Fluff pulp sheet and absorbent article

Abstract

To provide a pulp sheet for fluff pulp, which can produce fluff pulp with an excellent fibrillation property during production and a high absorption performance by using wood pulp derived from broadleaf trees.SOLUTION: A pulp sheet for fluff pulp according to an aspect of the present invention contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and a surfactant. The pulp sheet is configured in that: a mass ratio of the bleached hardwood kraft pulp to the bleached softwood kraft pulp is 15 / 85 or more and 50 / 50 or less; a content of the surfactant is 0.15 kg / t or more and 4.50 kg / t or less; according to determination of water absorptiveness by Klemm method specified in JIS-P8141 (2004), when measuring a sample with a basis weight of 200 g / m2, a water absorption height at 1 minute after the start of measurement is 25 mm or more and 40 mm or less; and a rate of water absorption at 1 to 2 minutes after the start of measurement is 5 mm / min or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pulp sheet for fluff pulp. [Background technology]

[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 absorbency and defibration properties, is widely used (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-211411 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, wood pulp derived from hardwoods is relatively cheaper than pulp derived from softwoods, but hardwood pulp has shorter and more densely packed fibers than softwood pulp, which reduces the bulkiness of the pulp sheet and may result in undefibrated pulp when the pulp sheet for fluff pulp is defibrated into fluff pulp. Furthermore, when hardwood pulp is used for fluff pulp, the short fiber length reduces the voids in the absorbent article, which may result in a decrease in the water absorption capacity and water absorption rate. Improved absorption performance, such as water absorption capacity and water absorption rate, is also required for fluff pulp used in absorbent articles. Although under-defibration can be prevented by strengthening the defibration, in that case, normally defibrated fibers may become over-defibrated, producing fine fibers, which may reduce the water absorption rate of the fluff pulp.

[0006] The present invention was made based on the above circumstances, and aims to provide a pulp sheet for fluff pulp that can produce fluff pulp that has excellent defibration properties during production and high absorption performance, even when using wood pulp derived from broad-leaved trees. [Means for solving the problem]

[0007] A pulp sheet for fluff pulp according to one embodiment of the present invention contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and a surfactant, the mass ratio of the bleached hardwood kraft pulp to the bleached softwood kraft pulp being 15 / 85 or more and 50 / 50 or less, the content of the surfactant being 0.15 kg / t or more and 4.50 kg / t or less, and the pulp sheet has a basis weight of 200 g / m in a water absorbency test according to the Klemm method specified in JIS-P8141 (2004). 2 When the sample is measured, the water absorption height one minute after the start of measurement is 25 mm or more and 40 mm or less, and the water absorption rate between one and two minutes after the start of measurement is 5 mm / min or more. [Effects of the Invention]

[0008] According to the present invention, a pulp sheet for fluff pulp can be provided that uses wood pulp derived from broad-leaved trees and that can produce fluff pulp that is excellent in defibration during production and has high absorbency. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiment of the present invention] A pulp sheet for fluff pulp according to one embodiment of the present invention contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and a surfactant, the mass ratio of the bleached hardwood kraft pulp to the bleached softwood kraft pulp being 15 / 85 or more and 50 / 50 or less, the content of the surfactant being 0.15 kg / t or more and 4.50 kg / t or less, and the pulp sheet has a basis weight of 200 g / m in a water absorbency test according to the Klemm method specified in JIS-P8141 (2004). 2When the sample is measured, the water absorption height one minute after the start of measurement is 25 mm or more and 40 mm or less, and the water absorption rate between one and two minutes after the start of measurement is 5 mm / min or more.

[0010] This pulp sheet for fluff pulp is made by blending hardwood bleached kraft pulp and softwood bleached kraft pulp in a balanced manner at a specific mass ratio, which gives the fluff pulp the liquid absorbency of the softwood bleached kraft pulp and the surface density and skin irritation suppression effects of the hardwood bleached kraft pulp. Furthermore, in this pulp sheet for fluff pulp, which contains wood pulp derived from hardwood, which has short fiber length and densely packed fibers and therefore tends to have low bulkiness, adding a surfactant in a specific content range can further improve bulkiness while suppressing a decrease in absorption performance, thereby improving defibration ability during the manufacturing process. Furthermore, in a water absorbency test using the Klemm method, if the water absorption height one minute after the start of measurement is 25 mm to 40 mm and the water absorption rate between one and two minutes after the start of measurement is 5 mm / min or higher, fluff pulp with good water absorption capacity and rate can be obtained, even if it contains wood pulp derived from hardwood. Therefore, the pulp sheet for fluff pulp uses wood pulp derived from hardwood, and fluff pulp with excellent defibration properties during production and high absorption performance can be produced. Here, "kg / t" indicates the mass [kg] per ton of bone-dry pulp. "Klemm water absorbency" is measured in accordance with "Paper and paperboard - Water absorption test method - Klemm method" described in JIS-P8141 (2004).

