JP2013072150A - Tissue paper - Google Patents

Abstract

To provide a thin paper having excellent strength characteristics and excellent liquid permeability and liquid diffusibility.
The thin paper of the present invention comprises a fibrous material containing pulp fibers and rayon fibers, carboxymethyl cellulose having a degree of etherification of 0.2 to 0.6 or a salt thereof, and a wet paper strength enhancer. The basis weight is 10 to 30 g / m ² , and the crepe rate is 5 to 30%. The freeness of the pulp fibers is preferably 300 to 700 ml. The cross-sectional shape of the rayon fiber is preferably circular or Y-shaped.
[Selection figure] None

Description

  The present invention relates to a thin paper which is a thin paper having a relatively low basis weight, 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.

  Conventionally, it is known to contain carboxymethyl cellulose (hereinafter also referred to as CMC), which is a derivative of cellulose, for the purpose of imparting water degradability to paper containing pulp fibers. For example, Patent Document 1 describes that a water-insoluble fibrous CMC having a degree of etherification of 0.20 to 0.65 is used together with a wet paper strength enhancer as a component of a wiping paper such as a paper towel. Yes. Patent Document 2 describes a method for producing hydrolytic paper containing a water-swellable binder. As the water-swellable binder, fibrous CMC having a substitution degree of about 0.30 to 0.60 or a salt thereof is described. The use is described.

  Patent Document 3 discloses water having at least a part replaced with antibacterial metal ions as a component of the sheet for the purpose of enhancing the antibacterial properties of the sheet used for sanitary goods such as disposable diapers. It is described that an antibacterial agent composed of insoluble CMC is used, and it is also described that a CMC having a substitution degree of 0.4 to 1.0 is used as the CMC as the antibacterial agent. Further, in Patent Document 4, for the purpose of adjusting the zeta potential of pulp fibers to a specific range and maximizing the effects of papermaking chemicals such as a paper strength enhancer, the degree of substitution is 0.3 for pulp fibers. The addition of ~ 0.6 CMC is described.

JP-A-7-216781 JP 2005-194635 A JP-A-11-1895 JP 2001-262498 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 does not cause tearing during manufacturing, a high liquid permeability that allows the liquid to quickly permeate and diffuse during use, and quickly absorb the absorbent core disposed below the core wrap sheet. Although liquid diffusibility is required, the sheet strength, liquid permeability, and liquid diffusibility of the core wrap sheet are in a trade-off relationship, and it is difficult to achieve a good balance between the two. In addition, while thinning of the absorbent body is desired, the core wrap sheet constituting the absorbent body is also required to have a low basis weight. However, the reduction in the basis weight of the core wrap sheet may cause a decrease in sheet strength. Therefore, it is difficult to reduce the basis weight with the current core wrap sheet configuration.

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

  The present inventors pay attention to the water absorption amount of Krem obtained according to the water absorption test method by the Krem method of paper as defined in JIS P8141, as an index of liquid permeability and liquid diffusibility of thin paper, As a result of various investigations on the relationship with water absorption of Krem, as a fibrous material contained in thin paper, a combination of pulp fibers and rayon fibers that have progressed in fibrillation, and as a constituent of thin paper, a wet paper strength enhancer It has been found that the strength (tensile strength) and the water absorption of Krem are greatly improved by including low-substituted CMC having a degree of etherification in a specific range.

The present invention has been made based on the above knowledge, and includes a fibrous material containing pulp fibers and rayon fibers, carboxymethyl cellulose having a degree of etherification of 0.2 to 0.6 or a salt thereof, and a wet paper strength enhancer. The above-mentioned problems are solved by providing a thin paper containing, having a basis weight of 10 to 30 g / m ² and a crepe rate of 5 to 30%.

  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 and liquid diffusibility 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 is a fiber sheet mainly composed of a fibrous material, that is, a fiber sheet having a fibrous material content of 50% by mass or more, preferably 60% by mass or more. Contains rayon fiber.

