JP4494509B2 - Absorber and absorbent article - Google Patents

Description

  The present invention relates to an absorbent body used for absorbent articles such as sanitary napkins and absorbent articles using the absorbent body, and more particularly, an absorbent body that can easily remove redness such as menstrual blood absorbed by washing with water after use. And an absorbent article.

  As absorbent articles such as sanitary napkins and disposable diapers, absorbent bodies containing a water-absorbing polymer are known. As the water-absorbing polymer, water-absorbing polymers having carboxy groups and / or carboxylate groups such as polyacrylic acid-based water-absorbing polymers are mainly used, and various techniques for improving the water-absorbing polymers have been proposed. Yes.

  For example, Patent Document 1 discloses a technique for improving a water-absorbing polymer, in which an unneutralized carboxy group of a water-absorbing resin (water-absorbing polymer) having a predetermined degree of neutralization (50 to 85 mol%) is substituted with an alkali metal and / or Alternatively, a method of further neutralization using a water-soluble alkali compound containing ammonium and adjusting to a predetermined degree of neutralization (50.1 to 95 mol%) is described. According to the method described in Patent Document 1, the amount of water absorption (water absorption ratio) under pressure of the water-absorbing polymer, which is one of the important performances in absorbent article applications, is increased, and the water absorption under pressure is improved. ing.

  By the way, for some people represented by the Malay people whose main residence area is Indonesia, Malaysia, etc., it is customary to wash used sanitary napkins with water and wash away absorbed menstrual blood There is. Conventionally, sanitary napkins that have been mainly used in Malay ethnic spheres are composed of cloth napkins (for example, Patent Documents 2 to 4) and water-absorbing materials that mainly contain pulp fibers and do not contain water-absorbing polymers. Therefore, it can be washed with water, and absorbed menstrual blood and the like can be washed away with water. On the other hand, the sanitary napkin containing a water-absorbing polymer as described in Patent Document 1 adheres firmly to the water-absorbing polymer with coloring components such as hemoglobin in menstrual blood. It was difficult to wash away blood, and washing with water was difficult.

  However, a sanitary napkin that does not contain a water-absorbing polymer as described above has poor menstrual blood absorption / retention performance, and may cause so-called liquid return in which, for example, body fluid absorbed on the surface of the absorbent material oozes out. Therefore, in a conventional sanitary napkin that can be washed with water and does not contain a water-absorbing polymer, the use of a large amount of pulp fibers compensates for the lack of absorption performance. However, such sanitary napkins become thick due to the bulkiness of the pulp fibers, are particularly bulky when folded and packaged, are inconvenient to carry, and have a poor fit.

  At present, the present applicant has not found any prior art documents that have raised the above-mentioned problems relating to water washing of napkins. However, people who have a habit of cleaning napkins are thought to exist in areas other than the above-mentioned residential areas, and sanitary napkins that contain a water-absorbing polymer and are easy to wash are widely used in women's lifestyles. It is considered that it has the potential to greatly affect

Japanese Patent No. 3461860 JP 2006-288681 A JP 2001-353182 A JP 2004-337204 A

  Therefore, the subject of this invention is providing the absorber and absorbent article which are easy to wash with water, while containing a water absorbing polymer.

  As a result of various studies to solve the above problems, the present inventors have found that the water-absorbing polymer having a carboxy group and / or a carboxylate group such as a polyacrylic acid-based water-absorbing polymer as a water-absorbing polymer contained in the absorber. By using a polymer whose neutralization degree and centrifugal retention amount (water absorption ratio) are controlled within a specific range, the redness of the absorber due to absorbed menstrual blood and the like is greatly reduced by washing the absorber with water. And it was found that the absorption performance can be maintained. It was also found that the redness of absorbed menstrual blood increases when the amount of centrifugal retention (water absorption ratio) of the water-absorbing polymer increases.

  The present invention has been made on the basis of the above findings, and has a carboxy group and / or a carboxylate group, has a neutralization degree of 75 mol% or more, and has a centrifugal retention amount of 5 to 20 g / g based on JIS K 7223. The above-mentioned problems have been solved by providing an absorbent containing a functional polymer.

  The present invention also relates to an absorber comprising a water-absorbing polymer, wherein the absolute value of the difference between the zeta potential of the water-absorbing polymer in ion-exchanged water and the zeta potential of bovine hemoglobin in ion-exchanged water is 30 mV or less. By providing, the above-mentioned problems are solved.

  Further, the present invention contains a water-absorbing polymer, the water-absorbing polymer has a carboxy group and / or a carboxylate group and is neutralized with a neutralizing agent containing an alkali metal, and the degree of neutralization is The problem is solved by providing an absorbent body having an alkali content of 75 mol% or more and in which the alkali metal is uniformly distributed throughout the water-absorbing polymer.

  Moreover, this invention solves the said subject by providing the absorbent article which comprises the said absorber.

  The absorbent body and absorbent article of the present invention can be easily washed with water despite containing a water-absorbing polymer, and can remove redness caused by blood such as absorbed menstrual blood. It is suitable for people who have a habit of washing the article with water and then disposing it. Moreover, since the absorbent body and absorbent article of the present invention contain a water-absorbing polymer, the absorption performance is good, for example, liquid return can be effectively suppressed. Furthermore, since the thickness can be designed to be thin, it is possible to provide an absorbent article that is not bulky and has excellent portability and wearing feeling.

FIG. 1 is a perspective view showing the skin contact surface side (surface sheet side) of one embodiment of the sanitary napkin of the present invention. 2 is a cross-sectional view schematically showing a cross section taken along line XX of FIG. FIG. 3 is a perspective view schematically showing one embodiment of the absorbent body of the present invention. FIG. 4 is a perspective view schematically showing another embodiment of the absorbent body of the present invention. FIG. 5 is a perspective view schematically showing still another embodiment of the absorbent body of the present invention. 6 is a cross-sectional view schematically showing a cross-section in the width direction of the polymer sheet used in the absorbent body shown in FIG. FIG. 7 is a view corresponding to FIG. 2 showing another embodiment of the sanitary napkin of the present invention. FIG. 8 is a view corresponding to FIG. 2 of the sanitary napkin of Example 5.

  Hereinafter, the absorbent body of the present invention will be described together with the absorbent article of the present invention including the absorbent body based on a preferred embodiment thereof with reference to the drawings. The perspective view of the sanitary napkin which is one Embodiment of the absorbent article of this embodiment is shown by FIG. 2 is a cross-sectional view taken along line XX in FIG.

  The sanitary napkin 1 (hereinafter also referred to as napkin 1) of the present embodiment includes a front surface layer, a back surface layer, and an absorption layer that is disposed between both layers and contains a water-absorbing material. More specifically, the napkin 1 has a shape that is long in one direction as shown in FIG. 1, a top sheet 2 as a liquid-permeable surface layer, a back sheet 3 as a liquid-impermeable back layer, And the absorber 4 as a liquid holding | maintenance absorption layer arrange | positioned between the both sheets 2 and 3 is comprised. The absorbent body 4 has a shape that is long in one direction, and the longitudinal direction of the absorbent body 4 coincides with the longitudinal direction of the napkin 1 so that the absorbent body 4 is disposed at the center in the width direction of the napkin 1.

  As shown in FIG. 2, the top sheet 2 covers the whole area of the skin contact surface of the absorber 4, and the back sheet 3 covers the whole area of the non-skin contact surface of the absorber 4. The top sheet 2 and the back sheet 3 are joined to each other at an extended portion extending outward from the peripheral edge of the absorber 4 to form an end seal portion 6. An adhesive is applied on the non-skin contact surface of the back sheet 3 to form a fixing portion (not shown) for fixing the napkin 1 to shorts or the like. The top sheet 2 can be made of the same material as that conventionally known. For example, a hydrophilic nonwoven fabric or a perforated film is used. The back sheet 3 is made of, for example, a liquid-impermeable film sheet, and the liquid-impermeable film sheet may have water vapor permeability.

  In the present specification, the “longitudinal direction” is a direction along the long side direction of the absorbent article or its constituent members, and the “width direction” is a direction orthogonal to the longitudinal direction. Further, the “skin contact surface” is a surface of the absorbent article or a component thereof that faces the wearer's skin when the absorbent article is worn, and the “non-skin contact surface” refers to the absorbent article or its It is a surface which is directed to the underwear side (the side opposite to the wearer's skin side) when the absorbent article is worn in the constituent member.

  The absorbent body 4 of the present embodiment includes thin absorbent sheets 4a and 4b containing a water-absorbing polymer or fiber. More specifically, the absorbent body 4 has a structure in which two absorbent sheets 4a and 4a are overlapped to form a laminate, and another absorbent sheet 4b and 4b is overlapped on the upper and lower surfaces of the laminate. It consists of a laminate of four thin absorbent sheets. The absorbent sheet 4a and the absorbent sheet 4b have the same composition and differ only in dimensions, and the absorbent sheet 4a positioned inward in the thickness direction of the absorbent body 4 absorbs in the thickness direction outward. The dimension (length in the longitudinal direction and width direction) in plan view is smaller than that of the conductive sheet 4b. Since the absorbent body 4 has such a configuration, the absorption capacity at the center of the product is high, so that menstrual blood hardly spreads over the entire napkin, and a narrow range of washing is sufficient. Further, the absorbent body 4 is difficult to twist while the napkin is worn, and the absorbent body 4 is not easily biased when the napkin is washed, so that it is easy to squeeze. In addition, a composition may differ between the absorbent sheet 4a and the absorbent sheet 4b, and the arrangement | positioning form (order of lamination | stacking) of the absorbent sheets 4a and 4b may be changed.

  The absorber 4 may be substantially entirely covered with a covering sheet (not shown). When substantially the entire absorber is covered with a covering sheet, it is particularly effective for improving the shape stability of the absorber and preventing the water-absorbing polymer from falling off. The form of covering the absorbent body with the covering sheet is not particularly limited. For example, the form in which the upper surface (skin contact surface) and the left and right side faces of the absorbent body are covered with the covering sheet, and in addition to these faces, the absorbent body The form by which the lower surface (non-skin contact surface) is covered with a covering sheet.

  When the absorbent body 4 is coated with the covering sheet, extreme movement and dropping off of the water-absorbing polymer contained in the absorbent body 4 can be effectively prevented during wearing or washing of the absorbent article. . Furthermore, since the handling property as the absorber 4 as a whole becomes good, it can be easily transported alone. Moreover, since it can be easily cut or cut into a desired shape, an absorbent body corresponding to the shape of the absorbent article can be easily produced.

  Moreover, the absorber 4 and the covering sheet may be joined by a predetermined means. By joining both, the rigidity as the whole absorber 4 coat | covered with the coating sheet increases, and handling property becomes still more favorable by it. As a means for joining the absorbent body and the covering sheet, for example, in addition to bonding with an adhesive or heat fusion, embossing performed on a normal sanitary napkin (absorbing body from above the covering sheet or the top sheet 2) 4 is formed).

  As the covering sheet, a material having a sufficient strength to prevent the water-absorbing polymer from dropping off and a material that does not hinder the permeation of excreted liquid is appropriately used. As the covering sheet, for example, a hydrophilic fiber sheet, a perforated film or the like is used, and as this hydrophilic fiber sheet, for example, paper such as tissue paper or various nonwoven fabrics (spunbond nonwoven fabric, spunbond-meltblown-spunbond nonwoven fabric). Spunbond-meltblown-meltblown-spunbond nonwoven fabric, thermal bond nonwoven fabric, needle punch nonwoven fabric, spunlace nonwoven fabric, airlaid nonwoven fabric, spunlace nonwoven fabric containing hydrophilic fibers such as acrylic and rayon, etc.). These nonwoven fabrics may be subjected to a hydrophilic treatment or a hole opening treatment as necessary, and may further be formed with slits, or may be subjected to a softening process such as embossing. Examples of the constituent fibers of these nonwoven fabrics include fibers using a thermoplastic resin such as polyethylene, polypropylene, and polyethylene terephthalate alone, or composite fibers using these resins. Moreover, hydrophilic fibers, such as rayon, cotton, lyocell, tencel, acetate, and natural pulp, can coexist in these nonwoven fabrics.

  Examples of the absorbent sheets 4a and 4b include an absorbent sheet described in [Embodiment of the invention] of JP-A-9-156014. In addition, a sheet in which the water-absorbent polymer is fixed between two thin sheets of paper due to the adhesive or the water-absorbent polymer when wet (including a laminated structure in which a plurality of layers of fiber assemblies are laminated, A sheet in which a water-absorbing polymer is interposed between one of the layers in the laminated structure); a water-absorbing polymer is dispersed at the time of manufacturing the nonwoven fabric, and the water-absorbing polymer is sprayed on the previously manufactured nonwoven fabric at the same time A sheet in which the water-absorbing polymer is immobilized; a sheet in which a water-absorbing polymer is directly polymerized and immobilized on a fiber assembly produced by a known card method or the like is preferably used as a thin absorbent sheet.

  Further, the absorbent body 4 is not limited to the structure including the absorbent sheets 4a and 4b described above, and for example, a conventionally used mixed product of water absorbent polymer and pulp fiber or a water absorbent polymer. And a pulp fiber laminate and the following absorbers A to C can also be used. The following absorbers A to C each have a laminated structure formed by laminating a plurality of layers made of fiber assemblies, and an absorption in which a water-absorbing polymer is interposed between one of the layers in the laminated structure. Is the body.

  Absorbent body A: an absorbent body in which the water-absorbing polymer 41 is wrapped with one fiber sheet 40 (see FIG. 3). The absorbent body A shown in FIG. 3 has a rectangular shape in plan view, and is incorporated into the napkin 1 with its longitudinal direction coinciding with the longitudinal direction of the napkin 1. A non-existing region 50 of the water-absorbing polymer 41 is formed at the center in the width direction of the absorbent body A. The non-existing area 50 has a linear shape extending in the longitudinal direction of the napkin 1 in plan view, and extends over substantially the entire length of the absorbent body A in the longitudinal direction. The non-existing area 50 is a concave portion in which one surface side of the absorber A is recessed in the thickness direction. When the absorbent body A is incorporated into the napkin 1, the recess (dent) may be directed to the skin contact surface side of the napkin 1 or may be directed to the non-skin contact surface side. The absorber A can be manufactured as follows, for example. The water-absorbing polymer is applied so that the non-existing area 50 is formed in the central region sandwiched between both sides of the fiber sheet by spreading the water-absorbing polymer in a stripe shape on one surface of the vertically long fiber sheet. Scatter. And the absorber A is obtained by wrapping the disperse | distributed water absorbing polymer in the both sides of this fiber sheet. As the fiber sheet 40, a sheet containing pulp fiber, synthetic fiber, or the like can be used, and examples thereof include paper and nonwoven fabric. Moreover, as the fiber sheet 40, the hydrophilic sheet mentioned later can also be used.

  By adopting the absorbent body A, the absorption performance can be improved by the effective use of the absorbent body, and the drainage of the washing water can be enhanced to enable rapid washing. Absorber A has a non-existing region of the water-absorbing polymer in the center portion in the width direction, and the rigidity in the center portion in the width direction is lower than in other parts, so that the wearability is improved. It is done.

  Absorbent body B: an absorbent body in which a water-absorbing polymer 41 and a synthetic fiber nonwoven fabric 45 are interposed between two fiber sheets 40 (see FIG. 4). The absorbent body B shown in FIG. 4 has a rectangular shape in plan view, and is incorporated into the napkin 1 with its longitudinal direction coinciding with the longitudinal direction of the napkin 1. The water-absorbing polymer 41 in the absorbent body B is supported on the nonwoven fabric 45. That is, the water-absorbing polymer 41 enters the space formed by the constituent fibers (synthetic fibers) of the non-woven fabric 45, and even if stress is applied to the non-woven fabric 45 from the outside, extreme movement and dropout are unlikely to occur. .

  Adoption of the absorbent body B suppresses the movement of the water-absorbing polymer mainly due to the action of the nonwoven fabric, suppresses the twist of the absorbent body that occurs when the napkin is squeezed during wearing or washing, and exhibits stable absorption characteristics. As a result, the cleaning water can be easily replaced.

  Absorbent body C: an absorbent body including a polymer sheet 46 in which a water-absorbing polymer 41 is interposed between two fiber sheets 40, 40, and absorbs water over at least one side of the polymer sheet 46. Absorber in which the polymer 41 is not interposed, the polymer sheet 46 is bent at a fold line substantially parallel to the one side portion, and the one side portion is located at the center in the width direction of the absorber ( See Fig. 5. Fig. 6 is a schematic cross-sectional view in the width direction orthogonal to the longitudinal direction of the polymer sheet 46. The absorbent body C shown in FIG. 5 has a rectangular shape in plan view, and is incorporated into the napkin 1 with its longitudinal direction coinciding with the longitudinal direction of the napkin 1. The polymer sheet 46 in the absorbent body C does not include the water-absorbing polymer 41 over the entire longitudinal side portions 46s and 46s, and is C-shaped in a cross-sectional view in the width direction as shown in FIG. The both side portions 46s, 46s in the longitudinal direction are respectively located in the center portion in the width direction of the absorbent body C. The longitudinal side portions 46s and 46s may be abutted as shown in FIG. 5, or one may be overlaid on the other. Further, when the absorbent body C is incorporated into the napkin 1, both side portions 46s, 46s in the longitudinal direction of the polymer sheet 46 which are abutted or overlapped may be directed to the skin contact surface side of the napkin 1, and non-skin contact You may face to the surface side.

