Pulp sheets and absorbent articles for fluff pulp

Abstract

The present invention provides a pulp sheet for fluff pulp that exhibits good defibration properties during manufacturing and good water absorption performance of the resulting absorbent article, even when using pulp composed of bleached kraft pulp from coniferous trees including cedar. [Solution] A pulp sheet for fluff pulp according to one aspect of the present invention contains raw material pulp made from bleached softwood kraft pulp and a surfactant, wherein the raw material wood of the bleached softwood kraft pulp includes cedar wood, the surfactant includes 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 pulp fibers is 8% by 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. Preferably, 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.

Description

[Technical Field]

[0001] This invention relates to pulp sheets for fluff pulp and absorbent articles. [Background technology]

[0002] Fluff pulp is produced by mechanically defibrating wood pulp and is used as an absorbent component in absorbent products such as disposable diapers.

[0003] For fluff pulp used in such absorbent articles, wood pulp derived from coniferous trees, which has good bulkiness, moisture absorption, and defibrillation properties, is widely used (see Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2012-211411 [Overview of the project] [Problems that the invention aims to solve]

[0005] Pine wood, with its long pulp fibers, is frequently used as the type of coniferous tree for this purpose. When the pulp fibers are long, they do not pack tightly together, allowing for the formation of a bulky pulp sheet for fluff pulp. A bulky pulp sheet for fluff pulp is easier to break down when defibrating into fluff pulp, enabling the production of a uniform absorbent material free from the inclusion of undefibrated pulp fibers. This type of pulp for fluff pulp is produced in regions where pine wood is readily available, such as North America and Europe.

[0006] On the other hand, when manufacturing pulp for fluff pulp domestically, it is difficult to obtain the industrially required quantity of pine wood as a conifer, and therefore cedar wood must be used. Compared to pine wood, cedar wood has shorter pulp fibers, and in pulp sheets for fluff pulp, the pulp fibers tend to pack together tightly, making it difficult to form bulky sheets. If the pulp sheets for fluff pulp are not bulky, they are difficult to unravel when defibrating the fluff pulp, and there is a risk that the absorbent material will contain uneven and undefibrated pulp fibers.

[0007] To reduce the inclusion of unfibrillated pulp, one could consider increasing the fibrillation strength. However, increasing the fibrillation strength can lead to over-fibrillation of pulp fibers that can be fibrillated at normal strength, resulting in the generation of fine fibers. This can cause pulp fibers to easily detach during the process of manufacturing absorbent articles from pulp sheets for fluff pulp, potentially causing parts of the absorbent material to be missing or partially thinned. In addition, if the pulp fiber length is short, the voids in the absorbent article decrease, reducing the rate of liquid absorption. A reduced absorption rate makes it easier for liquid to remain on the surface of the absorbent article, and the dry feeling of the surface during use also tends to decrease.

[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 defibrillability, the defibrillability of the pulp will improve, but the affinity between pulp fibers and water will decrease, which may reduce the absorption performance of the fluff pulp after defibrillation.

[0009] The present invention was made based on the circumstances described above, and aims to provide a pulp sheet for fluff pulp that exhibits good defibration properties during manufacturing and good water absorption performance of the resulting absorbent article, even when using raw material pulp composed of bleached kraft pulp made from coniferous trees including cedar. [Means for solving the problem]

[0010] A pulp sheet for fluff pulp according to one aspect of the present invention contains raw material pulp made from bleached softwood kraft pulp and a surfactant, wherein the raw material wood of the bleached softwood kraft pulp includes cedar wood, the surfactant includes 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 pulp fibers is 8% by 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. [Effects of the Invention]

[0011] According to the present invention, even when using raw material pulp composed of bleached softwood kraft pulp containing cedar wood, it is possible to provide a pulp sheet for fluff pulp that exhibits good defibration properties during manufacturing and good water absorption performance of the resulting absorbent article. [Modes for carrying out the invention]

