Water-disintegrable sheet and production method for the same

Abstract

To provide a water-disintegratable sheet having improved water-disintegratability compared to conventional sheets.SOLUTION: A water-disintegrable sheet is a substantially water-dispersible sheet containing cellulose fibers. The water-disintegrable sheet contains at least one surfactant selected from an anionic surfactant and an amphoteric surfactant, and a polysaccharide derivative having a cationic group. The cellulose fibers are preferably cellulose fibers derived from waste paper. The cellulose fibers are preferably made from cellulose fibers having a fibrillation degree of 1.6% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-disintegrable sheet and a method for producing the same. [Background technology]

[0002] As a conventional technique relating to water-disintegrable sheets containing fibers such as pulp, the present applicant has previously proposed a water-disintegrable sheet obtained by impregnating water-disintegrable paper made from fibers and surfactants with an aqueous detergent (see Patent Document 1).

[0003] The applicant also proposed a water-disintegrable sheet that uses cellulose fibers derived from waste paper as the fibers and contains a surfactant (see Patent Document 2). The water-disintegrable sheet described in this document has the advantage that, by containing cellulose fibers derived from waste paper, it has high water-disintegrability even if its water absorption rate is inferior to that of virgin cellulose fibers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-194635 A [Patent Document 2] Patent Publication No. 2021-172904 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the water-disintegrable sheets described in Patent Documents 1 and 2, it is possible to rapidly disintegrate the sheets to the fiber level in water. However, as the performance of water-disintegrable sheets has improved in recent years, further improvement in the water-disintegrability of these types of water-disintegrable sheets is required. In particular, when cellulose fibers derived from waste paper are used as the fibers, there is still room for improvement in the water-disintegrable sheets described in Patent Documents 1 and 2. Therefore, an object of the present invention is to provide a water-disintegratable sheet having improved water-disintegratability compared to conventional sheets. [Means for solving the problem]

[0006] The present invention relates to a water-disintegratable sheet containing cellulose fibers and which is substantially dispersible in water. In one embodiment, At least one surfactant selected from an anionic surfactant and an amphoteric surfactant; A polysaccharide derivative having a cationic group; It is preferred that the compound contains

[0007] The present invention also relates to a method for producing a cellulose fiber spunbonded fiber spunbonded fiber, comprising the steps of: mixing cellulose fibers with at least one surfactant selected from an anionic surfactant and an amphoteric surfactant to obtain a mixed liquid; a papermaking process of papermaking a base sheet using the mixed liquid; and a step of adding a polysaccharide derivative having a cationic group during or after the step of obtaining the mixed liquid or the step of forming the paper. Effect of the Invention

[0008] According to the present invention, there is provided a water-disintegratable sheet having improved water-disintegratability compared to conventional water-disintegratable sheets. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described below based on its preferred embodiments. The present invention relates to a water-disintegrable sheet. The water-disintegrable sheet is a substantially water-dispersible sheet that does not disintegrate when impregnated with an aqueous chemical, but disintegrates quickly and at the fiber level when discarded in a large amount of water. The degree of disintegration of the water-disintegrable sheet is expressed by the ease of disintegration defined in JIS P 4501-1993 (toilet paper), and the lower this value, the better the water-disintegrability. The ease of disintegration of the water-disintegrable sheet of the present invention is preferably 110 seconds or less, more preferably 100 seconds or less, and even more preferably 90 seconds or less.

[0010] The water-disintegratable sheet of the present invention is a sheet containing cellulose fibers and substantially dispersible in water, and is preferably a wet sheet impregnated with an aqueous chemical. The cellulose fibers may be natural cellulose fibers or non-natural cellulose fibers. Examples of natural cellulose fibers include bleached wood pulp such as softwood bleached kraft pulp (NBKP), softwood bleached sulfite pulp (NBSP), and hardwood bleached kraft pulp (LBKP); and non-wood pulp such as cotton pulp and hemp pulp. Examples of non-natural cellulose fibers include modified pulp such as cationic pulp and mercerized pulp; and regenerated cellulose fibers such as rayon, lyocell, and cupra. These fibers may be used alone or in combination of two or more.

[0011] When wood pulp is used as the cellulose fiber, the wood pulp can include both virgin pulp and cellulose fiber derived from waste paper (i.e., waste paper pulp). The cellulose fiber derived from waste paper includes cellulose fiber obtained by recycling paper produced from virgin pulp as a raw material, and cellulose fiber obtained by recycling waste paper, but does not include virgin pulp itself.

[0012] Waste paper can be anything that has been collected as a raw material for papermaking. In Japan, the Notice on the Implementation of the Law for the Promotion of Effective Utilization of Resources (enforced on October 25, 1991) defines waste paper as follows: Definition of waste paper: Paper, paper products, books, and other items that are entirely or partially made of paper, that have been used once or not and have been collected, or that have been discarded, but are useful and can be used as raw materials for paper (including those imported after collection), or have the potential to be used as raw materials for paper. However, this does not include those generated during the papermaking process at the factories or business premises (hereinafter referred to as "factories, etc.") of paper manufacturers, or those generated when processing is carried out at the factories, etc. of paper manufacturers (including cases where the paper manufacturers commission other businesses to process the products before shipping them), and that are not shipped as products and are used by the paper manufacturers as raw materials for paper.

[0013] Examples of waste paper that can be used in the present invention include newspapers, magazines, cardboard, "white and cardboard" (e.g. white, cream white and lined white), extra white, medium white, "imitation and colored paper" (e.g. imitation, colored paper, Kent, white art, flyers, beverage cartons, office paper), "ticket and medium-smooth paper" (e.g. special cut, separate cut, medium-smooth paper), brown imitation paper (e.g. cut brown, plain brown, miscellaneous bags, kraft cardboard), "mount paper, ticket and cardboard" (e.g. wrap, upper mount paper, mount paper, miscellaneous paper), etc. One of these types can be used alone or two or more types can be used in combination. Among these waste papers, from the viewpoint of reliably imparting the desired properties (water-disintegrability, wet strength) to the water-disintegrable sheet, "imitation and colored paper" (inked wood-free paper and beverage cartons) are preferred, and beverage cartons such as milk cartons are more preferred.

