Pulp sheets for fluff pulp, fluff mats, absorbent articles, and methods for manufacturing pulp sheets for fluff pulp

Abstract

The object of this invention is to provide a pulp sheet for fluff pulp that can produce a fluff mat in which the occurrence of skin irritation is suppressed, and that also has excellent defibrillation properties. [Solution] The present invention relates to a pulp sheet for fluff pulp containing coniferous tree pulp, This invention relates to a pulp sheet for fluff pulp in which the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 40% by mass or less, and when the chlorine concentration in 100 mL of hot water extract obtained by extracting 2 g of the pulp sheet for fluff pulp in 100 mL of hot water at 100°C for 1 hour in accordance with JIS P 8133-2:2013 is measured by ion chromatography, the chlorine concentration is 0.60 mg / L or less.

Description

[Technical Field]

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

[0002] Fluff pulp is made by breaking down wood pulp until it becomes cotton-like. Fluff pulp is used as an absorbent material in absorbent products such as disposable diapers and sanitary napkins.

[0003] Conventionally, fluff pulp used in absorbent articles has been made from softwood pulp with good defibration properties (for example, Patent Document 1). In Patent Document 1, fluff pulp is obtained by mechanically defibrating raw material pulp (bleached softwood 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 being investigated how to obtain a pulp sheet for fluff pulp that can reduce the amount of absorbent liquid returning and suppress skin irritation by setting 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 Publication No. 2012-211411 [Patent Document 2] International Publication No. 2022 / 138870 [Overview of the initiative] [Problems that the invention aims to solve]

[0006] As mentioned above, pulp sheets for fluff pulp containing bleached hardwood kraft pulp or bleached softwood kraft pulp are known, but when conventional pulp sheets for fluff pulp are defibrated to form fluff mats, skin irritation can occur, and improvement is needed. In addition, when conventional pulp sheets for fluff pulp are defibrated, the defibration ability is sometimes insufficient, and improvement is 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 can form a fluff mat that can suppress the occurrence of skin irritation and has excellent defibrillation properties. [Means for solving the problem]

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

[0009] [1] A pulp sheet for fluff pulp containing coniferous pulp, The hardwood pulp content in the pulp sheet for fluff pulp is 40% by mass or less of the total pulp components. A pulp sheet for fluff pulp in which the chlorine concentration in 100 mL of hot water extract obtained by extracting 2 g of the pulp sheet for fluff pulp in 100 mL of hot water at 100°C for 1 hour in accordance with JIS P 8133-2:2013 is measured by ion chromatography and the chlorine concentration is 0.60 mg / L or less. [2] The 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% by mass or less. [3] A fluff mat formed from a pulp sheet for fluff pulp as described in [1] or [2]. [4] An absorbent article comprising the fluff mat described in [3]. [5] The manufacturing method of a pulp sheet for fluff pulp includes a cooking process of cooking pulp raw materials into unbleached pulp, a bleaching process, a chlorine removal process, and a sheet forming process, The chlorine removal process is provided after the bleaching process, In the chlorine removal process, a method for manufacturing a pulp sheet for fluff pulp in which hydrogen peroxide treatment is performed. [6] In the chlorine removal process, heating treatment is performed so that the pulp slurry temperature becomes 30°C or higher and 120°C or lower. The manufacturing method of a pulp sheet for fluff pulp according to [5]. [7] The heating treatment time in the chlorine removal process is 10 minutes or more and 150 minutes or less. The manufacturing method of a pulp sheet for fluff pulp according to [6].

Advantages of the Invention

[0010] According to the present invention, it is possible to obtain a pulp sheet for fluff pulp that can manufacture a fluff mat capable of suppressing the occurrence of skin rashes, and that has excellent fibrillation properties.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a schematic diagram for explaining the configuration of a fluff mat manufacturing apparatus used for manufacturing a fluff mat.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be based on typical embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0013] (Pulp Sheet for Fluff Pulp) This embodiment relates to a pulp sheet for fluff pulp containing coniferous pulp, wherein the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 40% by mass or less, and when the chlorine concentration in 100 mL of hot water extract obtained by extracting 2 g of the pulp sheet for fluff pulp in 100 mL of hot water at 100°C for 1 hour in accordance with JIS P 8133-2:2013 is measured by ion chromatography, the chlorine concentration is 0.60 mg / L or less.

[0014] In this specification, "fluff pulp" refers to defibrated pulp, meaning pulp that has been fibrousized or shredded. "Pulp sheet for fluff pulp" refers to a pulp sheet used to produce fluff pulp before defibration. That is, "fluff pulp" is obtained by defibrating the "pulp sheet for fluff pulp," and the "fluff pulp" formed into a sheet is called "fluff mat." In this embodiment, the "pulp sheet for fluff pulp" is obtained, for example, by papermaking a slurry containing raw pulp.

[0015] In this embodiment, a pulp sheet for fluff pulp is extracted with hot water in accordance with JIS P 8133-2:2013, and the chlorine concentration in the obtained hot water extract is analyzed by ion chromatography.