  Since the absorbent body C has a relatively high liquid permeability in the thickness direction, the use of the absorbent body C increases the drainage of the washing water and enables rapid cleaning.

  As other embodiment of the absorber 4, the absorber (henceforth the absorber D) as described in Unexamined-Japanese-Patent No. 2006-110329 or Unexamined-Japanese-Patent No. 2007-283086 is mentioned, for example. The absorber D is an absorber in which a water-absorbing polymer is supported on a fiber web. In the absorbent body D, the water absorbent polymer is entangled in the fiber gap of the long fiber in the fiber web or the long fiber is cut to become a short fiber, or the water absorbent polymer is fixed to the fiber gap by hot melt or the like. Yes. In the absorbent body D, the crimp rate (JIS L0208) of the constituent fibers (long fibers) is preferably 10 to 90%, more preferably 10 to 60%, and still more preferably 10 to 50%. Since the long fibers are crimped, the absorbent body D is easily deformed flexibly as a whole, and when the absorbent body D is incorporated into an absorbent article, it is deformed into a wearable fit or concave shape. Therefore, it is possible to improve the deformability to the concave shape when improving the leak-proof property. In addition, the adoption of the absorbent body D allows the water-absorbing polymer to easily get entangled in the constituent fibers of the absorbent body D even if a hand-holding operation is performed during cleaning of the absorbent article, so that the water-absorbing polymer flows out of the article during the cleaning. Is prevented. The crimp of the long fiber and the short fiber in the absorbent body D may be two-dimensional or three-dimensional. The crimp rate of the long fiber is defined as a percentage of the difference between the length A when the long fiber is stretched and the length B of the original long fiber before stretching, to the length A: Is calculated from Crimp rate (%) = {(A−B) / A} × 100 The measurement was performed at 23 ± 2 ° C. and humidity of 50 ± 5%, and the sample was stored in the same environment for 24 hours or more before measurement. Measure with

  The absorber 4 preferably contains a specific water-absorbing polymer (hereinafter also referred to as a water-absorbing polymer A) as a water-absorbing material. The main effect of the absorbent body 4 or napkin 1 of this embodiment (easy washing with water and removal of redness of absorbed menstrual blood) is largely due to the action of the water-absorbing polymer A. Hereinafter, the water-absorbing polymer A will be described.

  In addition, the absorbent body and absorbent article of the present invention preferably have a degree of neutralization and a centrifugal retention amount, which will be described later, in a specific range which will be described later, respectively, and preferably various other physical properties which will be described later in addition to these characteristics ( Water absorption polymer by vortex method, water absorption rate by DW method, bulk specific gravity, liquid flow rate under pressure at 2.0 kPa, absorption amount under pressure at 2.0 kPa, etc. are within the specific ranges described below ( It is preferred to contain a water-absorbing polymer A). In the present invention, the term “contains the water-absorbing polymer A” means that the average of the measured values of the degree of neutralization and the centrifugal retention amount of the water-absorbing polymer in at least a predetermined part of the absorbent body or the absorbent article is specified later. Means within range. It is even better if the average of the measured values of various properties described later other than the degree of neutralization and the centrifugal retention amount of the water-absorbing polymer at the predetermined site is within a specific range described later. Here, as the “predetermined part”, for example, a part (excretion part facing part) facing the excretion part of the absorbent article wearer in the absorbent body or the absorbent article can be mentioned. In particular, the average of the measured values of the neutralization degree and the centrifugal retention amount of the water-absorbing polymer in the entire absorbent body or absorbent article as well as a predetermined part (excretion part facing part) is within a specific range described later. In particular, it is preferable that the average of measured values of various physical properties to be described later including the degree of neutralization and the retained centrifugal amount is within a specific range described later. When a certain amount of water-absorbing polymer with specific physical properties is contained in a predetermined part of the absorber, but various physical property values (such as centrifugal retention amount and neutralization degree) of the water-absorbing polymer in the entire absorber are out of the specific range described later. The effect of the present invention may not be sufficiently achieved.

  The water-absorbing polymer A used in the present invention is a water-absorbing resin having a carboxy group and / or a carboxylate group in its structural unit. Such a water-absorbing polymer generally includes a polymer or copolymer of acrylic acid or an alkali metal acrylate, and examples thereof include polyacrylic acid and a salt thereof and polymethacrylic acid and a salt thereof. As the polyacrylate and polymethacrylate, sodium salts can be preferably used. In addition, acrylic acid or methacrylic acid, maleic acid, itaconic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2-hydroxyethyl (meth) acrylate, styrenesulfonic acid, etc. A copolymer obtained by copolymerizing the above-mentioned comonomer within a range that does not deteriorate the performance of the water-absorbing polymer can also be preferably used as the water-absorbing polymer A.

  Specific examples of the water-absorbing polymer having a carboxyl group and / or a carboxylate group include, for example, a polyacrylic acid crosslinked polymer and copolymer, a starch-acrylonitrile graft polymer hydrolyzate, a starch-acrylic acid graft crosslinked polymer, Examples thereof include saponified vinyl acetate-acrylic acid ester copolymers. These polyacrylic acid-based water-absorbing polymers are polymers that contain at least 50 mol% of acrylic acid monomer units and are substantially insoluble in water, but have a high degree of swelling.

  A particularly preferable water-absorbing polymer having a carboxy group and / or a carboxylate group constituting the water-absorbing polymer A is a polymer of acrylic acid or an alkali metal acrylate. When the water-absorbing polymer A is composed of such a water-absorbing polymer, it is particularly effective in terms of control of water-absorbing physical properties, production cost, safety and the like.

  The water-absorbing polymer A used in the present invention preferably has a neutralization degree of 75 mol% or more. In particular, when the water-absorbing polymer A is an acrylic acid cross-linked polymer, the degree of neutralization is preferably 75 to 95 mol%, particularly 80 to 90 mol%. In the present invention, the reason for setting the neutralization degree of the water-absorbing polymer having a carboxy group and / or a carboxylate group as high as 75 mol% or higher is mainly in the menstrual blood absorbed by the absorbent body 4. This is to prevent hemoglobin, which is the main red component, from adhering to the water-absorbing polymer. That is, the portion of the absorber 4 that absorbs blood such as menstrual blood is reddish, but the main cause of this redness is in hemoglobin in the blood. Therefore, in order to easily remove this redness by washing the napkin with water, it is effective to reduce the adhesion rate or adhesion strength of hemoglobin to the water-absorbing polymer. As a result of various studies focusing on the isoelectric point of hemoglobin (the pH value at which the sum of electric charges becomes zero) from the above viewpoint, the present inventors have conducted various studies, and as a result, the water-absorbing polymer comprising an acrylic acid cross-linked polymer. It was found that the redness of the napkin caused by blood can be easily removed by washing with water by adjusting the neutralization degree of the polymer to 75 mol% or more. Although the phenomenon that occurs between the water-absorbing polymer having a neutralization degree of 75 mol% or more and hemoglobin is not clear, the neutralization degree of the water-absorbing polymer composed of the acrylic acid cross-linked polymer is 75 mol% or more, When the absorbent article is washed with water, the pH in the vicinity of the molecular chain of the water-absorbing polymer is higher than the isoelectric point of hemoglobin (usually pH 6.8 to 7), so that electric repulsion occurs between the water-absorbing polymer and hemoglobin. As a result of this, the adhesion rate or adhesion strength of hemoglobin to the water-absorbing polymer is reduced, and it is assumed that hemoglobin is easily detached by washing with water. When the neutralization degree of the water-absorbing polymer A is less than 75 mol%, redness caused by blood cannot be sufficiently removed even if the napkin 1 is washed with water. The degree of neutralization is measured as follows.

<Method for measuring the degree of neutralization>
First, a neutralization titration curve of the main chain polymer of the water-absorbing polymer is prepared. For example, when the water absorbent polymer is an acrylic acid crosslinked polymer, the main chain polymer of the water absorbent polymer is polyacrylic acid. The case where the water-absorbing polymer is an acrylic acid crosslinked polymer will be described below as an example. A sodium hydroxide solution was appropriately added dropwise to an ion exchange aqueous solution of polyacrylic acid (Wako Pure Chemical Industries, average molecular weight 250,000), and the pH of the solution was measured using a pH meter. At this time, the degree of neutralization was calculated from the molecular weight of polyacrylic acid and the number of moles of sodium hydroxide added, and the neutralization degree was plotted on the horizontal axis and the pH was plotted on the vertical axis to draw a neutralization titration curve. The degree of neutralization was in the range of 50 to 100%. As the pH meter, Horiba pH ion meter D53 and electrode type 6583 were used. Next, 0.1 g of the water-absorbing polymer was put into 20 ml of ion-exchanged water, and after stirring for 10 minutes, the pH of the stirred solvent was measured. From the obtained pH value, the neutralization titration curve was used for the purpose. The degree of neutralization was calculated. The measurement is performed at 23 ± 2 ° C. and humidity 50 ± 5%, and the sample is measured after being stored in the same environment for 24 hours or more.

  Regarding the measurement of the degree of neutralization, instead of the above method, the amount of sodium in the water-absorbing polymer was quantified by elemental analysis, and the following theoretical structural formula (1) (theory applied to acrylic acid-based water-absorbing polymers) The target neutralization degree may be calculated based on the structural formula. Moreover, it may replace with the said method and may calculate the target neutralization degree from the value measured by the method based on JISK0113-1997. A method based on JIS K0113-1997 is a method in which a 0.1N potassium hydroxide aqueous solution is used as a titrant to perform potentiometric titration, and an end point is determined by an inflection point method.

  The neutralization degree of the water-absorbing polymer can be adjusted, for example, by neutralizing the water-absorbing polymer with an alkali compound. This neutralization process will be described later.

  The water-absorbing polymer A used in the present invention has a carboxy group and / or a carboxylate group, and preferably has a degree of neutralization of preferably 75 mol% or more, and further has a centrifugal retention amount based on JIS K 7223. Is preferably 5 to 20 g / g. The centrifugal retention amount of the water-absorbing polymer is a property related to the water absorption amount (water absorption magnification) of the water-absorbing polymer. Generally, a water-absorbing polymer having a large centrifugal retention amount has a large water absorption amount (water absorption magnification). Therefore, in order to improve the absorption performance of the absorbent body in the absorbent article, it can be said that it is effective to increase the value of the centrifugal retention amount of the water-absorbing polymer contained in the absorbent body. In particular, when designing the thickness of the absorbent article to be thin, a method of blending a large amount of water-absorbing polymer into the absorbent body with a high basis weight is effective, but when such a method is employed in the absorbent article, When the absorbent article is washed with water, the absorbent polymer absorbs a large amount of washing water, which may cause the absorbent article to expand and rupture. As a result of various studies to solve such problems, the present inventors have controlled the water absorption ratio of the water-absorbing polymer, and further controlled the absorption rate, so that the absorbent article expands and bursts during washing. It was found that the operation of washing and squeezing absorbent articles becomes easier. On the other hand, the purpose of increasing the degree of neutralization of the water-absorbing polymer described in Patent Document 1 is to increase the osmotic pressure of the obtained water-absorbing polymer, increase the water absorption rate, or increase the water absorption ratio (under pressure). Because.

On the other hand, from the viewpoint of removing redness caused by absorbed blood, which is a problem specific to the present invention, an increase in the amount of the water-absorbing polymer centrifuged and the water absorption speed have undesirable effects. That is, when the centrifugal retention amount of the water-absorbing polymer increases, redness due to absorbed blood increases, and it becomes more difficult to remove such redness by washing with water. In addition, the increase in the water absorption rate facilitates the absorption of hemoglobin in the blood together with the washing water when the absorbent article is washed with water, and the swelling of the water-absorbing polymer causes the article to expand in a short period of time. In addition, it is difficult to apply mechanical force to the absorbent article, and dirty water between various members, pulp, and water-absorbing polymer constituting the article is difficult to escape. Therefore, in the present invention, from the viewpoint of the balance between absorption performance and redness removal, the penetration density of ions by increasing the crosslinking density in the water-absorbing polymer A more than that of a normal water-absorbing polymer and increasing the degree of neutralization. This offsets the pressure increase effect. This can be easily understood from the following explanation by the publication “Superabsorbent Polymer” published by Kyoritsu Publishing.
“According to Flory, the factors that give water absorption are based on the osmotic pressure generated because the affinity between the polyelectrolyte and water and the concentration of mobile ions are higher inside the gel, and the network structure as a willingness to suppress water absorption. Determined by rubber elasticity.
Q ^5/3 (water absorption) = {( ^1/2 × i / V _u × 1 / S ^1/2 ) ² + (1 / 2−X ₁ ) / V ₁ } × V ₀ / ν = {(ion Osmotic pressure) + (affinity of polyelectrolyte with water)} / crosslink density i / V _u : concentration of charge fixed to the network
1 / S ^1/2 : Ionic strength of electrolyte in external solution (1 / 2−X ₁ ) / V ₁ : Affinity of network and water V ₀ / ν: Crosslink density ”

  If the centrifugal retention amount of the water-absorbing polymer A according to JIS K 7223 is less than 5 g / g, the absorption performance may be insufficient, and if it exceeds 20 g / g, it is difficult to remove redness caused by blood by washing with water. There is a risk of becoming. The centrifugal retention amount of the water-absorbing polymer A is more preferably 7 to 15 g / g. The centrifugal retention amount is measured as follows.

<Measuring method of centrifugal retention>
The measurement of the centrifugal retention amount is performed according to JIS K 7223 (1996). Nylon woven fabric (mesh opening 255, sold by Sanriku Manufacturing Co., Ltd., product name: nylon net, standard: 250 x mesh width x 30 m) is cut into a rectangle with a width of 10 cm and a length of 40 cm and folded in half at the center in the longitudinal direction. Both ends are heat-sealed to produce a nylon bag having a width of 10 cm (inner dimension: 9 cm) and a length of 20 cm. 1.00 g of the water-absorbing polymer as a measurement sample is precisely weighed and placed uniformly at the bottom of the produced nylon bag. The nylon bag containing the sample is immersed in physiological saline (0.9 mass% sodium chloride water) adjusted to 25 ° C. After 30 minutes from the start of immersion, the nylon bag is taken out from the physiological saline, suspended in a vertical state for 1 hour and drained, and then dehydrated using a centrifugal dehydrator (Kokusan Co., Ltd., model H-130C special model). The dehydration condition is 143 G (800 rpm) for 10 minutes. After dehydration, the mass of the sample is measured, and the target centrifugal retention amount is calculated according to the following formula.
Centrifugal retention amount (g / g) = (a′−b−c) / c; where a ′ is the total mass (g) of the sample and the nylon bag after centrifugal dehydration, and b is before the water absorption of the nylon bag (dried) Mass) (g), c represents the mass (g) of the sample before water absorption (during drying). The measurement was performed 5 times (n = 5), the values at each of the upper and lower points were deleted, and the average value of the remaining three points was taken as the measured value. The measurement is performed at 23 ± 2 ° C. and humidity 50 ± 5%, and the sample is measured after being stored in the same environment for 24 hours or more.

  The adjustment of the centrifugal retention amount of the water-absorbing polymer can be performed, for example, by adjusting the surface crosslinking degree of the water-absorbing polymer. Generally, when the surface cross-linking degree of the water-absorbing polymer increases (surface cross-linking treatment proceeds), the centrifugal retention amount (water absorption magnification) tends to decrease. Specifically, for example, by performing surface cross-linking treatment (post-crosslinking treatment) again on the water-absorbing polymer that has been subjected to surface cross-linking treatment manufactured by a conventional method, the centrifugal retention amount can be adjusted to the above range. Is possible. Further, the centrifugal retention amount can be adjusted by increasing the degree of crosslinking of the entire water-absorbing polymer regardless of whether or not surface crosslinking is performed. The degree of cross-linking of the water-absorbing polymer A used in the present invention (the degree of surface cross-linking or the degree of cross-linking of the whole water-absorbing polymer) is at a higher level than that of a normal water-absorbing polymer. In order to realize the degree, it is preferable to take a method such as increasing the amount of the crosslinking agent, raising the reaction temperature, or taking a longer reaction time.

  The water-absorbing polymer A used in the present invention preferably has a water absorption rate of 30 seconds or more, particularly 40 to 120 seconds, according to the vortex method. In addition, in this invention, since the evaluation of the water absorption rate by the vortex method is evaluated by measuring time, the longer the measurement time, the lower the water absorption rate. If the water-absorbing polymer A is such a relatively slow water-absorbing polymer, the absorbent 4 (absorbent sheets 4a and 4b) is broken by preventing the water-absorbing polymer from swollen rapidly during washing. Can be prevented. In particular, when the water absorption rate of the water-absorbing polymer A is in the above range, menstrual blood leakage during wearing is more effectively prevented, and the redness of the napkin can be obtained without applying excessive force to the napkin during washing. Since it is easily removed, the napkin is not easily broken during washing with water. The water-absorbing polymer whose water absorption rate by the vortex method is in the above range is, for example, the particle size of the water-absorbing polymer, the primary cross-linking density, the adjustment of the degree of surface cross-linking (post-crosslinking treatment), shape control, various surfactants and polyhydric alcohols. It can be obtained by surface treatment of a water-absorbing polymer with hydrophilic powder or the like. The water absorption rate by the vortex method is measured as follows.