  As the pulp fiber used in the present invention, a known pulp fiber can be used without particular limitation. For example, softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), softwood bleached sulfite pulp (NBSP), thermo Wood pulp such as mechanical pulp (TMP); bast fibers such as straw, cocoon, husk, etc .; non-wood pulp such as straw, bamboo, kenaf, hemp, etc. These may be used alone or in combination of two or more. Can be used. Among these pulp fibers, NBKP is particularly preferably used in the present invention because the strength of paper produced using this is high. 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 freeness of the pulp fiber used in the present invention is preferably in the range of 300 to 700 ml, particularly 400 to 700 ml, particularly 500 to 680 ml. Freeness is a value indicated by Canadian Standard Freeness (CSF) stipulated in JIS P8121, and beating pulp fibers (a process of mechanically tapping and grinding pulp fibers in the presence of water). ). The pulp fibers can be beaten according to a conventional method using a known beater such as a beater or a disc refiner with respect to a paper material (slurry) in which pulp fibers are dispersed. Usually, the smaller the freeness value of the pulp fibers, the stronger the degree of beating, and the greater the damage of the fibers due to beating, the more fibrillation proceeds. Pulp fibers having a freeness in the above range, particularly NBKP, tend to be entangled with each other because fibrillation is in progress. Therefore, from the viewpoint of lower basis weight or improved liquid permeability and liquid diffusibility, etc. When quantification (density reduction) is attempted, even if the number of inter-fiber bonding points of the fibrous material decreases, the strength of each inter-fiber bond exceeds 700 ml of freeness, and fibrillation is progressing relatively. Not as high as NBKP. On the other hand, 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. Therefore, a thin paper containing pulp fibers (NBKP) having a freeness of 300 to 700 ml can have good strength properties (tensile strength) and liquid permeability.

  In the present invention, rayon fibers are used in addition to pulp fibers as the fibrous material. According to the knowledge of the present inventors, the strength characteristics (tensile strength) of the thin paper is increased by using together the pulp fibers having advanced fibrillation (pulp fibers having a freeness in the range of 300 to 700 ml) and rayon fibers. As well as improving, the water absorption amount of Krem, which is an index of liquid permeability and liquid diffusibility, is also greatly improved. The reason is that rayon fibers are regenerated fibers compared to normal pulp fibers such as NBKP, so hydrogen bonds are low and bulky due to the difference in cross-sectional shape, so that the bulky rayon fibers are contained in thin paper. Thus, the thin paper sheet has a high-gap structure in which a large number of relatively large gaps are formed, and such a high-gap structure is presumed to particularly contribute greatly to the improvement of the water absorption amount of Krem. In addition, the liquid permeability is improved due to the high voids, while the pulp fibers that have advanced fibrillation are presumed to contribute mainly to the improvement of the strength characteristics of the thin paper.

  There are various types of rayon fibers having different fiber cross-sectional shapes (cross-sectional shapes perpendicular to the direction in which the fibers extend). For example, fiber cross-sections such as circular, Y-shaped, hollow flat, and ribbon flat There is a rayon fiber having a shape. In the present invention, various rayon fibers can be used regardless of the fiber cross-sectional shape, and in particular, since the fiber cross-sectional shape is a circular shape or a Y-shape, the high voids are formed in the thin paper because the fiber itself is bulky. Therefore, the present invention is preferably used in the present invention because it is easy to impart a simple structure and hardly lowers the strength characteristics. Examples of the rayon fiber having a circular fiber cross-sectional shape include commercially available products such as corona SB (2.2 dtex × 5 mm), corona SB (5.6 dtex × 5 mm) (manufactured by Daiwabo Rayon Co., Ltd.). Examples of rayon fibers having a Y-shaped fiber cross section include commercially available products such as Corona SBA (1.9 dtex × 5 mm) and Corona SBA (7.8 dtex × 8 mm) (above, manufactured by Daiwabo Rayon Co., Ltd.). Can be mentioned.

  The rayon fibers used in the present invention are preferably those having a fineness of 0.8 to 20 dtex and a fiber length of 1 to 20 mm from the viewpoint of more surely exhibiting the effects of using the rayon fibers. Of 1.0 to 15 dtex and a fiber length of 2 to 15 mm is preferable, and in particular, a fineness of 1.5 to 8.0 dtex and a fiber length of 3 to 10 mm are preferable.