[0012] [Description of Embodiments of the Invention] A pulp sheet for fluff pulp according to one aspect of the present invention contains raw material pulp made from bleached softwood kraft pulp and a surfactant, wherein the raw material wood of the bleached softwood kraft pulp includes cedar wood, the surfactant includes 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 pulp fibers is 8% by 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 softwood kraft pulp containing cedar wood, which has short fiber length of pulp, is likely to be densely packed with pulp fibers, and is likely to be difficult to form a bulky pulp sheet for fluff pulp, and in the length-weighted fiber length distribution of the pulp fibers, the content ratio of pulp fibers having a fiber length exceeding 0.2 mm and less than 0.6 mm is 8% by mass or more. In such a 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 or more and 4.00 or less, so that the bulkiness can be further improved while suppressing the decrease in absorption performance, and thus the defiberization property during the manufacturing process can be improved. Further, a good balance can be set between the liquid absorption rate of the fluff pulp after defiberization of the pulp sheet for fluff pulp and the water retention amount under a loaded state. Therefore, even when using a raw material pulp composed of softwood kraft pulp containing cedar wood, the pulp sheet for fluff pulp has good defiberization property during production and good water absorption performance of the resulting absorbent article. Thereby, the pulp sheet for fluff pulp can improve the smooth feeling on the surface of the resulting absorbent article.

[0014] The above nonionic surfactant is a polyoxyalkylene alkyl ether, and the content of the above cationic surfactant is preferably 0.075 kg / t or more and 2.250 kg / t or less. Since the above nonionic surfactant is a polyoxyalkylene alkyl ether, even when using a raw material pulp composed of a softwood sun-dried kraft pulp containing cedar wood, the absorption rate of the liquid in the fluff pulp after defibrating the pulp sheet for fluff pulp and the water retention amount in the state of applying a load are both good, and the bulkiness can be further improved, so the defibratability during the manufacturing process can be further improved. Also, since the content of the above cationic surfactant is 0.075 kg / t or more and 2.250 kg / t or less, even when using a raw material pulp composed of a softwood sun-dried kraft pulp containing cedar wood, the absorption rate of the liquid in the fluff pulp after defibrating the pulp sheet for fluff pulp and the water retention amount in the state of applying a load are both good, and the bulkiness can be further improved, so the defibratability during the manufacturing process can be further improved. "kg / t" indicates the mass [kg] per 1 t of absolutely dry pulp. <0*********>[ <0*********>[

[0015] <0*********>[ The pulp sheet for the fluff pulp has a specific burst strength of 0.90 kPa·m<*********>[ 2 / g or more and 1.30 kPa·m<*********>[ 2 / g or less. Since the specific burst strength of the pulp sheet for the fluff pulp is within the above range, even when using a raw material pulp composed of a softwood sun-dried kraft pulp containing cedar wood, the defibratability during the manufacturing process can be further improved. <0*********>[ <0*********>[

[0016] <0*********>[ The absorbent article according to another aspect of the present invention uses the pulp sheet for the fluff pulp. Since the absorbent article uses the pulp sheet for the fluff pulp, the absorption rate of the liquid in the fluff pulp after defibrating the pulp sheet for fluff pulp and the water retention amount in the state of applying a load can be set in a good balance. Therefore, the absorbent article can improve the smooth feeling on the surface. <0*********>[ <0*********>[

[0017] <0*********>[ [Details of Embodiments of the Present Invention]<0*********>[ The following describes in detail a pulp sheet for fluff pulp according to one embodiment of the present invention. Unless otherwise specified, the content (amount added in oven-dry) of each material blended into the paper substrate described below refers to the mass ratio to the oven-dry mass of the pulp in the paper substrate.

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

[0019] (Raw pulp) The raw material pulp consists of bleached softwood kraft pulp (NBKP). In the pulp sheets for this fluff pulp, pine wood, such as radiata pine, and various types of cedar are preferably used as the raw material wood for the bleached softwood kraft pulp.

[0020] (Pulp content) The content of cedar wood in the bleached softwood 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. The effects of the present invention can be more fully realized when the content of cedar wood in the bleached softwood kraft pulp is 30% by mass or more.