<Measurement method of water absorption rate by vortex method>
A 100 mL glass beaker, 50 mL of physiological saline (0.9% by mass sodium chloride water) and a magnetic stirrer chip (center diameter 8 mm, both ends diameter 7 mm, length 30 mm, surface coated with fluororesin ) And place the beaker on a magnetic stirrer (HPS-100 manufactured by ASONE). The rotational speed of the magnetic stirrer is adjusted to 600 ± 60 rpm, and the physiological saline is stirred. 2.0 g of the water-absorbing polymer as a measurement sample is put into the liquid at the center of the vortex of the saline solution being stirred, and the water absorption rate (seconds) of the water-absorbing polymer is measured in accordance with JIS K 7224 (1996). taking measurement. Specifically, the stopwatch is started when the absorption of the water-absorbing polymer into the beaker is completed, and stopped when the stirrer tip is covered with the test liquid (when the vortex disappears and the liquid surface becomes flat). Stop the watch and record the time (in seconds) as the water absorption rate by vortex method. In the measurement, n = 5 was measured, the values at each of the upper and lower points were deleted, and the average value of the remaining three points was taken as the measured value. These measurements are performed at 23 ± 2 ° C. and a humidity of 50 ± 5%, and the samples are stored for 24 hours or more in the same environment before the measurement.

  In addition, the water absorption rate of the water-absorbing polymer A used in the present invention can also be evaluated by the measured value of the DW method generally used in the technical field. The water absorption rate by the vortex method serves as an index for the water-absorbing polymer to fix a certain amount of liquid, whereas the water absorption rate by the DW method expresses the behavior of the water-absorbing polymer to absorb and absorb the liquid. , Including the amount of water present in the gap between adjacent water-absorbing polymers. The water absorption rate according to the DW method is useful as an index of the shape retention of the absorbent body during production and after liquid absorption, particularly the shape retention after liquid absorption.

  The water absorption rate (unit: ml / 0.3 g · 30 sec) by the DW method is measured using a device (Demand Wettability Tester) generally known as a device for performing the DW method. Specifically, in the apparatus, the level of the physiological saline solution is set at the same level as the surface of the polymer spray table (70 mmφ, a table in which No. 2 filter paper is placed on the glass filter No. 1), and the polymer spray table Sprinkle 0.3 g of the water-absorbing polymer to be measured on the surface. The water absorption at the time when the water-absorbing polymer is sprayed is set to 0, and the water absorption after 30 seconds is measured. The amount of water absorption is measured by a burette scale indicating the amount of decrease in the saline water level. The value of the water absorption obtained is taken as the water absorption rate by the DW method. The water absorption rate by the DW method can be designed by the shape, particle size, bulk specific gravity, degree of crosslinking, etc. of the water-absorbing polymer. The measurement is performed at 23 ± 2 ° C. and humidity 50 ± 5%, and the sample is measured after being stored in the same environment for 24 hours or more.

  For example, when the absorbent body 4 is produced by spreading a water-absorbing polymer on a water-containing fiber web and superimposing another fiber web on the spread water-absorbing polymer, the water-absorbing polymer When the water absorption speed by the DW method is too high, the moisture content in the absorbent body 4 is increased, and drying defects are likely to occur. On the other hand, if the water absorption rate by the DW method is too slow, the adhesiveness of the water-absorbing polymer does not work, and sufficient adhesion between the layers cannot be obtained. As a result, the water-absorbing polymer may come out of the absorber 4. Therefore, from this point of view, when the absorber 4 is manufactured as described above, the water absorption rate by the DW method of the water-absorbing polymer used in the absorber 4 is 2 to 20 ml / 0.3 g · 30 sec. In particular, it is preferably in the range of 4 to 15 ml / 0.3 g · 30 sec.

The water-absorbing polymer A used in the present invention preferably has a bulk specific gravity of 0.5 to 0.8 g / cm ³ , particularly 0.55 to 0.7 g / cm ³ . Bulk specific gravity is useful as an index of various characteristics of the water-absorbing polymer, such as control of water absorption speed, maintenance of water absorption repeatedly, ease of discharge of blood and washing liquid when washing absorbent articles, and bulk specific gravity is in the above range. This gives good results for these properties. The bulk specific gravity is measured as follows.

<Method of measuring bulk specific gravity>
The bulk specific gravity was measured according to JIS K6219-2 2005. The water-absorbing polymer to be measured was poured into the center of a cylindrical container (a stainless steel container having a diameter of 100 mm, capacity 1000 ml) having a known mass and volume from a height of 50 mm or less from the lower end of the container. At this time, a sufficient amount of the water-absorbing polymer was poured into the cylindrical container so that the poured water-absorbing polymer formed a triangular pyramid above the upper end of the cylindrical container. Then, the excess water-absorbing polymer above the upper end of the cylindrical container is wiped off using a spatula, the weight of the container is measured in this state, and the weight of the container is subtracted from the measured value. Was calculated by dividing the mass by the volume of the container. The measurement is performed at 23 ± 2 ° C. and humidity 50 ± 5%, and the sample is measured after being stored in the same environment for 24 hours or more.

  By the way, in absorbent articles such as sanitary napkins and disposable diapers, excretion fluid such as urine and menstrual blood is taken into the absorbent body through a surface layer (surface sheet), and a fiber material such as pulp forms in the absorbent body. It is absorbed and held by an absorption mechanism that is once held in the space and then fixed by the water-absorbing polymer in the absorbent body. That is, the absorption speed of the liquid in the absorbent article depends not only on the speed at which the water-absorbing polymer actually fixes the liquid, but also on the diffusion / permeation speed of the liquid in the absorbent body. The water absorption rate by the vortex method and the water absorption rate by the DW method mainly evaluate the “speed at which the water-absorbing polymer fixes the liquid”, and the “diffusion / permeation speed of the liquid in the absorber” It can be evaluated by the following pressure passing rate under pressure. The following water-absorbing polymer having a slow liquid passage speed under pressure (small value of the liquid passage speed under pressure) is likely to cause inhibition of liquid diffusion in the absorbent body due to gel blocking, especially in repeated absorption of liquid. Even if the speed at which the liquid of the water-absorbing polymer itself is fixed (the water absorption speed evaluated by the vortex method or the DW method described above) is sufficiently high, the absorption speed of the liquid in the absorbent article using the water-absorbing polymer Is not enough and can be slow.

  The water-absorbing polymer A used in the present invention preferably has a liquid flow rate under pressure of 2.0 kPa of 150 ml / min or more, particularly 200 to 2000 ml / min, particularly 250 to 1500 ml / min. Here, the load of 2.0 kPa substantially corresponds to the pressure applied to the absorbent body when the absorbent article is being washed. In order to enhance the cleaning property of the absorbent article, that is, to make it easier to remove redness derived from blood by washing the absorbent article with water, the absorbent article used in the absorbent article (absorber) is adhered or absorbed. It is effective to make it easy to wash away hemoglobin, and in addition to this, it is effective to make it easy to discharge the dirty cleaning liquid from the absorbent article, particularly the absorbent body. The liquid flow rate is effective as an index for evaluating the water-absorbing polymer from such a viewpoint. When the liquid flow rate of the water-absorbing polymer is less than 150 ml / min, the water-absorbing polymer saturated and swollen by the liquid absorption They adhere to each other under load and prevent the liquid from passing through, so that gel blocking is likely to occur, and the washing water may not be easily drained from the napkin. By setting the liquid-absorbing polymer flow rate to 150 ml / min or more, gel blocking is less likely to occur, and dirty cleaning liquid is easily excreted from the absorbent article. In particular, even when blood is discharged repeatedly, when a lot of blood is discharged at once, or when the napkin is under pressure such as when sitting or closed, the permeability of the liquid to the absorber (I.e., the rate at which excretion fluid is taken into the napkin through the surface layer is increased), and adhesion to the skin is less likely to occur, or liquid leakage is less likely to occur. Further, when the liquid flow rate is within the above range, improvement of the overall performance relating to the absorbability of the water-absorbing polymer can be expected, that is, urine or loose stool can be expected to have the same effect as that for blood. The “penetration of the liquid into the absorber” can be evaluated by <Measurement method of absorption time> described later.

Further, the larger the value of the liquid flow rate, the more preferable from the viewpoint of preventing the occurrence of gel blocking. However, when it is 2000 ml / min or less, particularly in a thin absorbent body having few hydrophilic fibers such as pulp. Can sufficiently fix the liquid in the absorber, and can effectively prevent leakage from the end of the absorber. In addition, it is possible to effectively suppress the accumulation of liquid on the surface of the absorbent article at a portion where the liquid easily flows, such as the crotch portion in the standing position, the stomach side when lying on the back, and the back side when lying on the back. In addition, the thin absorber here is about 300 g / m ² or less (preferably 250 g / m ² or less, more preferably 200 g / m ² or less) in terms of pulp basis weight, and the thickness under no load is less than 4 mm. It is an absorber satisfying at least one of the above. Moreover, the range of the liquid flow rate is an appropriate range for using the water-absorbing polymer most efficiently. Of course, even in the case of a water-absorbing polymer having a liquid flow rate exceeding 2000 ml / min, the necessary performance as an absorbent can be ensured by using the water-absorbing polymer in combination with a large amount of pulp, in this case, Since the function of preventing gel blocking can be carried out by a large amount of pulp, it is not always necessary to carry out the water-absorbing polymer alone.

  The liquid passing speed is measured using a measuring method and a measuring apparatus described in Japanese Patent Application Laid-Open No. 2003-235889. Specifically, the flow rate under pressure at 2.0 kPa is measured by the following procedure. The following measurement is performed at 23 ± 2 ° C. and a relative humidity of 50 ± 5%. Before the measurement, the sample is stored in the same environment for 24 hours or more.

<Measurement method of liquid flow rate under pressure>
In a 100 mL glass beaker, a sufficient amount of physiological saline (0.9% by mass sodium chloride water) to swell the measurement sample water-absorbing polymer 0.32 ± 0.005 g, for example, the saturated absorption amount of the water-absorbing polymer. Immerse it in 5 times more saline and leave it for 30 minutes. Separately, at the lower end of an opening of a vertically standing cylinder (inner diameter 25.4 mm), a wire mesh (mesh opening 150 μm, biocolumn sintered stainless steel filter 30SUS sold by Sansho Co., Ltd.) and a capillary (with an inner diameter of 2 mm) ( A filtration cylindrical tube having an inner diameter of 4 mm and a length of 8 cm) is prepared, and the contents of the beaker including the swollen measurement sample are put into the cylindrical tube with the cock closed. Next, a cylindrical rod having a diameter of 2 mm with a wire mesh having an opening of 150 μm and a diameter of 25 mm is inserted into the filtration cylindrical tube so that the wire mesh and the measurement sample are in contact with each other. Place a weight so that the load of. After standing in this state for 1 minute, the cock is opened to flow the liquid, and the time until the liquid level in the filtration cylindrical tube reaches the 40 mL scale line from the 60 mL scale line (that is, 20 mL of liquid passes) (T ₁ ) (Seconds). Using the measured time T ₁ (seconds), the flow rate at 2.0 kPa is calculated from the following equation. In the equation, T ₀ (seconds) is a value obtained by measuring the time required for 20 ml of physiological saline to pass through the wire mesh without putting the measurement sample in the filtering cylindrical tube. Flow rate (ml / min) = 20 × 60 / (T ₁ −T ₀ ) The value obtained by the above formula is divided by the thickness of the swollen water-absorbing polymer layer in the cylinder, and converted to a value per 20 mm. Thus, the liquid passing speed under pressure is set. The measurement was performed 5 times (n = 5), the values at each of the upper and lower points were deleted, and the average value of the remaining three points was taken as the measured value. Incidentally, a more detailed method for measuring the flow rate under pressure is described in paragraphs [0008] and [0009] of JP-A No. 2003-235889, and the measuring device is shown in FIGS. 2.

  The water-absorbing polymer A used in the present invention has an absorption amount under pressure at 2.0 kPa of 5 to 20 g / g, particularly 7 to 15 g / g. The amount of absorption under pressure is a measure of how much liquid can be absorbed by the water-absorbing polymer in the absorbent body when pressure such as body pressure is applied to the absorbent body by wearing the absorbent article. The higher the absorption amount under pressure of the water-absorbing polymer, the better the absorption performance, but from the viewpoint of removing redness caused by absorbed blood, which is a specific object of the present invention, the increase in absorption amount under pressure is Undesirable effects. That is, when the amount of water-absorbing polymer absorbed under pressure increases, redness caused by absorbed blood increases, and it becomes more difficult to remove such redness by washing with water. Therefore, in the present invention, from the viewpoint of the balance between absorption performance and redness removal, it is preferable to set the absorption amount under pressure of the water-absorbent polymer A within the specific range. The absorption under pressure at 2.0 kPa is measured as follows.

<Measurement method of absorption under pressure>
The amount of absorption under pressure is measured using a measuring method and measuring apparatus described in JP-A-2003-235889. Measurement is performed as follows in an environment of 25 ± 2 ° C. and a relative humidity of 50% ± 5%. That is, 0.10 g of a sample (water-absorbing polymer) was weighed in a cylindrical plastic tube (inner diameter 30 mm, height 60 mm) with a nylon mesh (JIS Z8801-1: 2000) having a mesh opening of 63 μm attached to the bottom surface, and the cylindrical plastic. Place the sample vertically on the nylon mesh so that the sample is almost uniform in thickness, and apply a weight of 29.5mm outside diameter x 22mm thickness inside the cylindrical plastic tube so that the pressure of 2.0kPa is applied to the sample. insert. The mass of the cylindrical plastic tube and the weight is measured in advance. Next, a cylindrical plastic tube containing a sample and a weight in a petri dish (diameter: 120 mm) containing 60 ml of physiological saline is vertically immersed with the nylon mesh side as the bottom surface. At this time, the cylindrical plastic tube is immersed to the depth of the bottom of the petri dish. After 60 minutes, the cylindrical plastic tube containing the sample and the weight is pulled up from the water, and the mass is weighed. The mass of the cylindrical plastic tube and the weight that have been measured in advance is subtracted, and the mass of the physiological saline absorbed by the sample is calculated. . A value obtained by multiplying the mass of the absorbed physiological saline by 10 is defined as an absorbed amount under pressure (g / g). The measurement is performed at 23 ± 2 ° C. and humidity 50 ± 5%, and the sample is measured after being stored in the same environment for 24 hours or more.

  By the way, regarding the liquid retention amount (liquid absorption amount) of the water-absorbing polymer A used in the present invention, the preferable numerical range of the above-mentioned two characteristics (centrifugal retention amount and absorption amount under pressure at 2.0 kPa) is any Is 5 to 20 g / g, particularly 7 to 15 g / g, and the water-absorbing polymer A has a characteristic that the numerical ranges of these two characteristics coincide. Here, since the centrifugal retention amount indicates the liquid absorption amount of the water-absorbing polymer without pressure, the numerical range of the centrifugal retention amount and the absorption amount under pressure at 2.0 kPa coincides, that is, both are The water-absorbing polymer A, which is substantially the same, has a constant liquid absorption amount regardless of the pressure. In general, the amount of centrifugal retention and the amount of absorption under pressure are closely related to the degree of crosslinking (gel strength) of the water-absorbing polymer. The lower the degree of crosslinking (the lower the degree of crosslinking), the higher the value of centrifugal retention. The value of the amount of absorption under pressure is low, and the amount of centrifugal retention and the amount of absorption under pressure are approximately inversely proportional. Like the water-absorbing polymer A, the water-absorbing polymer in which the centrifugal retention amount and the absorption amount under pressure show substantially the same value is considered to be a special water-absorbing polymer that is particularly well-crosslinked. In general, a water-absorbing polymer having low gel strength is less likely to swell the polymer chain due to cross-linking, so that it easily swells under no pressure and increases the centrifugal retention, while constituting a water-absorbing polymer under pressure. The gel cannot withstand pressurization, and the absorption amount under pressure tends to be low. Therefore, when such a water-absorbing polymer with low gel strength is used, it is difficult to sufficiently wash away blood absorbed under no pressure by washing with water. In addition, for example, when a water-absorbing polymer having a high water absorption amount under pressure, such as the water-absorbing polymer used in Examples 1 to 10 of Patent Document 1, the blood absorbed under pressure is sufficiently washed away by washing with water. It is difficult. Further, as in Comparative Example 2, a water-absorbing polymer with low gel strength is expected to have a high centrifugal retention amount, and when such a water-absorbing polymer with a high centrifugal retention amount is used, no (low) pressure is applied. It is difficult to sufficiently wash off the absorbed blood by washing with water.

  The water-absorbing polymer A used in the present invention can be produced, for example, as follows. The manufacturing method of the water absorbing polymer A demonstrated below has the following processes 1-3. That is, the water-absorbing polymer A preferably used in the present invention is produced by sequentially subjecting a water-absorbing polymer having a carboxy group and / or a carboxylate group to a surface cross-linking treatment to a surface cross-linking treatment and a neutralization treatment. It is a thing.

  Step 1: A step of producing a water-absorbing polymer having a carboxy group and / or a carboxylate group. Step 2: A step of subjecting the water-absorbing polymer obtained in Step 1 to surface cross-linking treatment. Step 3: A step of neutralizing the water-absorbing polymer obtained in Step 2.

  Step 1 can be performed using a conventionally known method for producing a polyacrylic acid-based water-absorbing polymer. Examples of the method for producing a water-absorbing polymer usable in Step 1 include (i) a reverse phase suspension polymerization method using an anionic surfactant described in Japanese Patent No. 2721658 as a dispersant, and (ii) An aqueous solution polymerization method described in JP-A-2003-235889 can be mentioned. The surface of the water-absorbent polymer particles obtained in step 1 may be crosslinked with a crosslinking agent. That is, the water-absorbing polymer obtained in step 1 may be a water-absorbing polymer whose particle surface is subjected to a crosslinking treatment.

