Water-disintegrable paper and method for manufacturing water-disintegrable paper

Abstract

To provide water-disintegrable paper that has excellent tensile strength during use, superior water-disintegrable property when immersed in water, and consideration for environmental conservation.SOLUTION: The water-disintegrable paper of the present invention includes pulp in which at least a part of hydroxy groups of cellulose is substituted with sulfate ester groups.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to hydrolyzable paper and a method for producing the same.

Background Art

[0002] Conventionally, various hydrolyzable papers that can be flushed down the drain after use have been proposed. For example, for toilet paper, toilet cleaners, wet tissues, disposable cleaning sheets, etc., those that can be flushed down the drain after use have been proposed and are in widespread use.

[0003] When in use, the hydrolyzable paper is required to be excellent in strength, for example, tensile strength, for achieving usage purposes such as wiping off dirt or polishing an object.

[0004] Patent Document 1 relates to hydrolyzable paper with less impact on the global environment. However, it is difficult to say that the hydrolyzable paper described in the document is sufficient from the viewpoint of natural environment conservation in that it uses thermally adhesive synthetic fibers such as polypropylene.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, an object of the present invention is to provide a hydrolyzable paper that is excellent in tensile strength during use, excellent in hydrolyzability when immersed in water, and considerate of natural environment conservation, and a method for producing the same.

Means for Solving the Problems

[0007] In order to achieve the above object, the hydrolyzable paper of the present invention is characterized by containing pulp in which at least a part of the hydroxyl groups of cellulose is substituted with sulfate ester groups.

[0008] The manufacturing method of the hydrolyzable paper of the present invention is characterized by including a step of papermaking a suspension containing pulp in which at least a part of the hydroxyl groups of cellulose is substituted with a sulfate group using a paper machine.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a hydrolyzable paper that is excellent in tensile strength during use, excellent in hydrolyzability when immersed in water, and considerate of natural environment conservation, and a manufacturing method thereof.

Embodiments for Carrying Out the Invention

[0010] The hydrolyzable paper of the present invention may contain pulp in which at least a part of the hydroxyl groups of cellulose is substituted with a sulfate group (hereinafter referred to as "sulfate group-introduced pulp"), and may contain sulfate group-introduced pulp in a part thereof, or may be entirely composed of sulfate group-introduced pulp.

[0011] The sulfate group-introduced pulp is a fibrous member in which a plurality of cellulose fibers are aggregated, and at least a part of the hydroxyl groups (-OH groups) of the cellulose (a chain polymer in which D-glucose is β(1→4) glycosidically bonded) constituting the contained cellulose fibers is substituted with a sulfate group represented by the formula (1).

[0012] (-OSO3 - ) r ·Z r+ (1) In formula (1), r is an independent natural number from 1 to 7, Z r+is at least one selected from the group consisting of hydrogen ions, alkali metal ions, monovalent transition metal ions, ammonium ions, aliphatic ammonium ions, aromatic ammonium ions, and cationic polymers when r = 1, and is at least one selected from the group consisting of alkaline earth metal ions, polyvalent metal ions, and compounds containing two or more cationic functional groups (e.g., diamine, etc.) in the molecule when r ≥ 2.

[0013] <Physical properties of pulp with sulfate group introduction> The physical properties of the pulp with sulfate group introduction are not particularly limited, but are, for example, as follows.

[0014] <Amount of introduced sulfate group> The amount of introduced sulfate group per 1 g (solid content mass) of the pulp with sulfate group introduction is preferably adjusted to be, for example, 0.6 mmol / g or more, 0.8 mmol / g or more, 1 mmol / g or more, 1.2 mmol / g or more.

[0015] The upper limit is not particularly limited, but from the viewpoint of suppressing the disintegration of fibers and the increase in cost due to the decrease in crystallinity, for example, the amount of introduced sulfate group per 1 g (solid content mass) of the pulp with sulfate group introduction is 9.9 mmol / g or less, 5 mmol / g or less. Also, from the viewpoint of hydrolyzability, for example, the amount of introduced sulfate group per 1 g (solid content mass) of the pulp with sulfate group introduction is 1.4 mmol / g or less.

[0016] <Measurement method of amount of introduced sulfate group> The amount of introduced sulfate group in the pulp with sulfate group introduction can be evaluated by the amount of sulfur introduced due to the sulfate group or by directly measuring the sulfate group. For example, the amount of introduced sulfate group in the pulp can be measured with a CHNS / O elemental analyzer. Also, the amount of introduced sulfate group in the pulp can be calculated by measuring the electrical conductivity.

[0017] <Crystallinity> The pulp with sulfate group introduced, for example, has a cellulose I-type crystal structure as its crystal structure, and its crystallinity may be 75% or less. Also, from the viewpoint of maintaining the fiber shape, the crystallinity of the pulp with sulfate group introduced is preferably 30% or more. Further, from the viewpoint of handleability in the preparation of the pulp with sulfate group introduced, the crystallinity of the pulp with sulfate group introduced is, for example, 30% or more, 40% or more.

