Pulp sheet for fluff pulp and absorbent article

Abstract

One aspect of the present invention is a pulp sheet that is for fluff pulp and contains: starting material pulp formed from conifer bleached kraft pulp; and a surfactant. The starting material wood for the conifer bleached kraft pulp includes cedar, and the surfactant includes a non-ionic surfactant and a cationic surfactant. The percentage of pulp fibers that have a fiber length of greater than 0.2 mm but less than 0.6 mm on a length-weighted fiber length distribution for the pulp fibers is at least 8 mass%, and the mass ratio of the cationic surfactant to the non-ionic surfactant is 0.25–4.00. The non-ionic surfactant is preferably a polyoxyalkylene alkyl ether, and the cationic surfactant content is preferably 0.075–2.250 kg / t.

Description

Fluff pulp sheet and absorbent article

[0001] The present invention relates to a pulp sheet for fluff pulp and an absorbent article. This application claims priority to Japanese Application No. 2024-153366, filed September 5, 2024, and incorporates by reference all of the contents of the above-mentioned Japanese application.

[0002] Fluff pulp is produced by mechanically disintegrating wood pulp, and is used as an absorbent material in absorbent articles such as disposable diapers.

[0003] As the pulp for the fluff pulp used in such absorbent articles, wood pulp derived from coniferous trees, which has good bulkiness, moisture absorption properties and defibration properties, is widely used (see Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2012-211411

[0005] Pine, which has long pulp fiber length, is often used as such a coniferous tree species. In a pulp sheet for fluff pulp, if the pulp fiber length is long, the pulp fibers are not densely packed together, and a bulky pulp sheet for fluff pulp can be formed. If the pulp sheet for fluff pulp is bulky, it becomes easier to disintegrate when defibrating into fluff pulp, and absorbent articles can be produced that are uniform and free of undefibrated pulp fibers. Such pulp for fluff pulp is produced in regions where pine wood is easily available, such as North America and Europe.

[0006] On the other hand, when producing pulp for fluff pulp in Japan, it is difficult to obtain pine wood in the industrially required quantities as a conifer, and cedar wood must be used. Cedar wood has shorter pulp fiber length than pine wood, and the pulp fibers in the pulp sheet for fluff pulp tend to be densely packed together, making it difficult to form a bulky sheet. If the pulp sheet for fluff pulp is not bulky, it will be difficult to disintegrate when defibrating into fluff pulp, and there is a risk that the absorbent article will contain uneven, undefibrated pulp fibers.

[0007] One method of reducing the amount of undefibrated pulp is to increase the defibration strength. However, increasing the defibration strength results in over-defibration of pulp fibers that can be defibrated at a normal defibration strength, making it more likely that fine fibers will be produced. This can lead to pulp fibers becoming more likely to come loose during the process of manufacturing absorbent articles from pulp sheets for fluff pulp, which can cause parts of the absorbent body of the absorbent article to chip or become thinner in parts. In addition, when the pulp fiber length is short, there are fewer voids in the absorbent article, which reduces the liquid absorption rate. When the absorption rate decreases, liquid tends to remain on the surface of the absorbent article, making the surface feel less smooth when the absorbent article is in use.

[0008] Furthermore, if a surfactant that inhibits hydrogen bonding between pulp fibers is added to a pulp sheet for fluff pulp in order to improve defibration, the defibration ability of the pulp will improve, but the affinity between the pulp fibers and water will decrease, which may result in a decrease in the absorption performance of the fluff pulp after defibration.

[0009] The present invention was made based on the above circumstances, and aims to provide a pulp sheet for fluff pulp that has good defibration properties during production and good water absorption performance of the resulting absorbent article, even when using raw material pulp composed of softwood bleached kraft pulp including cedar wood.

[0010] A pulp sheet for fluff pulp according to one embodiment of the present invention contains raw material pulp composed of softwood bleached kraft pulp and a surfactant, wherein the raw material wood of the softwood bleached kraft pulp includes cedar wood, the surfactant includes a nonionic surfactant and a cationic surfactant, and in the length-weighted fiber length distribution of the pulp fibers, the content of pulp fibers having a fiber length greater than 0.2 mm and less than 0.6 mm is 8 mass% or more, and the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25 or more and 4.00 or less.

[0011] According to the present invention, even when raw material pulp composed of bleached softwood kraft pulp including cedar wood is used, a pulp sheet for fluff pulp can be provided that has good defibration properties during production and good water absorption performance of the resulting absorbent article.

[0012] [Description of an embodiment of the present invention] A pulp sheet for fluff pulp according to one aspect of the present invention contains raw material pulp composed of softwood bleached kraft pulp and a surfactant, wherein the raw material wood of the softwood bleached kraft pulp includes cedar wood, the surfactant includes a nonionic surfactant and a cationic surfactant, and in the length-weighted fiber length distribution of the pulp fibers, the content of pulp fibers having a fiber length greater than 0.2 mm and less than 0.6 mm is 8 mass% or more, and the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25 or more and 4.00 or less.

