JP2013102930A - Thin paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide thin paper having excellent strength properties, and superior liquid permeability and liquid diffusibility.SOLUTION: This thin paper includes a first layer and a second layer overlapping it, and is used such that the first layer first comes into contact with a liquid. The first layer contains hydrophilic bulky fiber having a fiber roughness of 0.30 mg/m or above, and pulp fiber. The second layer contains specific pulp fiber having a fiber roughness of 0.10-0.20 mg/m, and a wet paper strength-reinforcing agent, and the freeness of the fiber contained in the second layer is 450-700 ml. The total basis weight of the first layer and the second layer is 10-30 g/m, and a crepe rate is 5-20%.

Description

  The present invention relates to a thin paper which is a thin paper having a relatively low basis weight, and in particular, a thin paper used for absorbing liquid, and a core wrap sheet which covers an absorbent core in absorbent articles such as disposable diapers and sanitary napkins. As a suitable thin paper.

  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 acts as a sheet for receiving absorber-forming materials such as wood pulp and superabsorbent resin during the production of the absorber, and after the production it wraps the absorbent core and stabilizes the shape of the absorbent core Fulfills. Conventionally, water-permeable sheets such as thin paper and nonwoven fabric are used as the core wrap sheet.

  Conventionally, from the viewpoint of improving liquid permeability and liquid diffusibility, it has been known that the thin paper has a multilayer structure in which a plurality of layers having different configurations and functions are laminated. For example, in Patent Document 1, as a thin paper suitable as a core wrap sheet for covering an absorbent core, paper is made by mixing bulky cellulose fibers, and a surface layer in contact with a liquid first, and one or more layers overlaid thereon. An absorbent paper having a base layer is described. In the absorbent paper described in Patent Document 1, the surface layer can quickly absorb the liquid and transfer it to the base layer, and the base layer can strongly absorb the liquid from the surface layer and diffuse it throughout. Therefore, the liquid flow of absorption / permeation / diffusion is considered to be ideal.

Patent Document 2 describes a composite absorbent paper in which a permeable absorbent paper and a diffusible absorbent paper are integrated. The permeable absorbent paper has a bulky cross-linking having a fiber roughness of 0.30 mg / m or more. Cellulose fibers and heat-meltable adhesive fibers are contained, the diffusible absorbent paper contains the bulky crosslinked cellulose fibers, hydrophilic fine fibers, and the heat-meltable adhesive fibers, and the permeable absorbent paper. It is also described that the basis weight of each of the diffusible absorbent papers is 20 to 60 g / m ² . Further, in Patent Document 2, the bulky crosslinked cellulose fiber does not swell even when wet with a liquid and does not decrease in strength. Therefore, an absorbent paper including the liquid absorbent space temporarily absorbs the liquid. It is also described that can be stably held. According to Patent Document 2, when the composite absorbent paper described in Patent Document 2 is used as a core wrap sheet covering an absorbent core, body fluid is quickly absorbed by the permeable absorbent paper to form the diffusible absorbent paper. It is said that the diffusible absorbent paper can quickly diffuse the body fluid from the permeable absorbent paper over the entire area.

JP-A-6-287886 JP-A-8-112307

  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.

  As a result of various investigations on the thin paper having a two-layer structure, the present inventors have incorporated a hydrophilic bulky fiber having a relatively high fiber roughness into the first layer that comes into contact with the liquid first, and the first layer is liquid. A high diffusion layer that has a high permeation rate and can exhibit capillary action, and the second layer that overlaps the first layer contains pulp fibers that have relatively low fiber roughness, so that the liquid permeation of the second layer By reducing the speed compared to the first layer, the liquid permeability and liquid diffusion of the thin paper as a whole due to the difference in the liquid permeation speed between the first layer and the second layer and the capillary phenomenon of the first layer. It has been found that the performance is greatly improved.

The present invention has been made based on the above knowledge, and comprises a first layer and a second layer that overlaps the first layer, and is a thin paper that is used so that the first layer first comes into contact with a liquid, The first layer contains hydrophilic bulky fibers and pulp fibers having a fiber roughness of 0.30 mg / m or more, and the second layer comprises specific pulp fibers having a fiber roughness of 0.10 to 0.20 mg / m. The fiber freeness contained in the second layer is 450 to 700 ml, and the total basis weight of the first layer and the second layer is 10 to 30 g / m ^2. The above-mentioned problems are solved by providing a thin paper having a crepe rate of 5 to 20%.

  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 comprises a first layer and a second layer that overlaps the first layer, and is used so that the first layer first comes into contact with the liquid. The thin paper of the present invention, for example, in an absorbent article comprising a top sheet that forms a skin facing surface, a back sheet that forms a non-skin facing surface, and an absorbent core interposed between both sheets. It can be used as a core wrap sheet for covering the core. In that case, between the surface sheet and the absorbent core, the surface sheet and the first layer of the thin paper of the present invention face each other (the absorbent core and the second layer of the thin paper of the present invention face each other). By placing the thin paper on the first layer, the first layer first comes into contact with a liquid (body fluid such as urine).