[0018] <Measurement method of crystallinity> The crystallinity of the pulp with sulfate group introduced can be measured, for example, using an X-ray diffractometer.

[0019] <Average fiber length> The average fiber length of the pulp with sulfate group introduced is not particularly limited, and is, for example, 0.2 mm to 2 mm, 0.2 mm to 1.8 mm, 0.2 mm to 1.5 mm, 0.2 mm to 1 mm.

[0020] <Short fiber rate (%)> Also, the pulp with sulfate group introduced may contain pulp with a short fiber length as follows. Examples of this pulp with a short fiber length (hereinafter referred to as "short fiber") include pulp having a fiber length of 0.04 mm or more and 0.2 mm or less in the fiber length distribution. The content rate (%) of short fiber (i.e., short fiber rate (%)) in the pulp with sulfate group introduced is, for example, 10% or more, 15% or more.

[0021] From the viewpoint of handleability, the content rate (%) of the short fiber (i.e., short fiber rate (%)) in the pulp with sulfate group introduced is, for example, 10% to 70%, 10% to 60%, 10% to 50%, 10% to 45%, 15% to 45% in the fiber length distribution.

[0022] <Average fiber width> The average fiber width of the pulp with sulfate group introduced is not particularly limited, and is, for example, 5 μm to 100 μm, 10 μm to 50 μm, 20 μm to 40 μm, 20 μm to 30 μm.

[0023] <Method for Measuring Average Fiber Length, Average Fiber Width, and Fiber Distribution> The average fiber length and average fiber width of the pulp with sulfate group introduced can be measured, for example, using a fiber tester or a fiber length distribution measuring instrument manufactured by Lorenz & Betzler and conforming to ISO 16065-2:2007. Also, the fiber length distribution and fiber width distribution in the pulp with sulfate group introduced can be measured, for example, using a fiber length distribution measuring instrument conforming to ISO 16065-2:2007.

[0024] <Viscosity> When the crystallinity of the pulp with sulfate group introduced is below the aforementioned value, for example, the dispersion (suspension) has a predetermined viscosity. For example, when the crystallinity of the pulp with sulfate group introduced is 70% or less, the viscosity in the dispersion (suspension) obtained by dispersing the pulp with sulfate group introduced in water is 1000 mPa·s or more, 5000 mPa·s or more, 10000 mPa·s or more. In particular, when the crystallinity of the pulp with sulfate group introduced is 60% or less, the viscosity of the dispersion (suspension) tends to increase. Also, when the average fiber length is 1 mm or less, this tendency becomes stronger.

[0025] <Method for Measuring Viscosity> The viscosity (mPa·s) of the pulp with sulfate group introduced can be measured, for example, at a measurement temperature of 20°C using a B-type viscometer, and measurements are carried out at a rotational speed of 6 rpm and a rotational speed of 60 rpm, and the thixotropy index TI value can also be calculated from each viscosity value. TI value = (viscosity at rotational speed of 6 rpm) / (viscosity at rotational speed of 60 rpm)

[0026] The TI value can be adjusted as appropriate. When a high TI value is required, the lower limit value of the TI value is, for example, 3 or more, 4 or more, 5 or more. Also, the upper limit value of the TI value is, for example, 10 or less, 8 or less, 6 or less, 5 or less. On the other hand, when a low TI value is suitable, the lower limit value is, for example, 1 or more, and the upper limit value is, for example, 3 or less, 2.5 or less.

[0027] The sulfuric acid ester group-introduced pulp can be obtained, for example, by the method shown below, but is not limited to this method.

[0028] The outline of this method is to prepare the sulfuric acid ester group-introduced pulp by subjecting a fiber raw material containing cellulose (such as wood-based pulp (hereinafter simply referred to as "wood pulp")) to chemical treatment. This chemical treatment process includes a contact step of bringing the fiber raw material into contact with a sulfuric acid ester group-donating compound described later and urea or a urea derivative (hereinafter referred to as "urea etc."), and a reaction step of subjecting the fiber raw material after this contact step to a heating reaction to substitute a part of the hydroxyl groups of cellulose with sulfuric acid ester groups.

[0029] In this specification, the fiber raw material refers to fibrous pulp containing cellulose molecules. Pulp is a fibrous member in which a plurality of cellulose fibers are aggregated. These cellulose fibers are aggregates of a plurality of fine fibers (such as microfibrils). And this fine fiber is an aggregate of a plurality of cellulose molecules (hereinafter sometimes simply referred to as "cellulose"), which are chain-like polymers in which D-glucose is β(1→4)-glucosidically bonded. Also, it is preferable to wash the fiber raw material in advance. For example, by filtering and dehydrating with water on a 200-mesh or 235-mesh sieve, too fine fine fibers and dust can be sieved out, which is desirable because the handleability during preparation is improved. In other words, pulp is an aggregate of cellulose fibers of a size that can become residues of 200 mesh or 235 mesh. The water may be tap water, but is preferably ion-exchanged water or pure water, and the same applies hereinafter.