[0016] The chlorine concentration in 100 mL of hot water extract should be 0.60 mg / L or less, preferably 0.55 mg / L or less, more preferably 0.50 mg / L or less, and even more preferably 0.45 mg / L or less. The lower limit of the chlorine concentration in the hot water extract is not particularly limited and may be 0 mg / L. In this embodiment, by making the chlorine concentration in the hot water extract obtained by hot water extraction of the pulp sheet for fluff pulp below the above upper limit, it is possible to suppress the occurrence of skin irritation during use when a fluff mat is formed from the pulp sheet for fluff pulp.

[0017] In this embodiment, for example, in the manufacturing process of pulp sheets for fluff pulp, a chlorine removal step is provided after bleaching the pulp raw materials, and hydrogen peroxide treatment is performed in the chlorine removal step, thereby adjusting the chlorine concentration contained in the hot water extract to a desired range. It is also preferable to heat the chlorine in the chlorine removal step under appropriate conditions. Furthermore, the chlorine concentration can be easily brought within the predetermined range by appropriately adjusting the pulp raw materials.

[0018] The pulp sheet for fluff pulp of this embodiment exhibits good defibration properties when fluffed. In this specification, defibration properties can be evaluated by the defibration time (seconds) required until there is no undefibrated material left. Specifically, the shorter the defibration time, the better the defibration properties are judged to be, and good defibration properties can increase the production efficiency of fluff mats. Furthermore, good defibration properties make it easier to obtain fluff mats in which liquid backflow is suppressed. In addition, good defibration properties reduce the amount of undefibrated material in the fluff mat, which not only improves the appearance of the fluff mat but also improves the ability of the fluff mat to maintain its shape. When used as an absorbent layer in sanitary materials such as disposable diapers, it reduces the possibility that the shape of the absorbent layer will collapse due to movement during use, thereby reducing the absorbent performance of the disposable diaper.

[0019] The basis weight of the pulp sheet for fluff pulp in this embodiment is not particularly limited and should be manufactured at a basis weight that can be produced in the papermaking apparatus used for papermaking. For example, the basis weight of the pulp sheet for fluff pulp may be 100 g / m². 2 Preferably, it should be 150 g / m² or more. 2 It is more preferable that the amount be greater than or equal to 200 g / m². 2 It is even more preferable that the above conditions are met. Furthermore, the basis weight of the pulp sheet for fluff pulp should be 1500 g / m². 2 Preferably, it is 1400g / m² 2 It is more preferable that the following conditions apply: 1300 g / m² 2 The following is even more preferable: The basis weight of the pulp sheet for fluff pulp shall be measured in accordance with JIS P 8124:2011.

[0020] The density of the pulp sheet for fluff pulp in this embodiment is not particularly limited, but it is preferably 0.3 g / cm 3 or more, more preferably 0.4 g / cm 3 or more, and even more preferably 0.5 g / cm 3 or more. Also, the density of the pulp sheet for fluff pulp is preferably 0.95 g / cm 3 or less, more preferably 0.90 g / cm 3 or less, and even more preferably 0.85 g / cm 3 or less. The density of the pulp sheet for fluff pulp is measured in accordance with JIS P 8118:2014.

[0021] The specific bursting strength of the pulp sheet for fluff pulp in this embodiment measured in accordance with JIS P 8131:2009 is preferably 0.5 kPa·m 2 / g or more, more preferably 0.7 kPa·m 2 / g or more, and even more preferably 0.9 kPa·m 2 / g or more. Also, the specific bursting strength of the pulp sheet for fluff pulp is preferably 5.0 kPa·m 2 / g or less, more preferably 4.5 kPa·m 2 / g or less, and even more preferably 4.0 kPa·m 2 / g or less.

[0022] (Raw pulp) The pulp sheet for fluff pulp in this embodiment contains softwood pulp. The pulp sheet for fluff pulp in this embodiment may also contain hardwood pulp, but the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is preferably 40% by mass or less, more preferably 30% by mass or less, even 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 the total pulp components in the pulp sheet for fluff pulp. By setting the hardwood pulp content to 0% by mass, the defibrillability of the fluff pulp can be more effectively enhanced. On the other hand, by including hardwood pulp within the above range, it is possible to suppress the backflow of liquid absorbed by the fluff mat. In a fluff mat where backflow is suppressed, the occurrence of skin irritation is more effectively suppressed.

[0023] The content of softwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is preferably 60% by mass or more, more preferably 70% by mass or more, even 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. Furthermore, there is no particular upper limit to the content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp, and it may be 100% by mass.

[0024] Examples of coniferous and hardwood pulps 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 chemical groundwood pulp (CGP); and mechanical pulps such as crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Furthermore, coniferous and hardwood pulps may also be dissolved pulp (DP).

[0025] In particular, the coniferous pulp contained in the pulp sheet for fluff pulp is preferably bleached coniferous kraft pulp. The raw material for bleached coniferous kraft pulp preferably contains at least one species selected from the group consisting of pine, fir, and cedar, and more preferably contains at least one species selected from the group consisting of pine and fir. Furthermore, in this embodiment, it is preferable to use pine and fir in combination.

