Pulp sheet for fluff pulp, fluff mat, absorbent article, and manufacturing method of pulp sheet for fluff pulp

Abstract

To provide a pulp sheet for fluff pulp with suppressed discoloration and excellent fibrillation properties.SOLUTION: In a pulp sheet for fluff pulp containing a conifer pulp, a pulp sheet for fluff pulp is characterized in that a content of a hardwood pulp in a total pulp component in the pulp sheet for fluff pulp is 30 mass% or under, ISO whiteness variation calculated by the following formula is 1.5% or under. ISO whiteness variation (%)=(B0(%)-B1(%)) / B0(%)×100; in the formula above, B1 is ISO whiteness of the pulp sheet for fluff pulp after heating at 105°C for 2 hrs measured according to JIS P 8154-1:2008, and B0 is ISO whiteness of the pulp sheet for fluff pulp before heating.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pulp sheet for fluff pulp, a fluff mat, an absorbent article, and a method for producing a pulp sheet for fluff pulp. [Background technology]

[0002] Fluff pulp is wood pulp that has been defibrated until it becomes cotton-like. Fluff pulp is used as a water-absorbing material in absorbent articles such as disposable diapers and sanitary napkins.

[0003] Conventionally, fluff pulp used in absorbent articles is made from softwood pulp, which has good defibration properties (for example, Patent Document 1). In Patent Document 1, fluff pulp is obtained by mechanically defibrating raw material pulp (softwood bleached kraft pulp) with a moisture content of 35% or less.

[0004] Furthermore, Patent Document 2 discloses a pulp sheet for fluff pulp containing bleached hardwood kraft pulp and bleached softwood kraft pulp. In this document, it is studied to obtain a pulp sheet for fluff pulp that can reduce the amount of absorbed liquid returning and prevent skin rash by adjusting the content ratio of bleached hardwood kraft pulp and bleached softwood kraft pulp within a predetermined range. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-211411 [Patent Document 2] International Publication No. 2022 / 138870 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, pulp sheets for fluff pulp containing bleached hardwood kraft pulp or bleached softwood kraft pulp are known, but conventional pulp sheets for fluff pulp tend to discolor under high temperature conditions and the defibration properties of the pulp sheets for fluff pulp are sometimes insufficient, so improvements were needed.

[0007] Therefore, in order to solve the problems of the conventional technology, the present inventors have conducted research with the aim of providing a pulp sheet for fluff pulp that is inhibited from fading and has excellent defibration properties. [Means for solving the problem]

[0008] Examples of specific embodiments of the present invention are given below.

[0009] [1] A pulp sheet for fluff pulp containing softwood pulp, The content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 30% by mass or less, A pulp sheet for fluff pulp, having an ISO brightness change of 1.5% or less as calculated by the following formula: ISO whiteness change (%) = (B0 (%) - B1 (%)) / B0 (%) x 100 In the above formula, B1 is the ISO brightness of the pulp sheet for fluff pulp measured in accordance with JIS P 8154-1:2008 after heating at 105°C for 2 hours, and B0 is the ISO brightness of the pulp sheet for fluff pulp before heating. [2] Pulp sheets for fluff pulp contain softwood pulp; The pulp sheet for fluff pulp according to [1], wherein the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 15 mass% or less. [3] A fluff mat formed from the fluff pulp sheet described in [1] or [2]. [4] An absorbent article comprising the fluff mat described in [3]. [5] The method includes a cooking step of cooking a pulp raw material to produce unbleached pulp, a bleaching step, a color adjustment step, and a sheeting step, The color adjustment step is performed after the bleaching step, A method for producing a pulp sheet for fluff pulp, in which hydrogen peroxide treatment is carried out in the color adjustment step. [6] A method for producing a pulp sheet for fluff pulp according to [5], wherein in the color adjustment process, a heating treatment is carried out so that the pulp slurry temperature is 30°C or higher and 100°C or lower. [7] A method for producing a pulp sheet for fluff pulp according to [6], wherein the heating treatment time in the color adjustment step is 10 minutes or more and 120 minutes or less. [Effects of the Invention]

[0010] According to the present invention, a pulp sheet for fluff pulp can be obtained that is inhibited from fading and has excellent defibration properties. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] (Fluff pulp sheet) This embodiment relates to a pulp sheet for fluff pulp containing softwood pulp, in which the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 30 mass% or less. The pulp sheet for fluff pulp of this embodiment has an ISO brightness change of 1.5% or less, calculated by the following formula: ISO whiteness change (%) = (B0 (%) - B1 (%)) / B0 (%) x 100 In the above formula, B1 is the ISO brightness of the pulp sheet for fluff pulp measured in accordance with JIS P 8154-1:2008 after heating at 105°C for 2 hours, and B0 is the ISO brightness of the pulp sheet for fluff pulp before heating.