[0014] When the cellulose fibers contained in the water-decomposable sheet are derived from waste paper, the cellulose fibers are typically derived from wood pulp (NBKP, NBSP, LBKP, etc.). The water-disintegrable sheet may be composed of 100% by mass of virgin pulp, may contain both virgin pulp and cellulose fiber derived from waste paper, or may be composed of 100% by mass of cellulose fiber derived from waste paper. When the water-disintegrable sheet contains cellulose fiber derived from waste paper, the proportion of cellulose fiber derived from waste paper contained in the water-disintegrable sheet is preferably 50% by mass or more, more preferably 80% by mass or more, from the viewpoint of promoting the reuse of waste paper.

[0015] It is required that the water-disintegrable sheet has water-disintegrability and quickly disintegrates and disperses when it is put into a large amount of water. In order to meet such a requirement and improve the water-disintegrability, it is preferable that the cellulose fibers contained in the water-disintegrable sheet are made from cellulose fibers having a fibrillation degree of a predetermined value or less. The fibrillation degree is an index showing the degree of fibrillation of the cellulose fibers (particularly external fibrillation). The higher the fibrillation degree value, the more advanced the fibrillation of the cellulose fibers is. Cellulose fibers with a relatively high fibrillation degree have more advanced external fibrillation than cellulose fibers with a relatively low fibrillation degree, and the fibrils on the outside of the fibers are fluffy and have an increased specific surface area, which promotes physical entanglement by the fibrils and strengthens the bonds between the fibers, resulting in a decrease in the water-disintegrability of the paper, which is difficult to disintegrate and disperse even when put into a large amount of water. Therefore, from the viewpoint of improving the water-disintegrability of the water-disintegrable sheet, it is preferable that the fibrillation degree of the cellulose fibers contained in the water-disintegrable sheet is equal to or less than a predetermined value. Cellulose fibers derived from waste paper have a higher fibrillation degree than virgin pulp, and due to this, the water-disintegrability of paper containing cellulose fibers derived from waste paper is generally inferior to that of paper made of virgin pulp. In contrast to this, the water-disintegrable sheet of the present invention has a sufficiently high water-disintegrability even when cellulose fibers derived from waste paper are used as the raw material for the cellulose fibers. Therefore, the cellulose fibers contained in the water-disintegratable sheet of the present invention exhibit high water-disintegratability even when the cellulose fibers used as raw materials have a high fibrillation degree, preferably 1.6% or less.

[0016] From the viewpoint of further improving the water disintegrability, it is preferable that the cellulose fibers contained in the water-disintegrable paper of the present invention are made from cellulose fibers having a low fibrillation degree. From this viewpoint, it is preferable that the cellulose fibers contained in the water-disintegrable paper of the present invention are made from cellulose fibers having a fibrillation degree of 1.6% or less, particularly 1.4% or less. The lower the fibrillation degree of the cellulose fibers used as the raw material, the more it contributes to improving the water disintegrability of the water-disintegrable paper, but a realistic lower limit for the fibrillation degree is 0.8%.

[0017] The fibrillation degree of cellulose fibers is measured by the following method. Specifically, the fibrillation degree is measured using a commercially available fiber image analysis analyzer (Valmet FS5 manufactured by Valmet Automation) according to the manual. The measurement principle is to prepare an aqueous dispersion of the fiber to be measured, inject this aqueous dispersion into a tube with an inner diameter of 0.5 mm and allow it to flow in one direction, and capture the flowing state with an imaging means such as a CCD camera in the presence of a light source. Based on the obtained image, the fibrillation part of each fiber is distinguished from the other parts. Then, the "ratio of the area of ​​the fibrillation part to the total area of ​​the fiber" (hereinafter also referred to as the "fibril area ratio") is measured. This fibrillation area ratio is the fibrillation degree. A small fibrillation degree means a small fibrillation area ratio, i.e., external fibrillation has not progressed much.

[0018] The cellulose fibers are preferably made from cellulose fibers having an average fiber length within a predetermined range. This also improves the water disintegrability of the water disintegratable sheet. From this perspective, the cellulose fibers used as the raw material for the water disintegratable sheet preferably have an average fiber length of 0.5 mm or more and 3.0 mm or less, more preferably 0.6 mm or more and 1.5 mm or less, and even more preferably 0.8 mm or more and 1.3 mm or less. The fiber length of the cellulose fibers does not substantially change before and after papermaking.

[0019] The average fiber length of the cellulose fibers can be measured using the measuring device (Valmet FS5) used in the above-mentioned measurement of the fibrillation degree, according to the manual.

[0020] It is preferable to use cellulose fibers derived from waste paper as the cellulose fibers contained in the water-disintegrable sheet, since this contributes to reducing the environmental load. By actively using cellulose fibers derived from waste paper, it is possible to contribute to preventing and solving various environmental problems, such as preventing global warming and reducing waste. In addition, by using cellulose fibers derived from waste paper as a raw material, it is expected that the manufacturing cost of the water-disintegrable sheet can be reduced. However, as mentioned above, there was a problem that the water-disintegrable sheet containing cellulose fibers derived from waste paper is difficult to improve in water disintegrability compared to a water-disintegrable sheet made of virgin pulp. The present inventors have conducted extensive research to improve this point, and have unexpectedly found that by incorporating a combination of a specific surfactant and a specific polysaccharide derivative in a water-disintegrable sheet, the water-disintegrability of the water-disintegrable sheet is improved compared to conventional methods. Furthermore, the inventors have also found that this excellent water-disintegrability is exhibited not only when the water-disintegrable sheet mainly contains virgin pulp, but also when the water-disintegrable sheet mainly contains cellulose fibers derived from waste paper.

[0021] In detail, the water-disintegrable sheet of the present invention preferably contains at least one surfactant selected from an anionic surfactant and an amphoteric surfactant. Such a surfactant has a function of improving the water-disintegrability of the water-disintegrable sheet. This function becomes more remarkable when a surfactant is used in combination with a specific polysaccharide derivative. When the water-disintegrable sheet contains such a surfactant, the surfactant is adsorbed to the surface of the cellulose fiber in the water-disintegrable sheet via the polysaccharide derivative having a cationic group described later, thereby improving the water-disintegrability of the water-disintegrable sheet compared to conventional methods. In particular, even when the water-disintegrable sheet mainly contains cellulose fiber derived from waste paper, excellent water-disintegrability is exhibited.

