WO2022138870A1

WO2022138870A1 - Pulp sheet for fluff pulp

Info

Publication number: WO2022138870A1
Application number: PCT/JP2021/048036
Authority: WO
Inventors: 徹森下
Original assignee: 大王製紙株式会社
Priority date: 2020-12-24
Filing date: 2021-12-23
Publication date: 2022-06-30
Also published as: JP7238216B1; JPWO2022138870A1; CN116583642A; JP2023041874A; JP2023067942A; JP7223217B2

Abstract

A pulp sheet for fluff pulp according to one aspect of the present invention contains broad-leaved tree bleached kraft pulp and needle-leaved tree bleached kraft pulp. The mass ratio of the broad-leaved tree bleached kraft pulp relative to the needle-leaved tree bleached kraft pulp is 15/85 to 50/50, and the acacia material content of the source wood material for the broad-leaved tree bleached kraft pulp is 20 mass% to 100 mass%. It is preferable for the kappa number of the broad-leaved tree bleached kraft pulp to be 0.3 or less.

Description

Pulp sheet for fluff pulp

The present invention relates to a pulp sheet for fluff pulp.
This application claims priority based on Japanese Application No. 2020-215691 filed on December 24, 2020, and incorporates all the contents described in the above Japanese application.

Fluff pulp is produced by defibrating wood pulp by mechanical treatment, and is used as an absorbent member for absorbent articles such as disposable disposable diapers.

As the pulp for fluff pulp used for such absorbent articles, wood pulp derived from coniferous trees having good bulkiness, moisture absorption and defibency is widely used (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-21411

On the other hand, wood pulp derived from broadleaf tree is relatively cheaper than pulp derived from softwood, but wood pulp derived from broadleaf tree has a shorter fiber length and densely packed fibers than pulp derived from softwood, so that it is an absorbent article. When wood pulp derived from hardwood is used for, the absorption rate of liquid may be likely to decrease. Further, in an absorbent article, it is required to improve not only the water absorption performance but also the effect of suppressing skin irritation.

The present invention has been made based on the above circumstances, and provides a pulp sheet for fluff pulp capable of producing an absorbent article having both absorption rate and relapse property and suppressing skin irritation. With the goal.

The pulp sheet for fluff pulp according to one aspect of the present invention contains broad-leaved tree kraft pulp and softwood bleached kraft pulp, and the mass ratio of the above-mentioned broad-leaved tree bleached kraft pulp to the above-mentioned softwood bleached kraft pulp is 15/85 or more and 50/50 or less. The content of the acacia material in the raw material wood of the broad-leaved bleached kraft pulp is 20% by mass or more and 100% by mass or less.

According to the present invention, it is possible to provide a pulp sheet for fluff pulp capable of producing an absorbent article in which the amount of reversion of the water absorbing liquid is reduced and skin irritation is suppressed.

[Explanation of Embodiment of the present invention]
The pulp sheet for fluff pulp according to one aspect of the present invention contains broad-leaved tree kraft pulp and softwood bleached kraft pulp, and the mass ratio of the above-mentioned broad-leaved tree bleached kraft pulp to the above-mentioned softwood bleached kraft pulp is 15/85 or more and 50/50 or less. The content of the acacia material in the raw material wood of the broad-leaved bleached kraft pulp is 20% by mass or more and 100% by mass or less.

The fluff pulp pulp sheet contains broad-leaved kraft pulp and softwood kraft pulp in a well-balanced manner at a specific mass ratio to impart bulkiness and liquid absorbability to the absorbent article by the softwood bleached kraft pulp. , The surface density of the broad-leaved bleached kraft pulp, the effect of reducing the amount of reversion of the water-absorbing liquid, and the effect of suppressing skin irritation can be imparted. Further, since the content of the acacia material in the raw material wood of the hardwood bleached kraft pulp is 20% by mass or more and 100% by mass or less, a fixed amount or a single amount of the acacia material having a wide fiber width can be blended, so that the pulp is uniform. Since the voids between the fibers can be sufficiently secured, it is possible to further achieve both the absorption rate and the reversion property in the absorbent article. Therefore, the fluff pulp pulp sheet can provide a fluff pulp pulp sheet capable of producing an absorbent article in which the amount of reversion of the water-absorbing liquid is reduced and skin irritation is suppressed.

The copper value of the above hardwood bleached kraft pulp is preferably 0.3 or less. When the copper value of the hardwood bleached kraft pulp is 0.3 or less, the effect of suppressing skin irritation can be improved. The copper value is measured according to JIS-P8211 (2011).