[0030] The fiber raw material used in this method is not particularly limited as long as it contains cellulose as described above. For example, what is generally called pulp may be used, or those containing cellulose isolated from jellyfish, seaweed, etc. may also be used. Any material composed of cellulose molecules may be used. Examples of the pulp include wood pulp, dissolving pulp, cotton-based pulp such as cotton linter, non-wood pulp such as wheat straw, bagasse, paper mulberry, trifoliate orange, hemp, kenaf, and fruit, and waste paper-based pulp prepared from waste newspapers, waste magazines, cardboard waste, etc., but are not limited thereto. From the perspective of easy availability, wood pulp is easy to use as a fiber raw material.

[0031] There are various types of this wood pulp, but it is not particularly limited in use. For example, it includes pulp for papermaking such as softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), and thermomechanical pulp (TMP). When using the pulp as a fiber raw material, one type of pulp may be used alone, or two or more types of pulp may be used in combination.

[0032] Thus, the pulp with sulfate group introduced is derived from natural materials and is environmentally friendly.

[0033] The sulfate group donor compound is not particularly limited as long as it can donate a sulfate group to the fiber raw material. For example, it includes sulfamic acid, sulfamate, and sulfuryl compounds having a sulfonyl group with two oxygen atoms covalently bonded to sulfur. One type of these compounds may be used alone, or two or more types may be used in combination. Since the sulfate group donor compound has a lower acidity, higher introduction efficiency of the sulfate group, lower cost, and higher safety compared to sulfuric acid, etc., sulfamic acid is preferred. Hereinafter, the case where sulfamic acid is used as the sulfate group donor compound and urea is used as the urea, etc. will be taken as an example for explanation.

[0034] <Contact step> The contacting step is a step of bringing a fibrous raw material containing cellulose into contact with sulfamic acid and urea. This contacting step is not particularly limited as long as it can cause the above contact. For example, the fibrous raw material may be immersed in a reaction solution in which sulfamic acid and urea are dissolved in a solvent to impregnate the reaction solution into the fibrous raw material, or the reaction solution may be applied to the fibrous raw material, or sulfamic acid and urea may be separately applied, impregnated, or spray-sprayed onto the fibrous raw material. Among these, if the method of immersing the fibrous raw material in the reaction solution to impregnate the reaction solution into the fibrous raw material is used, it is easy to homogeneously bring sulfamic acid and urea into contact with the fibrous raw material.

[0035] The solvent for dissolving sulfamic acid and urea is not particularly limited. For example, protic polar solvents such as water, ethanol, methanol, acetic acid, formic acid, 2-propanol, nitromethane, and aqueous ammonia, aprotic polar solvents such as acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), dimethyl sulfide (DMS), and dimethylacetamide (DMA), and nonpolar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, and 1,4-dioxane can be mentioned. The above solvents may be used alone or in combination of two or more. In particular, water is preferred from the viewpoint of easily dissolving sulfamic acid and urea.

[0036] In addition, the product in a state where sulfamic acid and urea are brought into contact with the fibrous raw material by this contacting step may be referred to as "reaction solution-impregnated fiber".

[0037] <Contact amount of reaction solution> In the contact of the reaction solution with the fiber raw material, it is preferable that the sulfamic acid and urea in the reaction solution are in a predetermined ratio with respect to the fiber raw material. Specifically, the contact is made such that the amounts of sulfamic acid and urea in the reaction solution with respect to the fiber raw material in the reaction solution-impregnated fiber when subjected to the reaction step are appropriate amounts. More specifically, the contact amount of sulfamic acid with respect to the fiber raw material (solid content mass in dry mass) in the reaction solution-impregnated fiber immediately before being subjected to the heating reaction in the reaction step is adjusted to be approximately the same as or more than the contact amount of urea.

[0038] For example, the reaction solution is prepared such that the mixing ratio of sulfamic acid and urea, in terms of mass ratio, the value obtained by dividing the mass part of sulfamic acid with respect to 100 mass parts of the solid content mass of the fiber raw material in the reaction solution-impregnated fiber immediately before being subjected to the heating reaction by the mass part of urea with respect to 100 mass parts of the solid content mass of the fiber raw material in the reaction solution-impregnated fiber immediately before being subjected to the heating reaction (sulfamic acid / urea) is 0.8 or more, 0.85 or more, 1 or more.

[0039] Also, for example, the contact amount of sulfamic acid is adjusted to be 70 mass parts or more, 100 mass parts or more, 200 mass parts or more with respect to 100 mass parts of the solid content mass of the fiber raw material in the reaction solution-impregnated fiber immediately before being subjected to the heating reaction.

[0040] Also, for example, the contact amount of urea, that is, the contact amount of urea with respect to the solid content mass of the fiber raw material in the reaction solution-impregnated fiber immediately before being subjected to the heating reaction, is adjusted to be 20 mass parts or more, 30 mass parts or more, 50 mass parts or more with respect to 100 mass parts of the solid content mass of the fiber raw material while maintaining the above relationship with sulfamic acid. Also, the upper limit value of the contact amount of urea is not particularly limited, but for example, it is 350 mass parts or less, 300 mass parts or less, 250 mass parts or less with respect to 100 mass parts of the solid content mass of the fiber raw material.

