Pulp sheet for fluff pulp, fluff mat, absorbent article, and method for producing pulp sheet for fluff pulp

Abstract

The present invention addresses the problem of providing a pulp sheet for fluff pulp that suppresses discoloration and which excellent defibrillation properties. The present invention relates to a pulp sheet for fluff pulp, the sheet having a hot water extract pH of 7.0-9.5 as measured in accordance with JIS P 8133-2:2013. Additionally, the present invention relates to a pulp sheet for fluff pulp containing softwood pulp, wherein the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 30 mass% or less, and the ISO whiteness change is 1.5% or less. Furthermore, the present invention relates to a fluff mat and absorbent article formed from the pulp sheet for fluff pulp, as well as a method for manufacturing the pulp sheet for fluff pulp.

Description

Fluff pulp pulp sheet, fluff mat, absorbent article, and method for manufacturing fluff pulp pulp sheet

[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.

[0002] Fluff pulp is made by defibrating wood pulp into a flocculent form, and 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 has been made from softwood pulp, which has good defibration properties (see, for example, Patent Document 1). In Patent Document 1, fluff pulp is obtained by mechanically defibrating raw material pulp (softwood bleached kraft pulp) having 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. It is studied to obtain a pulp sheet for fluff pulp that can reduce the amount of absorbed liquid returning and prevent skin rashes by adjusting the content ratio of bleached hardwood kraft pulp and bleached softwood kraft pulp within a predetermined range.

[0005] JP 2012-211411 A International Publication No. 2022 / 138870

[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 may have insufficient defibration properties, 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.

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

[0009] [1] A pulp sheet for fluff pulp, the pH of the hot water extract of which is measured in accordance with JIS P 8133-2:2013 is 7.0 to 9.5. [2] A pulp sheet for fluff pulp according to [1], the ISO brightness of which is 80% or more, measured in accordance with JIS P 8148:2018. [3] A pulp sheet for fluff pulp according to [1] or [2], the pulp sheet for fluff pulp contains softwood pulp, and the content of hardwood pulp relative to all pulp components in the pulp sheet for fluff pulp is 30% by mass or less. [4] A pulp sheet for fluff pulp according to any one of [1] to [3], the pulp sheet for fluff pulp contains softwood pulp, and the content of hardwood pulp relative to all pulp components in the pulp sheet for fluff pulp is 15% by mass or less. [5] A pulp sheet for fluff pulp containing softwood pulp, wherein the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 30 mass% or less, and the ISO brightness change calculated by the following formula is 1.5% or less: ISO brightness change (%) = (B0 (%) - B1 (%)) / B0 (%) x 100 In the above formula, B1 is the ISO brightness of the pulp sheet for fluff pulp after heating at 105°C for 2 hours, measured in accordance with JIS P 8154-1:2008, and B0 is the ISO brightness of the pulp sheet for fluff pulp before heating. [6] The pulp sheet for fluff pulp according to [5], wherein the pulp sheet for fluff pulp contains softwood pulp, and the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 15% by mass or less. [7] A fluff mat formed from the pulp sheet for fluff pulp according to any one of [1] to [6]. [8] The fluff mat according to [7], wherein 5 parts by mass of the fluff mat is mixed with 20 parts by mass of artificial urine containing 1.94% by mass of urea, 0.8040% by mass of sodium chloride, 0.2045% by mass of magnesium sulfate heptahydrate, and 0.0835% by mass of calcium chloride dihydrate, and the pH of the squeezed liquid from the fluff mat after allowing to stand in a sealed state at 40°C for 1 hour is 6.6 or higher. [9] An absorbent article comprising the fluff mat according to [7] or [8].

[10] A method for producing a pulp sheet for fluff pulp, comprising a cooking step in which a pulp raw material is cooked to produce unbleached pulp, a bleaching step, a heating step, and a sheet forming step, the heating step being performed after the bleaching step.

[11] A method for producing a pulp sheet for fluff pulp according to

[10] , wherein the heating step is performed so that the pulp slurry temperature is 30°C or higher and 100°C or lower.

[12] A method for producing a pulp sheet for fluff pulp according to

[10] or

[11] , wherein the heating time in the heating step is 10 minutes or longer and 120 minutes or shorter.

[13] A method for producing a pulp sheet for fluff pulp according to any one of

[10] to

[12] , wherein the pulp slurry concentration in the heating treatment is 0.5% by mass or longer and 40% by mass or shorter.

[14] The method for producing a pulp sheet for fluff pulp according to any one of

[10] to

[13] , wherein the pH of the pulp slurry during the heating treatment is 2.0 or more and 9.0 or less.

[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.

[0011] FIG. 1 is a schematic diagram illustrating the configuration of a fluff mat manufacturing device used to manufacture the fluff mat.

[0012] 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.

[0013] (Pulp sheet for fluff pulp) A first embodiment of the present invention relates to a pulp sheet for fluff pulp, the pH of a hot water extract measured in accordance with JIS P 8133-2:2013 being 7.0 to 9.5.

[0014] A second embodiment of the present invention 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% by 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 Brightness Change (%) = (B0 (%) - B1 (%)) / B0 (%) × 100. In the formula, B1 is the ISO brightness of the pulp sheet for fluff pulp after heating at 105°C for 2 hours, measured in accordance with JIS P 8154-1:2008, and B0 is the ISO brightness of the pulp sheet for fluff pulp before heating.

[0015] 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.