[0013] In this specification, "fluff pulp" refers to defibrated pulp, i.e., pulp that has been fiberized or shredded. Also, a "pulp sheet for fluff pulp" refers to a pulp sheet before defibration that is used to produce fluff pulp. In other words, by defibrating a "pulp sheet for fluff pulp," "fluff pulp" is obtained, and the "fluff pulp" formed into a sheet is called a "fluff mat." In this embodiment, a "pulp sheet for fluff pulp" is obtained, for example, by papermaking a slurry containing raw material pulp.

[0014] In this embodiment, the ISO brightness of the pulp sheet for fluff pulp is measured in accordance with JIS P 8148:2018. At this time, the ISO brightness of the pulp sheet for fluff pulp is measured before and after heating at 105°C for 120 minutes. Then, the change in ISO brightness is calculated using the following formula. ISO whiteness change (%) = (B0 (%) - B1 (%)) / B0 (%) x 100 In the above formula, B1 is the ISO brightness of the pulp sheet for fluff pulp measured in accordance with JIS P 8154-1:2008 after heating at 105°C for 2 hours, and B0 is the ISO brightness of the pulp sheet for fluff pulp before heating. The ISO whiteness change is preferably 1.5% or less, more preferably 1.3% or less, and even more preferably 1.1% or less. The lower limit of the ISO whiteness change is not particularly limited and may be 0%.

[0015] In this embodiment, for example, in the manufacturing process of a pulp sheet for fluff pulp, a color adjustment step is performed after bleaching the pulp raw material, and hydrogen peroxide treatment is performed in the color adjustment step, thereby adjusting the ISO brightness change to a desired range. It is also preferable to heat the pulp under appropriate conditions in the color adjustment step. Furthermore, by appropriately adjusting the raw pulp material, it is also easy to adjust the ISO brightness change to a predetermined range.

[0016] The pulp sheet for fluff pulp of this embodiment has good defibration properties when fluffed. In this specification, defibration properties can be evaluated by the defibration time (seconds) required until all undefibrated material is gone. Specifically, the shorter the defibration time, the better the defibration property can be determined, and good defibration property can increase the production efficiency of fluff mats. Furthermore, good defibration property makes it easier to obtain a fluff mat in which liquid backflow is suppressed. Furthermore, good defibration property reduces the amount of undefibrated material in the fluff mat, which not only improves the appearance of the fluff mat but also improves the fluff mat's ability to maintain its shape. When used as an absorbent layer in sanitary materials such as disposable diapers, it is possible to reduce the possibility that the shape of the absorbent layer will be distorted due to movement during use, resulting in a decrease in the absorption performance of the disposable diaper.

[0017] In the pulp sheet for fluff pulp of this embodiment, the ISO brightness measured in accordance with JIS P 8148:2018 is preferably 80% or more, more preferably 81% or more, even more preferably 82% or more, and particularly preferably 83% or more. The ISO brightness of the pulp sheet for fluff pulp is preferably 93% or less. By adjusting the ISO brightness of the pulp sheet for fluff pulp within the above range, a pulp sheet for fluff pulp with a more excellent appearance can be obtained. Furthermore, by adjusting the ISO brightness of the pulp sheet for fluff pulp within the above range, a fluff mat with high brightness can be obtained.

[0018] The basis weight of the pulp sheet for fluff pulp of this embodiment is not particularly limited, and it may be manufactured to a basis weight that can be produced by the papermaking machine used for papermaking. For example, the basis weight of the pulp sheet for fluff pulp is 100 g / m 2 It is preferable that the weight is 150 g / m or more. 2 More preferably, it is 200 g / m or more. 2 The basis weight of the pulp sheet for fluff pulp is more preferably 1500 g / m 2 Preferably, it is 1400 g / m or less.2 More preferably, it is 1300 g / m or less. 2 It is more preferable that the basis weight of the pulp sheet for fluff pulp is measured in accordance with JIS P 8124:2011.

[0019] The density of the pulp sheet for fluff pulp of this embodiment is not particularly limited, but is preferably 0.3 g / cm 3 It is preferable that the concentration is 0.4 g / cm or more. 3 More preferably, it is 0.5 g / cm or more. 3 The density of the pulp sheet for fluff pulp is more preferably 0.95 g / cm or more. 3 Preferably, it is 0.90 g / cm or less. 3 More preferably, it is 0.85 g / cm or less. 3 The density of the pulp sheet for fluff pulp is measured in accordance with JIS P 8118:2014.

[0020] The specific burst strength of the fluff pulp sheet of this embodiment measured in accordance with JIS P 8131:2009 is 0.5 kPa m 2 / g or more is preferable, and 0.7 kPa m 2 / g or more is more preferable, and 0.9 kPa m 2 / g or more is more preferable. The burst strength of the pulp sheet for fluff pulp is 5.0 kPa m 2 / g or less, and 4.5 kPa m 2 / g or less is more preferable, and 4.0 kPa m 2 It is more preferable that the saturation coefficient is 1 / g or less.