[Details of Embodiments of the present invention]
Hereinafter, the pulp sheet for fluff pulp according to the embodiment of the present invention will be described in detail. Unless otherwise specified, the blending amount (absolute dry internal addition amount) of each material to be blended in the pulp sheet base material described below refers to the mass ratio of the pulp of the pulp sheet base material to the absolute dry mass.

<Pulp sheet for fluff pulp>
The pulp sheet for fluff pulp can be obtained by making a slurry containing raw material pulp.

(Raw material pulp)
As the raw material pulp, for example, virgin pulp can be used. As the raw material pulp used for the above-mentioned pulp sheet for fluff pulp, chemical pulp is preferable. As the chemical pulp, a combination of softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP) is preferable. Since the pulp sheet for fluff pulp contains softwood bleached kraft pulp, the bulkiness of the absorbent article and the absorbability of the liquid can be improved. In addition, since the pulp sheet for fluff pulp contains hardwood bleached kraft pulp, the fineness of the surface of the absorbent article is enhanced, the effect of reducing the amount of reversion of the water absorbing liquid of the absorbent article and the effect of suppressing skin irritation are improved. can.

(Hardwood bleached kraft pulp)
As the hardwood bleached kraft pulp, hardwood bleached kraft pulp produced from acacia wood or eucalyptus wood is preferable.

Acacia lumber is a material that does not shrink due to drying, is strong against impact, is strong and hard, and the pulp obtained from acacia lumber inherits the original properties, and is a useful raw material pulp with high moisture absorption and drying properties. Is. Eucalyptus wood belongs to the genus Eucalyptus, and in particular, Eucalyptus globulus, Eucalyptus grandis, Eucalyptus europhila, Eucalyptus nighttens, Eucalyptus regnance, etc. have been widely used as raw material pulp materials for paper production from ancient times, and the resulting pulp is The fiber cavity (lumen) is hard to be crushed and is rigid, and by blending this pulp fiber, a bulky and low density pulp sheet for fluff pulp can be obtained. As for hardwood bleached kraft pulp, acacia wood has a wider fiber width than eucalyptus wood, so it is bulky, and when combined with softwood bleached kraft pulp, the absorption rate of liquid does not decrease much, so acacia wood is more suitable. preferable.

(Content of acacia wood in the raw wood of hardwood kraft pulp)
The lower limit of the content of acacia wood in the raw wood of the hardwood kraft pulp is preferably 20% by mass, more preferably 50% by mass. The upper limit of the content of the acacia material is preferably 100% by mass, more preferably 80% by mass. Since the content of acacia in the raw wood of the broadleaf kraft pulp of the fluff pulp pulp sheet is within the above range, the fiber length is shorter than that of the coniferous bleached kraft pulp, and the fibers are easily clogged with each other. Even if the fibers are oriented in any direction (for example, the length direction, the width direction, and the thickness direction of the absorbent article), the voids between the fibers can be uniformly secured particularly well. , It is possible to achieve both the absorption rate and the reversion property required for the pulp sheet for fluff pulp. If it is out of the above range, for example, if the proportion of rigid eucalyptus material is large, the voids derived from rigidity will increase, but the voids are likely to vary depending on the direction in which the fibers are oriented. It is not preferable that the absorption rate and the reversion property are likely to be uneven in the article, and as a result, these performances are likely to be deteriorated.

The lower limit of the average fiber width of hardwood unbleached kraft pulp is preferably 16.7 μm, more preferably 16.9 μm. If the average fiber width is less than the above lower limit, the voids between the fibers become dense in the absorbent article, the absorption rate may decrease, and fogging may easily occur. On the other hand, the upper limit of the average fiber width is preferably 18.2 μm, more preferably 17.7 μm. If the average fiber width exceeds the upper limit, the contact area between the pulp fibers in the pulp sheet for fluff pulp becomes too large, the bonding force between the fibers becomes high, and the pulverizability during the manufacturing process may decrease. .. If the pulverizability is too low, the absorbent article may be overcrushed and fine fibers may be generated in the manufacturing process of the absorbent article, and the absorption rate of the absorbent article may be lowered. Here, the "average fiber width" means the weight average fiber width. The weight average fiber width was determined by using a fiber length measuring machine "FiberLab" manufactured by Metso Automation Co., Ltd. to obtain the JAPAN TAPPI pulp and paper test method No. 52 Measure fibers with a fiber length of 0.1 mm or more according to "Pulp and Paper-Fiber Length Test Method-Optical Automatic Measurement".