[0021] (Surfactants) The pulp sheet for fluff pulp contains surfactants including nonionic and cationic surfactants. In the pulp sheet for fluff pulp, which contains raw material pulp made from bleached softwood kraft pulp including cedar wood, where the pulp fiber length is short and the fibers are densely packed, making the bulkiness of the pulp sheet tend to be low, the inclusion of nonionic and cationic surfactants as surfactants improves the bulkiness of the pulp sheet for fluff pulp, and ensures uniform and even interfiber spacing regardless of the orientation of the bleached softwood kraft pulp fibers. Therefore, the defibration properties of the pulp sheet for fluff pulp are improved, and the liquid absorption rate and water retention capacity under load in the fluff pulp after defibration can be set to a good balance, resulting in good 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. As a nonionic surfactant, polyoxyalkylene alkyl ethers are preferred, even when using raw material pulp composed of bleached coniferous kraft pulp containing cedar wood, from the viewpoint of further improving the bulkiness of the pulp sheet for the fluff pulp and further improving the effect of suppressing the decrease in defibration during the manufacturing process, the rate of liquid absorption in the fluff pulp, and the decrease in water retention under load.

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

[0024] Furthermore, the surfactant may include anionic surfactants as well as nonionic surfactants and cationic surfactants, as long as it does not impair the effects of the present invention. Examples of anionic surfactants include alkylbenzene sulfonic acid and its salts, alpha-olefin sulfonates, alkyl sulfate salts, alkyl ether sulfate salts, methyl tauric acid, alaninates and their salts, ether carboxylic acids and their salts, sulfosuccinates, and polyoxyalkylene alkyl ethers.

[0025] The lower limit of the surfactant content is 0.15 kg / t in terms of solid content, preferably 0.30 kg / t, and more preferably 0.60 kg / t. By containing surfactant within a specific range, the bulkiness of the pulp sheet for fluff pulp can be further improved, thereby improving the defibration process during manufacturing. If the surfactant content is below the lower limit, it may not be possible to sufficiently increase the bulkiness of the pulp sheet for fluff pulp. 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, it may reduce the liquid absorption rate and water retention capacity under load in the fluff pulp after defibration of the pulp sheet for fluff pulp.

[0026] The lower limit of the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25, with 0.67 being more preferable. If the mass ratio of the cationic surfactant to the nonionic surfactant is less than 0.25, when using raw material pulp made from bleached softwood kraft pulp containing cedar wood, the absorption rate of liquid in the fluff pulp tends to decrease, and the absorbent article obtained from the pulp sheet for the fluff pulp may tend to have a reduced smooth feel. On the other hand, the upper limit of the mass ratio of the cationic surfactant to the nonionic surfactant is 4.00, with 1.50 being preferable. If the mass ratio of the cationic surfactant to the nonionic surfactant exceeds 4.00, when using raw material pulp made from bleached softwood kraft pulp containing cedar wood, the water retention capacity of the fluff pulp under load tends to decrease, and the absorbent article obtained from the pulp sheet for the fluff pulp may tend to have a reduced smooth feel. Even when using raw pulp composed of bleached kraft pulp made from coniferous trees including cedar, the defibrillability of the pulp can be improved and the balance between the liquid absorption rate and water retention capacity under load in the fluff pulp can be improved.

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

[0028] (Other additives) Other additives may be added to the pulp sheets for fluff pulp as needed. Examples of additives include fillers, pigments, sizing agents, coagulants, oil resistant agents, aluminum sulfate, yield enhancers, water drainage enhancers, dry strength enhancers, wet strength enhancers, coloring pigments, and water-resistant agents, which can be used individually or in combination.