[0022] Examples of the anionic surfactant include fatty acid salts, alkyl sulfate salts, alkyl benzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl diallyl ether sulfonates, alkyl phosphates, naphthalene sulfonate-formaldehyde condensates, aromatic sulfonate-formaldehyde condensates, polyoxyethylene alkyl ether sulfate salts, polyoxyethylene alkyl allyl ether sulfate salts, carboxylic acid-type polymer surfactants, etc. These anionic surfactants can be used alone or in combination of two or more. From the viewpoint of improving the water-disintegrability of a water-disintegrable sheet compared to conventional ones, particularly from the viewpoint of improving the water-disintegrability of a water-disintegrable sheet using cellulose fibers derived from waste paper as the cellulose fibers, it is preferable to use an alkyl sulfate ester salt such as a dialkyl sulfosuccinate or lauryl sulfate as the anionic surfactant.

[0023] In terms of further improving the water-disintegrability of the water-disintegrable sheet, it is preferable that the carbon number of each alkyl group in the dialkyl sulfosuccinate is independently from 5 to 18. As the dialkyl sulfosuccinate, for example, a commercially available product such as Pelex OT-P manufactured by Kao Corporation can be used.

[0024] In terms of further improving the water-disintegrability of the water-disintegrable sheet, it is preferable that the carbon number of each alkyl group in the alkyl sulfate ester salt is independently from 5 to 18. As the alkyl sulfate ester salt, for example, a commercially available product such as EMALE 2F-30 manufactured by Kao Corporation can be used.

[0025] Examples of amphoteric surfactants include alkyl dimethylaminoacetic acid betaine, alkyl dimethylamine oxide, alkyl carboxymethyl hydroxyethyl imidazolinium betaine, alkyl amidopropyl betaine, etc. These amphoteric surfactants can be used alone or in combination of two or more. From the viewpoint of improving the water-disintegrability of a water-disintegrable sheet compared to conventional ones, particularly from the viewpoint of improving the water-disintegrability of a water-disintegrable sheet using cellulose fibers derived from waste paper as the cellulose fibers, it is preferable to use an alkyldimethylamine oxide as the amphoteric surfactant.

[0026] In terms of further improving the water-disintegrability of the water-disintegrable sheet, it is preferable that the number of carbon atoms in each alkyl group in the alkyldimethylamine oxide is independently 5 to 18. As the amphoteric surfactant, for example, a commercially available product such as Amphitol 20N manufactured by Kao Corporation can be used.

[0027] In addition, when the water-disintegrable sheet contains an anionic surfactant and / or an amphoteric surfactant, the total content of the anionic surfactant and the amphoteric surfactant is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, based on the mass of the water-disintegrable sheet. In addition, the total content of the anionic surfactant and the amphoteric surfactant is preferably 1.0% by mass or less, more preferably 0.9% by mass or less, based on the mass of the water-disintegrable sheet. When the total content of the anionic surfactant and the amphoteric surfactant is 0.1% by mass or more, the surfactant is easily adsorbed to the surface of the negatively charged cellulose fiber via the polysaccharide derivative having a cationic group described later, and the function of the surfactant to improve the water disintegrability of the water-disintegrable sheet can be effectively expressed. In addition, when the total content of the anionic surfactant and the amphoteric surfactant is 1.0% by mass or less, the surfactants repel each other, which makes it difficult for the surfactant to be adsorbed to the surface of the negatively charged cellulose fiber. From this viewpoint, the content of the anionic surfactant and the amphoteric surfactant is preferably from 0.1% by mass to 1.0% by mass, and more preferably from 0.2% by mass to 0.9% by mass.

[0028] The contents of the anionic surfactant and the amphoteric surfactant relative to the mass of the water-disintegrable sheet are calculated by the following method. The charge amount of white water obtained when the substrate sheet described later is made is measured using a particle charge meter (PCD-T3 manufactured by MTG). Specifically, the charge amount (A) of the dispersion in which cellulose fibers are dispersed in water and the charge amount (C) of the mixture obtained by mixing the dispersion with the surfactant are measured. Separately, the charge amount (B) of the surfactant and the content (D) of the surfactant in the mixture are measured in advance. Then, the content of the anionic surfactant and the amphoteric surfactant relative to the mass of the water-disintegrable sheet, i.e., the amount of the surfactant remaining in the cellulose fibers, is calculated based on the following formula (1). Content = [(B)-(C)] / [(A)+(B)]×(D)×100··(1)

[0029] The water-disintegratable sheet of the present invention preferably contains a polysaccharide derivative having a cationic group in addition to the above-mentioned anionic surfactant. Since the polysaccharide derivative has a cationic group, it often exhibits cationic properties as a whole.

[0030] An example of the cationic group in the polysaccharide derivative having a cationic group is a quaternary ammonium group. Examples of polysaccharides in the polysaccharide derivative having a cationic group include sodium alginate, trant gum, guar gum, starch, xanthan gum, gum arabic, carrageenan, galactomannan, gelatin, casein, albumin, and purpuran. Specific examples of polysaccharide derivatives having a cationic group include quaternary ammonium guar gum, which is a cationic guar gum, and quaternary ammonium starch, which is a cationic starch, etc. These can be used alone or in combination of two or more.