  In the thin paper of the present invention, the content ratio of the pulp fiber and the rayon fiber (ratio on the mass basis of both fibers in the total fibrous material in the thin paper) is pulp fiber / rayon fiber = 95 / 5-50 on a mass basis. / 50 is preferable, and 90/10 to 70/30 is more preferable. If the rayon fiber is excessively present in the thin paper exceeding the content ratio, it is not preferable because the paper strength may be lowered. The content of the pulp fiber is preferably 60 to 95% by mass, more preferably 70 to 90% by mass in the thin paper. The content of the rayon fiber is preferably 5 to 40% by mass, more preferably 10 to 30% by mass in the thin paper.

  In the thin paper of the present invention, other fibers can be used as the fibrous material in addition to the pulp fibers and rayon fibers described above. Other fibers used in the present invention include, for example, synthetic fibers such as polyester, polyethylene, and polypropylene; mercerized pulp obtained by alkali treatment of pulp fibers, and crosslinked pulp obtained by crosslinking the intramolecular and / or intermolecular regions of pulp fibers with a crosslinking agent. Modified cellulose fibers such as (for example, chemically cross-linked cellulose fibers known as HBA) and the like can be mentioned, and one of these can be used alone or in combination of two or more. However, the content of fibers other than pulp fibers and rayon fibers is 10 in the thin paper from the viewpoint of more reliably obtaining the effect (improvement of strength and water absorption of clem water) by the combined use of pulp fibers and rayon fibers. It is preferable to set it as mass% or less, and 0 mass%, that is, it is still more preferable to use only a pulp fiber and a rayon fiber as a fibrous material.

  The thin paper of the present invention contains carboxymethyl cellulose (hereinafter also referred to as low-substituted CMC) having a degree of etherification of 0.2 to 0.6 or a salt thereof in addition to the above-described fibrous materials such as pulp fibers and rayon fibers. . Examples of the salt of the low-substituted CMC include sodium salts, potassium salts, ammonium salts and the like of the low-substituted CMC. In the present invention, the sodium salt of the low-substituted CMC is mainly used. Further, the low-substituted CMC and its salt used in the present invention may be in the form of powder or fiber.

  CMC is a cellulose derivative synthesized by reacting monochloroacetic acid or the like using wood pulp, linter pulp or the like as a raw material, and is obtained by substituting a part of hydrogen atoms of the hydroxyl group of cellulose with a carboxymethyl group. The functional properties of CMC largely depend on the degree of etherification (the degree of substitution of carboxymethyl groups per anhydroglucose unit of cellulose), and in general, highly substituted CMCs with a degree of etherification exceeding 0.6 (degree of etherification 0.6 ~ 1.5) is soluble in water, but low-substituted CMC having a degree of etherification of 0.6 or less (degree of etherification of about 0.2-0.6) is hardly soluble or insoluble in water. When CMC is put into water, it absorbs water and swells to gel and maintains its swelling state.

  Regarding CMC as a component of paper, conventionally, highly substituted CMC is used as a dry paper strength enhancer, and low substituted CMC reduces the wet strength of paper as described in Patent Documents 1 and 2. It has been used for the purpose of imparting water degradability to paper. As a result of various studies on the effectiveness of the low substitution CMC other than imparting water disintegration, the present inventors have found that the low substitution CMC has a centrifugal retention measured in accordance with JIS K7223 (1996) as compared with the high substitution CMC. As a result of further investigation, it was found that when used as a component in a thin paper containing pulp fiber and rayon fiber as a fibrous material, the low-substituted CMC is stronger than the high-substituted CMC. In particular, it has been found that the effect of improving the dry tensile strength) and the water absorption of Klem (liquid diffusibility) is large, and the effect of decreasing the bending rigidity value is also large. The reduction in the bending rigidity value of the thin paper means an improvement in the softness of the thin paper. In particular, the thin paper is used in absorbent articles such as disposable diapers and sanitary napkins. When used as a core wrap sheet covering the outer surface, it is desirable that the thin paper has high flexibility.