[0029] [Physical properties of pulp sheets for fluff pulp] (density) The density is measured in accordance with "Paper and cardboard - Test methods for thickness, density and specific volume" as described in JIS-P8118(2014). The lower limit of the density of the pulp sheet for fluff pulp is 0.50 g / cm³. 3 Preferably, 0.52 g / cm³ 3 More preferably, 0.53 g / cm³ 3 This is even more preferable. The upper limit of the density of the pulp sheet for fluff pulp mentioned above is 0.65 g / cm³. 3 Preferably, 0.62 g / cm³ 3 More preferably, 0.60 g / cm³ 3is more preferable. When the density of the pulp sheet for fluff pulp is within the above range, in the pulp sheet for fluff pulp obtained by adding a surfactant to the above softwood kraft pulp, the fibrillation property during the manufacturing process can be improved, and a fluff pulp that can easily ensure voids between fibers uniformly without unevenness can be obtained. Therefore, the liquid absorption rate and the water retention amount under a loaded state in the fluff pulp can be improved. The density is measured in an atmosphere of 23 ± 1°C and 50 ± 2% RH as described in "Paper, Paperboard and Pulp - Standard Conditions for Conditioning and Testing" specified in JIS - P8111 (1998).

[0030] (Grammage) The grammage is measured in accordance with "Paper and Paperboard - Method for Measuring Grammage" described in JIS - P8124 (2011). As the grammage of the pulp sheet for fluff pulp, for example, it can be 300.0 g / m 2 or more and 1500.0 g / m 2 or less.

[0031] (Specific Bursting Strength) The specific bursting strength of the pulp sheet for fluff pulp can be used as an index of fibrillation property. The specific bursting strength [kPa·m 2 / g] of the pulp sheet for fluff pulp is obtained by dividing the bursting strength of the paper expressed in kilopascals (kPa) measured in accordance with JIS - P8131 (2009) by the grammage.

[0032] As the lower limit of the specific bursting strength of the pulp sheet for fluff pulp, 0.90 kPa·m 2 / g is preferable, and 0.93 kPa·m 2 / g is more preferable. When the above specific bursting strength is 0.90 kPa·m 2 / g or more, the absorbency of the fluff pulp and absorbent articles produced from the pulp sheet for fluff pulp in a short period can be improved, and a smooth feeling can be achieved well. As the upper limit of the specific bursting strength of the pulp sheet for fluff pulp, 1.30 kPa·m 2 / g is preferable, and 1.25 kPa·m 2 / g is more preferable, and 1.20 kPa·m 2 / g is more preferable, and 1.15kPa·m 2 / g is particularly preferred. The above specific burst strength is 1.30 kPa·m 2 By having a value of 1 / g or less, undisintegrated material is less likely to be mixed into the fluff pulp and absorbent articles produced from the pulp sheet for fluff pulp, and the decrease in the liquid absorption rate and water retention capacity under load in the fluff pulp can be reduced.

[0033] [Method for manufacturing pulp sheets for fluff pulp] The method for manufacturing the pulp sheet for fluff pulp is not particularly limited, but for example, it includes a digestion step of digesting raw wood to produce unbleached pulp, a deligninization step of removing lignin, a bleaching step of bleaching to produce bleached pulp, a beating step of beating the bleached pulp to a desired freeness, a step of preparing a pulp slurry, and a step of papermaking the pulp slurry. A dewatering and washing step may be appropriately included between the above steps.

[0034] (Cooking process) In the digestion process, the raw wood is digested to produce unbleached pulp. White liquor and softwood chips, which are the raw wood, are placed in a digester and digested, and the resulting (unwashed) pulp slurry mixed with black liquor is removed from the bottom of the continuous digester. The digestion method can be arbitrarily selected from commercially available Kraft improvement methods such as MCC, EMCC, ITC, Lo-Solids, KobudoMari, Compact method, etc., and the digester can be either a continuous digester or a batch digester. Furthermore, there are no particular limitations on the digestion conditions (digestion temperature, H-factor which is a single factor obtained by multiplying the influence of digestion temperature and digestion time, the content ratio of active alkali or effective alkali, etc.).

[0035] (Deligninization process) In the deligninization process, unbleached pulp is deliginated. Alkaline chemicals and oxygen are added to the unbleached pulp, and the lignin is decomposed under high temperature and pressure, and eluted by the alkaline chemicals. The deligninization process can be carried out at low concentration (pulp concentration: 3%~8%), medium concentration (pulp concentration: 8%~15%), or high concentration (pulp concentration: 20%~30%), and there are no specific restrictions on the method used.

