absorbent articles

Abstract

To provide a pulp sheet for fluff pulp, having high absorption performance and excellent workability in the production of fluff pulp.SOLUTION: In a pulp sheet for fluff pulp according to one embodiment of the present invention, when percentage contents are added up for all pulp fibers at fiber length intervals of 0.02 mm, pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm account for 42.6% or more. An average value of the percentage contents at the fiber length intervals of 0.02 mm in the pulp fibers having the fiber length of 0.5 mm or more and less than 1.1 mm is 1.00% or more and 1.70% or less, and a standard deviation σ of the percentage contents is 0.58% or less. When percentage contents are added up at fiber width intervals of 1 μm, pulp fibers having a fiber width of 10 μm or more and less than 35 μm account for 90.6% or more. An average value of the percentage contents at the fiber width intervals of 1 μm in the pulp fibers having the fiber width of 10 μm or more and less than 35 μm is 3.1% or more and 3.9% or less, and a standard deviation σ of the percentage contents is 2.90% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention provides absorbent articles Regarding. [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 absorption properties 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, although wood pulp derived from broad-leaved trees is relatively cheaper than pulp derived from softwoods, when hardwood pulp is used for fluff pulp, the short fiber length reduces the voids in the absorbent article, which may lead to a decrease in the amount and speed of water absorption. Furthermore, hardwood pulp has shorter fiber length and higher fiber density than softwood pulp, which means that workability, such as defibration ability and ease of forming an absorbent body, is poor, and productivity tends to decrease. In particular, among hardwood pulps, acacia has shorter fiber length than eucalyptus, which may lead to a significant decrease in workability.

[0006] The present invention was made based on the above circumstances, and aims to provide a pulp sheet for fluff pulp that has high absorption performance and good workability during the production of fluff pulp, even when it contains 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 hardwood kraft pulp and softwood kraft pulp, and when the content of all pulp fibers is calculated at intervals of 0.02 mm in fiber length, the proportion of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm is 42.6% or more, and the average content of the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm at intervals of 0.02 mm in fiber length is 1.00% or more and 1.70% or less, The standard deviation σ of the content rate at every 0.02 mm fiber length interval is 0.58% or less, and when the content rate for all pulp fibers is tallied at every 1 μm fiber width interval, the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 90.6% or more, the average content rate at every 1 μm fiber width interval for the pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 3.1% or more and 3.9% or less, and the standard deviation σ of the content rate at every 1 μm fiber width interval is 2.90% or less. [Effects of the Invention]

[0008] According to the present invention, a pulp sheet for fluff pulp can be provided which has high absorption performance and good workability during the production of fluff pulp, even when containing wood pulp derived from broad-leaved trees. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the distribution of the average values ​​of the content when measured at fiber length intervals of 0.02 mm in Example 1. [Figure 2] FIG. 2 is a diagram showing the distribution of the average values ​​of the content when measured at intervals of 1 μm across the fiber width in Example 1. [Figure 3]FIG. 3 is a diagram showing the distribution of average values ​​of the content when measured at fiber length intervals of 0.02 mm in Comparative Example 1. [Figure 4] FIG. 4 is a diagram showing the distribution of the average values ​​of the content when measured at intervals of 1 μm across the fiber width in Comparative Example 1. [Figure 5] FIG. 5 is a diagram showing the distribution of average values ​​of the content when measured at fiber length intervals of 0.02 mm in Comparative Example 2. [Figure 6] FIG. 6 is a diagram showing the distribution of the average values ​​of the content when measured at intervals of 1 μm across the fiber width in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Description of the embodiment of the present invention] A pulp sheet for fluff pulp according to one embodiment of the present invention contains hardwood kraft pulp and softwood kraft pulp, and when the content of all pulp fibers is calculated at intervals of 0.02 mm in fiber length, the proportion of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm is 42.6% or more, and the average content of the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm at intervals of 0.02 mm in fiber length is 1.00% or more and 1.70% or less, The standard deviation σ of the content rate at every 0.02 mm fiber length interval is 0.58% or less, and when the content rate for all pulp fibers is tallied at every 1 μm fiber width interval, the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 90.6% or more, the average content rate at every 1 μm fiber width interval for the pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 3.1% or more and 3.9% or less, and the standard deviation σ of the content rate at every 1 μm fiber width interval is 2.90% or less.