[0013] The pulp sheet for fluff pulp contains bleached coniferous kraft pulp, including cedar, which has short fiber lengths and tends to pack closely together, making it difficult to form a bulky pulp sheet for fluff pulp. The length-weighted fiber length distribution of the pulp fibers contains 8% by mass or more of pulp fibers with a fiber length of more than 0.2 mm and less than 0.6 mm. In the pulp sheet for fluff pulp, the surfactant contains a nonionic surfactant and a cationic surfactant, and the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25 to 4.00, thereby further improving bulkiness while suppressing a decrease in absorbency, thereby improving defibration performance during the manufacturing process. Furthermore, the pulp sheet for fluff pulp can achieve a good balance between the liquid absorption rate of the fluff pulp after defibration and the water retention capacity under load. Therefore, even when the fluff pulp sheet is made from raw material pulp composed of bleached softwood kraft pulp including cedar, it has good defibration properties during production and good water absorption performance of the resulting absorbent article, thereby improving the smooth feel of the surface of the resulting absorbent article.

[0014] It is preferable that the nonionic surfactant is a polyoxyalkylene alkyl ether and the content of the cationic surfactant is 0.075 kg / t or more and 2.250 kg / t or less. When the nonionic surfactant is a polyoxyalkylene alkyl ether, even when a raw material pulp composed of softwood bleached kraft pulp containing cedar is used, the bulkiness of the fluff pulp after defibration can be further improved while maintaining both a good liquid absorption rate and a good water retention capacity under load in the fluff pulp, thereby further improving defibration performance during the manufacturing process. Furthermore, when the content of the cationic surfactant is 0.075 kg / t or more and 2.250 kg / t or less, the bulkiness of the fluff pulp after defibration can be further improved while maintaining both a good liquid absorption rate and a good water retention capacity under load in the fluff pulp, thereby further improving defibration performance during the manufacturing process, even when a raw material pulp composed of softwood bleached kraft pulp containing cedar is used. "kg / t" indicates the mass [kg] per ton of bone dry pulp.

[0015] The pulp sheet for fluff pulp has a specific burst strength of 0.90 kPa·m ２ / g or more 1.30kPa・m ２ When the burst strength of the pulp sheet for fluff pulp is within the above range, the defibration property during the production process can be further improved, even when raw material pulp made of bleached softwood kraft pulp containing cedar wood is used.

[0016] An absorbent article according to another aspect of the present invention uses the fluff pulp sheet. Because the absorbent article uses the fluff pulp sheet, it is possible to achieve a good balance between the liquid absorption rate of the fluff pulp after the fluff pulp sheet is defibrated and the water retention capacity under load. Therefore, the absorbent article can have an improved surface feel.

[0017] [Details of the embodiment of the present invention] A pulp sheet for fluff pulp according to one embodiment of the present invention will be described in detail below. Note that the content (bone-dry internal amount) of each material blended into the paper base material described below refers to the mass ratio relative to the bone-dry mass of the pulp in the paper base material unless otherwise specified.

[0018] <Pulp sheet for fluff pulp> The pulp sheet for fluff pulp contains raw material pulp composed of softwood bleached kraft pulp and a surfactant. The pulp sheet for fluff pulp can be obtained by papermaking a slurry containing the raw material pulp and the surfactant.

[0019] (Raw material pulp) The raw material pulp is made of bleached softwood kraft pulp (NBKP). In the pulp sheet for fluff pulp, pine woods such as radiata pine and various cedars are preferably used as raw material woods for bleached softwood kraft pulp.

[0020] (Pulp content) The content of cedar wood in the softwood bleached kraft pulp is preferably 30% by mass, more preferably 40% by mass, even more preferably 50% by mass, and even more preferably 60% by mass. By having the cedar wood content in the softwood bleached kraft pulp be 30% by mass or more, the effects of the present invention can be more effectively exhibited.

[0021] (Surfactant) The fluff pulp sheet contains surfactants including a nonionic surfactant and a cationic surfactant. Cedar wood has short pulp fibers that are densely packed, which tends to result in low bulkiness of the resulting pulp sheet. In the fluff pulp sheet containing raw pulp made from softwood bleached kraft pulp containing cedar wood, the inclusion of a nonionic surfactant and a cationic surfactant as surfactants improves the bulkiness of the fluff pulp sheet and ensures uniform interfiber voids regardless of the orientation direction of the softwood bleached kraft pulp fibers. This improves the defibration ability of the fluff pulp sheet and allows for a good balance between the liquid absorption rate and water retention capacity under load in the fluff pulp after defibration of the fluff pulp sheet, thereby improving water absorption performance.