[0021] (Raw pulp) The pulp sheet for fluff pulp of this embodiment contains softwood pulp. The pulp sheet for fluff pulp of this embodiment may contain hardwood pulp, but the content of hardwood pulp relative to all pulp components in the pulp sheet for fluff pulp is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less. The content of hardwood pulp relative to all pulp components in the pulp sheet for fluff pulp may be 0% by mass. By setting the content of hardwood pulp to 0% by mass, the defibration ability of the fluff pulp can be more effectively improved. On the other hand, by containing hardwood pulp within the above range, it is possible to prevent liquid absorbed by the fluff mat from returning back.

[0022] The content of softwood pulp relative to all pulp components in the pulp sheet for fluff pulp is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit of the content of hardwood pulp relative to all pulp components in the pulp sheet for fluff pulp is not particularly limited, and may be 100% by mass.

[0023] Examples of softwood pulp and hardwood pulp include chemical pulps such as sulfite pulp (SP), soda pulp (AP), bleached kraft pulp (BKP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP), semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-groundwood pulp (CGP), and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. The softwood pulp and hardwood pulp may also be dissolving pulp (DP).

[0024] In particular, the softwood pulp contained in the pulp sheet for fluff pulp is preferably softwood bleached kraft pulp. The raw material for softwood bleached kraft pulp preferably contains at least one species selected from the group consisting of Pinus, Douglas fir, and Cedar, and more preferably contains at least one species selected from the group consisting of Pinus and Douglas fir. In this embodiment, it is also preferable to use a combination of Pinus and Douglas fir.

[0025] The Canadian Standard Freeness (CSF) of the softwood pulp measured in accordance with JIS P 8121-2:2012 is preferably 600 ml or more, more preferably 640 ml or more, and even more preferably 670 ml or more, where the Canadian Standard Freeness (CSF) of the softwood pulp is a value measured on the softwood pulp before papermaking.

[0026] When hardwood pulp is contained in the pulp sheet for fluff pulp, the hardwood pulp is preferably bleached hardwood kraft pulp. The raw material for the hardwood bleached kraft pulp preferably includes at least one species selected from the group consisting of Acacia, Eucalyptus, Quercus, Fagus, and Castanopsis, and more preferably at least one species selected from the group consisting of Acacia and Eucalyptus. In this embodiment, it is preferable to use a combination of Acacia and Eucalyptus as raw materials for the hardwood bleached kraft pulp.

[0027] The Canadian Standard Freeness (CSF) of hardwood pulp measured in accordance with JIS P 8121-2:2012 is preferably 370 ml or more, more preferably 400 ml or more, and even more preferably 430 ml or more, where the Canadian Standard Freeness (CSF) of hardwood pulp is a value measured on the hardwood pulp before papermaking.

[0028] The pulp sheet for fluff pulp of this embodiment may contain other raw material pulps in addition to softwood pulp and hardwood pulp. Examples of other raw material pulps include non-wood pulp and deinked pulp. Examples of non-wood pulp include cotton-based pulps such as cotton linter and cotton lint, and non-wood pulps such as bamboo pulp, hemp, straw, and bagasse. Examples of deinked pulp include deinked pulp made from recycled paper. In this case, the content of the other raw material pulps is preferably 10% by mass or less of the total pulp components in the pulp sheet for fluff pulp.

[0029] The length-weighted average fiber length of the softwood pulp used as the raw material pulp is preferably 1.50 mm or more, more preferably 1.75 mm or more, and even more preferably 2.00 mm or more, and is preferably 3.50 mm or less, more preferably 3.20 mm or less, and even more preferably 3.00 mm or less. When hardwood pulp is used as the raw material pulp, the length-weighted average fiber length of the hardwood pulp is preferably 0.50 mm or more, more preferably 0.60 mm or more, and even more preferably 0.65 mm or more, and is preferably 1.20 mm or less, more preferably 1.10 mm or less, and even more preferably 1.0 mm or less. By setting the fiber lengths of the various pulps contained in the pulp sheet for fluff pulp within the above ranges, it becomes easier to control the thickness and density of the pulp sheet for fluff pulp within appropriate ranges. Furthermore, by setting the fiber lengths of the various pulps contained in the pulp sheet for fluff pulp within the above ranges, it becomes possible to effectively prevent the liquid absorbed in the fluff mat from returning when the pulp sheet for fluff pulp is fluffed. The length-weighted average fiber lengths of the various pulps contained in the pulp sheet for fluff pulp are measured in accordance with JIS P 8226-2:2011.

