WO2012086374A1

WO2012086374A1 - Tissue paper and method for producing tissue paper

Info

Publication number: WO2012086374A1
Application number: PCT/JP2011/077524
Authority: WO
Inventors: 拓也幸田; 糸井　隆; 舛木　哲也; 和田　正
Original assignee: 花王株式会社
Priority date: 2010-12-21
Filing date: 2011-11-29
Publication date: 2012-06-28
Also published as: MY184185A

Abstract

This tissue paper is mainly composed of an assembly of two kinds of hydrophilic cellulose fibers that have different fiber coarsenesses, and a paper strengthening agent is added thereto. First pulp having a fiber coarseness of 0.13-0.16 mg/m and second pulp having a fiber coarseness of 0.17-0.20 mg/m are contained as the two kinds of hydrophilic cellulose fibers, and the fiber coarseness difference between the first pulp and the second pulp contained therein is 0.01-0.07 mg/m. The assembly has a freeness of 400-550 ml.

Description

Thin paper and thin paper manufacturing method

The present invention (first and second inventions described later) relates to a thin paper, and more particularly to a thin paper suitable as a core wrap sheet for covering an absorbent core in absorbent articles such as disposable diapers and sanitary napkins. Moreover, this invention (3rd invention mentioned later) is related with the manufacturing method of a low basic weight thin paper. Moreover, this invention (4th invention mentioned later) is related with absorbent articles, such as a disposable diaper, an absorption pad, and a sanitary napkin.

Thin paper is a thin paper with a relatively low basis weight, but requires paper strength (such as tensile strength) that does not tear when used. As a method for improving paper strength, conventionally, a method of adding a paper strength enhancer has been employed. For example, Patent Document 1 includes a dry paper strength enhancer and a wet paper strength enhancer, and the tensile strength is specified. Household hygiene tissue paper in range is described. The household sanitary thin paper described in Patent Document 1 is applied to uses such as roll paper, tissue paper, dust paper, etc. where sensory characteristics such as flexibility and touch feeling are important, and disclosed in Patent Document 1. The main technology that is being used aims to achieve both of these sensory characteristics and paper strength.

In addition, a technique using a plurality of types of hydrophilic cellulose fibers having different fiber roughness as a constituent fiber of paper is known. The fiber roughness is used as a scale representing the fiber thickness in a fiber having a nonuniform fiber thickness, such as wood pulp. For example, Patent Document 2 mainly includes two types of fibers having different fiber roughness (bulky cellulose fibers and hydrophilic fine fibers), and the hydrophilic fine fibers are unevenly distributed on one surface side in the thickness direction. Absorbent paper is described. According to the absorbent paper described in Patent Document 2, since it has a layer having excellent liquid permeability and a layer having excellent liquid diffusibility in the thickness direction, it is said that the liquid absorbability is excellent. Patent Document 2 discloses an absorbent body in which an absorbent polymer is sandwiched between two sheets of absorbent paper as an example of use of the absorbent paper described in Patent Document 2.

Also, for example, in absorbent articles such as disposable diapers and sanitary napkins, low basis weight thin paper is used as a core wrap sheet covering the absorbent core. Thus, the thin paper used for the core wrap sheet is required to have high permeability in order to smoothly transfer the body fluid to the absorbent core during use, and is torn during production and use of absorbent articles such as diapers. Paper strength (such as tensile strength) that does not occur is required. In order to increase the permeability, a method of reducing the basis weight of the thin paper and reducing the density of the thin paper is effective. However, such a method can reduce the number of interfiber bonding points due to a decrease in the number of constituent fibers of the thin paper. This causes a decrease, and the paper strength decreases.

Here, as means for improving the paper strength (tensile strength, etc.) of thin paper with a low basis weight, it is known to fibrillate raw material pulp or increase the amount of paper strength agent added. Regarding the addition of a paper strength agent, for example, techniques described in Patent Document 1 and Patent Document 3 are known. Patent Documents 1 and 3 each disclose a technique of adding a cationic polymer wet paper strength agent or an anionic polymer dry paper strength agent to a raw pulp slurry.

Further, as this type of absorbent article, it comprises a liquid-permeable top sheet, a liquid-impermeable back sheet and a vertically long absorbent body disposed between both sheets, and the absorbent body is made of wood pulp or the like. There is known a structure including an absorbent core including a hydrophilic fiber and a water-absorbing polymer, and a core wrap sheet covering the absorbent core. The core wrap sheet serves as a sheet for receiving an absorbent core-forming material such as a water-absorbing polymer at the time of manufacturing the absorbent body, and plays a role of wrapping and shaping the absorbent core after the manufacture. Conventionally, water-permeable sheets such as thin paper and nonwoven fabric are used as the core wrap sheet.

Conventionally, in absorbent articles, the ability to absorb and retain soft stool has been a problem. Specifically, a situation occurs in which soft stool remains on the surface sheet without passing through the surface sheet, or soft stool that has permeated through the surface sheet returns to the surface sheet without being held by the absorber. And it brings about complicated skin wiping work. Therefore, various techniques have been proposed for the purpose of promptly moving the soft stool away from the skin and improving the performance of accommodating and holding the soft stool at a position far from the skin (absorbability such as soft stool).

For example, in Patent Document 4, a liquid permeable second sheet is provided between a surface sheet and an absorbent body as an absorbent article excellent in soft stool absorbability, and the core wrap sheet constituting the absorbent body is the second article. A non-woven fabric located between the sheet and the absorbent core constituting the absorbent body and having a density in the range of 0.01 to 0.2 g / cm ³ , and a crepe paper covering the non-skin facing side of the absorbent core What is composed of is described.

Patent Document 5 discloses a predetermined range of pore sizes (pore diameters) and distributions of pores formed by entanglement of constituent fibers as a low-diffusibility transmission paper for absorbent articles obtained by a wet papermaking method. Are controlled. The low-diffusibility transmission paper described in Patent Document 5 includes a hydrophilic fiber as a constituent fiber and is treated with a sizing agent so as to have a specific pore diameter distribution. It exhibits diffusibility and high permeability and is useful as a sub-layer sheet (second sheet) disposed between the top sheet and the absorber (core wrap sheet).

Also, a sheet having a relatively low basis weight such as a core wrap sheet is required to have a sheet strength that does not cause tearing during manufacturing in addition to having high liquid permeability. As a method for improving sheet strength, conventionally, a method of adding a paper strength enhancer has been adopted. For example, Patent Literature 1 includes a dry paper strength enhancer and a wet paper strength enhancer, and the tensile strength is specified. Household hygiene tissue paper in range is described. The household sanitary thin paper described in Patent Document 1 is applied to uses such as roll paper, tissue paper, dust paper, etc. where sensory characteristics such as flexibility and touch feeling are important, and disclosed in Patent Document 1. The main technology that is being used aims to achieve both of these sensory characteristics and sheet strength.

Japanese Patent Laid-Open No. 2005-124484 JP-A-8-291495 JP 2005-344274 A Japanese Patent No. 4390747 JP 2009-148322 A

Some absorbent articles such as disposable diapers and sanitary napkins include a liquid-retaining absorbent, and the absorbent includes an absorbent core containing wood pulp, a superabsorbent resin, and the like. What is comprised including the core wrap sheet | seat which coat | covers the outer surface of a core is known. The core wrap sheet serves as a sheet for receiving an absorber-forming material such as wood pulp or a highly water-absorbent resin during production of the absorbent body, and plays a role of wrapping and shaping the absorbent core after production. Conventionally, water-permeable sheets such as thin paper and nonwoven fabric are used as the core wrap sheet.

The core wrap sheet has a sheet strength that can withstand the conveyance tension during manufacture, and high liquid permeability that allows liquid to quickly permeate during use and allows the absorbent core disposed under the core wrap sheet to absorb liquid quickly. Required. In order to increase the liquid permeability, a method of reducing the basis weight of the constituent fibers of the sheet and reducing the density of the sheet is effective. However, such a method reduces the number of constituent fibers and the fibers of the constituent fibers resulting therefrom. Since the number of inter-bonding points is reduced, the sheet strength may be reduced. The sheet strength and liquid permeability of the core wrap sheet are in a trade-off relationship, and it is difficult to achieve a good balance between the two.

Also, the fibrillation of the raw pulp fibers of the thin paper can improve the paper strength (tensile strength, etc.), but also lowers the permeability.

Further, increasing the addition of the paper strength agent causes sticking of the raw material to the paper mesh and the dryer and contamination of the drainage in the production process, leading to a decrease in productivity. For this reason, the amount of the paper strength agent is limited, and it is difficult to sufficiently improve the paper strength (such as tensile strength) of the low basis weight thin paper.

Also, Patent Document 1 does not describe anything about the order of adding the cationic polymer wet paper strength agent and the anionic polymer dry paper strength agent to the raw pulp slurry. Further, the technique described in Patent Document 3 relates to a papermaking molded body used for a heat-generating molded body, and Patent Document 3 does not describe anything about a technique relating to a method for producing a low basis weight thin paper.

Moreover, as for the core wrap sheet | seat of patent document 4, the site | part opposingly arranged by the skin opposing surface of an absorptive core is comprised with the nonwoven fabric which uses synthetic fiber as a constituent fiber, and constituent fibers are heat-seal | fused. It is fixed. Therefore, even if the synthetic fiber (constituent fiber) is hydrophilized, there is a possibility that inconveniences such as clogging occur when loose stool containing solid matter passes through the core wrap sheet, Unless such a disadvantage is prevented by making the distance relatively long, the absorbability of soft stool may be lowered. However, if the interfiber distance in the nonwoven fabric as the core wrap sheet is increased, the absorbent core-forming material such as the water-absorbing polymer that has fallen off from the absorbent core may pass through the nonwoven fabric and leak to the outside. In the core wrap sheet, it has been difficult to achieve both improvement of soft stool absorbability and prevention of leakage of the absorbent core forming material. In order to solve this problem, the absorbent article described in Patent Document 1 has a multilayered absorbent body and prevents the absorbent polymer from falling off by forming a layer that does not contain the absorbent polymer in the upper layer.

In order to increase the liquid permeability of the core wrap sheet, a method of reducing the basis weight of the constituent fibers of the sheet and reducing the density of the sheet is effective. Since the number of inter-fiber bonding points of the constituent fibers is reduced, the sheet strength may be reduced. When the sheet strength of the core wrap sheet decreases, the core wrap sheet may be damaged during manufacture, and the absorbent core forming material may leak from the damaged portion during use. The sheet strength and liquid permeability of the core wrap sheet are in a trade-off relationship, and it is difficult to achieve a good balance between the two. Patent Documents 1, 4 and 5 do not disclose effective means for solving such problems.

As a result of various investigations on the relationship between strength and liquid permeability in paper, the present inventors have found that, as a constituent fiber of paper, pulp having a relatively large fiber diameter (thick pulp) and relatively small pulp (thin pulp) As a result of further finding out that the liquid permeability can be improved while minimizing the decrease in strength, the fiber roughness as an index of the fiber diameter is in a specific range. It is effective for coexistence of strength characteristics and liquid permeability to use a kind of pulp (hydrophilic cellulose fiber) whose difference in fiber roughness between both pulps is in a specific range as a constituent fiber of paper. It was found (first finding).

The present invention (the first invention) is based on the first knowledge, and is a thin paper mainly composed of an aggregate of two kinds of hydrophilic cellulose fibers having different fiber roughnesses and to which a paper strength enhancer is added. The two kinds of hydrophilic cellulose fibers include a first pulp having a fiber roughness of 0.13 to 0.16 mg / m and a second pulp having a fiber roughness of 0.17 to 0.20 mg / m. A thin paper having a fiber roughness difference of 0.01 to 0.07 mg / m and a freeness of the aggregate of 400 to 550 ml. .

In addition, as a result of various investigations on the relationship between strength and liquid permeability in paper, the present inventors have found that when liquid permeability is improved by lowering paper basis weight (lower density), the lower basis weight is a concern. It was found that a decrease in strength can be prevented by using a specific pulp in which fibrillation has progressed as a constituent fiber and using two or more paper strength enhancers in combination (second finding).

The present invention (second invention) was made on the basis of the second finding, mainly composed of softwood bleached kraft pulp having a freeness of 400 to 550 ml, and two or more kinds of paper strength enhancers added thereto, The present invention relates to a thin paper having a basis weight of 10 to 14.5 g / m ² , a density of 0.05 to 0.2 g / cm ³ and a crepe rate of 5 to 30%.

The present invention (third invention) is a thin paper production method for producing a thin paper having a basis weight of 30 g / m ² or less by papermaking and drying a raw material slurry prepared from a raw material containing softwood bleached kraft pulp, After adding the wet paper strength agent (a) made of a cationic polymer having a cationic group to the pulp slurry of the softwood bleached kraft pulp as a raw material slurry, the following low molecular dry paper strength agent (b) and polymer A thin paper using a raw material slurry prepared by adding a dry paper strength agent (c) at the same time or adding a low molecular weight dry strength agent (b) and then adding a polymer dry strength agent (c). It relates to a manufacturing method.
(B) Low molecular weight anionic polymer having an anionic group having a weight average molecular weight (Mw) of 0.2 to 500,000 (c) Polymer having an anionic group having a weight average molecular weight (Mw) of 500 to 30 million Anionic polymer

The present invention (fourth invention) comprises an absorbent core, the absorbent core comprising hydrophilic fibers and a water-absorbing polymer and having a shape that is long in one direction, and a core that covers the absorbent core An absorbent article configured to include a wrap sheet, wherein the core wrap sheet includes high liquid permeability paper disposed to face a skin facing surface of the absorbent core, and the high liquid permeability The paper has a basis weight of 8 to 20 g / m ² , a density of 0.05 to 0.2 g / cm ³ , a liquid permeation time measured by the following method of 600 seconds or less, and in the transport direction during production. The present invention relates to an absorbent article having a dry tensile strength of 600 cN / 25 mm or more.

<Measurement method of liquid permeation time>
Two cylinders with an inner diameter of 35 mm that open at the top and bottom are arranged vertically with the axes of both cylinders aligned, the sheet to be measured is sandwiched between the upper and lower cylinders, and in that state, in the upper cylinder, 10 g ± 1 g of a highly viscous liquid (viscosity 290 mPa · s) obtained by mixing glycerin and ion-exchanged water at a mass ratio of the former: the latter = 94: 6 is supplied. The supplied highly viscous liquid passes through the measurement target sheet or is absorbed by the measurement target sheet and disappears from the upper cylinder. The time from when the supply of the high-viscosity liquid is started until the liquid surface of the high-viscosity liquid reaches the same position as the surface of the sheet to be measured is measured, and the time is defined as the liquid permeation time.

According to the present invention (the first and second inventions), a thin paper having good strength characteristics and excellent liquid permeability is provided.

According to the manufacturing method of the present invention (third invention), a low basis weight thin paper having high permeability and having a paper strength (such as tensile strength) that does not cause tearing during the manufacture and use of absorbent articles such as diapers. Can be manufactured.

According to the present invention (fourth invention), there is provided an absorbent article that is excellent in absorbability of high-viscosity liquids such as soft stool and in which leakage of the absorbent core-forming material is prevented.

FIG. 1 is an explanatory diagram of a method for measuring the liquid permeation time. FIG. 2 is a schematic view showing a preferred production apparatus used for carrying out the production method of the present invention (third invention). FIG. 3 is a schematic view showing another preferred production apparatus used for carrying out the production method of the present invention (third invention). FIG. 4 is a schematic view showing another preferred production apparatus used for carrying out the production method of the present invention (third invention). FIG. 5 is a schematic view showing another preferred production apparatus used for carrying out the production method of the present invention (third invention). FIG. 6 is a view showing a disposable diaper that is an embodiment of the absorbent article of the present invention (fourth invention), and schematically illustrates a state in which the elastic member of each part is stretched and expanded in a planar shape. It is a top view of the surface side (surface sheet side). 7 is a cross-sectional view schematically showing a cross section taken along the line II (cross section in the width direction) of FIG. FIG. 8: is sectional drawing which shows typically the cross section of the width direction of the absorber in other embodiment of the absorbent article of this invention (4th invention).

The present invention (first and second inventions) relates to a thin paper having good strength characteristics and excellent liquid permeability.

The present invention (third invention) relates to a method for producing thin paper that can balance both the transparency and paper strength (tensile strength, etc.) in a trade-off relationship.

The present invention (fourth invention) relates to an absorbent article which is excellent in absorbability of a highly viscous liquid such as soft stool and in which leakage of the absorbent core-forming material is prevented.

Hereinafter, the thin paper of the present invention (first invention) will be described in detail. The thin paper of the present invention (first invention) contains an aggregate of two types of hydrophilic cellulose fibers having different fiber roughness as an essential component. Fiber roughness is used as a measure of fiber thickness in fibers with uneven fiber thickness, such as wood pulp, and is measured using a commercially available fiber roughness meter as described later. Is done. That is, the thin paper of the present invention includes an aggregate of two types of hydrophilic cellulose fibers having different thicknesses, thereby achieving both strength characteristics and liquid permeability.

The thin paper of the present invention (first invention) has a fiber roughness of 0.13 to 0.16 mg / m, preferably 0.135 to 0.155 mg / m, more preferably as the two types of hydrophilic cellulose fibers. Is 0.14 to 0.15 mg / m of the first pulp, and the fiber roughness is 0.17 to 0.20 mg / m, preferably 0.175 to 0.195 mg / m, more preferably 0.18 to 0.18 mg / m. The second pulp is 0.19 mg / m, and the second pulp is thicker than the first pulp. Thus, by using a relatively thick pulp as a part of the constituent fibers of the paper, the paper becomes rough and the liquid permeability is improved. Pulp is obtained by converting plant fibers such as wood, kidneys and leaves into single fibers by a chemical or mechanical method.

The difference in fiber roughness between the first pulp and the second pulp contained in the thin paper is 0.01 to 0.07 mg / m, preferably 0.02 to 0.06 mg / m, and more preferably 0. 0.03 to 0.05 mg / m. If the difference in fiber roughness between the two pulps is less than 0.01 mg / m, the effect of improving the liquid permeability is poor, and if the difference in fiber roughness exceeds 0.07 mg / m, the strength of the paper may be significantly reduced. .

The average fiber length of each of the first pulp and the second pulp is preferably 2 to 3 mm, more preferably 2.2 to 2.8 mm. When the average fiber lengths of both pulps are in the above-mentioned ranges, the effects of good balance between fibers and good formation of thin paper are obtained. The average fiber length of both pulps may be the same or different. The fiber roughness and average fiber length are each measured as follows.