The lower limit of the weight average fiber length (hereinafter, also referred to as the average fiber length) of the hardwood unbleached kraft pulp is preferably 0.76 mm, more preferably 0.80 mm. If the average fiber length is less than the above lower limit, the bulkiness of the pulp sheet for fluff pulp tends to decrease, and the pulverizability during the manufacturing process may decrease. On the other hand, the upper limit of the average fiber length is preferably 0.92 mm, more preferably 0.86 mm. When the average fiber length exceeds the upper limit, the voids are likely to vary depending on the direction in which the fibers are oriented in the absorbent article, and the absorption rate and the reversability may decrease. The weight average fiber length was determined by using a fiber length measuring machine "FiberLab" manufactured by Mezzo Automation Co., Ltd., and the JAPAN TAPPI pulp and paper test method No. 52 Measure fibers with a fiber length of 0.1 mm or more according to "Pulp and Paper-Fiber Length Test Method-Optical Automatic Measurement".

The copper value of the above hardwood bleached kraft pulp is preferably 0.3 or less. If the copper value exceeds the upper limit, the lignin in the fiber cannot be sufficiently removed, the water absorption of the pulp fiber becomes low, the amount of reversion is reduced, and fog may easily occur.

The lower limit of the sulfurization degree of the white liquor for evaporating hardwood kraft pulp is preferably 25%, more preferably 28%. If the sulfurization degree is less than 25%, the pulp fibers tend to be painful and the absorbent articles become dense, so that the absorption rate tends to decrease and fog may occur. On the other hand, the upper limit of the sulfurization degree is preferably 32%, more preferably 30%. When the sulfurization degree exceeds the upper limit, the pulp fibers are less likely to be painful and remain rigid, the voids of the absorber become uneven, the amount of reversion is likely to decrease, and fogging may occur. The above-mentioned sulfurization degree is calculated as the ratio of sodium sulfide to the total of sodium sulfide and caustic soda according to the following formula.
Degree of sulfurization (%) = (Na ₂ S / (NaOH + Na ₂ S)) × 100

(Freeness of unbeaten pulp of hardwood bleached kraft pulp)
The Canadian standard freeness (CSF) of unbeaten pulp of hardwood bleached kraft pulp is preferably adjusted to 520 ml or more and 580 ml or less. If the freeness of unbeaten pulp of broadleaf bleached kraft pulp is less than 520 ml, the dehydration property deteriorates during the production of pulp sheets, and it is necessary to mechanically enhance the dehydration, for example, by strengthening the press dehydration in a paper machine. Not only the bond between the pulp sheets becomes stronger, but also the bulkiness of the pulp sheet becomes lower, which may reduce the pulverizability at the time of manufacturing. On the other hand, when the Canadian standard freeness of the unbeaten pulp exceeds 580 ml, the voids between the fibers become too large in the pulp sheet, and crushing unevenness is likely to occur during pulverization, and in the absorbent article, the reversion is reduced and fog is generated. It may be more likely to occur.

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. On the other hand, the upper limit of the content of the hardwood bleached kraft pulp is preferably 50% by mass, more preferably 40% by mass. The above-mentioned "content of broad-leaved bleached kraft pulp in fluff pulp pulp sheet" is the same even when it contains other pulp other than broad-leaved bleached kraft pulp and softwood bleached kraft pulp. Since the content of the broad-leaved bleached kraft pulp is in the above range, the fibers are particularly good even in the broad-leaved bleached kraft pulp having a short fiber length and easily clogged with each other when mixed with the coniferous bleached kraft pulp. Since the gap between them can be secured, it is possible to achieve both the absorption rate and the reversion property required for the pulp sheet for fluff pulp.

(Coniferous bleached kraft pulp)
In the pulp sheet for fluff pulp, pine trees typified by radiata pine and various cedars are preferably used as the raw material wood for coniferous bleached kraft pulp.

(Pulp content)
The lower limit of the mass ratio of the broadleaf tree bleached kraft pulp to the softwood bleached kraft pulp in the pulp used for the fluff pulp 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, the voids between the fibers in the absorbent article are likely to be uneven, and there is a possibility that reversion is likely to occur and fogging is likely to occur. 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, the absorbent articles may become dense, the absorption rate may decrease, and fogging may easily occur.
Since the mass ratio of the broad-leaved bleached kraft pulp to the coniferous bleached kraft pulp is within the above range, even if the broad-leaved bleached kraft pulp having a short fiber length and the fibers are easily clogged with each other is mixed in the coniferous bleached kraft pulp. , Regardless of the direction in which the bleached kraft pulp fibers are oriented, the voids between the fibers can be secured evenly and uniformly. Therefore, the absorption rate required for the pulp sheet for fluff pulp and the effect of suppressing reversion and fog required for the absorbent article can be improved.