[0030] (optional ingredient) The pulp sheet for fluff pulp may contain additives as needed. Examples of additives include softeners, fillers, pigments, sizing agents, coagulants, oil-resistant agents, aluminum sulfate, retention aids, drainage aids, dry strength agents, wet strength agents, coloring pigments, waterproofing agents, antistatic agents, sodium sulfate, surfactants, and pH adjusting chemicals (sodium hydroxide, etc.). The pulp sheet for fluff pulp of this embodiment may contain a softener. By including a softener in the pulp sheet for fluff pulp, it is possible to more effectively improve defibration properties.

[0031] (Method for manufacturing pulp sheets for fluff pulp) The method for producing a pulp sheet for fluff pulp according to this embodiment preferably includes a cooking step in which the pulp raw material is cooked to produce unbleached pulp, a bleaching step, a color adjustment step, and a sheeting step. A dehydration and washing step may be provided between each step as appropriate. A prehydrolysis step may be provided before the cooking step, an oxygen delignification step may be provided before the bleaching step, or a cold alkali step may be provided after the bleaching step. Furthermore, a beating step in which the bleached pulp is beaten to a desired freeness may be provided before the sheeting step.

[0032] (Cooking process) In the cooking step, the pulp raw material is cooked to obtain unbleached pulp. A known cooking method can be used. The cooking conditions in the cooking step are not particularly limited, but for example, when using the kraft cooking method, the sulfidity of the cooking liquor is preferably 15 to 45%, the cooking temperature is preferably 130 to 170°C, the effective alkali addition rate is preferably 5 to 30 mass% per bone-dry wood mass, and the cooking time is preferably 45 to 500 minutes. The kappa number of the unbleached pulp obtained through the cooking step is preferably 10 to 70.

[0033] (Pre-hydrolysis step) A prehydrolysis step can be performed before the cooking step. In the prehydrolysis step, broadleaf or coniferous wood is heated in the presence of water to perform a prehydrolysis treatment. The amount of water relative to the broadleaf or coniferous wood (liquid ratio: amount of water (parts by mass) / amount of broadleaf or coniferous wood (parts by mass)) is preferably 1.0 to 10, more preferably 1.5 to 8.0, even more preferably 2.0 to 7.0, and even more preferably 2.7 to 5.0. A liquid ratio of 1.0 or more is preferred because hydrolysis proceeds sufficiently and the reaction is uniform. A liquid ratio of 10 or less is preferred because the amount of heat required to heat to the desired temperature is reduced, making it economical. The method of adding water is not particularly limited. For example, water may be added from an external source, water originally contained in the broadleaf or coniferous wood may be used, or water contained in the steam may be used when steam is used during heating. In addition to water, chemicals that directly or indirectly assist the hydrolysis of polysaccharides, such as alkalis, acids, and chelating agents, may also be added.

[0034] (Oxygen delignification process) In the process for producing a pulp sheet for fluff pulp, it is preferable to provide an oxygen delignification step after the cooking step and before the bleaching step. In the oxygen delignification step, alkaline chemicals and oxygen are added to unbleached pulp, and the lignin is decomposed at high temperature and pressure and dissolved in the alkaline chemicals. Delignification in the oxygen delignification step can reduce the amount of bleaching chemicals used in the subsequent multi-stage bleaching step, minimizing deterioration of pulp quality. As the oxygen delignification method, a known medium consistency method or high consistency method can be applied as is, but the medium consistency method, which is currently widely used and is performed at a pulp consistency of 8 to 15% by mass, is preferred.

[0035] In the medium-consistency oxygen delignification process, caustic soda or oxidized kraft white liquor can be used as the alkali, and oxygen gas can be oxygen from a cryogenic separation process, oxygen from a PSA (Pressure Swing Adsorption), or oxygen from a VSA (Vacuum Swing Adsorption). Oxygen gas and alkali are added to a medium-consistency pulp slurry in a medium-consistency mixer. After thorough mixing, the mixture is sent to a reactor capable of maintaining the pulp, oxygen, and alkali mixture under pressure for a certain period of time, where delignification occurs. The oxygen gas addition rate is preferably 0.5 to 3 mass% per bone-dry pulp mass, the alkali addition rate is preferably 0.5 to 4 mass%, the reaction temperature is preferably 80 to 120°C, the reaction time is preferably 15 to 100 minutes, and the pulp consistency is preferably 8 to 15 mass%. Other known conditions can be used.

[0036] (bleaching process) In the bleaching step, the oxygen delignified pulp is bleached to obtain bleached pulp. The bleaching method is not particularly limited, and any known bleaching method can be used. Examples of bleaching methods include an ozone bleaching stage (Z), a chlorine dioxide bleaching stage (D), an alkali extraction stage (E), an oxygen bleaching stage (O), a hydrogen peroxide bleaching stage (E / P), a peracid bleaching stage (PA), an acid washing stage (a), or an acid treatment stage (A). In this embodiment, the bleaching steps are preferably performed in the order D0-E / P-D1. Note that the Z stage is preferably not performed because it significantly damages the pulp fibers, causing a loss of fiber stiffness and thus deteriorating the defibration properties of the pulp sheet for fluff pulp.