  Examples of the water-absorbing polymer having a carboxy group and / or a carboxylate group produced in Step 1 include a polymer of a monomer containing (meth) acrylic acid and / or an alkali metal salt thereof prepared in Step I, which will be described later. Is mentioned.

  The degree of neutralization of the water-absorbing polymer obtained in the step 1 is preferably 50% or more, more preferably 65% or more and less than 75%, from the viewpoint of water absorption characteristics and reaction efficiency of the crosslinking agent. The degree of neutralization is measured by the measurement method described above.

  In the step 2, crosslinking treatment (post-crosslinking treatment) is performed on the surface of the water-absorbing polymer particles obtained in the step 1. When the surface of the particles has already been subjected to crosslinking treatment in Step 1, that is, when the starting material in Step 2 is a water-absorbing polymer that has been subjected to surface crosslinking treatment, It has been given. By performing such post-crosslinking treatment, the degree of cross-linking in the vicinity of the surface of the water-absorbing polymer is increased compared to the case where no post-crosslinking treatment is performed, thereby making the molecular chain network finer and While preventing hemoglobin from penetrating into the deep part, the centrifugal retention amount of the water-absorbing polymer is lowered. Therefore, the post-crosslinking treatment is effective as a method for adjusting the centrifugal retention amount of the water-absorbing polymer according to JIS K 7223 to the specific range (5 to 20 g / g). The post-crosslinking treatment can be performed by the same method as the surface cross-linking treatment performed in step 1. Examples of the crosslinking agent used for the surface crosslinking treatment performed in Step 2 include the crosslinking agent used in Step I described later.

  From the viewpoint of suppressing penetration of hemoglobin, which is the cause of redness, into the deep part of the water-absorbing polymer, the crosslinking used in the surface crosslinking treatment performed in the step 2 is larger than the addition amount of the crosslinking agent used in the surface crosslinking treatment performed in the step 1. It is preferable to increase the addition amount of the agent. The type of the crosslinking agent used in step 1 or step 2 may be the same or different.

  In the step 3, the water-absorbing polymer obtained after the cross-linking treatment obtained in the step 2 is neutralized using a basic compound (neutralizing agent), and one of unneutralized carboxy group or carboxylate group is obtained. Neutralize part. In this neutralization treatment, the treatment conditions such as the amount of neutralizing agent used are adjusted so that the degree of neutralization of the finally obtained water-absorbing polymer is 75 mol% or more as described above. The neutralization process performed at the process 3 can be performed in the same procedure as the neutralization process of a conventionally well-known water absorbing polymer. The neutralization treatment is performed in the presence of water. The amount of water used in the neutralization treatment is 30 to 600 parts by mass with respect to 100 parts by mass of the water-absorbing polymer. A particularly preferable range of the amount of water used (water content of the water-absorbing polymer) in the neutralization treatment in Step 3 is 100 parts by mass or more, particularly 100 to 500 parts by mass with respect to 100 parts by mass of the water-absorbing polymer.

  In the present specification, “mass” means “mass at the time of drying” unless otherwise specified. The “mass at the time of drying” of the absorbent article and the constituent members of the absorbent article is measured as follows. Measuring method of mass at the time of drying: The object to be measured is left in an environment of constant temperature and humidity of 25 ° C. and 30% humidity for 24 hours, and then the mass is measured in the environment, and the measured value is measured. This is the “mass when dried” of the object.

  Examples of the basic compound (neutralizing agent) used in Step 3 include water-soluble carbonate compounds such as sodium bicarbonate, sodium carbonate, potassium bicarbonate, and potassium carbonate; sodium hydroxide, potassium hydroxide, water glass, and the like. A water-soluble hydroxide compound is mentioned. Among these neutralizing agents, sodium hydrogen carbonate and sodium carbonate are particularly preferably used in the present invention because they dissolve and exhibit weak alkalinity, and suppress an increase in water absorption capacity associated with the breakage of the crosslinking by alkali. Of course, a strongly basic compound such as sodium hydroxide can also be used as a neutralizing agent. In this case, the water content of the water-absorbing polymer is increased in advance before neutralization, or a low concentration aqueous solution is gradually added. Neutralization can be performed while keeping the water absorption factor low by appropriately selecting the conditions such as adding to the reaction temperature and performing the reaction at as low a temperature as possible.

  Examples of the neutralization method in Step 3 include a method of adding an aqueous solution in which a predetermined amount of a basic compound is dissolved in a water-absorbing polymer; a water-absorbing polymer and a predetermined amount of a powdered basic compound are mixed. Furthermore, the method of adding water etc. are mentioned. In addition, in order to suppress the power required for stirring in the reaction vessel, or to increase the stirring efficiency and perform the reaction as uniformly as possible, a predetermined amount of a basic compound is added to the water-absorbing polymer adjusted to a predetermined water content. A dissolved aqueous solution may be added, or a powdered basic compound may be added. When the water-absorbing polymer is pre-hydrated, 30 to 200 parts by mass of water is added to 100 parts by mass of the water-absorbing polymer. In addition, when adding an aqueous solution in which a predetermined amount of a basic compound is dissolved, the amount of water combined with the water contained in the alkaline aqueous solution is used as the amount of water used in the neutralization treatment. From the viewpoint of water resistance, hydrolysis resistance of crosslinking, and drying efficiency of the water-absorbing polymer.

  In the neutralization treatment in Step 3, a dispersant is used in addition to the neutralizing agent from the viewpoint of suppressing the power necessary for stirring of the reaction vessel or increasing the stirring efficiency and performing the reaction as uniformly as possible. Can do. As the dispersant, for example, sugar ester or the like can be used. The usage-amount of a dispersing agent is 0.2-5 mass parts normally with respect to 100 mass parts of water absorbing polymers.

  In addition, you may perform the said process 2 and the said process 3 by changing the order of a process. Moreover, the said process 2 can be abbreviate | omitted by fully bridge | crosslinking a water absorbing polymer in the said process 1. FIG.

  After completion of the step 3, the water-absorbing polymer A used in the present invention is obtained by washing the water-absorbing polymer obtained as necessary to remove the dispersant and further drying and removing water. It is done. The water-absorbing polymer A obtained in this way is classified according to the particle size as necessary.

  Moreover, the water absorbing polymer A used for this invention can be manufactured also with the manufacturing method which has the following process I and II. Hereinafter, this manufacturing method will be described.

Step I: Polymerizing a monomer containing (meth) acrylic acid and / or an alkali metal salt thereof to obtain a polymer, crosslinking the polymer with a crosslinking agent, or (meth) acrylic acid and / or an alkali metal salt thereof Is a step of preparing a polymer having a centrifugal retention amount of 5 to 20 g / g in accordance with JIS K 7223 by polymerizing a monomer containing Agent / monomer] is 0.15 / 100 to 40/100.
Step II: A step of bringing the polymer obtained in Step I above into contact with a basic compound and / or water and performing a neutralization treatment so that the degree of neutralization of the polymer is 75 mol% or more.

  The step I is publicly known except that a polymer having a specific centrifugal retention amount is prepared using a monomer containing (meth) acrylic acid and / or an alkali metal salt thereof and a crosslinking agent at a specific mass ratio. The polyacrylic acid-based water-absorbing polymer production method can be used. Examples of the known production method include the reverse phase suspension polymerization method (i) and the aqueous solution polymerization method (ii). In Step I, the polymer obtained by polymerizing a monomer containing (meth) acrylic acid and / or an alkali metal salt thereof in the presence of a crosslinking agent may be further subjected to crosslinking treatment with a crosslinking agent.

  The polymer of the monomer containing (meth) acrylic acid and / or its alkali metal salt prepared in the above step I is a single polymer of (meth) acrylic acid from the viewpoint of blood absorbability control, safety, production cost, and the like. A polymer, a copolymer thereof, or a cross-linked product thereof. Examples of the homopolymer of (meth) acrylic acid include polyacrylic acid and polymethacrylic acid. Examples of the copolymer of (meth) acrylic acid include acrylic acid or methacrylic acid, maleic acid, itaconic acid, acrylamide, Copolymers obtained by copolymerizing co-monomers such as 2-acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2-hydroxyethyl (meth) acrylate, or styrenesulfonic acid, starch-acrylic acid Examples thereof include a graft copolymer. The amount of the comonomer of the copolymer is preferably in a range that does not deteriorate blood absorption performance. Moreover, as an alkali metal salt of (meth) acrylic acid, sodium salts, such as polyacrylic acid and polymethacrylic acid, are preferable.

  Among these, (meth) acrylic acid or an alkali metal salt homopolymer or copolymer cross-linked product thereof, starch-acrylic acid graft copolymer cross-linked product is preferable, and acrylic acid or alkali metal acrylate single salt A cross-linked polymer is more preferred. These polymers usually contain 50 mol% or more of acrylic acid monomer units, preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and are substantially insoluble in water. Although it is a polymer having a high degree of swelling.

  The crosslinking agent used in the step I includes a compound having two or more polymerizable unsaturated groups in the molecule, or a reactive group capable of reacting with two or more carboxy groups and / or carboxylate groups in the molecule. For example, a compound having two or more hydroxyl groups in the molecule, a compound having two or more polymerizable double bonds, a compound having two or more epoxy groups, and the like can be given.

  Examples of compounds having two or more hydroxyl groups in the molecule include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, polyoxypropylene, sorbitan fatty acid ester, trimethylolpropane, and pentaerythritol. Trit, 1,3-propanediol, sorbitol and the like can be mentioned.

Examples of the compound having two or more polymerizable double bonds in the molecule include bis (meth) acrylamide, allyl (meth) acrylamide, di- or polyester of (meth) acrylic acid by polyol (for example, diethylene glycol diacrylate, trimethylol). Propane triacrylate, polyethylene glycol diacrylate, etc.), unsaturated mono-or polyols derived from the reaction of C ₁ -C ₁₀ polyhydric alcohols with 2 to 8 C ₂ -C ₄ alkylene oxides per hydroxyl group or Examples thereof include polycarboxylic acid di- or polyester (for example, ethoxylated trimethylolpropane triacrylate and the like).

  Compounds having two or more epoxy groups in the molecule include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin triglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylol. Examples thereof include polyglycidyl ethers such as propane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, hydrogenated bisphenol A type diglycidyl ether.

  Among these crosslinking agents, a compound having two or more polymerizable double bonds and a compound having two or more epoxy groups in the molecule are preferable, and a compound having two or more epoxy groups in the molecule is more preferable. Specifically, ethylene glycol diglycidyl ether and trimethylolpropane polyglycidyl ether are particularly preferable.

  In the step I, the amount of the crosslinking agent used is 0.15 / 100 to 40/100 in terms of mass ratio of [crosslinking agent / monomer] from the viewpoint of blood absorption performance and removal of redness caused by absorbed blood. 0.2 / 100 to 30/100 is preferable, and 0.3 / 100 to 20/100 is more preferable.

  In the step II, the polymer obtained in the step I is brought into contact with a basic compound and / or water to neutralize the polymer. In this neutralization treatment, the treatment conditions such as the amount of neutralizing agent used are adjusted so that the degree of neutralization of the finally obtained water-absorbing polymer is 75 mol% or more.

  The neutralization process in the said process II can be performed in presence of water in the same procedure as a well-known neutralization process. The water content of the water-absorbing polymer in this neutralization treatment is preferably 100% by mass or more, and more preferably 100 to 600% by mass with respect to the polymer obtained in Step I.

  As the basic compound used in Step II, the same basic compound (neutralizing agent) used in Step 3 can be used. In particular, water-soluble carbonate compounds such as sodium hydrogen carbonate and sodium carbonate, or water-soluble hydroxide compounds such as sodium hydroxide, potassium hydroxide and water glass are preferred. A water-soluble carbonate compound and a water-soluble hydroxide compound may be used in combination.

  Examples of the shape of the water-absorbing polymer A used in the present invention include particles and fibers. The particulate water-absorbing polymer includes an amorphous type, a block type, a bowl type, a spherical agglomeration type, a spherical type and the like due to the difference in shape, and any type can be used.

  The water-absorbing polymer used in the present invention (which is a general term for the water-absorbing polymer used in the absorbent or absorbent article of the present invention and includes the above-described water-absorbing polymer A. Hereinafter, the same unless otherwise specified). It is preferable to have the following characteristics in relation to hemoglobin which is the main red component. That is, the absolute value ΔV of the difference between the zeta potential V1 in the ion exchange water of the water-absorbing polymer used in the present invention and the zeta potential V2 in the ion exchange water of bovine hemoglobin is 30 mV or less, particularly 5 to 20 mV. It is preferable. When the absolute value ΔV of the zeta potential difference between the water-absorbing polymer and bovine hemoglobin is in such a range, strong charge repulsion occurs between them, and hemoglobin in blood such as menstrual blood absorbed by the absorber is thereby absorbed. , It becomes difficult to adhere to the water-absorbing polymer in the absorbent body. Therefore, the redness of the absorbent body or absorbent article due to the absorbed blood can be easily removed by washing the absorbent body or absorbent article with water.

  In the present invention, the zeta potential is determined by the electrophoretic light scattering measurement method (also known as laser Doppler method), which is obtained from each migration velocity when an external electric field is applied to the water-absorbing polymer or bovine hemoglobin in ion-exchanged water. Means. As a zeta potential measuring device, for example, a device using the principle of electrophoretic light scattering measurement method such as “ELSZ-2 zeta potential / particle size measuring system” manufactured by Otsuka Electronics Co., Ltd. can be used. The zeta potential is measured as follows.

<Method for measuring zeta potential>
In 10000 parts by mass of ion-exchanged water adjusted to pH 7.0, 5 parts by mass of the water-absorbing polymer to be measured or bovine hemoglobin (so that the concentration in the ion-exchanged water is 0.05% by mass) is dispersed, A water-absorbing polymer dispersion and bovine hemoglobin dispersion are prepared. The zeta potential of the bovine hemoglobin dispersion is measured by adjusting the pH so that the pH is equal to that of the water-absorbing polymer dispersion to be measured. To adjust the pH of ion-exchanged water and bovine hemoglobin dispersion, hydrochloric acid or sodium hydroxide is used as necessary, and a commercially available pH meter (for example, Horiba pH ion meter D53, electrode type 6583) is used to measure pH. it can. As the water-absorbing polymer to be measured, a particulate polymer having passed through a sieve having an aperture of 106 μm is used. If the water-absorbing polymer particles are too large to be measured (if the water-absorbing polymer particles are too large, the water-absorbing polymer will settle in the ion exchange water, making it difficult to measure the zeta potential). As described above, the opening of the sieve is adjusted as appropriate, and the size of the particles used for the measurement is adjusted. About the obtained dispersion liquid, the zeta potential of a water-absorbing polymer or bovine hemoglobin is measured using a zeta potential measuring device. During the measurement of the zeta potential, the water temperature of the dispersion is 23 ± 2 ° C., and the humidity of the measurement chamber is 50 ± 5%. The measurement is repeated three times for each sample, and the average value thereof is taken as the zeta potential of the sample.

  The zeta potential V1 of the water-absorbing polymer used in the present invention is preferably −40 to 5 mV, more preferably −35 to −5 mV. On the other hand, the zeta potential V2 of bovine hemoglobin is usually in the range of −15 to 10 mV (showing a positive potential on the acidic side from the isoelectric point and a negative potential on the alkaline side from the isoelectric point).

  The water-absorbing polymer used in the present invention is preferably a polyacrylic acid-based water-absorbing polymer, that is, an acrylic acid-based resin. The water-absorbing polymer in which the zeta potential V1 is in the above range (the absolute value ΔV of the zeta potential difference with bovine hemoglobin is in the above range) is, for example, a polyacrylic acid-based water-absorbing polymer, treated as follows. Can be obtained by applying Examples of the polyacrylic acid-based water-absorbing polymer include polymers of monomers containing the aforementioned (meth) acrylic acid and / or alkali metal salts thereof.

  The zeta potential V1 correlates with the charge density on the surface of the water-absorbing polymer, and the charge density is closely related to the amount of centrifugal retention of the water-absorbing polymer. That is, when the centrifugal retention amount of the water-absorbing polymer is reduced, the absolute value of the zeta potential V1 of the water-absorbing polymer tends to decrease. Using this, the zeta potential V1 can be adjusted. As described above, since the centrifugal retention amount of the water-absorbing polymer can be adjusted by the surface cross-linking degree of the water-absorbing polymer, the zeta potential V1 of the water-absorbing polymer can be set to a desired value by adjusting the surface cross-linking degree of the water-absorbing polymer. Can be adjusted to the range. For example, when the surface cross-linking degree of the water-absorbing polymer is increased, the centrifugal retention amount is decreased, and the absolute value of the zeta potential V1 is decreased.

  The zeta potential V1 can be adjusted by adjusting the degree of neutralization of the water-absorbing polymer, for example. From the viewpoint of setting the absolute value ΔV of the zeta potential difference between the water-absorbing polymer and bovine hemoglobin in the above range, the degree of neutralization of the water-absorbing polymer is 70 to 95 mol%, particularly 75 to 90 mol%, more preferably 80 to 90 mol%. It is preferable that it is mol%. Regarding the degree of neutralization, the explanation in the water-absorbing polymer A described above is appropriately applied.