(Other pulp)
The pulp sheet for fluff pulp may contain other pulps other than hardwood kraft pulp and softwood kraft pulp. Examples of the other pulp include soda pulp, sulfite pulp, chemithermomechanical pulp, chemilifiner mechanical pulp, thermochemimechanical pulp and the like. However, when the lignin in the fiber is not sufficiently removed, the water absorption of the pulp fiber is lowered, the amount of reversion is reduced, and fogging is likely to occur. Therefore, bleached pulp from which the lignin is sufficiently removed is preferable. When the other pulp is contained, the content of the other pulp is preferably 10% by mass or less based on the total pulp raw material.

(Other additives)
If necessary, other additives can be added to the pulp sheet for fluff pulp. Additives include, for example, fillers, pigments, sizing agents, coagulants, oil resistant agents, aluminum sulfate bands, yield improvers, drainage improvers, dry paper strength enhancers, wet paper strength enhancers, colored pigments, and water resistant agents. Etc. can be used alone or in combination of two or more.

[Physical characteristics of pulp sheet for fluff pulp]
(Basis weight)
The basis weight is measured in accordance with "Paper and Paperboard-Measurement Method of Basis Weight" described in JIS-P8124 (2011). The basis weight of the pulp sheet for fluff pulp can be, for example, 300.0 g / cm ² or more and 1500.0 g / cm ² or less.

(density)
Density is measured according to "Paper and Paperboard-Test Methods for Thickness, Density and Specific Volume" described in JIS-P8118 (2014). As the lower limit of the density of the pulp sheet for fluff pulp, 0.52 g / cm ³ is preferable, and 0.53 g / cm ³ is more preferable. The upper limit of the density of the pulp sheet for fluff pulp is preferably 0.60 g / cm ³ and more preferably 0.59 g / cm ³ . When the density of the pulp sheet for fluff pulp is within the above range, it is possible to improve the crushability in the manufacturing process of the pulp sheet for fluff pulp, which is a mixture of the bleached broadleaf kraft pulp and the bleached coniferous kraft pulp, and to make it even and uniform. It is possible to obtain an absorbent article that easily secures voids between fibers. Therefore, it is possible to obtain an absorbent article capable of achieving a good balance between the absorption rate, which is the contradictory performance of the absorbent article, and the amount of reversion of the water-absorbing liquid.
The density is measured in an atmosphere of 23 ± 1 ° C. and 50 ± 2% RH as described in “Paper, Paperboard and Pulp-Standard Temperature for Humidity Control and Testing” described in JIS-P8111 (1998). ..

(Ratio burst strength)
The specific burst strength is a value obtained by dividing the burst strength of paper expressed in kilopascals (kPa) units measured in accordance with JIS-P8131 (2009) by the basis weight. As the lower limit of the specific burst strength, 1.20 kPa · m ² / g is preferable, and 1.22 kPa · m ² / g is more preferable. When the specific burst strength of the pulp sheet for fluff pulp is less than 1.20 kPa · m ² / g, it becomes overcrushed and the fibers are easily cut, so that the absorbent article becomes dense, the absorption rate decreases, and fog occurs. It may be easier to do. On the other hand, as the upper limit of the specific burst strength of the pulp sheet for fluff pulp, 1.58 kPa · m ² / g is preferable, and 1.44 kPa · m ² / g is more preferable. When the specific burst strength of the pulp sheet for fluff pulp exceeds 1.58 kPa · m ² / g, the pulverizability during the manufacturing process is poor, and the obtained absorbent article has many voids, so that the water absorbing liquid reverts. There is a risk that fogging will occur easily as well as being easy to do. When the specific burst degree of the pulp sheet for fluff pulp is within the above range, the crushability during the manufacturing process can be improved in the pulp sheet for fluff pulp in which the above-mentioned broad-leaved bleached kraft pulp and the coniferous bleached kraft pulp are mixed. In the absorbent article, it becomes easy to secure the voids between the fibers evenly and uniformly, so that the absorption rate of the absorbent article and the reversion amount of the water-absorbing liquid, which are contradictory performances, can be balanced and both can be improved.
The specific burst degree measurement is performed in an atmosphere of 23 ± 1 ° C. and 50 ± 2% RH as described in “Paper, Paperboard and Pulp-Standard Temperature for Humidity Control and Testing” described in JIS-P8111 (1998). Measure with.