  As one of the main features of the thin paper of the present invention, two types of fibers having different fiber roughness are used, and fibers having relatively large fiber roughness (hydrophilic bulky fibers having a fiber roughness of 0.30 mg / m or more). ) In the first layer in contact with the liquid, and fibers having a relatively low fiber roughness (specific pulp fibers having a fiber roughness of 0.10 to 0.20 mg / m) are layered on the first layer. The point which is made to contain in the 2nd layer to do is mentioned. 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 contains two kinds of fibers having different thicknesses, and the thick fibers (bulky fibers) of them are contained in the first layer and the thin fibers are contained in the second layer. Therefore, the first layer is bulky compared to the second layer. In general, a bulky fiber layer has a large number of fibers in a relatively sparse state and has a relatively large number of inter-fiber gaps. Therefore, the bulky fiber layer is not bulky and a large number of fibers are relatively dense. The liquid permeation speed is faster than the fiber layer present in the state. Therefore, in the thin paper of the present invention, the relatively bulky first layer has a higher liquid transmission rate than the second layer, and there is a difference in the liquid transmission rate between the first layer and the second layer. Such a difference in liquid permeation rate causes liquid diffusion at or near the interface between the first layer and the second layer, which greatly contributes to the development of excellent liquid diffusibility by the thin paper of the present invention.

  In the present invention, in addition to the liquid diffusion utilizing the liquid permeation rate difference between the first layer and the second layer, the coarse fiber contained in the first layer is also used to utilize liquid diffusion due to capillary action. A hydrophilic bulky fiber is used as a thick fiber (bulky fiber) having a degree of 0.30 mg / m or more. According to the thin paper of the present invention having such a configuration, due to the liquid permeation speed difference between the first layer and the second layer, the interface between the first layer and the second layer or the vicinity thereof (the first layer has the In the vicinity of the interface), the liquid is diffused in the plane direction, and the diffused liquid is further diffused in the plane direction by the capillary phenomenon of the first layer and permeates in the thickness direction toward the second layer. Although the second layer itself has a low liquid permeation rate as compared with the first layer, it has good liquid permeability, so that the thin paper as a whole can exhibit excellent liquid permeability and liquid diffusibility. Moreover, since the freeness of a fiber (specific pulp fiber) is set to 450 to 700 ml and fibrillation is progressing, and the second layer contains a wet paper strength enhancer, as described later, It has excellent strength characteristics, and the excellent strength characteristics of the second layer greatly contribute to the improvement of the strength characteristics of the entire thin paper. Hereinafter, each layer (first layer, second layer) constituting the thin paper of the present invention will be described.

  As described above, the fiber roughness of the hydrophilic bulky fiber contained in the first layer is 0.30 mg / m or more, preferably 0.30 to 0.40 mg / m, and more preferably 0.32 to 0. .38 mg / m. When the fiber roughness of the hydrophilic bulky fiber is less than 0.30 mg / m, the bulkiness of the first layer is insufficient, and the liquid transmission speed difference between the first layer and the second layer described above becomes small, and the liquid of the thin paper The diffusibility may be insufficient.

<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 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.

  An example of the hydrophilic bulky fiber contained in the first layer is a bulky cellulose fiber. The bulky cellulose fiber is a cellulose fiber having a three-dimensional structure such as a twisted structure, a crimped structure, a bent and / or branched structure, and the fiber itself is bulky due to the three-dimensional structure. Bulky cellulose fibers (hydrophilic bulky fibers) include, for example, crosslinked cellulose fibers in which cellulose fibers are cross-linked with and / or between molecules with a cross-linking agent (for example, chemically cross-linked cellulose known as HBA) Fiber); such as mercerized pulp (for example, trade name “Porocenia”) in which cellulose fiber and the like are subjected to alkali treatment to increase the cross section of the fiber, and one of these is used alone or in combination of two or more. be able to. Among these, the crosslinked cellulose fiber is particularly preferably used in the present invention because it can maintain its bulkiness (three-dimensional structure) even in a wet state. The crosslinked cellulose fiber is preferably crosslinked both inside and between the molecules of the cellulose fiber. Examples of the cellulose fiber that is a material for the bulky cellulose fiber (hydrophilic bulky fiber) include regenerated cellulose fibers such as rayon, cupra, tencel, and lyocell, and semisynthetic cellulose fibers such as acetate.

  Examples of the cellulose fiber crosslinking agent used in the production process of bulky cellulose fibers include N-methylol compounds such as dimethylolethyleneurea and dimethyloldihydroxyethyleneurea; citric acid, tricarballylic acid, butanetetracarboxylic acid Examples thereof include polycarboxylic acids such as polyglycidyl ether compounds, and these can be used alone or in combination of two or more.

  It is preferable that the usage-amount of a crosslinking agent shall be 0.2-20 mass parts with respect to 100 mass parts of cellulose fibers. If it is less than 0.2 parts by mass, the bulk density of the bulky cellulose fibers is low because the crosslinking density is low, and there is a risk of twisting / sagging. If it becomes too rigid and stress is applied, the fiber may become brittle. Examples of the method for crosslinking cellulose fibers using a crosslinking agent include the following methods i) and ii). i) Cellulose fibers are impregnated with an aqueous solution of a crosslinking agent, if necessary, and a cellulose fiber is impregnated. The cellulose fibers are dehydrated so that the amount of the crosslinking agent aqueous solution reaches a designed adhesion amount, and then heated to a crosslinking temperature. Method. ii) A method in which an aqueous solution of a crosslinking agent is sprayed on cellulose fibers so as to have a design adhesion amount by spraying, and then the cellulose fibers are heated to a crosslinking temperature to cause a crosslinking reaction.