[0031] The surface of the cellulose fibers in the water-disintegrable sheet, particularly the surface of the cellulose fibers in the dispersion obtained when the water-disintegrable sheet is produced and dispersed in water, is negatively charged. Therefore, when the water-disintegrable sheet contains a polysaccharide derivative having a cationic group in addition to the surfactant, the polysaccharide derivative functions as an auxiliary agent that effectively adsorbs the negatively charged cellulose fiber surface and the surfactant. This allows the surfactant to effectively exert its function of improving the water disintegrability of the water-disintegrable sheet. Therefore, even if the sheet contains cellulose fibers with a high degree of fibrillation, such as cellulose fibers derived from waste paper, the water disintegrability of the sheet can be improved. The mechanism by which the polysaccharide derivative having a cationic group functions as an assistant to improve hydrolysis is not clear, but the present inventors believe it to be as follows, but are not bound by this theory. The negatively charged surface of the cellulose fiber and the polysaccharide derivative having a cationic group are attracted to each other, and the entire cellulose fiber is electrically neutralized, thereby making it easier for anionic surfactants or amphoteric surfactants to be adsorbed onto the surface of the cellulose fiber. From the viewpoint of improving the water-disintegrability of the water-disintegrable sheet compared to conventional ones, the polysaccharide derivative having a cationic group is preferably at least one selected from cationized guar gum and cationized starch.

[0032] As the polysaccharide derivative having a cationic group, commercially available products such as DD4280 manufactured by Seiko PMC Corporation and MEYPRO-BOND 111 manufactured by Sansho Corporation can also be used.

[0033] When the water-disintegrable sheet contains a polysaccharide derivative having a cationic group, the content of the polysaccharide derivative is preferably 0.1% by mass or more, more preferably 0.15% by mass or more, based on the mass of the water-disintegrable sheet. The content of the polysaccharide derivative is preferably 0.5% by mass or less, more preferably 0.4% by mass or less, based on the mass of the water-disintegrable sheet. When the content of the polysaccharide derivative is 0.1% by mass or more, the function of the assistant agent for effectively adsorbing the surface of the negatively charged cellulose fiber and the above-mentioned surfactant is sufficiently obtained. When the content of the polysaccharide derivative is 0.5% by mass or less, the surface of the cellulose fiber and the above-mentioned surfactant can be easily adsorbed. From this viewpoint, the content of the polysaccharide derivative is preferably 0.1% by mass or more and 0.5% by mass or less, more preferably 0.15% by mass or more and 0.4% by mass or less.

[0034] In the water-disintegrable sheet, the mass ratio R of the polysaccharide derivative having a cationic group to the anionic surfactant and the amphoteric surfactant is preferably 0.1 or more, more preferably 0.15 or more, and even more preferably 0.2 or more. The mass ratio R is preferably 3.0 or less, more preferably 2.75 or less, and even more preferably 2.5 or less. When the mass ratio R is 0.1 or more, the polysaccharide derivative having a cationic group can effectively function as an assistant that effectively adsorbs the surface of the negatively charged cellulose fiber and the above-mentioned surfactant. This makes it easier for the above-mentioned surfactant to be adsorbed on the surface of the cellulose fiber, and the function of the surfactant to improve the water disintegrability of the water-disintegrable sheet can be effectively expressed. Furthermore, when the mass ratio R is 3.0 or less, the polysaccharide derivatives having a cationic group repel each other, which can suppress the polysaccharide derivative from being less likely to act on the surface of the negatively charged cellulose fiber and the above-mentioned surfactant. From this viewpoint, the mass ratio R is preferably 0.1 or more and 3.0 or less, more preferably 0.15 or more and 2.75 or less, and further preferably 0.2 or more and 2.5 or less.

[0035] The water-disintegrable sheet of the present invention may further contain other fibers in addition to the above-mentioned cellulose fibers. Examples of the other fibers include biodegradable fibers made of polylactic acid, etc.; synthetic fibers such as polypropylene fibers, polyvinyl alcohol fibers, polyester fibers, and polyacrylonitrile fibers. These may be used alone or in combination of two or more. The proportion of the other fibers in the total fibers contained in the water-disintegrable sheet is preferably 50% by mass or less, more preferably 20% by mass or less.

[0036] The water-disintegrable sheet of the present invention preferably further contains a binder. The binder contributes to wet strength development when impregnated with an aqueous chemical and water-disintegrability when discarded in water. From the viewpoint of improving wet strength development and water-disintegrability, the water-disintegrable sheet preferably contains a water-soluble binder or a water-swellable binder as the binder.

[0037] The water-soluble binder is preferably one that, when the water-disintegrable sheet is in a wet state while holding the aqueous chemical described below, temporarily becomes insoluble, thereby functioning as a binder that maintains the bonds between the constituent fibers of the water-disintegrable sheet, and plays a role in maintaining the strength of the water-disintegrable sheet when in use. Examples of water-soluble binders having such functions include natural polysaccharides, polysaccharide derivatives (excluding polysaccharide derivatives having cationic groups), and synthetic polymers. The above-mentioned "temporary insolubilization of the water-soluble binder" typically occurs due to the action of a binder insolubilizing component (e.g., a binder crosslinking agent) in the aqueous chemical held in the water-disintegrable sheet.

[0038] Examples of natural polysaccharides include sodium alginate, trant gum, guar gum, xanthan gum, gum arabic, carrageenan, galactomannan, gelatin, casein, albumin, and purpuran. Examples of polysaccharide derivatives include carboxymethyl cellulose, carboxyethyl cellulose, carboxymethylated starch or a salt thereof, methyl cellulose, and ethyl cellulose. Examples of synthetic polymers include polyvinyl alcohol, polyvinyl alcohol derivatives, salts of polymers or copolymers of unsaturated carboxylic acids, salts of copolymers of unsaturated carboxylic acids and monomers copolymerizable with the unsaturated carboxylic acids, etc. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic anhydride, maleic acid, fumaric acid, etc.

[0039] Among the above-mentioned water-soluble binders, water-soluble binders having a carboxyl group are preferred because they have good performance as a binder and good affinity with a crosslinking agent described below. Examples of water-soluble binders having a carboxyl group include carboxymethyl cellulose (CMC), carboxyethyl cellulose, and salts thereof.

[0040] The water-swellable binder is preferably one that, when the water-disintegrable sheet is in a wet state holding an aqueous chemical, temporarily suppresses the swelling of the binder, functions as a binder that maintains the bonds between the constituent fibers of the water-disintegrable sheet, and plays a role in maintaining the strength of the water-disintegrable sheet when in use. An example of a water-swellable binder having such a function is fibrous polyvinyl alcohol.

[0041] Among the above-mentioned water-swellable binders, carboxymethyl cellulose is preferred because it has good performance as a binder.