[0016] In a first embodiment, a pulp sheet for fluff pulp is subjected to hot water treatment according to the method described in JIS P 8133-2:2013, and the pH of the resulting hot water extract is 7.0 to 9.5. More specifically, 2 g of the pulp sheet for fluff pulp is added to 100 ml of deionized water, boiled for 1 hour, cooled to 25°C, and the contents are filtered through a glass filter. To the resulting solution, a 1 mol / L potassium chloride solution is added to obtain a hot water extract, and the pH is measured. The pH of the hot water extract is preferably 7.1 or higher, more preferably 7.2 or higher, and even more preferably 7.3 or higher. The pH of the hot water extract is preferably 9.4 or lower, more preferably 9.3 or lower, and even more preferably 9.2 or lower.

[0017] In the first embodiment, for example, in the manufacturing process of a pulp sheet for fluff pulp, the pulp raw material is bleached, washed, and then heated under predetermined conditions, thereby adjusting the pH of the hot water extract to within a predetermined range. More specifically, it is preferable to adjust the pH of the slurry during the heating treatment to, for example, 2.0 to 9.0. Furthermore, by appropriately adjusting the raw pulp material, it is also easy to adjust the pH of the hot water extract to within the predetermined range.

[0018] In the first embodiment, fluff pulp can be made neutral to alkaline by adjusting the pH of the hot water extract obtained by subjecting a pulp sheet for fluff pulp to hot water treatment according to the method described in JIS P 8133-2: 2013 to a range of 7.0 to 9.5. When a fluff mat formed from such fluff pulp is used as a constituent material of a diaper, it can neutralize acidic urine and suppress the occurrence of skin rash.

[0019] For example, 20 parts by mass of artificial urine containing 1.94% by mass of urea, 0.8040% by mass of sodium chloride, 0.2045% by mass of magnesium sulfate heptahydrate, and 0.0835% by mass of calcium chloride dihydrate is added to 5 parts by mass of a fluff mat, and after leaving the mixture sealed at 40°C for 1 hour, the pH of the squeezed liquid from the fluff mat is preferably 6.6 or higher, more preferably 6.8 or higher, even more preferably 7.0 or higher, and particularly preferably 7.5 or higher. If the pH of the squeezed liquid from the fluff mat is within the above range, it means that the acidic urine has been neutralized, and the occurrence of skin rash is more effectively suppressed.

[0020] Furthermore, in the first embodiment, the liquid return rate in the fluff mat is preferably 30% or less, more preferably 28% or less, even more preferably 26% or less, particularly preferably 24% or less, and most preferably 20% or less. The liquid return rate in the fluff mat can be calculated using the following formula. Here, the liquid return rate in the fluff mat can be calculated by absorbing 20 g of artificial urine into the fluff mat, and then placing 10 sheets of filter paper (manufactured by ADVANTEC Co., Ltd., No. 1640) under pressure under the conditions described in the examples, and measuring the weight of liquid absorbed by the filter paper.

[0021] In a second embodiment, the ISO brightness of a fluff pulp pulp sheet is measured in accordance with JIS P 8148:2018. The ISO brightness of the fluff pulp pulp sheet is measured before and after heating at 105°C for 120 minutes. The ISO brightness change is then calculated using the following formula: ISO Brightness Change (%) = (B0 (%) - B1 (%)) / B0 (%) × 100. In the above formula, B1 is the ISO brightness of the fluff pulp pulp sheet after heating at 105°C for 2 hours, measured in accordance with JIS P 8154-1:2008, and B0 is the ISO brightness of the fluff pulp pulp sheet before heating. The ISO brightness 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 brightness change is not particularly limited and may be 0%.

[0022] In the second embodiment, for example, in the manufacturing process of a pulp sheet for fluff pulp, the ISO brightness change can be adjusted to a desired range by providing a heating treatment step after bleaching the pulp raw material. In particular, it is preferable to perform hydrogen peroxide treatment in the heating treatment step, thereby adjusting the ISO brightness change to a desired range. Furthermore, by appropriately adjusting the raw materials for the pulp, it is also easy to adjust the ISO brightness change to a predetermined range.

[0023] In the first embodiment, when the ISO brightness is measured by the same method as in the second embodiment and the ISO brightness change is calculated by the above formula, the ISO brightness 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 brightness change is not particularly limited and may be 0%.

[0024] The pulp sheets for fluff pulp of the first and second embodiments (hereinafter, the first and second embodiments are also collectively referred to as "the present embodiments") have good defibration properties when fluffing. 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 to be, 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.

[0025] 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. Furthermore, the ISO brightness of the pulp sheet for fluff pulp is preferably 93% or less. By setting 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 setting the ISO brightness of the pulp sheet for fluff pulp within the above range, a fluff mat with high brightness can be obtained.

[0026] 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 or more. ２ Preferably, the weight is 1400 g / m or less. ２ More preferably, it is 1300 g / m or less. ２ The basis weight of the pulp sheet for fluff pulp is measured in accordance with JIS P 8124:2011.

[0027] 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 density is 0.4 g / cm or more. ３ More preferably, it is 0.5 g / cm or more. ３ It is more preferable that the density of the pulp sheet for fluff pulp is 0.95 g / cm or more. ３ It is preferable that the density 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.

[0028] 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, and 0.7 kPa m ２ / g or more is more preferable, and 0.9 kPa m ２ The burst strength of the pulp sheet for fluff pulp is more preferably 5.0 kPa·m ２ / g or less, and ２ / g or less, and more preferably 4.0 kPa m２ It is more preferable that the SiO2 content is 1 / g or less.

[0029] (Raw material pulp) The pulp sheet for fluff pulp of this embodiment preferably 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 may be 0% by mass relative to all pulp components in the pulp sheet for fluff pulp. 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 in the fluff mat from flowing back.

[0030] 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.

[0031] 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).

[0032] 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 preferable to use both Pinus and Douglas fir.

[0033] 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.

[0034] 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 bleached hardwood 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 bleached hardwood kraft pulp.