  The zeta potential V1 can also be adjusted by treating the surface of the water-absorbing polymer with a cationic compound. The surface treatment of the water-absorbing polymer with a cationic compound is, for example, 1) a method of mixing a dry or water-containing water-absorbing polymer and a cationic compound in a dry state (dry blend method), or 2) a dry state. The water-absorbing polymer may be coated with an aqueous solution or dispersion of a cationic compound. Examples of the cationic compound include cationic polymer compounds such as cationized starch, cationic polyacrylamide, polyethyleneimine, and aminoalkyl (meth) acrylate / acrylamide copolymer; aluminum oxide, iron oxide, titanium oxide, and zinc oxide. And metal oxides such as The amount of the cationic compound used in the surface treatment is 0.01 to 5% by weight, particularly 0.02 to 3% by weight, and particularly 0.05 to 2% by weight, based on the dry water-absorbing polymer. preferable.

  Examples of the water-absorbing polymer in which the zeta potential V1 is in the above range (the absolute value ΔV of the zeta potential difference from bovine hemoglobin is in the above range) include the above-mentioned “having a carboxyl group and / or a carboxylate group. In addition, a water-absorbing polymer (water-absorbing polymer A) having a degree of neutralization of 75 mol% or more and a centrifugal retention amount of 5 to 20 g / g based on JIS K 7223 is exemplified.

  The water-absorbing polymer used in the present invention is in the form of particles, has a carboxy group and / or a carboxylate group, and has been neutralized with a neutralizing agent containing an alkali metal such as sodium, It is preferable that the degree of neutralization is 75 mol% or more, preferably 75 to 95 mol%, more preferably 80 to 90 mol%, and the alkali metal is uniformly distributed throughout the water-absorbing polymer. . As the neutralizing agent, a neutralizing agent that can be used in the production of the water-absorbing polymer A described above can be used. By using a water-absorbing polymer having such characteristics in an absorbent or absorbent article, the redness of the absorbent or absorbent article due to absorbed blood can be easily removed by washing the absorbent or absorbent article with water. It becomes possible to do. The aforementioned “water-absorbing polymer having a carboxyl group and / or carboxylate group and having a neutralization degree of 75 mol% or more and a centrifugal retention amount of 5 to 20 g / g in accordance with JIS K 7223” (water-absorbing polymer A) is: It has such characteristics.

  Here, “the alkali metal is uniformly distributed throughout the water-absorbing polymer” means that the surface of the water-absorbing polymer particles (the portion exposed to the outside in the water-absorbing polymer particles) and the inside (the water-absorbing polymer). This means a state in which the distribution concentration of alkali metal is substantially the same throughout the entire portion of the polymer particle excluding the surface, and more specifically, the alkali obtained by the following <Method for measuring distribution state of alkali metal> This means that the metal concentration ratio is within 1.3. The alkali metal concentration ratio is such that the water-absorbing polymer particles are divided into two parts, a central part and a surface layer part located outside the central part, and the average alkali metal concentration in the surface part when the average alkali metal concentration in the central part is 1. Concentration.

<Measurement method of alkali metal distribution state>
The distribution state of the alkali metal in the water-absorbing polymer particles is measured using an energy dispersive X-ray analyzer (EDX) attached to a scanning electron microscope (SEM) based on an enlarged cross-sectional image of the water-absorbing polymer particles. It can be measured by elemental analysis. First, a substrate provided with a plurality of water-absorbing polymer particles to be measured and an adhesive layer (for example, a double-sided tape such as Nichibanai stack double-sided paper NW-15S attached to one surface of a substrate such as stainless steel or copper) The particles are spread on the adhesive layer so that the particles do not overlap each other. Next, the entire water-absorbing polymer particles are embedded with a resin (for example, epoxy resin, methacrylic acid resin, polyester resin) to form a resin layer. The amount of the resin forming the resin layer is set to a minimum amount necessary for embedding the entire water-absorbing polymer particles with the resin, and an excessive amount of resin is not used. Next, using a microtome, the resin layer is cut into two in the thickness direction, thereby cutting the water-absorbing polymer particles in the resin layer. The intersection of the major axis and the minor axis on the cut surface of the water-absorbing polymer particles thus obtained is taken as the center of the water-absorbing polymer. Subsequently, mapping of the alkali metal is performed by EDX on the cut surface of the obtained water-absorbing polymer particles while being enlarged by SEM. In the operation of EDX, the X-ray extraction angle is 30 °, the X-ray folding time is 30 minutes, and a Si (Li) semiconductor detector can be used for X-ray detection. In this alkali metal mapping, the particle is separated from the center including the center and the center by dividing the space between the center of the water-absorbing polymer particle and an arbitrary point on the surface of the particle approximately in half. The surface layer portion is also divided into two, and the amount of X-rays specific to alkali metal atoms is counted for each of these two regions, and the alkali metal concentration is measured. Such an operation is repeated five times to calculate the average alkali metal concentration of each of the center portion and the surface layer portion, and the alkali metal concentration ratio is calculated by the following equation. Alkali metal concentration ratio = (average alkali metal concentration in the surface layer / average alkali metal concentration in the center)

  The alkali metal concentration ratio is preferably 1 to 1.3, more preferably 1 to 1.2, and still more preferably 1 to 1.1.

  Such a water-absorbing polymer in which the alkali metal is uniformly distributed throughout the polymer (the water-absorbing polymer having the alkali metal concentration ratio within 1.3) is, for example, a water-absorbing polymer (carboxy group and / or Or a water-absorbing polymer having a carboxylate group) is sequentially subjected to a surface crosslinking treatment and a neutralization treatment using a neutralizing agent containing an alkali metal in the presence of a predetermined amount of water (so-called post-neutralization treatment). Obtained by. The amount of water used in the neutralization treatment (water content of the water-absorbing polymer) is the neutralization in the above-described method for producing the water-absorbing polymer A (manufacturing method having steps 1 to 3, manufacturing method having steps I and II). It is preferable to control to 100 mass% or more with respect to a water absorbing polymer similarly to a process, especially 100-600 mass%.

  In general, when such post-neutralization treatment (neutralization treatment after surface cross-linking treatment) is applied to water-absorbing polymer particles, the surface of the particles and the vicinity thereof (surface layer portion) are more than the center portion of the particles. The alkali metal concentration is expected to be higher (the alkali metal concentration ratio exceeds 1.3), but the post-neutralization treatment was performed in the presence of a predetermined amount of water, and the degree of neutralization was 75 mol%. The water-absorbing polymer particles described above have a feature that the alkali metal distribution is uniform as described above.

  Regarding the water-absorbing polymer used in the present invention described above, the description regarding the water-absorbing polymer A described above is appropriately applied to points that are not particularly described.

In the case of a sanitary napkin, the content of the water-absorbing polymer A in the absorbent body 4 is 2 to 90 mass%, particularly 5 to 70 mass%, based on the total mass of the absorbent body 4. It is preferable in terms of the balance between softness and absorption performance during wearing. In particular, the napkin 1, when the thickness (7 g / cm ² Thickness under load) is less ultra-thin 2.5mm, the content of the water-absorbent polymer A, 20 to 90% by weight, in particular 30 It is preferable to set it to -70 mass% in terms of the balance between thinness and absorption performance. When a water-absorbing polymer other than the water-absorbing polymer A is contained in the absorber 4, the content of the water-absorbing polymer in the absorber 4 can be the same as the content of the water-absorbing polymer A. The distribution amount of the water-absorbing polymer (all the water-absorbing polymers in the absorber including the water-absorbing polymer A) in the absorbent body 4 is preferably 5 to 250 g / m ² , more preferably 10 to 200 g / m ² . is there. In addition, when applying the water-absorbing polymer of the present invention to an article that absorbs urine such as a diaper or a urine absorbing pad, the ratio of the water-absorbing polymer and fibers can be appropriately adjusted and used.

  In addition, from the viewpoint of suppressing texture and roughness of the absorption rate, texture such as a feeling of sensation, and appearance redness after washing, or in the absorbent sheets 4a and 4b of the present embodiment, the water-absorbing polymer associated with the tearing of the fiber web From the viewpoint of dropping off the strength and reducing the strength of the absorbent sheet, the water-absorbing polymer contained in the absorbent body 4 preferably has an average particle size of 200 to 600 μm, particularly 250 to 450 μm, especially 250 to 400 μm.

  In addition, among all the water-absorbing polymers contained in the absorbent body 4, the content of the water-absorbing polymer having a particle size of less than 250 μm is less than 20% by mass, particularly less than 15% by mass, so that it can be worn for a long time. Sometimes, the absorption time of the liquid into the napkin 1 is short, it is difficult for leakage to occur, and redness is easily removed, which is preferable. Further, in addition to the content of the water-absorbing polymer having a particle size of less than 250 μm being in the above range, the content of the water-absorbing polymer having a particle size of less than 150 μm is less than 5% by mass, particularly less than 3% by mass. This is preferable because the above-described effect can be more reliably exhibited.

  The “average particle size” and the “content of water-absorbing polymer having a particle size of less than 250 μm” and “content of water-absorbing polymer having a particle size of less than 150 μm” are measured by the following <Method for measuring particle size distribution>, respectively. The As is apparent from the following measurement method, the “water-absorbing polymer having a particle size of less than 250 μm or less than 150 μm” is not limited to a water-absorbing polymer having a spherical shape or a nearly spherical shape. The shape of the water-absorbing polymer is not limited.

<Measuring method of particle size distribution>
50 g of all the water-absorbing polymers contained in an absorbent article, for example, napkin 1 (absorbent body 4), are used in accordance with the standard of openings 850, 600, 500, 355, 300, 250, 150 defined in JIS Z8801. Using a sieve (for example, a standard sieve manufactured by Tokyo Screen Co., Ltd.) and a tray, sieving is performed using a shaker (for example, AS200 model manufactured by Lecce). The shaking condition is 50 Hz, the amplitude is 0.5 mm, and the shaking time is 10 minutes. The measurement was performed 3 times, and the average value was defined as the mass on the sieve. The mass on each sieve obtained was divided by 50 to determine the relative frequency, and a particle size cumulative curve was drawn. The particle diameter corresponding to the central cumulative value (50%) of the cumulative curve was taken as the average particle diameter. After the sieving operation, the “water-absorbing polymer having a particle size of 250 μm or more” is placed on the sieve having an opening of 250, and the “water-absorbing polymer having a particle size of less than 250 μm” is screened under the sieve having an opening of 250, that is, a sieve having an opening of 150. On the upper and lower trays, “water-absorbing polymer having a particle size of less than 150 μm” means what is on the tray after passing through a sieve having 150 openings. The sieving was performed 3 times, and the average value of 3 times was defined as the mass on each sieve. The mass on each obtained sieve was calculated as a mass percentage with respect to the total mass, and the abundance ratio of each particle size was calculated. The measurement is performed at 23 ± 2 ° C. and humidity 50 ± 5%, and the sample is measured after being stored in the same environment for 24 hours or more.

The napkin 1 can be made thin by containing the specific water-absorbing polymer described above. The thickness of the napkin 1 is preferably 1 to 10 mm, particularly 1 to 7 mm, and more preferably 1.5 to 5.5 mm because it does not feel strange while preventing leakage during wearing and is convenient for carrying. The thickness of the napkin here means the thickness of the napkin under a load of 7 g / cm ^{2 and} is measured by the following method.

<Method for measuring thickness>
Place the entire product to be measured (napkins) on a flat surface with the top sheet side up, without wrinkles or bending, and place 7 g / cm ^{2 on} the upper surface of the area where the absorber is placed. Apply a load and measure the thickness under that condition. Thickness meter PEACOCK DIAL UPRIGHT GAUGES R5-C (manufactured by OZAKI MFG.CO.LTD.) Is used for measuring the thickness. At this time, a plate (an acrylic plate having a thickness of about 5 mm) is disposed at the measurement portion between the tip of the thickness meter and the product, and the size of the plate is adjusted so that the load is 7 g / cm ² . The shape of the plate is circular or square. The measurement is performed at 23 ± 2 ° C. and humidity 50 ± 5%, and the sample is measured after being stored in the same environment for 24 hours or more.

  The absorbent body 4 (absorbent sheets 4a and 4b) contains fibers in addition to the water-absorbing polymer described above. As the fiber contained in the absorbent body 4, those normally used in the technical field can be appropriately used. Examples include natural fibers such as wood pulp and plant pulp such as conifer pulp and hardwood pulp, regenerated fibers such as cupra and rayon, semi-synthetic fibers such as acetate, synthetic fibers such as polyolefins, polyamides, and polyesters. These 1 type can be used individually or in mixture of 2 or more types.

  From the viewpoint that blood adhering to the napkin easily flows out quickly when the napkin is washed with water, it is preferable that the natural fiber includes a modified pulp obtained by subjecting the natural fiber to a crosslinking treatment. That is, the absorbent body 4 has a laminated structure in which a plurality of layers made of fiber assemblies are laminated, and a water-absorbing polymer is interposed between opposing layers in the laminated structure, and the fiber assemblies are modified. It is preferred to include pulp and natural fibers (preferably softwood and / or hardwood pulp). As a modified pulp, the below-mentioned crosslinked cellulose fiber and mercerized pulp can be used.

  The proportion of the modified pulp in the total fibers contained in the absorbent body 4 is preferably 20 to 100% by mass, and more preferably 35 to 80% by mass. Moreover, the ratio of the natural fibers such as softwood pulp in the total fibers contained in the absorbent body 4 is preferably 0 to 80% by mass, and more preferably 20 to 55% by mass.

The fiber content in the absorbent body 4 is preferably 10 to 98 mass%, more preferably 30 to 95 mass%, based on the total mass of the absorbent body 4. In the case of an ultra-thin napkin having a thickness (thickness under a load of 7 g / cm ² ) of 2.5 mm or less, it is preferably 10 to 70% by mass, particularly preferably 30 to 60% by mass.

  The absorber 4 is mainly composed of a water absorbing material (in this embodiment, a water absorbing polymer and a fiber). The water-absorbing material includes not only a material that itself retains liquid but also a material that retains liquid in the gap. The content of the water-absorbing material in the absorber 4 is preferably 90% by mass or more, and more preferably 95% by mass with respect to the total mass of the absorber 4.

  The content of the water-absorbing material in the absorbent body 4 is preferably 100% by mass from the viewpoint of water-absorbing performance, but the absorbent body 4 contains a hygroscopic agent and a deodorant as necessary in addition to the absorbent material. Etc. can be contained. Examples of the hygroscopic agent include silica gel, and examples of the deodorizer include activated carbon, activated clay, and a silver-containing compound.

  One preferred embodiment of the absorbent body 4 has a structure in which a plurality of hydrophilic sheets (layers of fiber aggregates) are overlapped and a water-absorbing polymer is sandwiched between the overlapping hydrophilic sheets. (Absorbers having a laminated structure in which a plurality of layers made of fiber assemblies are laminated, and having a water-absorbing polymer interposed between at least one of the layers in the laminated structure). Hereinafter, an absorber having such a structure (using a hydrophilic sheet) will be described.

  The hydrophilic sheet is preferably an absorbent paper containing bulky cellulose fibers and hydrophilic fine fibers. This absorbent paper (hydrophilic sheet) contains 30 parts by mass or more of bulky cellulose fibers, particularly 40 to 90 parts by mass, and less than 70 parts by mass of hydrophilic fine fibers with respect to 100 parts by mass of the absorbent paper. In particular, the content is preferably 103 to 60 parts by mass. The abundance ratio of these two kinds of fibers in the hydrophilic sheet may be different for each layer (hydrophilic sheet) constituting the absorber.

  As the bulky cellulose fiber, a) the average fiber length is preferably 0.8 to 20 mm, more preferably 1.5 to 5 mm, and b) the molecule and the molecule are crosslinked ( Is a crosslinked cellulose fiber), or c) when the network of cellulose fibers is formed, the fiber itself is bulky, that is, thick as a structure. Specifically, the fiber roughness is preferably 0.3 mg / m or more, More preferably, it is 0.3-2 mg / m, More preferably, it is 0.32-1 mg / m. Particularly preferred bulky cellulose fibers are those having all of the above-mentioned a) to c). The average fiber length and fiber roughness in this specification are measured as follows. “Fiber roughness” is used as a measure of fiber thickness in fibers with non-uniform fiber thickness, such as wood pulp.

<Measurement of average fiber length and fiber roughness>
It was measured using a fiber roughness meter FS-200 (manufactured by KAJAANI ELECTRONICS LTD.). First, in order to obtain the true mass of the measurement target fiber (cellulose fiber), 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 was accurately weighed from the obtained diluted solution to make a fiber roughness measurement solution, and the target average fiber length and fiber roughness were 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 was used for calculation of average fiber length.

  The bulky cellulose fiber provided with a) and b) can maintain its bulky structure even in a wet state. In addition, the bulky cellulose fiber having the above c), that is, the bulky cellulose fiber having a fiber roughness of 0.3 mg / m or more is bulky in the fiber web because the cellulose fiber is accumulated in a bulky state. This is preferable because a network structure is easily formed. Further, it is preferable because the movement resistance of the body fluid is small and the passage speed of the body fluid is increased. Examples of bulky cellulose fibers with a fiber roughness of 0.3 mg / m or more include softwood kraft pulp (“ALBACEL” (trade name) from Federal Paper Board Co. and “INDORAYON” (product from PTInti Indorayon Utama) Name)).