[0026] The Canadian standard filtration efficiency (CSF) of softwood pulp, measured in accordance with JIS P 8121-2:2012, is preferably 600 ml or higher, more preferably 640 ml or higher, and even more preferably 670 ml or higher. However, this Canadian standard filtration efficiency (CSF) of softwood pulp is the value measured for softwood pulp before papermaking.

[0027] When hardwood pulp is included in the pulp sheet for fluff pulp, the hardwood pulp is preferably bleached hardwood kraft pulp. The raw materials for the bleached hardwood kraft pulp preferably include 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 also preferable to use Acacia and Eucalyptus in combination as raw materials for the bleached hardwood kraft pulp.

[0028] The Canadian standard water-saturation fluid (CSF) of hardwood pulp, measured in accordance with JIS P 8121-2:2012, is preferably 370 ml or higher, more preferably 400 ml or higher, and even more preferably 430 ml or higher. However, this Canadian standard water-saturation fluid (CSF) of hardwood pulp is the value measured for hardwood pulp before papermaking.

[0029] The pulp sheet for fluff pulp in 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 pulps and deinked pulps. Examples of non-wood pulps include cotton pulps such as cotton linters and cotton lint, bamboo pulp, hemp, straw and bagasse and other non-wood pulps. Examples of deinked pulps include deinked pulps made from recycled paper. In this case, the content of other raw material pulps is preferably 10% by mass or less of the total pulp components in the pulp sheet for fluff pulp.

[0030] The length-weighted average fiber length of the softwood pulp used as raw material is preferably 1.50 mm or more, more preferably 1.75 mm or more, and even more preferably 2.00 mm or more. Furthermore, 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. Furthermore, when hardwood pulp is included as a 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. In addition, 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 keeping the fiber lengths of the various pulps contained in the pulp sheet for fluff pulp within the above range, it becomes easier to control the thickness and density of the pulp sheet for fluff pulp within an appropriate range. Furthermore, by keeping the fiber lengths of the various pulps contained in the pulp sheet for fluff pulp within the above range, it is possible to effectively suppress the backflow of liquid absorbed into the fluff mat when the pulp sheet for fluff pulp is made into fluff. The length-weighted average fiber length of the various pulps contained in the pulp sheet for fluff pulp is measured in accordance with JIS P 8226-2:2011.

[0031] (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, yield enhancers, water drainage enhancers, dry strength enhancers, wet strength enhancers, coloring pigments, water resistant agents, antistatic agents, sodium sulfate, surfactants, pH adjusting chemicals (such as sodium hydroxide), etc. The pulp sheet for fluff pulp in this embodiment may contain a softener. By including a softener in the pulp sheet for fluff pulp, it is possible to more effectively enhance its defibrillability.

[0032] (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 digestion step of digesting the pulp raw material to obtain unbleached pulp, a bleaching step, a chlorine removal step, and a sheeting step. A dewatering and washing step may be provided between each step as appropriate. Furthermore, a pre-hydrolysis step may be provided before the digestion step, an oxygen delignin step may be provided before the bleaching step, and a cold alkali step may be provided after the bleaching step. In addition, a beating step may be provided before the sheeting step to beat the bleached pulp to a desired freeness.

[0033] (Cooking process) In the digestion process, the pulp raw material is digested to obtain unbleached pulp. Known methods can be used for digestion. The digestion conditions in the digestion process are not particularly limited, but for example, when using the Kraft digestion method, the degree of sulfurization of the digested liquid is preferably 15-45%, the digestion temperature is preferably 130-170°C, the effective alkali addition rate is preferably 5-30% by mass per unit of oven-dry wood mass, and the digestion time is preferably 45-500 minutes. The copper number of the unbleached pulp obtained through the digestion process is preferably 10-70.

[0034] (Pre-hydrolysis step) A pre-hydrolysis step can be provided before the pulping step. In the pre-hydrolysis step, hardwoods or conifers are heated in the presence of water to perform pre-hydrolysis treatment. Here, the amount of water relative to the hardwoods or conifers (liquid ratio: amount of water (parts by mass) / amount of hardwoods or conifers (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 higher is preferable because it allows hydrolysis to proceed sufficiently and the reaction to become uniform. A liquid ratio of 10 or lower is preferable because it reduces the amount of heat required to heat to the desired temperature, making it more economical. The method of adding water is not particularly limited; water may be added from an external source, water originally contained in the hardwoods or conifers may be used, or if steam is used during heating, water contained in the steam may be used. In addition, chemicals that directly or indirectly assist in the hydrolysis of polysaccharides, such as alkalis, acids, and chelating agents, may be added along with the water.

[0035] (Oxygen delignin process) In the manufacturing process of pulp sheets for fluff pulp, it is preferable to include an oxygen delignin step after the digestion step and before the bleaching step. In the oxygen delignin step, an alkaline chemical and oxygen are added to the unbleached pulp, and the lignin is decomposed at high temperature and pressure and eluted by the alkaline chemical. By deligninizing in the oxygen delignin step, the amount of bleaching chemical used in the subsequent multi-stage bleaching step can be reduced, and the deterioration of pulp quality can be kept to a minimum. As for the oxygen delignin method, known medium-concentration methods or high-concentration methods can be applied as they are, but the medium-concentration method, in which the pulp concentration is 8 to 15% by mass and is currently used in general, is preferred.