<Measurement of fiber roughness and average fiber length>
It is measured using a fiber roughness meter FS-200 (manufactured by KAJAANI ELECTRONICS LTD.). The fiber (pulp) to be measured shall be unbeaten. First, in order to obtain the true weight of the fiber to be measured, the fiber is dried in a vacuum dryer at 100 ° C. for 1 hour to remove moisture present in the fiber. 1 g is accurately weighed from the fibers thus dried (error ± 0.1 mg). Next, while taking care not to damage the fibers as much as possible, the weighed fibers are completely disaggregated in 150 ml of water with the mixer attached to the fiber roughness meter, and this is until the total amount reaches 5000 ml. Diluted with water to obtain a diluted solution. 50 ml is accurately weighed from the diluted solution thus obtained to make a fiber roughness measurement solution, and the target fiber roughness and average fiber length are calculated according to the operation procedure of the fiber roughness meter. In addition, the value calculated by the following formula based on the said operation procedure is used for calculation of average fiber length.

The content ratio of the first pulp to the second pulp (first pulp / second pulp) is preferably 3/7 to 7/3, more preferably 4 from the viewpoint of the balance between strength characteristics and liquid permeability. / 6 to 6/4. If the second pulp having a relatively large fiber diameter is too small, sufficient liquid permeability may not be obtained. Conversely, if the second pulp is too large, the strength of the thin paper may be drastically reduced. .

The first pulp and the second pulp (hydrophilic cellulose fibers) are fibers having a fiber roughness in the above-mentioned range and having a hydrophilic surface, and the fibers have a high degree of freedom between each other in the wet state. If it can form, it can use without a restriction | limiting especially. Examples of such hydrophilic cellulose fibers include natural cellulose fibers such as wood pulp such as softwood bleached kraft pulp (NBKP) and hardwood bleached kraft pulp (LBKP), and non-wood pulp such as cotton pulp and straw pulp; rayon, cupra Recycled cellulose fibers such as: hydrophilic synthetic fibers such as polyvinyl alcohol fibers and polyacrylonitrile fibers; synthetic fibers such as polyethylene terephthalate (PET) fibers, polyethylene (PE) fibers, polypropylene (PP) fibers, and polyester fibers with surfactants The thing etc. which carried out the hydrophilization process are mentioned, These 1 type can be used individually or in mixture of 2 or more types.

Among these hydrophilic cellulose fibers, NBKP is particularly preferable, and the first pulp and the second pulp are each preferably NBKP. In addition, as NBKP used in the present invention (first invention), NBKP that is usually used in this type of paper can be used without any particular limitation. As NBKP, ECF (elementary chlorin-free) bleached pulp or TCF (total chlorin-free) bleached pulp that does not use a chlorine compound for pulp bleaching may be used.

The thin paper of the present invention (first invention) mainly comprises an aggregate of two types of hydrophilic cellulose fibers (first pulp and second pulp) having different fiber roughness. Here, “mainly” means that the contents of the first pulp and the second pulp are 50% by mass or more. The content is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, from the viewpoint of achieving both strength characteristics and liquid permeability.

In the present invention (first invention), the freeness of the aggregate of the two types of hydrophilic cellulose fibers (first pulp and second pulp) is set to 400 to 550 ml. That is, the freeness of each of the first pulp and the second pulp is in the range of 400 to 550 ml. Freeness is a value indicated by Canadian Standard Freeness (CSF) specified in JIS P8121, and is a value of pulp beating (a process of mechanically tapping and grinding pulp in the presence of water). It is a value indicating the degree. Usually, the smaller the freeness value, the stronger the degree of beating, the greater the damage of the fibers due to beating, and the more fibrillation proceeds. Fibers having a freeness in the above range are easily entangled with each other because fibrillation has progressed. For this reason, for example, from the viewpoint of improving liquid permeability, the fibers are made by reducing the basis weight (reducing density) of the thin paper. Even if the number of interfiber bonding points is reduced, the strength of each interfiber bond is higher than that of fibers in which the freeness exceeds 550 ml and the fibrillation has not progressed relatively. Accordingly, a thin paper mainly composed of an aggregate of fibers having a freeness of 400 to 550 ml can have good strength characteristics.

The freeness of the aggregate of the two types of hydrophilic cellulose fibers used in the present invention (first invention) is preferably 450 to 525 ml, more preferably 475 to 510 ml. When the freeness is less than 400 ml, the strength improvement effect due to the entanglement of the fibers is saturated, and the fiber cutting is promoted, and the permeation time may be delayed. The beating of the fiber aggregate is a known method such as a beader or a disc refiner for a stock (slurry) in which each hydrophilic cellulose fiber (first pulp and second pulp) constituting the fiber aggregate is mixed and dispersed. This can be carried out according to a conventional method using a beating machine.

The thin paper of the present invention (first invention) may contain fibers other than the first pulp and the second pulp, and the other fibers may not be hydrophilic cellulose fibers such as both pulps. Other fibers include, for example, hardwood bleached kraft pulp (LBKP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP) and other wood pulp; Non-wood pulp such as kenaf and hemp; synthetic fibers such as polyester fiber, rayon fiber, acrylic fiber, and the like. The content of these other fibers is preferably 20% by mass or less.

The paper strength enhancer is added to the thin paper of the present invention (first invention) from the viewpoint of obtaining good strength properties (tensile strength). The paper strength enhancer includes a dry paper strength enhancer that improves the dry paper strength and a wet paper strength enhancer that improves the wet paper strength, either of which may be used. In particular, carboxymethyl cellulose (CMC), which is a kind of dry paper strength enhancer, and a salt thereof are preferably used in the present invention (first invention) because they have high versatility and a low aggregation effect between fibers. That is, in the present invention (first invention), it is preferable that at least CMC or a salt thereof is added as a paper strength enhancer.

As the dry paper strength enhancer, conventionally known dry paper strength enhancers can be used, and examples thereof include CMC and salts thereof, polyacrylamide resins and salts thereof, cationized starch, polyvinyl alcohol (PVA) and the like. These 1 type can be used individually or in combination of 2 or more types. As the salt of CMC or polyacrylamide resin, sodium salt is mainly used. Examples of the polyacrylamide resin include cationic or anionic polyacrylamide (PAM). Among these dry paper strength enhancers, CMC and salts thereof, anionic PAM and salts thereof are particularly preferable.

As the wet paper strength enhancer, a conventionally known wet paper strength enhancer can be used. For example, epoxidized polyamide polyamine resin (PAE), urea-formalin resin, melamine-formalin resin, dialdehyde starch, polyethyleneamine, Examples include methylolated polyamide, and one of these can be used alone or two or more of them can be used in combination. Among these wet paper strength enhancers, PAE is particularly preferable.

In the present invention (first invention), when two or more kinds of paper strength enhancers are used, a preferable combination thereof includes two dry paper strength enhancers and one wet paper strength enhancer. Of these three types of paper strength enhancers, CMC salts and anionic PAM salts are preferred as the two dry paper strength enhancers, and PAE is preferred as the one wet strength agent.

In addition, as described above, when the CMC salt and the anionic PAM salt are used as the two dry paper strength enhancers, and the PAE is used as the one wet paper strength enhancer, the weight of the anionic PAM salt is as follows. The average molecular weight is preferably 8 million or more, particularly 10 million or more, particularly preferably 15 million or more, and the upper limit of the weight average molecular weight of the anionic PAM salt is preferably 25 million. Thus, in the case of using three kinds of specific paper strength enhancers, if the weight average molecular weight of the salt of anionic PAM which is one of them is in the above range (8 million to 25 million), an anion In addition to the effect of improving the strength of the thin paper by developing the adhesiveness of the salt of the PAM, the strength improvement effect of the thin paper can be obtained by improving the yield of the salt of the CMC. Is obtained. Also, when the weight average molecular weight of the anionic PAM salt is 25 million or less, the dispersibility and viscosity of the anionic PAM salt in water can be kept relatively low during the manufacture of the thin paper. Good results can be obtained in terms of prevention of dirt.

The addition amount of the paper strength enhancer in the thin paper of the present invention (first invention) is preferably 0.01 to 1.5% by weight, more preferably 0.03 to 0.5% by weight based on the dry weight of all the constituent fibers of the thin paper. 1.2% by mass. If the added amount of the paper strength enhancer is too small, sufficient strength properties such as tensile strength cannot be obtained. If the added amount of the paper strength enhancer is excessive, the thin paper is hardened (decrease in texture) and the thin paper There is a possibility that the formation of the thin paper may be deteriorated due to the sticking of the paper to the Yankee dryer or the attachment of the paper strength enhancer to the mesh drum at the time of manufacture.

When a combination of one or more dry paper strength enhancers and one or more wet paper strength enhancers is used as the paper strength enhancer, the total added mass of the dry paper strength enhancer and the wet paper strength enhancer The ratio to the total added mass (the former / the latter) is preferably 0.01 to 0.5, more preferably 0.03 to 0.35.

In addition, as described above, when two kinds of CMC salt and anionic PAM salt are used as the dry paper strength enhancer and one type of PAE is used as the wet paper strength enhancer, the dry mass of all the constituent fibers of the thin paper The amount of each paper strength enhancer added is preferably 0.05 to 0.5% by mass of CMC salt, more preferably 0.1 to 0.3% by mass, and preferably 0 to 0.3% of anionic PAM salt. 0.001 to 0.1% by mass, more preferably 0.02 to 0.05% by mass, and PAE is preferably 0.5 to 1.5% by mass, more preferably 0.6 to 1.2% by mass. It is.

The thin paper of the present invention (first invention) may contain other components other than the fibers such as the first pulp and the second pulp (hydrophilic cellulose fiber) and the paper strength enhancer described above. As other components, for example, fillers such as talc, dyes, color pigments, antibacterial agents, pH adjusters, yield improvers, water resistance agents, antifoaming agents and the like are generally used as raw materials for papermaking and additives. These can be used, and one of these can be used alone or in combination of two or more.

The thin paper of the present invention (first invention) can be produced by a known wet papermaking method. The wet papermaking method includes a stock preparation step for preparing a stock (slurry) made of an aqueous dispersion of fibers such as NBKP, and a paper making step for drying while transporting a fiber made from the stock into a fiber web. It is what has. The paper making process is usually divided into a wire part, a press part, a dryer part, a size press, a calendar part, etc., and is carried out sequentially. The above-mentioned dry paper strength enhancer and wet paper strength enhancer are usually added to the stock in the stock preparation step. Usually, the wet paper strength enhancer and the dry paper strength enhancer are added in the order of the paper strength enhancer. However, the order of addition of the paper strength enhancer in the present invention (first invention) is not limited to this, and the order of addition is as follows. May be reversed, or both may be added simultaneously. The wet papermaking method can be carried out according to a conventional method using a paper machine such as a long paper machine, a twin wire paper machine, an on-top paper machine, a hybrid paper machine, or a round paper machine.

The basis weight of the thin paper of the present invention (first invention) is preferably set to be relatively low from the viewpoint of improving liquid permeability, specifically 10 to 20 g / m ² , particularly 11 to 16 g / m ² . m ² , especially 12 to 14 g / m ² is preferred. If the basis weight is low, there is a concern about a decrease in paper strength. However, in the present invention (first invention), as described above, as a part of the constituent fibers, the fiber roughness is relatively small (the fiber diameter is thin). By using 1 pulp and setting the freeness of the aggregate of two types of fibers (first pulp and second pulp) within a specific range, and further using a paper strength enhancer, such concerns are eliminated. . If the basis weight of the thin paper is less than 10 g / m ² , the paper strength may be remarkably reduced, and if the basis weight of the thin paper exceeds 20 g / m ² , the effect of improving the liquid permeability may be poor.

From the same viewpoint, the density of the thin paper of the present invention (first invention) is preferably 0.05 to 0.2 g / cm ³ , more preferably 0.1 to 0.2 g / cm ³ .

The basis weight of the thin paper is measured as follows. After conditioning the sample (thin paper) under the conditions of JIS P8111, a 10 cm square (area 100 cm ² ) measurement piece was cut out from the sample, and the weight of the measurement piece was measured with a two-digit balance below the decimal point. The basis weight of the measurement piece is calculated by dividing the measured value by the area. About 10 measurement pieces cut out from the sample, the basis weight is calculated according to the above procedure, and the average value thereof is taken as the basis weight of the sample.

Also, the density of thin paper is measured as follows. 10 sheets of 20 cm square samples (thin paper) are stacked to form a laminated body, and after cooling and solidifying the laminated body with liquid nitrogen, the vicinity of the center of the laminated body is cut with a cutter. Then, of the 10 samples, one having no shear applied to the cross section generated by cutting with the cutter is selected, and the thickness of the selected sample is measured with an optical microscope. In addition, the thickness of the sample is not the length (apparent thickness) from the bottom to the top of the concavo-convex part when the sample has concavo-convex parts such as crepes described later, but the part where the constituent fibers are deposited Length (substantial thickness). The weight W of the 20 cm square sample whose thickness has been measured in this way is measured using a balance with two decimal places. The target density is calculated by dividing the weight W of the sample by the volume V of the sample calculated by the following equation (that is, by W / V). In the following formula, T is the thickness (cm) of the sample, A is the crepe rate (%) of the sample, and B is the length of one side (20 cm) of the sample. The crepe rate is measured by a measurement method described later. When the thin paper to be measured does not have a crepe (when the crepe rate is 0%), A = 0 in the following equation. V = {T × B × B × (100 + A) / 100}

The thin paper of the present invention (first invention) may have crepes (crepe-like wrinkles). When the thin paper of the present invention (first invention) has a crepe, the crepe is produced when the dried fiber web (thin paper) is peeled off from the Yankee dryer or the like in the dryer part with a doctor knife or the like. It is preferable that The crepe rate is measured as follows.

<Measurement method of crepe rate>
A rectangular shape of 200 mm in the length direction (conveying direction when manufacturing the thin paper, MD) and 100 mm in the width direction (direction orthogonal to the MD, CD) is cut out from the thin paper to be measured. The length C of the MD immediately after the rectangular sample is immersed in water for 10 minutes is measured, and the crepe rate is calculated by the following equation. Crepe rate (%) = {(C−200) / 200} × 100
For example, when the length C of the MD after immersion for 10 minutes is 220 mm, the crepe rate of the thin paper calculated by the above formula is 10%.

Thin paper with crepe has higher liquid permeability than thin paper without crepe, and the higher the crepe rate, the higher the liquid permeability. However, as the crepe rate increases, the strength properties (tensile strength) tend to decrease. In the present invention (first invention), based on such knowledge, the crepe rate of the thin paper is 5 to 30%, particularly 5 to 20%, especially 7 to 15 from the viewpoint of the balance between liquid permeability and strength characteristics. % Is preferable.

The dry tensile strength in the conveying direction (Machine Direction, MD for short) of the thin paper of the present invention (first invention) having the above-described configuration is 600 cN / 25 mm or more, preferably 600 to 1500 cN / 25 mm, more preferably 700 to 1200 cN / 25 mm, even more preferably 800 to 1200 cN / 25 mm, and still more preferably 900 to 1200 cN / 25 mm. The dry tensile strength in the direction perpendicular to MD (Cross machine Direction, CD for short) is 150 cN / 25 mm or more, preferably 150 to 350 cN / 25 mm, and more preferably 180 to 300 cN / 25 mm. A thin paper having a dry tensile strength of each of MD and CD in the above range has a practically sufficient strength. For example, the thin paper is used as a core wrap sheet for covering an absorbent core in an absorbent article such as a disposable diaper. When applied, it is difficult to cause inconveniences such as tearing of the core wrap sheet (thin paper) during manufacture of the absorbent article. The dry tensile strength is measured as follows.

<Measurement method of dry tensile strength>
The sheet to be measured (thin paper) is allowed to stand for 12 hours in an environment of a room temperature of 23 ° C. ± 2 ° C. and a relative humidity of 50% RH ± 2%, and is conditioned to a constant state. A rectangular shape with dimensions of 150 mm for MD and 25 mm for CD is cut out from the humidity-adjusted sheet, and the cut out rectangular shape is used as a sample. This sample is attached to a chuck of a tensile tester (manufactured by Shimadzu Autograph AG-1kN) without tension so that its MD is in the tensile direction. The distance between chucks is 100 mm. The sample is pulled at a pulling speed of 300 mm / min, and the maximum strength until the sample breaks is measured. The measurement is performed 5 times, and the average of these values is taken as the MD dry tensile strength. Further, the dry tensile strength of CD is obtained by cutting a rectangular shape having dimensions of 150 mm for CD and 25 mm for MD from the humidity-controlled sheet, and using this as a sample, and pulling this sample so that the CD is in the tensile direction. Attached to the chuck of the testing machine without tension, the dry tensile strength of the CD is determined by the same procedure as described above.

Further, the liquid permeation time of the thin paper of the present invention (first invention) measured by the following method is 0.2 to 3 seconds, preferably 0.3 to 2.5 seconds, more preferably 0.5 to 2 seconds. It is. The shorter the liquid permeation time, the higher the liquid permeability and the higher the evaluation. The thin paper whose liquid permeation time is in the above range is excellent in liquid permeability. For example, when the thin paper is applied to a core wrap sheet covering an absorbent core in an absorbent article such as a disposable diaper, urine or the like It is possible to quickly permeate the excreted liquid and allow the absorbent core to quickly absorb the excreted fluid, and to improve the leak-proof property of the absorbent article.

<Measurement method of liquid permeation time>
As shown in FIG. 1, two

cylinders

91 and 92 having an inner diameter of 35 mm with upper and lower ends opened are arranged up and down with the axes of both

cylinders

91 and 92 aligned, and an 8 cm square measurement target sheet S ( A thin paper) is sandwiched between the upper and

lower cylinders

91 and 92. At this time, it is preferable that the upper and

lower cylinders

91 and 92 are connected by fitting the clip 93 to an annular flange portion provided at the lower end of the upper cylinder 91 and the upper end of the lower cylinder 92. Reference numeral 94 denotes a rubber packing having a through hole having the same diameter and the same shape as the inner diameters of the

cylinders

91 and 92. In this way, with the measurement sheet S sandwiched and fixed between the upper and

lower cylinders

91 and 92, a physiological saline (an aqueous solution having a sodium chloride concentration of 0.9 mass%) indicated by the symbol W in FIG. ) Is supplied in an amount of 40 g ± 1 g. The supplied physiological saline passes through the measurement target sheet S or is absorbed by the measurement target sheet S and disappears from the upper cylinder 91. The time from the start of the physiological saline supply until the physiological saline water surface is at the same position as the surface of the measurement target sheet S (the surface on the upper cylinder 91 side) is measured, and this time is defined as the liquid permeation time. .