[0011] The surfactant preferably includes a nonionic surfactant, an anionic surfactant, a cationic surfactant, or a combination thereof. By including a nonionic surfactant, an anionic surfactant, a cationic surfactant, or a combination thereof, the pulp sheet for fluff pulp containing wood pulp derived from hardwood can have improved bulkiness while maintaining good water absorption amount and water absorption rate, thereby further improving defibration ability during the production process.

[0012] The surfactant preferably contains a polyoxyalkylene alkyl ether or a polyoxyalkylene alkylamine derivative as a main component. When the surfactant contains a polyoxyalkylene alkyl ether or a polyoxyalkylene alkylamine derivative as a main component, the fluff pulp pulp sheet containing wood pulp derived from hardwood can have improved bulkiness while maintaining good water absorption capacity and water absorption rate, thereby further improving defibration properties during the manufacturing process.

[0013] The acacia content in the raw wood of the hardwood bleached kraft pulp is preferably 10% by mass or more and 100% by mass or less. By using acacia content in the raw wood of the hardwood bleached kraft pulp within the above range, a fixed amount or a single amount of acacia wood with a wide fiber width is blended, ensuring sufficient and uniform voids between the pulp fibers and further improving defibration during the fluff pulp manufacturing process. This allows the fluff pulp used in absorbent articles to have a higher water absorption capacity and water absorption speed.

[0014] The fluff pulp sheet has a density of 0.50 g / cm 3 More than 0.65g / cm 3 The specific burst strength is 1.0 kPa m or less. 2 / g or more 1.7kPa m 2 When the density and burst strength index of the pulp sheet for fluff pulp are within the above ranges, the defibration property during the manufacturing process can be further improved even for the pulp sheet for fluff pulp containing wood pulp derived from hardwood.

[0015] [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. The amount of each material (bone-dry internal amount) added to 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.

[0016] <Fluff pulp sheet> The pulp sheet for fluff pulp can be obtained by papermaking a slurry containing raw pulp.

[0017] (Raw pulp) As the raw material pulp, for example, virgin pulp can be used. The raw material pulp used in the pulp sheet for fluff pulp is preferably chemical pulp. A combination of softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP) is preferred as the chemical pulp. When the pulp sheet for fluff pulp contains softwood bleached kraft pulp, the bulkiness and liquid absorbency of the fluff pulp made using the pulp sheet for fluff pulp can be improved. Furthermore, when the pulp sheet for fluff pulp contains hardwood bleached kraft pulp, the surface density of the fluff pulp made using the pulp sheet for fluff pulp can be increased, and the effect of reducing the amount of absorbed liquid returning and the effect of suppressing skin rashes in absorbent articles made from the fluff pulp can be improved.

[0018] (Bleached hardwood kraft pulp) As the hardwood bleached kraft pulp, hardwood bleached kraft pulp produced from acacia wood or eucalyptus wood is preferred.

[0019] Acacia wood is a durable, hard material with minimal shrinkage upon drying, high impact resistance, and excellent durability. Pulp derived from acacia retains its original properties, exhibiting excellent moisture absorption and drying properties, making it a valuable raw material. Eucalyptus species, particularly Eucalyptus globulus, Eucalyptus grandis, Eucalyptus europhylla, Eucalyptus nitens, and Eucalyptus regnans, have long been widely used as raw pulp materials for papermaking. The resulting pulp has a rigid, resistant lumen, making it ideal for producing bulky, low-density fluff pulp sheets. Acacia wood is preferred for hardwood bleached kraft pulp because its fibers are thicker than those of eucalyptus, resulting in a higher bulk. When combined with softwood bleached kraft pulp, acacia wood exhibits minimal loss of water absorption.

[0020] (Acacia wood content in hardwood kraft pulp raw materials) The lower limit of the acacia content in the raw wood material for the hardwood kraft pulp is preferably 10% by mass, more preferably 50% by mass. The upper limit of the acacia content is preferably 100% by mass, more preferably 80% by mass. When the acacia content in the raw wood material for the hardwood kraft pulp of the fluff pulp pulp sheet is within the above range, even if the hardwood bleached kraft pulp has shorter fibers and more densely packed fibers than softwood bleached kraft pulp, and regardless of the direction in which the fibers are oriented (for example, the length, width, or thickness directions of an absorbent article produced from the fluff pulp pulp sheet), particularly uniform voids between fibers can be ensured, thereby achieving both the defibration ability and water absorption rate required for the fluff pulp pulp sheet. If the ratio falls outside the above range, for example, if the proportion of rigid eucalyptus wood is high, the number of voids due to the rigidity will increase, but since the fiber width is shorter than that of acacia wood, the voids are likely to vary depending on the direction in which the fibers are oriented.As a result, not only will the fluff pulp using this fluff pulp pulp sheet have low defibration ability, but it will also be prone to uneven water absorption speed, which may result in a decrease in water absorption speed.