  Although there is no restriction | limiting in particular in the method (the manufacturing method of a crosslinked cellulose fiber) for bridge | crosslinking a cellulose fiber like said b), For example, the crosslinking method of the fiber using a crosslinking agent is mentioned. Examples of such crosslinking agents include N-methylol compounds such as dimethylolethylene urea and dimethylol dihydroxyethylene urea; polycarboxylic acids such as citric acid, tricarballylic acid and butanetetracarboxylic acid; dimethylhydroxyethylene urea and the like. Polyols; Examples include crosslinkers of polyglycidyl ether compounds. In particular, a crosslinking agent of polycarboxylic acid or polyglycidyl ether compound that does not generate formalin or the like harmful to the human body during crosslinking is preferable.

  The amount of the crosslinking agent used is preferably 0.2 to 20 parts by mass with respect to 100 parts by mass of the cellulose fiber. If the amount of the crosslinking agent used is less than 0.2 parts by mass, the crosslinking density of the cellulose fibers is low, so that the elastic modulus may be greatly reduced when wet. If the amount used exceeds 20 parts by mass, the cellulose fibers Is too stiff and the cellulose fiber may become brittle when stress is applied, so the above range is preferable.

  In order to cross-link cellulose fibers using the cross-linking agent, for example, 1) A cellulose fiber is impregnated into an aqueous solution of the cross-linking agent, if necessary, and the aqueous solution of the cross-linking agent becomes the design adhesion amount. The cellulose fiber is dehydrated, and then the cellulose fiber is heated to the crosslinking temperature, or 2) the aqueous solution of the crosslinking agent is sprayed on the cellulose fiber so as to have a designed adhesion amount by spraying, and then heated to the crosslinking temperature. And cross-linking reaction. Examples of commercially available crosslinked cellulose fibers include “High Bulk Additive” manufactured by Weyerhaeuser Paper Co.

  In addition to a) and b) and / or c), the bulky cellulose fiber has d) a round cross-sectional shape of the fiber. Specifically, the roundness of the fiber cross-section is 0.5. More preferably, it is -1 and especially 0.55-1. Bulky cellulose fibers having a fiber cross-section roundness of 0.5 to 1 are preferred because they have low body fluid movement resistance and a high body fluid permeation rate. Particularly preferred bulky cellulose fibers are those having all of a) to d). The roundness of the fiber cross section is measured as follows.

<Measurement of roundness of fiber cross section>
The fiber to be measured is sliced in a cross-sectional direction orthogonal to the length direction. When slicing, be careful not to change the cross-sectional area of the fiber as much as possible. The cross section of the fiber obtained by slicing is imaged using an electron microscope, and the cross-sectional photograph is analyzed with an image analyzer (“Avio EXCEL” (trade name) manufactured by Nippon Avionics Co., Ltd.). The roundness of the target fiber cross section was obtained. In addition, 100 degrees of arbitrary fiber cross sections measured this roundness, and it was set as the average value. (Roundness of fiber cross section) = 4 × π × (cross section area of measurement fiber) / (perimeter of cross section area of measurement fiber) ²

  As described above, wood pulp is preferably used as the fiber material of bulky cellulose fibers, but generally the cross section of wood pulp is flattened by delignification treatment, and most of its roundness is less than 0.5. It is. In order to set the roundness of such wood pulp to 0.5 or more as described above, for example, such wood pulp may be mercerized to swell the cross section of the wood pulp. Examples of commercially available mercerized pulp that can be used in the present invention include “FILTRANIER” (trade name) manufactured by ITT Rayonier Inc. and “POROSANIER” (trade name) manufactured by the same company.

  Examples of the hydrophilic ultrafine fibers include fibrillated pulp and hydrophilic regenerated and synthetic fibers having a specific fiber diameter. Examples of the fibrillated pulp include those obtained by beatening chemically treated pulp such as softwood (NBKP), hardwood (LBKP) pulp, or crosslinked pulp. In addition, hydrophilic fibers such as regenerated cellulose fibers such as rayon, lyocell, and tencel, and synthetic fibers such as acetate and acrylic can be used. When using recycled fibers or synthetic fibers, use fibers that are as thin as possible, that is, those that are molded as thin as possible in a range that does not exceed 1 dtex, or those that obtain a fiber that does not exceed 1 dtex as a result of split processing, such as split fibers. Is preferred. Among them, tencel is preferable in that the fibers can be easily fibrillated with a relatively simple device, and can be refined by beating as in the case of pulp.

  The hydrophilic ultrafine fibers do not have to have the same fineness for all the fibers, and some of the fibers are thinned and thinned, such as fibrillated pulp, and some of the split fibers are It includes the case where it is divided and contains ultrafine fibers. The average fiber length of the hydrophilic ultrafine fibers is preferably 0.3 to 5 mm, more preferably 0.5 to 3 mm, and the diameter (fiber width) is preferably 5 to 100 μm. These can be measured using a pulp fiber length distribution measuring device (manufactured by Kajaani).

  The absorbent paper (hydrophilic sheet) preferably has a stable structure even when wet. In order to obtain the structural stability of the absorbent paper when wet, the above-described bulky paper is added to the absorbent paper. In addition to water-soluble cellulose fibers and hydrophilic fine fibers, heat-melting adhesive fibers, paper strength reinforcing agents, ordinary cellulose fibers (for example, wood pulp and non-wood pulp), etc. are blended, etc. It is effective to increase the wet strength. In particular, blending of a hot-melt adhesive fiber or a paper strength reinforcing agent is effective.

  As the hot-melt adhesive fibers, fibers that are melted by heating and bonded to each other can be used. Specifically, for example, polyolefin fibers such as polyethylene, polypropylene, and polyvinyl alcohol, polyester fibers, and polyethylene-polypropylene composite fibers. , Polyethylene-polyester composite fiber, low-melting point polyester-polyester composite fiber, polyvinyl alcohol-polypropylene composite fiber having a hydrophilic fiber surface, and 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 hot-melt adhesive fibers can be used alone or in combination of two or more. Examples of the hot-melt adhesive fibers preferably used in the present invention include polyvinyl alcohol fibers that are dissolved in hot water, and core-sheath type polyester fibers.

The absorbent paper (hydrophilic sheet) can be produced, for example, as follows. The concentration of bulky cellulose fibers is 0.16% by mass, the concentration of hydrophilic fine fibers is 0.05% by mass, and the thickness is 1 denier and the average fiber length is 3 mm. These were uniformly dispersed in water so that the concentration of Kuraray Co., Ltd., called PVA, was 0.01% by mass (0.022% by mass as a whole slurry) to obtain a slurry. This slurry was sprayed onto a papermaking wire having a wire opening diameter of 1.4 mm (12 mesh) to form a paper layer on the papermaking wire. The paper layer was dehydrated using a suction box. The dehydrated aqueous solution contained about 0.02% by mass of fibers, most of which were hydrophilic fine fibers. Next, after drying the paper layer with a dryer, 10% crepe was applied to obtain an absorbent paper having a basis weight of 80 g / m ² . This absorbent paper contained 80 parts by mass of bulky cellulose fibers, 15 parts by mass of hydrophilic fine fibers, and 5 parts by mass of PVA fibers with respect to 100 parts by mass of the absorbent paper. Further, this absorbent paper had a gradient in the existence ratio of hydrophilic fine fibers in the thickness direction.

  One of the other embodiments of the absorbent body 4 includes a mixed fiber body of fibers and a water-absorbing polymer. This mixed product is obtained, for example, by mixing fibers and a water-absorbing polymer in an air stream. The water-absorbing polymer in this mixed fiber is distributed almost uniformly throughout the mixed fiber, and like the water-absorbing polymer in the absorber using the hydrophilic sheet described above, It is not unevenly distributed in the area of the part. Hereinafter, an absorbent body having such a mixed product fiber will be described.

  Natural fibers such as wood pulp and synthetic fibers can be used as the fibers constituting the mixed fiber. The synthetic fiber preferably has an average fiber length of 0.1 to 30 mm, more preferably 0.5 to 25 mm, and even more preferably 1.5 to 15 mm, and belongs to a range generally referred to as a short fiber. Can be used. The fineness of the synthetic fiber of this short fiber is preferably 0.1 to 7.8 dtex, more preferably 0.5 to 5.6 dtex, and still more preferably 0.9 to 3.4 dtex.

  As the synthetic fiber, for example, a single synthetic fiber containing one kind of resin such as polyethylene, polypropylene, polyethylene terephthalate, or a composite synthetic fiber containing two or more kinds of these resins can be used. Among these, it is preferable to use composite synthetic fibers in that various well-known functionalities can be imparted, or melt adhesion between fibers and bulkiness of a mixed fiber (absorber) can be imparted. Examples of the composite synthetic fiber include a core-sheath type and a side-by-side type. Examples of the cross-sectional shape of the composite synthetic fiber include a circular shape, an irregular shape, a C shape, and a hollow shape. When a single synthetic fiber is used, a single synthetic fiber having an irregular cross-sectional shape is preferable.

  Synthetic pulp can also be used as the synthetic fiber. As the synthetic pulp, for example, a material made of a thermoplastic resin such as polyethylene, modified polyethylene, or polypropylene is preferably used. Synthetic pulp has an average fiber length of preferably 0.1 to 10 mm, more preferably 0.5 to 5 mm, and even more preferably 0.9 to 1.5 mm, similar to natural pulp such as wood pulp. It is preferable because it can be handled easily.

  Since the natural pulp is generally a material having high liquid absorption and diffusibility, the liquid absorption capacity of the mixed fiber can be increased by using it as a main constituent fiber of the mixed fiber. On the other hand, since the synthetic fiber is a material having a property of being melted by heating to a predetermined temperature, by using this as a main constituent fiber of the mixed product, the mixed product is produced in the manufacturing process of the mixed product. The strength of the entire mixed fiber body can be increased by a process such as heating the entire fiber body to melt the synthetic fiber. When synthetic fibers are used as the main constituent fibers of the mixed product, the mixed product is mainly composed of a nonwoven fabric such as an airlaid nonwoven fabric.

  In addition to the above-mentioned natural pulp and synthetic fiber, the mixed fiber is a short fiber of natural or (semi) synthetic hydrophilic fiber such as rayon, cotton, lyocell, tencel, acetate, polyvinyl alcohol fiber, acrylic, etc. May be included. In addition, the mixed product is different in size, composition, etc. (for example, size, thickness, shape in plan view, mixing ratio of fibers and water-absorbing polymer, etc.) are laminated. May be formed, and may be divided into arbitrary shapes.

  The napkin 1 of the present embodiment is configured to be able to remove redness caused by blood by washing with water by the action of the water-absorbing polymer described above having characteristics such as the degree of neutralization and the amount of centrifugal retention within a specific range. Although it has sufficient water washability, the napkin 1 may further contain a metal ion scavenger in order to further improve the water washability. Hereinafter, the metal ion scavenger will be described.

  Examples of the metal ion scavenger include ethylenediaminetetraacetic acid (EDTA) tetrasodium, nitrilotriacetic acid (NTA) trisodium, diethylenetriaminepentaacetic acid (DTPA) pentasodium, hydroxyethylethylenediaminetriacetic acid (HEDTA) trisodium, L-glutamic acid. Aminocarboxylate-based metal ion scavengers such as tetraacetic acid (GLDA) tetrasodium; phosphonate metal ion scavengers such as hydroxyethylidene diphosphonic acid (HEDP) tetrasodium; sodium tripolyphosphate (STPP), sodium pyrophosphate (TSPP), polymer phosphate metal ion scavengers such as sodium hexametaphosphate; builders for polymer detergents such as sodium polyacrylate, acrylic acid / maleic acid copolymer; trisodium citrate, citric acid Other organic metal ion scavengers such as ammonium; inorganic metal ion scavengers such as zeolite (crystalline aluminosilicate), sodium silicate, and the like. These may be used alone or in combination of two or more. Can be used. Of these, tetrasodium ethylenediaminetetraacetate (EDTA), trisodium citrate, sodium tripolyphosphate, sodium acrylate, and zeolite are preferred. Especially, trisodium citrate is highly water-soluble, so It is easy to move to the location, has a high redness removal effect, and has excellent biodegradability. Trisodium citrate is preferable because it is effective in weakening the affinity between hemoglobin contained in menstrual blood and the water-absorbing polymer and has a high redness removal effect.

  Examples of the method of containing the metal ion scavenger in the napkin 1 include a method of spraying as a solid (powder); an aqueous solution obtained by dissolving or dispersing the metal ion scavenger in an appropriate solvent such as water, and the aqueous solution And a method of spraying or applying the sucrose onto a predetermined part of the napkin 1 (a part where the metal ion scavenger is desired to be contained).

  Examples of the location of the metal ion scavenger include the interior of the absorbent body 4 and its peripheral portions from the viewpoint of efficiently capturing menstrual blood and capturing metal ions in the wash water. As the inside of the absorbent body, between the absorbent sheet 4b disposed on the surface and the periphery of the water-absorbent polymer, and the position farthest from the skin (position closest to the back sheet 2) and the absorbent sheet 4a positioned immediately above the absorbent sheet 4b Is preferred. When a metal ion scavenger is contained inside the absorber 4, the content of the metal ion scavenger is preferably 0.001 to 30% by mass, more preferably 0.01% with respect to the total mass of the absorber 4. -10 mass%.

  Moreover, as a peripheral site | part of the absorber 4 which can disperse | distribute a metal ion trapping agent, for example, A) The skin contact surface side (for example, between the surface sheet 2 and the absorber 4) rather than the absorber 4, B) Absorption Non-skin contact surface side of the body 4 (for example, between the absorber 4 and the back sheet 3), C) a region having a constant width (preferably 3 to 15 mm width) along the periphery of the absorber 4 is included. . In the napkin 1, the metal ion scavenger may be present at one location or may be present at a plurality of locations.

  When substantially the entire absorbent body 4 is covered with a covering sheet (not shown), the metal ion scavenger 10 may be disposed on the inside of the covering sheet, and may be disposed on the outside of the covering sheet. May be. That is, the metal ion scavenger 10 may be covered with the covering sheet together with the absorber 4, or may be disposed outside the covering sheet that covers the absorbing body 4.

  Particularly preferred locations of the metal ion scavenger are the surface and the periphery of the water-absorbing polymer and the portion B) on the non-skin contact surface side of the absorbent body 4. In this case, the absorbed menstrual blood and the like could be washed out with water most cleanly.

FIG. 7 shows an embodiment in which B) is adopted as the location of the metal ion scavenger. In the embodiment shown in FIG. 7, the metal ion scavenger 10 exists between the inner sheet 11 and the back sheet 3 disposed adjacent to the non-skin contact surface of the absorber 4. In FIG. 7, for ease of explanation, the metal ion scavenger 10 is described as if it forms a layer, but it does not necessarily form a layer in practice. Due to the presence of the inner sheet 11, the absorber 4 and the metal ion scavenger are separated from each other, and the metal ion scavenger can be prevented from entering the absorber 4 beyond the design value. As the inner sheet 11, the same sheet as the covering sheet can be used. The basis weight of the inner sheet 11 is preferably 10 to 20 g / m ² and the thickness is 0.05 to 0.15 mm.

  In the case where the metal ion scavenger is contained in the napkin 1, the content of the metal ion scavenger is preferably 0.00 with respect to 100 parts by mass of the total water-absorbing polymer contained in the napkin 1 from the viewpoint of washing menstrual blood and the like more cleanly from the napkin. It is 01-100 mass parts, More preferably, it is 0.1-50 mass parts, Most preferably, it is 0.5-20 mass parts.

The napkin 1 of this embodiment can remove redness due to menstrual blood by simple water washing. The degree of redness removal can be evaluated by the redness degree a ^* value of the red portion stained red by blood in the napkin after blood is injected and washed in accordance with the following procedures 1 to 3. The smaller the a ^* value, the lower the degree of red in the red part, which means that the blood has been washed away with water.

Procedure 1: Inject 12 g of blood into the sanitary napkin from the surface layer side of the sanitary napkin, leave it in an environment of 25 ° C. for 30 minutes, and then remove the sanitary napkin with water having a water temperature of 25 ° C. and a hardness of 12 ° DH. The sanitary napkin is squeezed by hand, and the water contained in the napkin is squeezed out as much as possible.
Procedure 2: On the surface layer side of the wet sanitary napkin obtained in the procedure 1, the red degree a ^* using a spectrocolorimeter for the five most reddish spots of the red part stained with blood ^. Measure the value.
Procedure 3: The average of the three measured values obtained by removing the maximum value and the minimum value from the five measured values obtained in the procedure 2 is defined as the red degree a ^* value of the sanitary napkin.

The a ^* value obtained according to the procedures 1 to 3 is a measure for evaluating the superiority or inferiority of the water-washing ability of the absorbent article. The smaller the a ^* value, the lower the degree of red in the red part. It means that the blood has been washed away by washing (excellent washing ability). The napkin 1 of the present embodiment having the above-described configuration has an a ^* value of 7 or less, preferably 5 or less, and has a practically sufficient water washing ability.

In the procedures 1 to 3, horse blood is used as blood to be injected into the napkin. More specifically, equine defibrinated blood manufactured by Japan Biotest Laboratory Co., Ltd. is used. The viscosity of this horse defibrinated blood is less than 15 mPa · S as measured with a (B type) viscometer TVB-10M (measurement temperature 25 ° C., rotor L adapter) manufactured by Toki Sangyo Co., Ltd.
In the above procedures 1 to 3, water used for washing the napkin is water prepared by dissolving calcium chloride and magnesium chloride in ion-exchanged water having an electric conductivity of 1 μS / cm or less, and calcium ions and magnesium. Water having an ion content ratio (calcium ion: magnesium ion) of 7: 3 and a German hardness of 12 ° DH is used.
In addition, Indonesian water for daily use, which is one of the countries that have a habit of washing used sanitary napkins, has different hardness depending on the region, but water with a German hardness of 12 ° DH used in the above steps 1 to 3 It is almost the same as domestic water used in at least part of Indonesia.