[Manufacturing method of pulp sheet for fluff pulp]
The method for producing the pulp sheet for fluff pulp is not particularly limited, but for example, a cooking step of cooking raw wood to make unbleached pulp, a delignin step of delignin, and bleaching to bleach to make bleached pulp. It has a step, a beating step of beating the bleached pulp so as to have a desired freeness, and a step of making a pulp slurry. A dehydration cleaning step can be appropriately provided between the steps.

(Creating process)
In the cooking process, the raw wood is steamed to make unbleached pulp. White liquor and raw wood chips (broad-leaved or coniferous trees) are put into a cooking kettle and steamed, and a pulp slurry containing the produced black liquor (unwashed) is taken out from the bottom of the continuous cooking kettle. The cooking method can be arbitrarily selected from commercially available craft improvement methods such as MCC, EMCC, ITC, Lo-Solids, KobudoMari, and Compact method, and the cooking pot may be either a continuous cooking pot or a batch pot. Further, the cooking conditions (H factor combined into one factor by multiplying the cooking temperature, the influence of the cooking temperature and the cooking time, the content ratio of the active alkali or the effective alkali, etc.) are not particularly limited.

(De-lignin process)
In the delignin step, unbleached pulp is delignin. Alkaline chemicals and oxygen are added to unbleached pulp, and lignin is decomposed at high temperature and high pressure and eluted with alkaline chemicals. The delignin step is not particularly limited to a method having a low concentration (pulp concentration: 3% to 8%), a medium concentration (pulp concentration: 8% to 15%), and a high concentration (pulp concentration: 20% to 30%).

(Washing process)
In the washing step, washing is performed by substituting, diluting or dehydrating the unbleached pulp. The cleaning method is not particularly limited, and cleaning can be performed using a known cleaning machine. For example, a replacement cleaning method, a dilution / dehydration method, a press cleaning method, or a cleaning method combining these methods is used. As the replacement cleaning type washing machine, a diffusion washer, a pressurized diffusion washer, a belt type washing machine and the like are used. As the dilution / dehydration type washer, a vacuum filter washer, a pressure washer, and the like are used. As the press cleaning method, a screw type press cleaning machine, a disc type press cleaning machine, a roll type press cleaning machine and the like are used.

In the present invention, it is preferable to remove lignin and reduce the copper value, so it is preferable to use a press washer that can easily remove lignin. The pulp concentration after washing by the press washing method is preferably 30% or more, more preferably 32% or more, still more preferably 35% or more. In dehydration by the press washing method, the water inside the fiber can also be squeezed out and removed, so that it is easier to sufficiently remove the lignin freed inside the pulp fiber as compared with other washing methods.

(Bleach process)
In the bleaching process, unbleached pulp that has been deligninized is bleached to obtain bleached pulp. The bleaching method is not particularly limited, and bleaching can be performed by a known bleaching method. For example, acid treatment, ozone bleaching, chlorine dioxide bleaching, hydrogen peroxide bleaching, and alkali extraction with these, alkali extraction with oxygen added, alkali extraction with oxygen and hydrogen peroxide added, etc. are carried out individually or in combination. can do.

In the bleaching step, it is preferable to use ozone bleaching, which can adjust the water absorption and reversion property of the pulp fiber by damaging the pulp fiber. The ozone bleaching method is not particularly limited, and any of high concentration (30% to 40%), medium concentration (8% to 15%), and low concentration (1% to 3%) can be used, but more fibers can be used. A high concentration method that is easily damaged is preferable.
As the ozone generator, a known device can be used. The generated ozone may be mixed with pulp as it is, or may be dissolved in water and then mixed with pulp.

In ozone bleaching, the lower the pH, the more the delignin is promoted, but the more the fiber is damaged, so it is preferable to adjust the pH according to the required quality of the pulp sheet for fluff pulp. The pH of the pulp sheet for fluff pulp in ozone bleaching is preferably 6 or less, more preferably 4 or less, still more preferably 2 to 3. It is preferable that the pH of the pulp sheet for fluff pulp in ozone bleaching is in the above range because it is easy to achieve both the absorption rate and the reversion property required for the pulp sheet for fluff pulp.

(Preparation process)
If necessary, the preparation process beats the bleached pulp to the desired freeness. Then, an additive corresponding to each paper layer is added to the slurry obtained by dispersing the pulp fiber in water as necessary and mixed to prepare a paper material for each paper layer.