[0011] The fluff pulp sheet contains softwood bleached kraft pulp, which results in superior bulkiness of the fluff pulp produced using the fluff pulp sheet. Furthermore, the fluff pulp sheet contains hardwood bleached kraft pulp, which increases the density of the fluff pulp surface, thereby improving the effect of reducing the amount of absorbed liquid returning and the effect of suppressing skin rash in absorbent articles produced from the fluff pulp. Furthermore, when the content of all pulp fibers in the pulp sheet for fluff pulp is calculated at intervals of 0.02 mm in fiber length, the proportion of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm is 42.6% or more, and when the content is calculated at intervals of 1 μm in fiber width, the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 90.6% or more. By setting the proportions of fiber length and fiber width within the above ranges, even when the pulp sheet for fluff pulp contains wood pulp derived from hardwood, the defibration property during the manufacturing process is good, improving workability during fluff pulp production. Furthermore, the pulp sheet for fluff pulp can be improved in reducing the amount of absorbed liquid returning. Therefore, even when the pulp sheet for fluff pulp contains wood pulp derived from hardwood, the pulp sheet for fluff pulp has high absorption performance and good workability during fluff pulp production. Furthermore, in the pulp sheet for fluff pulp, for pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm, which account for 42.6% or more of all pulp fibers, the average content per 0.02 mm fiber length interval when counted at 0.02 mm fiber length intervals is 1.00% or more and 1.70% or less, and the standard deviation σ of the content per 0.02 mm fiber length interval is 0.58% or less. Furthermore, for pulp fibers having a fiber width of 10 μm or more and less than 35 μm, which account for 90.6% or more of all pulp fibers, the average content per 1 μm fiber width interval when counted at 1 μm fiber width intervals is 3.1% or more and 3.9% or less, and the standard deviation σ of the content per 1 μm fiber width interval is 2.90% or less. By reducing the variations in the specific range of fiber length distribution and the specific range of fiber width distribution in this way, the pulp sheet for fluff pulp does not decrease the absorption rate even though it contains hardwood pulp, and can suppress backflow of absorbed liquid. Therefore, in an absorbent body using the pulp sheet for fluff pulp, rash can be reduced. Therefore, even if the pulp sheet for fluff pulp contains wood pulp derived from broad-leaved trees, it has high absorption performance and good workability during the production of fluff pulp.

[0012] The mass ratio of the hardwood kraft pulp to the softwood kraft pulp is preferably 25 / 75 or more and 38 / 62 or less. By blending hardwood kraft pulp and softwood kraft pulp in a balanced manner at the above mass ratio, the pulp sheet for fluff pulp can improve the effect of reducing the amount of absorbed liquid returning while maintaining the water absorption amount, water absorption rate, and bulkiness required for the pulp sheet for fluff pulp.

[0013] The acacia content in the raw wood of the hardwood bleached kraft pulp is preferably 5% by mass or more and 95% 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 further increases the water absorption capacity and water absorption speed of fluff pulp used in absorbent articles.

[0014] The fluff pulp sheet has a density of 0.50 g / cm 3 More than 0.65g / cm 3 When the density of the pulp sheet for fluff pulp is within the above range, 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] The pulp sheet for fluff pulp has a burst strength of 1.0 kPa·m 2 / g or more 1.7kPa m 2 When the burst strength of the pulp sheet for fluff pulp is within the above range, 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.

[0016] [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.

[0017] <Fluff pulp sheet> The pulp sheet for fluff pulp can be obtained by papermaking a slurry containing raw pulp.