[0042] The content of the water-soluble binder or water-swellable binder is preferably 1% by mass or more, more preferably 2% by mass or more, based on the mass of the water-disintegrable sheet. The content of the water-soluble binder or water-swellable binder is preferably 30% by mass or less, more preferably 15% by mass or less, and even more preferably 8% by mass or less, based on the mass of the water-disintegrable sheet. The content of the water-soluble binder or water-swellable binder is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 15% by mass or less, and even more preferably 2% by mass or more and 8% by mass or less. When the content of the water-swellable binder is within this range, the wet strength of the water-disintegrable sheet is improved.

[0043] Since the water-disintegrable sheet of the present invention has water-disintegrability, it easily disintegrates when it is disposed of in water or impregnated with an aqueous liquid. Therefore, in the present invention, when the water-disintegrable sheet is impregnated with an aqueous chemical to produce a wet water-disintegrable sheet, it is preferable to include a crosslinking agent for the binder in the aqueous chemical. The crosslinking agent crosslinks the binder to make it insoluble or temporarily suppress swelling, so that the binder does not dissolve in a small amount of water. However, if the binder is disposed of in a large amount of water, the binder, which has been temporarily suppressed from being insoluble or swelling, dissolves in water again, and disintegrates quickly and at the fiber level.

[0044] The crosslinking agent is appropriately selected according to the type of binder. For example, when the binder is a water-soluble binder having a carboxyl group such as the above-mentioned CMC, it is preferable to use a polyvalent metal ion as the crosslinking agent. In particular, it is preferable to use one or more divalent metal ions selected from the group consisting of alkaline earth metals, manganese, zinc, cobalt, and nickel, because the fibers constituting the water-disintegrable sheet are sufficiently bonded to develop a strength that can withstand use, and the water-disintegrability is sufficient. Among these metal ions, it is particularly preferable to use ions of calcium, strontium, barium, zinc, cobalt, and nickel.

[0045] The metal ions are added to the aqueous agent in the form of water-soluble metal salts such as hydroxides, chlorides, sulfates, nitrates, carbonates, formates, acetates, etc. The metal ions are preferably added in an amount of 1 / 4 mol or more, particularly 1 / 2 mol or more, per mol of carboxyl groups in the water-soluble binder present in the water-disintegrable sheet of the present invention, from the viewpoint of causing a sufficient crosslinking reaction.

[0046] On the other hand, when the above-mentioned water-swellable binder is used as the binder, it is preferable to use boric acid as the crosslinking agent. This causes a crosslinking reaction between polyvinyl alcohol and boric acid, which insolubilizes the polyvinyl alcohol. It is preferable that boric acid is mixed in the aqueous agent at a concentration of 1% to 5% by mass. In particular, when a polyvinyl alcohol with a high degree of polymerization is used, it is preferable that the concentration is 1% to 3% by mass, and when a polyvinyl alcohol with a medium or low degree of polymerization is used, it is preferable that the concentration is 3% to 5% by mass.

[0047] Regardless of whether the binder is water-soluble or water-swellable, it is preferable to mix an organic solvent in addition to the crosslinking agent described above in the aqueous agent in order to obtain a water-disintegrable sheet having sufficient strength. By using an organic solvent in combination, the generation of a crosslinked complex between the binder and the crosslinking agent is significantly increased, and the complex exists in an insoluble state, so that even if the amount of water in the aqueous agent impregnated into the water-disintegrable sheet is large, sufficient strength to withstand use is developed.

[0048] The organic solvent is preferably a water-soluble solvent.Specific examples of the organic solvent include monohydric alcohols such as ethanol, methanol, and isopropyl alcohol, glycols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, and hexylene glycol, mono- or diethers of these glycols and lower alcohols such as methanol, ethanol, propanol, and butanol, esters of the glycols and lower fatty acids, and polyhydric alcohols such as glycerin, sorbitol, and 3-methyl-1,3-butanediol.The amount of the organic solvent in the aqueous drug is preferably 1% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 50% by mass or less.

[0049] The aqueous agent is a medium containing water of 60% by mass or more and 90% by mass or less, and is blended with the above-mentioned crosslinking agent (i.e., metal ions or boric acid) and an organic solvent. In addition to these components, the aqueous agent may be blended with surfactants other than the above-mentioned surfactants, bactericides, deodorants, etc., as necessary, to improve the performance of the aqueous agent. As the surfactant, for example, a nonionic surfactant and a cationic surfactant are used.

[0050] The aqueous chemical is preferably impregnated in an amount of 50% by mass or more and 500% by mass or less, particularly 100% by mass or more and 500% by mass or less, and even more particularly 100% by mass or more and 300% by mass or less, based on the mass (dry basis) of the water-disintegrable sheet, in order to achieve a sufficient wiping effect.

[0051] The water-disintegrable sheet of the present invention has high strength when it is wet and impregnated with an aqueous chemical. Moreover, although it does not disintegrate in water when it is only impregnated with the aqueous chemical, it quickly disintegrates at the fiber level when it is discarded in a large amount of water.

[0052] Next, a preferred method for producing the water-disintegratable sheet of the present invention will be described. The manufacturing method of the present invention includes a step of mixing cellulose fibers with at least one surfactant selected from an anionic surfactant and an amphoteric surfactant to obtain a mixed liquid, and a papermaking step of using the mixed liquid to produce a base sheet. In detail, first, the cellulose fibers are dispersed in water to prepare a dispersion liquid. As the cellulose fibers, for example, the above-mentioned cellulose fibers derived from virgin pulp or waste paper can be used. The fibrillation degree of the cellulose fibers is preferably 1.6% or less. In addition to the cellulose fibers, other fibers may be used as necessary.

[0053] In preparing the dispersion, the cellulose fibers are thoroughly dispersed in water using a stirring device with stirring blades. When using cellulose fibers derived from waste paper as the cellulose fibers, depending on the properties of the cellulose fibers, treatment with a device used in a general wet papermaking method, such as a beater or refiner, may be used in combination.