The degree of etherification of the low-substituted CMC used in the present invention is preferably 0.2 to 0.6, more preferably 0.25 to 0.5, from the viewpoint of maximizing the effects of the low-substituted CMC described above. . A low-substituted CMC having an etherification degree of less than 0.2 is not preferable in the present invention because it may cause a decrease in water absorption of the clem. The degree of etherification is measured using an ashing measurement method as follows. That is, about 0.7 g of a sample (anhydride) was precisely weighed, wrapped in filter paper and placed in a magnetic crucible, and sufficiently ashed at 600 ° C. After cooling, transfer this to a 500 ml beaker, add about 250 ml of water and 35 ml of 0.05 mol / l sulfuric acid and boil for 30 minutes. After cooling this, a phenolphthalein indicator was added, the excess acid was back titrated with 0.1 mol / l potassium hydroxide, and the following formula was calculated.
Degree of etherification = 162 × A / (10000-80 × A)
Here, A is the number of ml of 0.05 mol / l sulfuric acid consumed by the bound alkali in 1 g of the sample.

  The content of the low-substituted CMC is preferably 0.05 to 20% by mass, more preferably 0.1 to 10% by mass, with respect to the dry mass of the entire fibrous material of the thin paper. If the content of the low-substituted CMC is too small, the significance of using the low-substituted CMC is weakened. If the content of the low-substituted CMC is too large, the thin paper may be hardened.

  The thin paper of the present invention contains a wet paper strength enhancer in addition to the low substituted CMC. When thin paper containing low-substituted CMC is used as a core wrap sheet in an absorbent article, when the bodily fluid such as urine comes into contact with the thin paper, the low-substituted CMC contained in the thin paper absorbs and swells the bodily fluid. As a result, there is a possibility that inconveniences such as tearing or twisting of the thin paper during use of the absorbent article may occur. Therefore, the wet strength (especially wet tensile strength) of the thin paper is improved by using the wet paper strength enhancer as a component of the thin paper in addition to the low-substituted CMC. Therefore, the inconvenience of using the low substituted CMC is avoided. It becomes possible. Moreover, as another effect by using a wet paper strength enhancer, especially when thin paper is used as a core wrap sheet in an absorbent article, the thin paper (core wrap sheet) due to the body pressure of the wearer of the absorbent article The effect of relieving compressive stress is mentioned, and further, the effect of reducing the amount of wetback due to clogging of the thin paper (core wrap sheet) (decrease in the porosity between the fibrous materials contained in the thin paper) is mentioned. These effects contribute to the gentleness of the absorbent article to the wearer's skin.

  As the wet paper strength enhancer used in the present invention, conventionally known ones can be used without particular limitation, and examples thereof include epoxidized polyamide polyamine resin (PAE), urea-formalin resin, melamine-formalin resin, dialdehyde starch, Examples thereof include polyethyleneamine and methylolated polyamide, and these can be used alone or in combination of two or more. Among these wet paper strength enhancers, PAE is particularly preferably used in the present invention because the wet paper strength of paper produced using it is high.

  The content of the wet paper strength enhancer is preferably 0.1 to 2.0% by mass, more preferably 0.5 to 1.0% by mass, with respect to the dry mass of the total fibrous material of the thin paper. When the content of the wet paper strength enhancer is too small, the significance of using the wet paper strength enhancer is lessened. When the content of the wet paper strength enhancer is too high, 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 reduced due to the sticking of the paper to the Yankee dryer or the adhesion of the paper strength enhancer to the mesh drum at the time of manufacture.

  The thin paper of the present invention may further contain a dry paper strength enhancer in addition to the above-described components (pulp fiber, rayon fiber, low substitution CMC, wet paper strength enhancer). The dry paper strength enhancer herein is a dry paper strength enhancer other than the low-substituted CMC and its salt (the low-substituted CMC and salt used in the present invention also have a function as a dry paper strength enhancer. ) As the dry paper strength enhancer used in the present invention, conventionally known ones can be used without particular limitation. For example, highly substituted CMC (CMC having a degree of etherification exceeding 0.6) and salts thereof, polyacrylamide resins And salts thereof, cationized starch, polyvinyl alcohol (PVA), and the like. One of these can be used alone, or two or more can be used in combination. The salt of the highly substituted CMC or polyacrylamide resin is synonymous with the salt of the low substituted CMC described above. Examples of the polyacrylamide resin include cationic or anionic polyacrylamide (PAM). Among these dry paper strength enhancers, high substitution CMC is particularly effective because it improves paper strength.

  From the same viewpoint as the wet paper strength enhancer, the content of the dry paper strength enhancer is preferably 0.01 to 2.0% by mass, more preferably 0, based on the dry mass of the total fibrous material of the thin paper. 0.05 to 1.0 mass%.