[0036] In the oxygen delignin process using the medium-concentration method, caustic soda or oxidized Kraft white liquor can be used as the alkali, and oxygen from cryogenic separation, PSA (Pressure Swing Adsorption), or VSA (Vacuum Swing Adsorption) can be used as the oxygen gas. The oxygen gas and alkali are added to a medium-concentration pulp slurry in a medium-concentration mixer, and after thorough mixing, the mixture of pulp, oxygen, and alkali is sent to a reaction tower capable of holding it under pressure for a certain period of time for deligninization. The oxygen gas addition rate is preferably 0.5 to 3% by mass per oven-dry pulp mass, the alkali addition rate is preferably 0.5 to 4% by mass, the reaction temperature is preferably 80 to 120°C, the reaction time is preferably 15 to 100 minutes, and the pulp concentration is preferably 8 to 15% by mass. Other known conditions can be applied.

[0037] (bleaching process) In the bleaching process, the pulp that has undergone oxygen delignin is bleached to obtain bleached pulp. The bleaching method is not particularly limited and can be bleached using known bleaching methods. Examples of bleaching methods include an ozone bleaching stage (Z), a chlorine dioxide bleaching stage (D), an alkaline 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, for example, it is preferable to perform the steps in the order of D0-E / P-D1. Note that the Z stage is preferable to avoid because it causes significant damage to the pulp fibers, resulting in a loss of fiber rigidity and thus worsening the defibrillability of the pulp sheet for fluff pulp.

[0038] The bleaching conditions in stages D0 and D1 are not particularly limited, but the addition rate of chlorine dioxide 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 concentration is preferably 5 to 15% by mass, and the pH at the end of the reaction is preferably 2 to 6. Similarly, the bleaching conditions in stages E / P are not particularly limited, but the addition rate of hydrogen peroxide 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 concentration is preferably 5 to 15% by mass, and the pH at the end of the reaction is preferably 10 to 12.

[0039] (Cold alkali process) In this embodiment, bleached pulp may be further subjected to alkaline treatment to obtain bleached pulp after cold alkaline treatment. The treatment method is not particularly limited, but caustic soda can be used as the alkali. The addition rate of caustic soda 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 concentration is preferably 5 to 15% by mass.

[0040] (Chlorine removal process) In this embodiment, it is preferable to provide a chlorine removal step after the bleaching step, in which chlorine introduced during the bleaching step and other steps is removed. It is preferable that hydrogen peroxide treatment is performed in the chlorine removal step. If a hydrogen peroxide treatment step is provided as the final step of the bleaching step, that step corresponds to the chlorine removal step. Alternatively, a hydrogen peroxide treatment step may be provided separately from the bleaching step.

[0041] In the chlorine removal process, heating treatment may be applied. The pulp slurry temperature in the heating treatment process is preferably 30°C or higher, more preferably 35°C or higher, and even more preferably 40°C or higher. Furthermore, the pulp slurry temperature in the heating treatment process is preferably 120°C or lower, and more preferably 100°C or lower. While the pulp slurry temperature in the heating treatment process is preferable as long as it is within the above range, it does not necessarily have to be a constant temperature.

[0042] If heating is performed in the chlorine removal process, 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. Furthermore, the heating time is preferably 600 minutes or less, more preferably 300 minutes or less, even more preferably 150 minutes or less, and particularly preferably 120 minutes or less.

[0043] In this embodiment, the chlorine removal efficiency can be further improved by performing the heat treatment under the above conditions. As a result, it becomes easier to adjust the chlorine concentration in the hot water extract obtained by hot water extraction of the pulp sheet for fluff pulp to a desired range.

[0044] If heating is performed in the chlorine removal process, the heating method in the heating process is not particularly limited. Steam may be directly introduced into the pulp slurry for heating, a jacket-type heating device may be used, or the 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 process may be used for temperature retention. If a heating container is used in the heating process, the material may be concrete, metal, or resin. A dedicated heating tank may be used as the heating container, or the residence time until the sheet formation process may be utilized.

[0045] The pH of the pulp slurry in the chlorine removal process is preferably 2.0 or higher, more preferably 2.5 or higher, and even more preferably 3.0 or higher. Furthermore, the pH of the pulp slurry in the chlorine removal process is preferably 9.0 or lower, more preferably 8.5 or lower, and even more preferably 8.0 or lower. While the pH of the pulp slurry in the chlorine removal process is preferable as long as it is within the above range, it does not necessarily have to be a constant pH.

[0046] The concentration of the pulp slurry in the chlorine removal process is preferably 0.5% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more. Furthermore, 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 chlorine removal process is preferable within the above range, it does not necessarily have to be a constant concentration.

[0047] In this embodiment, by providing a chlorine removal step, it becomes easy to adjust the chlorine concentration in the hot water extract obtained by hot water extraction of the pulp sheet for fluff pulp to a desired range.

[0048] (Washing process) A washing step may be provided after each of the above-described steps. The washing step is preferably a dewatering washing step. In the dewatering washing step, the pulp after each step is diluted and washed by combining dewatering. The washing method is not particularly limited and can be washed using a known washing machine. For example, a displacement washing method, a dilution-dewatering method, a press washing method, or a washing method combining these may be used.