[0018] (raw pulp) The raw material pulp used for the fluff pulp sheet is a combination of softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP). The inclusion of softwood bleached kraft pulp in the fluff pulp sheet results in fluff pulp using the fluff pulp sheet having excellent bulk. Furthermore, the inclusion of hardwood bleached kraft pulp in the fluff pulp sheet increases the density of the fluff pulp surface, thereby improving the effect of reducing the amount of absorbed liquid returning and the effect of suppressing skin rash in absorbent articles manufactured from the fluff pulp.

[0019] (Bleached hardwood kraft pulp) As the hardwood bleached kraft pulp, hardwood bleached kraft pulp produced from acacia wood or eucalyptus wood is preferred.

[0020] 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.

[0021] (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 5% by mass, more preferably 20% by mass, and even more preferably 50% by mass. The upper limit of the acacia content is preferably 95% by mass, more preferably 90% by mass, and even 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 interfiber voids can be ensured, thereby achieving both the defibration 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.

[0022] In the pulp sheet for fluff pulp, when the content of all pulp fibers is calculated at fiber length intervals of 0.02 mm, the proportion of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm is 42.6% or more, preferably 45.0% or more. Furthermore, when the content of all pulp fibers is calculated at fiber width intervals of 1 μm, the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 90.6% or more, preferably 91.0% or more. Thus, by setting the fiber length and fiber width ratios of all pulp fibers within the above ranges, even when the pulp sheet for fluff pulp contains wood pulp derived from hardwood, the defibration property during the manufacturing process is good, improving workability during fluff pulp manufacturing. Furthermore, the pulp sheet for fluff pulp can be improved in reducing the amount of absorbed liquid returning. Therefore, even if the pulp sheet for fluff pulp contains wood pulp derived from broad-leaved trees, it has high absorption performance and good workability during the production of fluff pulp.

[0023] In this pulp sheet for fluff pulp, the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm account for 42.6% or more of the total pulp fibers, and when counted at intervals of 0.02 mm in fiber length, the average content for each 0.02 mm interval is 1.00% or more and 1.70% or less. Here, the measurement of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm will be explained. Softwood kraft pulp has a wide range of fiber content up to approximately 5 mm or more, while hardwood kraft pulp has a relatively low fiber content in the range of less than 0.50 mm and over 1.1 mm. Therefore, for a pulp sheet for fluff pulp that combines both, the inventors have found that the effects of the pulp sheet for fluff pulp of the present invention can be achieved by using the fiber content of 0.50 mm or more and less than 1.1 mm as an indicator. The standard deviation σ of the content when pulp fibers are measured at 0.02 mm intervals is 0.58% or less, preferably 0.56% or less, and more preferably 0.54% or less. If the standard deviation σ of the fiber length of all pulp fibers exceeds 0.58%, the pulp sheet for fluff pulp may have a reduced absorption rate and a reduced effect of suppressing backflow of absorbed liquid. The above fiber length is the ISO weight-weighted average fiber length measured using a fiber length measuring instrument "VALMET FS5" manufactured by Valmet in accordance with JIS-P8226:2011 (ISO16065-2:2007) "Pulp - Fiber length measurement method by optical automatic analysis."

[0024] When all pulp fibers have a fiber length of 0.5 mm or more but less than 1.1 mm, measured at 0.02 mm intervals, the lower limit of the average fiber length is 0.5 mm, preferably 0.6 mm. The upper limit of the average fiber length is 0.8 mm, preferably 0.7 mm. If the average fiber length is less than 0.5 mm, the bulkiness of the pulp sheet for fluff pulp is likely to decrease, and there is a risk of reduced defibration ability during the manufacturing process. The upper limit of the average fiber length is 0.8 mm, preferably 0.7 mm. If the average fiber length exceeds 0.8 mm, fluff pulp using the pulp sheet for fluff pulp is likely to have variations in voids depending on the fiber orientation direction, which may result in a reduced water absorption rate.