Further, the thin paper of the present invention (first invention) is also excellent in air permeability. The reason is mainly because it mainly comprises an aggregate of two types of hydrophilic cellulose fibers having different fiber roughness. In order to investigate the relationship between the use of two types of hydrophilic cellulose fibers having different fiber roughness and the breathability of thin paper, the present inventors prepared two types of thin paper (samples A and B) having different pulp compositions. The air permeability was measured. Sample A includes the first pulp and the second pulp, and is Example 1 to be described later. Sample B is the second pulp (NBKP having a fiber roughness of 0.18 mg / m) in Example 1 to be described later. A thin paper manufactured in the same procedure as in Example 1 except that only the first pulp (NBKP with a fiber roughness of 0.15 mg / m) was used as the fiber material without using it. Both samples A and B had a basis weight of 13 g / m ² . The air permeability is measured as follows.

<Measurement method of air permeability>
The air permeability is measured according to JIS P8117. After preparing 32 sheets of 15 cm square measurement object sheets (thin paper) and drying them with hot air dryer for 30 minutes with hot air at 105 ° C., all 32 sheets are stacked to form one laminate, and the laminate is B Set on the air permeability meter. Then, in the B-type air permeability meter, the time required to reach 300 cc is measured with 0 cc of the marked line as a start. The above operation is performed 5 times, and the average value of the obtained five measurement times is defined as the air permeability of the measurement target sheet (thin paper). The unit of air permeability is “s / 32P · 300 cc” and represents the time (seconds) required for 300 cc of air to escape through 32 sheets. It can be evaluated that the smaller the value of the air permeability, the easier the air can escape and the better the air permeability.

Sample B using only the first pulp as the fiber material had an air permeability in the range of 2.1 to 2.7 s / 32 P · 300 cc, whereas the fiber material had two kinds of fiber roughness different from each other. Sample A using pulp (first and second pulp) has an air permeability in the range of 1.6 to 2.2 s / 32 P · 300 cc. Sample A has a higher air permeability than sample B. Was small. From this, it can be seen that it is effective to improve the air permeability of the thin paper to make the thin paper mainly composed of an aggregate of two kinds of hydrophilic cellulose fibers having different fiber roughnesses. It is apparent that the thin paper of the present invention (first invention) is excellent in air permeability.

The thin paper of the present invention (first invention) has good strength characteristics (tensile strength) and excellent liquid permeability and air permeability, and is suitable for various applications in which such features are utilized. In particular, the thin paper of the present invention (first invention) is suitable as a core wrap sheet for covering a liquid-retaining absorbent core in absorbent articles such as disposable diapers and sanitary napkins, and excretory liquid is urine or the like. Even in the case of relatively low viscosity, such as loose stool, even if it is relatively high viscosity, the excretory fluid can be quickly permeated and absorbed into the absorbent core, and the leak-proof property of the absorbent article Can contribute to improvement.

As an example of the absorbent article of the present invention using the thin paper of the present invention (first invention), an absorbent article comprising an absorbent core and a core wrap sheet covering the absorbent core, the core wrap sheet However, what is the thin paper of this invention (1st invention) mentioned above is mentioned. More specifically, the absorbent article of the present invention includes a liquid-permeable surface sheet that forms a skin-facing surface, a liquid-impermeable or water-repellent back sheet that forms a non-skin-facing surface, and a space between these two sheets. The liquid-retaining absorbent is disposed on the surface, and the absorbent is configured to include the absorbent core and the core wrap sheet (thin paper of the first invention). The core wrap sheet (thin paper of the first invention) preferably covers at least the skin facing surface and the non-skin facing surface of the absorbent core. The skin facing surface is a surface of the absorbent article or a component thereof (for example, an absorbent core) that is directed to the skin side of the wearer when the absorbent article is worn, and the non-skin facing surface is the absorbent article or It is the surface of the component that is directed to the side opposite to the skin side (clothing side) when the absorbent article is worn. As the top sheet, the back sheet and the absorbent core, those usually used in this type of absorbent article can be used without any particular limitation. The absorbent article of the present invention can be applied to unfolded or pants-type disposable diapers, sanitary napkins, incontinence pads, and the like.

Hereinafter, the thin paper of the present invention (second invention) will be described in detail. The thin paper of the present invention (second invention) contains softwood bleached kraft pulp (NBKP) having a freeness of 400 to 550 ml as an essential component. Freeness is a value indicated by Canadian Standard Freeness (CSF) specified in JIS P8121, and is a value of pulp beating (a process of mechanically tapping and grinding pulp in the presence of water). It is a value indicating the degree. Usually, the smaller the freeness value, the stronger the degree of beating, the greater the damage of the fibers due to beating, and the more fibrillation proceeds. NBKP in which the freeness is in the above range is easily entangled with each other because fibrillation is progressing. Therefore, from the viewpoint of improving liquid permeability, the basis weight of the thin paper is reduced (reducing density). Even if the number of interfiber bonding points decreases, the strength of each interfiber bond is higher than that of NBKP in which the freeness exceeds 550 ml and the fibrillation has not progressed relatively. Therefore, a thin paper mainly composed of NBKP having a freeness of 400 to 550 ml can have good strength characteristics.

The freeness of NBKP used in the present invention (second invention) is preferably 475 to 525 ml, more preferably 490 to 510 ml. When the freeness is less than 400 ml, the strength improvement effect due to the entanglement of the fibers is saturated, and the fiber cutting is promoted, and the permeation time may be delayed. NBKP beating can be carried out according to a conventional method using a known beating machine such as a beader or a disc refiner with respect to a stock (slurry) in which NBKP is dispersed. Further, as NBKP used in the present invention (second invention), NBKP that is usually used in this type of paper can be used without any particular limitation. As NBKP, ECF (elementary chlorin-free) bleached pulp or TCF (total chlorin-free) bleached pulp that does not use a chlorine compound for pulp bleaching may be used.

The thin paper of the present invention (second invention) is mainly NBKP having a freeness of 400 to 550 ml. Here, “mainly” means that the content of NBKP having a freeness in such a range is 50% by mass or more. The content is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, from the viewpoint of obtaining good strength characteristics.

The fiber roughness of NBKP used in the present invention (second invention) is preferably 0.1 to 0.2 mg / m, more preferably 0.12 to 0.18 mg / m. The fiber roughness is used as a scale representing the fiber thickness in a fiber having a nonuniform fiber thickness, such as wood pulp. The average fiber length of NBKP used in the present invention is preferably 1 to 4 mm, and more preferably 2 to 3 mm. The fiber roughness and average fiber length are each measured by the above method.

The thin paper of the present invention (second invention) may contain fibers other than NBKP, and the other fibers may not be hydrophilic cellulose fibers such as NBKP. Other fibers include, for example, hardwood bleached kraft pulp (LBKP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP) and other wood pulp; Non-wood pulp such as kenaf and hemp; synthetic fibers such as polyester fiber, rayon fiber, acrylic fiber, and the like. The content of these other fibers is preferably 50% by mass or less.

In the thin paper of the present invention (second invention), two or more paper strength enhancers are added from the viewpoint of obtaining good strength characteristics (tensile strength). Paper strength enhancers include dry paper strength enhancers that improve dry paper strength and wet paper strength enhancers that improve wet paper strength. Two or more types of paper strength enhancers include dry paper strength enhancers. It is possible to select two or more types from either one of the agent and the wet paper strength enhancer, but from the viewpoint of obtaining particularly excellent strength characteristics, one or more of the dry paper strength enhancer and the wet paper strength enhancer It is preferable to use a combination with one or more.

As the dry paper strength enhancer, conventionally known dry paper strength enhancers can be used. For example, carboxymethyl cellulose (CMC) and salts thereof, polyacrylamide resins and salts thereof, cationized starch, polyvinyl alcohol (PVA). These can be used, and one of these can be used alone or in combination of two or more. As the salt of CMC or polyacrylamide resin, sodium salt is mainly used. Examples of the polyacrylamide resin include cationic or anionic polyacrylamide (PAM). Among these dry paper strength enhancers, CMC and salts thereof, anionic PAM and salts thereof are particularly preferable.

In the present invention (second invention), a particularly preferred combination of paper strength enhancers is two dry paper strength enhancers and one wet paper strength enhancer. Of these three types of paper strength enhancers, CMC salts and anionic PAM salts are preferred as the two dry paper strength enhancers, and PAE is preferred as the one wet strength agent.

In addition, when the CMC salt and the anionic PAM salt are used as the two types of dry paper strength enhancers, and the PAE is used as the one wet paper strength enhancer, the weight average of the anionic PAM salt is used. The molecular weight is preferably 8 million or more, particularly 10 million or more, especially 15 million or more, and the upper limit of the weight average molecular weight of the anionic PAM salt is preferably 25 million. Thus, in the case of using three kinds of specific paper strength enhancers, if the weight average molecular weight of the salt of anionic PAM which is one of them is in the above range (8 million to 25 million), an anion In addition to the effect of improving the strength of the thin paper by developing the adhesiveness of the salt of the PAM, the strength improvement effect of the thin paper can be obtained by improving the yield of the salt of the CMC. Is obtained. Also, when the weight average molecular weight of the anionic PAM salt is 25 million or less, the dispersibility and viscosity of the anionic PAM salt in water can be kept relatively low during the manufacture of the thin paper. Good results can be obtained in terms of prevention of dirt.

The total amount of the two or more kinds of paper strength enhancing agents added to the thin paper of the present invention (second invention) is preferably 0.01 to 1.5% by weight, more preferably based on the dry weight of all the constituent fibers of the thin paper. Is 0.03 to 1.2% by mass. If the total amount of the paper strength enhancer is too small, sufficient strength properties such as tensile strength cannot be obtained. If the total amount of the paper strength enhancer is too large, in addition to curing the thin paper (decrease in texture), There is a possibility that the formation of the thin paper may be deteriorated due to the sticking of the paper to the Yankee dryer or the adhesion of the paper strength enhancer to the mesh drum during the production of the thin paper.

In addition, when a combination of one or more dry paper strength enhancers and one or more wet paper strength enhancers is used as the two or more paper strength enhancers, the total added mass of the dry paper strength enhancer and the wet paper The ratio (the former / the latter) of the force enhancer to the total added mass is preferably 0.01 to 0.5, more preferably 0.03 to 0.35.

The thin paper of the present invention (second invention) may contain components other than the above-described fibers such as NBKP and a paper strength enhancer. As other components, for example, fillers such as talc, dyes, color pigments, antibacterial agents, pH adjusters, yield improvers, water resistance agents, antifoaming agents and the like are generally used as raw materials for papermaking and additives. These can be used, and one of these can be used alone or in combination of two or more.

The thin paper of the present invention (second invention) can be produced by a known wet papermaking method. The wet papermaking method includes a stock preparation step for preparing a stock (slurry) made of an aqueous dispersion of fibers such as NBKP, and a paper making step for drying while transporting a fiber made from the stock into a fiber web. It is what has. The paper making process is usually divided into a wire part, a press part, a dryer part, a size press, a calendar part, etc., and is carried out sequentially. The above-mentioned dry paper strength enhancer and wet paper strength enhancer are usually added to the stock in the stock preparation step. Usually, the wet paper strength enhancer and the dry paper strength enhancer are added in the order of the paper strength enhancer. However, the order of addition of the paper strength enhancer in the present invention (second invention) is not limited to this, and the order of addition is as follows. May be reversed, or both may be added simultaneously. The wet papermaking method can be carried out according to a conventional method using a paper machine such as a long paper machine, a twin wire paper machine, an on-top paper machine, a hybrid paper machine, or a round paper machine.

The thin paper of the present invention (second invention) has a basis weight and density set relatively low from the viewpoint of improving liquid permeability. Specifically, the basis weight is 10 to 14.5 g / m ² , The density is preferably 11 to 14 g / m ² and the density is 0.05 to 0.2 g / cm ³ , preferably 0.1 to 0.2 g / cm ³ . When the basis weight and the density are so low, there is a concern about a decrease in paper strength. In the present invention (second invention), as described above, NBKP having a freeness in a specific range is used and two or more paper strengths are used. By using the enhancer in combination, such concerns are eliminated. When the basis weight of the thin paper is less than 10 g / m ² or the density is less than 0.05 g / cm ³ , the paper strength may be remarkably reduced, and the basis weight of the thin paper is more than 14.5 g / m ² or the density is 0. If it exceeds 2 g / cm ³ , the effect of improving the liquid permeability may be poor. The basis weight and density of the thin paper are each measured by the above method.

The thin paper of the present invention (second invention) has a crepe (crepe-like wrinkles), and the crepe rate is set to 5 to 30%. The crepe in the thin paper of the present invention (second invention) is preferably a dry crepe which is produced when a dry fiber web (thin paper) is peeled off from a Yankee dryer or the like in the dryer part with a doctor knife or the like. The crepe rate is measured by the above method.

Thin paper with crepe has higher liquid permeability than thin paper without crepe, and the higher the crepe rate, the higher the liquid permeability. However, as the crepe rate increases, the strength properties (tensile strength) tend to decrease. In the present invention (second invention), based on such findings, the crepe rate of the thin paper is 5 to 30%, preferably 5 to 20%, more preferably 7 from the viewpoint of the balance between liquid permeability and strength characteristics. ~ 15%.

The dry tensile strength in the transport direction (Machine Direction, abbreviated MD) during the production of the thin paper of the present invention (second invention) having the above-described configuration is 600 cN / 25 mm or more, preferably 600 to 1500 cN / 25 mm, more preferably 700 to 1200 cN / 25 mm, even more preferably 800 to 1200 cN / 25 mm, and still more preferably 900 to 1200 cN / 25 mm. The dry tensile strength in the direction perpendicular to MD (Cross machine Direction, CD for short) is 150 cN / 25 mm or more, preferably 150 to 350 cN / 25 mm, and more preferably 180 to 300 cN / 25 mm. A thin paper having a dry tensile strength of each of MD and CD in the above range has a practically sufficient strength. For example, the thin paper is used as a core wrap sheet for covering an absorbent core in an absorbent article such as a disposable diaper. When applied, it is difficult to cause inconveniences such as tearing of the core wrap sheet (thin paper) during manufacture of the absorbent article. The dry tensile strength is measured by the above method.

The liquid permeation time of the thin paper of the present invention (second invention) measured by the above method is 0.2 to 3 seconds, preferably 0.3 to 2.5 seconds, more preferably 0.5 to 2 seconds. It is. The shorter the liquid permeation time, the higher the liquid permeability and the higher the evaluation. The thin paper whose liquid permeation time is in the above range is excellent in liquid permeability. For example, when the thin paper is applied to a core wrap sheet covering an absorbent core in an absorbent article such as a disposable diaper, urine or the like It is possible to quickly permeate the excreted liquid and allow the absorbent core to quickly absorb the excreted fluid, and to improve the leak-proof property of the absorbent article.

The thin paper of the present invention (second invention) has good strength characteristics (tensile strength) and excellent liquid permeability, and is suitable for various applications in which such features are utilized. In particular, the thin paper of the present invention (second invention) is suitable as a core wrap sheet for covering a liquid-retaining absorbent core in absorbent articles such as disposable diapers and sanitary napkins, and excretory fluid is urine or the like. Even in the case of relatively low viscosity, such as loose stool, even if it is relatively high viscosity, the excretory fluid can be quickly permeated and absorbed into the absorbent core, and the leak-proof property of the absorbent article Can contribute to improvement.

As an example of the absorbent article of the present invention using the thin paper of the present invention (second invention), an absorbent article comprising an absorbent core and a core wrap sheet covering the absorbent core, the core wrap sheet However, what is the thin paper of this invention (2nd invention) mentioned above is mentioned. More specifically, the absorbent article of the present invention includes a liquid-permeable surface sheet that forms a skin-facing surface, a liquid-impermeable or water-repellent back sheet that forms a non-skin-facing surface, and a space between these two sheets. The liquid-retaining absorbent is disposed on the surface, and the absorbent is configured to include the absorbent core and the core wrap sheet (thin paper of the second invention). The core wrap sheet (thin paper of the second invention) preferably covers at least the skin facing surface and the non-skin facing surface of the absorbent core. The skin facing surface is a surface of the absorbent article or a component thereof (for example, an absorbent core) that is directed to the skin side of the wearer when the absorbent article is worn, and the non-skin facing surface is the absorbent article or It is the surface of the component that is directed to the side opposite to the skin side (clothing side) when the absorbent article is worn. As the top sheet, the back sheet and the absorbent core, those usually used in this type of absorbent article can be used without any particular limitation. The absorbent article of the present invention can be applied to unfolded or pants-type disposable diapers, sanitary napkins, incontinence pads, and the like.

Although the second invention has been described as one independent invention different from the first invention described above, the second invention may be an embodiment of the first invention. That is, the second invention is “a softwood bleached kraft pulp having a freeness of 400 to 550 ml, mainly containing two or more kinds of paper strength enhancers, a basis weight of 10 to 14.5 g / m ² , a density May be 0.05 to 0.2 g / cm ³ and a crepe rate of 5 to 30% ”or“ an aggregate of two types of hydrophilic cellulose fibers having different fiber roughness ”. A thin paper to which a paper strength enhancer is added, wherein the two kinds of hydrophilic cellulose fibers include a first pulp having a fiber roughness of 0.13 to 0.16 mg / m and a fiber roughness of 0.17. -0.20 mg / m of the second pulp, and the fiber roughness difference between the contained first pulp and the second pulp is 0.01-0.07 mg / m, Body freeness is 400-550ml Configuration requirements), and freeness is mainly composed of softwood bleached kraft pulp is 400 ~ 550 ml, are added two or more paper strength agent, basis weight of 10 ~ 14.5 g / m ^2, density 0 0.05 to 0.2 g / cm ³ and a crepe rate of 5 to 30% (the above is a constituent requirement of the second invention). In the latter case, the “aggregate of two kinds of hydrophilic cellulose fibers having different fiber roughness” (aggregate having a freeness of 400 to 550 ml) in the constituent requirements of the first invention is the same as “freeness in the constituent requirements of the second invention. In other words, “first pulp and second pulp” in the constituent elements of the first invention are respectively softwood bleached kraft pulp (NBKP). ).