[0049] (Sheet formation process) In the sheet-forming process, the bleached pulp obtained through the chlorine removal process is dispersed in water to prepare a slurry. The pulp concentration in the slurry is preferably 0.01 to 10% by mass. Furthermore, if additives are to be added as needed, it is preferable to add the additives to the slurry.

[0050] The sheet-forming process includes the step of forming the slurry into paper using a paper machine. The paper machine used in the paper-making process is not particularly limited, but for example, a wire screen paper machine, a cylinder screen paper machine, a hybrid former, a gap former, etc., can be used. Furthermore, when forming the paper, it may be formed into a single layer, or multiple layers may be formed by combining them.

[0051] (Fluff mat) This embodiment relates to a fluff mat formed from the pulp sheet for fluff pulp described above. In this specification, a fluff mat is formed into a sheet from fluff pulp obtained by defibrating the pulp sheet for fluff pulp described above. When the fluff mat of this embodiment is used, for example, as a component material for a diaper, it can suppress the occurrence of skin rash. Furthermore, the fluff mat of this embodiment has excellent water absorption and can retain liquid after absorbing it. Therefore, the backflow of liquid is suppressed in the fluff mat of this embodiment. And in a fluff mat where backflow is suppressed, the occurrence of skin rash is more effectively suppressed.

[0052] The conditions for defibrating pulp sheets for fluff pulp are not particularly limited; for example, known defibrating machines and pulverizers can be used.

[0053] Fluff mats are formed by layering fluff pulp under an airflow. Specifically, The fluff pulp, which has been defibrated, is transported by air and laminated onto a metal mesh or a porous substrate such as tissue or nonwoven fabric to form the material.

[0054] (Analytical items) This embodiment may also relate to an absorbent article having the fluff mat described above. Examples of absorbent articles include disposable diapers, urine pads, light incontinence pads, and sanitary napkins. Since the fluff mat of this embodiment can neutralize particularly acidic urine, the absorbent article is preferably a disposable diaper, urine pad, or light incontinence pad. [Examples]

[0055] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0056] [Preparation of coniferous pulp] [Cooking] Chips of the genera *Pinus sieboldiana* and *Pinus genus* were mixed in an oven-dry mass ratio of 60:40. 200g of the mixture was taken (oven-dry mass) and placed in a 2.5-liter autoclave. Kraft pulping was performed under the following conditions: liquid ratio of 5, pulp sulfurization degree of 28%, alkali addition rate of 22%, pulping temperature of 165°C, and pulping time of 120 minutes. The black liquor and pulp were then separated, and the pulp was refined using a flat screen with a 10-cut screen plate to obtain unbleached pulp with a copper number of approximately 30.

[0057] [Oxygen delignin] 70.0 g of unbleached pulp was taken by oven-dry weight, and caustic soda was added to the oven-dry pulp mass to a concentration of 2.0% by mass. The mixture was then diluted with deionized water to adjust the pulp concentration to 10% by mass. This was placed in a heated autoclave, and 99.9% commercially available compressed oxygen gas was injected to set the gauge pressure to 0.5 MPa. Delignin was performed at 95°C for 60 minutes. The resulting pulp was diluted to 3% by mass with deionized water, then dehydrated and washed using a Buchner funnel.

[0058] [bleaching] 60g of kraft pulp, after alkaline oxygen deligninization, was collected by its oven-dry mass, placed in a plastic bag, and the pulp concentration was adjusted to 10% by mass using deionized water. Then, chlorine dioxide was added to a concentration of 2.0% by mass relative to the oven-dry mass of pulp. This was immersed in a constant temperature water bath at 70°C for 60 minutes to perform the D0 stage treatment. The resulting pulp was diluted to 3% by mass with deionized water, then dehydrated and washed using a Buchner funnel. The pulp after the D0 stage was placed in a plastic bag, and deionized water was added to adjust the pulp concentration to 10% by mass. Then, caustic soda was added in an amount of 1.0% by mass and hydrogen peroxide in an amount of 0.2% by mass relative to the mass of the oven-dried pulp, and the mixture was thoroughly mixed. After that, the E / P stage treatment was performed by immersion in a constant temperature water bath at 70°C for 90 minutes. The obtained pulp was diluted to 3% by mass with deionized water, and then dehydrated and washed using a Buchner funnel. The pulp after the E / P stage was placed in a plastic bag, and the pulp concentration was adjusted to 10% by mass using deionized water. Then, 1.0% by mass of caustic soda and 0.3% by mass of hydrogen peroxide were added relative to the weight of the oven-dried pulp, and the mixture was thoroughly mixed. After that, the P0 stage treatment was performed by immersion in a constant temperature water bath at 70°C for 90 minutes. The resulting pulp was diluted to 3% by mass with deionized water, and then dehydrated and washed using a Buchner funnel. The pulp after step P0 was placed in a plastic bag, and the pulp concentration was adjusted to 10% by mass using deionized water. Then, chlorine dioxide was added so that it was 0.2% relative to the mass of the oven-dried pulp, and the pulp was immersed in a constant temperature water bath at 70°C for 60 minutes to perform bleaching in step D1. The resulting bleached softwood pulp was diluted to 3% by mass with deionized water, and then dehydrated and washed using a Buchner funnel.