[0025] In this pulp sheet for fluff pulp, the pulp fibers with a fiber width of 10 μm or more and less than 35 μm, which account for 90.6% or more of all pulp fibers, have an average content of 3.1% or more and 3.9% or less per 1 μm interval when counted at 1 μm intervals. Here, the measurement of pulp fibers with a fiber width of 10 μm or more and less than 35 μm will be explained. Softwood kraft pulp has a wide fiber content up to approximately 55 μm or more, while hardwood kraft pulp has an extremely low fiber content in the range of less than 10 μm and over 35 μm. Therefore, for a pulp sheet for fluff pulp that is a mixture of both, the inventors have found that the effects of the pulp sheet for fluff pulp of the present invention can be achieved by using the fiber content of 10 μm or more and less than 35 μm as an indicator. The standard deviation σ of the content when pulp fibers are measured at 0.02 mm intervals is 2.9% or less, preferably 2.8% or less, and more preferably 2.6% or less. If the standard deviation σ of the fiber width of all pulp fibers exceeds 2.9%, the pulp sheet for fluff pulp may have a reduced absorption rate and a reduced effect of suppressing backflow of absorbed liquid. The fiber width was measured using a fiber length measuring instrument "VALMET FS5" manufactured by Valmet in accordance with JIS-P8226:2011 (ISO16065-2:2007) "Pulp - Fiber length measurement method by optical automatic analysis."

[0026] For all pulp fibers, the lower limit of the average fiber width when measuring pulp fibers with a fiber width of 10 μm or more and less than 35 μm at 1 μm intervals is 15 μm, preferably 18 μm. The upper limit of the average fiber width is 30 μm, preferably 27 μm. If the average fiber width is less than 15 μm, the interfiber gaps in fluff pulp produced using the pulp sheet for fluff pulp may become dense, resulting in a reduced water absorption rate. If the average fiber width exceeds 30 μm, 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 defibration properties during the manufacturing process. If defibration properties are too low, over-defibration may occur during the manufacturing process of fluff pulp using the pulp sheet for fluff pulp, resulting in the generation of fine fibers, which may reduce the water absorption rate of the fluff pulp.

[0027] 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).

[0028] 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

[0029] (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.

[0030] (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.

[0031] (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 preferably 25 / 75, more preferably 28 / 72. If the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp is less than 25 / 75, even if the proportion of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm in the total pulp fibers is 42.6% or more and the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 90.6% or more, the voids between the fibers in the absorbent article obtained from the fluff pulp sheet are likely to be uneven, leading to increased reversion 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 preferably 38 / 62, more preferably 35 / 65. If the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp exceeds 38 / 62, even if the fiber width of the hardwood bleached kraft pulp is within the specified range, the pulp sheet for fluff pulp may become dense and the water absorption rate may decrease.

[0032] (Other pulps) The pulp sheet for fluff pulp may contain pulps other than hardwood kraft pulp and softwood 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 pulps are contained, the content of such pulps is preferably 10% by mass or less of the total pulp raw material.

[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] (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.

[0035] The basis weight of the fluff pulp sheet is 200 g / m 2The lower limit of the water absorption height one minute after the start of measurement is preferably 25 mm, more preferably 27 mm, and even more preferably 29 mm. If the water absorption height one minute after the start of measurement is less than 25 mm, the fluff pulp and absorbent articles made from the pulp sheet for fluff pulp may 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 preferably 40 mm. If the water absorption height one minute after the start of measurement exceeds 40 mm, the water absorption capacity is too high, which may cause 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 increases, 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.

[0036] The basis weight of the fluff pulp sheet is 200 g / m 2 The lower limit of the water absorption rate from 1 to 2 minutes after the start of measurement is preferably 5 mm / min, more preferably 7 mm / min, and even more preferably 9 mm / min. If the water absorption rate from 1 to 2 minutes after the start of measurement is less than 5 mm / min, 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 2Even 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.

[0037] (density) The density is measured in accordance with "Paper and paperboard - Test methods for thickness, density and specific volume" as specified in JIS-P8118 (2014). The lower limit of the density of the pulp sheet for fluff pulp is 0.50 g / cm. 3 is preferred, and 0.52 g / cm 3 More preferably, 0.55 g / cm 3 The upper limit of the density of the pulp sheet for fluff pulp is 0.65 g / cm. 3 is preferred, and 0.62 g / cm 3 is more preferable, and 0.60 / cm 3 When the density of the pulp sheet for fluff pulp is within the above range, the defibration property during the manufacturing process can be improved, and fluff pulp can be obtained that easily secures uniform voids between fibers. 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).