(Papermaking process)
Next, using these raw material slurries, paper is made with a paper machine in the neutral range so that the pH is 6 or more and 8 or less. In the papermaking process, the raw material pulp is made using a paper machine that makes the pulp raw material ejected onto the traveling wire. The paper machine is not particularly limited, and a known paper machine such as a long net paper machine, a circular net paper machine, a hybrid former, a gap former, or the like can be used, and the paper is made into a sheet. To. The pulp sheet for fluff pulp can be produced by laminating one layer or a plurality of layers, but one layer is preferable because it is easy to make the density in the layer uniform.

According to the pulp sheet for fluff pulp, it is possible to produce an absorbent article that has both absorption rate and reversion property and suppresses skin irritation.

[Fluff pulp]
The fluff pulp can be obtained by defibrating the fluff pulp pulp sheet into fibers by mechanical treatment. The pulp sheet for fluffed pulp used for the fluffed pulp in the present invention may be in the form of a veil or a roll, but if it is in the form of a roll, it is preferable because it is easy to improve the productivity of the absorbent article.

In the present invention, the apparatus used for fluffing, that is, mechanical processing for defibrating is not particularly limited. A known defibrator used for manufacturing absorbent articles such as disposable diapers can be used, and a defibrator that utilizes frictional force or shearing force as a mechanical treatment can be preferably used. As a method of the defibrating machine used for fluffing, for example, a hammer type crusher, an impact type crusher, a roll type crusher, a shet airflow type crusher and the like can be used.

[Absorbable article]
The absorbent article is an absorbent article using the pulp sheet for fluff pulp. Since the absorbent article uses the pulp sheet for fluff pulp, it is possible to achieve both an absorption rate and a reversion property, and it is possible to suppress skin irritation. The absorbent article is not particularly limited, and examples thereof include disposable diapers, urine absorbing pads, light incontinence pads, and sanitary napkins.

The method for producing the absorbent article is not particularly limited, and it can be produced by a known method. For example, a disposable diaper can be manufactured by a manufacturing machine manufactured by Mizuko Co., Ltd., Toa Kiko Co., Ltd., or Airhal Trimer Co., Ltd., for example, by a panel type, a leghole type, a vertical flow type, a horizontal flow type, or the like.

<Other embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[Examples 1 to 14 and Comparative Examples 1 to 4, Reference Example 1]
The pulp sheets for fluff pulp of Examples 1 to 14 and Comparative Examples 1 to 4 were prepared by the following procedure.

(Creating process)
(1) Hardwood Acacia and eucalyptus are mixed so as to have a predetermined mass ratio, a white liquid having a predetermined sulfide degree is added, and a liquid ratio of 6.0 (L / kg) and a maximum temperature of 170 ° C. are used by a rotary autoclave. It was steamed to obtain unbleached kraft pulp having a copper value of about 16.
(2) Unbleached kraft with a copper value of about 30 by adding a white liquid having a predetermined sulfide degree to coniferous cedar and cooking it with a rotary autoclave at a liquid ratio of 6.0 (L / kg) and a maximum temperature of 170 ° C. Obtained pulp.

(Washing process)
After diluting the unbleached pulp to a pulp concentration of about 2%, No. 1 was placed in the Buchner funnel. 2 Filter paper (manufactured by ADVANTEC) was laid and the pulp concentration was dehydrated to about 12%. Then, in the case of press dehydration shown in Table 1, the unbleached pulp was sandwiched between square filter papers (manufactured by ADVANTEC) and pressure was applied with a press machine to dehydrate the pulp to a pulp concentration of 33%. This washing step was performed twice with and without press dehydration.

(Bleach process)
(1) Hardwood (1-1) Acid-treated Unbleached kraft pulp was prepared at a pulp concentration of 10% and pH 3.0, and acid-treated at 90 ° C. for 3 hours.
(1-2) Ozone bleaching The acid-treated pulp was ozone bleached at 45 ° C. with 8.1% concentration ozone gas for about 2 minutes. For ozone bleaching, ozone gas from a laboratory ozone generator of PSA Ozonizer SGA-01A-PSA4 manufactured by Sumitomo Precision Products Co., Ltd. was used.
(1-3) Chlorine dioxide bleaching The pulp after ozone bleaching is bleached with chlorine dioxide at a chlorine dioxide addition rate of 1.5%, a pulp concentration of 10% by mass, and 70 ° C. Obtained pulp.
In addition, during each bleaching step, after diluting to a pulp concentration of about 2%, the Büchner funnel was filled with No. Two filter papers (manufactured by ADVANTEC) were laid, and a dilution washing step of dehydrating the pulp concentration to about 12% was carried out twice.
(2) The unbleached kraft pulp of softwood was bleached with chlorine dioxide for 30 minutes at 70 ° C. with a chlorine dioxide addition rate of 1.5% and a pulp concentration of 10% by mass. Subsequently, alkaline hydrogen peroxide bleaching was performed at an alkali addition rate of 1%, a hydrogen peroxide addition rate of 0.3%, a pulp concentration of 10% by mass, and 70 ° C. for 120 minutes. Subsequently, alkali treatment was carried out at 70 ° C. with a sodium hydroxide addition rate of 0.2% and a pulp concentration of 10% by mass for 120 minutes. Subsequently, chlorine dioxide bleaching was carried out at a chlorine dioxide addition rate of 0.3%, a pulp concentration of 10% by mass, and 70 ° C. for 150 minutes to obtain softwood bleached kraft pulp.
In addition, during each bleaching step, after diluting to a pulp concentration of about 2%, the Büchner funnel was filled with No. Two filter papers (manufactured by ADVANTEC) were laid, and a dilution washing step of dehydrating the pulp concentration to about 12% was carried out twice.