[0022] Examples of nonionic surfactants include ethylene and / or propylene oxide adducts of higher alcohols, polyhydric alcohol-type nonionic surfactants, ethylene oxide adducts of higher fatty acids, ester compounds of polyhydric alcohols and fatty acids, ethylene oxide adducts of ester compounds of polyhydric alcohols and fatty acids, and sulfosuccinates. Even when raw material pulp is made from bleached softwood kraft pulp containing cedar, polyoxyalkylene alkyl ethers are preferred as nonionic surfactants, from the viewpoint of further improving the bulkiness of the pulp sheet for fluff pulp and further improving the defibration property during the manufacturing process, the liquid absorption rate of the fluff pulp, and the effect of suppressing a decrease in water retention capacity under load.

[0023] Examples of cationic surfactants include fatty acid amine derivatives, quaternary ammonium salts, ester cations, methyl sulfate cations, ethylene oxide adduct ammonium chloride, acetate salts, polyoxyalkylene alkylamine derivatives, fatty acid-polyethylene polyamine condensates, amidoamine compounds, etc. Fatty acid amine derivatives are preferred as cationic surfactants, even when raw material pulp composed of bleached softwood kraft pulp containing cedar is used, from the viewpoint of further improving the bulkiness of the pulp sheet for fluff pulp and further improving the defibration property during the manufacturing process and the effect of suppressing a decrease in the liquid absorption rate and water retention capacity under load in the fluff pulp.

[0024] In addition, the surfactant may contain an anionic surfactant other than the nonionic surfactant and the cationic surfactant, as long as the effects of the present invention are not impaired. Examples of the anionic surfactant include alkylbenzenesulfonic acid and its salts, alphaolefin sulfonate, alkyl sulfate, alkyl ether sulfate, methyl tauric acid, alaninate and its salts, ether carboxylic acid and its salts, sulfosuccinate, and polyoxyalkylene alkyl ether.

[0025] The lower limit of the surfactant content is 0.15 kg / t, preferably 0.30 kg / t, and more preferably 0.60 kg / t, calculated as solids. By containing a surfactant within a specific range, the bulkiness of the pulp sheet for fluff pulp can be further improved, thereby improving defibration properties during the manufacturing process. If the surfactant content is below the lower limit, the bulk of the pulp sheet for fluff pulp may not be sufficiently increased. On the other hand, the upper limit of the surfactant content is 4.50 kg / t, preferably 3.00 kg / t, and more preferably 2.40 kg / t. If the surfactant content exceeds the upper limit, the liquid absorption rate of the fluff pulp after defibration of the pulp sheet for fluff pulp and the water retention capacity under load may be reduced.

[0026] The lower limit of the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25, and 0.67 is more preferable. If the mass ratio of the cationic surfactant to the nonionic surfactant is less than 0.25, when raw material pulp composed of softwood bleached kraft pulp containing cedar is used, the liquid absorption rate of the fluff pulp is likely to decrease, and the absorbent article obtained from the pulp sheet for fluff pulp may be prone to a decrease in dryness. On the other hand, the upper limit of the mass ratio of the cationic surfactant to the nonionic surfactant is 4.00, and preferably 1.50. If the mass ratio of the cationic surfactant to the nonionic surfactant exceeds 4.00, when raw material pulp composed of softwood bleached kraft pulp containing cedar is used, the water retention capacity of the fluff pulp under load is likely to decrease, and the absorbent article obtained from the pulp sheet for fluff pulp may be prone to a decrease in dryness. Even when raw material pulp is made from bleached coniferous kraft pulp containing cedar wood, the surfactant contains a nonionic surfactant and a cationic surfactant, the content of pulp fibers with a fiber length greater than 0.2 mm and less than 0.6 mm in the length-weighted fiber length distribution of the pulp fibers is 8 mass% or more, and the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25 or more and 4.00 or less, thereby improving the pulp defibration ability and achieving a good balance between the liquid absorption rate in the fluff pulp and the water retention capacity under load.

[0027] The content of the cationic surfactant is preferably 0.075 kg / t or more and 2.250 kg / t or less, more preferably 0.100 kg / t or more and 1.500 kg / t or less, even more preferably 0.150 kg / t or more and 1.500 kg / t or less, even more preferably 0.200 kg / t or more and 1.000 kg / t or less, and particularly preferably 0.200 kg / t or more and 0.800 kg / t or less. By having a content of the cationic surfactant of 0.075 kg / t or more and 2.250 kg / t or less, even when using raw material pulp composed of softwood bleached kraft pulp containing cedar, the bulkiness of the fluff pulp after defibration can be further improved while maintaining both the liquid absorption rate and the water retention capacity under load in the fluff pulp, thereby further improving defibration ability during the manufacturing process.

[0028] (Other Additives) Other additives may be added to the pulp sheet for fluff pulp as needed. Examples of additives include fillers, pigments, sizing agents, coagulants, oil-proofing agents, aluminum sulfate, retention aids, drainage aids, dry strength agents, wet strength agents, coloring pigments, and waterproofing agents, which may be used alone or in combination.