[0059] [Chlorine removal process] Bleached softwood pulp was placed in a beaker, and the pulp concentration was adjusted to 10% by mass using deionized water. The slurry was then placed in a shaker heated to 60°C, and hydrogen peroxide was added to a concentration of 1.0% relative to the mass of the oven-dried pulp. The beaker was then covered and shaken for 60 minutes to adjust the color. The resulting color-adjusted pulp was diluted to 3% by mass with deionized water, and then dehydrated and washed using a Buchner funnel.

[0060] [Preparation of hardwood pulp] [Cooking] Acacia and eucalyptus wood chips were mixed in an oven-dry mass ratio of 70:30. 200g of the mixture was taken (oven-dry mass) and placed in a 2.5-liter autoclave. Kraft pulping was performed under the following conditions: liquid ratio of 5, sulfurization degree of the pulp of the pulp, alkali addition rate of 20%, pulping temperature of 155°C, and pulping time of 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 copper number of approximately 18.

[0061] [Oxygen delignin] 70.0 g of unbleached pulp was taken by oven-dry weight, and caustic soda was added to the oven-dry pulp mass to a concentration of 2.0% by mass. The mixture was then diluted with deionized water to adjust the pulp concentration to 10% by mass. This was placed in a heated autoclave, and 99.9% commercially available compressed oxygen gas was injected to set the gauge pressure to 0.5 MPa. Delignin was performed at 95°C for 60 minutes. The resulting pulp was diluted to 3% by mass with deionized water, then dehydrated and washed using a Buchner funnel.

[0062] [bleaching] 60g of kraft pulp, after alkaline oxygen deligninization, was collected by its oven-dry mass, placed in a plastic bag, and the pulp concentration was adjusted to 10% by mass using deionized water. Then, chlorine dioxide was added to a concentration of 1.0% by mass relative to the oven-dry mass of pulp. This was immersed in a constant temperature water bath at 70°C for 60 minutes to perform the D0 stage treatment. The resulting pulp was diluted to 3% by mass with deionized water, then dehydrated and washed using a Buchner funnel. The pulp after the D0 stage was placed in a plastic bag, and deionized water was added to adjust the pulp concentration to 10% by mass. Then, caustic soda was added in an amount of 1.0% by mass and hydrogen peroxide in an amount of 0.2% by mass relative to the mass of the oven-dried pulp, and the mixture was thoroughly mixed. After that, the E / P stage treatment was performed by immersion in a constant temperature water bath at 70°C for 90 minutes. The obtained pulp was diluted to 3% by mass with deionized water, and then dehydrated and washed using a Buchner funnel. The pulp after the E / P stage was placed in a plastic bag, and the pulp concentration was adjusted to 10% by mass using deionized water. Then, chlorine dioxide was added so that it was 0.2% by mass relative to the mass of the oven-dried pulp, and the bag was immersed in a constant temperature 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 deionized water, and then dehydrated and washed using a Buchner funnel.

[0063] [Chlorine removal process] Bleached hardwood pulp was placed in a beaker, and the pulp concentration was adjusted to 10% by mass using deionized water. The slurry was then placed in a shaker heated to 60°C, and hydrogen peroxide was added to a concentration of 1.0% relative to the mass of the oven-dried pulp. The beaker was then covered and shaken for 60 minutes to adjust the color. The resulting color-adjusted pulp was diluted to 3% by mass with deionized water, and then dehydrated and washed using a Buchner funnel.

[0064] (Example 1) After the chlorine removal process, bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 100:0 to obtain a slurry with a pulp concentration of 1% by mass. This slurry was then processed using a circular standard hand-formed papermaking machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a basis weight of 750 g / m². 2 The papermaking process was carried out to obtain a pulp sheet for fluff pulp.

[0065] (Example 2) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the amount of hydrogen peroxide added in the chlorine removal process after obtaining bleached softwood pulp was set to 0.5%.

[0066] (Example 3) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the amount of hydrogen peroxide added in the chlorine removal process after obtaining bleached softwood pulp was set to 1.5%.

[0067] (Example 4) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the pulp concentration in the chlorine removal process after obtaining bleached softwood pulp was set to 1% by mass.

[0068] (Example 5) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the pulp concentration in the chlorine removal process after obtaining bleached softwood pulp was set to 20% by mass.

[0069] (Example 6) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the shaking treatment time in the chlorine removal process after obtaining bleached softwood pulp was set to 90 minutes.

[0070] (Example 7) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the shaking treatment time in the chlorine removal process after obtaining bleached softwood pulp was set to 120 minutes.

[0071] (Example 8) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the temperature of the chlorine removal process after obtaining bleached softwood pulp was set to 80°C.

[0072] (Example 9) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the temperature of the chlorine removal process after obtaining bleached softwood pulp was set to 100°C.

[0073] (Example 10) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that bleached coniferous pulp was prepared by mixing chips of pine and fir trees in an oven-dry mass ratio of 70:30.

