JP5074621B2 - Tissue paper - Google Patents

Description

  The present invention relates to a thin paper, and 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.

  The thin paper is a thin paper having a relatively low basis weight, but is required to have a paper strength (such as tensile strength) that does not cause tearing during use. 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.

Japanese Patent Laid-Open No. 2005-124484 JP-A-8-291495

  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.

  Accordingly, an object of the present invention is to provide a thin paper having good strength characteristics and excellent liquid permeability.

  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. I found out.

  The present invention has been made on the basis of the above findings, and is 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 hydrophilic cellulose fiber contains 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. By providing a thin paper in which the difference in fiber roughness between the first pulp and the second pulp is 0.01 to 0.07 mg / m, and the freeness of the aggregate is 400 to 550 ml. It has been solved.

  The present invention also provides an absorbent article using the thin paper.

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

FIG. 1 is an explanatory diagram of a method for measuring the liquid permeation time.

  Hereinafter, the thin paper of the present invention will be described in detail. The thin paper of the present 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.

  In the thin paper of the present invention, the two kinds of hydrophilic cellulose fibers have a fiber roughness of 0.13 to 0.16 mg / m, preferably 0.135 to 0.155 mg / m, and more preferably 0.14 to 0.14. The first pulp is 0.15 mg / m, 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 0.19 mg / m. The second pulp is contained, 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 mass ratio between the first pulp and 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 each of the first pulp and the second pulp is preferably NBKP. Further, as NBKP used in the present invention, NBKP 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 is mainly composed of an aggregate of two kinds 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 80% by mass, more preferably 80 to 100% by mass, from the viewpoint of achieving both strength characteristics and liquid permeability.

  In the present 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 (C.S.F.) 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 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 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.

  From the viewpoint of obtaining good strength characteristics (tensile strength), a paper strength enhancer is added to the thin paper of the present invention. 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 because of their high versatility and low aggregation effect between fibers. That is, in the present invention, at least CMC or a salt thereof is preferably 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, conventionally known wet paper strength enhancers 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, when two or more kinds of paper strength enhancers are used, a preferable combination thereof includes two kinds of dry paper strength enhancers and one kind of 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 preferably 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 is preferably 0.01 to 1.5% by mass, more preferably 0.03 to 1.2% by mass, based on the dry mass of all the constituent fibers of the thin paper. It is. 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 lowered 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 addition amount of each paper strength enhancer is preferably 0.05 to 0.5% by mass, more preferably 0.1 to 0.3% by mass of CMC salt, 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 may contain other components other than the fibers such as the first pulp and the second pulp (hydrophilic cellulose fibers) 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 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, but the order of addition of the paper strength enhancer in the present invention is not limited to this, and the order of addition may be reversed. 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 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 , especially 12 -14 g / m ² is preferred. When the basis weight is low, there is a concern about a decrease in paper strength, but in the present invention, as described above, the first pulp having relatively small fiber roughness (thin fiber diameter) is used as a part of the constituent fibers. In addition, the concern is eliminated by setting the freeness of the aggregate of the two types of fibers (first pulp and second pulp) within a specific range and using a paper strength enhancer in combination. 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 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.

  The density of the 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 may have crepes (crepe-like wrinkles). When the thin paper of the present invention has a crepe, the crepe 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 a dryer part with a doctor knife or the like. . 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, based on such knowledge, from the viewpoint of balance between liquid permeability and strength properties, the crepe rate of the thin paper is 5 to 30%, particularly 5 to 20%, especially 7 to 15%. preferable.

  The dry tensile strength in the transport direction (Machine Direction, MD for short) of the thin paper of the present 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. More preferably, it is 800 to 1200 cN / 25 mm, and even more preferably 900 to 1200 cN / 25 mm. Further, the dry tensile strength in a direction orthogonal to MD (Cross machine direction, abbreviated as CD) 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 testing machine (manufactured by Shimadzu Autograph AG-1kN) without tension so that the 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.

  Moreover, the liquid permeation | transmission time of the thin paper of this invention measured by the following method is 0.2 to 3 second, Preferably it is 0.3 to 2.5 second, More preferably, it is 0.5 to 2 second. 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. .

The thin paper of the present 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 using 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 two kinds of fiber roughness as the fiber material were 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 clear that the thin paper of the present invention is excellent in air permeability.

  The thin paper of the present invention has good strength characteristics (tensile strength), 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 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 has a relatively low viscosity such as urine. Not only in the case of, but also in the case of relatively high viscosity such as loose stool, the excretory fluid can be quickly permeated and absorbed into the absorbent core, which can contribute to the improvement of the leak-proof property of the absorbent article .

  As an example of the absorbent article of the present invention using the thin paper of the present invention, an absorbent article comprising an absorbent core and a core wrap sheet covering the absorbent core, the core wrap sheet is the book described above. What is the thin paper of invention 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 absorbent body is configured to include the absorbent core and the core wrap sheet (thin paper of the present invention). The core wrap sheet (thin paper of the present 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.

  EXAMPLES 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%”.

[Example 1]
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, trade name “Serogen WS-C”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is used as the first paper 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. 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 1.

[Examples 2 to 5 and Comparative Examples 1 to 5]
A thin paper was produced in the same manner as in Example 1 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 5, 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.

The details of the pulp (NBKP) used in Examples and Comparative Examples are as follows (described in ascending order of fiber roughness). These pulps were obtained through Nippon Paper Pulp Trading or Itochu Corporation.
・ Fiber roughness 0.09mg / 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]
Various evaluation results of each sample (thin paper) of Examples and Comparative Examples are as 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 scope of the present 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, good strength characteristics, and liquid permeability. It can be seen that this is an excellent thin paper. In particular, Example 5 which is a form using two dry paper strength enhancers and one wet paper strength enhancer is generally better in strength properties 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 1, 2 and 5) or a liquid permeation time of more than 3 seconds ( It is Comparative Examples 1, 3 and 4), 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, in Comparative Example 1, the difference in fiber roughness between the first pulp and the second pulp exceeds 0.07 mg / m. Therefore, since Comparative Examples 2, 3 and 5 use only one kind of hydrophilic cellulose fiber, it is surmised that Comparative Example 4 is because the freeness of the aggregate is out of the specific range.

91, 92 Cylinder 93 Clip 94 Packing S Sheet to be measured (thin paper)
W saline

Claims (6)

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. cage, the difference in degree of fiber roughness of the first pulp and a second pulp are contained is 0.01~0.07mg / m, Ri freeness is 400~550ml der of the aggregate,
The fiber roughness of the first pulp and the second pulp is measured according to the operation procedure of the fiber roughness meter using a fiber roughness meter FS-200 (manufactured by KAJAANI ELECTRONICS LTD.). A thin paper that is the average value of the fiber roughness of many fibers .   The thin paper according to claim 1, wherein an 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 a 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. Tissue paper according to any one of claims 1 to 4 basis weight of 10 to 20 g / m ^2.   An absorbent article using the thin paper according to any one of claims 1 to 5.

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