[0029] [Physical Properties of Fluff Pulp Pulp Sheet] (Density) The density is measured in accordance with "Paper and Paperboard - Test Methods for Thickness, Density and Specific Volume" described in JIS-P8118 (2014). The lower limit of the density of the fluff pulp pulp sheet is 0.50 g / cm. ３ is preferred, and 0.52 g / cm ３ More preferably, 0.53 g / cm ３ The upper limit of the density of the pulp sheet for fluff pulp is 0.65 g / cm ３ is preferred, and 0.62 g / cm ３ More preferably, 0.60 g / cm ３is even more preferable. When the density of the pulp sheet for fluff pulp is within the above range, the pulp sheet for fluff pulp, which is made by adding a surfactant to the bleached softwood kraft pulp, can have improved defibration properties during the manufacturing process, and can produce fluff pulp that is easy to ensure uniform voids between fibers without unevenness. Therefore, the liquid absorption rate and water retention capacity under load in the fluff pulp can be improved. The density is measured in an atmosphere of 23±1°C and 50±2% RH in accordance with JIS-P8111 (1998) "Paper, paperboard and pulp - Standard conditions for humidity control and testing."

[0030] (Basis Weight) Basis weight is measured in accordance with "Paper and paperboard - Method for measuring basis weight" described in JIS-P8124 (2011). The basis weight of the pulp sheet for fluff pulp is, for example, 300.0 g / m ２ More than 1500.0g / m ２ It can be as follows:

[0031] (Burst strength index) The burst strength index of a pulp sheet for fluff pulp can be used as an index of defibration ability. ２ / g] is calculated by dividing the burst strength of the paper, measured in kilopascals (kPa) according to JIS-P8131 (2009), by the basis weight.

[0032] The lower limit of the specific burst strength of the pulp sheet for fluff pulp is 0.90 kPa m ２ / g is preferred, and 0.93 kPa m ２ / g. The specific burst strength is more preferably 0.90 kPa·m ２ / g or more, the fluff pulp and absorbent articles produced from the pulp sheet for fluff pulp can have improved short-term absorbency and a good dry feel. ２ / g is preferred, and 1.25 kPa m ２ / g is more preferable, and 1.20 kPa m ２ / g is more preferable, and 1.15 kPa m ２ / g is particularly preferable. ２ By having a viscosity of 1 / g or less, the fluff pulp and absorbent articles made from the fluff pulp pulp sheet are less likely to contain undisintegrated particles, and the decrease in the liquid absorption rate and water retention capacity of the fluff pulp under load can be reduced.

[0033] [Method for manufacturing a pulp sheet for fluff pulp] The method for manufacturing a pulp sheet for fluff pulp is not particularly limited, but may include, for example, a cooking step in which raw wood is cooked to produce unbleached pulp, a delignification step in which delignification is performed, a bleaching step in which bleached pulp is bleached to produce bleached pulp, a beating step in which the bleached pulp is beaten to a desired freeness, a step in which a pulp slurry is prepared, and a step in which the pulp slurry is made into paper. Note that a dehydration and washing step can be appropriately provided between the above steps.

[0034] (Cooking Process) In the cooking process, raw wood is cooked to produce unbleached pulp. White liquor and raw wood coniferous wood chips are placed in a digester and cooked, and the resulting (unwashed) pulp slurry mixed with black liquor is removed from the bottom of the continuous digester. The cooking method can be selected from commercially available kraft modified processes such as MCC, EMCC, ITC, Lo-Solids, KobudoMari, and Compact. The digester can be either a continuous or batch type, and there are no particular restrictions on the cooking conditions (cooking temperature, H factor obtained by multiplying the influence of cooking temperature and cooking time into a single factor, active alkali or effective alkali content, etc.).

[0035] (Delignification process) In the delignification process, unbleached pulp is delignified. Alkaline chemicals and oxygen are added to the unbleached pulp, and the lignin is decomposed at high temperature and pressure and dissolved in the alkaline chemicals. In the delignification process, there is no particular restriction on the method, whether it is low consistency (pulp consistency: 3% to 8%), medium consistency (pulp consistency: 8% to 15%), or high consistency (pulp consistency: 20% to 30%).

[0036] (Washing Process) In the washing process, the unbleached pulp is washed by a combination of displacement, dilution, and dehydration. The washing method is not particularly limited, and washing can be performed using a known washing machine. For example, a displacement washing method, a dilution / dehydration method, a press washing method, or a combination of these methods can be used. Washers for the displacement washing method include a diffusion washer, a pressure diffusion washer, and a belt-type washer. Washers for the dilution / dehydration method include a vacuum filter washer and a pressure filter washer. Press washing methods include a screw-type press washer, a disk-type press washer, and a roll-type press washer.

[0037] In the present invention, since it is preferable to remove lignin and reduce the kappa number, it is preferable to use a press washer, which easily removes lignin. The pulp concentration after washing using the press washing method is preferably 30% or more, more preferably 32% or more, and even more preferably 35% or more. Dehydration using the press washing method can also squeeze and remove moisture from inside the fibers, making it easier to sufficiently remove free lignin from inside the pulp fibers than other washing methods.