[0037] The bleaching conditions in the D0 and D1 stages are not particularly limited, but the chlorine dioxide addition rate is preferably 0.05 to 5.0 mass%, the bleaching temperature is preferably 30 to 90°C, the bleaching time is preferably 1 to 240 minutes, the pulp consistency is preferably 5 to 15 mass%, and the pH at the end of the reaction is preferably 2 to 6. The bleaching conditions in the E / P stage are not particularly limited, but the hydrogen peroxide addition rate is preferably 0.05 to 5.0 mass%, the bleaching temperature is preferably 30 to 90°C, the bleaching time is preferably 1 to 240 minutes, the pulp consistency is preferably 5 to 15 mass%, and the pH at the end of the reaction is preferably 10 to 12.

[0038] (cold alkali process) In this embodiment, the bleached pulp may be further treated with an alkali to obtain bleached pulp after cold alkali treatment. The treatment method is not particularly limited, but caustic soda can be used as the alkali. The caustic soda addition rate is preferably 5.0 to 20.0%, the bleaching temperature is preferably 20 to 50°C, the bleaching time is preferably 1 to 240 minutes, and the pulp consistency is preferably 5 to 15% by mass.

[0039] (color tone adjustment process) In this embodiment, a color tone adjusting step is preferably performed after the bleaching step, and a hydrogen peroxide treatment is preferably performed in the color tone adjusting step. When a hydrogen peroxide treatment step is performed as the final step of the bleaching step, this step corresponds to the color tone adjusting step. Alternatively, a hydrogen peroxide treatment step may be performed separately from the bleaching step.

[0040] In the color tone adjusting step, a heating treatment may be performed. The pulp slurry temperature in the heating treatment step is preferably 30°C or higher, more preferably 35°C or higher, and even more preferably 40°C or higher. The pulp slurry temperature in the heating treatment step is preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 80°C or lower. The pulp slurry temperature in the heating treatment step is preferably within the above range, but does not have to be a constant temperature.

[0041] When a heating treatment is performed in the color tone adjustment step, the heating time is preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 20 minutes or more, and particularly preferably 30 minutes or more, and is preferably 600 minutes or less, more preferably 300 minutes or less, and even more preferably 120 minutes or less.

[0042] When heating treatment is performed in the color adjustment step, the heating method in the heating treatment step is not particularly limited. Steam may be directly introduced into the pulp slurry to heat it, a jacket-type heating device may be used, or the pulp slurry may be left standing in a heated atmosphere at a temperature higher than room temperature. Alternatively, the temperature of the pulp slurry maintained from the previous step may be used to maintain the temperature. When a heating container is used in the heating treatment step, the material may be concrete, metal, or resin. A dedicated heating tank may be used as the heating container, or the residence time before the sheeting step may be utilized.

[0043] The pH of the pulp slurry in the color adjustment step is preferably 2.0 or higher, more preferably 2.5 or higher, and even more preferably 3.0 or higher. The pH of the pulp slurry in the color adjustment step is preferably 9.0 or lower, more preferably 8.5 or lower, and even more preferably 8.0 or lower. The pH of the pulp slurry in the color adjustment step is preferably within the above range, but does not have to be a constant pH.

[0044] The concentration of the pulp slurry in the color tone adjusting step is preferably 0.5% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more. The concentration of the pulp slurry is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. While the concentration of the pulp slurry in the color tone adjusting step is preferably within the above range, it does not have to be a constant concentration.

[0045] In this embodiment, by providing a color tone adjustment step, it becomes easy to adjust the ISO whiteness change amount within a desired range.

[0046] (Cleaning process) A washing step may be performed after each of the above steps. The washing step is preferably a dehydration washing step. In the dehydration washing step, the pulp after each step is diluted and dehydrated to perform washing. The washing method is not particularly limited, and washing can be performed using a known washing machine. For example, a displacement washing method, a dilution / dehydration method, a press washing method, or a washing method combining these methods can be used.

[0047] (Sheeting process) In the sheeting process, the bleached pulp obtained through the color adjustment process is dispersed in water to prepare a slurry. The pulp concentration in the slurry is preferably 0.01 to 10% by mass. If additives are added as needed, the additives are preferably added to the slurry.

[0048] The sheet-forming process includes a step of making paper from the slurry using a paper machine. The paper machine used in the paper making process is not particularly limited, but for example, a Fourdrinier paper machine, a cylinder paper machine, a hybrid former, a gap former, or the like can be used. Furthermore, when making paper, the paper may be made into a single layer, or may be made into multiple layers.