[0035] The Canadian Standard Freeness (CSF) of the 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 the hardwood pulp is a value measured on the hardwood pulp before papermaking.

[0036] 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 pulps 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.

[0037] 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. The length-weighted average fiber length of the softwood pulp 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 included 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. The length-weighted average fiber length of the hardwood pulp 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, the thickness and density of the pulp sheet for fluff pulp can be easily controlled within appropriate ranges. Furthermore, by setting the fiber lengths of the various pulps contained in the pulp sheet for fluff pulp within the above range, it is 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.

[0038] (Optional Components) 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.

[0039] (Method for manufacturing a pulp sheet for fluff pulp) The method for manufacturing a pulp sheet for fluff pulp in this embodiment preferably includes a cooking step in which the pulp raw material is cooked to produce unbleached pulp, a bleaching step, a heating treatment 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.

[0040] (Cooking Step) In the cooking step, the pulp raw material is cooked to obtain unbleached pulp. Known cooking methods 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.

[0041] (Prehydrolysis 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 for heating. In addition to water, chemicals that directly or indirectly assist the hydrolysis of polysaccharides, such as alkalis, acids, or chelating agents, may also be added.

[0042] (Oxygen Delignification Step) In the manufacturing process of 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 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.

[0043] 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 pressure swing adsorption (PSA), or oxygen from a vacuum swing adsorption (VSA). Oxygen gas and alkali are added to a medium-consistency pulp slurry in a medium-consistency mixer. After thorough mixing, the mixture is transferred to a reactor capable of holding the pulp, oxygen, and alkali under pressure for a certain period of time for delignification. 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.

[0044] (Bleaching Step) In the bleaching step, the pulp that has been subjected to oxygen delignification 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 of D0-E / P-D1. Note that the Z stage is preferably not performed because it causes significant damage to the pulp fibers, resulting in a loss of fiber rigidity and thus deteriorating the defibration ability of the pulp sheet for fluff pulp.

[0045] 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% by 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% by 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% by 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% by mass, and the pH at the end of the reaction is preferably 10 to 12.

[0046] (Cold Alkali Step) In this embodiment, the bleached pulp may be further treated with an alkali to obtain bleached pulp after the 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.

[0047] (Heating Treatment Step) In this embodiment, a heating treatment step is preferably performed after the bleaching step, the cold alkali step, or the washing step. In the heating treatment step, the pulp slurry is maintained at a temperature higher than room temperature for 30 minutes or more. 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, even more preferably 80°C or lower, and particularly preferably 60°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.

[0048] The heating time in the heating treatment step may be 1 minute or more, 10 minutes or more, 20 minutes or more, 30 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 5 hours or more, 8 hours or more, or 10 hours or more. The heating time in the heating treatment step is preferably 100 hours or less.

[0049] The pH of the pulp slurry in the heating treatment step is preferably 2.0 or higher, more preferably 2.5 or higher, even more preferably 3.0 or higher, even more preferably 4.0 or higher, and particularly preferably 5.0 or higher. The pH of the pulp slurry in the heating treatment 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 heating treatment step is preferably within the above range, but does not have to be a constant pH.

[0050] The concentration of the pulp slurry in the heating treatment 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 heating treatment step is preferably within the above range, it does not have to be a constant concentration.

[0051] In this embodiment, by setting the heating conditions in the heating treatment step and the pH of the pulp slurry within the above ranges, it becomes easy to set the pH of the hot water extract obtained by hot water treatment of the pulp sheet for fluff pulp using the method described in JIS P 8133-2:2013 within the range of 7.0 to 9.5.

[0052] The heating method in the heating treatment step is not particularly limited, and the pulp slurry may be heated by directly introducing steam, by using a jacket-type heating device, or by being left to stand 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.

[0053] This embodiment includes a cooking step in which the pulp raw material is cooked to produce unbleached pulp, a bleaching step, a washing step, a heating step, and a sheeting step. The pH of the pulp slurry in the heating step is preferably 2.0 or higher, more preferably 2.5 or higher, even more preferably 3.0 or higher, even more preferably 4.0 or higher, and particularly preferably 5.0 or higher. The pH of the pulp slurry in the heating 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 heating step is preferably within the above range, but does not have to be a constant pH.

[0054] In this embodiment, the heating treatment step may be a color tone adjustment step. When color tone adjustment is performed in the heating treatment step, it is preferable to perform hydrogen peroxide treatment. When a hydrogen peroxide treatment step is performed as the final step of the bleaching step, this step corresponds to the color tone adjustment step. Furthermore, a hydrogen peroxide treatment step may be performed separately from the bleaching step.

[0055] When a hydrogen peroxide treatment step is provided in the heating treatment step, the hydrogen peroxide treatment 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.

[0056] When a hydrogen peroxide treatment step is provided in the heating treatment step, the concentration of the pulp slurry 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. The pulp slurry concentration in the hydrogen peroxide treatment step is preferably within the above range, but does not have to be a constant concentration.

[0057] In this embodiment, by providing the hydrogen peroxide treatment step, it becomes easy to adjust the ISO brightness change amount to within a desired range.

[0058] (Washing Process) A washing process may be performed after the above-described processes. The washing process is preferably a dehydration washing process. In the dehydration washing process, the pulp after each process 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.

[0059] The cleaning step is preferably performed after the bleaching step, but it is not limited to being performed after the bleaching step, and may be performed between each step as needed.

[0060] (Sheeting Step) In the sheeting step, first, the bleached pulp obtained through the heating step is dispersed in water to prepare a slurry. The pulp concentration in the slurry is preferably 0.01 to 10% by mass. If an additive is added as needed, it is preferable to add the additive to the slurry.