[0038] (Bleaching step) In the bleaching step, the delignified unbleached pulp is bleached to produce bleached pulp. The bleaching method is not particularly limited, and any known bleaching method can be used. For example, acid treatment, ozone bleaching, chlorine dioxide bleaching, hydrogen peroxide bleaching, or any of these methods in combination with alkali extraction, alkali extraction with the addition of oxygen, or alkali extraction with the addition of oxygen and hydrogen peroxide can be used alone or in combination.

[0039] In the bleaching process, it is preferable to use ozone bleaching, which can adjust the water absorption of pulp fibers by damaging them. The ozone bleaching method is not particularly limited, and can be carried out at high consistency (30-40%), medium consistency (8-15%), or low consistency (1-3%), but a high consistency method, which is more likely to damage the fibers, is preferred. Any known ozone generator can be used. The generated ozone can be mixed with the pulp directly, or dissolved in water and then mixed with the pulp.

[0040] In ozone bleaching, the lower the pH, the more accelerated delignification is while the less damage to the fibers is caused, so it is preferable to adjust the pH according to the required quality of the pulp sheet for fluff pulp. The pH in ozone bleaching of the pulp sheet for fluff pulp is preferably 6 or less, more preferably 4 or less, and even more preferably 2 to 3. When the pH in ozone bleaching of the pulp sheet for fluff pulp is within the above range, the water retention capacity of the fluff pulp after defibration when subjected to a required load can be improved.

[0041] (Preparation Step) In the preparation step, a pulp slurry is prepared. If necessary, the bleached pulp is beaten to a desired freeness in the preparation step. Thereafter, surfactants and other additives are added as necessary to prepare a paper stock.

[0042] (Papermaking process) Next, these raw material slurries are used to make paper in a papermaking machine in a neutral range so that the pH is 6 or more and 8 or less. In the papermaking process, raw material pulp is made using a papermaking machine that makes paper from pulp raw material sprayed onto a traveling wire. The papermaking machine is not particularly limited, and known papermaking machines such as Fourdrinier papermaking machines, cylinder papermaking machines, hybrid formers, and gap formers can be used, and the paper is made into a sheet. Pulp sheets for fluff pulp can be produced by combining one or more layers, but a single layer is preferred because it is easier to achieve a uniform density within the layer.

[0043] The pulp sheet for fluff pulp has excellent defibration properties during production, and the absorbent article using the pulp sheet for fluff pulp has a well-balanced water absorption performance.

[0044] [Fluff pulp] Fluff pulp can be obtained by mechanically defibrating the pulp sheet for fluff pulp into fibers. The pulp sheet for fluff pulp used in the present invention may be in the form of a bale or a roll, but the roll form is preferred because it facilitates improving the productivity of absorbent articles using fluff pulp.

[0045] In the present invention, there are no particular limitations on the device used for the mechanical treatment for defibration. Known defibrators used in the manufacture of absorbent articles such as disposable diapers can be used, and defibrators that utilize frictional force or shear force for mechanical treatment can be suitably used. Examples of defibrator types that can be used include hammer-type defibrators, impact-type defibrators, roll-type defibrators, and jet airflow defibrators.

[0046] [Physical Properties of Fluff Pulp] (Settling Rate) The liquid absorption rate of fluff pulp can be evaluated by its settling rate. Fluff pulp obtained by defibrating a pulp sheet for fluff pulp is used to measure the settling rate. The fluff pulp is compressed into a disk shape, then floated on water, and the time required for the entire sample to become wetted with water is measured. Cedar-derived softwood pulp has shorter fibers and more densely packed fibers than pine-derived softwood pulp, which may reduce its compatibility with water. Furthermore, the inclusion of a surfactant increases the hydrophobicity of the pulp fibers, potentially further reducing the liquid absorption rate of fluff pulp. Therefore, the settling rate is used as a measure of the short-term absorbency of fluff pulp.

[0047] The upper limit of the sedimentation rate for a 0.5 g sample of fluff pulp obtained after defibration is preferably 1.0 sec / 0.5 g, more preferably 0.9 sec / 0.5 g, and particularly preferably 0.8 sec / 0.5 g. When the sedimentation rate is 1.0 sec / 0.5 g or less, the fluff pulp and absorbent articles produced from the pulp sheet for fluff pulp can have improved short-term absorbency and a smooth feel. When the sedimentation rate is within the above range, the pulp sheet for fluff pulp can produce fluff pulp with good short-term absorbency.

[0048] The sedimentation rate was measured as follows: 0.5 g of fluff pulp obtained by defibrating the pulp sheet for fluff pulp was placed in a plastic syringe (TERUMO Corporation, Terumo Syringe, 50 ml, model number SS-50ESZ) with the tip cut off to expose the inside of the cylinder, and the volume was 5 cc (5 cm ３The sample is compressed for 10 seconds until it becomes a disc-shaped sample. Ion-exchanged water is then placed in a 500 ml beaker, and the sample is left at room temperature for 1 minute. The sample is then dropped from a height of 30 mm above the water surface, and the time from when the sample comes into contact with the water surface until the entire sample is wetted with water is measured.