[0049] (Fluffy Mat) This embodiment relates to a fluff mat formed from the above-mentioned pulp sheet for fluff pulp. The fluff mat in this specification is a sheet-shaped product of fluff pulp obtained by defibrating the above-mentioned pulp sheet for fluff pulp. When the fluff mat of this embodiment is used, for example, as a constituent material for a diaper, it can suppress the occurrence of skin rash. In addition, the fluff mat of this embodiment has excellent water absorption properties and can retain liquid after absorbing it. Therefore, the fluff mat of this embodiment suppresses liquid from flowing back.

[0050] The conditions for defibrating the pulp sheet for fluff pulp are not particularly limited, and for example, a known defibrator or grinder can be used.

[0051] Fluff mats are formed by laminating fluff pulp under an air flow. It is formed by air-transporting defibrated fluff pulp and layering it on a metal mesh or a porous substrate such as tissue or nonwoven fabric.

[0052] (Absorbent articles) This embodiment may relate to an absorbent article having the fluff mat described above. Examples of absorbent articles include disposable diapers, urine absorption pads, light incontinence pads, sanitary napkins, etc. Since the fluff mat of this embodiment can neutralize particularly acidic urine, the absorbent article is preferably a disposable diaper, a urine absorption pad, or a light incontinence pad. [Example]

[0053] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0054] [Preparation of softwood pulp] [Cooking] Douglas fir and pine chips were mixed in a bone-dry mass ratio of 60:40, and 200 g of bone-dry mass was taken and placed in a 2.5-liter autoclave. Kraft cooking was carried out under the following conditions: liquor ratio 5, cooking liquor sulfidity 28%, alkali addition rate 22%, cooking temperature 165°C, and cooking time 120 minutes. The black liquor and pulp were then separated, and the pulp was refined using a flat screen equipped with a 10-cut screen plate to obtain unbleached pulp with a kappa number of approximately 30.

[0055] [Oxygen delignification] 70.0 g of unbleached pulp was collected on an oven-dry basis, and caustic soda was added to the pulp to a concentration of 2.0% by mass. The pulp was then diluted with ion-exchanged water to a pulp concentration of 10% by mass. This was placed in a heated autoclave, and oxygen delignification was carried out at 95°C for 60 minutes under a gauge pressure of 0.5 MPa using commercially available 99.9% compressed oxygen gas. The resulting pulp was diluted to 3% by mass with ion-exchanged water, and then dehydrated and washed using a Buchner funnel.

[0056] [bleaching] After alkaline oxygen delignification, 60 g of the kraft pulp was collected on an oven-dry basis and placed in a plastic bag. The pulp concentration was adjusted to 10% by mass using ion-exchanged water, and chlorine dioxide was added to the oven-dry pulp to a concentration of 2.0% by mass. The bag was immersed in a thermostatic water bath at 70°C for 60 minutes to carry out the D0 stage treatment. The resulting pulp was diluted to 3% by mass with ion-exchanged water, and then dehydrated and washed using a Buchner funnel. The pulp after the D0 stage was placed in a plastic bag and ion-exchanged water was added to adjust the pulp concentration to 10% by mass. Caustic soda and hydrogen peroxide were then added to the bone-dry pulp to a concentration of 1.0% by mass and 0.2% by mass, respectively, and mixed thoroughly. The pulp was then immersed in a thermostatic water bath at 70°C for 90 minutes to undergo E / P stage treatment. The resulting pulp was diluted to 3% by mass with ion-exchanged water, then dehydrated and washed using a Buchner funnel. The pulp after the E / P stage was placed in a plastic bag and adjusted to a pulp concentration of 10% by mass using ion-exchanged water. Caustic soda and hydrogen peroxide were then added to the bone-dry pulp to a concentration of 1.0% by mass and 0.3% by mass, respectively, and mixed thoroughly. The pulp was then immersed in a thermostatic water bath at 70°C for 90 minutes to undergo P0 stage treatment. The resulting pulp was diluted to 3% by mass with ion-exchanged water, then dehydrated and washed using a Buchner funnel. The pulp after the P0 stage was placed in a plastic bag and adjusted to a pulp concentration of 10% by mass using ion-exchanged water. Chlorine dioxide was then added to the bone-dry pulp to a concentration of 0.2% by mass, and the pulp was immersed in a thermostatic water bath at 70°C for 60 minutes to perform bleaching in the D1 stage. The resulting bleached softwood pulp was diluted to 3% by mass with ion-exchanged water, then dehydrated and washed using a Buchner funnel.

[0057] [Color adjustment process] Bleached softwood pulp was placed in a beaker and adjusted to a pulp concentration of 10% by mass using ion-exchanged water. The slurry was then placed in a shaker heated to 60°C and hydrogen peroxide was added to the bone-dry pulp to a concentration of 1.0%. The beaker was then covered and shaken for 60 minutes to adjust the color. The color-adjusted pulp was then diluted to 3% by mass with ion-exchanged water and dehydrated and washed using a Buchner funnel.