Hereinafter, a method for producing a thin paper of the present invention (third invention) will be described based on its preferred embodiments with reference to the drawings.
FIG. 2 schematically shows an embodiment of a manufacturing apparatus (hereinafter also simply referred to as manufacturing apparatus 1A) used in the thin paper manufacturing method of the present invention (third invention). The manufacturing apparatus 1A shown in FIG. 2 is roughly divided into a raw material slurry adjusting unit 2 and a paper making unit 7. The raw material slurry adjusting unit 2 adjusts the raw material slurry obtained by adding the wet paper strength agent (a), the low molecular weight dry paper strength agent (b), and the polymer dry strength force agent (c) to the softwood bleached kraft pulp. It is used. The papermaking unit 7 is used for papermaking and drying the raw slurry adjusted by the raw slurry adjusting unit 2 to obtain a desired thin paper.
The Y direction in FIGS. 2 to 5 is the conveyance direction (Machine Direction: MD for short) at the time of manufacturing the thin paper.

As shown in FIG. 2, the raw material slurry adjusting unit 2 of the manufacturing apparatus 1 A includes a pulper 21 that sufficiently disaggregates the softwood bleached kraft pulp raw material from the upstream side toward the downstream side to form a water suspension, and a pipe line And a refiner 23 for beating the softwood bleached kraft pulp raw material in the water suspension. Further, a liquid feed pump 24 for sending the water suspension from the pulper 21 to the refiner 23 is attached to the pipe line 22.

Further, as shown in FIG. 2, the raw material slurry adjusting unit 2 of the manufacturing apparatus 1A has a wet paper strength agent (a) made of a cationic polymer having a cationic group on the downstream side of the refiner 23 via a conduit 31. The first slurry storage tank 32 for storing the suspension added with the is added. Further, a wet paper strength agent adding portion 33 for adding the wet strength paper agent (a) is attached to the pipe line 31. In the first slurry storage tank 32, the suspension obtained by adding the wet paper strength agent (a) to the NBKP suspension is sufficiently stirred and mixed.

Further, as shown in FIG. 2, the raw material slurry adjusting unit 2 of the manufacturing apparatus 1 A has a wet paper strength made of a cationic polymer having a cationic group via a pipe line 41 on the downstream side of the first slurry storage tank 32. The low molecular dry paper strength agent (b) comprising a low molecular anionic polymer having an anionic group having a weight average molecular weight (Mw) of 0.2 to 500,000 was further added to the suspension to which the agent (a) was added. A second slurry storage tank 42 for storing the suspension is provided. Further, a low molecular dry paper strength agent adding section 43 for adding the low molecular weight dry paper strength agent (b) is attached to the pipe line 41, and the suspension is stored in the second slurry from the first slurry storage tank 32. A liquid feed pump 44 for feeding to the tank 42 is attached. In the second slurry storage tank 42, the suspension to which the wet paper strength agent (a) and the low molecular weight dry strength agent (b) are added is sufficiently stirred and mixed.

Further, as shown in FIG. 2, the raw material slurry adjusting unit 2 of the manufacturing apparatus 1A changes the flow rate by changing the size of the discharge port on the downstream side of the second slurry storage tank 42 via the conduit 51. A seed box 52 is provided. By changing the size of the discharge port of the seed box 52 and changing the flow rate, the basis weight of the thin paper finally produced can be changed. For example, by reducing the size of the discharge port of the seed box 52 and reducing the flow rate, the basis weight of the thin paper can be lowered. In addition, a liquid feed pump 53 for sending the suspension from the second slurry storage tank 42 to the seed box 52 is attached to the pipe line 51.

Further, as shown in FIG. 2, the raw material slurry adjusting unit 2 of the manufacturing apparatus 1 A filters the fiber lump (floc) and the like from the raw material slurry uniformly through the pipe 61 on the downstream side of the seed box 52. A filtration screen 62 is provided. In addition, the pipe 61 is supplied with dilution water from the upstream side toward the downstream side, and a dilution water supply unit 63 for dilution, and causes turbulence when the liquid is fed through the pipe 61 to produce fibers from the raw slurry. Polymer dry paper strength agent (c) comprising a fan pump 64 for crushing and uniforming a lump of floc and the like, and a polymer anionic polymer having an anionic group having a weight average molecular weight (Mw) of 500 to 30 million ) Is attached.

As shown in FIG. 2, the manufacturing apparatus 1 A, on the downstream side of the filter screen 62, papermaking and drying the raw material slurry adjusted by the raw material slurry adjusting unit 2 through a conduit 66 to obtain thin paper. It has. The paper making unit 7 can use a known paper making apparatus, and is usually configured to include a former, a wire part, a press part, a dry part, and a winder part. The former adjusts the raw material slurry adjusted by the raw material slurry adjusting unit 2 to a predetermined concentration and supplies it to the wire part. A wire part forms the raw material slurry supplied from the former as a paper layer on a papermaking net. The press part squeezes and dehydrates the paper layer in a state where the paper layer formed in the wire part is sandwiched between felts of a press roll to form a wet paper. In the dry part, the wet paper formed in the press part is dried by one or a plurality of dryers. In this case, what combines drying and dehydration is also included. The winder part winds up the paper dried in the dry part as thin paper.

Next, an embodiment of the thin paper manufacturing method of the present invention (third invention) will be described using the manufacturing apparatus 1A of the present embodiment described above with reference to FIG.
The method for producing a thin paper of the present invention (third invention) is a method for producing a thin paper having a basis weight of 30 g / m ² or less by making a paper slurry prepared from raw materials containing softwood bleached kraft pulp and drying it.
In this embodiment, after adding the wet paper strength agent (a) shown below consisting of a cationic polymer having a cationic group to the pulp slurry of softwood bleached kraft pulp as a raw material slurry, the low molecular dry paper shown below The raw material slurry prepared by adding the force agent (b) and then further adding the polymer dry paper force agent (c) shown below is used. This will be specifically described below.

First, softwood bleached kraft pulp raw material is put into the pulper 21, and the pulp raw material is sufficiently disaggregated. As the softwood bleached kraft pulp (NBKP) to be input, NBKP that is usually used in this type of paper can be used without particular limitation. As NBKP, ECF (elementary chlorin-free) bleached pulp or TCF (total chlorin-free) bleached pulp that does not use a chlorine compound for pulp bleaching may be used. The input amount of softwood bleached kraft pulp (NBKP) is preferably such that the concentration of the NBKP suspension is 0.5 to 5.0% by mass, and more preferably 1.0 to 4.0% by mass. preferable.

The fiber roughness of the softwood bleached kraft pulp (NBKP) used in this embodiment is preferably 0.1 to 0.3 mg / m, more preferably 0.12 to 0.25 mg / m. The fiber roughness is used as a scale representing the fiber thickness in a fiber having a nonuniform fiber thickness, such as wood pulp. Further, the average fiber length of NBKP used in this embodiment is preferably 1 to 4 mm, more preferably 2 to 3 mm. The fiber roughness and average fiber length are each measured by the above method.

Next, the NBKP suspension sufficiently disaggregated by the pulper 21 is supplied to the refiner 23 through the conduit 22 using the liquid feed pump 24. Then, the refiner 23 beats the softwood bleached kraft pulp raw material in the suspension. The pulper 21 and refiner 23 are used to beat the softwood bleached kraft pulp (NBKP) so that the freeness is preferably 650 ml or less. Here, freeness is a value indicated by Canadian standard freeness (CSF) specified in JIS P811, and pulp beating (pulp is mechanically beaten in the presence of water and ground. This is a value indicating the degree of processing. Usually, the smaller the freeness value, the stronger the degree of beating, the greater the damage of the fibers due to beating, and the more fibrillation proceeds. NBKP in which the freeness is in the above range is easily entangled with each other because fibrillation is progressing. Therefore, from the viewpoint of improving liquid permeability, the basis weight of the thin paper is reduced (reducing density). Even if the number of interfiber bonding points is decreased, the strength of each interfiber bond is higher than NBKP in which the freeness exceeds 650 ml and the fibrillation is not progressing relatively. Therefore, if the freeness is 650 ml or less, the thin paper mainly composed of NBKP can have good strength characteristics.

The freeness of NBKP used in the present embodiment is more preferably 300 to 650 ml, particularly preferably 450 to 550 ml, and still more preferably 480 to 530 ml. When the freeness is less than 300 ml, the effect of improving the strength due to the entanglement of the fibers is saturated, and the cutting of the fibers is promoted, and the permeation time may be delayed.

The thin paper produced in this embodiment is preferably mainly composed of NBKP having a freeness of 300 to 650 ml. Here, “mainly” means that the content of NBKP having a freeness in such a range is 50% by mass or more. The content is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, from the viewpoint of obtaining good strength characteristics.

The raw material put into the pulper 21 may contain fibers other than softwood bleached kraft pulp (NBKP), and other fibers may not be hydrophilic cellulose fibers such as NBKP. Other fibers include, for example, hardwood bleached kraft pulp (LBKP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP) and other wood pulp; Non-wood pulp such as kenaf and hemp; synthetic fibers such as polyester fiber, rayon fiber, acrylic fiber, and the like. The content of these other fibers is preferably 50% by mass or less in the thin paper produced in this embodiment.

Next, the NBKP suspension thoroughly beaten by the pulper 21 and the refiner 23 is added to the first slurry storage tank 32 while adding the wet paper strength agent (a) using the wet paper strength agent addition unit 33. Transport. Then, in the first slurry storage tank 32, the wet paper strength agent (a) and the suspension of NBKP are sufficiently stirred and mixed.

Examples of the wet paper strength agent (a) comprising a cationic polymer having a cationic group include polyamide polyamine epichlorohydrin resin (epoxidized polyamide polyamine resin (PAE)), urea-formalin resin, meamine-formalin resin, and dialdehyde starch. , Polyethyleneamine, methylolated polyamide, and the like, and these can be used alone or in combination of two or more. Among these wet paper strength agents, epoxidized polyamide polyamine resin (PAE) is preferable from the viewpoint of a wide papermaking pH range that can be used and reduction of environmental load that does not contain formalin.

The addition amount of the wet paper strength agent (a) is 0.1-2. From the viewpoint of dirt in the process and wet strength of the paper with respect to the dry mass of all the constituent fibers of the thin paper produced in this embodiment. It is preferable to add so that it may become 0 mass%, and it is still more preferable to add so that it may become 0.2-1.5 mass%. When one kind of epoxidized polyamide polyamine resin (PAE) is used as the wet paper strength agent (a), PAE is preferably 0 with respect to the dry mass of all the constituent fibers of the thin paper produced in this embodiment. 0.5 to 1.5% by mass, more preferably 0.6 to 1.2% by mass.

Next, in the step of adjusting the raw material, the low molecular dry paper strength agent (b) shown below is added and then diluted, and after dilution, the polymer dry paper strength agent (c) shown below is added, and then the fan Uniform using a pump 64 and a filter screen 62. This will be specifically described below.

A suspension of softwood bleached kraft pulp (NBKP) added with wet paper strength agent (a) sufficiently stirred and mixed in the first slurry storage tank 32 is passed through the pipeline 41 by the liquid feed pump 44 to the second. At the time of sending to the slurry storage tank 42, the low molecular dry paper strength agent adding unit 43 is used to transport the slurry into the second slurry storage tank 42 while adding the low molecular weight dry paper strength agent (b). Then, in the second slurry storage tank 42, the low molecular dry paper strength agent (b), the wet strength paper strength agent (a) and the suspension of NBKP are sufficiently stirred and mixed.

The low molecular weight dry paper strength agent (b) is a low molecular weight anionic polymer having an anionic group having a weight average molecular weight (Mw) of 0.2 to 500,000 from the viewpoint of sticking to a Yankee dryer and formation. A low molecular anion polymer having an anionic group having a weight average molecular weight (Mw) of 0.5 to 450,000, and a low molecular anion having an anionic group having a weight average molecular weight (Mw) of 1 to 400,000 More preferably, it is a polymer. Examples of the low molecular weight dry paper strength agent (b) include salts of carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and the like, and one of these can be used alone or in combination of two or more. Among these low molecular dry paper strength agents, a salt of carboxymethyl cellulose (CMC) is preferable from the viewpoint of versatility and solubility. The degree of substitution (etherification degree) of CMC can theoretically be up to 3, but is preferably in the range of 0.5 to 1.5 from the viewpoint of productivity and the like. In addition, sodium salt is mainly used as the salt of CMC.

The addition amount of the low molecular weight dry strength agent (b) is 0.01 to 0 with respect to the dry weight of all the constituent fibers of the thin paper produced in this embodiment from the viewpoint of in-process dirt and dry strength. It is preferable to add it so that it may become 0.5 mass%, and it is still more preferable to add so that it may become 0.1-0.3 mass%. When one kind of carboxymethylcellulose (CMC) salt is used as the low molecular weight dry paper strength agent (b), the CMC salt is contained in the dry mass of all the constituent fibers of the thin paper produced in this embodiment. The amount is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.3% by mass.
However, when the concentration of the low molecular weight dry paper strength agent (b) is from 0.1 to 0.3% by mass, the low molecular weight dry paper strength agent (b) falls off from the pulp during paper making in low basis weight paper such as thin paper. It is difficult to obtain sufficient paper strength. Although increasing the concentration of the low-molecular dry paper strength agent (b) increases the paper strength, there is concern about dirt in the process, so the upper limit of the amount of the low-molecular dry strength material (b) is specified. It is preferable to add other dry paper strength agents. Therefore, in the thin paper manufacturing method of the present invention, as described later, the polymer dry paper strength agent (c) is added as another dry paper strength agent. Hereinafter, this embodiment will be specifically described.

Next, as shown in FIG. 2, the softwood bleached kraft pulp to which the wet paper strength agent (a) and the low molecular weight dry strength force agent (b) sufficiently stirred and mixed in the second slurry storage tank 42 was added. NBKP) is sent to the seed box 52 through the pipe 51 by the liquid feed pump 53. And the flow volume is adjusted so that the size of the discharge port of the seed box 52 may be changed to obtain a thin paper having a target basis weight (30 g / m ² or less).

Next, a suspension of softwood bleached kraft pulp (NBKP) to which wet flow strength agent (a) and low molecular weight dry strength strength agent (b) are added, whose flow rate is adjusted, is passed through line 61 to a filtration screen 62. In this embodiment, first, the dilution water is supplied and diluted using the dilution water supply unit 63 in this embodiment. By dilution, the concentration of the NBKP suspension is preferably 0.01 to 1.0% by mass, and more preferably 0.05 to 0.5% by mass.

In this embodiment, the diluted suspension of softwood bleached kraft pulp (NBKP) to which the wet paper strength agent (a) and the low molecular weight dry strength agent (b) are added is then added to the fan. A pump 64 is used to convey to the filtration screen 62 while causing turbulence.

In this embodiment, the suspension of softwood bleached kraft pulp (NBKP) to which the wet paper strength agent (a) and the low molecular weight dry strength agent (b) are added is then conveyed by turbulent flow. However, the polymer dry paper strength agent (c) is added using the polymer dry paper strength agent addition unit 65 and conveyed to the filter screen 62. Due to the turbulent flow of the fan pump 64, in this embodiment, the anionic polymer dry paper strength agent (c) is added to the pulp fiber in the suspension to which the cationic wet strength material (a) is adhered. The adhering materials attached while entangled the low molecular weight dry paper strength agent (b) are separated from the aggregates (floc) that are linked by the charge of the anionic polymer dry strength agent (c). It ’s hard to get worse. Moreover, in this embodiment, since the said block (floc) can be removed also by this filter screen 62, it is hard to worsen a texture further.

As described above, the polymer dry paper strength agent (c) needs to be added from the viewpoint of improving the yield of pulp, wet paper strength agent (a), and low molecular weight dry strength agent (b). The weight average molecular weight (Mw) of the polymer dry paper strength agent (c) is a polymer having 500 to 30 million anionic groups, and the weight average molecular weight (Mw) of the polymer dry paper strength agent (c) is ) In the acrylic polyacrylamide resin (PAM) having 8 to 25 million is preferably 0.1% mol to 80% mol, and the weight average molecular weight (Mw) is 6 to 20 million. The ratio of sodium acrylate in the acrylic polyacrylamide resin (PAM) is preferably 1% mol to 50% mol.

The addition amount of the polymer dry paper strength agent (c) is 0.001 to 0.000 from the viewpoint of dry paper strength and formation with respect to the dry mass of all the constituent fibers of the thin paper produced in this embodiment. It is preferable to add so that it may become 1 mass%, and it is still more preferable to add so that it may become 0.01-0.08 mass%. When an acrylic polyacrylamide resin (PAM) is used as the polymer dry paper strength agent (c), the PAM is preferably 0.00 with respect to the dry mass of all the constituent fibers of the thin paper produced in this embodiment. The content is 001 to 0.1% by mass, more preferably 0.02 to 0.05% by mass.

As a paper strength enhancer, the ratio of the added weight of one kind of wet strength paper (a) to the total added weight of the low molecular weight strength paper strength agent (b) and the high molecular weight strength strength paper strength agent (c) (the former / The latter is preferably from 0.5 to 10, more preferably from 1 to 5.

Next, the raw material slurry from which the block (floc) has been removed is conveyed to the paper making unit 7 in the next step through the pipe 66, and paper making and drying are performed in the paper making unit 7 to produce thin paper. Specifically, the raw material slurry adjusted by the raw material slurry adjusting unit 2 is adjusted to a predetermined concentration by the former of the paper making unit 7, and the raw material slurry supplied from the former is made by the wire part of the paper making unit 7. Form as a paper layer on the net. Thereafter, the paper layer formed in the wire part is pressed and dehydrated in the press part of the paper making unit 7 to form wet paper, and the wet paper formed in the press part is used in the dry part of the paper making unit 7, for example Then, dry the paper using a Yankee dryer, air-through dryer, etc. to produce thin paper. In addition, the manufactured thin paper is wound up by the winder part of the papermaking unit 7, for example.

The method for producing a thin paper according to this embodiment is suitable for producing a thin paper having a basis weight of 30 g / m ² or less. In this embodiment, the desired basis weight (30 g / m ² or less) is obtained by adjusting the flow rate by the seed box 52 of the raw slurry adjusting unit 2 or by adjusting the flow rate to a predetermined concentration by the former of the paper making unit 7. Adjust to a thin paper. From the viewpoint of improving liquid permeability, the basis weight is preferably 10 to 14.5 g / m ² , and more preferably 11 to 14 g / m ² . From the same viewpoint, the density of the thin paper produced is preferably 0.05 to 0.2 g / cm ³ , and more preferably 0.1 to 0.2 g / cm ³ . When the basis weight and the density are so low, there is a concern about a decrease in paper strength. However, as described above, the thin paper produced in this embodiment has a cationic group in the pulp slurry of softwood bleached kraft pulp (NBKP). A raw material prepared by adding a wet paper strength agent (a) made of a cationic polymer having a low molecular weight, then adding a low molecular weight dry strength agent (b), and then further adding a high molecular weight dry strength agent (c). By using slurry, such concerns are eliminated. If the basis weight of the thin paper is less than 10 g / m ² or the density is less than 0.05 g / cm ³ , the paper strength may be remarkably reduced, and the basis weight of the thin paper is more than 30 g / m ² or the density is 0. If it exceeds 2 g / cm ³ , the effect of improving the liquid permeability may be poor. The basis weight and density of the thin paper are each measured by the above method.