  The first layer contains pulp fibers in addition to the hydrophilic bulky fibers. The reason why pulp fibers are contained in the first layer is to suppress a decrease in strength characteristics that are a concern due to the use of hydrophilic bulky fibers by the pulp fibers connecting the hydrophilic bulky fibers. In particular, when the content ratio of the hydrophilic bulky fibers is set to be larger than that of the pulp fibers in the first layer, the small bulk made between the pulp fibers in the high voids created between the hydrophilic bulky fibers occupying the majority. A structure in which the air gap is slightly mixed in the first layer is obtained, whereby the capillary force can be enhanced while maintaining the permeability.

  As the pulp fibers contained in the first layer, known pulp fibers can be used without any particular limitation. For example, softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), softwood bleached sulfite pulp (NBSP) ), Wood pulp such as thermomechanical pulp (TMP); bast fibers such as cocoon, cocoon, husk, etc .; non-wood pulp such as cocoon, bamboo, kenaf, hemp, etc., one of these alone or two of them A combination of the above 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 content mass ratio (hydrophilic bulky fiber / pulp fiber) of the hydrophilic bulky fiber and pulp fiber in the first layer is preferably 4/6 to 9/1 from the viewpoint of the balance between liquid diffusibility and strength characteristics. More preferably, it is 5/5 to 8/2. If there are too few hydrophilic bulky fibers with a fiber roughness of 0.30 mg / m or more, the bulkiness of the first layer will be insufficient, and the difference in liquid permeation rate between the first layer and the second layer will be reduced. There is a possibility that the diffusibility may be insufficient, and conversely, if there are too many hydrophilic bulky fibers, the strength of the first layer may be drastically reduced.

  In addition to the above-described hydrophilic bulky fibers and pulp fibers having a fiber roughness of 0.30 mg / m or more, the first layer can further contain heat-fusible adhesive fibers as fibers. The heat-fusible adhesive fiber is a fiber that melts and adheres to each other by heating. By including this fiber in the first layer, the bulky structure of the first layer is more stably maintained. The content of the heat-fusible adhesive fiber is preferably 10% by mass or less, more preferably 8% by mass or less, based on the dry mass of all the fibers in the first layer.

  Examples of the heat-fusible adhesive fibers include polyolefin fibers such as polyethylene, polypropylene, polyvinyl alcohol, polyacrylic acid and salts thereof, polyester fibers, polyethylene-polypropylene composite fibers, polyethylene-polyester composite fibers, and low melting point polyesters. Examples thereof include a polyester composite fiber, a polyvinyl alcohol-polypropylene composite fiber having a hydrophilic fiber surface, and a polyvinyl alcohol-polyester composite fiber. When using a composite fiber, any of a core-sheath type composite fiber and a side-by-side type composite fiber can be used. These heat-fusible adhesive fibers can be used alone or in combination of two or more. Examples of the hot-melt adhesive fiber preferably used in the present invention include polyvinyl alcohol and polyester.

  In addition to the various fibers described above, the first layer can further contain a dry paper strength enhancer. As the dry paper strength enhancer contained in the first layer, conventionally known ones can be used without particular limitation. For example, carboxymethyl cellulose (CMC) and its salt, polyacrylamide resin and its salt, cationized starch , Polyvinyl alcohol (PVA), etc., and one of these can be used alone or two or more can be used in combination. 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, and PVA are particularly preferable.

  As will be described later, when the first layer is produced by a wet papermaking method, a paper strength enhancer may be added to the first layer. A so-called internal addition method in which an enhancer is added, and a so-called external addition method in which a paper strength enhancer is applied to a fiber web obtained by making fibers from a paper material by various application methods such as coating, impregnation, and spraying. In the present invention, any addition method can be used. However, the first layer tends to generate paper dust and fluff due to containing hydrophilic bulky fibers. According to the method, since the yield of the paper strength enhancer may be reduced, the first layer is preferably provided with a paper strength enhancer (dry paper strength enhancer) by the external addition method.

  The content of the dry paper strength enhancer is preferably 0.1 to 5% by mass, more preferably 0.2 to 2% by mass, based on the dry mass of all the fibers in the first layer. If the content of the dry paper strength enhancer is too low, the significance of using the dry paper strength enhancer (prevention of paper dust and fluff, improvement of strength properties such as dry tensile strength) will be weakened, and the dry paper strength enhancer will be contained. If the rate is too high, the thin paper will harden (decrease in texture), and the paper will not 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. There is a risk of inviting.

  The first layer may contain components other than the above-described fibers (hydrophilic bulky fibers having a fiber roughness of 0.30 mg / m or more, pulp fibers, etc.) and a dry paper strength enhancer. Other components include, for example, wet paper strength enhancers such as epoxidized polyamide polyamine resin (PAE), fillers such as talc, dyes, color pigments, antibacterial agents, pH adjusters, yield improvers, water resistance agents, water proofing agents. Those generally used as papermaking raw materials and additives such as foaming agents are mentioned, and one of these can be used alone or in combination of two or more.