[0021] The lower limit of the weight-average fiber length (hereinafter also referred to as the average fiber length) of hardwood kraft pulp fibers is preferably 0.76 mm, more preferably 0.80 mm. If the average fiber length is below the lower limit, the bulkiness of the pulp sheet for fluff pulp tends to decrease, which may result in reduced defibration during the manufacturing process. On the other hand, the upper limit of the average fiber length is preferably 0.92 mm, more preferably 0.86 mm. If the average fiber length exceeds the upper limit, the fluff pulp using the pulp sheet for fluff pulp tends to have variations in voids depending on the fiber orientation direction, which may result in a reduced water absorption rate. The weight-average fiber length was measured for fibers with a fiber length of 0.1 mm or more using a fiber length measuring instrument "FiberLab" manufactured by Metso Automation in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 52, "Pulp and Paper - Fiber Length Test Method - Optical Automatic Measurement."

[0022] The lower limit of the weight-average fiber width (hereinafter also referred to as the average fiber width) of hardwood kraft pulp fibers is 16.7 μm, preferably 16.9 μm. If the average fiber width is below the lower limit, the interfiber gaps in the fluff pulp produced using the pulp sheet for fluff pulp may become dense, potentially reducing the water absorption rate. On the other hand, the upper limit of the average fiber width is 18.2 μm, more preferably 17.7 μm. If the average fiber width exceeds the upper limit, the contact area between pulp fibers in the pulp sheet for fluff pulp may become too large, increasing the bonding strength between the fibers and reducing the defibration ability during the manufacturing process. If the defibration ability is too low, over-defibration may occur during the fluff pulp manufacturing process using the pulp sheet for fluff pulp, resulting in the generation of fine fibers, potentially reducing the water absorption rate of the fluff pulp. The weight average fiber width was measured for fibers with a fiber length of 0.1 mm or more using a fiber length measuring device "FiberLab" manufactured by Metso Automation in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 52 "Pulp and Paper - Fiber Length Test Method - Optical Automatic Measurement."

[0023] The kappa number of the bleached hardwood kraft pulp is preferably 0.3 or less. If the kappa number exceeds the upper limit, the lignin in the fibers is not sufficiently removed, the water absorption of the pulp fibers is reduced, and skin rashes may easily occur. The kappa number is measured in accordance with JIS-P8211 (2011).

[0024] The lower limit of the sulfidity of the white liquor used to cook hardwood kraft pulp is preferably 25%, more preferably 28%. If the sulfidity is less than 25%, the pulp fibers are easily damaged, and the fluff pulp using the pulp sheet for fluff pulp becomes dense, which may result in a reduced water absorption rate. On the other hand, the upper limit of the sulfidity is preferably 32%, more preferably 30%. If the sulfidity exceeds the upper limit, the pulp fibers are less likely to be damaged and remain rigid, which may result in unevenness in the voids in absorbent articles obtained from the pulp sheet for fluff pulp, increasing the amount of backflow and potentially causing rashes. The sulfidity was calculated according to the following formula, as the ratio of sodium sulfide to the total of sodium sulfide and caustic soda. Sulfidity (%)=(Na2S / (NaOH+Na2S))×100

[0025] (Freeness of unbeaten hardwood bleached kraft pulp) The Canadian Standard Freeness (CSF) of the unbeaten pulp of hardwood bleached kraft pulp is preferably adjusted to 520 ml or more and 580 ml or less. If the freeness of the unbeaten pulp of hardwood bleached kraft pulp is less than 520 ml, dewatering will be poor during pulp sheet production, and it will be necessary to mechanically strengthen dewatering, for example by strengthening press dewatering in a paper machine. This not only strengthens the bonds between pulp fibers but also reduces the bulkiness of the pulp sheet, which may reduce defibration ability during production. On the other hand, if the Canadian Standard Freeness of the unbeaten pulp exceeds 580 ml, there will be too many voids between the fibers in the pulp sheet, which may lead to uneven defibration during defibration.

[0026] The lower limit of the content of hardwood bleached kraft pulp in the pulp sheet for fluff pulp is preferably 15% by mass, more preferably 20% by mass. Meanwhile, the upper limit of this content is preferably 50% by mass, more preferably 40% by mass. By containing the hardwood bleached kraft pulp in the above range and adding a surfactant in a predetermined range, when mixed with softwood bleached kraft pulp, even hardwood bleached kraft pulp, which has short fibers and tends to be densely packed together, can be particularly well maintained in interfiber spaces, thereby improving defibration ability while maintaining the water absorption amount and water absorption rate required for the pulp sheet for fluff pulp.