The thin paper produced in this embodiment has crepes (crepe-like wrinkles), and the crepe rate is preferably set to 5% or more, and is preferably set to 5 to 30%. Further preferred. The crepe in the thin paper produced in this embodiment is preferably a dry crepe that is produced when a dry fiber web (thin paper) is peeled off from a Yankee dryer or the like in the dryer part with a doctor knife or the like. The crepe rate is measured by the above method.

Thin paper with crepe has higher liquid permeability than thin paper without crepe, and the higher the crepe rate, the higher the liquid permeability. However, as the crepe rate increases, the strength properties (tensile strength) tend to decrease. In the present embodiment, based on such knowledge, the crepe rate of the thin paper produced in the present embodiment is preferably 5 to 30% from the viewpoint of the balance between liquid permeability and strength characteristics. % Is more preferable, and 7 to 15% is particularly preferable.

The dry tensile strength in the MD direction of the thin paper produced in this embodiment is 60 cN / gsm or more, preferably 60 to 150 cN / gsm, more preferably 60 to 100 cN / gsm, and more preferably 60 to 90 cN. / Gsm is particularly preferable. Further, the dry tensile strength of the thin paper produced in this embodiment in the CD direction perpendicular to the MD direction is 13 cN / gsm or more, preferably 13 to 50 cN / gsm, and preferably 13 to 40 cN / gsm. More preferably, it is 13 to 30 cN / gsm. A thin paper having a dry tensile strength in each of the MD direction and the CD direction within the above range has a practically sufficient strength. For example, the thin paper is coated with a core wrap that covers an absorbent core in an absorbent article such as a disposable diaper. When applied to a sheet, it is difficult to cause inconveniences such as tearing of a core wrap sheet (thin paper) when manufacturing an absorbent article. Regarding the unit of tensile strength, the unit “cN / gsm” used for the third invention is the same as the unit “cN / 25 mm” used for the first invention described above.

The wet tensile strength in the MD direction of the thin paper produced in this embodiment is 13 cN / gsm or more, preferably 13 to 60 cN / gsm, more preferably 13 to 50 cN / gsm, and more preferably 13 to 30 cN. / Gsm is particularly preferable. Further, the dry tensile strength of the thin paper produced in the present embodiment in the CD direction perpendicular to the MD direction is 5 cN / gsm or more, preferably 5 to 20 cN / gsm, and 5 to 15 cN / gsm. Further preferred is 5 to 12 cN / gsm.
The thin paper having the wet tensile strength in the MD direction and the CD direction in the above ranges has a practically sufficient strength. For example, the thin paper is unlikely to cause inconvenience when using a diaper. The dry tensile strength is measured by the above method, and the wet tensile strength is measured as follows.

<Measurement method of wet tensile strength>
After immersing a sheet of the same size as the measurement target sheet (thin paper) used in <Method for measuring dry tensile strength> in a large amount of water for 5 seconds, and then draining the water for 10 seconds, <Measurement of dry tensile strength> The maximum strength until fracture is measured with the same tensile tester and measurement method as in Method>.

Further, the liquid permeation time of the thin paper of this embodiment measured by the above method is 3 seconds or less, preferably 0.2 to 3 seconds, and more preferably 0.3 to 2.5 seconds. Preferably, it is 0.5 to 2 seconds. The shorter the liquid permeation time, the higher the liquid permeability and the higher the evaluation. The thin paper whose liquid permeation time is in the above range is excellent in liquid permeability. For example, when the thin paper is applied to a core wrap sheet covering an absorbent core in an absorbent article such as a disposable diaper, urine or the like It is possible to quickly permeate the excreted liquid and allow the absorbent core to quickly absorb the excreted fluid, and to improve the leak-proof property of the absorbent article.

The thin paper produced in this embodiment has good strength characteristics (tensile strength) and excellent liquid permeability, and is suitable for various applications in which such features are utilized. In particular, the thin paper produced in this embodiment is suitable as a core wrap sheet for covering a liquid-retaining absorbent core in absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads, Not only in the case of relatively low viscosity, such as urine, but also in the case of relatively high viscosity, such as loose stool, the excretory fluid can be quickly permeated and absorbed by the absorbent core. It can contribute to the improvement of sex.

The thin paper produced in this embodiment may contain other components other than the fibers such as NBKP and the paper strength enhancing agents (a), (b), and (c) described above. As other components, for example, fillers such as calcium carbonate and talc, dyes, color pigments, deodorants, antibacterial agents, pH adjusters, yield improvers, water resistance agents, antifoaming agents, etc. What is used as a raw material or an additive is mentioned, These 1 type can be used individually or in combination of 2 or more types.

The thin paper manufacturing method of the present invention (third invention) is not limited to the embodiment described above. For example, in the above-described embodiment, after adding a wet paper strength agent (a) made of a cationic polymer having a cationic group to a pulp slurry of softwood bleached kraft pulp (NBKP), a low molecular weight dry strength material (b ), And then a raw material slurry prepared by further adding a polymer dry paper strength agent (c), but a cationic polymer having a cationic group in the pulp slurry of softwood bleached kraft pulp (NBKP) After adding the wet paper strength agent (a) consisting of the above, a raw material slurry prepared by simultaneously adding the low molecular weight dry strength agent (b) and the high molecular weight dry strength agent (c) may be used. Thus, by simultaneously adding the low-molecular dry paper strength agent (b) and the high-molecular dry paper strength agent (c), the production line can be made compact by simplifying the chemical addition step.

Further, as a manufacturing apparatus used in the present invention (third invention), a manufacturing apparatus 1B shown in FIG. 3 can be used instead of the manufacturing apparatus 1A shown in FIG. The manufacturing apparatus 1B shown in FIG. 3 differs from the manufacturing apparatus 1A shown in FIG. 2 in the position of the polymer dry paper strength agent adding section 65. Specifically, in the manufacturing apparatus 1B shown in FIG. 3, a polymer dry paper strength agent adding unit 65 is arranged in the pipe line 61 connecting the seed box 52 and the filtration screen 62 from the upstream side to the downstream side. Then, the dilution water supply unit 63 is arranged, and then the fan pump 64 is arranged. Also in the embodiment using the manufacturing apparatus 1B shown in FIG. 3, the same effect as the embodiment using the manufacturing apparatus 1A shown in FIG. 2 can be expected.

Further, as a manufacturing apparatus used in the present invention (third invention), a manufacturing apparatus 1C shown in FIG. 4 can be used instead of the manufacturing apparatus 1A shown in FIG. The manufacturing apparatus 1C illustrated in FIG. 4 does not include the fan pump 64 and the position of the polymer dry paper strength agent adding unit 65 is different from that of the manufacturing apparatus 1A illustrated in FIG. Specifically, in the manufacturing apparatus 1 C shown in FIG. 4, a polymer dry paper strength agent adding unit 65 is arranged in a pipe line 66 connecting the filtration screen 62 and the paper making unit 7. In the embodiment using the manufacturing apparatus 1 C shown in FIG. 4, the same operational effects as those in the embodiment using the manufacturing apparatus 1 A shown in FIG. 2 can be expected. Note that the manufacturing apparatus 1C illustrated in FIG. 4 does not include the fan pump 64, but may include the fan pump 64 instead of the filtration screen 62.

Further, as a manufacturing apparatus used in the present invention (third invention), a manufacturing apparatus 1D shown in FIG. 5 can be used instead of the manufacturing apparatus 1A shown in FIG. Compared with the manufacturing apparatus 1A shown in FIG. 2, the manufacturing apparatus 1D shown in FIG. 5 does not have the second slurry storage tank 42, the pipe line 51, and the liquid feed pump 53, and adds a low molecular dry paper strength agent. The attachment position of the part 43 is different. Specifically, in the manufacturing apparatus 1 D shown in FIG. 5, a low molecular dry paper strength agent adding section 43 is attached in the middle of the pipeline of the polymer dry paper strength agent adding section 65. According to the manufacturing apparatus 1D, the suspension of the softwood bleached kraft pulp (NBKP) to which the wet paper strength agent (a) sufficiently stirred and mixed in the first slurry storage tank 32 is added is fed by the liquid feed pump 44. It is sent to the seed box 52 through the pipe 41. Then, when the suspension whose flow rate is adjusted in the seed box 52 is transported to the filtration screen 62 through the pipe 61, first, it is diluted using the dilution water supply unit 63, and then using the fan pump 64. , And transported to the filter screen 62 while causing turbulence. According to the manufacturing apparatus 1D, the polymer dry paper strength agent adding unit 65 is used to convey a suspension of softwood bleached kraft pulp (NBKP) to which the wet strength material (a) is added by turbulent flow. When adding the molecular dry paper strength agent (c), the low molecular dry paper strength agent (b) is added to the polymer dry paper strength agent (c) using the low molecular dry paper strength agent addition unit 43. To do. Also in the embodiment using the manufacturing apparatus 1D shown in FIG. 5, the same effect as the embodiment using the manufacturing apparatus 1A shown in FIG. 2 can be expected.

Hereinafter, the absorbent article of the present invention (the fourth invention) will be described with reference to the drawings based on a disposable diaper which is a preferred embodiment thereof. The diaper 1 of the present embodiment is a so-called unfolded disposable diaper, as shown in FIGS. 6 and 7, a liquid-permeable surface sheet 12 that forms a skin facing surface, and a liquid impermeable material that forms a non-skin facing surface. It has a back sheet 13 that is permeable or water repellent (hereinafter collectively referred to as “liquid impervious”), and an absorbent body 14 that is disposed between the two

sheets

12 and 13 and is formed substantially vertically. Yes. The top sheet 12, the back sheet 13, and the absorber 14 all have a vertically long shape in one direction X. Each of the top sheet 12 and the back sheet 13 has a size larger than that of the absorber 14, and extends outward from the peripheral edge of the absorber 14. As shown in FIG. 7, the width of the top sheet 12 in the width direction Y is smaller than the width of the back sheet 13 in the width direction Y.

As shown in FIG. 6, the diaper 1 has, in the longitudinal direction X, a dorsal side portion A that is arranged on the back side of the wearer when worn, and a ventral side portion B that is arranged on the ventral side of the wearer when wearing, And a crotch part C on which the wearer's crotch is arranged when worn. The crotch portion C is located at the center of the diaper 1 in the longitudinal direction X. The diaper 1 has an hourglass shape in which both side edges of the crotch part C are curved in an inward arc shape, and the center part in the longitudinal direction X is inwardly bounded in a plan view as shown in FIG. Yes.

In the present specification, the longitudinal direction is a direction along the long side of an absorbent article (disposable diaper) or a constituent member (for example, an absorbent core), and the width direction is a direction orthogonal to the longitudinal direction. 6 to 8, the direction indicated by the symbol X is the longitudinal direction of the diaper 1 (absorbent core 140), and the direction indicated by the symbol Y is the width direction of the diaper 1 (absorbent core 140). Further, the skin facing surface is a surface that is directed to the wearer's skin when the absorbent article (disposable diaper) is worn in the absorbent article (disposable diaper) or a component thereof, and the non-skin facing surface is absorbent. In the article (disposable diaper) or a component thereof, the surface is directed to the side opposite to the skin side (clothing side) when the absorbent article (disposable diaper) is worn.

As shown in FIG.6 and FIG.7, each side part along the longitudinal direction X of the diaper 1 is provided with a side sheet 162 to which an elastic member 161 is fixed in an extended state on one side edge part. A pair of three-dimensional gathers are formed in the crotch part C at the time. In addition, elastic members 163 are arranged along the longitudinal direction X on the left and right leg portions arranged around the wearer's legs, and a pair of leg portions when worn is contracted by the elastic member 163. Leg gathers are formed. As shown in FIG. 7, the pair of

side sheets

162, 162, the top sheet 12, the absorber 14, the elastic member 163, and the back sheet 13 are joined by a known joining means such as a hot melt adhesive.

Moreover, as shown in FIG. 6, the waist elastic member 164 is arrange | positioned in the waist opening end part of the back side part A and the abdominal side part B, and the waist gathers are formed. The waist elastic member 164 has a belt-like form, and is sandwiched and fixed between the top sheet 12 and the back sheet 13 over substantially the entire width of the diaper 1 along the width direction Y of the diaper 1. In addition, a plurality of waistline gather forming elastic members 165 are disposed on the left and right sides of the waistline portion of the back side portion A to form a pair of left and right waistline gathers. The waistline gather forming elastic member 165 is arranged substantially linearly along the width direction Y, and is sandwiched and fixed between the top sheet 12 and the back sheet 13.

As shown in FIG. 6, a pair of

fastening tapes

18 and 18 are provided on both side edges along the longitudinal direction X of the back side A of the diaper 1. More specifically, the both sides along the longitudinal direction X of each of the back side portion A and the ventral side portion B extend outward in the width direction Y from both side edge portions along the longitudinal direction X of the absorbent body 14. Side flaps 17 and 17 are formed, and a fastening tape 18 is attached to each side flap 17 so as to extend outward in the width direction Y. A fastening portion 181 made of a male member of a mechanical surface fastener is attached to the fastening tape 18.

Also, a non-skin facing surface of the ventral side B of the diaper 1 is formed with a to-be-attached region 19 made of a female member of a mechanical surface fastener. The to-be-bonded region 19 is formed by bonding and fixing a female member of a mechanical hook-and-loop fastener to the non-skin facing surface of the back sheet 13 with a known bonding means (for example, an adhesive or heat seal). The fastening part 181 of the tape 18 can be detachably fastened.

Hereinafter, the absorber 14 will be described in detail. As shown in FIGS. 6 and 7, the absorbent body 4 includes an absorbent core 140 and a core wrap sheet 15 that covers the absorbent core 140. As shown in FIG. 6, the absorbent core 140 has a shape that is long in one direction (longitudinal direction X of the diaper 1), and the longitudinal central portion is constricted.

The absorbent core 140 includes a hydrophilic fiber and a water-absorbing polymer. The hydrophilic fiber can be used without particular limitation as long as it is a fiber having a hydrophilic surface and can form a sheet in which the fibers have a high degree of freedom in the wet state. Examples of such hydrophilic fibers include natural cellulose fibers such as wood pulp such as softwood kraft pulp and hardwood kraft pulp and non-wood pulp such as cotton pulp and straw pulp; regenerated cellulose fibers such as rayon and cupra; polyvinyl alcohol fiber , Hydrophilic synthetic fibers such as polyacrylonitrile fibers; synthetic fibers such as polyethylene terephthalate (PET) fibers, polyethylene (PE) fibers, polypropylene (PP) fibers, and polyester fibers that have been hydrophilized with a surfactant. These 1 type can be used individually or in mixture of 2 or more types.

In addition, as the water-absorbing polymer, various polymers conventionally used in the technical field can be used without particular limitation. For example, polyacrylic acid soda, (acrylic acid-vinyl alcohol) copolymer, polyacrylic acid Cross-linked soda, (starch-acrylic acid) graft polymer, (isobutylene-maleic anhydride) copolymer and saponified product thereof, potassium polyacrylate, cesium polyacrylate, and the like. Or a mixture of two or more. As the water-absorbing polymer, particles are usually used, but fibers may be used. The particulate water-absorbing polymer includes an amorphous type, a block type, a bowl type, a spherical particle agglomeration type, a spherical type and the like due to the difference in shape, and any type can be used.

The total content of the hydrophilic fiber and the water-absorbing polymer in the absorbent core 140 is, for example, 70 to 100% by mass, preferably 85 to 100% by mass, more preferably 95 to 100% by mass with respect to the mass of the absorbent core 140. 100% by mass. The content ratio of the hydrophilic fiber to the water-absorbing polymer is preferably hydrophilic fiber: water-absorbing polymer = 1/9 to 9/1 from the viewpoint of sufficiently holding and fixing urine, loose stool, and the like. / 7 to 7/3 is more preferable. For the absorbent core 140, other components other than the hydrophilic fiber and the water-absorbing polymer, for example, various additives such as pH buffer material, hydrophilic fine powder, deodorant, non-hydrophilic fiber, etc., if necessary May be included.

The basis weight of the absorbent core 140 is preferably 200 to 600 g / m ² , particularly 300 to 600 g / m ² , from the viewpoint of sufficiently holding and fixing urine, loose stool and the like. From the same viewpoint, the density of the absorbent core 140 is preferably 0.10 to 0.30 g / cm ³ , more preferably 0.15 to 0.30 g / cm ³ . Further, the thickness of the absorbent core 140 under no load is preferably 1.5 to 3.5 mm, more preferably 1.7 to 3.0 mm.

As shown in FIG. 7, the core wrap sheet 15 is disposed so as to face the skin facing surface 140 a of the absorbent core 140 (located on the skin facing surface 140 a side of the absorbent core 140). And covering both

side edges

140s, 140s along the longitudinal direction X of the absorbent core 140 (disposed on the non-skin facing surface 140b side of the absorbent core 140) And a low liquid permeability sheet 152. More specifically, the core wrap sheet 15 includes two

sheets

151 and 152 having different dimensions in the width direction Y, one of which is the longitudinal direction X and width of the absorbent core 140. A highly liquid-permeable paper 151 having substantially the same dimensions as the length in the direction Y (the length in the longitudinal direction and the width direction of the absorbent core here means the maximum length in each direction), One sheet is a low liquid permeability sheet 152 wider than the high liquid permeability paper 151. The high liquid permeable paper 151 and the low liquid permeable sheet 152 have the same length in the longitudinal direction X. The high liquid permeability paper 151 covers substantially the entire skin facing surface 140a of the absorbent core 140. The low liquid permeable sheet 152 covers substantially the entire area of the non-skin facing surface 140b of the absorbent core 140, and extends outward in the width direction Y from both

side edge portions

140s, 140s of the absorbent core 140. The protruding portion is wound up on the highly liquid permeable paper 151 disposed opposite to the skin facing surface 140 a of the absorbent core 140 and covers both side edges along the longitudinal direction X of the highly liquid permeable paper 151. The high liquid permeable paper 151 and the absorbent core 140 and the low liquid permeable sheet 152 and the absorbent core 140 may be joined by a known joining means such as a hot melt adhesive. .