(Papermaking process)
The obtained bleached kraft pulp is diluted to a concentration of about 2% without beating, and then hand-cut to a basis weight of 800 g / m ² using a semi-automatic sheet machine (manufactured by Kumagai Riki Kogyo Co., Ltd.). It was created. In this way, pulp sheets for fluff pulp of Examples 1 to 14 and Comparative Examples 1 to 4 were obtained.

Various evaluations were made on the pulp sheet for fluff pulp obtained as described above.

(Weight average fiber length and weight average fiber width of pulp fiber)
The weight average fiber length and weight average fiber width of the hardwood unbleached kraft pulp (copper value of about 16) of Examples 1 to 14 and Comparative Examples 1 to 4 after the cooking step and the washing step were measured. The weight average fiber length and the weight average fiber width were determined by using a fiber length measuring machine "FiberLab" manufactured by Mezzo Automation Co., Ltd., and the JAPAN TAPPI pulp and paper test method No. According to 52 "Pulp and Paper-Fiber Length Test Method-Optical Automatic Measurement", fibers with a fiber length of 0.1 mm or more were measured. The fiber analyzer "FiberLab" can measure the length and width of the pulp fiber with high accuracy by image analysis when the diluted pulp fiber passes through the measurement cell inside the fiber analyzer.

(Density of pulp sheet for fluff pulp)
The density of each pulp sheet for fluff pulp was measured according to "Paper and Paperboard-Test Method for Thickness, Density and Specific Volume" described in JIS-P8118 (2014).

(Specific burst strength of pulp sheet for fluff pulp)
For the specific burst strength of each pulp sheet for fluff pulp, the burst strength of paper expressed in kilopascals (kPa) units measured in accordance with JIS-P8131 (2009) was divided by the basis weight.

(Crushability of pulp sheet for fluff pulp)
As for the crushability of each fluff pulp pulp sheet, 5 g of fluff pulp cut into 10 mm × 10 mm is placed in a laboratory mixer and the pulp is crushed. Then, the state of the pulp was confirmed every 10 seconds, and the time until the pulp mass disappeared was measured. If the pulverizability is inferior, unevenness may occur in the absorbability and reversion of the liquid in the absorber, and the performance of both may deteriorate. The evaluation was made according to the following four stages based on Reference Example 1 of 100% coniferous trees. When the evaluations are A and B, the pulverizability in the pulp sheet for fluff pulp is good.
A: It can be handled in the same defibration time as the fluff pulp of Reference Example 1.
B: It takes a little longer to defibrate than the fluff pulp of Reference Example 1, but it can be actually used.
C: It takes longer to defibrate than the fluff pulp of Reference Example 1, but it can be actually used.
D: The time required for defibration is clearly longer than that of the fluff pulp of Reference Example 1, and it cannot be used in practice.

(Absorption rate of fluff pulp)
As a procedure for measuring the absorption rate of each fluff pulp, 5 g of fluff pulp first cut into 10 mm × 10 mm was placed in a laboratory mixer and pulverized. Next, 0.5 g of the pulverized pulp prepared in the above pulverizability test was compressed into a disk shape to prepare a sample, and then the time until the sample was dropped on the water surface and settled under the water surface was measured. The evaluation was made according to the following four stages based on Reference Example 1 of 100% coniferous trees. When the evaluation is A and B, the absorption rate in the fluff pulp is good.
A: It is equivalent to the fluff pulp of Reference Example 1 and quickly settles.
B: It takes a little longer to settle than the fluff pulp of Reference Example 1, but it can be actually used.
C: It takes longer to settle than the fluff pulp of Reference Example 1, but it can be actually used.
D: It is clearly slower to settle than the fluff pulp of Reference Example 1, and cannot be used in practice.