[0038] (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 1.0 kPa m 2 / g is preferred, and 1.1 kPa m 2 / g is more preferable, and 1.2 kPa m 2If 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 1.7 kPa m 2 / g is preferred, and 1.6 kPa m 2 / g is more preferable, and 1.5 kPa m 2 / g is even 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).

[0039] [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.

[0040] (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.

[0041] (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%).

[0042] (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.

[0043] 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.

[0044] (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.

[0045] 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.

[0046] 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.

[0047] (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, other additives are added as needed to prepare the paper stock.

[0048] (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.

[0049] The pulp sheet for fluff pulp has high absorption performance and good workability during the production of fluff pulp, even when it contains wood pulp derived from broad-leaved trees.

[0050] [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.

[0051] 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.

[0052] [Absorbent articles] The absorbent article uses a fluff pulp sheet. The use of the fluff pulp sheet in 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.

[0053] 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.

[0054] <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]

[0055] 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.

[0056] [Examples 1 to 19 and Comparative Examples 1 to 5] Pulp sheets for fluff pulp of Examples 1 to 19 and Comparative Examples 1 to 5 were produced by the following procedure. Note that Comparative Example 1 reproduces the composition of an existing pulp sheet for fluff pulp that is commercially available.

[0057] (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.

[0058] (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.

[0059] (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%.

[0060] (Paper making process) The obtained hardwood kraft pulp and softwood kraft pulp were diluted to a consistency of about 2% without beating, and adjusted to the blending ratios shown in Table 2. 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 In this way, the pulp sheets for fluff pulp of Examples 1 to 19 and Comparative Examples 1 to 5 were obtained.

[0061] (Pulp fiber content at intervals of 0.02 mm in fiber length, content at intervals of 1 μm in fiber width, and standard deviation) The fiber length and fiber width of the unbleached hardwood kraft pulps of Examples 1 to 19 and Comparative Examples 1 to 5 after the cooking and washing processes were measured. The fiber length and fiber width were measured using a Valmet fiber length analyzer, "VALMET FS5," in accordance with JIS-P8226:2011 (ISO16065-2:2007) "Pulp - Fiber length measurement method by optical automatic analysis." The "VALMET FS5" fiber analyzer can measure the length and width of pulp fibers with high accuracy by analyzing the images of diluted pulp fibers as they pass through the measurement cell inside the fiber analyzer. The fiber analyzer was used to calculate the content of all pulp fibers at 0.02 mm fiber length intervals, and then the proportion of pulp fibers with lengths in the range of 0.5 mm or more and less than 1.1 mm was determined.The average content of pulp fibers in the range of 0.5 mm or more and less than 1.1 mm fiber length intervals and the standard deviation σ of the content of pulp fibers in the range of 0.02 mm fiber length intervals were calculated. The content of all pulp fibers was calculated at 1 μm fiber width intervals, and the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm was determined.The average content of pulp fibers with a fiber width of 10 μm or more and less than 35 μm was calculated for each 1 μm fiber width interval and the standard deviation σ of the content of each 1 μm fiber width interval. The standard deviation measurement values ​​were calculated from n=10,000 or more measurements using a fiber analyzer. The calculation results are shown in Table 1.