As one of the main features of the diaper 1 of the present embodiment, the highly liquid-permeable paper 151 that is directly disposed on the skin facing surface 140a of the absorbent core 140 without any other member has good strength characteristics. The point which is excellent in liquid permeability is mentioned.

That is, the basis weight and density of the high liquid permeability paper 151 are set to be relatively low from the viewpoint of improving the liquid permeability. Specifically, the basis weight of the high liquid permeability paper 151 is 8 to 20 g. / M ² , preferably 10 to 14.5 g / m ² , more preferably 11 to 14 g / m ² , and the density of the highly liquid-permeable paper 51 is 0.05 to 0.2 g / cm ³ , The amount is preferably 0.07 to 0.20 g / cm ³ , more preferably 0.10 to 0.20 g / cm ³ . If the basis weight of the highly liquid permeable paper 151 is less than 8 g / m ² or the density is less than 0.05 g / cm ³ , the paper strength may be remarkably reduced, and the basis weight of the highly liquid permeable paper 151 is 20 g. If the density exceeds / m ² or the density exceeds 0.2 g / cm ³ , the effect of improving the liquid permeability may be poor. The basis weight and density of the highly liquid-permeable paper 151 (core wrap sheet 15) are measured as follows.

<Measurement method of basis weight of core wrap sheet>
After conditioning the sample (core wrap sheet) under the conditions of JIS P8111, a 10 cm square (100 cm ² ) measurement piece was cut out from the sample, and the weight of the measurement piece was measured with a two-digit scale below the decimal point. The basis weight of the measurement piece is calculated by dividing the measured value by the area. About 10 measurement pieces cut out from the sample, the basis weight is calculated according to the above procedure, and the average value thereof is taken as the basis weight of the sample.

<Method of measuring the density of the core wrap sheet>
Ten 20 cm square samples (core wrap sheets) are stacked to form a laminate, and the laminate is cooled and solidified with liquid nitrogen, and then the vicinity of the center of the laminate is cut with a cutter. Then, of the 10 samples, one having no shear applied to the cross section generated by cutting with the cutter is selected, and the thickness of the selected sample is measured with an optical microscope. In addition, the thickness of the sample is not the length (apparent thickness) from the bottom to the top of the concavo-convex part when the sample has concavo-convex parts such as crepes described later, but the part where the constituent fibers are deposited Length (substantial thickness). The weight W of the 20 cm square sample whose thickness has been measured in this way is measured using a balance with two decimal places. The target density is calculated by dividing the weight W of the sample by the volume V of the sample calculated by the following equation (that is, by W / V). In the following formula, T is the thickness (cm) of the sample, A is the crepe rate (%) of the sample, and B is the length of one side (20 cm) of the sample. The crepe rate is measured by the measurement method. When the core wrap sheet to be measured does not have a crepe (when the crepe rate is 0%), A = 0 in the following equation. V = {T × B × B × (100 + A) / 100}

Such a low basis weight, low density high liquid permeability paper 151 has a liquid permeation time (liquid permeation time of a highly viscous liquid) measured by the following method of 600 seconds or less, preferably 400 seconds or less. More preferably, it is 300 seconds or less. The shorter the liquid permeation time, the higher the liquid permeability and the higher the evaluation. The high liquid permeability paper 151 having a liquid permeation time in the above range is excellent in liquid permeability and has a relatively low viscosity excretion such as loose stool and menstrual blood in addition to a relatively low viscosity excretion such as urine. Can be quickly permeated and absorbed quickly by the absorbent core 40, and the surface liquid residue is hardly generated.

<Measurement method of liquid permeation time>
As shown in FIG. 1, two

cylinders

91 and 92 having an inner diameter of 35 mm with upper and lower ends open are arranged vertically with the axes of both

cylinders

91 and 92 aligned, and the sheet S (high liquid) to be measured A transparent paper) is sandwiched between the upper and

lower cylinders

91 and 92. At this time, it is preferable that the upper and

lower cylinders

cylinders

91 and 92. In this manner, with the sheet S to be measured sandwiched and fixed between the upper and

lower cylinders

91 and 92, the viscosity of 290 mPa · s (A & D Co., Ltd.) indicated by the symbol W in FIG. Measure with a vibratory viscometer CJV 5000. Put about 10 g of high viscosity liquid into the sample container, set it in the viscometer, insert the sensitive plate at a predetermined level, select the measurement range to 50 mV, and press the measurement switch to start the measurement. 10 g ± 1 g of a highly viscous liquid of 60 seconds after the start of measurement, measured at 25 ° C.). The supplied highly viscous liquid passes through the measurement target sheet S or is absorbed by the measurement target sheet S and disappears from the upper cylinder 91. The time until the liquid level of the high-viscosity liquid reaches the same position as the surface of the sheet S to be measured (the surface on the upper cylinder 91 side) from the start of the supply of the high-viscosity liquid is measured. And The highly viscous liquid is prepared by mixing glycerin and ion exchange water at a mass ratio of the former: the latter = 94: 6.

Thus, while the high liquid permeability paper 151 has a liquid permeation time of 600 seconds or less and excellent liquid permeability, the low liquid permeation constituting the core wrap sheet 15 together with the high liquid permeability paper 151. The liquid sheet 152 has inferior liquid permeability because the liquid permeation time exceeds 600 seconds. That is, in the absorbent core 140 according to the present embodiment, the skin facing surface 140a that directly receives excretion fluid such as loose stool is covered with the highly liquid permeable paper 151 that is excellent in liquid permeability, and is located on the opposite side. The skin facing surface 140b and the

side edge portions

140s and 140s are covered with a low liquid permeability sheet 152 having poor liquid permeability.

With such a covering form of the core wrap sheet 15, in the absorbent body 14, the liquid excreted when the diaper 1 is worn and transmitted through the top sheet 12 is quickly drawn into the absorbent body 14 by the action of the highly liquid-permeable paper 151. And is absorbed and held by the absorbent core 140. Further, since the non-skin facing surface 140b and both

side edges

140s, 140s of the absorbent core 140 are covered with the low liquid permeable sheet 152, the liquid once absorbed and held in the absorbent core 140 is absorbed by the absorbent core 140. Even if it leaks to the outside, it is prevented from leaking to the outside of the absorbent body 14 by the low liquid permeability sheet 152, and so-called side leakage is effectively prevented. From the viewpoint of ensuring the effect of preventing leakage by the low liquid permeable sheet 152, the liquid permeation time of the low liquid permeable sheet 152 is preferably 600 to 3000 seconds, more preferably 600 to 2000 seconds.

As the low-liquid-permeable sheet 152, paper, non-woven fabric, or the like can be used. In particular, crepe paper having crepe (crepe-like wrinkles) is preferably used. From the viewpoint of allowing the liquid permeation time to exceed 600 seconds, the basis weight of the low liquid permeability sheet 152 is preferably 13 to 20 g / m ² , more preferably 15 to 18 g / m ² . The density of the sheet 152 is preferably 0.10 to 0.30 g / cm ³ , more preferably 0.20 to 0.25 g / cm ³ , and the crepe rate of the low liquid permeability sheet 152 is preferably 5 to 20%, more preferably 7 to 15%. The crepe can be applied by a conventionally known method, and the crepe rate is measured by the above method (in the measurement method, “thin paper” is read as “sheet”).

The high-liquid-permeable paper 151 will be further described. The high-liquid-permeable paper 151 has the strength despite the fact that the basis weight and the density are set relatively low from the viewpoint of improving the liquid permeability as described above. Specifically, the dry tensile strength in the conveying direction (Machine 搬送 Direction, abbreviated as MD) during production is 600 cN / 25 mm or more, preferably 600 to 1500 cN / 25 mm, more preferably 700 to 1200 cN / 25 mm. It is. Highly liquid-permeable paper 151 having a dry tensile strength of MD in the above-mentioned range has a practically sufficient strength, and is unlikely to be broken during manufacture of diaper 1. It is hard to wake up.

From the same viewpoint, the dry tensile strength in the direction perpendicular to the MD of the highly liquid-permeable paper 151 (Cross machine Direction, abbreviated as CD) is preferably 150 cN / 25 mm or more, more preferably 150 to 350 cN / 25 mm, Particularly preferred is 170 to 300 cN / 25 mm. The dry tensile strength is measured by the above method (in the measurement method, “thin paper” is read as “highly liquid permeable paper”).

The high liquid permeability paper 151 may have a crepe (crepe-like wrinkles). When the highly liquid permeable paper 151 has a crepe, the crepe is generated when a dry fiber web (highly liquid permeable paper 151) is peeled off from the Yankee dryer or the like in the dryer part with a doctor knife or the like. A dry crepe is preferred. Paper having a crepe has higher liquid permeability than paper having no crepe, and the liquid permeability increases as the crepe rate increases. However, as the crepe rate increases, the strength properties (tensile strength) tend to decrease. In the present invention, based on such knowledge, from the viewpoint of balance between liquid permeability and strength characteristics, the crepe rate of the high liquid permeability paper 151 is 5 to 30%, particularly 5 to 20%, especially 7 to 15%. % Is preferable. The crepe rate is measured by the above method.

As such a high liquid permeability paper 151 having good strength characteristics and excellent liquid permeability, the following high liquid permeability paper A is preferably used. Highly liquid permeable paper A is a thin paper mainly composed of an aggregate of two types of hydrophilic cellulose fibers having different fiber roughness, to which a paper strength enhancer is added, and as the two types of hydrophilic cellulose fibers, And a first pulp having a fiber roughness of 0.13 to 0.16 mg / m and a second pulp having a fiber roughness of 0.17 to 0.20 mg / m. The difference in fiber roughness between the second pulp and the second pulp is 0.01 to 0.07 mg / m, and the freeness of the aggregate is 400 to 550 ml. The high liquid permeability paper A is basically the same as the thin paper of the first invention described above. Hereinafter, with respect to the highly liquid-permeable paper A, components that are different from the thin paper of the first invention described above will be mainly described, and components that are not particularly described in the highly liquid-permeable paper A will be described with respect to the thin paper of the first invention. Applicable as appropriate.

When two or more kinds of paper strength enhancers are used in the highly liquid-permeable paper A, as a preferred combination thereof, 1) a combination of one dry paper strength enhancer and one wet paper strength enhancer, and 2) A combination of two dry paper strength enhancers and one wet paper strength enhancer. In the combination of 1) above, the one dry paper strength enhancer is preferably an anionic PAM salt, and the one wet paper strength enhancer is preferably PAE. In the combination 2), the two dry paper strength enhancers are preferably CMC salts and anionic PAM salts, and one wet paper strength enhancer is preferably PAE.

The high liquid permeability paper A is excellent in air permeability in addition to strength characteristics and liquid permeability. The reason is mainly because it mainly comprises an aggregate of two types of hydrophilic cellulose fibers having different fiber roughness. In order to investigate the relationship between the use of two types of hydrophilic cellulose fibers having different fiber roughness and the breathability of thin paper, the present inventors prepared two types of thin paper (samples A and B) having different pulp compositions. The air permeability was measured. Sample A includes the first pulp and the second pulp as the fiber material, and is a high liquid permeability paper II described later. Sample B includes only the first pulp as the fiber material, and the high liquid permeability described later. Paper I. Both samples A and B had a basis weight of 13 g / m ² . The air permeability is measured as follows.

Sample B (highly liquid permeable paper I described later) using only the first pulp as the fiber material had an air permeability in the range of 2.1 to 2.7 s / 32 P · 300 cc, whereas the fiber material Sample A (highly liquid permeable paper II described later) using two kinds of pulps (first and second pulps) having different fiber roughnesses as described above has an air permeability of 1.6 to 2.2 s / 32 P · In the range of 300 cc, the value of air permeability of sample A was smaller than that of sample B. From this, it can be seen that it is effective to improve the air permeability of the thin paper to make the thin paper mainly composed of an aggregate of two kinds of hydrophilic cellulose fibers having different fiber roughnesses. It is clear that the highly liquid-permeable paper A is excellent in air permeability.

The high liquid permeable paper 151 is not limited to the above-described high liquid permeable paper A, and may be any paper in which the basis weight, density, liquid permeation time, and MD dry tensile strength are within the above ranges. For example, the highly liquid-permeable paper 151 is mainly composed of NBKP (softwood bleached kraft pulp) having a freeness of 400 to 550 ml, preferably 475 to 525 ml, more preferably 490 to 510 ml. It may be a thin paper (crepe paper) that is added and has a crepe rate of 5 to 30%, preferably 5 to 20%, more preferably 7 to 15%. Here, “mainly” means that the content of NBKP having a freeness in such a range is 50% by mass or more. The content is preferably 50 to 100% by mass, more preferably 80 to 100% by mass, from the viewpoint of obtaining good strength characteristics. In such crepe paper, the description of the highly liquid-permeable paper A is appropriately applied to points that are not particularly described, such as specific examples of the paper strength enhancer.

If the formation material of each part in the diaper 1 is demonstrated, as the surface sheet 12 and the back surface sheet 13, various things conventionally used in the said technical field can be used. As the top sheet 12, various liquid-permeable sheet materials such as a nonwoven fabric and an apertured film can be used. As the back sheet 13, various liquid impervious materials such as a resin film having no moisture permeability, a resin film having fine pores and moisture permeability, a nonwoven fabric such as a water-repellent nonwoven fabric, and a laminate of these and other sheets. Or water repellent materials can be used. Moreover, as the side sheet 162, the same thing as the back surface sheet 13 can be used.

The diaper 1 of this embodiment is used in the same manner as a known unfolded disposable diaper. In the diaper 1 of the present embodiment, the portion of the core wrap sheet 15 that is disposed on the skin facing surface 140a side of the absorbent core 140 is the highly liquid-permeable paper 151. Compared to the absorbent article described in Patent Document 4, which is formed of a nonwoven fabric that is excellent in absorbability (repeated absorbability) of excretory liquids such as loose stool, the absorbent core-forming material such as a water-absorbing polymer Leakage hardly occurs and the manufacturing cost is reduced. Moreover, since the site | part arrange | positioned at the non-skin opposing surface 140b side of the absorptive core 140 in the core wrap sheet | seat 15 of the diaper 1 of this embodiment is the low liquid permeability sheet | seat 152, it is hard to raise | generate a side leak.

The present invention (fourth invention) is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention. For example, the core wrap sheet 15 in the above embodiment is composed of the high liquid permeable paper 151 and the low liquid permeable sheet 152, but may be composed of only the high liquid permeable paper 151. In that case, the core wrap sheet 15 may be composed of two high liquid permeability papers 151. For example, in the embodiment shown in FIG. 7, the low liquid permeability sheet 152 may be replaced with the high liquid permeability paper 151. good.

Alternatively, as shown in FIG. 8, the core wrap sheet 15 may be composed of a single sheet of high liquid permeability 151. In the embodiment shown in FIG. 8, as the core wrap sheet 15, one sheet of high liquid permeability paper 151 having a width that is two to three times the length of the absorbent core 140 in the width direction Y is used. . The absorbent body 14 shown in FIG. 8 has an absorbent core 140 placed at the center in the width direction Y of one sheet of high liquid permeability paper 51, and both sides of the high liquid permeability paper 151 in the width direction Y. Are folded back to the upper surface side of the absorbent core 140, and both edge portions in the width direction Y of the high liquid permeability paper 151 are joined by a known joining means such as a hot melt adhesive. Is formed into a cylindrical shape and obtained by turning it upside down.

Further, the absorbent article of the present invention (fourth invention) is a deployable disposable diaper having a fastening tape, a pants-type disposable diaper, an absorbent pad, a sanitary napkin, etc., previously formed in a pants shape. Also good.

In relation to the above-described embodiment, the present invention further discloses the following articles (thin paper, absorbent article, thin paper manufacturing method).
<1> A thin paper mainly composed of an aggregate of two types of hydrophilic cellulose fibers having different fiber roughness, and having a paper strength enhancer added thereto,
The two types of hydrophilic cellulose fibers have a fiber roughness of 0.13 to 0.16 mg / m, preferably 0.135 to 0.155 mg / m, more preferably 0.14 to 0.15 mg / m. 1 pulp and a second pulp having a fiber roughness of 0.17 to 0.20 mg / m, preferably 0.175 to 0.195 mg / m, more preferably 0.18 to 0.19 mg / m. The difference in fiber roughness between the first pulp and the second pulp contained is 0.01 to 0.07 mg / m, preferably 0.02 to 0.06 mg / m, and more preferably 0.03 to 0.03 mg / m. A thin paper having a freeness of 400 to 550 ml at 0.05 mg / m.

<2> The thin paper according to <1>, wherein each of the first pulp and the second pulp has an average fiber length of 2 to 3 mm, preferably 2.2 to 2.8 mm.
<3> The content mass ratio of the first pulp to the second pulp (first pulp / second pulp) is 3/7 to 7/3, preferably 4/6 to 6/4 <1> or <2> Thin paper according to <4> The thin paper according to any one of <1> to <3>, wherein each of the first pulp and the second pulp is softwood bleached kraft pulp (NBKP).
<5> The thin paper according to any one of <1> to <4>, wherein the content of the first pulp and the second pulp is 70 to 100% by mass, preferably 80 to 100% by mass.
<6> The thin paper according to any one of <1> to <5>, wherein the aggregate has a freeness of 450 to 525 ml, preferably 475 to 510 ml.
<7> The thin paper according to any one of <1> to <6>, wherein at least carboxymethylcellulose or a salt thereof is added as the paper strength enhancer.
<8> The thin paper according to any one of <1> to <7>, wherein the basis weight is 10 to 20 g / m ² , preferably 11 to 16 g / m ² , and more preferably 12 to 14 g / m ² .