[0074] (Example 11) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that bleached softwood pulp and bleached hardwood pulp after the chlorine removal process were mixed in an oven-dry mass ratio of 95:5 during papermaking.

[0075] (Example 12) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that bleached softwood pulp and bleached hardwood pulp after the chlorine removal process were mixed in an oven-dry mass ratio of 85:15 during papermaking.

[0076] (Example 13) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that bleached softwood pulp and bleached hardwood pulp after the chlorine removal process were mixed in an oven-dry mass ratio of 70:30 during papermaking.

[0077] (Example 13) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 85:15 before the chlorine removal process, a color adjustment treatment was performed while maintaining the same ratio, and then papermaking was carried out.

[0078] (Comparative Example 1) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that 1.0% chlorine dioxide was added instead of hydrogen peroxide in the chlorine removal process after obtaining bleached softwood pulp.

[0079] (Comparative Example 2) A pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that the chlorine removal process was not carried out.

[0080] (Comparative Example 3) In Example 1, a pulp sheet for fluff pulp was obtained by performing the same procedure as in Example 1, except that bleached softwood pulp and bleached hardwood pulp were mixed in an oven-dry mass ratio of 50:50 during papermaking.

[0081] (Comparative Example 4) In Example 1, a pulp sheet for fluff pulp was obtained by performing the same procedure 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.

[0082] (Measurement and evaluation) [Chlorine] In accordance with JIS P 8133-2:2013, 2 g of pulp sheet for fluff pulp was extracted in 100 mL of hot water at 100°C for 1 hour to obtain 100 mL of hot water extract. The chloride ion concentration in the hot water extract was quantified using ion chromatography (manufacturer: Thermo Fisher Scientific, model: RFIC Integrion).

[0083] [Reverse rate] A fluff mat used to measure the backflow rate was prepared using the following method. The fluff mat was prepared in an environment of 23°C and 50% relative humidity using the fluff mat preparation apparatus 100 shown in Figure 1. The fluff mat preparation apparatus 100 was assembled in the configuration shown in Figure 1 using a pulp defibration machine 5 (manufactured by Maruto Seiki Co., Ltd.), a stainless steel sieve 24 with a mesh opening of 180 μm (manufactured by Nonaka Rikaki Seisakusho Co., Ltd., inner diameter 100 mm x inner height 45 mm), a column 20 made from a PET resin plate cut to 70 cm x 40 cm (manufactured by AcrySunday Co., Ltd., Sunday PET, thickness 0.5 mm), a polypropylene powder funnel 30 (manufactured by AS ONE Corporation, model No. 169, mouth diameter 120 mm, leg outer diameter 30 mm, leg length 27 mm), and a household vacuum cleaner 40 (manufactured by Hitachi Home & Life Solutions Co., Ltd., model CV-CF4). First, the pulp defibration machine and a household vacuum cleaner were started. The household vacuum cleaner was set to low power (suction power of approximately 80W), and the fluff pulp without undefibrated material, obtained during the evaluation of defibration properties described above, was fed in small amounts from the top of the fluff mat production device. This was continued until the entire amount of defibrated pulp had been fed in, forming the fluff mat. Once the entire amount had been discharged, the pulp defibration machine and the household vacuum cleaner were stopped. After removing the column, the fluff mat (10 cm in diameter) was carefully removed from a sieve with a mesh size of 180 μm to avoid damaging its shape. The side that had been in contact with the stainless steel mesh was designated as the wire side of the fluff mat. Center sheets cut into 10 cm diameter circles (manufactured by Oji Nepia Co., Ltd., basis weight 25 g / m²) were placed above and below the removed fluff mat. 2A center sheet was placed on top of the surface of the fluffy mat, and a circular stainless steel plate was placed on top of the center sheet. The fluffy mat was then pressed with a manual press (vise press, manufactured by AS ONE Corporation, model number MP-001) at the press pressure listed in Table 1 so that the thickness of the fluffy mat was 4.2 mm, thereby obtaining a fluffy mat with a center sheet. It was removed from the press without damaging its shape and used for reverse measurement. The backflow rate of the fluff mat with a center sheet was measured under conditions of 23°C and 50% relative humidity. 2 A fluff mat was placed on a 5mm thick acrylic plate with the wire side facing up. After inserting a 2mm thick spacer, another 5mm thick acrylic plate was placed on top, and it was pressed for 10 minutes using a tabletop press. After pressing, the top acrylic plate was removed, and it was left to stand for 30 minutes. A stainless steel base plate (5mm thick, 11cm x 11cm) was placed on a horizontal laboratory table, and two fluff mats were placed on top of it with the wire side facing up (total basis weight of fluff mat: 200g / m²). 2 ). On top of that, a stainless steel strike-through plate (10cm x 10cm, 85mm thick, weighing 665g) with a 25mm diameter hole in the center was placed, and after 10 seconds, 20g of artificial urine was poured into the hole of the strike-through plate. After the artificial urine was completely absorbed, the strike-through plate was immediately removed. Next, an 11cm x 11cm polyethylene sheet was placed on top of the center sheet, and an 11cm x 11cm chloroprene rubber sponge sheet (manufactured by AS ONE Corporation, 10mm thick, hardness (Asker C hardness meter): 45 degrees) was placed on top of that, and an 11cm x 11cm 5mm thick acrylic plate was placed on top of that, and a 2.2kg weight was placed on top of that. The total weight of the polyethylene sheet, sponge rubber sheet, two acrylic plates, and 2.2kg weight was 2.31kg, and the area of ​​the fluff mat was 0.00785m² 2Therefore, the pressure applied to the fluff mat was 2.9 kPa. The mat was pressurized at 2.9 kPa for 3 minutes. Next, the polyethylene sheet, sponge rubber sheet, two acrylic plates, and 2.2 kg weight were removed, and 10 sheets of 11 cm x 11 cm square filter paper (manufactured by ADVANTEC Co., Ltd., No. 1640), which were humidity-controlled and of known weight in an environment of 23°C and 50% relative humidity, were placed so that the front side was in contact with the center sheet of the fluff mat with a center sheet. The clear file, urethane rubber sheet, two acrylic plates, and 2.2 kg weight were placed back on top, and artificial urine was absorbed into the filter paper while pressurizing for 2 minutes. After 2 minutes, the 10 sheets of filter paper were removed and their weight was measured, and the return rate was measured using the following formula. The artificial urine used here was prepared by the following procedure. First, methylene blue (manufactured by Kanto Chemical Co., Ltd.) was dissolved in deionized water to prepare a methylene blue aqueous solution with a concentration of 0.50 mass%. Next, 19.40 g of urea (manufactured by Kanto Chemical Co., Ltd.), 8.040 g of sodium chloride (manufactured by Kanto Chemical Co., Ltd.), 2.045 g of magnesium sulfate heptahydrate (manufactured by Kanto Chemical Co., Ltd.), and 0.835 g of calcium chloride dihydrate were weighed out in order into a 500 ml beaker. An appropriate amount of deionized water was added, and then 1.50 g of 0.50% by mass methylene blue aqueous solution was added dropwise. Then, the solution was transferred to a 1 L volumetric flask and diluted to 1 L to obtain artificial urine.