  The thin paper of the present invention may contain other components other than the above-described fibrous materials (pulp fibers, rayon fibers), low-substituted CMC, and wet and dry paper strength enhancers. 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 consists of a stock preparation process for preparing a stock (slurry) made of an aqueous dispersion of a fibrous material, and a paper making step for drying while transporting a fiber material made from the stock material into a fiber web. It 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. Additives such as the low substitution CMC, the wet paper strength enhancer, and the dry paper strength enhancer described above are usually added to the stock in the stock preparation step. Usually, the low-substituted CMC, the wet paper strength enhancer, and the dry paper strength enhancer are added to the stock in this order. However, the order of addition of additives in the present invention is not limited to this, and the order of addition is reversed. Each additive 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 usually has a single-layer structure and is composed of a single fiber web obtained by a wet papermaking method.

  In the paper preparation step, when low-substitution CMC is added to the paper, it is preferable to add the low-substitution CMC while applying a high shearing force to the paper. When low-substitution CMC is added under normal stirring conditions without applying a high shearing force to the paper stock, especially when a fibrous material is used as the low-substitution CMC, the added fibrous low-substitution CMC As in the case before the addition, since the state of the fiber bundle in which the fibers are entangled and bundled is easy to maintain, the adhesion area with the fibrous material such as pulp fibers and water is reduced, and the effect of adding the low substitution CMC is sufficient. May not be obtained. In contrast, when a fibrous low-substituted CMC is added while applying a high shearing force to the stock, the fibrous low-substituted CMC is unwound from the state of the fiber bundle before the addition and dispersed in the stock. The bonding area with the low-substitution CMC fibrous material and water increases, and the effect of adding the low-substitution CMC can be sufficiently obtained. Examples of a method for applying a high shearing force to the paper include a method of stirring the paper using a pulper, a disaggregator, a beater, or the like.

  In addition, in this way, when the fibrous low-substituted CMC is added to the paper while applying a high shearing force to the paper, the added fibrous low-substituted CMC is highly advanced before the paper making process. It is preferable to swell. Here, the highly swollen state means a state where the degree of swelling of the fibrous low-substituted CMC is 70 to 100%. If the swelling degree of the fibrous low-substituted CMC is in such a range in the paper stock, the specific gravity of the low-substituted CMC is close to that of water. Therefore, the fibrous material such as the low-substituted CMC or pulp fibers adsorbed thereto is obtained. It is easy to be uniformly dispersed in the stock, and as a result, the texture of the thin paper is improved. Further, among the high-swelling fibrous low-substituted CMCs, those present at the intersections of fibrous materials such as pulp fibers are crushed and bonded by a fiber web press or the like in the paper making process. Since the area increases, it contributes to the improvement of the paper strength of the thin paper, and what exists in the portion other than the intersection contributes to the improvement of the flexibility of the thin paper. As a method for highly swelling fibrous low-substituted CMC, for example, a 1% by mass aqueous solution of fibrous CMC is prepared, water is sufficiently immersed in the fibrous CMC to swell, and then high shear is applied. The method of adding this fibrous CMC to the pulp slurry in the stirring pulper is mentioned. The degree of swelling is measured as follows. That is, 1 g of fibrous CMC was put in a mesh bag and immersed in water for 1 hour, and then the weight measured after dehydration with a centrifugal dehydrator (700 rpm × 10 minutes) was set to a value of 100% swelling, and the sample to be measured was subjected to the same conditions. Then, the weight after dehydration is divided by the value of the degree of swelling of 100%, and the value expressed in percentage is defined as the degree of swelling of the sample.

In the thin paper of the present invention, the basis weight is set to be relatively low from the viewpoint of being suitable for a core wrap sheet having a thin absorbent body. Specifically, the basis weight is 10 to 30 g / m. ² , preferably 12 to 28 g / m ² , more preferably 15 to 25 g / m ² . When the basis weight is so low, there is a concern about a decrease in paper strength. However, in the present invention, such a concern is eliminated by adopting the configuration of the thin paper described above. 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 30 g / m ² , the thin paper may be hard.

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 thin paper of the present invention has crepes (crepe-like wrinkles), and the crepe rate is set to 5 to 30%. The crepe in the thin paper of the present invention is preferably a dry crepe 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 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, the crepe rate of the thin paper is 5 to 30%, preferably 5 to 20%, and more preferably 7 to 15% from the viewpoint of the balance between liquid permeability and strength characteristics. .