<9> Mainly composed of softwood bleached kraft pulp with a freeness of 400 to 550 ml, preferably 475 to 525 ml, more preferably 490 to 510 ml, and two or more kinds of paper strength enhancers are added, and the basis weight is 10 to 14.5 g / m ² , preferably 11-14 g / m ² , density 0.05-0.2 g / cm ³ , preferably 0.1-0.2 g / cm ³ , crepe rate 5-30%, The thin paper according to any one of <1> to <7>, preferably 5 to 20%, more preferably 7 to 15%.
<10> The thin paper according to <9>, wherein a dry paper strength enhancer and a wet paper strength enhancer are added as the two or more paper strength enhancers.
<11> The total amount of the two or more kinds of paper strength enhancing agents is 0.01 to 1.5% by mass, preferably 0.03 to 1.2%, based on the dry mass of all the constituent fibers of the thin paper. The thin paper according to <9> or <10>, which is% by mass.
<12> When the combination of one or more dry paper strength enhancers and one or more wet paper strength enhancers is used as the two or more paper strength enhancers, the total added mass of the dry paper strength enhancer Any one of <9> to <11>, wherein the ratio of the added weight of the wet paper strength enhancer (the former / the latter) is 0.01 to 0.5, preferably 0.03 to 0.35. The thin paper described in 1.
<13> The dry paper strength enhancer is at least one selected from the group consisting of carboxymethylcellulose and salts thereof, polyacrylamide resins and salts thereof, cationized starch, and polyvinyl alcohol. <10> to <12> The thin paper according to any one of the above.
<14> The wet paper strength enhancer is at least one selected from the group consisting of epoxidized polyamide polyamine resin, urea-formalin resin, melamine-formalin resin, dialdehyde starch, polyethyleneamine and methylolated polyamide < The thin paper according to any one of 10> to <13>.
<15> The composition according to any one of <9> to <14>, wherein two or more kinds of paper strength enhancing agents and two kinds of paper strength enhancing agents are added. Tissue paper.
<16> The <15> description, wherein the two kinds of dry paper strength enhancers are a salt of carboxymethyl cellulose and an anionic polyacrylamide, and the one wet paper strength enhancer is an epoxidized polyamide polyamine resin. Tissue paper.
<17> The thin paper according to <16>, wherein the anionic polyacrylamide salt has a weight average molecular weight of 8 million or more, preferably 10 million or more, more preferably 15 million or more, and 25 million or less.

<18> The dry tensile strength in the conveying direction during the production of the thin paper is 600 to 1500 cN / 25 mm, preferably 700 to 1200 cN / 25 mm, more preferably 800 to 1200 cN / 25 mm, and still more preferably 900 to 1200 cN / 25 mm. The thin paper according to any one of <1> to <17>, wherein the dry tensile strength in the direction perpendicular to the direction is 150 to 350 cN / 25 mm, preferably 180 to 300 cN / 25 mm.
<19> The liquid permeation time of the thin paper measured by the following method is 0.2 to 3 seconds, preferably 0.3 to 2.5 seconds, more preferably 0.5 to 2 seconds <1> to < The thin paper according to any one of 18>.
<Measurement method of liquid permeation time>
Two cylinders with an inner diameter of 35 mm that open at the top and bottom are arranged vertically with the axes of both cylinders aligned, and an 8 cm square measurement sample is sandwiched between the upper and lower cylinders. 40 g ± 1 g of physiological saline is supplied. The supplied physiological saline passes through the measurement sample or is absorbed by the sample and disappears from the upper cylinder. The time from the start of the supply of the physiological saline to the time when the surface of the physiological saline reaches the same position as the surface of the measurement sample is measured, and the time is defined as the liquid permeation time.

<20> An absorbent article using the thin paper according to any one of <1> to <19>.
<21> The absorbent article according to <20>, wherein the absorbent article includes an absorbent core and a core wrap sheet covering the absorbent core, and the core wrap sheet is the thin paper.

<22> A method for producing a thin paper that produces a paper having a basis weight of 30 g / m ² or less by paper-making and drying a raw material slurry prepared from a raw material containing softwood bleached kraft pulp,
After adding the wet paper strength agent (a) made of a cationic polymer having a cationic group to the pulp slurry of the softwood bleached kraft pulp as the raw material slurry, the following low molecular dry paper strength agent (b) and high Thin paper using a raw material slurry prepared by adding a molecular dry paper strength agent (c) at the same time, or adding a low molecular weight dry strength agent (b) and then adding a polymer dry strength agent (c). Manufacturing method.
(B) Low molecular weight dry paper strength agent which is a low molecular weight anionic polymer having an anionic group having a weight average molecular weight (Mw) of 0.2 to 500,000 (c) Weight average molecular weight (Mw) of 500 to 30 million Polymer dry paper strength agent which is a polymer anionic polymer having an anionic group of

<23> The amount of the low-molecular dry paper strength agent (b) added is 0.01 to 0.5% by mass, preferably 0.1 to 0.5% by mass with respect to the dry mass of all the constituent fibers of the thin paper as the production target. <22> The manufacturing method of the thin paper as described in <22> which is 0.3 mass%.
<24> The amount of the polymer dry paper strength agent (c) added is 0.001 to 0.1% by mass, preferably 0.01 to 0.1% by mass with respect to the dry mass of all the constituent fibers of the thin paper as the production target. The method for producing thin paper according to <22> or <23>, which is 0.08% by mass.
<25> Ratio of the added mass of one kind of the wet paper strength agent (a) and the total added mass of the low molecular weight dry strength agent (b) and the high molecular weight dry strength agent (c) [(a) / (B) and (c)] is 0.5 to 10, preferably 1 to 5, The method for producing a thin paper according to any one of <22> to <24>.

<26> The raw material slurry is obtained by adding the wet paper strength agent (a) to the pulp slurry of the softwood bleached kraft pulp, then adding the low molecular weight dry strength agent (b), and then further drying the polymer. The method for producing thin paper according to any one of <22> to <25>, which is adjusted by adding a paper strength agent (c).
<27> The step of adjusting the raw material is performed after the low-molecular dry paper strength agent (b) is added and diluted, and after the dilution, the polymer dry paper strength agent (c) is added, and then a fan pump and filtration The method for producing thin paper according to <26>, wherein the paper is homogenized using at least one of the screens.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to such examples. Unless otherwise specified, “%” means “mass%”. In the examples and comparative examples of the first invention, “A” is added before the number (for example, “Example A1”), and the examples and comparative examples of the second invention are preceded by “ B ”(for example,“ Example B1 ”), the examples of the third invention and the comparative example are preceded by“ C ”(for example,“ Example C1 ”), and the fourth embodiment is carried out. In Examples and Comparative Examples, “D” is added before the number (for example, “Example D1”).

[Example A1]
NBKP having a fiber roughness of 0.15 mg / m is used as the first pulp (pulp having a relatively small fiber diameter), and the fiber roughness is 0.18 mg / in as the second pulp (a pulp having a relatively large fiber diameter). m NBKP was used. The first pulp and the second pulp are mixed so that the content ratio of the two pulps (first pulp / second pulp) is 5/5 to obtain an aggregate of fibers, and the aggregate is uniformly in water. The slurry was dispersed to prepare a slurry having a fiber concentration of 2% by mass, and this slurry was passed through a beating machine to adjust the freeness of the aggregate to 500 ml. Further, CMC sodium salt (dry paper strength enhancer, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name “Serogen WS-C”) is added to the slurry as a first strength enhancer, and all fibers in the slurry are dried. Next, 0.2% by mass is added to the mass, and then PAE (wet paper strength enhancer, manufactured by Seiko PMC Co., Ltd., trade name “WS4030”) is used as the second paper strength enhancer, and all fibers in the slurry are dried. 0.78% by mass with respect to the mass was added, and the components were sufficiently stirred so that each component was uniform. The slurry thus obtained was spread on a wire mesh paper wire having a wire opening diameter of 90 μm (166 mesh), a paper layer was formed on the wire mesh paper wire, and 6 ml / (cm ² · sec) was formed using a suction box. After dewatering the paper layer at speed, the paper layer was dried with a dryer. The thin paper thus obtained was used as a sample of Example A1.

[Examples A2 to A6 and Comparative Examples A1 to A5]
A thin paper was produced in the same manner as in Example A1 except that the type of pulp (fiber roughness), freeness, usage form of the paper strength enhancer, and the like were appropriately changed, and were used as samples of the respective examples and comparative examples. In Example A5, in addition to the first and second paper strength enhancers, an anionic PAM sodium salt (dry paper strength enhancer, manufactured by MT Aquapolymer, trade name “ Acofloc A95 ", weight average molecular weight 17 million) was used.

Details of the pulp (NBKP) used in Examples A1 to A6 and Comparative Examples A1 to A5 are as follows (in the order of increasing fiber roughness). These pulps were obtained through Nippon Paper Pulp Trading or Itochu Corporation.
・ Fiber roughness 0.09mg / m (Brand name "Cenibra", made by Cenibra)
-Fiber roughness 0.13mg / m (trade name "Northwood", manufactured by ConFor)
-Fiber roughness 0.15mg / m (Brand name "Cariboo", Cariboo Pulp and Paper Company)
・ Fiber roughness 0.16mg / m (trade name "Botnia", manufactured by BOTNIA)
-Fiber roughness 0.17mg / m (trade name "Alabama Pine", manufactured by Alabama Pine, Inc)
-Fiber roughness 0.18mg / m (trade name "ARAUCO", manufactured by ARAUCO)
・ Fiber roughness 0.2mg / m (trade name "Crofton CK", Unifibra)

[Evaluation]
The various evaluation results of each sample (thin paper) of Examples A1 to A6 and Comparative Examples A1 to A5 are shown in Table 1 below. The dry tensile strength and the liquid permeation time were measured by the methods described above.

As is apparent from the results shown in Table 1, the aggregate is mainly composed of two types of hydrophilic cellulose fibers having different fiber roughness, and the freeness of the aggregate is in the specific range (within the range of the first invention). ), The thin paper of each example has a dry tensile strength of MD of 600 cN / 25 mm or more, a dry tensile strength of CD of 150 cN / 25 mm or more, a liquid permeation time of 2 seconds or less, and has good strength characteristics and liquid permeation. It turns out that it is a thin paper with excellent properties. In particular, Example A5, which is a form using two dry paper strength enhancers and one wet paper strength enhancer, has generally better strength characteristics and liquid permeability than the other examples. The effectiveness of the combination of the three kinds of paper strength enhancers is clear.

On the other hand, as is clear from the results shown in Table 1, the thin paper of each comparative example has an MD dry tensile strength of less than 600 cN / 25 mm (Comparative Examples A1, A2, and A5) or a liquid permeation time of more than 3 seconds ( Comparative Examples A1, A3, and A4), which do not have both strength characteristics and liquid permeability at a high level. The reason why each comparative example is inferior to each example in terms of strength characteristics and liquid permeability is that, in Comparative Example A1, the difference in fiber roughness between the first pulp and the second pulp exceeds 0.07 mg / m. Therefore, since Comparative Examples A2, A3, and A5 use only one kind of hydrophilic cellulose fiber, it is surmised that Comparative Example A4 is because the freeness of the aggregate is out of the specific range.

[Example B1]
NBKP (manufactured by Cariboo Pulp and Paper Company, trade name “Cariboo”, manufactured in North America, fiber roughness 0.15 mg / m, average fiber length 2.44 mm) is uniformly dispersed in water to give a slurry having a fiber concentration of 2% by mass. The slurry was passed through a beater to adjust the freeness of NBKP to 500 ml. Furthermore, while diluting this slurry, PAE (trade name “WS4030”, manufactured by Seiko PMC Co., Ltd.) as a wet paper strength enhancer was added in an amount of 0.78% by mass with respect to the dry mass of all the fibers in the slurry. Next, 0.2% by mass of sodium salt of CMC (trade name “Serogen WS-C”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a dry paper strength enhancer is added to the dry mass of all fibers in the slurry. The mixture was sufficiently stirred so that each component was uniform, and adjusted to a slurry having a solid content concentration of 0.1% by mass. The slurry thus obtained was spread on a wire mesh paper wire having a wire opening diameter of 90 μm (166 mesh), a paper layer was formed on the wire mesh paper wire, and 6 ml / (cm ² · sec) was formed using a suction box. After the paper layer was dehydrated at a speed, the paper layer was dried with a dryer, and the paper layer was peeled off from the dry surface with a doctor blade, and a crepe was applied at a speed ratio of the dryer and the winding. The thin paper (crepe paper) thus obtained was used as the sample of Example B1.

[Examples B2 to B7 and Comparative Examples B1 to B7]
A thin paper (crepe paper) was produced in the same manner as in Example B1 except that the freeness of NBKP, the charged amounts of various raw materials, the crepe rate, and the like were changed as appropriate, and used as samples for each example and each comparative example. In Examples B4 to B7, two types of dry paper strength enhancers (dry paper strength enhancers 1 and 2) and one wet paper strength enhancer were used. The same sodium salt of CMC as in Example B1 was used, and the anionic PAM sodium salt was used as the dry paper strength enhancer 2 (Examples B4 to B6 were manufactured by MT Aquapolymer, trade name “Acofloc A95”, weight average molecular weight 1700. Ten; Example B7 uses a product name “DA4119” manufactured by Seiko PMC Co., Ltd., with a weight average molecular weight of 2 million), and the same PAE as Example B1 was used as a wet paper strength enhancer.

[Evaluation]
The various evaluation results of each sample (thin paper) of Examples B1 to B7 and Comparative Examples B1 to B7 are as shown in Tables 2 and 3 below. The dry tensile strength and the liquid permeation time were measured by the methods described above.

As is apparent from the results shown in Table 2, 1) NBKP having freeness in the specific range as a main component, 2) two or more kinds of paper strength enhancers are added, and 3) basis weight, density, and crepe rate. Each of the thin papers of each example in the specific range has an MD dry tensile strength of 600 cN / 25 mm or more, a CD dry tensile strength of 150 cN / 25 mm or more, and a liquid permeation time of 2 seconds or less. It can be seen that the thin paper has good characteristics and excellent liquid permeability. The weight average molecular weight of the salt of anionic PAM (dry paper strength enhancer 2) in Examples B4 to B7 in the form of using two types of dry paper strength enhancer and one wet paper strength enhancer Since Examples B4 to B6 having a weight average molecular weight of 17 million resulted in a higher dry tensile strength than Example B7 having a weight average molecular weight of 2 million, a total of three paper strength enhancers were used. In such a form, it can be seen that the strength improvement effect of the thin paper becomes more remarkable by using an anionic PAM salt having a large weight average molecular weight as one of them.

On the other hand, as is clear from the results shown in Table 3, the thin paper of each comparative example has an MD dry tensile strength of less than 600 cN / 25 mm (Comparative Examples B2 and B4) or a liquid permeation time of more than 3 seconds (Comparative Example). B1, B3, and B5 to B7), and the strength characteristics and liquid permeability are not compatible at a high level. The reason why each comparative example is inferior to each example in terms of strength characteristics and liquid permeability is that the comparative example B1 does not satisfy all of the above 1) to 3), so the comparative example B2 satisfies the above 2) Since Comparative Example B3 does not satisfy 2) and 3), Comparative Examples B4 to B6 do not satisfy 3), and Comparative Example B7 does not satisfy 1) and 3). It is guessed.

[Example C1]
Using the manufacturing apparatus 1A shown in FIG. 2 (circular former type paper machine, paper making speed 400 m / min, width 2000 mm), the softwood bleached kraft pulp raw material was put into the pulper 21 and beaten by the refiner 23. NBKP (Cariboo Pulp) is used as a raw material for bleached kraft pulp.
and Paper Company, trade name “Cariboo”, manufactured in North America, fiber roughness 0.15 mg / m, average fiber length 2.44 mm) was used. The freeness of the softwood bleached kraft pulp (NBKP) was adjusted by the pulper 21 and the refiner 23 to 500 ml. Next, the epoxidized polyamide polyamine resin (PAE) which is the wet paper strength agent (a) was added using the wet paper strength agent adding section 33 and sufficiently stirred and mixed in the first slurry storage tank 32. The addition amount of PAE was 0.78 mass% with respect to the dry mass of all the constituent fibers of a thin paper. Next, using the low molecular dry paper strength agent adding portion 43, a salt of carboxymethyl cellulose (CMC) having a weight average molecular weight (Mw) of 100,000, which is a low molecular dry paper strength agent (b), is added, 2 In the slurry storage tank 42, the mixture was sufficiently stirred and mixed. The addition amount of the salt of CMC was 0.2 mass% with respect to the dry mass of all the constituent fibers of the thin paper. Next, dilution water was supplied using the dilution water supply part 63, and it diluted so that it might become 0.11 mass%. Next, while causing turbulent flow using the fan pump 64, the polymer dry paper strength agent adding section 65 is used, and the weight average molecular weight (Mw) of the polymer dry paper strength agent (c) is 1, A 7 million acrylic polyacrylamide resin (PAM) was added and conveyed to the filter screen 62 to prepare a raw material slurry. The amount of PAM added was 0.03% by mass relative to the dry mass of all the constituent fibers of the thin paper. Thus, the raw material slurry adjusted by the raw material slurry adjustment part 2 was paper-made and dried in the paper making part 7, and the thin paper was manufactured. A thin paper having a basis weight of 11.0 g / m ² was manufactured by adjusting with the seed box 52 of the raw material slurry adjusting unit 2 and the former of the paper making unit 7.

[Example C2]
Using the production apparatus 1A shown in FIG. 2, adjustment was made by using the seed box 52 of the raw material slurry adjusting unit 2 and the former of the paper making unit 7 to produce a thin paper having a basis weight of 13.0 g / m ² , as in Example C1. Thin paper.

[Example C3]
Using the manufacturing apparatus 1 C shown in FIG. 4, the softwood bleached kraft pulp raw material was put into the pulper 21 and beaten by the refiner 23. Softwood bleached kraft pulp raw material is NBKP (Cariboo Pulp and Paper Company, trade name "Cariboo", North America, fiber roughness 0.15m
g / m, average fiber length 2.44 mm). The freeness of the softwood bleached kraft pulp (NBKP) was adjusted by the pulper 21 and the refiner 23 to 500 ml. Next, the epoxidized polyamide polyamine resin (PAE) which is the wet paper strength agent (a) was added using the wet paper strength agent adding section 33 and sufficiently stirred and mixed in the first slurry storage tank 32. The addition amount of PAE was 0.78 mass% with respect to the dry mass of all the constituent fibers of a thin paper. Next, using the low molecular dry paper strength agent adding portion 43, a salt of carboxymethyl cellulose (CMC) having a weight average molecular weight (Mw) of 100,000, which is a low molecular dry paper strength agent (b), is added, 2 In the slurry storage tank 42, the mixture was sufficiently stirred and mixed. The addition amount of the salt of CMC was 0.2 mass% with respect to the dry mass of all the constituent fibers of the thin paper. Next, dilution water was supplied using the dilution water supply unit 63, diluted to 0.13 mass%, and conveyed to the filtration screen 62. Next, an acrylic polyacrylamide resin (PAM) having a weight average molecular weight (Mw) of 17 million, which is a polymer dry paper strength agent (c), is obtained using the polymer dry paper strength agent addition unit 65. The raw material slurry was prepared by adding. The amount of PAM added was 0.03% by mass relative to the dry mass of all the constituent fibers of the thin paper. Thus, the raw material slurry adjusted by the raw material slurry adjustment part 2 was paper-made and dried in the paper making part 7, and the thin paper was manufactured. A thin paper having a basis weight of 13.0 g / m ² was manufactured by adjusting with the seed box 52 of the raw material slurry adjusting unit 2 and the former of the paper making unit 7.