[0027] (softwood bleached kraft pulp) In the pulp sheet for fluff pulp, pines such as radiata pine and various cedars are preferably used as raw material wood for softwood bleached kraft pulp.

[0028] (pulp content) The lower limit of the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp in the pulp used in the fluff pulp sheet is 15 / 85, preferably 20 / 80. If the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp is less than 15 / 85, even if the fiber width of the hardwood bleached kraft pulp is within the specified range, the gaps between the fibers of the absorbent article obtained from the fluff pulp sheet are likely to be uneven, leading to increased reversal and the risk of skin rash. On the other hand, the upper limit of the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp is 50 / 50, preferably 40 / 60. If the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp exceeds 50 / 50, even if the fiber width of the hardwood bleached kraft pulp is within the specified range, the fluff pulp sheet may become dense and the water absorption rate may decrease. By ensuring that the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp is within the above range and by including a surfactant within a predetermined range, even if hardwood bleached kraft pulp, which has short fiber length and tends to pack tightly, is mixed into the softwood bleached kraft pulp, uniform interfiber voids can be secured regardless of the orientation direction of the hardwood bleached kraft pulp fibers, thereby improving defibration performance while maintaining the water absorption capacity and water absorption speed required for a pulp sheet for fluff pulp.

[0029] (Other pulps) The pulp sheet for fluff pulp may contain pulps other than hardwood bleached kraft pulp and softwood bleached kraft pulp. Examples of such pulps include soda pulp, sulfite pulp, chemi-thermomechanical pulp, chemi-refined mechanical pulp, and thermo-chemi-mechanical pulp. However, if the lignin in the fibers is not sufficiently removed, the amount and rate of water absorption of the pulp fibers tend to decrease, so bleached pulp from which lignin has been sufficiently removed is preferred. When such other pulps are contained, the content of such other pulps is preferably 10% by mass or less of the total pulp raw material.

[0030] (surfactant) The fluff pulp sheet contains a surfactant. In fluff pulp pulp sheets containing wood pulp derived from hardwood, which tends to have low bulk due to short fiber length and dense fiber packing, adding a surfactant within a specific range can further improve bulkiness and thereby improve defibration during the manufacturing process. However, surfactants contain hydrophilic and lipophilic groups (hydrophobic groups), and adding too much surfactant can increase the hydrophobicity of the pulp fibers, potentially reducing the water absorption capacity and water absorption rate. For this reason, it is preferable to select a surfactant suitable for hardwood-derived wood pulp. While known surfactants can be used, it is preferable to select a surfactant that contains a nonionic surfactant, an anionic surfactant, a cationic surfactant, or a combination thereof. By including a nonionic surfactant, an anionic surfactant, a cationic surfactant, or a combination thereof, the bulkiness of the fluff pulp pulp sheet containing hardwood-derived wood pulp can be improved while suppressing a decrease in water absorption capacity and water absorption rate, thereby further improving defibration during the manufacturing process.

[0031] Nonionic surfactants include, for example, ethylene and / or propylene oxide adducts of higher alcohols, polyhydric alcohol nonionic surfactants, ethylene oxide adducts of higher fatty acids, ester compounds of polyhydric alcohols and fatty acids, and ethylene oxide adducts of ester compounds of polyhydric alcohols and fatty acids. Anionic surfactants include, for example, alkylbenzenesulfonic acid and its salts, alphaolefin sulfonates, alkyl sulfates, alkyl ether sulfates, methyl taurates, alaninates and their salts, ether carboxylic acids and salts, sulfosuccinates, and polyoxyalkylene alkyl ethers. Cationic surfactants include, for example, quaternary ammonium salts, ester cations, methyl sulfate cations, ethylene oxide adduct ammonium chloride, acetates, fatty acid derivatives, polyoxyalkylene alkylamine derivatives, and fatty acid-polyethylene polyamine condensates. Examples of amphoteric surfactants include sodium β-alkylaminopropionate, coconut fatty acid amidopropyl dimethylaminoacetic acid betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, sodium laurylaminodipropionate, and fatty acid derivatives. Polyoxyalkylene alkyl ethers or polyoxyalkylene alkylamine derivatives are more preferred as the surfactants. When the main component of the surfactant is a polyoxyalkylene alkyl ether or a polyoxyalkylene alkylamine derivative, the fluff pulp sheet containing wood pulp derived from hardwood can further improve bulkiness while suppressing a decrease in water absorption amount and water absorption rate, thereby further improving defibration properties during the manufacturing process.

[0032] 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. If the surfactant content is below this 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 this upper limit, the water absorption amount and water absorption rate of the fluff pulp produced from the pulp sheet for fluff pulp may decrease.

[0033] (Other additives) Other additives may be added to the pulp sheet for fluff pulp as needed, such as 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.