In the procedure 1, the environment in which the napkin into which blood has been injected is allowed to stand for 30 minutes before washing is an air temperature of 25 ° C. and a humidity of 60%.
The napkin is washed by hand, and “the operation of putting about 100 g of water on the napkin with one hand and squeezing the napkin with the other hand” is repeated three times in 10 seconds. That is, the operation performed for 10 seconds is “sprinkle water → squeeze the napkin → spread water → squeeze the napkin → spread water → squeeze the napkin”. Therefore, the amount of water used for washing the napkin for 3 minutes in the procedure 1 is approximately 100 g as described above because the amount of water used in one water application operation is approximately 100 g as described above. 3 =) 5400 g. In the above formula, 100 × 3 corresponds to the amount of water used for 10 seconds, and 100 × 3 × 6 corresponds to the amount of water used for 1 minute.
When watering the napkin, use a beaker or the like, and do not squeeze the napkin while watering.
In Procedure 1, the pressure when hand-squeezing the napkin after washing the napkin for 3 minutes, that is, the gripping force of the hand is usually about 10 to 15 kg.
When measuring the red degree a ^* value of the red part, the measurement sample and the spectral color difference meter are brought into close contact with each other so that external light does not enter. As the spectral color difference meter, a simple spectral color difference meter “NF333” (pen type detector) manufactured by JASCO Corporation can be used.

Hereinafter, the napkin 1 of this embodiment is further demonstrated.
On the skin contact surface side (surface sheet 2 side) of the napkin 1, leakage prevention grooves 5 and 5 extending in the longitudinal direction of the napkin 1 are formed on both left and right sides in the longitudinal direction. Each leakage prevention groove 5 is formed by compacting and integrating the topsheet 2 and the absorber 4 from the topsheet 2 side by pressing means such as embossing. Each leak-proof groove 5 has a substantially symmetric shape with respect to the vertical center line of the napkin 1. The leakage prevention grooves 5 are connected to each other at their front and rear ends, thereby forming a closed shape as a whole. By forming the leak-proof grooves 5 and 5, body fluids flowing outward in the napkin width direction are blocked, and leakage (lateral leakage) from the side of the napkin 1 is effectively prevented and cleaning is performed. Since the decomposition of the napkin at the time can be suppressed, it is easy to perform the washing operation and blood can be easily washed away. Furthermore, the fact that the leak-proof grooves 5 and 5 have reached the vicinity of the lower part of the absorber 4 in order to prevent water from flowing through the entire absorber during cleaning and to prevent blood from remaining due to the absorber being biased. preferable.

  An end seal portion 6 is formed on the periphery of the napkin 1 at a position spaced outward from the absorber 4. The end seal portion 6 in the present embodiment is formed by integrating the top sheet 2 and the back sheet 3. More specifically, in the present embodiment, the top sheet 2 and the back sheet 3 extend from the peripheral edge portion of the absorbent body 4, and are joined to each other by a heat embossing process at the extended portions. Is formed. The end seal portion 6 has an effect of preventing the water absorbent material constituting the absorbent body 4 from flowing out when the napkin 1 is washed (when wet). It is preferable that the end seal portion 6 is not provided with a material that causes swelling or the like due to water used for the absorbent body 4 from the viewpoint of not separating each sheet material that is a constituent material of the end seal portion during cleaning. Further, the end seal portion 6 is formed by heat embossing with an adhesive such as hot melt disposed at a predetermined portion of the sheet material, thereby improving and stabilizing the flexibility of the seal portion and the seal strength when wet. From the viewpoint of making it more preferable.

  The napkin 1 of the present embodiment is used by being attached to an undergarment in the same manner as a normal sanitary napkin of this type. Since the napkin 1 of the present embodiment includes the absorber 4 containing the specific water-absorbing polymer described above, the napkin 1 can be easily washed with water while having practically sufficient absorption performance. It is easy to wash away the blood adhering to the napkin 1 with water. For this reason, it can be suitably used for people who have a habit of discarding the used napkin after washing with water. In addition, since the napkin 1 of the present embodiment contains a water-absorbing polymer, the napkin 1 can be designed to have a small thickness, is not bulky, and has excellent portability and wearing feeling.

  As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not restrict | limited to the said embodiment. For example, the absorbent article (sanitary napkin) of the present invention may not include the leak-proof groove 5, the adhesive portion (not shown), the wing portion, the rear flap portion, and the like included in the embodiment. good. Each of the wing part and the rear flap part is a part extending outward from the both side edges in the longitudinal direction of the absorbent body 4, and the wing part is normally opposed to the excretion part disposed to face the excretion part of the napkin wearer. The rear flap part is located behind the wing part in the napkin longitudinal direction.

  Further, the absorbent article to which the absorbent body of the present invention can be applied, or the absorbent article of the present invention is not limited to sanitary napkins, but is used for disposable diapers, incontinence pads, urine-absorbing pads, pet diapers, pet sheets, etc. Is also applicable. The water-absorbing polymer (water-absorbing polymer A) used in the present invention has a reduced water absorption ratio by adjusting the centrifugal retention amount to the specific range, and further has a liquid passing rate under pressure of 2.0 kPa. When adjusted to the specified range, the liquid flow rate under pressure is high, so the absorption rate under repetition or pressure is very fast, and the liquid can diffuse quickly to the details of the absorber. Moreover, even if it swells, there is little so-called gel feeling, which leads to an improvement in uncomfortable feeling when worn.

  All the parts of only the one embodiment described above can be used together as appropriate.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to such examples.

  Hereinafter, a method for synthesizing the water-absorbing polymer used in this example will be described. The synthesis method is as follows: synthesis of a water-absorbing polymer (corresponding to the step 1), crosslinking treatment of the water-absorbing polymer (corresponding to the step 2), neutralization treatment of the water-absorbing polymer (corresponding to the step 3) Proceeded in the order.

[Synthesis Example 1]
(Synthesis of water-absorbing polymer)
Polyoxyalkylene ether phosphate 0.1% (as opposed to acrylic acid mass) as a dispersant in SUS304 5L reaction vessel (using anchor blade) equipped with stirrer, reflux condenser, monomer dropping port, nitrogen gas inlet tube, thermometer , Active ingredient amount), and 1500 ml of normal heptane was added. The temperature was raised to 90 ° C. while stirring in an atmosphere of nitrogen gas. On the other hand, in a 2 L three-necked flask, acrylic acid as a monomer aqueous solution was prepared from 80% acrylic acid (manufactured by Toagosei Co., Ltd., act. 80.6%), ion-exchanged water, 48% sodium hydroxide aqueous solution (manufactured by Asahi Glass Co., Ltd., act. 49.7%). 1000 g of sodium (72% neutralized product) was obtained. After adding 0.25 g of N-acylated glutamic acid soda (trade name: Amisoft PS-11) dissolved in ion-exchanged water 4.41 g to this monomer aqueous solution, 550 g (hereinafter referred to as monomer aqueous solution A). ), 250 g (hereinafter referred to as monomer aqueous solution B), and 250 g (hereinafter referred to as monomer aqueous solution C).

Next, 2,2′-azobis (2-amidinopropane) dihydrochloride (Wako Pure Chemical Industries, trade name V-50) 0.05 g, polyethylene glycol (Kao, K-PEG6000 LA) 0.5 g, citric acid 4 g of ammonium iron (III) (manufactured by Kanto Chemical) and 10 g of ion-exchanged water were mixed and dissolved to prepare an initiator (A) solution. Further, 0.6 g of sodium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 10 g of ion-exchanged water to prepare an initiator (B) solution. Further, a titanium citrate aqueous solution (50% citric acid and 7.6% (TiO ₂ ) titanyl sulfate aqueous solution mixed at a mass ratio of 20/27) was prepared. To monomer aqueous solution A, 12 g of initiator (A) solution is added to prepare monomer A. To monomer aqueous solution B, 5 g of initiator (B) solution is added to prepare monomer B. To monomer aqueous solution C, initiator ( B) Monomer C was prepared by adding 5 g of the solution and 2 g of a titanium citrate aqueous solution (citric acid / Ti molar ratio = 2, Ti amount 0.015% to acrylic acid mass).

  Subsequently, the monomer A, the monomer B, and the monomer C, which were allowed to stand for 5 minutes or more, were dropped from the monomer dropping port through the monomer dropping port in this order and polymerized. After completion of monomer dropping, azeotropic dehydration was performed using a dehydrating tube to adjust the water content of the water-absorbing polymer (hydrogel), and then ethylene glycol diglycidyl ether (manufactured by Nagase ChemteX, trade name Denacol EX- 810) A solution of 0.5 g in 10 g of ion-exchanged water was added. Thereafter, 2 g of a 60% 1-hydroxyethylidene-1,1′-diphosphonic acid aqueous solution (trade name Bride ADPA-60A, manufactured by Rhodia) was added. After cooling, normal heptane was removed and dried to obtain a water-absorbing polymer.

[Crosslinking treatment of water-absorbing polymer]
100 g of the water-absorbing polymer obtained in [Synthesis of water-absorbing polymer] was charged into the same reaction vessel (using anchor blade) as that used in [Synthesis of water-absorbing polymer], and 300 ml of normal heptane was added. While stirring in a nitrogen atmosphere, the temperature was raised to 75 ° C. Thereafter, 60 g of ion-exchanged water was dropped from the dropping port using a dropping funnel, and then ethylene glycol diglycidyl ether (trade name Denacol EX-810, manufactured by Nagase ChemteX) as a crosslinking agent was added to 10 g of ion-exchanged water. 0.0 g dissolved was added. After refluxing for 1.5 hours, normal heptane was removed and dried to obtain a water-absorbing polymer having a particle surface crosslinked.

[Neutralization treatment of water-absorbing polymer]
As a dispersant for 100 g of the dry water-absorbing polymer obtained in the above-mentioned [Crosslinking of water-absorbing polymer] in the same reaction vessel (using anchor blades) as used in [Synthesis of water-absorbing polymer]. Sucrose fatty acid ester (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-770) is charged with 2% (weight of water-absorbing polymer, amount of active ingredient), and neutralized with 5 times the amount of water-absorbing polymer. 12.5 g of sodium hydrogen carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) was added as an agent and gradually added dropwise. The obtained water-absorbing polymer was washed with isopropanol, the dispersant was washed, filtered and dried to obtain a water-absorbing polymer with an adjusted neutralization degree.

[Synthesis Examples 2 to 5]
Five types of water-absorbent particles whose surfaces were crosslinked by Synthesis Examples 2 to 5 according to [Synthesis of water-absorbing polymer], [Crosslinking treatment of water-absorbing polymer] and [Neutralization treatment of water-absorbing polymer]. A polymer was obtained. Synthesis Examples 1 to 5 differ only in the amount of the crosslinking agent used in [Cross-linking of water-absorbing polymer], 5 g in Synthesis Example 2, 1 g in Synthesis Example 3, 0.2 g in Synthesis Example 4, and Synthesis Example 5 In this case, 0.05 g was used.

[Synthesis Examples 6-9]
According to Synthesis Examples 6 to 8 according to Synthesis Example 1, three types of water-absorbing polymers whose particle surfaces were crosslinked were obtained. Synthesis Examples 6 to 8 differ only in the amount of the neutralizing agent used in the above [Neutralization of water-absorbing polymer], 7.7 g in Synthesis Example 6, 17.5 g in Synthesis Example 7, and 26 in Synthesis Example 8 .8 g was used. Further, Synthesis Example 9 was carried out in the same manner as in Synthesis Example 1 except that [Neutralization treatment of water absorbent polymer] was not performed after [Crosslinking treatment of water absorbent polymer].

[Synthesis Example 10]
According to the method for producing a water-absorbing polymer having the steps I and II, a water-absorbing polymer was produced as follows. That is, in a 5 L reaction vessel (using a Foudra blade) similar to that used in Synthesis Example 1, sucrose fatty acid ester (manufactured by Mitsubishi Chemical Foods, trade name Ryoto Sugar Ester S-770) as a dispersant is 2% (relative to water absorption). The mass of the active polymer and the amount of the active ingredient) was added, and 2000 ml of cyclohexane was added. While stirring in a nitrogen atmosphere, the temperature was raised to 73 ° C. On the other hand, in a 2 L three-necked flask, 1000 g of sodium acrylate (85% neutralized product, concentration 47%) as a monomer aqueous solution was obtained from 80% acrylic acid, ion-exchanged water, and 48% sodium hydroxide aqueous solution. In this monomer aqueous solution, 1.1 g of sodium persulfate and 15 g of ethylene glycol diglycidyl ether (manufactured by Nagase ChemteX, trade name Denacol EX-810) as a crosslinking agent (3.4% based on the mass of the monomer (acrylic acid)) Was dissolved. Subsequently, the monomer solution which left still for 5 minutes or more was dripped and polymerized in the said 5 L reaction container using the microtube pump from the monomer solution dripping port. After aging for 1 hour, a solution obtained by dissolving 74 g of 30% aqueous sodium hydroxide solution in 625 g of ion-exchanged water was further added using a dropping funnel from the dropping port. Thereafter, the water content was dehydrated to 35% by mass, and after cooling, cyclohexane was removed and dried to obtain a neutralized water-absorbing polymer.

[Synthesis Example 11]
Into the same reaction vessel (using anchor blades) as used in the above [Synthesis of water-absorbing polymer], 100 g of water-absorbing polymer taken from a commercially available disposable diaper (Merry's M size, manufactured by Kao Corporation) was charged. 300 ml of heptane was added. While stirring in a nitrogen atmosphere, the temperature was raised to 90 ° C. Thereafter, 60 g of ion-exchanged water was dropped from the dropping port using a dropping funnel, and then ethylene glycol diglycidyl ether (trade name Denacol EX-810, manufactured by Nagase ChemteX) as a crosslinking agent was added to 10 g of ion-exchanged water. 0.0 g dissolved was added. After refluxing for 1.5 hours, normal heptane was removed and dried to obtain a water-absorbing polymer having a particle surface crosslinked. 2 g of sucrose fatty acid ester (product name: Ryoto Sugar Ester S-770, manufactured by Mitsubishi Chemical Foods) as a dispersant for 100 g of the dried water-absorbing polymer thus obtained (weight of water-absorbing polymer, amount of active ingredient) ), 12.5 g of sodium hydrogen carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) as a neutralizing agent was added to 5 times the amount of ion-exchanged water of the water-absorbing polymer, and the solution was gradually added dropwise. The obtained water-absorbing polymer was washed with isopropanol, the dispersant was washed, filtered and dried to obtain a neutralized water-absorbing polymer.

[Synthesis Example 12]
A water-absorbing polymer was produced using an aqueous solution polymerization method as follows. That is, 81.8 g of acrylic acid, 0.25 g of N, N′-methylenebisacrylamide and 241 g of deionized water were charged in a reaction vessel, and the temperature of the contents was kept at 1 to 2 ° C. while stirring and mixing. Next, after flowing nitrogen into the liquid layer of the contents to make the oxygen concentration less than 0.02%, 1% hydrogen peroxide aqueous solution 1 g, 0.2% ascorbic acid aqueous solution 1.2 g and 2% 2.8 g of an aqueous 2,2′-azobisamidinopropane dihydrochloride aqueous solution was added and mixed to initiate polymerization (about 5 ° C.). With the polymerization, the temperature continued to rise, and polymerization was carried out while maintaining the temperature at 70 to 80 ° C. for about 8 hours under hermetically sealed to obtain a hydrogel containing a crosslinked polymer. The obtained hydrogel containing the crosslinked polymer was shredded to a size of 3 to 7 mm with an internal mixer to obtain a shredded gel, and then 48% sodium hydroxide aqueous solution 67 was added to 325.0 g of the shredded gel. .5 g was added to neutralize 72 equivalent% of the carboxyl groups to obtain a neutralized chopped gel. Next, this neutralized chopped gel is laminated to a thickness of about 5 cm on a stainless steel tray that is 20 cm long × 20 cm wide × 10 cm high, has no top plate, and has a 4 mm mesh wire mesh on the bottom plate. And it dried with the ventilation type band dryer (made by Inoue Metal) on the conditions of 150 degreeC and the wind speed of 2.0 m / s, and obtained the dried body. The dried product was pulverized and sieved using a sieve having an opening of 150 μm and a sieve having the same size of 710 μm to obtain a water-absorbing polymer having a particle size of 150 to 710 μm.

  Next, 100 g of the water-absorbing polymer was charged into the same reaction vessel (using anchor blades) as used in Synthesis Example 1, and 300 ml of normal heptane was added. While stirring in a nitrogen atmosphere, the temperature was raised to 90 ° C. Thereafter, 60 g of ion-exchanged water was dropped from the dropping port using a dropping funnel, and then ethylene glycol diglycidyl ether (trade name Denacol EX-810, manufactured by Nagase ChemteX) as a crosslinking agent was added to 10 g of ion-exchanged water. .5 g dissolved was added. After refluxing for 1.5 hours, normal heptane was removed and dried to obtain a water-absorbing polymer having a particle surface crosslinked. 2 g of sucrose fatty acid ester (product name: Ryoto Sugar Ester S-770, manufactured by Mitsubishi Chemical Foods) as a dispersant for 100 g of the dried water-absorbing polymer thus obtained (weight of water-absorbing polymer, amount of active ingredient) ), 12.5 g of sodium hydrogen carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) as a neutralizing agent was added to 5 times the amount of ion-exchanged water of the water-absorbing polymer, and the solution was gradually added dropwise. The obtained water-absorbing polymer was washed with isopropanol, the dispersant was washed, filtered and dried to obtain a neutralized water-absorbing polymer.