[0036] (Washing process) In the washing process, unbleached pulp is washed by a combination of displacement, dilution, or dewatering. The washing method is not particularly limited, and known washing machines can be used. For example, displacement washing, dilution and dewatering, press washing, or a combination of these methods can be used. Washing machines used for displacement washing include diffusion washers, pressurized diffusion washers, and belt-type washing machines. Washing machines used for dilution and dewatering include vacuum filter washing machines and pressurized filter washing machines. Press washing machines used include screw-type press washing machines, disc-type press washing machines, and roll-type press washing machines.

[0037] In this invention, it is preferable to remove lignin and reduce the kappa number, therefore it is preferable to use a press washing machine that can easily remove lignin. The pulp concentration after washing by the press washing method is preferably 30% or more, more preferably 32% or more, and even more preferably 35% or more. Since dewatering by the press washing method can also squeeze out and remove moisture from inside the fibers, it is easier to sufficiently remove lignin that is free inside the pulp fibers compared to other washing methods.

[0038] (bleaching process) In the bleaching process, the unbleached pulp, which has undergone deligninization, is bleached to produce bleached pulp. The bleaching method is not particularly limited and can be done using known bleaching methods. For example, acid treatment, ozone bleaching, chlorine dioxide bleaching, hydrogen peroxide bleaching, or a combination of these, including alkaline extraction, alkaline extraction with added oxygen, and alkaline extraction with added oxygen and hydrogen peroxide, can be carried out individually 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 method of ozone bleaching is not particularly limited and can be carried out at high concentrations (30-40%), medium concentrations (8-15%), or low concentrations (1-3%), but a high-concentration method that is more likely to damage the fibers is preferred. Any known ozone generator can be used. The generated ozone may be mixed directly with the pulp, or it may be dissolved in water before being mixed with the pulp.

[0040] In ozone bleaching, a lower pH promotes deligninization while reducing damage to the fibers. Therefore, it is preferable to adjust the pH according to the required quality of the pulp sheet for fluff pulp. The pH for ozone bleaching of pulp sheets for fluff pulp is preferably 6 or less, more preferably 4 or less, and even more preferably 2 to 3. By keeping the pH within the above range during ozone bleaching of pulp sheets for fluff pulp, the water retention capacity of the fluff pulp after defibration can be improved under the required load.

[0041] (Preparation process) In the preparation process, a pulp slurry is prepared. If necessary, the bleached pulp is beaten to achieve the desired freeness. Then, surfactants and other additives are added as needed to prepare the pulp.

[0042] (Paper making process) Next, these raw material slurries are used to make paper in a paper machine in a neutral range so that the pH is between 6 and 8. In the above paper-making process, the raw pulp is made using a paper machine that makes paper from pulp raw materials sprayed onto a moving wire. The paper machine is not particularly limited, and known paper machines such as wire mesh paper machines, cylinder mesh paper machines, hybrid formers, and gap formers can be used to make paper in the form of a sheet. Pulp sheets for fluff pulp can be manufactured by combining one or more layers, but a single layer is preferred because it is easier to make the density within the layer uniform.

[0043] This pulp sheet for fluff pulp exhibits excellent defibration properties during manufacturing, and the absorbent properties of absorbent articles using this pulp sheet are well-balanced.

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

[0045] In the present invention, the apparatus used for the mechanical treatment to defibrate is not particularly limited. Known defibraters used in the manufacture of absorbent articles such as disposable diapers can be used, and defibraters that utilize frictional force or shear force as the mechanical treatment can be suitably used. Examples of defibraters include hammer-type defibraters, impact-type defibraters, roll-type defibraters, and sheath-type airflow defibraters.

[0046] [Physical properties of fluff pulp] (Sinking velocity) The absorption rate of liquid in fluff pulp can be evaluated by its sedimentation rate. The sedimentation rate is measured using fluff pulp obtained by defibrating a pulp sheet for fluff pulp production. After compressing the fluff pulp into a disc shape, it is floated on water, and the time required for the entire sample to become wet is measured. Coniferous pulp derived from cedar has shorter fiber lengths and denser fibers compared to coniferous pulp derived from pine, which may reduce its compatibility with water. Furthermore, the presence of surfactants increases the hydrophobicity of the pulp fibers, potentially further reducing the liquid absorption rate of the fluff pulp. Therefore, the sedimentation rate is used as a measure of the short-term absorbency of fluff pulp.