[0034] [Physical properties of pulp sheets for fluff pulp] (Basic weight) The 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 / cm 2 More than 1500.0g / cm 2 It can be as follows:

[0035] (Klemm absorbency) Klemm absorbency is measured by immersing the bottom edge of a piece of paper vertically in water and measuring the height of the paper absorbed by capillary action. It is measured in accordance with JIS-P8141 (2004). Klemm absorbency measures the absorbency of a sample after it has been in contact with water for a relatively long time. However, for absorbent products, absorbency over a shorter period of time is important, so it is measured as follows. After preparing a sample using a fluff pulp sheet, the height [mm] at 1 minute after the start of the measurement and the water absorption rate [mm / min] between 1 and 2 minutes after the start of the measurement are measured in a water absorption test at room temperature. The height at 1 minute after the start of the measurement is used as a measure of the amount of water absorbed by the fluff pulp sheet, and the water absorption rate between 1 and 2 minutes after the start of the measurement is used as a measure of the water absorption rate of the fluff pulp sheet.

[0036] The basis weight of the fluff pulp sheet is 200 g / m 2 The lower limit of the water absorption height one minute after the start of measurement is 25 mm, preferably 27 mm, and more preferably 29 mm. If the water absorption height one minute after the start of measurement is below the lower limit, the fluff pulp and absorbent articles made from the pulp sheet for fluff pulp will have a low water absorption capacity, which may cause skin irritation. On the other hand, the upper limit of the water absorption height one minute after the start of measurement is 40 mm. If the water absorption height one minute after the start of measurement exceeds the upper limit, the water absorption capacity will be too high, resulting in a decrease in the water absorption rate between one and two minutes after the start of measurement. In the fluff pulp and absorbent articles made from the pulp sheet for fluff pulp, the amount of absorbed liquid that flows back will increase, which may cause skin irritation. When the water absorption height one minute after the start of measurement is within the above range, the pulp sheet for fluff pulp can produce fluff pulp with good water absorption capacity.

[0037] The basis weight of the fluff pulp sheet is 200 g / m 2The lower limit of the water absorption rate from 1 to 2 minutes after the start of measurement is 5 mm / min, preferably 7 mm / min, and more preferably 9 mm / min. If the water absorption rate from 1 to 2 minutes after the start of measurement is below the lower limit, the fluff pulp and absorbent articles produced from the pulp sheet for fluff pulp will have a low water absorption rate, resulting in an increased amount of absorbed liquid returning, which may cause skin rash. When the water absorption rate from 1 to 2 minutes after the start of measurement is within the above range, the pulp sheet for fluff pulp can produce fluff pulp with a good water absorption rate. When the pulp sheet for fluff pulp has both the water absorption height 1 minute after the start of measurement and the water absorption rate from 1 to 2 minutes after the start of measurement within the above range, fluff pulp with excellent water absorption rate and water absorption rate can be produced, and absorbent articles with little return and reduced rash can be obtained. Here, the basis weight of the pulp sheet for fluff pulp is 200 g / m 2 Even if the sample exceeds this limit, it must be defibrated using a standard defibrator in accordance with JIS-P8220 (2012) "Pulp - Defibration method", and then defibrated using JIS-P8222 (1998) "Pulp - Preparation method for test handsheets - Method using a standard handsheet machine" to a basis weight of 200 g / m. 2 It is also possible to prepare a sample and then measure it.

[0038] (density) The density is measured in accordance with JIS-P8118 (2014) "Paper and paperboard - Test methods for thickness, density and specific volume." The lower limit of the density of the pulp sheet for fluff pulp is 0.52 g / cm. 3 is preferred, and 0.53 g / cm 3 The upper limit of the density of the pulp sheet for fluff pulp is 0.60 g / cm. 3 is preferred, and 0.59 g / cm 3When the density of the pulp sheet for fluff pulp is within the above range, the pulp sheet for fluff pulp, which is made by mixing the above-mentioned bleached hardwood kraft pulp and bleached softwood kraft pulp and adding a surfactant, 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 water absorption amount and water absorption speed required for fluff pulp can be improved. The density is measured 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).