[0061] The sheet-forming process includes a step of making paper from the slurry using a paper machine. The paper machine used in the papermaking process is not particularly limited, and 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 a plurality of layers.

[0062] (Fluff Mat) This embodiment relates to a fluff mat formed from the above-mentioned pulp sheet for fluff pulp. In this specification, the fluff mat 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.

[0063] 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.

[0064] Fluff mats are formed by laminating fluff pulp under an air flow, specifically by transporting defibrated fluff pulp by air and laminating it on a metal mesh or a porous substrate such as tissue or nonwoven fabric.

[0065] (Absorbent Article) 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, and sanitary napkins. Because 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.

[0066] 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.

[0067] First Embodiment [Preparation of Softwood Pulp] [Cooking] Pinus and Douglas fir chips were mixed in an oven-dry mass ratio of 30:70, and 200 g of the mixture was taken in an oven-dry mass ratio of 200 g. The mixture was placed in a 2.5-liter autoclave and subjected to kraft cooking 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 screened using a flat screen equipped with a 10-cut screen plate to obtain unbleached pulp with a kappa number of approximately 30.

[0068] [Oxygen Delignification] 70.0 g of unbleached pulp was collected on an oven-dry basis, and caustic soda was added to the oven-dry pulp to a concentration of 2.0% by mass. The mixture was then diluted with ion-exchanged water to a pulp concentration of 10% by mass. The mixture 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 after injection of 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.

[0069] [Bleaching] 60 g of the kraft pulp after alkaline oxygen delignification was collected in an oven-dry weight ratio and placed in a plastic bag. The pulp concentration was adjusted to 10% by weight using ion-exchanged water, and then chlorine dioxide was added to the oven-dry pulp to a concentration of 2.0% by weight. The bag was immersed in a thermostatic water bath at 70°C for 60 minutes to perform D0 stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and then dehydrated and washed using a Buchner funnel. The pulp after D0 stage was placed in a plastic bag and adjusted to 10% by weight using ion-exchanged water. Caustic soda and hydrogen peroxide were then added to the oven-dry pulp to a concentration of 1.0% by weight and 0.2% by weight, respectively, and thoroughly mixed. The bag was then immersed in a thermostatic water bath at 70°C for 90 minutes to perform E / P stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and 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. Then, caustic soda and hydrogen peroxide were added to the bone-dry pulp mass at 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 perform a P-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 P stage was placed in a plastic bag and adjusted to a pulp concentration of 10% by mass using ion-exchanged water. Then, chlorine dioxide was added to the bone-dry pulp mass at 0.2% by mass, and the pulp was immersed in a thermostatic water bath at 70°C for 60 minutes to perform D1-stage bleaching. The resulting bleached softwood pulp was diluted to 3% by mass with ion-exchanged water and then dehydrated and washed using a Buchner funnel. The pulp after D1 stage was placed in a plastic bag and adjusted to a pulp concentration of 10% by mass using ion-exchanged water, after which chlorine dioxide was added to the bag so that the concentration was 1.0% based on the bone-dry pulp mass, and the bag was immersed in a thermostatic water bath at 70°C for 60 minutes to carry out bleaching in D2 stage. The resulting bleached softwood pulp was diluted to 3% by mass with ion-exchanged water, dehydrated and washed using a Buchner funnel, and a bleached softwood pulp slurry with a concentration of 10% by mass was obtained.

[0070] [Preparation of hardwood pulp] [Cooking] Eucalyptus and Acacia chips were mixed in an oven-dry mass ratio of 30:70, and 200 g of the mixture was taken in an oven-dry mass ratio of 1000 mg / kg, placed in a 2.5-liter autoclave, and subjected to kraft cooking 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 screened using a flat screen equipped with an 8-cut screen plate to obtain unbleached pulp with a kappa number of approximately 18.

[0071] [Oxygen Delignification] 70.0 g of unbleached pulp was collected on an oven-dry basis, and caustic soda was added to the oven-dry pulp to a concentration of 2.0% by mass. The mixture was then diluted with ion-exchanged water to a pulp concentration of 10% by mass. The mixture 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 by injecting 99.9% commercially available 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.

[0072] [Bleaching] 60 g of the kraft pulp after alkaline oxygen delignification was collected in an oven-dry weight ratio and placed in a plastic bag. The pulp concentration was adjusted to 10% by weight using ion-exchanged water, and chlorine dioxide was added to the oven-dry pulp to a concentration of 1.0% by weight. The bag was immersed in a thermostatic water bath at 70°C for 60 minutes to perform D0 stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and then dehydrated and washed using a Buchner funnel. The pulp after D0 stage was placed in a plastic bag and adjusted to 10% by weight using ion-exchanged water. Caustic soda and hydrogen peroxide were then added to the oven-dry pulp to a concentration of 1.0% by weight and 0.2% by weight, respectively, and thoroughly mixed. The bag was then immersed in a thermostatic water bath at 70°C for 90 minutes to perform E / P stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and 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 bag to give a concentration of 0.2% by mass based on the bone-dry pulp mass, and the bag 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. The pulp after the D1 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 bag to give a concentration of 1.0% by mass based on the bone-dry pulp mass, and the bag was immersed in a thermostatic water bath at 70°C for 60 minutes to perform bleaching in the D2 stage. The resulting bleached hardwood pulp was diluted to 3% by mass with ion-exchanged water, then dehydrated and washed using a Buchner funnel to obtain a bleached hardwood pulp slurry with a concentration of 10% by mass.