[0054] Next, the prepared dispersion liquid is mixed with the above-mentioned surfactant to obtain a mixed liquid. It is preferable to use a predetermined amount of surfactant based on the dry mass of all fibers constituting the obtained base sheet from the viewpoint of improving the water disintegrability of the water disintegrable sheet more than before. From this viewpoint, it is preferable to use 0.1 mass% or more of the surfactant based on the dry mass of all fibers constituting the base sheet, and more preferably 0.2 mass% or more. In addition, it is preferable to use 1.0 mass% or less of the surfactant based on the dry mass of all fibers constituting the base sheet, and more preferably 0.9 mass% or less. By using 0.1 mass% or more of the surfactant based on the dry mass of all fibers constituting the base sheet, the surfactant is easily adsorbed to the surface of the negatively charged fiber via the polysaccharide derivative having a cationic group, and the function of the surfactant to improve the water disintegrability of the water disintegrable sheet can be effectively expressed. In addition, by using 1.0 mass% or less of the surfactant based on the dry mass of all fibers constituting the base sheet, it is possible to suppress the surfactants from repelling each other, which makes it difficult for the surfactant to be adsorbed to the surface of the negatively charged fiber. From this viewpoint, the surfactant is preferably used in an amount of 0.1% by mass to 1.0% by mass, and more preferably 0.2% by mass to 0.9% by mass, based on the dry mass of all the fibers constituting the base sheet. The amount of the surfactant used can be set to an appropriate value depending on the type of cellulose fiber and the type of polysaccharide derivative described below.

[0055] In addition, it is preferable to mix the surfactant so that the adsorption rate of the surfactant to the cellulose fibers is a predetermined value or more, since the function of the surfactant in improving the water disintegratability of the water disintegratable sheet can be effectively exhibited. From this viewpoint, it is preferable to mix the surfactant so that the adsorption rate of the surfactant to the cellulose fibers is 50% or more, more preferably 55% or more, and even more preferably 60% or more, with 95% or less being realistic. The method for measuring the adsorption rate will be explained in the examples below.

[0056] The manufacturing method of the present invention further includes a step of mixing the mixed liquid with a polysaccharide derivative having a cationic group. The polysaccharide derivative having a cationic group can be of the above-mentioned type. The mixed liquid and the polysaccharide derivative having a cationic group can be mixed in any step. Specifically, for example, the polysaccharide derivative can be mixed in the middle of the step of obtaining the mixed liquid. Or, the polysaccharide derivative can be mixed in the middle of the papermaking step. In other words, (a) when a dispersion in which cellulose fibers are dispersed in water is mixed with a surfactant to obtain a mixed liquid, the polysaccharide derivative can be mixed together. Or, (b) before a dispersion in which cellulose fibers are dispersed in water is mixed with a surfactant to obtain a mixed liquid, the dispersion and the polysaccharide derivative can be mixed. When (b) is adopted when mixing the mixed liquid and the polysaccharide derivative, a surfactant can be mixed after the cellulose fibers are dispersed in water to obtain a dispersion. Regardless of whether (A) or (B) is used, the water-disintegratability of the resulting water-disintegratable sheet is improved over conventional methods, but (B) is preferred, since the inventors have found that the water-disintegratable sheet obtained by using (B) exhibits superior water-disintegratability compared to the water-disintegratable sheet obtained by using (A).

[0057] It is preferable to use a predetermined amount of a polysaccharide derivative having a cationic group relative to the dry mass of all fibers constituting the obtained base sheet, since it spreads throughout the cellulose fibers as an auxiliary agent that effectively adsorbs the surface of the negatively charged cellulose fibers and the surfactant in the mixed liquid. This makes it easier for the surfactant to be adsorbed to the entire cellulose fibers in the mixed liquid, and the function of the surfactant to improve the water disintegrability of the water disintegratable sheet can be effectively expressed. From this viewpoint, it is preferable to use 0.1% by mass or more of the polysaccharide derivative relative to the dry mass of all fibers constituting the base sheet in the mixed liquid, and more preferably 0.15% by mass or more. In addition, it is preferable to use 0.5% by mass or less of the polysaccharide derivative relative to the dry mass of all fibers constituting the base sheet in the mixed liquid, and more preferably 0.4% by mass or less. By using 0.1% by mass or more of the polysaccharide derivative relative to the dry mass of all fibers constituting the base sheet, the function as an auxiliary agent that effectively adsorbs the surface of the negatively charged fibers and the above-mentioned surfactant can be sufficiently obtained. Furthermore, by using the polysaccharide derivative in an amount of 0.5% by mass or less based on the dry mass of all the fibers constituting the base sheet, the surfactant can be easily adsorbed to the fiber surface via the polysaccharide derivative having a cationic group. From this viewpoint, the polysaccharide derivative is preferably used in an amount of 0.1% by mass or more and 0.5% by mass or less, more preferably 0.15% by mass or more and 0.4% by mass or less, based on the dry mass of all the fibers constituting the base sheet. The amount of the polysaccharide derivative used can be set to an appropriate value depending on the type of cellulose fiber and the type of the surfactant.

[0058] In addition, it is preferable that the mass ratio R of the polysaccharide derivative having a cationic group to the surfactant is within a predetermined range, since the polysaccharide derivative can effectively function as an auxiliary agent for effectively adsorbing the surfactant to the surface of the negatively charged cellulose fiber in the mixed liquid. As a result, the surfactant is easily adsorbed to the surface of the cellulose fiber in the mixed liquid via the polysaccharide derivative having a cationic group, and the function of the surfactant to improve the water disintegrability of the water disintegratable sheet can be effectively expressed. From this viewpoint, it is preferable to use the polysaccharide derivative so that the mass ratio R is 0.1 or more, more preferably 0.15 or more, and even more preferably 0.2 or more. In addition, it is preferable to use the polysaccharide derivative so that the mass ratio R is 3.0 or less, more preferably 2.75 or less, and even more preferably 2.5 or less. By using the polysaccharide derivative so that the mass ratio R is 0.1 or more, the polysaccharide derivative can effectively function as an auxiliary agent for effectively adsorbing the surfactant to the surface of the negatively charged fiber. This allows the surfactant to be easily adsorbed on the fiber surface, and the surfactant's function of improving the water-disintegrability of the water-disintegrable sheet can be effectively exerted. In addition, by using the polysaccharide derivative so that the mass ratio R is 3.0 or less, it is possible to suppress the polysaccharide derivatives from repelling each other, which makes it difficult for the polysaccharide derivative to act on the negatively charged fiber surface and the surfactant. From this viewpoint, it is preferable to use the polysaccharide derivative so that the mass ratio R is 0.1 to 3.0, more preferably 0.15 to 2.75, and even more preferably 0.2 to 2.5.