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

[0048] The method for measuring the sedimentation velocity is as follows: 0.5 g of fluff pulp obtained by defibrating the pulp sheet for fluff pulp is 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 is 5 cc (5 cm). 3 Compress the sample for 10 seconds until it reaches a circular shape. Then, add deionized water to a 500 ml beaker, leave the sample at room temperature for 1 minute, and drop the sample from a height of 30 mm above the water surface. Measure the time from when the sample touches the water surface until the entire sample is wet.

[0049] (Water retention capacity under load) The water retention capacity of fluff pulp under load is measured using fluff pulp obtained by defibrating fluff pulp sheets. After dissolving the fluff pulp in water, the water retention capacity is measured after applying a load to drain the water. Coniferous pulp derived from cedar has shorter fiber lengths and denser fibers than coniferous pulp derived from pine, resulting in higher water retention even under load. On the other hand, the presence of surfactants can increase the hydrophobicity of the pulp fibers, potentially reducing the water retention capacity under load. Therefore, 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 the fluff pulp under load is preferably 8.0 g, more preferably 8.5 g, and even more preferably 9.0 g. A water retention capacity of 8.0 g or more under load ensures sufficient absorbency over long periods in absorbent articles made from the pulp sheet for the fluff pulp, and prevents liquid from rising to the surface of the absorbent article under load, thereby improving the dry feel.

[0051] The method for measuring the water retention capacity of fluff pulp under load is as follows: Dissolve 1.0 g of fluff pulp obtained by defibrating a pulp sheet for fluff pulp in 200 ml of deionized water and stir for 30 seconds. Next, pour the mixture into a Buchner funnel (No. 1, standard: AF1) in 10 seconds under atmospheric pressure, and place a weight (cylindrical, weight 1,450 ± 2 g, outer diameter 60 ± 1 mm) on top. After 1 minute, remove the weight and measure the weight of the pulp as the measured value. Subtract the weight of 1.0 g of pulp from the measured value to determine the water retention capacity under load.

[0052] The pulp sheet for fluff pulp has a good balance of water absorption performance, as both the settling velocity of the fluff pulp after defibration and the water retention capacity under load are within the above range.

[0053] [Absorbent articles] The absorbent article uses a pulp sheet for fluff pulp. Because the absorbent article uses a pulp sheet for fluff pulp that can set a good balance between the rate of liquid absorption in the fluff pulp and the amount of water it can retain under load, the surface can be made dryer. The absorbent article is not particularly limited, but examples include disposable diapers, urine pads, light incontinence pads, and sanitary napkins.

[0054] The manufacturing method for the absorbent articles described above is not particularly limited and can be manufactured by known methods. For example, disposable diapers can be manufactured using manufacturing machines manufactured by Zuiko Co., Ltd., Toa Kiko Co., Ltd., or Erhard Leimer Co., Ltd., using methods such as panel type, leg hole type, vertical flow type, or horizontal flow type.

[0055] <Other Embodiments> The present invention is not limited to the embodiments described above, and can be implemented in various modified and improved forms in addition to those described above. [Examples]

[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 1-15, Comparative Examples 1-5, and Reference Examples 1-2] The pulp sheets for fluff pulp in Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 to 2 were prepared using the following procedure.

[0058] (Cooking process) Japanese cedar and pine wood were mixed in the mass ratios shown in Table 1, a white liquor with a predetermined degree of sulfurization was added, and the mixture was pulped in a rotary autoclave at a liquid ratio of 6.0 (L / kg) and a maximum temperature of 170°C to obtain unbleached coniferous kraft pulp with a copper number of approximately 30. Note that "-" in Table 1 indicates the absence of the corresponding component.