[0073] (Example 1) 60 g of bleached softwood pulp slurry with a concentration of 10% by mass after the D2 stage was placed in a plastic bag, and sulfuric acid was added to adjust the pH of the pulp slurry to 3.0, followed by leaving it to stand at 40°C for 12 hours for heat treatment. The treated pulp was diluted with ion-exchanged water to a concentration of approximately 1.0% by mass and then spun into a sheet with a basis weight of 750 g / m using a circular standard handsheet (manufactured by Kumagai Riki Kogyo Co., Ltd.). ２ A pulp sheet for fluff pulp was obtained.

[0074] Example 2 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that caustic soda was added to a 10% by mass concentration bleached softwood pulp slurry to adjust the pH of the pulp slurry to 5.5.

[0075] Example 3 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that caustic soda was added to a 10% by mass concentration bleached softwood pulp slurry to adjust the pH of the pulp slurry to 8.0.

[0076] (Example 4) In Example 2, ion-exchanged water was added to the bleached softwood pulp slurry, and the concentration of the bleached softwood pulp slurry during the heating treatment was set to 2 mass %, but the same operation as in Example 1 was carried out to obtain a pulp sheet for fluff pulp.

[0077] Example 5 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the bleached softwood pulp slurry in Example 2 was dehydrated to a concentration of 35% by mass.

[0078] Example 6 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the heating temperature of the bleached softwood pulp slurry was changed to 70°C.

[0079] (Example 7) In Example 2, the heating temperature of the bleached softwood pulp slurry was set to 60°C, and the slurry was allowed to cool to 25°C after 12 hours, but the same procedure as in Example 1 was carried out to obtain a pulp sheet for fluff pulp.

[0080] Example 8 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the heating treatment time of the bleached softwood pulp slurry in Example 2 was changed to 2 hours.

[0081] Example 9 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the heating treatment time of the bleached softwood pulp slurry in Example 2 was changed to 48 hours.

[0082] (Example 10) In the [Preparation of Softwood Pulp], the same operation as in Example 2 was carried out, except that chips of the genus Pinus and the genus Douglas fir were mixed in an oven-dry mass ratio of 70:30 to produce a pulp sheet for fluff pulp.

[0083] Example 11 A 10% by mass bleached softwood pulp slurry was heat-treated in the same manner as in Example 2. Also, 60 g of a 10% by mass bleached hardwood pulp slurry after the D2 stage was placed in a plastic bag, caustic soda was added to adjust the pH to 5.5, and the bag was left to stand at 40° C. for 12 hours to heat-treat the bleached hardwood pulp. A fluff pulp sheet was obtained in the same manner as in Example 1, except that the heat-treated bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 95:5 during papermaking.

[0084] Example 12 A pulp sheet for fluff pulp was obtained in the same manner as in Example 11, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 85:15 during papermaking.

[0085] Example 13 A pulp sheet for fluff pulp was obtained in the same manner as in Example 11, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 70:30 during papermaking.

[0086] Example 14: Pulps after D1 stage were prepared in the bleaching step of the softwood pulp preparation and hardwood pulp preparation. The bleached softwood pulp after D1 stage and the bleached hardwood pulp after D1 stage were mixed in an oven-dry mass ratio of 85:15 to obtain a mixed pulp slurry of bleached softwood pulp and bleached hardwood pulp with a concentration of 10% by mass. The same procedure as in Example 2 was carried out, except that caustic soda was added to the 10% by mass mixed pulp slurry to adjust the pH of the pulp slurry to 5.5.

[0087] Comparative Example 1 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the heating treatment was not carried out.

[0088] Comparative Example 2 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the pH of the bleached softwood pulp was set to 1.0.

[0089] Comparative Example 3 A pulp sheet for fluff pulp was obtained in the same manner as in Example 1, except that the pH of the bleached softwood pulp was set to 10.

[0090] Comparative Example 4 A pulp sheet for fluff pulp was obtained in the same manner as in Example 11, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 50:50 during papermaking.

[0091] Comparative Example 5 The same procedure as in Example 1 was carried out, except that the bleached softwood pulp slurry after the D2 stage, which had a concentration of 10% by mass, was replaced with a bleached hardwood pulp slurry after the D2 stage, which had a concentration of 10% by mass.

[0092] (Measurement and Evaluation) [ISO Brightness] The ISO brightness of each pulp was measured in accordance with JIS P 8148:2018.

[0093] [pH of Extract] The pH of the hot water extract of the pulp sheets for fluff pulp obtained in the Examples and Comparative Examples was measured in accordance with JIS P 8133-2:2013.

[0094] [Discoloration (change in whiteness)] Five fluff pulp sheets obtained in each of the Examples and Comparative Examples were placed in a blast dryer set at 105°C, and one sheet removed at a time after 0, 15, 30, 60, and 120 minutes. After conditioning for 4 hours at 23°C and a relative humidity of 50%, the ISO whiteness was measured according to JIS P 8148:2018. Discoloration (change in whiteness) was calculated according to the following formula: Discoloration (change in whiteness) (pt) = (B0 (%) - B1 (%)) / B0 (%) × 100, where B0 represents the ISO whiteness of the fluff pulp sheet after 0 minutes, and B1 represents the ISO whiteness of the fluff pulp sheet after 120 minutes.

[0095] [Defibrilability] A pulp sheet for fluff pulp conditioned at 23°C and a relative humidity of 50% was cut into 10 mm x 10 mm squares, and 3 g of each was weighed out and placed evenly in a Wonder Blender (manufactured by Osaka Chemical Co., Ltd., model WB-1, rotation speed 25,000 rpm), and defibrated for a predetermined time to produce fluff pulp. The fluff pulp was then defibrated using a standard circular handsheet machine to a basis weight of 25 g / m. ２ The time required for the undefibrated material to disappear by visual observation was taken as the defibration time.