[0041] The contact amounts of sulfamic acid and urea with respect to 100 mass parts of the solid content mass of the fiber raw material can be appropriately calculated according to the state of the reaction solution-impregnated fiber subjected to the reaction step, for example.

[0042] <State of the reaction liquid-impregnated fiber> As the state of the reaction liquid-impregnated fiber to be subjected to the subsequent reaction step described above, for example, the reaction liquid-impregnated fiber may be in its original state, that is, a state in which no active moisture removal is performed while the fiber raw material is in contact with the reaction liquid, or a state in which moisture has been actively removed from the state in which the fiber raw material is in contact with the reaction liquid.

[0043] The former (state without active moisture removal) reaction liquid-impregnated fiber includes those in a state where the fiber raw material is in contact with the reaction liquid (including, for example, a slurry state), or those prepared by taking out the fiber raw material from the state where the reaction liquid is in contact with the fiber raw material and allowing it to stand.

[0044] On the other hand, the latter (state with active moisture removal) reaction liquid-impregnated fiber refers to those in which moisture has been consciously removed from the state where the fiber raw material is in contact with the reaction liquid. For example, those prepared by taking out the fiber raw material from the state where the reaction liquid is in contact with the fiber raw material and naturally drying it by air drying or the like, those prepared by filtering and dehydrating the state where the reaction liquid is in contact with the fiber raw material, those prepared by further air drying the filtered and dehydrated ones, those prepared by further drying the filtered and dehydrated ones using a circulating air dryer, those prepared by further drying the filtered and dehydrated ones using a heating dryer, those prepared by drying the state where the reaction liquid is in contact with the fiber raw material using a circulating air dryer or a heating dryer, and the like.

[0045] Thus, the reaction liquid-impregnated fiber to be subjected to the reaction step may be in a state where no active moisture removal is performed as described above, or in a state where active moisture removal has been performed to remove a certain amount of moisture. Also, when removing moisture by drying, there is no particular problem even if the moisture content after drying is about 1%. In particular, if the latter method is used, the moisture in the reaction liquid-impregnated fiber to be subjected to the reaction step can be lowered, so that the reaction time in the heating reaction of the reaction step can be shortened. For this reason, there is an advantage that the productivity of the sulfuric acid ester group-introduced pulp can be improved. Also, if a method of performing a dehydration treatment is used, there is an advantage that the reaction liquid-impregnated fiber can be prepared more efficiently when treating a large amount of the reaction liquid.

[0046] In addition, when an actively drying method is used, the water content of the reaction liquid-impregnated fiber may be dried to about 1%, or the water may be removed by a method of drying to a bone-dry state that is considerably lower than 1%.

[0047] In this specification, a non-bone-dry state with a water content of 1% or more of the reaction liquid-impregnated fiber is also referred to as a wet state. For example, not only a state in which the reaction liquid is impregnated or a state in which dehydration treatment has been performed to some extent, but also a state in which drying treatment has been performed to some extent may be referred to as a wet state in this specification.

[0048] Also, the bone-dry state referred to in this specification means, for example, a state in which the water content is reduced to less than 1% by depressurizing in a desiccator containing a desiccant such as calcium chloride or phosphorus pentoxide, or by performing a long-time heat drying treatment.

[0049] Therefore, in the contact step, when using the latter method (reaction method in a state where active water removal is performed) described above, a method of making the water content of the reaction liquid-impregnated fiber in a non-bone-dry state may be used, or a method of making it in a bone-dry state may be used, but preferably a method of making it in a non-bone-dry state is used.

[0050] The water content of the reaction liquid-impregnated fiber in this specification is calculated using the following formula. Water content of reaction liquid-impregnated fiber (%) = 100 - (solid content mass (g) in reaction liquid-impregnated fiber / reaction liquid-impregnated fiber (g) at the time of water content measurement) × 100 = {(reaction liquid-impregnated fiber (g) at the time of water content measurement - solid content mass (g) in reaction liquid-impregnated fiber) / reaction liquid-impregnated fiber (g) at the time of water content measurement} × 100

[0051] The solid content mass (g) of the reaction liquid-impregnated fiber in the above formula refers to the dry mass of the reaction liquid-impregnated fiber. Specifically, it refers to the dry mass adjusted to a constant weight by drying the sample at 105 °C using a dryer or the like. For example, by putting the reaction liquid-impregnated fiber into a dryer and drying it under predetermined drying conditions (for example, temperature 105 °C, 2 hours) and measuring the mass, the mass of the dried product after the moisture is removed from the reaction liquid-impregnated fiber (that is, the one that is not removed under the above drying conditions. For example, the one containing the fiber raw material and the reagents in the reaction liquid, etc.) can be calculated. Also, the constant weight means a state where the moisture in the atmosphere in the treatment facility and the moisture in the raw material seemingly do not go in and out. Specifically, it means a state where the change amount of the mass measured continuously twice after drying for a certain time (for example, 2 hours) is within 1% of the mass at the start of drying (however, the second mass measurement should be at least half of the drying time required for the first time).