  The dry tensile strength in the conveying direction (Machine Direction, abbreviated as MD) of the thin paper of the present invention having the above-described configuration is preferably 800 cN / 25 mm or more, more preferably 800 to 1500 cN / 25 mm, orthogonal to MD. The dry tensile strength in the direction (Cross machine Direction, abbreviated as CD) is preferably 150 cN / 25 mm or more, more preferably 150 to 500 cN / 25 mm. Further, the wet tensile strength of MD of the thin paper of the present invention is preferably 150 cN / 25 mm or more, more preferably 150 to 500 cN / 25 mm, and the wet tensile strength of CD is preferably 90 cN / 25 mm or more, more preferably 90. ~ 200 cN / 25 mm. A thin paper having a dry tensile strength and a wet tensile strength within such ranges has sufficient strength for practical use. For example, a core wrap sheet for coating the thin paper with an absorbent core in an absorbent article such as a disposable diaper. When it is applied to, the core wrap sheet (thin paper) is not easily broken when the absorbent article is manufactured and used. The dry tensile strength and the wet tensile strength are 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 with a room temperature of 23 ° C. ± 2 ° C. and a relative humidity of 50% RH ± 2% so as to be in 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.

<Measurement method of wet tensile strength>
A sample of a sheet to be measured (thin paper) is prepared in the same procedure as in the above <Method for measuring dry tensile strength>. This sample is attached to a chuck of a tensile tester (manufactured by Shimadzu Autograph AG-1kN) with no tension so that its MD is in the tensile direction, and the tip of the brush is wetted with water. After the sample is wetted by applying water at a width of about 10 mm over the entire length in the tensile direction, the sample is pulled at a tensile rate of 300 mm / min, and the maximum strength until the sample breaks is measured. The measurement is performed 5 times, and the average value of these is taken as the wet tensile strength of MD. 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. It is attached to the chuck of the testing machine without tension, and the wet tensile strength of the CD is determined by the same procedure as described above.

  Further, the water absorption amount of the Krem in the thin paper of the present invention is preferably 0.2 g / 30 sec · 15 mm or more, more preferably 0.2 to 0.3 g / 30 sec · 15 mm. The fact that the amount of water absorbed by Krem in thin paper is in such a range is largely due to the formation of a highly voided structure therein, and the formation of the highly voided structure is due to the use of rayon fibers and low-substituted CMC. large. The thin paper having the Krem water absorption in such a range has sufficient liquid diffusibility for practical use. For example, the thin paper is applied to a core wrap sheet that covers an absorbent core in an absorbent article such as a disposable diaper. In this case, body fluid such as urine can be quickly absorbed by the absorbent core disposed below the core wrap sheet, and the liquid absorbency is improved. The Krem water absorption is measured as follows in accordance with the water absorption test method by the paper Krem method defined in JIS P8141.

<Measurement method of Krem water absorption>
The sheet to be measured (thin paper) is allowed to stand for 12 hours in an environment with a room temperature of 23 ° C. ± 2 ° C. and a relative humidity of 50% RH ± 2% so as to be in a constant state. A rectangular shape having a size of 150 mm for MD and 15 mm for CD is cut out from the moisture-conditioned sheet, and the cut out rectangular shape is used as a sample. A straight line (marked line) parallel to the short side is drawn with a pencil at a position 5 mm inward in the longitudinal direction from one short side of the sample. Then, the sample is suspended at the bottom of the electronic balance so that the long side of the sample is vertical, and the sample is quickly put into the measuring solution (saline) while maintaining the suspended state up to the marked line. . The sample is hung so that the marked line (straight line drawn with a pencil) is close to the measurement solution. Then, an increase in the weight of the sample 30 seconds after the sample is put in the measurement solution is measured with an electronic balance, and the measured value is defined as a Krem water absorption (g / 30 sec. 15 mm). The higher the Krem water absorption, the higher the rating. The electronic balance is electrically connected to a personal computer on which a commercially available electronic balance data capturing software (trade name RsCom Ver2.40: manufactured by A & D Co., Ltd.) is installed. The change in weight of the sample can be recorded.