[Example C4]
Using the manufacturing apparatus 1 D shown in FIG. 5, the softwood bleached kraft pulp raw material was put into the pulper 21 and beaten by the refiner 23. NBKP (manufactured by Cariboo Pulp and Paper Company, trade name “Cariboo”, produced in North America, fiber roughness 0.15 mg / m, average fiber length 2.44 mm) was used as a raw material for bleached kraft pulp. The freeness of the softwood bleached kraft pulp (NBKP) was adjusted by the pulper 21 and the refiner 23 to 500 ml. Next, the epoxidized polyamide polyamine resin (PAE) which is the wet paper strength agent (a) was added using the wet paper strength agent adding section 33 and sufficiently stirred and mixed in the first slurry storage tank 32. The addition amount of PAE was 0.78 mass% with respect to the dry mass of all the constituent fibers of a thin paper. Next, dilution water was supplied using the dilution water supply part 63, and it diluted so that it might become 0.13 mass%. Next, a carboxymethyl cellulose (CMC) salt having a weight average molecular weight (Mw) of 100,000 and a weight average molecular weight using the low molecular dry paper strength agent (b) part 43 and the polymer dry paper strength agent (c) part 65 An acrylic polyacrylamide resin (PAM) having a (Mw) of 17 million was simultaneously added in the middle of 65 pipes to prepare a raw material slurry. The addition amount of the salt of CMC was 0.2 mass% with respect to the dry mass of all the constituent fibers of the thin paper. The amount of PAM added was 0.03% by mass relative to the dry mass of all the constituent fibers of the thin paper. Next, the raw material slurry was adjusted using the fan pump 64 while causing turbulent flow. Thus, the raw material slurry adjusted by the raw material slurry adjustment part 2 was paper-made and dried in the paper making part 7, and the thin paper was manufactured. A thin paper having a basis weight of 13.0 g / m ² was manufactured by adjusting with the seed box 52 of the raw material slurry adjusting unit 2 and the former of the paper making unit 7.

[Comparative Example C1]
As in Example C1, the manufacturing apparatus 1A shown in FIG. 2 is used, but without adding the dry paper strength agent from the low molecular dry paper strength agent addition unit 43 and the polymer dry paper strength agent addition unit 65, the raw material slurry Adjusted. The raw material slurry thus adjusted was paper-made and dried at the paper-making unit 7 to produce thin paper. A thin paper having a basis weight of 11.5 g / m ² was manufactured by adjusting with the seed box 52 of the raw material slurry adjusting unit 2 and the former of the paper making unit 7.

[Comparative Example C2]
As in Example C1, the manufacturing apparatus 1A shown in FIG. 2 was used, but the raw material slurry was adjusted without adding the dry paper strength agent from the polymer dry paper strength agent addition unit 65. The raw material slurry thus adjusted was paper-made and dried at the paper-making unit 7 to produce thin paper. A thin paper having a basis weight of 11.0 g / m ² was manufactured by adjusting with the seed box 52 of the raw material slurry adjusting unit 2 and the former of the paper making unit 7.

[Comparative Example C3]
Using the manufacturing apparatus 1 A shown in FIG. 2, the softwood bleached kraft pulp raw material was put into the pulper 21 and beaten by the refiner 23. NBKP (manufactured by Cariboo Pulp and Paper Company, trade name “Cariboo”, produced in North America, fiber roughness 0.15 mg / m, average fiber length 2.44 mm) was used as a raw material for bleached kraft pulp. The freeness of the softwood bleached kraft pulp (NBKP) was adjusted by the pulper 21 and the refiner 23 to 500 ml. Next, the epoxidized polyamide polyamine resin (PAE) which is the wet paper strength agent (a) was added using the wet paper strength agent adding section 33 and sufficiently stirred and mixed in the first slurry storage tank 32. The addition amount of PAE was 0.78 mass% with respect to the dry mass of all the constituent fibers of a thin paper. Next, an acrylic polyacrylamide resin (PAM) having a weight average molecular weight (Mw) of 17 million, which is a polymer dry paper strength agent (c), is obtained using the polymer dry paper strength agent addition section 43. The mixture was added and sufficiently stirred and mixed in the second slurry storage tank 42. The amount of PAM added was 0.03% by mass relative to the dry mass of all the constituent fibers of the thin paper. Next, dilution water was supplied using the dilution water supply part 63, and it diluted so that it might become 0.13 mass%. Next, a low molecular weight dry paper strength agent (b) having a weight average molecular weight (Mw) of 100,000 is generated using the low molecular weight dry paper strength agent adding unit 65 while causing turbulence using the fan pump 64. Of carboxymethyl cellulose was added and conveyed to the filter screen 62 to prepare a raw material slurry. The amount of CMC added was 0.2% by mass relative to the dry mass of all the constituent fibers of the thin paper. Thus, the raw material slurry adjusted by the raw material slurry adjustment part 2 was paper-made and dried in the paper making part 7, and the thin paper was manufactured. A thin paper having a basis weight of 13.0 g / m ² was manufactured by adjusting with the seed box 52 of the raw material slurry adjusting unit 2 and the former of the paper making unit 7.

[Evaluation]
The various evaluation results of the samples (thin paper) of Examples C1 to C4 and Comparative Examples C1 to C3 are shown in Table 4 below. The dry tensile strength and wet tensile strength in the MD direction and CD direction, the crepe rate, and the liquid permeation time were measured by the methods described above.

As is apparent from the results shown in Table 4, it can be seen that the thin paper produced by the production methods of Examples C1 to C4 is a thin paper having good strength characteristics and excellent liquid permeability. On the other hand, the thin paper produced by the production method of Comparative Examples C1 to C3 was thin paper having inferior strength characteristics and poor liquid permeability as compared with the thin paper produced by the production methods of Examples C1 to C4. .

[Production Method of Highly Liquid Permeable Paper I]
NBKP (manufactured by Cariboo Pulp and Paper Company, trade name “Cariboo”, manufactured in North America) is uniformly dispersed in water to prepare a slurry with a fiber concentration of 2% by mass. Adjusted. Further, an anionic PAM sodium salt (dry paper strength enhancer, manufactured by MT Aqua Polymer, trade name “Akofloc A95”) as a first paper strength enhancer was added to this slurry with respect to the dry mass of all fibers in the slurry. 0.2 mass%, and then PAE (wet paper strength enhancer, trade name “WS4030”, manufactured by Seiko PMC Co., Ltd.) as the second paper strength enhancer, based on the dry weight of all the fibers in the slurry. Then, 0.2% by mass was added and sufficiently stirred so that each component was uniform. The slurry thus obtained was spread on a wire mesh paper wire having a wire opening diameter of 90 μm (166 mesh), a paper layer was formed on the wire mesh paper wire, and 6 ml / (cm ² · sec) was formed using a suction box. After the paper layer was dehydrated at a speed, the paper layer was dried with a drier, and a crepe was applied while peeling the paper layer with a doctor blade from the dry surface at a speed ratio of drier and winding. The thin paper (crepe paper) thus obtained was designated as a high liquid permeability paper I.

[Method for Producing Highly Liquid Permeable Paper II and III]
A thin paper (crepe paper) was produced in the same manner as the high liquid permeability paper I except that the type of pulp (fiber roughness), freeness, and the like were appropriately changed, and designated as high liquid permeability papers II and III, respectively. The high liquid permeability papers II and III are the above-described high liquid permeability paper A, respectively.

The details of the pulp (NBKP) used in the high liquid permeability papers I to III are as follows (described in ascending order of fiber roughness). These pulps were obtained through Nippon Paper Pulp Trading or Itochu Corporation.
-Fiber roughness 0.13mg / m (trade name "Northwood", manufactured by ConFor)
-Fiber roughness 0.15mg / m (Brand name "Cariboo", Cariboo Pulp and Paper Company)
-Fiber roughness 0.18mg / m (trade name "ARAUCO", manufactured by ARAUCO)
・ Fiber roughness 0.2mg / m (trade name "Crofton CK", Unifibra)

The various evaluation results of the high liquid permeability papers I to III are as shown in Table 5 below. The dry tensile strength and the liquid permeation time were measured by the methods described above.

[Example D1]
An unfolded disposable diaper as shown in FIGS. 6 and 7 was produced and used as a sample of Example D1. In Example D1, the core wrap sheet is composed of the two highly liquid permeable papers I, and the low liquid permeable sheet is not used. As the surface sheet, an air-through nonwoven fabric having a basis weight of 25 g / m ² and comprising synthetic fibers as constituent fibers was used. The air-through nonwoven fabric was composed of a core-sheath type composite fiber (thickness: 2.1 dtex, surface treatment with a surfactant, and liquid permeability) having a core made of polypropylene and a sheath made of linear polyethylene. As the back sheet, a composite film in which a porous film having a basis weight of 20 g / m ^{2 and} a spun pond made of polypropylene having a basis weight of 20 g / m ² are bonded with a 1.5 g / m ² hot-melt adhesive is used. It was. The porous film constituting the back sheet is obtained by uniformly mixing 100 parts by mass of a linear polyethylene resin having a density of 0.925 g / m ³ with 150 parts by mass of calcium carbonate and 4 parts by mass of an ester compound as a third component. After the inflation molding, the film was uniaxially stretched in the longitudinal direction. As the absorbent core, NB416 manufactured by Wafer User is used as the hydrophilic fiber, Sunwet IM997 manufactured by Sundia is used as the water-absorbing polymer, and the mass ratio of the hydrophilic fiber to the water-absorbing polymer is the former / the latter = 10. A mixed fiber type absorbent core having a basis weight of 470 g / m ² was used. The total length in the longitudinal direction of the absorbent core is 360 mm, the total length in the width direction (maximum length) is 110 mm, the basis weight is 470 g / m ² , the density is 0.17 g / cm ³ , and the thickness under no load is 2.7 mm. Met.

[Examples D2 to D4 and Comparative Example D1]
In Example D1, the core wrap sheet (one sheet disposed on the skin facing surface side of the absorbent core and another sheet disposed on the non-skin facing surface side of the absorbent core) is as shown in Table 6 below. Except for the construction, unfolded disposable diapers were produced in the same manner as in Example D1, and these were used as samples of Examples D2 to D4 and Comparative Example D1. The low liquid permeability sheet I used in Examples and Comparative Examples was a crepe paper having a basis weight of 16 g / m ² , a density of 0.23 g / cm ³ , and a crepe rate of 10%.

Various evaluation results of each sample (disposable diaper) of Examples and Comparative Examples are as shown in Table 6 below. Soft stool absorbability and side leakage prevention properties were evaluated by the following methods.

<Soft stool absorbability>
With a disposable diaper spread in a flat shape and fixed on a horizontal surface with the top sheet facing upward, 10 g pseudo-soft stool, which is a model of highly viscous liquid, is fixed to the center of the absorbent body using a syringe from the top sheet side. The batch injection was carried out at a high speed (6 seconds) and left for 5 minutes under a load of 3.5 kPa. At this time, an OHP film was sandwiched between a weight for applying a weight and a disposable diaper. Thereafter, the amount of pseudo-soft stool adhering to the OHP film was measured, and the measured value was defined as the skin adhesion amount. The amount absorbed by the absorbent core was defined as the amount of soft stool absorption. The smaller the skin adhesion amount and the greater the amount of loose stool absorption, the better the stool absorption and the higher the evaluation. The components of the artificial soft stool were bentonite 28.0 g, glycerin 14.0 g, ion-exchanged water 114.1 g, emulgen 130K 0.03% by mass aqueous solution (Kao) 14.2 g, and the viscosity was 300 mPa · s (A &・ Measured with a day vibration viscometer CJV 5000. Stir approximately 170 g of pseudo soft stool in a 300 ml beaker with a stirrer at 300 rpm for 60 seconds, immediately set in the viscometer, insert the sensitive plate at a predetermined level, and set the measurement range. Select 50 mV and start measurement by pressing the measurement switch.The value 60 seconds after the start of measurement, measured at 25 ° C.).

<Side leakage prevention>
A disposable diaper is expanded in a flat shape, and the top sheet is fixed on a horizontal plane with the top sheet facing upward, while pressing with 2 kPa through the top sheet against the center of the absorbent body of the diaper, 40 g of physiological saline Was injected and absorbed, and after 10 minutes from the injection of physiological saline, 40 g of physiological saline was injected and absorbed. This operation is repeated until the total injection amount of the physiological saline reaches 160 g. After the physiological saline is injected, whether or not the physiological saline flows outward from the side along the longitudinal direction of the diaper in the width direction (i.e., side leakage occurs). Whether or not there was) was visually observed. A case where no side leakage was observed even after the total injection amount of physiological saline reached 160 g, and no side leakage was observed after the total injection amount reached 120 g, but the total injection amount became 160 g. The case where lateral leakage was observed later was evaluated as Δ, and the case where lateral leakage was observed after the total injection amount reached 120 g was determined as ×.

As is clear from the results shown in Table 6, the disposable diaper of each example in which the core wrap sheet opposed to the skin-facing surface of the absorbent core is a specific highly liquid-permeable paper has the core wrap sheet Compared with the disposable diaper of the comparative example, which is a low liquid permeability sheet, the amount of loose stool attached to the skin is small, the amount of loose stool absorption is large and the stool absorbability is excellent, and the side leakage prevention property is also excellent. there were. In particular, the disposable diaper of Examples D2 to D4, in which the core wrap sheet disposed opposite to the non-skin facing surface of the absorbent core is a low liquid permeable sheet, the entire core wrap sheet is a specific high liquid permeable paper. As compared with the disposable diaper of Example D1, it is superior in preventing side leakage, and the effectiveness of the combination of such a high liquid permeability paper and a low liquid permeability sheet is clear.

Claims

A thin paper mainly composed of an assembly of two kinds of hydrophilic cellulose fibers having different fiber roughnesses, to which a paper strength enhancer is added,
The two kinds of hydrophilic cellulose fibers include a first pulp having a fiber roughness of 0.13 to 0.16 mg / m and a second pulp having a fiber roughness of 0.17 to 0.20 mg / m. A thin paper in which the difference in fiber roughness between the first pulp and the second pulp contained is 0.01 to 0.07 mg / m, and the freeness of the aggregate is 400 to 550 ml.
The thin paper according to claim 1, wherein the average fiber length of each of the first pulp and the second pulp is 2 to 3 mm.
The thin paper according to claim 1 or 2, wherein the content ratio of the first pulp to the second pulp (first pulp / second pulp) is 3/7 to 7/3.
The thin paper according to any one of claims 1 to 3, wherein at least carboxymethylcellulose or a salt thereof is added as the paper strength enhancer.
The thin paper according to any one of claims 1 to 4, having a basis weight of 10 to 20 g / m 2 .
Mainly composed of softwood bleached kraft pulp with a freeness of 400-550 ml, with two or more paper strength enhancers added, basis weight of 10-14.5 g / m 2 , density of 0.05-0.2 g The thin paper according to any one of claims 1 to 4, having a crepe rate of 5 to 30% / cm 3 .
The thin paper according to claim 6, wherein a dry paper strength enhancer and a wet paper strength enhancer are added as the two or more types of paper strength enhancers.
The thin paper according to claim 7, wherein the dry paper strength enhancer is at least one selected from the group consisting of carboxymethylcellulose and salts thereof, polyacrylamide resin and salts thereof, cationized starch, and polyvinyl alcohol.
The wet paper strength enhancer is at least one selected from the group consisting of epoxidized polyamide polyamine resin, urea-formalin resin, melamine-formalin resin, dialdehyde starch, polyethyleneamine and methylolated polyamide. 8. The tissue paper according to 8.
The thin paper according to any one of claims 6 to 9, wherein as the two or more kinds of paper strength enhancers, two kinds of dry paper strength enhancers and one kind of wet paper strength enhancer are added.
The thin paper according to claim 10, wherein the two kinds of dry paper strength enhancers are a salt of carboxymethyl cellulose and an anionic polyacrylamide, and the one wet paper strength enhancer is an epoxidized polyamide polyamine resin.
The thin paper according to claim 11, wherein the weight average molecular weight of the anionic polyacrylamide salt is 8 million or more.
13. The dry tensile strength in the transport direction at the time of manufacturing the thin paper is 600 to 1500 cN / 25 mm, and the dry tensile strength in a direction orthogonal to the transport direction is 150 to 350 cN / 25 mm. Tissue paper.
The thin paper according to any one of claims 1 to 13, wherein a liquid permeation time of the thin paper measured by the following method is 0.2 to 3 seconds.
<Measurement method of liquid permeation time>
Two cylinders with an inner diameter of 35 mm that open at the top and bottom are arranged vertically with the axes of both cylinders aligned, and an 8 cm square measurement sample is sandwiched between the upper and lower cylinders. 40 g ± 1 g of physiological saline is supplied. The supplied physiological saline passes through the measurement sample or is absorbed by the sample and disappears from the upper cylinder. The time from the start of the supply of the physiological saline to the time when the surface of the physiological saline reaches the same position as the surface of the measurement sample is measured, and the time is defined as the liquid permeation time.
An absorbent article using the thin paper according to any one of claims 1 to 14.
A method for producing thin paper, which produces a thin paper having a basis weight of 30 g / m 2 or less by papermaking and drying a raw material slurry prepared from a raw material containing softwood bleached kraft pulp,
After adding the wet paper strength agent (a) made of a cationic polymer having a cationic group to the pulp slurry of the softwood bleached kraft pulp as the raw material slurry, the following low molecular dry paper strength agent (b) and high Thin paper using a raw material slurry prepared by adding a molecular dry paper strength agent (c) at the same time, or adding a low molecular weight dry strength agent (b) and then adding a polymer dry strength agent (c). Manufacturing method.
(B) Low molecular weight dry paper strength agent which is a low molecular weight anionic polymer having an anionic group having a weight average molecular weight (Mw) of 0.2 to 500,000 (c) Weight average molecular weight (Mw) of 500 to 30 million Polymer dry paper strength agent which is a polymer anionic polymer having an anionic group of
The raw material slurry is obtained by adding the wet paper strength agent (a) to the pulp slurry of the softwood bleached kraft pulp, then adding the low molecular weight dry strength agent (b), and then further adding the polymer dry strength material. The method for producing thin paper according to claim 16, which is adjusted by adding (c).
The step of adjusting the raw material includes diluting after adding the low molecular dry paper strength agent (b), adding the polymer dry paper strength agent (c) after dilution, and then adding at least a fan pump and a filtration screen. The method for producing thin paper according to claim 17, wherein one is used to make uniform.