(Amount of reversion of water-absorbing liquid in absorbent articles)
The amount of reversion indicates the amount of reversion of the liquid absorbed by the absorber and released by applying pressure to the absorber. The amount of reversion of the water-absorbing liquid is determined by preparing a paper diaper using the pulp sheets for fluff pulp of Examples 1 to 14 and Comparative Examples 1 to 4, and then applying artificial urine to the absorber multiple times at intervals. Absorb. A filter paper was placed on the absorber, a load was applied, and the weight of the artificial urine absorbed by the filter paper was measured. The evaluation was made according to the following four stages based on Reference Example 1 of 100% coniferous trees. When the evaluations are A, B and C, the effect of suppressing the reversion of the water-absorbing liquid in the absorbent article is good.
A: The amount of reversion is smaller than that of the fluff pulp of Reference Example 1.
B: The amount of reversion is equivalent to that of the fluff pulp of Reference Example 1.
C: Although the amount of reversion is slightly larger than that of the fluff pulp of Reference Example 1, it can be actually used.
D: The amount of reversion is larger than that of the fluff pulp of Reference Example 1, and it cannot be actually used.

(Skin irritation of absorbent articles)
After making paper diapers using the pulp sheets for fluff pulp of Examples 1 to 14, Comparative Examples 1 to 4, and Reference Example 1, 50 monitors each used 10 sheets each, and rash occurred. The number of sheets generated was evaluated as a percentage. The evaluation was based on Example 1 in the following four stages. When the evaluation is A, B and C, the effect of suppressing skin rash is good.
A: The fog occurrence rate is superior to that of Reference Example 1.
B: The fog occurrence rate is slightly superior to that of Reference Example 1.
C: The fog occurrence rate is the same as that of Reference Example 1, and it can be actually used.
D: The fog occurrence rate is higher than that of Reference Example 1, and it cannot be actually used.

Table 2 shows the evaluation results of each example and comparative example.

As shown in Table 2, 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, and the content of acacia material in the raw wood of the hardwood bleached kraft pulp is 20 mass. In Examples 1 to 14 of% or more and 100% by mass or less, the crushability in the pulp sheet for fluff pulp, the absorption rate in the fluff pulp, the reversion amount of the water absorbing liquid in the absorbent article, and the effect of suppressing skin irritation. Good results were obtained in all cases.

On the other hand, Comparative Example 1 in which the content of the acacia material in the raw wood of the hardwood bleached kraft pulp was less than 20% by mass was inferior in the absorption rate in the fluff pulp and the effect of suppressing skin irritation in the absorbent article. In Comparative Example 2 in which the mass ratio of the hardwood bleached kraft pulp to the softwood bleached kraft pulp is less than 15/85, the pulverizability of the pulp sheet for fluff pulp is inferior, and the amount of reversion of the water absorbing liquid in the absorbent article is large. The effect of suppressing skin irritation was inferior. This is because when the amount of water absorption in the absorbent article is large, pressure is applied by the movement of the body even after the absorption of urine, and the urine returns to the surface of the absorbent article and touches the skin, causing rash. It is thought that it will be easier. Comparative Example 3 in which the mass ratio of the broadleaf bleached kraft pulp to the softwood bleached kraft pulp is more than 50/50 and the mass ratio is very high is the crushability and absorption rate in the pulp sheet for fluff pulp, and the absorbent article. The effect of suppressing skin irritation was inferior. It is considered that this is because the absorption rate of the pulp sheet for fluff pulp is slowed down, so that the contact time between excrement such as urine and the skin becomes long when the absorbent article is worn, and rash is likely to occur. Further, in Comparative Example 4 in which the mass ratio of the hardwood bleached kraft pulp slightly exceeded 50/50, the effect of suppressing skin irritation was inferior.

As a result of the above, it was shown that the absorbent article using the pulp sheet for fluff pulp has a good effect of reducing the amount of reversion of the water absorbing liquid and an effect of suppressing skin irritation.
The pulp sheet for fluff pulp of the present invention is suitable for an absorbent article.

Claims

Contains hardwood kraft pulp and softwood kraft pulp,
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.
A pulp sheet for fluff pulp having an acacia material content of 20% by mass or more and 100% by mass or less in the raw wood of the hardwood bleached kraft pulp.
The pulp sheet for fluff pulp according to claim 1, wherein the hardwood bleached kraft pulp has a copper value of 0.3 or less.