[0096] [Fluffy Mat Production] Fluffy mats were produced in an environment of 23°C and 50% relative humidity using the fluffy mat production device 100 shown in Figure 1. Here, the fluffy mat production device 100 was comprised of a pulp defibrator 5 (manufactured by Maruto Seiki Co., Ltd.), a stainless steel sieve 22 with a mesh size of 180 μm (manufactured by AS ONE Corporation, inner diameter 75 mm x inner height 20 mm), a stainless steel sieve 24 with a mesh size of 150 μm (manufactured by AS ONE Corporation, inner diameter 75 mm x inner height 20 mm), and a pulp sieve made from a PET resin plate (manufactured by Acri Sunday Co., Ltd., Sunday PET, thickness 0.5 mm) cut to 70 cm x 40 cm. The device was assembled as shown in Figure 1 using a ram 20, a polypropylene powder funnel 10 (manufactured by AS ONE Corporation, model number 166, opening diameter 180 mm, leg outer diameter 43 mm, leg length 48 mm), a polypropylene powder funnel 30 (manufactured by AS ONE Corporation, model number 169, opening diameter 120 mm, leg outer diameter 30 mm, leg length 27 mm), and a household vacuum cleaner 40 (manufactured by Hitachi Home & Life Solutions, Ltd., model number CV-CF4). First, the total weight of the 180 μm stainless steel sieve and the column was measured in advance. Next, the pulp defibrator and the household vacuum cleaner were started. The suction power of the household vacuum cleaner was set to a weak setting (suction power approximately 80 W), and the fluff pulp without undefibrated material obtained during the evaluation of [defibration ability] was added little by little from the top of the fluff mat preparation device. The weight of the fluff mat formed on a stainless steel sieve with 180 μm openings was measured from time to time, and the weight was measured to be 200 g / m ２ The fluff mat was formed until it reached 200 g / m ２After the temperature reached 100°C, the pulp defibrator and the household vacuum cleaner were stopped. After removing the column, the surface of the fluff mat was lightly pressed with a circular stainless steel plate to reshape it, and the fluff mat (diameter 75 mm) was gently removed from a sieve with 180 μm openings, taking care not to lose its shape. The surface that had been in contact with the stainless steel mesh was defined as the wire surface of the fluff mat.

[0097] [Measurement of Reverse Rate of Fluff Mat] The reverse rate of the fluff mat was measured under an environment of 23°C and a relative humidity of 50%. ２ The fluff mat was placed on a 5 mm thick acrylic plate with the wire side facing up. After a 2 mm thick spacer was inserted, another 5 mm thick acrylic plate was placed on top and pressed with a tabletop press for 10 minutes. After pressing, the acrylic plate placed on top was removed and left to stand for 30 minutes. A stainless steel base plate (5 mm thick, 11 x 11 cm) was placed on a horizontal laboratory table, and one fluff mat was placed on top with the wire side facing up. SAP (SA60SXII, manufactured by Sumitomo Seika Chemicals Co., Ltd.) was evenly sprinkled on top so that the SAP / fluff mat ratio was 0.35, and another fluff mat was placed on top with the wire side facing up (total basis weight of the fluff mats: 400 g / m ２ On top of that, a 11 cm x 11 cm square core wrap tissue (manufactured by Oji Nepia Co., Ltd., basis weight 16 g / m ２) was placed with the paper flow direction running vertically. A stainless steel strike-through plate (10 cm x 10 cm, 85 mm thick, weighing 665 g) with a 25 mm diameter hole in the center was placed on top of it, and after 10 seconds, 20 g of artificial urine was poured into the hole in the strike-through plate. After the artificial urine was completely absorbed, the strike-through plate was immediately removed. Next, an 11 cm x 11 cm square polyethylene sheet was placed on top of the core wrap tissue, and an 11 cm x 11 cm square chloroprene rubber sponge rubber sheet (manufactured by AS ONE Corporation, 10 mm thick, hardness (Asker C hardness scale): 45 degrees) was placed on top of that, and an 11 cm x 11 cm square 5 mm thick acrylic plate was placed on top of that, and a 2.2 kg weight was placed on top of that. The total weight of the polyethylene sheet, sponge rubber sheet, two acrylic plates, and 2.2 kg weight was 2.31 kg, and the area of ​​the fluff mat was 0.00442 m ２ Therefore, the pressure applied to the fluff mat was 5.1 kPa. A pressure of 5.1 kPa was applied for 3 minutes. Next, the polyethylene sheet, sponge rubber sheet, two acrylic plates, and 2.2 kg weight were removed, and ten sheets of 11 cm x 11 cm square filter paper (manufactured by ADVANTEC Co., Ltd., No. 1640) with a known weight and humidity conditioned in an environment of 23 ° C. and 50% relative humidity were placed on the front side of the core wrap tissue for disposable diapers. Then, a clear file, a urethane rubber sheet, two acrylic plates, and a 2.2 kg weight were placed on top again, and pressure was applied for 2 minutes to allow the filter paper to absorb the artificial urine. After 2 minutes, the ten filter papers were removed and their weights were measured, and the return rate was measured using the following formula. The artificial urine used here was prepared according to the following procedure. First, methylene blue (manufactured by Kanto Chemical Co., Ltd.) was dissolved in ion-exchange water to prepare a methylene blue aqueous solution with a concentration of 0.50% by mass. Next, 19.40 g of urea (Kanto Chemical Co., Inc.), 8.040 g of sodium chloride (Kanto Chemical Co., Inc.), 2.045 g of magnesium sulfate heptahydrate (Kanto Chemical Co., Inc.), and 0.835 g of calcium chloride dihydrate were weighed out in that order into a 500 ml beaker, and after adding an appropriate amount of ion-exchanged water, 1.50 g of a 0.50% by mass aqueous solution of methylene blue was added dropwise. The solution was then transferred to a 1 L volumetric flask and made up to 1 L to prepare artificial urine.