[Synthesis Example 13]
A water-absorbing polymer in a dry state obtained in Synthesis Example 9 (carboxyl group and / or carboxylate group and neutralization degree 72 mol%, centrifugal retention amount 10 g / g according to JIS K 7223), and surface treatment A dry state aluminum oxide powder (manufactured by Wako Pure Chemical Industries, Ltd.) as an agent (cationic compound) was mixed (dry blend method) to obtain a water-absorbing polymer with the zeta potential V1 adjusted to a predetermined range. The amount of aluminum oxide powder added was 0.5% by mass relative to the mass of the water-absorbing polymer.

  Neutralization degree of the water-absorbing polymer obtained in Synthesis Examples 1 to 13, amount of centrifugal retention, water absorption rate by vortex method, bulk specific gravity, liquid flow rate under pressure at 2.0 kPa, absorption amount under pressure at 2.0 kPa Were measured according to the measurement methods described above. The degree of neutralization was measured by the method using the neutralization titration curve described above. For some of the water-absorbing polymers obtained in Synthesis Examples 1 to 13, the water absorption rate by the DW method, the zeta potential V1, and the absolute value ΔV of the zeta potential difference between the water-absorbing polymer and bovine hemoglobin. The alkali metal concentration ratio was measured according to the measurement methods described above. These results are shown in Table 1 below. The zeta potential V2 of bovine hemoglobin subjected to the measurement of the absolute value ΔV of the zeta potential difference is +10 mV in Synthesis Examples 9 and 13, respectively, −9 mV in Synthesis Example 6, and in Synthesis Examples 1, 7, and 8-12, respectively. It was -12 mV.

[Example 1]
70 parts by mass of a crosslinked pulp (“High Bulk Additive HBA-S” manufactured by Weyerhauser Paper) having a fiber roughness of 0.32 mg / m and a fiber cross-section of 0.30, and a fiber roughness of 0.18 and a fiber cross-section 30 parts by weight of softwood kraft pulp (Skeena Cellulose Co. “SKEENA PRIME”) having a roundness of 0.32 is dispersed and mixed in water, and further, a paper strength reinforcing agent (polyamide) is added to 100 parts by dry weight of the mixed pulp. Epichlorohydrin resin (manufactured by Nippon PMC Co., Ltd., Kaimen WS-570) was dispersed and mixed with 1 part by weight of the resin component in water to obtain a predetermined concentration, and this dispersed mixture was dried at the forming part of a wet paper machine. The fiber web was formed so that the amount was 25 g / m ² . Next, the fiber web was dehydrated with a suction box until the water content became 100 parts by mass based on 100 parts by mass of the dry fiber web. Next, immediately before the press part, the water-absorbing polymer of Synthesis Example 1 was sprayed almost uniformly at a spraying basis weight of 30 g / m ² on the wet fiber web after dehydration. Next, a pre-paper-absorbing absorbent paper (basis weight 25 g / m ² ) having the same composition as that of the fiber web as a fiber aggregate is superposed on the surface of the fiber web where the water-absorbing polymer is dispersed. The laminated body of the fiber web and the absorbent paper was introduced into a dryer, and dried and integrated at a temperature of 130 ° C. to obtain an absorbent sheet having a water-absorbing polymer fixed therein. After the two absorbent sheets (length 90 mm, width 35 mm) are overlaid, the two absorbent sheets (length 200 mm, width 75 mm) are arranged above and below, and the longitudinal front and rear ends are curved. The absorbent was cut into a shape.

  An adhesive was applied to the non-skin contact surface side of the obtained absorber, and a back sheet was fixed on the non-skin contact surface of the absorber via the adhesive. Next, the entire surface of the skin contact surface of the absorbent is covered with a surface sheet, and the skin contact surface side of the surface sheet is embossed according to a conventional method to form a leak-proof groove, and a napkin precursor Got. An adhesive is applied to a predetermined portion of the non-skin contact surface (outer surface of the back sheet) of the napkin precursor obtained in this manner to form an adhesive part, and further, the extension from the peripheral part of the absorber in each of the front and back sheets. The end portion was subjected to end sealing according to a conventional method to obtain a napkin. In this napkin, an air-through nonwoven fabric (a perforated sheet used for a Kao Co., Ltd. Laurier Super Slim Guard) was used as the top sheet, and a polyethylene film having a thickness of 25 μm was used as the back sheet. The napkin generally has the structure shown in FIGS. The napkin thus obtained was used as a sample of Example 1.

In the napkin of Example 1, the content of the water-absorbing material (water-absorbing polymer and fiber) is 100% by mass with respect to the total mass of the absorber, and the water-absorbing property contained in the napkin (absorber). All of the polymers were the water-absorbing polymer A, and the content of the water-absorbing polymer A in the absorber was 40% by mass with respect to the total mass of the absorber. The thickness of the napkin of Example 1 (thickness under a load of 7 g / cm ² ) was 1.8 mm.

[Examples 2 to 4]
In Example 1, a napkin was prepared in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 2 was used as the water-absorbing polymer, and this was used as a sample of Example 2. Further, in Example 1, a napkin was produced in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 3 was used as the water-absorbing polymer, and this was used as a sample of Example 3. Further, in Example 1, a napkin was prepared in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 4 was used as the water-absorbing polymer, and this was used as a sample of Example 4.

Example 5
In Example 2, the napkin was prepared in the same manner as in Example 2 except that the absorber was replaced with the following, and the thickness of the napkin (thickness under a load of 7 g / cm ² ) was 5.5 mm. A sample of Example 5 was obtained.

(Absorber of Example 5)
A hot-melt adhesive (P-618B manufactured by Toyo Petrolite) was applied separately at a coating amount of 5 g / m ² , and separately prepared on the adhesive coating surface of a tissue paper (upper covering sheet) having a basis weight of 16 g / m ^2. A pulp fiber fiber web (basis weight 240 g / m ² , width 7 cm, length 17 cm) was placed. This tissue paper has larger dimensions than the fiber web. Next, from the top of the fiber web, 0.13 g of the water-absorbing polymer of Synthesis Example 2 was uniformly spread over the entire fiber web. Further, a tissue paper (basis weight 16 g / m ² ) as a lower covering sheet in which a hot-melt adhesive is applied at a coating amount of 5 g / m ² with the same size as the fiber web on the water-absorbing polymer spray surface of the fiber web. Are stacked so that the adhesive application surface faces the fiber web, and the portions extending from the fiber web in the upper coating sheet are wound up on the upper surface of the lower coating sheet, and then the upper and lower surfaces of the fiber web are Was inverted to obtain a rectangular absorbent body in a plan view in which substantially the entire absorbent body was covered with a tissue paper (coating sheet). A schematic cross-sectional view (corresponding to FIG. 2) of the napkin of Example 5 is shown in FIG. In FIG. 8, reference numeral 4 is an absorbent body, reference numeral 41 is a water-absorbing polymer, reference numeral 42 is a fiber web, reference numeral 43 is an upper covering sheet, and reference numeral 44 is a lower covering sheet.

Example 6
In Example 3, except that 1 g of trisodium citrate (94 parts by mass with respect to 100 parts by mass of the total water-absorbing polymer contained in the napkin) was sprayed as a metal ion scavenger between the absorber and the back sheet. A napkin was produced in the same manner as in Example 3, and this was used as the sample of Example 6. The thickness of the napkin of Example 6 (thickness under a load of 7 g / cm ² ) was 1.8 mm.

[Examples 7 to 9]
In Example 1, a napkin was produced in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 6 was used as the water-absorbing polymer, and this was used as a sample of Example 7. Further, in Example 1, a napkin was produced in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 7 was used as the water-absorbing polymer, and this was used as a sample of Example 8. Further, in Example 1, a napkin was produced in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 8 was used as the water-absorbing polymer, and this was used as a sample of Example 9.

Example 10
In Example 1, a napkin was produced in the same manner as in Example 1 except that the absorber was replaced with the following (mixed fiber), and this was used as a sample of Example 10.

(Absorber of Example 10)
100 parts by mass of defibrated pulp (fluff pulp) and 20 parts by mass of the water-absorbing polymer of Synthesis Example 1 are mixed in an air stream, and placed in a mold having a predetermined dimension (width 7 cm, length 17 cm) under the mold. Fibers were piled while suctioning from the inner surface of the metal mesh placed on the side. The basis weight of the mixed fiber thus obtained was 240 g / m ² . The mixed fiber was wrapped with a tissue paper having a basis weight of 16 g / m ² spray-coated with a hot melt adhesive to obtain an absorbent body.

[Examples 11 to 13]
In Example 10, a napkin was prepared in the same manner as in Example 10 except that the water-absorbing polymer of Synthesis Example 10 was used as the water-absorbing polymer used in the mixed fiber, and this was used as a sample of Example 11. In Example 10, a napkin was prepared in the same manner as in Example 10 except that the water-absorbing polymer of Synthesis Example 11 was used as the water-absorbing polymer used in the mixed fiber, and this was used as the sample of Example 12. did. In Example 10, a napkin was prepared in the same manner as in Example 10 except that the water-absorbing polymer of Synthesis Example 12 was used as the water-absorbing polymer used in the mixed fiber, and this was used as the sample of Example 13. did.

Example 14
In Example 1, a napkin was produced in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 13 was used as the water-absorbing polymer, and this was used as a sample of Example 14.

[Comparative Example 1]
A napkin was produced in the same manner as in Example 1 except that the water-absorbing polymer was changed to a commercially available water-absorbing polymer (manufactured by Nippon Shokubai Co., Ltd., trade name CAW4). Various characteristics such as the degree of neutralization and centrifugal retention of the commercially available water-absorbing polymer used in Comparative Example 1 were measured according to the measurement methods described above. In addition, regarding the commercially available water-absorbing polymer used in Comparative Example 1, the zeta potential V2 of bovine hemoglobin subjected to measurement of the absolute value ΔV of the zeta potential difference was +10 mV.

[Comparative Examples 2-3]
A napkin was prepared in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 5 was used as the water-absorbing polymer in Example 1, and this was used as a sample of Comparative Example 2. Further, in Example 1, a napkin was prepared in the same manner as in Example 1 except that the water-absorbing polymer of Synthesis Example 9 was used as the water-absorbing polymer, and this was used as a sample of Comparative Example 3.

[Comparative Example 4]
In Example 1, a napkin was prepared in the same manner as in Example 1 except that the water-absorbing polymer was changed to a nonionic water-absorbing polymer (Sumitomo Seika, Aqua Coke). did. Various characteristics such as the centrifugal retention amount of the nonionic water-absorbing polymer used in Comparative Example 4 were measured according to the measurement methods described above.

[Reference example]
A sanitary napkin “Super Maxi” (manufactured by Kao Corporation) marketed in Indonesia was used as a sample for reference. This super maxi does not contain a water-absorbing polymer.

[Evaluation]
For the sanitary napkins of Examples, Comparative Examples, and Reference Examples, the thickness was measured according to the measurement method, and the redness a ^* value was measured according to the procedures 1 to 3. Further, the state of the napkin after completion of the procedure 3 was visually observed, and it was confirmed whether or not the napkin was broken (washing breakage) due to washing with water. Moreover, as evaluation of the absorption performance of these sanitary napkins, the absorption time and the liquid return amount were measured by the following methods. These results are shown in Table 2 below. Table 1 below shows the characteristics of the water-absorbing polymer used in each sanitary napkin. In addition, regarding the red degree a ^* value, when the measured value is 1 or less, the measured value can be regarded as substantially 0 in consideration of the measurement error.

<Measurement method of absorption time>
With the sanitary napkin to be measured spread in a plane and fixed on a horizontal surface with the top sheet facing up, an acrylic plate with a cylindrical injection part is placed on the top sheet in the center of the absorber. Further, a weight is placed on the acrylic plate, and a load of 5 g / m ² is applied to the center of the absorber. The injection part provided on the acrylic plate has a cylindrical shape with an inner diameter of 10 mm, and the central axis of the cylindrical injection part coincides with the central axis in the longitudinal direction and the width direction of the acrylic plate, and the cylindrical injection part A through-hole having an inner diameter of 10 mm is formed so as to communicate between the inside and the surface sheet facing surface of the acrylic plate. Next, the acrylic plate is arranged so that the central axis of the cylindrical injection portion coincides with the central portion of the absorber in plan view, and 3 g of blood is injected from the cylindrical injection portion and absorbed by the sanitary napkin. The time (seconds) from when the blood reached the surface of the napkin until the total amount of 3 g was absorbed by the napkin was measured, and this was taken as the first absorption time. In addition, 3 minutes after the first blood injection, the above procedure is repeated until 3 g of blood is further injected (a total of 6 g of blood is injected) until the total amount of the reinjected blood is absorbed by the napkin. Time (seconds) was measured, and this was taken as the second absorption time. The smaller the value of these absorption times, the faster the absorption speed and the higher the evaluation. Table 1 below shows the absorption time for the second time (when 6 g of blood was injected). In addition, in the first time, when it exceeded 3 minutes until the total amount (3 g) of the injected blood was absorbed, the next 3 g was injected immediately after the total amount was absorbed.

<Measurement method of liquid return amount>
In <Measurement method of absorption time>, after 3 minutes from the third blood injection, the acrylic plate and the weight are removed, and the basis weight of 30 g / 7 cm × 7 cm is formed on the skin contact surface of the napkin (on the top sheet). Ten sheets of m ² absorbent paper (commercial tissue paper) were placed on top of each other, and a load of 68 g / cm ² was applied to the absorbent paper for 1 minute. After the loading, 10 sheets of absorbent paper were removed, and the weight of the 10 sheets of absorbent paper was measured. From this measured value and the measured value of the weight of 10 sheets of absorbent paper before the load obtained in advance, the mass (g) of blood absorbed in 10 sheets of absorbent paper is determined, and this mass is taken as the liquid return amount. did. The smaller the liquid return amount, the higher the napkin absorption performance and the higher the evaluation.

As is apparent from the results of Tables 1 and 2, each napkin of Examples 1 to 14 has a practically sufficient absorption performance and is sufficiently washed with water despite being as thin as 5.5 mm or less. It is possible to remove redness. On the other hand, the napkin of Comparative Examples 1 and 3 mainly has a neutralization degree of the water-absorbing polymer of less than 75 mol%, so that the a ^* value is larger than that of the Example and it is difficult to remove redness by washing with water. It can be seen that it is. Further, in Comparative Example 1, since the centrifugal holding amount was as high as 25 g / g, the cleaning was broken. In addition, the napkin of Comparative Example 2 has an a ^* value substantially the same as that of the example, but since the centrifugal retention amount exceeds 20 g / g, the cleaning breakage occurs and it is difficult to wash with water. Recognize. In addition, the napkin of Comparative Example 4 is mainly a nonionic water-absorbing polymer and does not have a partially neutralized carboxy group, so that the absorption capacity by osmotic pressure is not sufficient. It can be seen that the absorption performance is inferior. Moreover, although a reference example does not contain a water absorbing polymer, since the thickness of an absorber is large, it turns out that it has practically sufficient absorption performance.

In addition, among the examples in which the absolute value ΔV of the zeta potential difference was measured for the water-absorbing polymer, Comparative Examples 1, 2, and 3 in which ΔV exceeded 30 mV were detergency (a ^* value or washing) as compared to other examples. The property evaluated by tearing was inferior. From this, it can be seen that ΔV is effective as an index for evaluating detergency.

1 Sanitary napkin 2 Surface sheet (surface layer)
3 Back sheet (back layer)
4, A, B, C Absorber (absorption layer)
4a, 4b Absorbent sheet 5 Leak-proof groove 6 End seal part 10 Metal ion scavenger 11 Inner sheet 40 Fiber sheet 41 Water-absorbing polymer 45 Non-woven fabric 46 Polymer sheet 46s Longitudinal side portion 50 of polymer sheet Absence of water-absorbing polymer

Claims (8)

  An absorbent comprising a water-absorbing polymer having a carboxyl group and / or a carboxylate group and having a degree of neutralization of 75 mol% or more and a centrifugal retention amount of 5 to 20 g / g in accordance with JIS K 7223.   The absorbent body according to claim 1, wherein the water-absorbing polymer has a water absorption rate of 30 seconds or more by a vortex method.   The absorbent body according to claim 1 or 2, wherein the water-absorbing polymer has a liquid passing rate under pressure of 2.0 kPa of 150 ml / min or more.   The laminated structure formed by laminating | stacking the several layer which consists of a fiber assembly is provided, The said water absorbing polymer is interposed in the at least 1 interlayer of the interlayer in this laminated structure. Absorber.   The absorbent body according to claim 4, wherein the fiber assembly includes modified pulp and natural fibers.   An absorbent comprising a water-absorbing polymer, wherein an absolute value of a difference between a zeta potential of the water-absorbing polymer in ion-exchanged water and a zeta potential of bovine hemoglobin in ion-exchanged water is 30 mV or less.   A water-absorbing polymer, the water-absorbing polymer has a carboxyl group and / or a carboxylate group and is neutralized with a neutralizing agent containing an alkali metal, and the neutralization degree is 75 mol% or more. And an absorber in which the alkali metal is uniformly distributed throughout the water-absorbing polymer.   The absorbent article which comprises the absorber in any one of Claims 1-7.

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