheet-like substrate.

[0057] (Composition of the liquid composition: total 100% by mass of the following components) · Organic acid: as described in Tables 1 to 4. · Alkyl glycoside (nonionic surfactant): 0.5% by mass · Zinc sulfate (divalent or lower metal ion compound): 3.0% by mass · Propylene glycol monomethyl ether (organic solvent): 13.0% by mass · 1,2-propanediol (organic solvent): 7.0% by mass · Water: balance

[0058] For the hydrolyzable sheets of each example and comparative example, the hydrolyzability and wet tensile strength were measured by the above method. The results are shown in Table 1 below. Regarding the evaluation of hydrolysis, when the hydrolysis time is 100 seconds or less, it is rated as "A" (highest evaluation), when it exceeds 100 seconds and is 3600 seconds or less, it is rated as "B", and when it exceeds 3600 seconds, it is rated as "C" (lowest evaluation). Regarding the evaluation of wet tensile strength, when it is 400 cN / 25 mm or more, it is rated as "A" (highest evaluation), when it is 300 cN / 25 mm or more and less than 400 cN / 25 mm, it is rated as "B", and when it is less than 300 cN / 25 mm, it is rated as "C" (lowest evaluation).

[0059]

Table 1

[0060]

Table 2

[0061]

Table 3

[0062]

Table 4

[0063] 1 Sheet-like substrate 2 First layer 3 Second layer 4 Binder layer

Claims

1. A hydrolyzable sheet having a hydrolyzable sheet-like substrate containing fibers and a water-soluble binder, and a liquid composition held on the sheet-like substrate, wherein the fibers contain fibers derived from waste paper, and the liquid composition contains an organic acid.

2. The hydrolyzable sheet according to claim 1, wherein the fibers derived from waste paper contain metal ions of trivalent or higher.

3. The hydrolyzable sheet according to claim 2, wherein the metal ions of trivalent or higher contain aluminum ions.

4. The hydrolyzable sheet according to any one of claims 1 to 3, wherein the fibers derived from waste paper contain fibers derived from aluminum-coated paper containers.

5. The hydrolyzable sheet according to any one of claims 1 to 3, wherein the organic acid contains one or more selected from malic acid, citric acid, lactic acid, and acetic acid.

6. The hydrolyzable sheet according to any one of claims 1 to 3, wherein the pH of the liquid composition is 3.2 or more and 4.5 or less.

7. The hydrolyzable sheet according to any one of claims 1 to 3, wherein the water-soluble binder has a carboxyl group.

8. The hydrolyzable sheet according to any one of claims 1 to 3, wherein the liquid composition contains one or more selected from a surfactant and a metal ion compound of divalent or lower.

9. The hydrolyzable sheet according to any one of claims 1 to 3, wherein the sheet-like substrate has a laminated structure including a first layer mainly composed of the fibers derived from waste paper and a second layer composed of a fiber layer not containing the fibers derived from waste paper.

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