  Further, the liquid permeation time of the thin paper of the present invention is preferably 0.5 to 6 seconds, more preferably 1 to 5 seconds. The liquid permeation time is an index of the liquid permeation speed, and the liquid permeation speed is considered to be faster as the liquid permeation time is shorter. If the liquid permeation time is less than 0.5 seconds, the liquid permeation rate is too high, and the liquid diffusive effect may not be sufficiently exhibited. 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 liquid permeation time is measured as follows.

<Measurement method of liquid permeation time>
As shown in FIG. 1, two cylinders 91 and 92 having an inner diameter of 35 mm that are open at the upper and lower ends 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. Thus, in the state where the measurement sheet S (thin paper) is sandwiched and fixed between the upper and lower cylinders 91 and 92, the physiological saline (sodium chloride concentration of 0.9 mass) indicated by the symbol W in FIG. % Of aqueous solution) is supplied. The supplied physiological saline passes through the measurement target sheet S (thin paper) and moves into the lower cylinder 92. The time from the start of the physiological saline supply until the physiological saline completely moves into the lower cylinder 92 is measured, and this time is defined as the liquid permeation time.

  Moreover, the bending rigidity value of the thin paper of the present invention is preferably 20 to 60 cN, more preferably 30 to 50 cN. A higher bending stiffness value indicates that the thin paper is harder and less likely to be deformed. The fact that the bending rigidity value of the thin paper of the present invention is in such a range is largely due to the use of the low replacement CMC, and the bending rigidity value is in such a range, the thin paper of the present invention is highly flexible and easy to bend. Has characteristics. A thin paper having a flexural rigidity value in such a range and high flexibility is particularly useful as a core wrap sheet for covering an absorbent core in an absorbent article such as a disposable diaper. The bending stiffness value is measured as follows.

<Measurement method of bending stiffness value>
Daiei Kagaku Seisaku Seisakusho Co., Ltd .: Handometer tester, which conforms to the stiffness measurement method specified in JIS L1096 (General Textile Testing Method) is used. Placed horizontally on a sample table with a slot adjusted to 20 mm in the MD direction of a 200 mm × 200 mm rectangular test piece (thin paper) with the longitudinal center of the test piece positioned at the center between the slots. To do. Fix the four corners of the test piece to the sample table with adhesive tape. Instruction when the blade adjusted so as to descend to the position 7 mm below (bottom position) from the surface of the sample stage is lowered at a constant speed of 200 mm / min from above the test piece, and the test piece is pressed with the blade Read the maximum value (cN) indicated by the meter (load meter). The measurement is performed five times, and the average value is calculated as the bending stiffness value. The measurement is carried out at a room temperature of 23 ± 2 ° C. and a relative humidity of 50% RH ± 5%.

  The thin paper of the present invention has good strength characteristics (tensile strength), excellent liquid permeability and liquid diffusibility, and excellent flexibility, 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 diffused and absorbed by the absorbent core, contributing to the improvement of the leak-proof property of the absorbent article Can do.

  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 (manufactured by Cariboo Pulp and Paper Company, trade name “Cariboo”) was uniformly dispersed in water to prepare a slurry having a fiber concentration of 2 mass%, and this slurry was applied to a beater to adjust the freeness of NBKP to 650 ml. Thereafter, rayon fibers are added to the slurry so that the ratio of pulp fibers (NBKP) to rayon fibers is 80/20, and low substitution CMC (powder) is added to the dry mass of all fibers in the slurry. Then, 0.2% by mass was added and sufficiently stirred. 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. The mixture was sufficiently stirred so that each component was uniform, and adjusted to a slurry having a solid content concentration of 0.2% 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) having a single layer structure thus obtained was used as the sample of Example 1.

[Examples 2 to 5 and Comparative Examples 1 to 3]
A thin paper (crepe paper) having a single-layer structure was used in the same manner as in Example 1 except that the composition and the like were changed as shown in Table 1 below, and these were used as samples of Examples 2 to 5 and Comparative Examples 1 to 3. When a fibrous low-substituted CMC is used, as described above, the fibrous low-substituted CMC is added while applying a high shearing force to the paper in the paper preparation process, and before the paper making process, The degree of swelling of the added fibrous low-substituted CMC was set to 70 to 100%. In Table 1 below, the numerical value (mass%) in the column of fibrous material means the proportion (mass basis) of the fibrous material in the total fibrous material in the thin paper, and in the column of components other than the fibrous material. A numerical value (mass%) means the ratio (mass standard) of the said component with respect to the fibrous material in a thin paper. Moreover, the detail of each component in following Table 1 is as follows.