[0039] (specific bursting strength) The burst strength index is the burst strength of paper measured in kilopascals (kPa) according to JIS-P8131 (2009) divided by the basis weight. The lower limit of the burst strength index is 1.20 kPa m 2 / g is preferred, and 1.22 kPa m 2 / g is more preferable. If the burst strength index of the pulp sheet for fluff pulp is less than the lower limit, the fluff pulp will be over-defibrated and the fibers will be easily cut, which may result in a denser fluff pulp, a lower water absorption rate, and a higher risk of skin rash. On the other hand, the upper limit of the burst strength index of the pulp sheet for fluff pulp is 1.58 kPa m 2 / g is preferred, and 1.44 kPa m 2 / g is more preferable. If the burst index of the pulp sheet for fluff pulp exceeds the upper limit, the defibration property during the manufacturing process will be poor, and the resulting fluff pulp will have many voids, which may make it easier for the absorbed liquid to flow back and cause skin rashes. When the burst index of the pulp sheet for fluff pulp is within the above range, the defibration property during the manufacturing process can be improved in a pulp sheet for fluff pulp that is a mixture of the hardwood bleached kraft pulp and the softwood bleached kraft pulp, and since it is easier to ensure uniform voids between fibers in the fluff pulp without unevenness, the water absorption rate of the fluff pulp can be improved. The burst index was measured 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).

[0040] [Method for manufacturing pulp sheets for fluff pulp] The method for producing the 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.

[0041] (Cooking process) In the cooking process, raw wood is cooked to produce unbleached pulp. White liquor and raw wood chips (hardwood or softwood) are placed in a digester and cooked, and the resulting (unwashed) pulp slurry mixed with black liquor is removed from the bottom of a 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. Furthermore, cooking conditions (e.g., cooking temperature, H factor (a factor obtained by multiplying the influence of cooking temperature and cooking time), and active or effective alkali content) are not particularly limited.

[0042] (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 then dissolved in the alkaline chemicals. The delignification process can be performed at any consistency, including low consistency (pulp consistency: 3% to 8%), medium consistency (pulp consistency: 8% to 15%), and high consistency (pulp consistency: 20% to 30%).

[0043] (Cleaning process) In the washing process, unbleached pulp is washed by a combination of displacement, dilution, and dehydration. There are no particular limitations on the washing method, and washing can be performed using a known washing machine. For example, displacement washing, dilution and dehydration, press washing, or a combination of these can be used. Washing machines for the displacement washing method include diffusion washers, pressure diffusion washers, and belt-type washers. Washing machines for the dilution and dehydration method include vacuum filter washers and pressure filter washers. Press washing methods include screw-type press washers, disk-type press washers, and roll-type press washers.

[0044] 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 within the fibers, making it easier to sufficiently remove free lignin from within the pulp fibers than other washing methods.

[0045] (bleaching process) 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.

[0046] 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 the high consistency method, which is more likely to damage the fibers, is preferred. Any known ozone generator can be used. The generated ozone may be mixed with the pulp as is, or may be dissolved in water and then mixed with the pulp.

[0047] 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. By keeping the pH in the above range in ozone bleaching of the pulp sheet for fluff pulp, the water absorption rate required of the pulp sheet for fluff pulp can be improved.

[0048] (Preparation process) In the preparation process, a pulp slurry is prepared. If necessary, the bleached pulp is beaten to a desired freeness in the preparation process. Thereafter, surfactants and other additives are added as needed to prepare the paper stock.

[0049] (Paper making process) Next, these raw material slurries are used to make paper in a papermaking machine in a neutral range so that the pH is between 6 and 8. In the papermaking process, the raw material pulp is made into paper 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.

[0050] According to the pulp sheet for fluff pulp, wood pulp derived from broad-leaved trees can be used to produce fluff pulp that has excellent defibration properties during production and high absorption performance.

[0051] [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.

[0052] 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.

[0053] [Absorbent articles] The absorbent article uses a fluff pulp sheet. By using the fluff pulp sheet, the absorbent article can improve the amount and speed of water absorption and suppress skin rash. The absorbent article is not particularly limited, but 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 those described above, with various modifications and improvements. [Example]

[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 18, Comparative Examples 1 to 4, and Reference Example 1] Pulp sheets for fluff pulp of Examples 1 to 18, Comparative Examples 1 to 4, and Reference Example 1 were produced by the following procedure.

[0058] (Cooking process) (1) Hardwood Acacia and eucalyptus were mixed in the mass ratio shown in Table 1, white liquor with a specified sulfidity was added, and the mixture was cooked in a rotary autoclave at a liquor ratio of 6.0 (L / kg) and a maximum temperature of 170°C, yielding unbleached hardwood kraft pulp with a kappa number of approximately 16. Note that "-" in Table 1 indicates that the corresponding component was not included. (2) Coniferous trees White liquor with a specified sulfidity was added to the cedar, and the mixture was cooked in a rotary autoclave at a liquor ratio of 6.0 (L / kg) and a maximum temperature of 170°C to obtain unbleached softwood kraft pulp with a kappa number of approximately 30.