[0062] 1 to 6 show examples of the distribution of the average content values ​​for each 0.02 mm fiber length interval when totaling all pulp fibers at 0.02 mm fiber length intervals, and the average content values ​​for each 1 μm fiber width interval when totaling all pulp fibers at 1 μm fiber width intervals. FIG. 1 shows the distribution of the average content values ​​for each 0.02 mm fiber length interval for Example 1, and FIG. 2 shows the distribution of the average content values ​​for each 1 μm fiber width interval for Example 1. FIG. 3 shows the distribution of the average content values ​​for each 0.02 mm fiber length interval for Comparative Example 1, and FIG. 4 shows the distribution of the average content values ​​for each 1 μm fiber width interval for Comparative Example 1. FIG. 5 shows the distribution of the average content values ​​for each 0.02 mm fiber length interval for Comparative Example 2, and FIG. 6 shows the distribution of the average content values ​​for each 1 μm fiber width interval for Comparative Example 2.

[0063] [Table 1]

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

[0065] (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).

[0066] (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.

[0067] (Defibrillation of pulp sheets for fluff pulp) The defibration ability of each fluff pulp pulp sheet was evaluated based on the burst strength index of the fluff pulp pulp sheet using the following five-level evaluation criteria. When the evaluation was A, B, C, or D, the defibration ability of the fluff pulp pulp sheet was good, with A being the best. Furthermore, D was slightly inferior, but still acceptable for practical use. 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 m 2 / 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 0.9 kPa m 2 / g. E: Specific burst strength is 1.9 kPa m 2 / g or more or 0.8kPa m 2 / g or less.

[0068] (Klemm water 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.

[0069] (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 1 minute after the start of measurement in the Klemm water absorbency of the fluff pulp pulp sheet, and the water absorption rate was evaluated based on the water absorption rate measured 1 to 2 minutes after the start of measurement in the Klemm water absorbency. The evaluation criteria were as follows: 4 levels for absorption amount and 5 levels for absorption rate. If the absorption amount was rated A, B, or C, the fluff pulp pulp sheet had a good absorption amount. If the absorption rate was rated A, B, C, or D, the fluff pulp pulp sheet had a good absorption rate. (1) Absorption amount 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 the Klemm water absorbency measurement is 24 mm or less. (2) Water absorption rate 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 from 1 minute to 2 minutes after the start of the Klemm water absorption measurement is 4 mm / min. E: The water absorption rate during the first 1 to 2 minutes after the start of the Klemm water absorption measurement is 3 mm / min or less.

[0070] (Workability) To evaluate the workability during fluff pulp production, each pulp sheet for fluff pulp with a basis weight of 200 g / m2 was cut into 2 cm x 2 cm pieces and crushed in a commercially available mixer (Tescom Co., Ltd., Mixer TM856). The amount of paper dust generated during crushing was evaluated. The amount of pulp accumulation increased from E to A. The evaluation was based on the following five levels. Grades A, B, C, and D indicate good workability. A: When the pulp sheet is crushed, paper dust flies around and there is a small amount of pulp accumulated on the mixer walls. B: Paper dust flies when the pulp sheet is crushed, and some pulp accumulates on the mixer walls. C: Paper dust flies when the pulp sheet is crushed, and a small amount of pulp accumulates on the mixer walls. D: Paper dust flies around when the pulp sheet is crushed, and some pulp accumulates on the mixer walls, but this is not a problem. E: Paper dust was scattered during pulp sheet crushing, and a large amount of pulp accumulated on the mixer walls, making it unsuitable for practical use.

[0071] (Skin irritation from absorbent articles) Disposable diapers were made using the fluff pulp sheets of Examples 1 to 19 and Comparative Examples 1 to 5, and then a total of 220 monitors were asked to use 10 sheets each of Examples 1 to 19 and Comparative Examples 1 to 5, and the number of sheets that developed a rash was evaluated as a percentage. The evaluation was based on the following five levels. Ratings of A, B, C, and D indicate that the effect of suppressing skin rash is better than that of Comparative Example 1, which has the same composition as the existing product. A: The incidence of rash is better than that of Comparative Example 1. B: The incidence of rash is slightly better than that of Comparative Example 1. C: The incidence of rash is slightly better than that of Comparative Example 1. D: The incidence of rash is slightly better than that of Comparative Example 1, and the product is usable. E: The incidence of rash is equivalent to that of Comparative Example 1, and is at the same level as that of the existing product.

[0072] The evaluation results for each of the examples and comparative examples are shown in Table 2.