[0098]

[0099] [pH when fluff pulp and artificial urine are mixed] A pulp sheet for fluff pulp conditioned at 23°C and a relative humidity of 50% was cut into 10mm x 10mm squares, and 3g of the pulp was weighed out and placed evenly in a Wonder Blender (Osaka Chemical Co., Ltd., model WB-1, rotation speed 25,000 rpm) and defibrated for 20 seconds to produce fluff pulp. 5g of the fluff pulp produced by the above method was taken and spread thinly on aluminum foil, and 20g of the artificial urine used in [Measurement of the fluff mat return rate] was sprinkled on it using a pipette. The fluff pulp was then placed in a plastic bag with a zipper and left to stand in an oven at 40°C for 1 hour. After 1 hour, the fluff pulp was squeezed by hand, and the pH of the squeezed liquid was measured.

[0100] [Sensory evaluation (rash)] Using fluff mats formed from the fluff pulp sheets of the Examples and Comparative Examples, disposable diapers were produced with reference to the description in Japanese Patent No. 5,849,759. 20 monitors were asked to wear the disposable diapers, and the presence or absence of rash was evaluated. The evaluation criteria were as follows: A: 0 people developed rash B: 1-2 people developed rash C: 3-4 people developed rash D: 5 or more people developed rash

[0101]

[0102]

[0103] In the examples, pulp sheets for fluff pulp were obtained that exhibited less discoloration and better defibration properties than the comparative examples.Furthermore, in the examples, fluff mats that could suppress the occurrence of skin rashes were obtained.

[0104] Second Embodiment [Preparation of Softwood Pulp] [Cooking] Chips of Douglas fir and Pinus genus were mixed in an oven-dry mass ratio of 60:40, and 200 g of the mixture was taken in an oven-dry mass ratio of 200 g. The mixture was placed in a 2.5-liter autoclave and subjected to kraft cooking 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 screened using a flat screen equipped with a 10-cut screen plate to obtain unbleached pulp with a kappa number of approximately 30.

[0105] [Oxygen Delignification] 70.0 g of unbleached pulp was collected on an oven-dry basis, and caustic soda was added to the oven-dry pulp to a concentration of 2.0% by mass. The mixture was then diluted with ion-exchanged water to a pulp concentration of 10% by mass. The mixture 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 after injection of 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.

[0106] [Bleaching] 60 g of the kraft pulp after alkaline oxygen delignification was collected in an oven-dry weight ratio and placed in a plastic bag. The pulp concentration was adjusted to 10% by weight using ion-exchanged water, and then chlorine dioxide was added to the oven-dry pulp to a concentration of 2.0% by weight. The bag was immersed in a thermostatic water bath at 70°C for 60 minutes to perform D0 stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and then dehydrated and washed using a Buchner funnel. The pulp after D0 stage was placed in a plastic bag and adjusted to 10% by weight using ion-exchanged water. Caustic soda and hydrogen peroxide were then added to the oven-dry pulp to a concentration of 1.0% by weight and 0.2% by weight, respectively, and thoroughly mixed. The bag was then immersed in a thermostatic water bath at 70°C for 90 minutes to perform E / P stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and 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. Then, caustic soda and hydrogen peroxide were added to the bone-dry pulp mass at 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 carry out the 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. Then, chlorine dioxide was added to the bone-dry pulp mass at 0.2% by mass, and the pulp was immersed in a thermostatic water bath at 70°C for 60 minutes to carry out the D1 stage bleaching. The resulting bleached softwood pulp was diluted to 3% by mass with ion-exchanged water, then dehydrated and washed using a Buchner funnel.

[0107] [Color Adjustment Step] 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 then dehydrated and washed using a Buchner funnel.

[0108] [Preparation of hardwood pulp] [Cooking] Acacia and Eucalyptus chips were mixed in a bone dry mass ratio of 70:30, and 200 g of bone dry mass was collected 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 screened using a flat screen equipped with an 8-cut screen plate to obtain unbleached pulp with a kappa number of approximately 18.

[0109] [Oxygen Delignification] 70.0 g of unbleached pulp was collected on an oven-dry basis, and caustic soda was added to the oven-dry pulp to a concentration of 2.0% by mass. The mixture was then diluted with ion-exchanged water to a pulp concentration of 10% by mass. The mixture 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 after injection of 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.

[0110] [Bleaching] 60 g of the kraft pulp after alkaline oxygen delignification was collected in an oven-dry weight ratio and placed in a plastic bag. The pulp concentration was adjusted to 10% by weight using ion-exchanged water, and chlorine dioxide was added to the oven-dry pulp to a concentration of 1.0% by weight. The bag was immersed in a thermostatic water bath at 70°C for 60 minutes to perform D0 stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and then dehydrated and washed using a Buchner funnel. The pulp after D0 stage was placed in a plastic bag and adjusted to 10% by weight using ion-exchanged water. Caustic soda and hydrogen peroxide were then added to the oven-dry pulp to a concentration of 1.0% by weight and 0.2% by weight, respectively, and thoroughly mixed. The bag was then immersed in a thermostatic water bath at 70°C for 90 minutes to perform E / P stage treatment. The resulting pulp was diluted to 3% by weight with ion-exchanged water and 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 with 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 in a Buchner funnel.

[0111] [Color Adjustment Step] 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 then dehydrated and washed using a Buchner funnel.

[0112] (Example 101) The bleached softwood pulp and the bleached hardwood pulp after the color adjustment step 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 using a circular standard hand mill (manufactured by Kumagai Riki Kogyo Co., Ltd.) to produce a pulp with a basis weight of 750 g / m. ２ A pulp sheet for fluff pulp was obtained.