[0052] Note that the state of the fiber raw material when contacting the reaction liquid is not particularly limited. For example, it may be in a dried state or in a wet state (that is, a moist state).

[0053] <Preliminary drying process in the contact process> In the above example, in the method for preparing the reaction liquid-impregnated fiber in the contact process, a method for preparing the reaction liquid-impregnated fiber in a state where active moisture removal is performed has been described. However, when using a method for removing moisture while heating in this method (preliminary drying process) (for example, directly heating and drying the one in a state where the reaction liquid and the fiber raw material are in contact, or heating and drying the one that has been dehydrated, etc.), it is desirable to adjust the heating temperature to be below a predetermined temperature. The drying temperature in this preliminary drying process is not particularly limited, but it is preferably adjusted to a temperature that can remove the moisture contained in the reaction liquid-impregnated fiber and the surrounding moisture and at which the above reaction does not proceed. For example, as the drying temperature in the preliminary drying process, the ambient temperature of the reaction liquid-impregnated fiber can be adjusted to be 100 °C or lower. On the other hand, from the viewpoint of workability, it is preferably adjusted to be 50 °C or higher. Therefore, the drying temperature of the preliminary drying process in the contact process is preferably 50 °C to 100 °C, 70 °C to 100 °C.

[0054] <Moisture adjustment step in the contacting step> The contacting step may include a moisture adjustment step of adjusting the moisture content of the fiber raw material to be in contact with the reaction solution within a predetermined range. This moisture adjustment step is a step of adjusting by drying or humidifying the fiber raw material so that it has a predetermined moisture content. By including this moisture adjustment step, the moisture content in the fiber raw material when contacting the reaction solution or the like can be made somewhat uniform, so there is a possibility of improving the product stability in continuous operation. Also, if the fiber raw material is dried to some extent to reduce the moisture content (for example, the moisture content is 1% to 10%), there is an advantage that the storage stability can be improved.

[0055] <Reaction step> As described above, the reaction solution-impregnated fiber prepared in the contacting step is subjected to the reaction step in the next step. This reaction step is a step of reacting the cellulose fiber contained in the fiber raw material, sulfamic acid, and urea in the reaction solution-impregnated fiber supplied from the contacting step, and substituting at least a part of the hydroxyl groups in the cellulose fiber with the sulfate ester group of sulfamic acid to introduce a sulfate ester group into the cellulose fiber contained in the fiber raw material. That is, this reaction step is a step of performing a reaction of substituting at least a part of the hydroxyl groups in the cellulose fiber contained in the reaction solution-impregnated fiber with a sulfate ester group.

[0056] This reaction step is not particularly limited as long as it is a method capable of substituting at least a part of the hydroxyl groups of the cellulose fiber in the reaction solution-impregnated fiber with a sulfate ester group. For example, a method of promoting the reaction by heating the reaction solution-impregnated fiber can be used. Hereinafter, the case of performing the reaction by this heating method will be taken as an example and described.

[0057] <Reaction temperature in the reaction step> The reaction temperature in the reaction step is not particularly limited, but it is preferably a temperature at which a sulfuric acid ester group can be introduced into the cellulose fibers constituting the fiber raw material while suppressing thermal decomposition and hydrolysis reactions of the fibers. For example, the atmospheric temperature of the reaction liquid-impregnated fibers subjected to the reaction step is adjusted to be 100°C to 200°C, 120°C to 200°C, 120°C to 180°C, or 120°C to 160°C. If the atmospheric temperature during heating is 200°C or lower, thermal decomposition and discoloration of the fibers can be suppressed.

[0058] In addition, the heater and the like used in the reaction step are not particularly limited. For example, those that can directly or indirectly heat the reaction liquid-impregnated fibers after the contact step while satisfying the above requirements can be used, and known dryers, vacuum dryers, microwave heating devices, autoclaves, infrared heating devices, hot press methods using a hot press machine (for example, AH-2003C manufactured by AS ONE Corporation), etc. can be used. In particular, from the viewpoint of operability, since gas may be generated in the reaction step, it is preferable to use a circulation blow-type dryer.

[0059] <Reaction time in the reaction step> When using the above heating method as the reaction step, the heating time (that is, the reaction time) is not particularly limited. For example, when the reaction temperature is adjusted to be within the above range, it is 1 minute or more, 5 minutes or more, 10 minutes or more, 15 minutes or more, and from the viewpoints of operability and cost, it is 5 minutes to 300 minutes, 5 minutes to 120 minutes.

[0060] By performing the above steps, pulp with a sulfuric acid ester group introduced can be prepared.