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

[0060] (bleaching process) (1) Hardwood (1-1) Ozone bleaching Unbleached kraft pulp was bleached for approximately 2 minutes with 8.1% ozone gas at 45°C. For the ozone bleaching, ozone gas from a laboratory ozone generator, PSA Ozonizer SGA-01A-PSA4 manufactured by Sumitomo Precision Products Co., Ltd., was used. (1-2) Chlorine dioxide bleaching The pulp after ozone bleaching was further bleached with chlorine dioxide at a chlorine dioxide addition rate of 1.5%, a pulp consistency of 10% by mass, and 70°C to obtain bleached hardwood kraft pulp. Between each bleaching process, the pulp was diluted to a pulp consistency of approximately 2%, and then a dilution and washing process was carried out twice, in which No. 2 filter paper (manufactured by ADVANTEC) was placed in a Buchner funnel and the pulp consistency was dewatered to approximately 12%. (2) Coniferous trees The unbleached 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. This was followed by alkaline hydrogen peroxide bleaching 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. This was followed by alkali treatment at 70°C for 120 minutes with a sodium hydroxide addition rate of 0.2%, a pulp consistency of 10% by mass. This was followed by chlorine dioxide bleaching 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 pulp consistency of approximately 2%, and then a dilution and washing process was carried out twice, in which No. 2 filter paper (manufactured by ADVANTEC) was placed in a Buchner funnel and the pulp consistency was dewatered to approximately 12%.

[0061] (Paper making process) The obtained bleached hardwood kraft pulp and bleached softwood kraft pulp were diluted to a consistency of about 2% without beating, and the blending ratios shown in Table 2 were adjusted to the values ​​shown in Table 2. The surfactants shown in Table 2 were then added. The adjusted pulp slurry was then used in a semi-automatic sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) to produce a sheet with a basis weight of 800 g / m. 2 Handmade sheets were prepared so that the following was achieved: In this manner, pulp sheets for fluff pulp were obtained for Examples 1 to 18, Comparative Examples 1 to 4, and Reference Example 1. Note that Reference Example 1 is a pulp sheet for fluff pulp equivalent to a commercially available product.

[0062] [Table 1]

[0063] [Table 2]

[0064] The pulp sheet for fluff pulp obtained as described above was subjected to various evaluations.

[0065] (Weight average fiber length and weight average fiber width of pulp fibers) The weight-average fiber length and weight-average fiber width of the unbleached hardwood kraft pulps of Examples 1 to 18 and Comparative Examples 1 to 4 after the cooking and washing processes were measured. The weight-average fiber length and weight-average fiber width were measured for fibers with a fiber length of 0.1 mm or more using a fiber length measuring instrument "FiberLab" manufactured by Metso Automation, in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 52, "Pulp and Paper - Fiber Length Test Method - Optical Automatic Measurement." The fiber analyzer "FiberLab" can measure the length and width of pulp fibers with high accuracy by analyzing the image of diluted pulp fibers as they pass through the measurement cell inside the fiber analyzer.

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

[0067] (Specific burst strength of pulp sheet for fluff pulp) The specific burst strength of each fluff pulp pulp sheet was calculated by dividing the burst strength of the paper, measured in kilopascals (kPa) in accordance with JIS-P8131 (2009), by the basis weight.

[0068] (Defibrillation of pulp sheets for fluff pulp) The defibration property of each fluff pulp pulp sheet was evaluated based on the burst strength index of the fluff pulp pulp sheet using the following four-level evaluation criteria: A, B, and C indicate good defibration property of the fluff pulp pulp sheet. A: Specific burst strength is 1.2 kPa m 2 / g or more 1.5kPa m 2 / g or less. B: Specific burst strength is 1.6 kPa m 2 / g or 1.1 kPa m2 / g. C: Specific burst strength is 1.7 kPa m 2 / g or 1.0 kPa m 2 / g. D: Specific burst strength is 1.8 kPa m 2 / g or more or 0.9kPa m 2 / g or less.

[0069] (Klemm absorbency) The Klemm water absorbency of each fluff pulp pulp sheet was measured in accordance with "Paper and paperboard - Water absorbency test method - Klemm method" described in JIS-P8141 (2004), and the height [mm] at 1 minute after the start of measurement and the water absorption rate [mm / min] from 1 to 2 minutes after the start of measurement were measured. The Klemm water absorbency is based on a basis weight of 200 g / m 2 The values ​​are measured by preparing pulp sheets for each fluff pulp.