[0049] (Water retention capacity under load) The water retention capacity of fluff pulp under load is measured using fluff pulp obtained by defibrating a pulp sheet for fluff pulp. After dissolving the fluff pulp in water, a load is applied and the water retention capacity is measured after draining. Compared to pine-derived softwood pulp, cedar-derived softwood pulp has shorter fibers and more densely packed fibers, resulting in a higher water retention capacity even under load. On the other hand, the inclusion of a surfactant increases the hydrophobicity of the pulp fibers, which may reduce the water retention capacity under load. For this reason, the water retention capacity under load is used as a measure of the long-term absorbency of fluff pulp.

[0050] The lower limit of the water retention capacity of fluff pulp under load is preferably 8.0 g, more preferably 8.5 g, and even more preferably 9.0 g. When the water retention capacity under load is 8.0 g or more, an absorbent article made from the pulp sheet for fluff pulp can obtain sufficient absorbency over a long period of time and can suppress liquid from floating up on the surface of the absorbent article under load, thereby improving the dry feeling.

[0051] The water retention capacity of fluff pulp under load was measured as follows: 1.0 g of fluff pulp obtained by defibrating a pulp sheet for fluff pulp was dissolved in 200 ml of ion-exchanged water and stirred for 30 seconds. Next, the mixture was poured into a Buchner funnel (No. 1, specification: AF1) under atmospheric pressure for 10 seconds, and a weight (cylindrical, weight 1,450±2 g, outer diameter 60±1 mm) was placed on top. After 1 minute, the weight was removed, and the weight of the pulp was measured and used as the measured value. The water retention capacity under load was calculated by subtracting 1.0 g of the pulp weight from the measured value.

[0052] When the fluff pulp pulp sheet has the settling rate of the fluff pulp after defibration and the water retention capacity under load both within the above ranges, an absorbent article with well-balanced water absorption performance can be obtained.

[0053] [Absorbent Article] The absorbent article uses a pulp sheet for fluff pulp. The absorbent article uses the pulp sheet for fluff pulp, which allows for a good balance between the liquid absorption rate of the fluff pulp and the water retention capacity under load, thereby improving the surface smoothness. The absorbent article is not particularly limited, and examples thereof include disposable diapers, urine absorption pads, light incontinence pads, and sanitary napkins.

[0054] The method for producing the absorbent article is not particularly limited, and the absorbent article can be produced by a known method. For example, disposable diapers can be produced using manufacturing machines manufactured by Zuikosha, Toa Kiko Co., Ltd., or Erhardt & Reimer, using a panel type, leg hole type, vertical flow type, horizontal flow type, or the like.

[0055] Other Embodiments The present invention is not limited to the above-described embodiment, and can be implemented in various other forms, including modifications and improvements, in addition to the above-described forms.

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0057] [Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 to 2] Pulp sheets for fluff pulp of Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 to 2 were prepared by the following procedure.

[0058] (Cooking step) Cedar and pine wood were mixed in the mass ratio shown in Table 1, and white liquor having a predetermined sulfidity was added. Cooking was carried out in a rotary autoclave at a liquor ratio of 6.0 (L / kg) and a maximum temperature of 170°C, yielding unbleached softwood kraft pulp with a kappa number of approximately 30. In Table 1, "-" indicates that the corresponding component was not contained.

[0059] (Washing process) After diluting the unbleached pulp to a pulp consistency of about 2%, No. 2 filter paper (manufactured by Advantec Co., Ltd.) was placed in a Buchner funnel and dewatered to a pulp consistency of about 12%. The unbleached pulp was then sandwiched between square filter papers (manufactured by Advantec Co., Ltd.) and pressure was applied using a press to dewater it to a pulp consistency of 33%. This washing process was carried out twice.

[0060] (Bleaching Process) Unbleached softwood kraft pulp was subjected to chlorine dioxide bleaching at 70°C for 30 minutes with a chlorine dioxide addition rate of 1.5% and a pulp consistency of 10% by mass. Subsequently, alkaline hydrogen peroxide bleaching was performed at 70°C for 120 minutes with an alkali addition rate of 1%, a hydrogen peroxide addition rate of 0.3%, and a pulp consistency of 10% by mass. Subsequently, alkaline treatment was performed at 70°C for 120 minutes with a sodium hydroxide addition rate of 0.2%, a pulp consistency of 10% by mass. Subsequently, chlorine dioxide bleaching was performed at 70°C for 150 minutes with a chlorine dioxide addition rate of 0.3%, a pulp consistency of 10% by mass, to obtain bleached softwood kraft pulp. Between each bleaching process, the pulp was diluted to a consistency of approximately 2%, and then a dilution and washing process was performed twice using No. 2 filter paper (manufactured by ADVANTEC) placed in a Buchner funnel to dehydrate the pulp consistency to approximately 12%.