[0059] After the mixture is obtained in this manner, the mixture is dehydrated and pressed to form a base sheet. The basis weight of the cellulose fiber in the base sheet is 15 g / m 2 More than 60g / m 2 It is preferable to set the above values ​​from the viewpoint of the physical properties of the base sheet, namely, wet strength and water disintegratability, as well as the texture of the base sheet. For dewatering and pressing, a papermaking machine used in a general wet papermaking method, such as a cylinder papermaking machine or a Fourdrinier papermaking machine, can be used. The base sheet formed by dehydration contains water, for example, from 80% by mass to 90% by mass. The pressing is performed by compressing the base sheet formed by dehydration from both sides. For example, a thick felt can be used to compress the base sheet. By pressing, the proportion of water contained in the base sheet can be reduced to 40% by mass or more and 70% by mass or less.

[0060] The base sheet obtained by pressing is then subjected to a drying step. The base sheet can be dried using a heating and drying device used in a general wet papermaking method, such as a Yankee dryer. As for the heating and drying conditions, when using a Yankee dryer, the temperature of the peripheral surface is preferably set to 90°C or higher and 140°C or lower. The moisture content of the base sheet after drying is preferably 10% by mass or lower.

[0061] The manufacturing method of the present invention further includes a step of adding (externally adding) a water-soluble binder or a water-swellable binder to the base sheet after the papermaking step. The water-soluble binder and the water-swellable binder may be of the types described above. Any method may be adopted as a method for adding the binder to the base sheet. For example, the binder may be added before the base sheet is completely dried, or the binder may be added to the base sheet after drying. The binder may be added by spraying the base sheet, or by immersing the base sheet in the binder.

[0062] In the manufacturing method of the present invention, instead of the above-mentioned (A) and (B), the water disintegrability of the obtained water-disintegrable sheet can also be improved compared to the conventional method by adding (externally adding) a polysaccharide derivative having a cationic group to the base sheet obtained using the mixed liquid containing the above-mentioned surfactant after the papermaking process. In detail, the above-mentioned polysaccharide derivative can be added to the base sheet before adding the water-soluble binder or water-swellable binder to the paper-made base sheet. The polysaccharide derivative may be added before the base sheet is completely dried, or may be added to the base sheet after drying. The polysaccharide derivative may also be added by spraying the base sheet, or by immersing the base sheet in the polysaccharide derivative.

[0063] Once the base sheet is obtained in this manner, the above-mentioned aqueous agent is added to the base sheet to form a wet sheet. By the above steps, the water-disintegratable sheet of the present invention can be obtained.

[0064] The water-disintegrable sheet thus obtained can be used, for example, as a cleaning sheet for cleaning objects or for wiping the human body. In particular, it can be used, for example, as a cleaning sheet for use around water, such as a toilet, washroom, or kitchen. Alternatively, it can be used as a cleaning sheet for the buttocks, body wipes for nursing care, makeup remover sheets, etc. The water-disintegrable sheet of the present invention is particularly useful as a cleaning sheet for a toilet, since it disintegrates quickly even when it is disposed of by flushing it into the water supply or sewerage system after use.

[0065] While the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit of the present invention. For example, the water-disintegrable sheet may have a flat surface with substantially no convexities. Alternatively, the water-disintegrable sheet may have an uneven surface. Examples of water-disintegrable sheets having an uneven surface include the sheets described in JP 2021-065488 A.

[0066] The number of laminated base sheets in the water-disintegrable sheet is not particularly limited, and the water-disintegrable sheet may have a single-layer structure consisting of one base sheet, or may have a laminate structure consisting of two or more base sheets laminated in the thickness direction. EXAMPLES

[0067] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass".

[0068] [Examples 1 and 2] Waste paper pulp A (fibrillation degree 1.34%, average fiber length 0.87 mm) was dispersed in water to prepare a dispersion. Cationic starch (manufactured by Seiko PMC, product name DD4280) was added to this dispersion in an amount relative to the cellulose fibers derived from waste paper pulp A as shown in Table 1, and the two were thoroughly mixed. Next, sodium dialkyl sulfosuccinate (manufactured by Kao, Pelex OT-P) was added to this in an amount relative to the cellulose fibers derived from waste paper pulp A as shown in Table 1, and thoroughly mixed to obtain a mixed solution. Then, a base sheet was obtained by hand-making. This base sheet was dried with a Yankee dryer heated to 130°C.

[0069] A carboxymethylcellulose aqueous solution was sprayed onto the obtained base sheet so that the amount added to the base sheet was 4.0%. The base sheet was then impregnated with the aqueous chemicals shown below. The amount of impregnation was twice the mass of the base sheet. In this way, a water-disintegrable sheet was produced. The basis weight of the water-disintegrable sheet was 40 g / m 2 It was.

[0070] [Aqueous medicine] Alkyl glucoside 0.2% CaCl23% Propylene glycol monomethyl ether 13% 3-Methyl-1,3-butanediol 5% Water balance

[0071] [Examples 3 and 4] A cationized guar gum (MEYPRO-BOND 111, manufactured by Sansho Co., Ltd.) was used instead of the cationized starch in Examples 1 and 2. A water-disintegrable sheet was produced in the same manner as in Example 1 except for this.

[0072] Example 5 Sodium lauryl sulfate (Emeral 2F-30, manufactured by Kao Corporation) was used instead of sodium dialkyl sulfosuccinate in Example 4. A water-disintegrable sheet was produced in the same manner as in Example 4 except for this.

[0073] Example 6 Lauryl dimethylamine oxide (Amphitol 20N, manufactured by Kao Corporation) was used in place of sodium dialkyl sulfosuccinate in Example 4. A water-disintegrable sheet was produced in the same manner as in Example 4 except for this.