Pulp fiber No. 1: NBKP with a freeness of 650 ml.
Pulp fiber No. 2: NBKP of freeness 740 ml (unbeaten).
Pulp fiber No. 3: NBKP with 500 ml freeness.
・ Rayon fiber No. 1: (Product name “Corona SBA” manufactured by Daiwabo Rayon Co., Ltd., fineness 1.9 dtex, fiber length 5 mm, fiber cross-sectional shape is Y-shaped ”).
・ Rayon fiber No. 2: (Product name “Corona SBA” manufactured by Daiwabo Rayon Co., Ltd., fineness 7.8 dtex, fiber length 8 mm, fiber cross-sectional shape is Y-shaped ”).
・ Rayon fiber No. 3: (Product name “Corona SB” manufactured by Daiwabo Rayon Co., Ltd., fineness 2.2 dtex, fiber length 5 mm, fiber cross-sectional shape is circular).
-Modified cellulose fiber: (trade name “HBA” manufactured by U.S. Warehauser).
Low-substitution CMC (powder): (Nippon Paper Chemical Co., Ltd. trade name “Sunrose SLD-F1”, degree of etherification 0.28, average particle size 50-60 μm).
Low-substitution CMC (fibrous): (trade name “Kickolate LD-A” manufactured by Nichirin Chemical Industries, Ltd., degree of etherification 0.45, average fiber length 1.36 mm).
-Highly substituted CMC: (Daiichi Kogyo Seiyaku Co., Ltd. brand name "Serogen WS-C", etherification degree 0.65).
-Wet paper strength enhancer: PAE (manufactured by Seiko PMC, trade name “WS4030”).
Dry paper strength enhancer other than CMC: PVA (Kuraray Co., Ltd., trade name “VPB107-1”).

[Evaluation]
About each sample (thin paper) of an Example and a comparative example, dry tensile strength, wet tensile strength, Krem water absorption, liquid permeation time, and bending rigidity value were measured by the above-mentioned method. The results are shown in Table 2 below.

  As shown in Table 2, since the thin paper of Examples 1 to 5 has sufficient tensile strength, the strength characteristics are good, the liquid permeation time is short, and the Krem water absorption is high. Since the liquid permeability and liquid diffusibility are excellent and the bending rigidity value is low, it can be seen that the film has high flexibility and is easy to bend. On the other hand, the thin papers of Comparative Examples 1 and 3 are inferior in liquid permeability, liquid diffusibility, and flexibility compared to the thin papers of Examples 1 to 5 because they have low Krem water absorption and high bending rigidity values. It turns out that it is a thing. Moreover, it turns out that the thin paper of the comparative example 2 is a thin paper with a low intensity | strength characteristic compared with the thin paper of Examples 1-5. In order to obtain a thin paper having good strength characteristics and excellent liquid permeability, liquid diffusibility, and flexibility, in addition to pulp fibers and wet paper strength enhancers, rayon fibers and low substituted CMCs may be used as in the present invention. It is clear that it is important to make it an essential component.

Claims (6)

Containing a fibrous material containing pulp fibers and rayon fibers, carboxymethylcellulose having a degree of etherification of 0.2 to 0.6 or a salt thereof, and a wet paper strength enhancer, having a basis weight of 10 to 30 g / m ² , Thin paper with a crepe rate of 5-30%.   The thin paper according to claim 1, wherein the freeness of the pulp fiber is 300 to 700 ml.   The thin paper according to claim 1 or 2, wherein a fiber cross-sectional shape of the rayon fiber is circular or Y-shaped.   The thin paper according to any one of claims 1 to 3, wherein the rayon fiber has a fineness of 0.8 to 6 dtex and a fiber length of 1 to 20 mm.   The thin paper according to any one of claims 1 to 4, wherein a content ratio of the pulp fiber to the rayon fiber is pulp fiber / rayon fiber = 95/5 to 50/50 on a mass basis.   An absorbent article using the thin paper according to any one of claims 1 to 5.

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