  The second layer contains specific pulp fibers having a fiber roughness of 0.10 to 0.20 mg / m. As described above, what is particularly important regarding the characteristics of the second layer is that the liquid permeation rate is slower than that of the first layer. From this viewpoint, in the present invention, the fibers constituting the second layer are the first fibers. A specific pulp fiber having a fiber roughness smaller than that of the constituent fibers (hydrophilic bulky fibers) of the layer is used so that the second layer does not become bulkier than the first layer. The fiber roughness of the specific pulp fiber contained in the second layer is preferably 0.12 to 0.20 mg / m, more preferably 0.15 to 0.20 mg / m. Moreover, the average fiber length of the specific pulp fiber contained in the second layer is preferably 1 to 3 mm, more preferably 2 to 2.8 mm, from the viewpoint of the texture of the thin paper.

  As the specific pulp fiber contained in the second layer, a pulp fiber having a fiber roughness in the above range can be used, and as this pulp fiber, a known pulp fiber can be used without particular limitation, for example, The same pulp fibers (NBKP etc.) contained in the first layer can be used. Therefore, in the present invention, the specific pulp fiber contained in the second layer and the pulp fiber contained in the first layer may be the same. A hydrophilic bulky fiber having a fiber roughness of 0.30 mg / m or more contained in the first layer is usually produced by subjecting the cellulose fiber to a specific treatment (treatment with a crosslinking agent, alkali treatment, etc.). The specific pulp fiber having a fiber roughness of 0.10 to 0.20 mg / m contained in the second layer usually does not require such specific treatment. Accordingly, NBKP or the like having a fiber roughness in the range of 0.10 to 0.20 mg / m can be used as the specific pulp fiber of the second layer as it is.

  In addition to the specific pulp fiber having a fiber roughness of 0.10 to 0.20 mg / m, the second layer may further contain other fibers having a fiber roughness outside the above range. However, the content rate of fibers other than the specific pulp fiber from the viewpoint of more reliably generating the liquid permeation rate difference from the first layer described above, thereby obtaining excellent liquid permeability and liquid diffusibility as a whole thin paper. Is preferably 30% by mass or less in the second layer, and more preferably 0% by mass, that is, only specific pulp fibers are used as the fibers in the second layer. The content of the specific pulp fiber is preferably 70 to 100% by mass, more preferably 80 to 100% by mass in the second layer.

  The freeness of the fibers contained in the second layer (if the fibers contained in the second layer are only specific pulp fibers, the freeness of the specific pulp fibers) is 450 to 700 ml, preferably 480 to 680 ml, more preferably Is 480-650 ml. Freeness is a value indicated by Canadian Standard Freeness (CSF) stipulated in JIS P8121, and is a value of beating of fibers (treatment of mechanically tapping and grinding fibers in the presence of water). It is a value indicating the degree. The beating of the fibers 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 the stock (slurry) in which the fibers are dispersed. Usually, the smaller the value of the freeness of the fiber, the stronger the degree of beating, the greater the damage of the fiber due to beating, and the more fibrillation proceeds. The fibers having the freeness in the above range (the specific pulp fibers) are easily entangled with each other because the fibrillation is in progress. Therefore, when the basis weight of the thin paper (second layer) is reduced, the fibers of the fibers Even if the number of interbonding points is reduced, the strength of each interfiber bond is higher than that of fibers in which the freeness exceeds 700 ml and relative fibrillation has not progressed. On the other hand, when the freeness is less than 450 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, the second layer containing fibers (specific pulp fibers) having a freeness of 450 to 700 ml can have good strength characteristics (tensile strength) and liquid permeability.

  The second layer further contains a wet paper strength enhancer in addition to the specific pulp fiber. As the wet paper strength enhancer contained in the second layer, conventionally known ones can be used without particular limitation. For example, epoxidized polyamide polyamine resin (PAE), urea-formalin resin, melamine-formalin resin, Aldehyde starch, polyethyleneamine, methylolated polyamide and the like can be mentioned, and one of 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 0.2 to 2% by mass, more preferably 0.5 to 1% by mass, based on the dry mass of all the fibers in the second layer. If the content of the wet paper strength enhancer is too small, the significance of using the wet paper strength enhancer (improvement of strength properties such as wet tensile strength) will be reduced. If the content of the wet paper strength enhancer is too high, the thin paper will be used. In addition to curing (decrease in texture), 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 attachment of the paper strength enhancer to the mesh drum during the production of the thin paper.

  The second layer may contain components other than the specific pulp fiber having a fiber roughness of 0.10 to 0.20 mg / m and the wet paper strength enhancer. Other components include, for example, dry paper strength enhancers such as CMC, fillers such as talc, dyes, color pigments, antibacterial agents, pH adjusters, yield improvers, water resistance agents, antifoaming agents, etc. What is used as a papermaking raw material and an additive is mentioned, These 1 type can be used individually or in combination of 2 or more types.

  The 1st layer which comprises the thin paper of this invention, and the 2nd layer superimposed on this can each be manufactured by a well-known wet papermaking method. The wet papermaking method has a stock preparation process for preparing a stock (slurry) made of an aqueous dispersion of fibers, and a paper making process for making a fiber web by drawing fibers from the stock and drying them. It is. 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 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.