[0061] <Washing step after the reaction step> After the reaction step, a washing step for washing the pulp with a sulfuric acid ester group introduced may be included. The surface of the pulp with a sulfuric acid ester group introduced is acidic due to the influence of sulfamic acid (sulfuric acid ester group donor compound). In addition, the unreacted reaction liquid also exists. Therefore, providing a washing step to surely terminate the reaction, remove the excess reaction liquid, and make it in a neutral state can improve the handleability.

[0062] This washing step is not particularly limited. For example, it may be possible as long as the pulp with sulfate group introduction becomes almost neutral. For example, a method of washing with pure water or the like until the pulp with sulfate group introduction becomes neutral can be used. Further, neutralization washing using an alkaline solution or the like may be performed. When performing such neutralization washing, examples of the alkaline compound contained in the alkaline solution include inorganic alkaline compounds and organic alkaline compounds. Examples of the inorganic alkaline compound include hydroxides, carbonates, and phosphates of alkali metals. Examples of the organic alkaline compound include ammonia, aliphatic amines, aromatic amines, aliphatic ammonium, aromatic ammonium, heterocyclic compounds, and hydroxides of heterocyclic compounds.

[0063] In addition, the separation of the pulp with sulfate group introduction in the washing step is not particularly limited. For example, it may be possible as long as the pulp with sulfate group introduction and the washing water can be filtered. For example, the washing of the pulp with sulfate group introduction after the reaction can be performed using a stainless steel sieve with an aperture of 243 μm (70 mesh) to 20 μm (635 mesh), an aperture of 132 μm (120 mesh) to 45 μm (300 mesh), or an aperture of 75 μm (200 mesh) to 45 μm (300 mesh).

[0064] As described above, the hydrolyzed paper may contain the pulp with sulfate group introduction in a part thereof. In this case, the hydrolyzed paper may contain pulp other than the pulp with sulfate group introduction.

[0065] Examples of pulps other than the pulp with a sulfate group introduced include pulps such as wood pulp (unmodified pulp) that can be used in the preparation of the aforementioned pulp with a sulfate group introduced, and pulps subjected to chemical modification other than the introduction of a sulfate group (sulfation). Examples of the chemical modification include oxidation of at least a part of the hydroxyl groups of cellulose (for example, introduction of a carboxyl group using an oxidation reaction with a TEMPO (2,2,6,6 - tetramethylpiperidine 1 - oxyl) catalyst), phosphation, phosphitization, carboxymethylation, and the like. The pulp other than the pulp with a sulfate group introduced may be subjected to one kind of chemical modification or two or more kinds of chemical modifications. The physical properties of the pulp other than the pulp with a sulfate group introduced are not particularly limited. Also, as the pulp other than the pulp with a sulfate group introduced, commercially available products may be used, or it may be prepared in-house. There are no particular limitations on the method for in-house preparation of the pulp subjected to chemical modification other than the aforementioned sulfation, and a conventionally known method may be used.

[0066] In the hydrolyzable paper, the mass ratio of the blending amount (SP) of the pulp with a sulfate group introduced to the blending amount (OP) of the pulp other than the pulp with a sulfate group introduced is not particularly limited, but for example, SP:OP = 100:0 to 1:99, SP:OP = 100:0 to 5:95.

[0067] <Physical properties of the hydrolyzable paper> The physical properties of the hydrolyzable paper are not particularly limited, but for example, they are as follows.

[0068] <Grammage, thickness, and density> From the viewpoints of strength during use and hydrolyzability when immersed in water, the grammage of the hydrolyzable paper is, for example, 5 g / m 2 ~1500 g / m 2 、5 g / m 2 ~1000 g / m 2 、40 g / m 2 ~1000 g / m 2 、40 g / m 2 ~500 g / m 2It is as follows. In addition, the thickness of the hydrolyzed paper is not particularly limited, and is, for example, 50 μm to 5000 μm. Incidentally, the density (g / cm 3 ) of the hydrolyzed paper can be calculated by dividing the basis weight (g / m 2 ) of the hydrolyzed paper by the thickness (μm) of the hydrolyzed paper.

[0069] <Specific tensile strength> The specific tensile strength of the hydrolyzed paper is, for example, 20 N·m / g or more, 21 N·m / g or more, 25 N·m / g or more. The specific tensile strength (N·m / g) can be calculated by multiplying the value obtained by dividing the tensile strength (kN / m) by the basis weight (g / m 2 ) by 1000. The tensile strength can be measured using a tensile testing machine (for example, Autograph manufactured by Shimadzu Corporation, model number: AG-1500N) (JIS P 8113:2016).

[0070] Next, the manufacturing method of the hydrolyzed paper of the present invention will be described with examples. However, this manufacturing method is merely illustrative, and the hydrolyzed paper of the present invention may be manufactured by any method.

[0071] The manufacturing method of this example includes a step of papermaking a suspension containing pulp with an introduced sulfate group using a paper machine. The suspension may contain pulp other than the pulp with an introduced sulfate group. Regarding the mass ratio of the pulp other than the pulp with an introduced sulfate group and the blending amount (SP) of the pulp with an introduced sulfate group to the blending amount (OP) of the pulp other than the pulp with an introduced sulfate group, it is the same as that described for the hydrolyzed paper.