[0113] Example 102 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that the amount of hydrogen peroxide added in the color adjustment step after obtaining bleached softwood pulp was set to 0.5%.

[0114] Example 103 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that the amount of hydrogen peroxide added in the color adjustment step after obtaining bleached softwood pulp was set to 1.5%.

[0115] Example 104 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that the pulp concentration in the color tone adjusting step after obtaining bleached softwood pulp was set to 1 mass %.

[0116] Example 105 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that the pulp concentration in the color tone adjusting step after obtaining bleached softwood pulp was set to 20% by mass.

[0117] Example 106 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that the shaking treatment time in the color adjustment step after obtaining bleached softwood pulp was changed to 90 minutes.

[0118] Example 107 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that the shaking treatment time in the color adjustment step after obtaining bleached softwood pulp was changed to 120 minutes.

[0119] Example 108 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that the temperature in the color tone adjustment step after obtaining bleached softwood pulp was set to 80°C.

[0120] Example 109 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that bleached softwood pulp was produced by mixing chips of Pinus and Douglas fir in an oven-dry mass ratio of 70:30.

[0121] (Example 110) A pulp sheet for fluff pulp was obtained by the same operation as in Example 101, 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.

[0122] (Example 111) A pulp sheet for fluff pulp was obtained by the same operation as in Example 101, 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 85:15 during papermaking.

[0123] (Example 112) A pulp sheet for fluff pulp was obtained by the same operation as in Example 101, 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 70:30 during papermaking.

[0124] (Example 113) 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. After that, the same operations as in Example 101 were carried out to obtain a pulp sheet for fluff pulp.

[0125] Comparative Example 101 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that 1.0% of chlorine dioxide was added instead of hydrogen peroxide in the color adjustment step after obtaining bleached softwood pulp.

[0126] Comparative Example 102 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 50:50 during papermaking.

[0127] Comparative Example 103 A pulp sheet for fluff pulp was obtained in the same manner as in Example 101, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 0:100 during papermaking.

[0128] (Measurement and Evaluation) [ISO Brightness] The ISO brightness of the fluff pulp pulp sheet was measured in accordance with 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: Change in ISO brightness = (B0 (%) - B1 (%)) / B0 (%) × 100 In the above formula, B1 is the ISO brightness of the fluff pulp pulp sheet after heating at 105°C for 2 hours, measured in accordance with JIS P 8154-1:2008, and B0 is the ISO brightness of the fluff pulp pulp sheet before heating.

[0129] [Defibrilability] Evaluation of the defibration ability of the pulp sheet for fluff pulp was carried out in an environment of 23°C and 50% relative humidity. The pulp sheet for fluff pulp, which had been conditioned in an environment of 23°C and 50% relative humidity, was cut into 10 mm x 10 mm squares, and 3 g of each was weighed out and placed evenly into a Wonder Blender (manufactured by 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 flocculent pulp formed by defibration is referred to as "fluff pulp"). Subsequently, the fluff pulp was immersed in water and gently stirred with a rod, and then cut into a basis weight of 25 g / 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.

[0130]

[0131]

[0132] 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.

[0133] 5 Pulp defibrator 10 Polypropylene powder funnel 20 Column 22, 24 Stainless steel sieve 30 Polypropylene powder funnel 40 Vacuum cleaner (suction machine) 22 Stainless steel sieve with 180 μm opening 100 Fluff mat making device

Claims

1. A pulp sheet for fluff pulp, having a pH of 7.0 to 9.5 when extracted with hot water as measured in accordance with JIS P 8133-2:2013.

2. A pulp sheet for fluff pulp as described in claim 1, having an ISO brightness of 80% or more measured in accordance with JIS P 8148:2018.

3. The pulp sheet for fluff pulp according to claim 1, wherein the pulp sheet for fluff pulp contains coniferous pulp, and the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 30 mass% or less.

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

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

6. The pulp sheet for fluff pulp according to claim 5, wherein the pulp sheet for fluff pulp contains coniferous pulp, and the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 15 mass% or less.

7. A fluff mat formed from the pulp sheet for fluff pulp according to any one of claims 1 to 6.

8. A fluff mat as described in claim 7, in which 5 parts by weight of the fluff mat is mixed with 20 parts by weight of artificial urine containing 1.94% by weight of urea, 0.8040% by weight of sodium chloride, 0.2045% by weight of magnesium sulfate heptahydrate and 0.0835% by weight of calcium chloride dihydrate, and the pH of the squeezed liquid from the fluff mat after being left in a sealed state at 40°C for 1 hour is 6.6 or higher.

9. An absorbent article comprising the fluff mat according to claim 7.

10. A method for manufacturing a pulp sheet for fluff pulp, comprising a cooking process for cooking pulp raw material to produce unbleached pulp, a bleaching process, a heating process, and a sheet forming process, the heating process being performed after the bleaching process.

11. A method for producing a pulp sheet for fluff pulp as described in claim 10, wherein in the heating treatment step, heating treatment is carried out so that the pulp slurry temperature is 30°C or higher and 100°C or lower.

12. A method for producing a pulp sheet for fluff pulp as described in claim 10, wherein the heating treatment time in the heating treatment step is 10 minutes or more and 120 minutes or less.

13. A method for producing a pulp sheet for fluff pulp as described in claim 10, wherein the pulp slurry concentration in the heating treatment is 0.5 mass% or more and 40 mass% or less.

14. A method for producing a pulp sheet for fluff pulp as described in claim 10, wherein the pH of the pulp slurry during the heating treatment is 2.0 or more and 9.0 or less.

Images