[0059] (Washing process) After diluting the unbleached pulp to a pulp concentration of approximately 2%, a No. 2 filter paper (manufactured by ADVANTEC) was placed in a Buchner funnel, and the pulp was dewatered to a pulp concentration of approximately 12%. Then, the unbleached pulp was sandwiched between square filter paper (manufactured by ADVANTEC), and pressure was applied using a press to dewater it to a pulp concentration of 33%. This washing process was repeated twice.

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

[0061] (Paper making process) The obtained bleached softwood kraft pulp was diluted to a concentration of approximately 2% without beating, and adjusted to the content ratios listed in Table 1. Then, the surfactants listed in Table 1 were added. Using the adjusted pulp slurry, a sheet was formed with a basis weight of 700 g / m² using a semi-automatic sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.). 2 Hand-formed sheets were created to achieve the desired result. In this way, pulp sheets for fluff pulp were obtained for Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 to 2. For Reference Examples 1 and 2, commercially available pulp sheets for fluff pulp that do not contain surfactants were prepared.

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

[0063] [Table 1]

[0064] The pulp sheets for fluff pulp obtained in the manner described above were evaluated.

[0065] (Length-weighted fiber length distribution of pulp fibers) The length-weighted fiber length of unbleached kraft pulp from Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 to 2 after the pulping and washing processes was measured. The length-weighted fiber length was measured for fibers with a length of 0.1 mm or more using a Valmet Fiber Image Analyzer (Valmet FS5) manufactured by Valmet, in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 52 "Pulp and Paper - Fiber Length Test Method - Optical Automatic Measurement". The percentage [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 pulp fibers was then calculated.

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

[0067] (Evaluation of fibrillation based on specific burst strength) Specific burst strength [kPa·m] of each pulp sheet for fluff pulp 2The bursting strength of the paper, expressed in kilopascals (kPa) according to JIS-P8131 (2009), was determined by dividing it by the basis weight. Specific bursting strength was measured under an atmosphere of 23±1℃ and 50±2%RH, as described in JIS-P8111 (1998) "Paper, cardboard and pulp - Standard conditions for humidity control and testing". The defibration properties of the pulp sheet for fluff pulp were evaluated in three stages based on the power load during defibration in the defibration machine. The evaluation result was a specific bursting strength of 1.30 kPa·m. 2 In cases A and B, where the values ​​are less than or equal to / g, the defibrillation properties of the pulp sheets for fluff pulp are good. A: Excellent defibrillation properties (specific burst strength of 1.1 kPa·m) 2 / g or less). B: Good defibrillability (specific burst strength of 1.1 kPa·m) 2 / g exceeds 1.30kPa·m 2 / g or less). C: Poor fibrillation properties (specific burst strength of 1.30 kPa·m) 2 / g super).

[0068] (Settling velocity of fluff pulp) The absorption rate of liquid in the fluff pulp was evaluated by the sedimentation rate. First, a pulp sheet for fluff pulp was cut into 10 mm x 10 mm squares, 5 g was measured out, and placed in a blender (WARING, model: HGBSS, stainless steel container: 2 L capacity). The sample was defibrated at HIGH speed to obtain fluff pulp. Next, 0.5 g of fluff pulp was placed in a plastic syringe (TERUMO, Terumo syringe, inner diameter 29 mm, 50 ml, model SS-50ESZ) with the tip cut off to expose the inside of the cylinder, and a volume of 5 cc (5 cm³) was obtained. 3 A disc-shaped sample was prepared by compressing it for 10 seconds until it reached a certain consistency. After leaving the sample at room temperature for 1 minute, deionized water was placed in a 500cc beaker, and the sample was dropped from a height of 30mm above the water surface. The time [seconds / 0.5g] from when the sample touched the water surface until the entire sample was wet was measured. The evaluation criteria were as follows, in three stages. If the evaluation is A or B, the settling velocity of the fluff pulp is good. A: The sinking velocity is 0.8 seconds / 0.5g or less. B: The sinking velocity is greater than 0.8 seconds / 0.5g and less than or equal to 1.0 seconds / 0.5g. C: The sinking velocity exceeds 0.9 seconds / 0.5g.