[0072] As the paper machine, for example, one including a wire part, a press part, a dryer part, and a reel part may be used. In this paper machine, in the wire part, the suspension is ejected onto a rotating wire to form wet paper, in the press part, the wet paper is carried by a rotating felt or felt and dehydrated by applying pressure, in the dryer part, heat is applied to the dehydrated wet paper to dry it, and in the reel part, the dried hydrolyzed paper is wound around a reel drum.

Example

[0073] (Preparation of pulp with sulfate group introduction) Softwood kraft pulp (NBKP) with an average fiber length of 2.54 mm manufactured by Maruizumi Paper Co., Ltd. (hereinafter sometimes simply referred to as "pulp") was washed with a large amount of ion-exchanged water and then drained with a sieve having an opening of 75 μm (200 mesh). When the solid content concentration of a part of the pulp thus obtained was measured, it was 21.6% by mass. As the ion-exchanged water, self-prepared water having an electric conductivity of >0.2 μS / cm was used, and hereinafter it is referred to as pure water. Thereafter, the wet pulp was spread on an aluminum pad and placed in a dryer under an atmosphere of 105°C and dried for about 1 hour until the moisture content reached about 1%.

[0074] <Contact step> 1000 g of the reaction solution was added to 20 g (solid content mass) of the pulp, and the reaction solution was impregnated into the pulp. As the reaction solution, an aqueous solution in which the mixing ratio of sulfamic acid and urea was sulfamic acid:urea = 2:1 (180 g / L:90 g / L) in terms of concentration ratio (g / L) was used. As the sulfamic acid, that manufactured by Fuso Chemical Industry Co., Ltd. with a purity of 99.8% was used, and as the urea, that manufactured by FUJIFILM Wako Pure Chemical Corporation with a purity of 99.0% and model number: special grade reagent was used.

[0075] The pulp impregnated with the reaction solution was dehydrated by suction filtration and spread on an aluminum tray. Then, this aluminum pad was placed in a dryer under an atmosphere of 80°C and dried to prepare a reaction solution-impregnated pulp. The moisture content of this reaction solution-impregnated pulp was 5% or less. For the suction filtration, filter paper (manufactured by Advantech Co., Ltd., model number: No. 2) was used.

[0076] <Reaction step> The reaction liquid-impregnated pulp was subjected to a heating reaction using a dryer. The temperature of the constant temperature bath of the dryer was 140 °C, and the heating time was 30 minutes. The reaction liquid-impregnated pulp after heating was washed until it became neutral to prepare a sulfuric acid ester group-introduced pulp with an introduced amount of sulfuric acid ester group of 1.4 mmol / g. The washing was carried out by adding a large amount of pure water to the reaction liquid-impregnated pulp to form a slurry, and then adding sodium hydrogen carbonate (manufactured by Nacalai Tesque, Inc., purity 99.5%) until no bubbles were generated and neutralizing it.

[0077] (Manufacture of hydrolyzed paper) First, the sulfuric acid ester group-introduced pulp (SP) and the unbeaten softwood kraft pulp (OP) were mixed so that SP:OP (mass ratio) = 0:100, 5:95, 10:90, 20:80, 30:70, 50:50, 100:0, and the slurry obtained by dispersing it in pure water was poured into a stainless steel sieve with an opening size of 63 μm (235 mesh), and then washed with a large amount of pure water (the end point of washing was when the electrical conductivity of the filtrate became 100 μS / cm or less), and a slurry for manufacturing hydrolyzed paper with a solid content concentration of 1.0 mass% was prepared.

[0078] Next, 3.75 g of the slurry for manufacturing hydrolyzed paper was weighed by solid content mass in a 5 L plastic container, and tap water was added and dispersed well until the solid content concentration became 0.2 mass% to 0.5 mass%. This diluted slurry (pulp suspension) was used with a hand sheet machine described in JIS P 8222:2015 - Method for preparing test hand sheets for pulp - Method by standard hand sheet machine, and except for using a wire mesh with an opening size of 0.154 mm (100 mesh, size: 25 cm × 25 cm), a hand sheet (hydrolyzed paper) was manufactured according to the method compliant with JIS P 8222:2015 (target basis weight 60 g / m 2 ). In addition, the "drainage time" in Table 1 and Table 2 described later is the elapsed time until the water on the wire mesh dehydrates during the manufacture of this hand sheet (hydrolyzed paper).

[0079] The obtained hand-sheet paper (hydrolyzed paper) was conditioned by a method conforming to JIS P 8111, and then its thickness, density, specific tensile strength, hydrolyzability, and water retention were measured, calculated, or evaluated by the following methods. Also, the moisture content of the obtained hand-sheet paper (hydrolyzed paper) was measured by the following method.

[0080] (Thickness) It was measured in accordance with JIS P 8118:2014 using a paper thickness gauge (manufactured by Citizen Fine Device Co., Ltd., model number: MEI-11 (indicator: manufactured by Citizen Fine Device Co., Ltd., model number: SA-CD1)).