  In the thin paper of the present invention, the first layer and the second layer are integrated. The method for integrating the first layer and the second layer is not particularly limited as long as both can be integrated. For example, the first layer and the second layer in a dry state separately produced by a wet papermaking method are used. Is used to obtain a laminated body, and press the laminated body through a pair of embossing rolls to integrate the two, or a method of integrating the two by a bonding means such as an adhesive or an adhesive. be able to. In the former method, the laminate may be pressed from the first layer side to the second layer side, or may be pressed in the opposite direction. In the thin paper obtained by the former method, a concave portion is usually formed in which the first layer and the second layer are integrally recessed.

  In the present invention, as a method for integrating the first layer and the second layer, the wet fiber webs of the first layer and the second layer obtained in the wet papermaking process are continuously integrated in the wet papermaking process. The method of making it preferable is. When both layers are integrated by such a method, the fibers of both layers are intertwined more closely, and the liquid moves smoothly between the two layers. Specific examples of the method for integrating the first layer and the second layer in the wet papermaking process include the following methods. That is, the slurry for forming the first layer is supplied to a paper machine to form a paper layer (fiber web) on the wire. Separately from this, the slurry for forming the second layer is supplied to another paper machine to form a paper layer (fiber web) on the wire. These paper layers (fiber webs) are picked up from the respective wires, overlapped with each other in a wet state, and then pressed and dehydrated and dried to obtain a thin paper in which the first layer and the second layer are integrated. It is done.

  Moreover, the following method is mentioned as another specific example of the method of integrating a 1st layer and a 2nd layer in a wet papermaking process. That is, the slurry for forming the first layer and the slurry for forming the second layer are respectively supplied onto the wires at once from two rows of papermaking nozzles to form a paper layer (fiber web) having a two-layer structure. Next, the paper layer (fiber web) is taken up from the wire, pressed and dehydrated, and dried to obtain a thin paper in which the first layer and the second layer are integrated.

  The thin paper of the present invention may have a pressed part that is pressed in the thickness direction from the first layer side toward the second layer side, and it is particularly preferable to have a plurality of the pressed parts. . The said to-be-pressed part can be formed by well-known embossing etc. In the pressed portion, at least the first layer side of the thin paper is a concave portion, and a portion corresponding to the concave portion on the second layer side protrudes in a convex shape depending on the embossing conditions and the like. The thin paper having the pressed portion is (1) in particular, scattering of paper dust caused by the first layer is effectively prevented, (2) the pressed portion (concave portion) and the portion not pressed (flat portion) ) And a mixture of a plurality of layers, a coarse and dense structure is formed in the surface direction of the thin paper, thereby enhancing the capillary force. (3) Strengthening the interfacial adhesion between the first layer and the second layer. It can produce effects such as

The thin paper of the present invention is set to have a relatively low basis weight from the viewpoint of being suitable for a core wrap sheet of a thin absorbent body, specifically, the first layer, the second layer, The total basis weight is 10 to 30 g / m ² , preferably 12 to 25 g / m ² , and more preferably 15 to 20 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 (particularly, the configuration of the second layer). 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 first layer is preferably 10-22 g / m ² , more preferably 10-18 g / m ² , and the basis weight of the second layer is preferably 8-15 g / m ² , more preferably 8 ˜12 g / m ² .

The basis weight of the thin paper (first layer, second layer) is measured as follows. After conditioning the sample (thin paper or first layer or second layer) under the conditions of JIS P8111, a 10 cm square (100 cm ² ) measurement piece is cut out from the sample, and the weight of the measurement piece is less than the decimal point. Measure with a two-digit balance and divide the measured value by the area to calculate the basis weight of the measurement piece. 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. When the thin paper is formed by integrating the first layer and the second layer in a stacked state, the first layer is peeled off from the thin paper, and the basis weight (first weight) of the remaining second layer is determined according to the above procedure. The basis weight of the first layer alone is calculated by subtracting the basis weight of the second layer alone from the basis weight of the thin paper separately measured according to the above procedure. .

  The thin paper of the present invention has crepes (crepe-like wrinkles), and the crepe rate is set to 5 to 20%. 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 having a length of 200 mm in the length direction (conveying direction when manufacturing the measurement target sheet, MD) and a width of 100 mm in the width direction (direction orthogonal to MD, CD) is cut out from the measurement target sheet (thin paper). 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 MD length C after immersion for 10 minutes is 220 mm, the crepe rate of the sheet calculated by the above formula is 10%. It is.

  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 20%, preferably 8 to 18%, more preferably 10 to 15% from the viewpoint of the balance between liquid permeability and strength characteristics. .

  The thin paper of the present invention having the above-described structure preferably has a liquid permeation time measured by the following method of 1 to 4 seconds, more preferably 1 to 3 seconds, and the liquid permeation time of the first layer and the first time. The difference from the liquid permeation time of the two layers is preferably 0.5 to 3 seconds, more preferably 0.5 to 2 seconds. The liquid permeation time is an index of the liquid permeation rate, and the shorter the liquid permeation time, the faster the liquid permeation rate, and the higher the liquid permeation rate. The thin paper having the liquid permeation time in the above range (1 to 4 seconds) is excellent in liquid permeability. 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 such a case, it is possible to allow urine or other excretory fluid to quickly permeate without being stored between the wearer's skin and the face sheet, and to be absorbed quickly by the absorbent core. Improvement can be expected. In addition, as described above, particularly with respect to the improvement of the liquid diffusibility of the entire thin paper, the interface between the first layer and the second layer or the vicinity thereof due to the difference in the liquid permeation rate between the first layer and the second layer ( The diffusion in the surface direction of the liquid in the vicinity of the interface in the first layer is important, and from the viewpoint of more surely expressing the liquid diffusion in or near the interface, the first layer and the second layer The liquid permeation time difference is preferably in the above range (0.5 to 3 seconds).