[0061] (Papermaking process) The obtained bleached softwood kraft pulp was diluted to a consistency of about 2% without beating, and the content was adjusted to the content shown in Table 1, and then a surfactant shown in Table 1 was added. Then, using the adjusted pulp slurry, a semi-automatic sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) was used to make a paper with a basis weight of 700 g / m ２ Handmade sheets were prepared so that the following results were obtained: In this manner, pulp sheets for fluff pulp were obtained in Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 and 2. Note that for Reference Examples 1 and 2, commercially available pulp sheets for fluff pulp that did not contain a surfactant were prepared.

[0062] The product names of the surfactants used are as follows: (1) Nonionic surfactants (Examples 1 to 10, Examples 12 to 15) Polyoxyalkylene alkyl ether: "Meikasurf PA-100" manufactured by Meisei Chemical Industry Co., Ltd. (Example 11) Di-2-ethylhexyl sulfosuccinate sodium salt: "Kuritop R-601" manufactured by Kurita Water Industries Ltd. (2) Cationic surfactants (Examples 1 to 11, Examples 13 to 15) Fatty acid amine derivative: "Prosoft TQ236" manufactured by Riken Green Co., Ltd. (Example 12) Polyoxyalkylene alkylamine derivative: "Peremin B-320" manufactured by Miyoshi Oil & Fats Co., Ltd.

[0063]

[0064] The pulp sheets for fluff pulp obtained as described above were evaluated.

[0065] (Length-weighted fiber length distribution of pulp fibers) The length-weighted fiber lengths of the unbleached kraft pulps of Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 and 2 after the cooking and washing processes were measured. The length-weighted fiber lengths were measured for fibers with a fiber length of 0.1 mm or more using a Valmet Fiber Image Analyzer (Valmet FS5) manufactured by Valmet Corporation in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 52, "Pulp and Paper—Fiber Length Test Method—Optical Automatic Measurement." The content [mass%] of pulp fibers with a fiber length greater than 0.2 mm and less than 0.6 mm in the length-weighted fiber length distribution of the pulp fibers was then calculated.

[0066] (Density of pulp sheet for fluff pulp) The density of each pulp sheet for fluff pulp was measured in accordance with "Paper and paperboard - Test methods for thickness, density and specific volume" described in JIS-P8118 (2014).

[0067] (Evaluation of defibration ability based on burst strength) The burst strength [kPa·m ２ / g] was determined by dividing the burst strength of the paper, expressed in kilopascals (kPa), measured in accordance with JIS-P8131 (2009), by the basis weight. Bursting index measurements were performed in an atmosphere of 23±1°C and 50±2% RH, in accordance with "Paper, paperboard and pulp - Standard conditions for humidity control and testing" as described in JIS-P8111 (1998). The defibration properties of the pulp sheets for fluff pulp were evaluated on a three-point scale based on the power load when defibrated with a defibrator. The evaluation results showed that the bursting index was 1.30 kPa·m ２ In the cases of A and B where the specific rupture strength is 1.1 kPa·m or less, the defibration property of the pulp sheet for fluff pulp is good. A: Excellent defibration property (burst specific strength is 1.1 kPa·m ２ / g or less). B: Good defibration properties (burst strength is 1.1 kPa m ２ / g and above 1.30 kPa m ２ / g or less). C: Poor defibration (burst strength is 1.30 kPa m ２ / g).

[0068] (Sedimentation rate of fluff pulp) The liquid absorption rate of fluff pulp was evaluated by the sedimentation rate. First, a pulp sheet for fluff pulp was cut into a size of 10 mm length x 10 mm width, and 5 g was measured out and placed in a blender (manufactured by WARING, model: HGBSS, SUS container: capacity 2 L). The sample was defibrated at a high speed to obtain fluff pulp. Next, 0.5 g of fluff pulp was placed in a plastic syringe (manufactured by TERUMO, Terumo syringe, inner diameter 29 mm, 50 ml, model number SS-50ESZ) with the tip cut off to expose the cylindrical interior, and the sample was poured into a volume of 5 cc (5 cm ３ ) to prepare a disk-shaped sample. After leaving the sample at room temperature for 1 minute, ion-exchanged water was placed in a 500 cc beaker and the sample was dropped from a height of 30 mm above the water surface. The time [seconds / 0.5 g] from when the sample contacted the water surface until the entire sample was wetted with water was measured. The evaluation criteria were based on the following three levels. If the evaluation was A or B, the sedimentation rate of the fluff pulp was good. A: The sedimentation rate was 0.8 seconds / 0.5 g or less. B: The sedimentation rate was more than 0.8 seconds / 0.5 g and 1.0 seconds / 0.5 g or less. C: The sedimentation rate was more than 0.9 seconds / 0.5 g.