[0070] (Absorption performance of pulp sheets for fluff pulp) The absorption performance of the fluff pulp pulp sheet was evaluated based on the absorption amount measured at the height of the Klemm absorbency one minute after the start of measurement, and the absorption rate was evaluated based on the Klemm absorbency rate measured between one and two minutes after the start of measurement. The evaluation criteria were as follows: A, B, and C indicate that the fluff pulp pulp sheet had good absorption amount and absorption rate. (1) A: The height measured one minute after the start of the Klemm water absorbency measurement is between 29 mm and 40 mm. B: The height measured one minute after the start of measurement in Klemm's water absorbency is 27 mm or more and 28 mm or less. C: The height measured one minute after the start of measurement in Klemm's water absorbency is 25 mm or more and 26 mm or less. D: The height measured one minute after the start of measurement in Klemm's water absorbency is 41 mm or more or 24 mm or less. (2) A: The water absorption rate during the first 1 to 2 minutes of the Klemm water absorption measurement is 9 mm / min or more. B: The water absorption rate during the first 1 to 2 minutes after the start of the Klemm water absorption measurement is 7 mm / min or more and 8 mm / min or less. C: The water absorption rate during the first 1 to 2 minutes after the start of the Klemm water absorption measurement is 5 mm / min or more and 6 mm / min or less. D: The water absorption rate during the first 1 to 2 minutes after the start of the Klemm water absorption measurement is 4 mm / min or less.

[0071] (Skin irritation from absorbent articles) Disposable diapers were produced using the fluff pulp sheets of Examples 1 to 18, Comparative Examples 1 to 4, and Reference Example 1, and then a total of 220 monitors were asked to use 10 sheets each of Reference Example 1, Examples 1 to 18, and Comparative Examples 1 to 4, and the number of sheets that developed a rash was evaluated as a percentage. The evaluation was based on Reference Example 1 and rated on the following four-point scale. Evaluations of A, B, and C indicate a good effect of suppressing skin rash. A: The incidence of rash is better than that of Reference Example 1. B: The incidence of rash is slightly better than that of Reference Example 1. C: The incidence of rash is the same as in Reference Example 1, and the material is usable. D: The incidence of rash was higher than that of Reference Example 1, making it practically unusable.

[0072] The evaluation results for each of the examples and comparative examples are shown in Table 3.

[0073] [Table 3]

[0074] As shown in Table 3, Examples 1 to 18, in which the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp was 15 / 85 or more and 50 / 50 or less, the surfactant content was 0.15 kg / t or more and 4.50 kg / t or less, the water absorption height 1 minute after the start of measurement in the Klemm method was 25 mm or more and 40 mm or less, and the water absorption rate between 1 and 2 minutes after the start of measurement was 5 mm / min or more, showed good results in all aspects: defibration ability, water absorption amount and water absorption rate in the pulp sheet for fluff pulp, and the effect of suppressing skin rash in absorbent articles.

[0075] On the other hand, Comparative Example 1, which had a low content of hardwood bleached kraft pulp, was inferior in the water absorption rate of the pulp sheet for fluff pulp and in the skin rash suppression effect of the absorbent article. Comparative Example 2, which had a high content of hardwood bleached kraft pulp, was inferior in the water absorption amount of the pulp sheet for fluff pulp and in the skin rash suppression effect of the absorbent article. Comparative Example 3, which had a low content of surfactant, was inferior in the water absorption rate of the pulp sheet for fluff pulp and in the skin rash suppression effect of the absorbent article. Comparative Example 4, which had a high content of surfactant, was inferior in all of the defibration ability, water absorption amount and water absorption rate of the pulp sheet for fluff pulp, and the skin rash suppression effect of the absorbent article.

[0076] The above results demonstrate that the pulp sheet for fluff pulp uses wood pulp derived from broad-leaved trees, has excellent defibration properties during production, has high absorption performance, and can be used to produce absorbent articles with good skin rash suppression effects. [Industrial Applicability]

[0077] The pulp sheet for fluff pulp of the present invention is suitable for absorbent articles.

Claims

1. Contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and surfactants, The mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp is 15 / 85 or more and 50 / 50 or less, The content of the surfactant is 0.15 kg / t or more and 4.50 kg / t or less, The density is 0.50 g / cm 3 or more and 0.65 g / cm 3 or less, In the water absorption test by the Klemm method specified in JIS-P8141 (2004), the basis weight was 200 g / m ２ A pulp sheet for fluff pulp, in which the water absorption rate between 1 minute and 2 minutes after the start of measurement when the sample is measured is 5 mm / min or more.

2. 2. The pulp sheet for fluff pulp according to claim 1, wherein the surfactant comprises a nonionic surfactant, an anionic surfactant, a cationic surfactant, or a combination thereof.

3. 3. The pulp sheet for fluff pulp according to claim 1 or 2, wherein the main component of the surfactant is a polyoxyalkylene alkyl ether or a polyoxyalkylene alkylamine derivative.

4. 4. The pulp sheet for fluff pulp according to claim 1, 2 or 3, wherein the content of acacia wood in the raw wood material of the hardwood bleached kraft pulp is 10% by mass or more and 100% by mass or less.

5. Specific burst strength of 1.0 kPa·m ２ / g or more 1.7kPa・m ２ The pulp sheet for fluff pulp according to any one of claims 1 to 4, wherein the tensile strength is 1 / g or less.

6. An absorbent article using a pulp sheet for fluff pulp described in any one of claims 1 to 5.

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