<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 sample S (thin paper) Or the first layer or the second layer) 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 manner, with the measurement sample S sandwiched and fixed between the upper and lower cylinders 91 and 92, a physiological saline (aqueous solution having a sodium chloride concentration of 0.9% by mass) indicated by the symbol W in FIG. 40 g ± 1 g is supplied. The supplied physiological saline passes through the measurement sample S or is absorbed by the measurement sample S and disappears from the upper cylinder 91. The time from when the physiological saline starts to be supplied until the physiological water surface reaches the same position as the surface of the measurement sample S (the surface on the upper cylinder 91 side) is taken as the liquid permeation time.

  When measuring the liquid permeation time for each of the first and second layers of thin paper, the first and second layers are peeled off from the thin paper and used as a measurement sample, but each layer can be peeled off. If it is difficult, separate sheets corresponding to the first layer and the second layer are prepared, and the prepared sheets are used as measurement samples. The sheet to be prepared separately has the same composition as the first layer or the second layer in thin paper, and in addition to mechanical conditions (papermaking conditions) such as papermaking speed, press roll pressure, touch roll pressure, pulp slurry concentration, thickness, density, water content The sheet characteristics such as rate and crepe rate should be the same as much as possible.

  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 0.4 g / 30 sec · 15 mm. The fact that the amount of water absorbed by the Krem in the thin paper is in such a range is largely due to the formation of a highly voided structure in the interior, and the formation of the highly voided structure is particularly the case of the hydrophilic bulky fibers of the first layer. The place by use is big. A thin paper having a Krem water absorption in such a range has practically sufficient liquid permeability and liquid diffusibility. 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 the sheet, 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.

  The dry tensile strength in the transport direction (Machine Direction, abbreviated as MD) of the thin paper of the present invention is preferably 600 cN / 25 mm or more, more preferably 650 to 1500 cN / 25 mm, and the thin paper of the present invention. The wet tensile strength in the direction perpendicular to MD (Cross machine Direction, abbreviated as CD) is preferably 50 cN / 25 mm or more, more preferably 60 to 120 cN / 25 mm. A thin paper having a dry tensile strength and a wet tensile strength within the above ranges 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 and use of the absorbent article. In particular, the fact that the dry tensile strength of the MD of the thin paper is in the above range mainly contributes to the prevention of inconvenience that the thin paper is torn due to a sudden tension change in the transport tension and the paper splicing during the manufacture of the thin paper. The fact that the wet tensile strength of CD is in the above range is mainly due to movement or friction after the body fluid excretion of the wearer (such as infants) of the absorbent article when thin paper is used as the core wrap sheet in the absorbent article. This contributes to the prevention of inconvenience that the core wrap sheet is torn and the absorbent core forming material (wood pulp, superabsorbent resin, etc.) comes out on the top sheet. The fact that the dry tensile strength of the MD of the thin paper and the wet tensile strength of the CD are in the above ranges are largely due to the presence of the second layer, and the excellent tensile strength characteristics of the second layer are the fibers in the second layer ( This is largely due to the fact that the freeness of the specific pulp fibers is in the specific range and that the second layer contains a wet paper strength enhancer. 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.

<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 (Shimadzu Autograph AG-1kN) without tension so that the CD 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 of these values is taken as the wet tensile strength of CD.

  The thin paper of the present invention has good strength characteristics (tensile strength) and excellent liquid permeability and liquid diffusibility, 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. The thin paper of the present invention is particularly effective when the excretory fluid has a relatively low viscosity such as urine, and is therefore particularly useful as a core wrap sheet in a disposable diaper.

  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 of the absorbent core. In that case, between the surface sheet and the absorbent core, the surface sheet and the first layer of the thin paper of the present invention face each other (the absorbent core and the second layer of the thin paper of the present invention face each other). By arranging the thin paper in this manner, the first layer first comes into contact with the liquid (body fluid such as urine). 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]
The hydrophilic bulky fiber and the specific pulp fiber (pulp fiber A) are mixed so that the content ratio of both fibers (hydrophilic bulky fiber / specific pulp fiber) is 80/20 to obtain an aggregate of fibers, For the first layer, the aggregate is uniformly dispersed in water to prepare a slurry (paper material) having a fiber concentration of 2% by mass, the slurry is subjected to a beating machine, and the freeness of the aggregate is adjusted to 820 ml. A slurry was obtained.
Also, a specific pulp fiber (pulp fiber A) is uniformly dispersed in water to prepare a slurry (paper material) having a fiber concentration of 2% by mass, and the slurry is subjected to a beating machine to adjust the freeness of the specific pulp fiber to 500 ml. Then, a predetermined amount of PAE is added as a wet paper strength enhancer, and after sufficient stirring so that each component is uniform, a predetermined amount of PVA aqueous solution containing PVA as a dry paper strength enhancer is further added, The mixture was sufficiently stirred so that each component was uniform to prepare a slurry for the second layer having a solid concentration of 0.1% by mass.
The slurry for the first layer and the slurry for the second layer are respectively spread on a wire mesh paper making wire having a wire opening diameter of 90 μm (166 mesh), a paper layer is formed on the wire mesh paper making wire, and a suction box is used. After dehydrating the paper layer at a rate of 6 ml / (cm ² · sec), the wet first paper layer obtained from the first layer slurry and the wet second paper layer obtained from the second layer slurry. The two paper layers are stacked in a wet state, then pressed and dehydrated, further dried with a dryer, and the paper layer is peeled off from the dry surface with a doctor blade, and the crepe is applied with a speed ratio of the dryer and winding. Granted. The two-layered thin paper (crepe paper) thus obtained was used as the sample of Example 1.