[0081] (Density) Density (g / cm 3 ) was calculated by dividing the basis weight (g / m 2 ) by the thickness (μm).

[0082] (Specific tensile strength) The hand-sheet paper (hydrolyzed paper) was cut into a size of 1.5 cm × 23 cm, and the tensile strength (kN / m) was measured in accordance with JIS P 8113:2006 using a tensile testing machine (Autograph manufactured by Shimadzu Corporation, model number: AG-1500N), except that the distance between the grips was set to 10 cm. The specific tensile strength (N·m / g) was calculated by multiplying the value obtained by dividing this tensile strength (kN / m) by the basis weight (g / m 2 ) by 1000.

[0083] (Hydrolyzability) A 100 mL beaker containing 80 mL of pure water (20 °C) was placed on a magnetic stirrer (manufactured by Toyo Seisakusho Co., Ltd., model C-2s (18 w)), a single-sided cross-shaped stir bar (diameter 30 mm, thickness 9 mm) was inserted, and the rotation speed was set to scale 10. A strip-shaped cut hand-sheet paper (hydrolyzed paper) of 10 cm × 1.5 cm was put into it, and the state after 60 seconds was visually evaluated according to the following evaluation criteria.

[0084] Hydrolysis evaluation criteria AA: It was completely hydrolyzed. A: Slightly unhydrolyzed parts remained. B: There were many unhydrolyzed parts. C: It was not hydrolyzed.

[0085] (Water retention rate) A sample equivalent to 0.5 g of absolute dry mass was collected from the pulp suspension. The sample was placed in a centrifuge cup, subjected to suction filtration to form a uniform mat shape, and suction was stopped when water was drawn from the surface. Then, it was centrifugally dehydrated (equivalent to 3000G (3000 rpm), for 30 minutes), and the water retention rate was calculated by the following formula from the mass before drying and the mass after drying in a dryer under an atmosphere of 105 °C for 2 - 3 hours. Water retention rate (%) = 100×(mass before drying (g) - mass after drying (g)) / mass after drying (g)

[0086] (Moisture content) The moisture content of the hand-squeezed paper (hydrolyzed paper) after conditioning for 8 hours in an atmosphere of 23 °C and 50% relative humidity was calculated by the following formula. Moisture content (%) = 100 - (absolute dry mass of hand-squeezed paper (hydrolyzed paper) (g) / mass of hand-squeezed paper (hydrolyzed paper) after conditioning (g))×100

[0087] Table 1 shows the drainage time during the production of the hand-squeezed paper (hydrolyzed paper), and the basis weight, thickness, density, tensile strength ratio, hydrolyzability, water retention rate, and moisture content of the hand-squeezed paper (hydrolyzed paper). Table 2 shows the results of conducting the same experiment using pulp with a sulfonic acid ester group introduction amount of 1.09 mmol / g instead of the pulp with a sulfonic acid ester group introduction amount of 1.4 mmol / g as the sulfonic acid ester group-introduced pulp. Note that the sulfonic acid ester group-introduced pulp with a sulfonic acid ester group introduction amount of 1.09 mmol / g was prepared in the same manner as the sulfonic acid ester group-introduced pulp with a sulfonic acid ester group introduction amount of 1.4 mmol / g, except that in the aforementioned contact step, as the reaction solution, an aqueous solution mixed so that the mixing ratio of sulfamic acid and urea was sulfamic acid:urea = 2:3 (200 g / L:300 g / L) in terms of concentration ratio (g / L) was used.

[0088]

Table 1

[0089]

Table 2

[0090] As shown in Table 1 and Table 2, it was confirmed that the hydrolyzed paper containing the sulfuric acid ester group-introduced pulp exhibits excellent tensile strength and equivalent excellent hydrolyzability, superior to the blank hydrolyzed paper composed only of unbeaten softwood kraft pulp (OP) with SP:OP (mass ratio) = 0:100, that is.

[0091] As described above, the present invention has been described with reference to the embodiments and examples, but the present invention is not limited to the above embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Claims

1. A hydrolyzed paper characterized by containing pulp in which at least a part of the hydroxyl groups of cellulose is substituted with sulfate ester groups.

2. The hydrolyzed paper according to Claim 1, further characterized by containing pulp other than the pulp in which at least a part of the hydroxyl groups of the cellulose is substituted with sulfate ester groups.

3. The hydrolyzed paper according to Claim 1 or 2, characterized in that the specific tensile strength is 20 N·m / g or more.

4. A method for producing a hydrolyzed paper, characterized by including a step of papermaking a suspension containing pulp in which at least a part of the hydroxyl groups of cellulose is substituted with sulfate ester groups using a paper machine.

5. The method for producing a hydrolyzed paper according to Claim 4, characterized in that the suspension further contains pulp other than the pulp in which at least a part of the hydroxyl groups of the cellulose is substituted with sulfate ester groups.

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