[0074] Example 7 In Example 4, virgin pulp (fibrillation degree 0.92%, average fiber length 2.02 mm) was dispersed in water to prepare a dispersion liquid instead of the recycled paper pulp A. A water-disintegratable sheet was produced in the same manner as in Example 4 except for this.

[0075] Example 8 In Example 4, waste paper pulp B (fibrillation degree 1.56%, average fiber length 1.03 mm) was dispersed in water to prepare a dispersion liquid instead of waste paper pulp A. A water-decomposable sheet was produced in the same manner as in Example 4 except for this.

[0076] Comparative Example 1 A water-disintegrable sheet was produced in the same manner as in Example 1, except that the cationized starch and sodium dialkyl sulfosuccinate were not used.

[0077] [Comparative Examples 2 and 3] In Examples 1 and 2, no cationized starch was used. Except for this, a water-disintegrable sheet was produced in the same manner as in Example 1.

[0078] Comparative Example 4 Benzalkonium chloride (Kao Corporation, Sanisol C) was used instead of sodium dialkylsulfosuccinate in Comparative Example 3. A water-disintegrable sheet was produced in the same manner as in Comparative Example 3 except for this.

[0079] Comparative Example 5 Benzalkonium chloride (Sanisol C, manufactured by Kao Corporation) was used instead of sodium lauryl sulfate in Example 5. A water-disintegrable sheet was produced in the same manner as in Example 5 except for this.

[0080] 〔evaluation〕 For the water-disintegrable sheets obtained in the Examples and Comparative Examples, the content of anionic surfactant and amphoteric surfactant relative to the mass of the water-disintegrable sheet, and the content of polysaccharide derivative having a cationic group relative to the mass of the water-disintegrable sheet were measured using the methods described above. Moreover, the mass ratio R was calculated for each of the water-disintegrable sheets obtained in the examples and comparative examples. The adsorption rate of anionic surfactant or amphoteric surfactant to cellulose fiber and the water disintegration time of the water disintegratable sheets obtained in the Examples and Comparative Examples were evaluated by the following methods. The results are shown in Table 1 below.

[0081] [Evaluation of Adsorption Rate] The charge amount of the white water obtained when the base sheet was made was measured using a particle charge meter (PCD-T3 manufactured by MTG Co., Ltd.). Specifically, the charge amount (A) of the dispersion in which the pulp (cellulose fiber) used in the examples and comparative examples was dispersed in water, and the charge amount (C) of the mixed liquid obtained by mixing the dispersion with the surfactant were measured. Separately, the charge amount (B) of the surfactant was measured in advance. Then, the adsorption rate of the surfactant to the cellulose fiber (i.e., the surfactant content) was calculated based on the following formula (2). Adsorption rate (active agent content) = [(B)-(C)] / [(A)+(B)] × 100 (2) It can be evaluated that the higher the adsorption rate, the more effectively the function of the anionic surfactant or amphoteric surfactant in improving the water-disintegrability of the water-disintegrable sheet is exhibited.

[0082] [Evaluation of water dissolution time] A 300 ml beaker containing 300 ml of water (water temperature 20±5°C) and a rotor (disk-shaped with a diameter of 35 mm and a thickness of 12 mm) is placed on a magnetic stirrer, and the rotor's rotation speed is set to 600±10 rpm. A water-disintegrable sheet having a rectangular shape in plan view of 70 mm x 60 mm is placed in the beaker, and a stopwatch is started. The rotation speed of the rotor is reduced to about 500 rpm at first due to the resistance of the test piece present in the water, but increases as the disintegration and dispersion of the test piece progresses. When the rotation speed of the rotor recovers to 540 rpm, the stopwatch is stopped, and the time is measured in 1-second units. The above measurement is performed five times for one type of water-disintegrable sheet, and the average of the measured values ​​is regarded as the hydrolysis time of the water-disintegrable sheet. The shorter the hydrolysis time, the better the hydrolysis and the easier it is to disintegrate and disperse in water.

[0083] [Table 1]

[0084] As is clear from the results shown in Table 1, the water-disintegratable sheets obtained in the respective Examples have improved water-disintegratability compared to the water-disintegratable sheets obtained in the respective Comparative Examples.

Claims

1. A step of mixing cellulose fibers with at least one surfactant selected from anionic surfactants and amphoteric surfactants to obtain a mixture, A papermaking process in which a base sheet is formed using the aforementioned mixture, A method for producing a substantially water-dispersible hydrolyzable sheet, comprising the steps of: obtaining the aforementioned mixture, adding a polysaccharide derivative having a cationic group during or after the papermaking process;

2. The manufacturing method according to claim 1, wherein the fibrility of the cellulose fiber is 1.6% or less.

3. A step of dispersing the cellulose fibers in water to obtain a dispersion, The manufacturing method according to claim 1 or 2, comprising the step of mixing the polysaccharide derivative, the dispersion, and at least one surfactant selected from the anionic surfactant and the amphoteric surfactant.

4. A step of dispersing the cellulose fibers in water to obtain a dispersion, A step of mixing the polysaccharide derivative and the dispersion, The manufacturing method according to claim 1 or 2, comprising the step of mixing at least one surfactant selected from the anionic surfactant and the amphoteric surfactant with the dispersion.

5. The polysaccharide derivative is used in an amount of 0.1% by mass or more and 0.5% by mass or less relative to the dry mass of all the fibers constituting the base sheet. The manufacturing method according to claim 1 or 2, wherein the surfactant is used in an amount of 0.1% by mass or more and 1.0% by mass or less with respect to the dry mass of all the fibers constituting the base sheet.

6. The manufacturing method according to claim 1 or 2, wherein the polysaccharide derivative is used such that the mass ratio of the polysaccharide derivative to the surfactant is 0.1 or more and 3.0 or less.

7. The manufacturing method according to claim 1 or 2, wherein the surfactant is mixed such that the adsorption rate of the surfactant to the cellulose fibers is 50% or more.

8. A substantially water-dispersible hydrolyzable sheet containing cellulose fibers, At least one surfactant selected from anionic surfactants and amphoteric surfactants, Polysaccharide derivatives having cationic groups, A water-soluble sheet containing [a specific ingredient].