[0084]

number

[0085] [Susceptibility to skin irritation] Using fluff mats formed from the pulp sheets for fluff pulp described in the examples and comparative examples, disposable diapers were manufactured with reference to the description in Japanese Patent No. 5849759. Twenty monitors wore these diapers, and the presence or absence of skin irritation was evaluated. The evaluation criteria were as follows. A: Number of people who experienced skin irritation: 0 B: 1-2 people experienced a rash. C: Three or more people developed a rash.

[0086] [Defibrating property] The defibration properties of the pulp sheet for fluff pulp were evaluated under conditions of 23°C and 50% relative humidity. The pulp sheet for fluff pulp, which had been humidified under these conditions, was cut into 10mm x 10mm squares, and 3g 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 create a cotton-like pulp (hereinafter, the cotton-like pulp obtained by defibration will be referred to as "fluff pulp"). Subsequently, the fluff pulp was immersed in water and gently stirred with a rod, and then processed using a circular standard hand-made pulp machine to a basis weight of 25g / m². 2 Handmade paper for evaluating the defibrillation properties was prepared. The handmade paper for evaluating defibrillation properties was observed visually, and the defibrillation time (seconds) required for the unfibrillated material to disappear was used as an indicator for evaluating defibrillation properties.

[0087] [Table 1]

[0088] [Table 2]

[0089] Compared to the comparative example, the example yielded a fluff mat that could suppress the occurrence of skin irritation. Furthermore, the example yielded a pulp sheet for fluff pulp with excellent defibration properties. [Explanation of Symbols]

[0090] 5. Pulp defibrating machine 20 columns 24 Stainless steel sieves 30 Polypropylene Powder Funnels 40 Vacuum cleaner (suction machine) 100 Fluff Mat Manufacturing Apparatus

Claims

1. A pulp sheet for fluff pulp containing coniferous tree pulp, The content of hardwood pulp relative to the total pulp components in the pulp sheet for fluff pulp is 40% by mass or less. A pulp sheet for fluff pulp in which 2 g of the pulp sheet for fluff pulp is extracted in 100 mL of hot water at 100°C for 1 hour in accordance with JIS P 8133-2:2013, and when the chlorine concentration in 100 mL of hot water extract is measured by ion chromatography, the chlorine concentration is 0.60 mg / L or less.

2. The pulp sheet for fluff pulp contains softwood pulp. 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% by mass or less.

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

4. An absorbent article comprising the fluff mat described in claim 3.

5. This process includes a pulping step to obtain unbleached pulp by pulping raw materials, a bleaching step, a chlorine removal step, and a sheet formation step. The chlorine removal step is provided after the bleaching step. A method for manufacturing a pulp sheet for fluff pulp, wherein the chlorine removal step involves hydrogen peroxide treatment.

6. The method for producing a pulp sheet for fluff pulp according to claim 5, wherein in the chlorine removal step, a heating treatment is performed so that the pulp slurry temperature is 30°C or higher and 120°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 chlorine removal step is 10 minutes or more and 150 minutes or less.

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