[0073] [Table 2]

[0074] As shown in Table 2, Examples 1 to 19 contain hardwood kraft pulp and softwood kraft pulp, and when all pulp fibers are counted at 0.02 mm fiber length intervals, the proportion of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm is 42.6% or more, the average content of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm for each 0.02 mm fiber length interval is 1.00% or more and 1.70% or less, and the standard deviation σ is 0.58% or less, and when all pulp fibers are counted at 1 μm fiber width intervals, the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm is 90.6% or more, the average content of pulp fibers with a fiber width of 10 μm or more and less than 35 μm for each 1 μm fiber width interval is 3.1% or more and 3.9% or less, and the standard deviation σ is 2.9% or less. These examples have good defibration ability and water absorption. Good results were obtained in terms of water absorption rate, workability during production of fluff pulp, and rash prevention effect in absorbent articles.

[0075] On the other hand, Comparative Example 1, which contained only softwood bleached kraft pulp, was inferior in defibration ability and absorption speed, and also in the effect of suppressing rashes in absorbent articles.Comparative Example 2, which contained only hardwood bleached kraft pulp, was inferior in defibration ability, absorption amount, absorption speed, workability, and the effect of suppressing rashes in absorbent articles. Furthermore, in Comparative Examples 3, 4, and 5, which did not satisfy the following conditions: the proportion of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm was 42.6% or more when totaled at 0.02 mm fiber length intervals for all pulp fibers, the average content of pulp fibers with a fiber length of 0.5 mm or more and less than 1.1 mm at each 0.02 mm fiber length interval was 1.00% or more and 1.70% or less, and the standard deviation σ was 0.58% or less; and the proportion of pulp fibers with a fiber width of 10 μm or more and less than 35 μm was 90.6% or more when totaled at 1 μm fiber width intervals, the average content of pulp fibers with a fiber width of 10 μm or more and less than 35 μm at each 1 μm fiber width interval was 3.1% or more and 3.9% or less, and the standard deviation σ was 2.9% or less, the workability during production of fluff pulp or the rash-suppressing effect in absorbent articles was inferior.

[0076] The above results demonstrate that the pulp sheet for fluff pulp has high absorption performance and good workability during the production of fluff pulp, even when it contains wood pulp derived from broad-leaved trees. [Industrial Applicability]

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

Claims

1. An absorbent article using a pulp sheet for fluff pulp, The pulp sheet for fluff pulp is Contains bleached hardwood kraft pulp and bleached softwood kraft pulp. When the content of all pulp fibers is tallied at intervals of 0.02 mm in fiber length, the proportion of pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm is 42.6% or more, and the average content of the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm at intervals of 0.02 mm in fiber length is 1.00% or more and 1.70% or less, the standard deviation σ of the content of the pulp fibers having a fiber length of 0.5 mm or more and less than 1.1 mm at intervals of 0.02 mm in fiber length is 0.41% or more and 0.58% or less; When the content of all pulp fibers is totaled at intervals of 1 μm in fiber width, the proportion of pulp fibers having a fiber width of 10 μm or more and less than 35 μm is 90.6% or more, and the average content of the pulp fibers having a fiber width of 10 μm or more and less than 35 μm at intervals of 1 μm in fiber width is 3.1% or more and 3.9% or less, An absorbent article in which the standard deviation σ of the content of the pulp fibers having a fiber width of 10 μm or more and less than 35 μm at intervals of 1 μm in fiber width is 2.5% or more and 2.90% or less.

2. 2. The absorbent article according to claim 1, wherein the mass ratio of said hardwood kraft pulp to said softwood kraft pulp is 25 / 75 or more and 38 / 62 or less.

3. 3. The absorbent article according to claim 1, wherein the content of acacia wood in the raw wood of the hardwood bleached kraft pulp is 5% by mass or more and 95% by mass or less.

4. Density is 0.50 g / cm ３ 0.65g / cm or more ３ The absorbent article according to claim 1, claim 2 or claim 3, wherein:

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

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