[Examples 2 to 5 and Comparative Example 3]
Except for changing the composition and the like as shown in Table 1 below, thin paper (crepe paper) having a two-layer structure was produced in the same manner as in Example 1, and these were used as samples of Examples 2 to 5 and Comparative Example 3. In Example 4, instead of the specific pulp fiber (pulp fiber A) as a constituent fiber of the first layer, an aggregate of fibers is obtained using a pulp fiber B that is not a specific pulp fiber, and the aggregate is submerged in water. A slurry (paper) having a fiber concentration of 2% by mass was prepared by uniformly dispersing the slurry, and the slurry was subjected to a beating machine to adjust the freeness of the aggregate to 780 ml. Further, in contrast to Example 1, in Comparative Example 3, a layer made of only specific pulp fibers (pulp fibers A) is formed as a first layer (a layer in contact with the liquid first), hydrophilic bulky fibers and specific pulp fibers (pulp). The layer made of the fiber A) is the second layer, and the configuration itself is the same as that of the first embodiment.

[Comparative Example 1]
Hydrophilic bulky fibers and pulp fibers are mixed so that the mass ratio of both fibers (hydrophilic bulky fibers / pulp fibers) is 80/20 to obtain an aggregate of fibers, and the aggregate is uniformly in water. The slurry was dispersed to prepare a slurry (paper material) having a fiber concentration of 2% by mass, and the slurry was subjected to a beating machine to adjust the freeness of the aggregate to 820 ml. While diluting this slurry, a predetermined amount of PAE was added as a wet paper strength enhancer, and after sufficiently stirring each component to be uniform, the PVA aqueous solution containing PVA as a dry paper strength enhancer was further added. A predetermined amount was charged and stirred sufficiently so that each component was uniform, to prepare 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 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 single-layered thin paper (crepe paper) thus obtained was used as a sample of Comparative Example 1. In Tables 1 and 2 below, the composition of the “single layer” of Comparative Example 1 is listed in the column for the first layer.

[Comparative Example 2]
The specific pulp fiber (pulp fiber A) is uniformly dispersed in water to prepare a slurry (paper material) having a fiber concentration of 2% by mass. The slurry is subjected to a beating machine to reduce the freeness of the specific pulp fiber (pulp fiber A). Adjusted to 500 ml. Further, while diluting the slurry, a predetermined amount of PAE was added as a wet paper strength enhancer, and the mixture was sufficiently stirred so that each component was uniform, thereby preparing 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 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) having a single layer structure thus obtained was used as a sample of Comparative Example 2. In Tables 1 and 2 below, the composition and the like of the “single layer” of Comparative Example 2 are listed in the second layer column.

In Table 1 below, the numerical value (mass%) in the fiber column means the ratio (mass basis) of the fiber to the total fibers in the first layer or the second layer, and is a component other than the fiber (additive). The numerical value (mass%) in a column means the ratio (mass basis) of the said component with respect to the dry mass of all the fibers in a 1st layer or a 2nd layer. Moreover, the detail of each component in following Table 1 is as follows.
Hydrophilic bulky fiber: HBA with a fiber roughness of 0.32 mg / m.
Pulp fiber A (specific pulp fiber): NBKP (trade name “Cariboo”, manufactured by Cariboo Pulp and Paper Company) having a fiber roughness of 0.15 mg / m.
Pulp fiber B (non-specific pulp fiber): LBKP (trade name “Riau”, manufactured by Asia Pacific Resources International Limited) having a fiber roughness of 0.06 mg / m.
Paper strength enhancer: PVA (Dry paper strength enhancer, Kuraray Co., Ltd., trade name “VPB107-1”), CMC (Dry paper strength enhancer, Daiichi Pharmaceutical Industries, trade name “WS-C”) PAE (wet paper strength enhancer, manufactured by Seiko PMC Co., Ltd., trade name “WS4030”).

[Evaluation]
About each sample (thin paper) of an Example and a comparative example, liquid permeation | transmission time, Klem water absorption, the dry tensile strength of MD, and the wet tensile strength of CD were measured by the said method, and the maximum absorption amount was measured by the following measuring method. The results are shown in Table 2 below.