[0058] [Hardwood pulp preparation] [Cooking] Acacia and eucalyptus chips were mixed in a bone dry mass ratio of 70:30, and 200g of bone dry mass was taken and placed in a 2.5 liter autoclave. Kraft cooking was carried out under the following conditions: liquor ratio 5, cooking liquor sulfidity 28%, alkali addition rate 20%, cooking temperature 155°C, and cooking time 120 minutes. The black liquor and pulp were then separated, and the pulp was refined using a flat screen with an 8-cut screen plate to obtain unbleached pulp with a kappa number of approximately 18.

[0059] [Oxygen delignification] 70.0 g of unbleached pulp was collected on an oven-dry basis, and caustic soda was added to the pulp to a concentration of 2.0% by mass. The pulp was then diluted with ion-exchanged water to a pulp concentration of 10% by mass. This was placed in a heated autoclave, and oxygen delignification was carried out at 95°C for 60 minutes under a gauge pressure of 0.5 MPa using commercially available 99.9% compressed oxygen gas. The resulting pulp was diluted to 3% by mass with ion-exchanged water, and then dehydrated and washed using a Buchner funnel.

[0060] [bleaching] After alkaline oxygen delignification, 60 g of the kraft pulp was collected on an oven-dry basis and placed in a plastic bag. The pulp concentration was adjusted to 10% by mass using ion-exchanged water, and chlorine dioxide was added to the oven-dry pulp to a concentration of 1.0% by mass. The bag was immersed in a thermostatic water bath at 70°C for 60 minutes to carry out the D0 stage treatment. The resulting pulp was diluted to 3% by mass with ion-exchanged water, and then dehydrated and washed using a Buchner funnel. The pulp after the D0 stage was placed in a plastic bag and ion-exchanged water was added to adjust the pulp concentration to 10% by mass. Caustic soda and hydrogen peroxide were then added to the bone-dry pulp to a concentration of 1.0% by mass and 0.2% by mass, respectively, and mixed thoroughly. The pulp was then immersed in a thermostatic water bath at 70°C for 90 minutes to undergo E / P stage treatment. The resulting pulp was diluted to 3% by mass with ion-exchanged water, then dehydrated and washed using a Buchner funnel. The pulp after the E / P stage was placed in a plastic bag and adjusted to a pulp concentration of 10% by mass using ion-exchanged water. Chlorine dioxide was then added to the bone-dry pulp to a concentration of 0.2% by mass, and the pulp was immersed in a thermostatic water bath at 70°C for 60 minutes to perform bleaching in the D1 stage. The resulting bleached hardwood pulp was diluted to 3% by mass with ion-exchanged water, then dehydrated and washed using a Buchner funnel.

[0061] [Color adjustment process] Bleached hardwood pulp was placed in a beaker and adjusted to a pulp concentration of 10% by mass using ion-exchanged water. The slurry was then placed in a shaker heated to 60°C and hydrogen peroxide was added to the bone-dry pulp to a concentration of 1.0%. The beaker was then covered and shaken for 60 minutes to adjust the color. The color-adjusted pulp was then diluted to 3% by mass with ion-exchanged water and dehydrated and washed using a Buchner funnel.

[0062] Example 1 The bleached softwood pulp and bleached hardwood pulp after the color adjustment process were mixed in an oven-dry mass ratio of 100:0 to obtain a slurry with a pulp concentration of 1% by mass. The slurry was then spun into a standard circular hand mill (manufactured by Kumagai Riki Kogyo Co., Ltd.) with a basis weight of 750 g / m. 2 A pulp sheet for fluff pulp was obtained.

[0063] Example 2 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the amount of hydrogen peroxide added in the color adjustment step after obtaining bleached softwood pulp was set to 0.5%.

[0064] Example 3 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the amount of hydrogen peroxide added in the color adjustment step after obtaining bleached softwood pulp was set to 1.5%.

[0065] Example 4 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the pulp concentration in the color adjustment step after obtaining bleached softwood pulp was set to 1 mass %.

[0066] Example 5 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the pulp concentration in the color adjustment step after obtaining bleached softwood pulp was set to 20 mass %.

[0067] Example 6 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the shaking treatment time in the color adjustment step after obtaining bleached softwood pulp was changed to 90 minutes.

[0068] Example 7 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the shaking treatment time in the color adjustment step after obtaining bleached softwood pulp was changed to 120 minutes.

[0069] Example 8 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the temperature in the color adjustment step after obtaining bleached softwood pulp was set to 80°C.

[0070] Example 9 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the bleached softwood pulp was produced by mixing chips of the genus Pinus and the genus Douglas fir in an oven-dry mass ratio of 70:30.