[0069] (Water retention capacity of fluff pulp under load) First, a pulp sheet for fluff pulp was cut into a length of 10 mm x width of 10 mm, and 5 g of the pulp was weighed out and placed in a blender (manufactured by WARING, model: HGBSS, SUS container: capacity 2 L). The sample was defibrated at high speed to obtain fluff pulp. Next, 200 ml of ion-exchanged water was placed in a beaker, and 1.0 g of fluff pulp was dissolved therein and stirred for 30 seconds to prepare a pulp slurry. The pulp slurry was poured into a Buchner funnel (No. 1, specification: AF1) for 10 seconds, and a weight (cylindrical, weight 1,450 ± 2 g, outer diameter 60 ± 1 mm) was placed on top. After 1 minute, the weight was removed and the weight of the pulp was measured. The pulp weight was subtracted from the measured value to obtain the water retention capacity [g] under load. The evaluation criteria were based on the following three levels. When the evaluation was A or B, the fluff pulp had a good water retention capacity under load. A: The water retention capacity under load was 9.0 g or more. B: The water retention capacity under load was 8.0 g or more but less than 9.0 g. C: The water retention capacity under load was less than 8.0 g.

[0070] (Balance of water absorption performance of water-absorbent article) The balance of water absorption performance of the surface of the water-absorbent article was evaluated based on the sedimentation rate of the fluff pulp and the water retention capacity under load. The evaluation criteria were as follows: 3 levels. When the evaluation was A or B, the balance of water absorption performance based on the sedimentation rate of the fluff pulp and the water retention capacity under load was good, the short-term absorbency was high and liquid was unlikely to remain on the surface of the water-absorbent article, and the long-term absorbency was high and liquid was unlikely to rise to the surface of the water-absorbent article under load. A: The evaluations of the sedimentation rate and the water retention capacity under load were both A or higher, indicating an excellent balance of water absorption performance. B: The evaluations of the sedimentation rate and the water retention capacity under load were both B or higher, indicating a good balance of water absorption performance. C: Either the evaluation of the sedimentation rate or the water retention capacity under load was C, indicating a poor balance of water absorption performance.

[0071] The evaluation results of Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 and 2 are shown in Table 2.

[0072]

[0073] As shown in Table 2, the fluff pulp pulp sheets of Examples 1 to 15, which contained raw material pulp composed of softwood bleached kraft pulp containing cedar wood and a surfactant, in which the content of pulp fibers with a fiber length of more than 0.2 mm and less than 0.6 mm in the length-weighted fiber length distribution of the pulp fibers was 8 mass % or more, and the mass ratio of cationic surfactant to nonionic surfactant was 0.25 to 4.00, were excellent in defibration properties, and the resulting fluff pulp and absorbent articles were also evaluated favorably. In particular, Examples 1 to 3 and Examples 7 and 8 obtained good results comparable to those of Reference Examples 1 and 2, which are commercially available products composed of softwood bleached kraft pulp containing a large amount of pine wood.

[0074] On the other hand, Comparative Example 1, which did not contain a surfactant, had a high burst ratio, resulting in undefibrated pulp remaining and poor defibration performance. Furthermore, the undefibrated pulp caused a decrease in settling rate and a decrease in water retention capacity. Comparative Example 2, which did not contain a nonionic surfactant, had poor settling rate and water retention capacity under load. Comparative Example 3, which did not contain a cationic surfactant, had poor defibration performance. Comparative Example 4, in which the mass ratio of cationic surfactant to nonionic surfactant exceeded 4.00, had poor settling rate and water retention capacity under load. Comparative Example 5, in which the mass ratio of cationic surfactant to nonionic surfactant was less than 0.25, had poor defibration performance.

[0075] The above results showed that the pulp sheet for fluff pulp has good defibration properties during manufacturing and good water absorption performance of the resulting absorbent article, even when using raw material pulp composed of softwood bleached kraft pulp including cedar wood.

[0076] The pulp sheet for fluff pulp of the present invention is suitable for use as an absorbent body in an absorbent article.

Claims

1. A pulp sheet for fluff pulp, comprising raw pulp composed of bleached softwood kraft pulp and a surfactant, wherein the raw wood for the bleached softwood kraft pulp comprises cedar wood, the surfactant comprises a nonionic surfactant and a cationic surfactant, the length-weighted fiber length distribution of the pulp fibers contains 8 mass% or more of pulp fibers with a fiber length greater than 0.2 mm and less than 0.6 mm, and the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25 or more and 4.00 or less.

2. A pulp sheet for fluff pulp according to claim 1, wherein the nonionic surfactant is a polyoxyalkylene alkyl ether, and the content of the cationic surfactant is 0.075 kg / t or more and 2.250 kg / t or less.

3. Specific burst strength is 0.90 kPa・m ２ / g or more 1.30kPa・m ２ 3. The pulp sheet for fluff pulp according to claim 1 or claim 2, wherein the tensile strength is 1 / g or less.

4. An absorbent article using the fluff pulp sheet according to claim 1 or 2.

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