<Measurement method of maximum absorption>
A rectangular absorbent core (10 cm long and 35 cm wide) obtained by mixing and laminating 7 g of pulp and 10 g of superabsorbent resin particles (manufactured by Sundia, IM997), two large and small samples with different dimensions only ( The absorbent is obtained by coating with a thin paper, and the absorbent is further interposed between the top sheet (air-through nonwoven fabric having a basis weight of 30 g / m ² ) and the back sheet (a moisture permeable film having a basis weight of 20 g / m ² ). The sample that was interposed was used as a measurement sample. In the measurement sample, the top sheet and the back sheet had the same shape and dimensions, and the constituent members were joined to each other with a hot-melt adhesive. The covering of the absorbent core with two large and small samples was as follows. That is, the entire surface of the absorbent core facing the surface sheet (skin facing surface) is covered with a small sample, and the entire surface of the absorbent core facing the back sheet (non-skin facing surface) is a large sample. The excess portion of the large sample (the portion not used for coating the absorbent core) was rolled up on the small sample covering the skin facing surface of the absorbent core. When the two large and small samples have a two-layer structure consisting of a first layer and a second layer, the small sample is placed so that the first layer faces the topsheet (the second layer is the absorbent core and The large sample is placed so that the first layer faces the absorbent core (placed so that the second layer forms the outer surface of the absorber).

  Then, on the slope of the test bench having a smooth slope with an inclination of 20 °, the measurement sample prepared by the above procedure is arranged such that the back sheet faces the slope and the longitudinal direction of the measurement sample is the slope of the slope. 40 g of physiological saline was injected at an injection rate of 5 g / sec into the center in the width direction of the site 11 cm away from the short side located on the upper side of the slope of the measurement sample. To do. After 5 minutes from the start of physiological saline injection, 40 g of physiological saline is injected again into the physiological saline injection site of the measurement sample at an injection rate of 5 g / second. Repeat until the leak is confirmed. The amount of saline injected at the time when it is visually confirmed that the saline leaks from the short side below the slope of the measurement sample is defined as the target maximum absorption amount. The larger the maximum absorption value, the larger the absorption capacity and the higher the evaluation.

  As shown in Table 2, each of the thin papers of the examples has a Krem water absorption of 0.2 g / 30 sec · 15 mm or more. From this, the thin papers of the examples have a high void structure formed therein. It is obvious that the liquid permeability and liquid diffusibility are excellent, and this excellent liquid permeability and liquid diffusibility is supported by the relatively large value of the maximum absorption amount. In addition, the thin papers of the examples all have a dry tensile strength of MD of 600 cN / 25 mm or more and a wet tensile strength of CD of 50 cN / 25 mm or more, and are excellent not only in liquid permeability and liquid diffusibility but also in strength characteristics. It is obvious. On the other hand, since both Comparative Examples 1 and 2 have a single-layer structure, the Comparative Example 1 has strength characteristics compared to the specific example of the two-layer structure including the first layer and the second layer. The result is inferior, and in Comparative Example 2, the liquid permeability and the liquid diffusibility are inferior, and both characteristics cannot be realized. Further, in Comparative Example 3, although the configuration itself of the thin paper is the same as Example 1, in the above <Measurement method of maximum absorption amount>, in contrast to Example 1, only from the specific pulp fiber (pulp fiber A). Since the layer consisting of the first layer (the layer in contact with the liquid first) and the layer consisting of the hydrophilic bulky fiber and the specific pulp fiber (pulp fiber A) is the second layer, the permeation and diffusion of the liquid is not performed smoothly, and therefore the maximum The result was inferior in absorption.

91, 92 Cylinder 93 Clip 94 Packing S Measurement sample W Saline

Claims (7)

A thin paper comprising a first layer and a second layer overlying the first layer, wherein the first layer is first used to contact the liquid,
The first layer contains hydrophilic bulky fibers and pulp fibers having a fiber roughness of 0.30 mg / m or more,
The second layer contains a specific pulp fiber having a fiber roughness of 0.10 to 0.20 mg / m and a wet paper strength enhancer, and the freeness of the fiber contained in the second layer is 450 to 700 ml. Yes,
A thin paper having a total basis weight of 10 to 30 g / m ² and a crepe rate of 5 to 20% between the first layer and the second layer. The liquid permeation time measured by the following method of the thin paper is 1 to 4 seconds, and the difference between the liquid permeation time of the first layer and the liquid permeation time of the second layer is 0.5 to 3 seconds. The thin paper according to claim 1.
<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 measurement sample and disappears from the upper cylinder. The time from the start of the physiological saline supply until the physiological water surface becomes the same position as the surface of the measurement sample is measured, and this time is defined as the liquid permeation time.   The thin paper according to claim 1 or 2, wherein the water absorption of the thin paper is 0.2 g / 30 sec · 15 mm or more.   The thin paper according to any one of claims 1 to 3, wherein the dry tensile strength in the transport direction during the manufacture of the thin paper is 600 cN / 25 mm or more, and the wet tensile strength in the direction orthogonal to the transport direction is 50 cN / 25 mm or more. .   The thin paper according to any one of claims 1 to 4, wherein a mass ratio of the hydrophilic bulky fibers and the pulp fibers in the first layer is the former / the latter = 4/6 to 9/1.   The said 1st layer is a thin paper as described in any one of Claims 1-5 containing 1-10 mass% of heat bondable adhesive fibers with respect to all the fibers in this 1st layer.   The thin paper according to any one of claims 1 to 6, wherein the first layer contains a dry paper strength enhancer.

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