[0071] Example 10 The same procedure as in Example 1 was carried out to obtain a pulp sheet for fluff pulp, except that bleached softwood pulp after the color adjustment process and bleached hardwood pulp after the color adjustment process were mixed in an oven-dry mass ratio of 95:5 during papermaking.

[0072] Example 11 The same operation as in Example 1 was performed to obtain a pulp sheet for fluff pulp, except that during papermaking, bleached softwood pulp after the color adjustment process and bleached hardwood pulp after the color adjustment process were mixed in an 85:15 bone dry mass ratio.

[0073] Example 12 The same operation as in Example 1 was performed to obtain a pulp sheet for fluff pulp, except that during papermaking, bleached softwood pulp after the color adjustment process and bleached hardwood pulp after the color adjustment process were mixed in an oven-dry mass ratio of 70:30.

[0074] Example 13 Before the color adjustment process, bleached softwood pulp and bleached hardwood pulp were mixed in an 85:15 bone dry mass ratio, and the color adjustment process was carried out at the same ratio.The same operations as in Example 1 were then carried out, except that a pulp sheet for fluff pulp was obtained.

[0075] (Comparative Example 1) A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that 1.0% chlorine dioxide was added instead of hydrogen peroxide in the color adjustment step after obtaining bleached softwood pulp.

[0076] (Comparative Example 2) A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that bleached softwood pulp and bleached hardwood pulp were mixed in a bone dry mass ratio of 50:50 during papermaking.

[0077] (Comparative Example 3) A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 0:100 during papermaking.

[0078] (Measurement and evaluation) [ISO whiteness] The ISO brightness of the fluff pulp pulp sheet was measured according to JIS P 8148:2018. The ISO brightness of the fluff pulp pulp sheet was measured before and after heating at 105°C for 120 minutes. The change in ISO brightness was calculated using the following formula. ISO whiteness change amount = (B0(%) - B1(%)) / B0(%) x 100 In the above formula, B1 is the ISO brightness of the pulp sheet for fluff pulp measured in accordance with JIS P 8154-1:2008 after heating at 105°C for 2 hours, and B0 is the ISO brightness of the pulp sheet for fluff pulp before heating.

[0079] [Defibrating property] The defibration property of the pulp sheet for fluff pulp was evaluated in an environment of 23°C and 50% relative humidity. The pulp sheet for fluff pulp, which had been conditioned at 23°C and 50% relative humidity, was cut into 10mm x 10mm squares, and 3g of each was weighed out and placed evenly into a Wonder Blender (Osaka Chemical Co., Ltd., Model WB-1, rotation speed 25,000 rpm). The pulp was defibrated for a predetermined time in 5-second intervals to form a flocculent pulp (hereinafter, the pulp flocculent by defibration is referred to as "fluff pulp"). Next, the fluff pulp was immersed in water and gently stirred with a stick, and then made into a sheet of paper with a basis weight of 25g / m using a standard circular handsheet machine. 2 The handsheets for defibration evaluation were visually observed, and the defibration time (seconds) required for all undefibrated material to disappear was used as an index for evaluating defibration ability.

[0080] [Table 1]

[0081] [Table 2]

[0082] In comparison with the comparative examples, the examples provided pulp sheets for fluff pulp that were less susceptible to discoloration and had excellent defibration properties.

Claims

1. A pulp sheet for fluff pulp containing softwood pulp, The content of hardwood pulp in the pulp sheet for fluff pulp is 30% by mass or less relative to the total pulp components, A pulp sheet for fluff pulp, having an ISO brightness change of 1.5% or less as calculated by the following formula: ISO whiteness change (%) = (B0 (%) - B1 (%)) / B0 (%) × 100 In the above formula, B1 is the ISO brightness of the pulp sheet for fluff pulp measured in accordance with JIS P 8154-1:2008 after heating at 105°C for 2 hours, and B0 is the ISO brightness of the pulp sheet for fluff pulp before heating.

2. the fluff pulp sheet contains softwood pulp; 2. The pulp sheet for fluff pulp according to claim 1, wherein the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 15 mass% or less.

3. A fluff mat formed from the pulp sheet for fluff pulp according to claim 1 or 2.

4. An absorbent article comprising the fluff mat of claim 3.

5. The method includes a cooking step of cooking a pulp raw material to produce unbleached pulp, a bleaching step, a color adjustment step, and a sheeting step, The color adjustment step is performed after the bleaching step, A method for producing a pulp sheet for fluff pulp, wherein the color adjustment step involves a hydrogen peroxide treatment.

6. The method for producing a pulp sheet for fluff pulp according to claim 5, wherein in the color tone adjusting step, a heating treatment is carried out so that the pulp slurry temperature is 30°C or higher and 100°C or lower.

7. The method for producing a pulp sheet for fluff pulp according to claim 6, wherein the heating treatment time in the color tone adjustment step is 10 minutes or more and 120 minutes or less.

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