[0069] (Water retention capacity of fluff pulp under load) First, a pulp sheet for fluff pulp was cut into 10mm x 10mm squares, 5g was measured out, and placed in a blender (WARING, model: HGBSS, stainless steel container: 2L capacity). The sample was defibrated at HIGH speed to obtain fluff pulp. Next, 200ml of deionized water was placed in a beaker, 1.0g of fluff pulp was dissolved in it, and the mixture was stirred for 30 seconds to prepare a pulp slurry. The pulp slurry was poured into a Buchner funnel (No. 1, standard: AF1) in 10 seconds, and a weight (cylindrical, weight 1,450±2g, outer diameter 60±1mm) was placed on top. After 1 minute, the weight was removed and the weight of the pulp was measured. The water content [g] under load was obtained by subtracting the pulp weight from the measured value. The evaluation criteria were as follows, in three stages. If the evaluation is A or B, the water retention capacity of the fluff pulp under load is good. A: The water retention capacity under load is 9.0g or more. B: The water retention capacity under load is 8.0g or more and less than 9.0g. C: The water retention capacity under load is less than 8.0g.

[0070] (Balance of water absorption performance of absorbent materials) The balance of water absorption performance on the surface of the absorbent material was evaluated based on the sedimentation rate of the fluff pulp and the water retention capacity under load. The evaluation criteria were as follows, in three stages. When the evaluation is 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 is good, the absorption is high in the short term and liquid does not easily remain on the surface of the absorbent material, and the absorption is high in the long term and liquid does not easily float to the surface of the absorbent material under load. A: Both the sedimentation velocity and the water retention capacity under load are evaluated as A or higher, indicating an excellent balance of water absorption performance. B: Both the sedimentation velocity and the water retention capacity under load are evaluated as B or higher, indicating a good balance of water absorption performance. C: Either the sedimentation velocity or the water retention capacity under load is rated C, indicating a poor balance in water absorption performance.

[0071] Table 2 shows the evaluation results for Examples 1 to 15, Comparative Examples 1 to 5, and Reference Examples 1 to 2.

[0072] [Table 2]

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

[0074] On the other hand, Comparative Example 1, which did not contain a surfactant, had poor defibration performance because undefibrated pulp remained due to its high specific degree of bursting. In addition, a decrease in sedimentation velocity and water retention capacity occurred due to the undefibrated pulp. Comparative Example 2, which did not contain a nonionic surfactant, exhibited inferior sedimentation velocity and water retention capacity under load. Comparative Example 3, which did not contain a cationic surfactant, exhibited inferior defibrillation properties. Comparative Example 4, in which the mass ratio of cationic surfactant to nonionic surfactant exceeded 4.50, showed inferior sedimentation velocity 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, showed inferior fibrillation properties.

[0075] The results above demonstrate that, even when using raw material pulp composed of bleached kraft pulp made from coniferous trees including cedar, the pulp sheet for fluff pulp exhibits good defibration properties during manufacturing and good water absorption performance in the resulting absorbent articles.

[0076] The pulp sheet for fluff pulp of the present invention is suitable as an absorbent material for absorbent articles.

Claims

1. It contains raw material pulp made from bleached coniferous kraft pulp and a surfactant, The raw wood for the above-mentioned bleached coniferous kraft pulp includes cedar wood. The above surfactant includes a nonionic surfactant and a cationic surfactant. In the length-weighted fiber length distribution of pulp fibers, the content of pulp fibers with a fiber length greater than 0.2 mm and less than 0.6 mm is 8% by mass or more. A pulp sheet for fluff pulp, wherein the mass ratio of the cationic surfactant to the nonionic surfactant is 0.25 or more and 4.00 or less.

2. The above nonionic surfactant is a polyoxyalkylene alkyl ether. The pulp sheet for fluff pulp according to claim 1, wherein 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 A pulp sheet for fluff pulp according to claim 1 or claim 2, wherein the amount is less than or equal to / g.

4. An absorbent article using a pulp sheet for fluff pulp as described in claim 1 or claim 2.

Images