JP2010214371A - Water absorbent, absorber, absorbable article and method for measuring absorption properties - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water absorbent which has excellent urine resistance; and the water absorbent which has not only excellent urine resistance but also excellent absorption properties that are stable to any composition of urine and show little change with time, and the production method and the application of the same. <P>SOLUTION: The water absorbent exhibits a specific or larger value of absorption capacity under pressure in a method in which the absorption capacity under pressure is measured in a new manner using a specific liquid to be absorbed. The present invention provides an absorber and an absorbable article in which the new absorption index led from this absorption capacity under pressure or from the resin concentration displays a specific or larger value using this water absorbent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a water-absorbing agent, an absorbent body, an absorbent article, and a method for measuring absorption characteristics. More specifically, the present invention relates to a water-absorbing agent having excellent urine resistance, a water-absorbing agent that can always exhibit excellent absorption characteristics regardless of the type of urine or other liquid to be absorbed, and its use, i.e., an absorber and an absorbent article. Furthermore, the present invention also relates to a method for measuring absorption characteristics that can easily and accurately predict the absorption behavior of a water-absorbing agent, an absorbent body and an absorbent article during actual use.

In recent years, hygienic materials such as paper diapers and sanitary napkins, so-called incontinence pads, have widely used water-absorbing resins (water-absorbing agents) as constituent materials for the purpose of absorbing body fluids such as urine and menstrual blood. ing.
Examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product, a hydrolyzate of starch-acrylic acid graft polymer, a saponified vinyl acetate-acrylic ester copolymer, an acrylonitrile copolymer, or an acrylamide. A hydrolyzate of a copolymer or a crosslinked product thereof, and a crosslinked product of a cationic monomer are known.
The characteristics that the water-absorbent resin should have include the water absorption rate, water absorption speed, gel strength, and the suction force that sucks up water from a substrate containing an aqueous liquid. It has been.

On the other hand, regarding applications of water-absorbing resins, water-absorbing resins that have a combination of the above-mentioned properties and exhibit superior performance (water-absorbing properties) when used in sanitary materials such as paper diapers and sanitary napkins. Various absorbers and absorbent articles using sapphire have been proposed.
For example, a water-absorbing resin (see Patent Document 1) that combines a specific gel volume, shear modulus, and extractable polymer content, a water-absorbing resin that specifies a water absorption amount, a water absorption rate, and gel strength, and the water-absorbing resin Paper diapers and sanitary napkins (see Patent Documents 2, 3 and 4), paper diapers (see Patent Document 5), water absorption resin having specific water absorption and absorption speed, gel stability, water absorption Water-absorbing articles using a water-absorbing resin with specified water absorption, water-absorbing component amount (see Patent Document 6), water-absorbing resin containing water-absorbing resin with specified water absorption amount, water absorption amount under pressure, gel breaking strength Sanitary goods (see Patent Document 7), paper diapers containing a water-absorbing resin that specifies the amount of water absorption and water absorption speed under pressure (see Patent Document 8), water absorption resin under pressure and water-absorbing resin that specifies the particle size Water-absorbing agent (see Patent Document 9), water absorption rate Water-absorbing agent containing a specific amount or more of a water-absorbing resin with a specified amount of water absorption under pressure in a short time (see Patent Document 10), a water-absorbing agent containing a specific amount or more of a water-absorbing resin with a specified deformation or suction index when loaded Known are composite materials (see Patent Document 11), absorbent articles (see Patent Document 12) using a resin that defines a pressure absorption index and a 16-hour extractability level.

  In recent years, absorbent articles such as paper diapers are becoming thinner, and the amount of water-absorbing resin used in the absorbent layer tends to increase. That is, in the absorbent layer of absorbent articles such as paper diapers, the weight ratio of the water absorbent resin to the total amount of the water absorbent resin and the fiber base material (hereinafter sometimes referred to as the resin concentration) is 0.3 or more, and more preferably 0.5 or more. It is becoming. However, it has been clarified that there are still problems when the above-described resins having various physical properties as described above are used for the absorbent articles having a high resin concentration. That is, although the water absorption characteristics of the absorbent article have been improved by the combination of various physical properties as described above, the water absorption characteristics of the resin are sufficiently high due to the composition of the liquid to be absorbed, especially when the resin concentration in the absorbent article is increased. The problem of not being able to demonstrate has been highlighted. For example, when the absorbent article is a paper diaper, the composition of urine changes depending on the age of the user, the food or drink to be taken, the medicine to be administered, etc., and the absorption behavior of the water-absorbent resin is significantly different from the expected The problem that there is has come to be advocated.

U.S. Pat. No. 4,654,039 JP 60-185550 A JP-A-60-185551 JP 60-185804 A JP-A-60-185805 JP 63-21902 A JP-A-63-99861 JP-A-2-34167 European Patent No. 339,461 European Patent No. 443,627 European Patent No. 532,002 European Patent No. 615,735

Accordingly, the object of the present invention is to provide a water-absorbing agent with little deterioration over time when urine is absorbed, excellent in urine resistance, and stable against any urine composition in addition to urine resistance. An object of the present invention is to provide a water-absorbing agent that is particularly suitable for an absorbent article having an absorption characteristic with little change with time and a high resin concentration.
Another object of the present invention is to clarify the absorption characteristics of the water-absorbent resin required when the resin ratio is a specific value, and to use the water-absorbent resin optimal for each resin ratio of the water-absorbent resin. It is an object of the present invention to provide an absorbent article and an absorbent article and an absorbent article that have a stable and high absorption amount, and that have a high absorption amount until a mole in a use form that is very close to actual use.

Further, another object of the present invention is to easily and accurately predict the absorption behavior of the water-absorbing agent, absorber or absorbent article during actual use, and to exhibit excellent absorption characteristics. It is an object of the present invention to provide a method for measuring absorption characteristics that is very useful for producing a selenium.

  As a result of diligent studies to achieve the above object, the present inventors have (i) deteriorated pressure absorption capacity observed using a specific liquid to be absorbed, and (ii) a specific operation using a specific liquid to be absorbed. Developed a new evaluation method that has not been proposed so far, the absorption capacity under degradation pressure and (iii) the absorption index under degradation pressure. It has been found that a water-absorbing agent exhibiting an absorption index can solve the above-mentioned problems, and has completed the present invention. Since parameter (i) does not require any specific operation, it will be referred to as the absorption capacity under static degradation and pressurization, and the four stages (1), (2), (3), (4) Although (1) and (4) are particularly important. Since the parameter (ii) is subjected to a specific operation, it is hereinafter referred to as absorption capacity under dynamic deterioration and pressure.

In addition, as a result of intensive studies on the relationship between the resin ratio in the absorbent body and the physical properties of the water-absorbing agent, the amount of absorption until the occurrence of leakage in the usage form very close to the actual use of the absorbent article is Depending on the specific relationship derived from the characteristics of the above-mentioned new specific absorption capacity under pressure or absorption index under pressure and the resin ratio in the absorber, and to increase the value of this relationship, It has been found that if the resin ratio is selected, the absorption amount of the absorbent body and the absorbent article in a usage form very close to actual use will increase, and the present invention has been completed.
The water-absorbing agent of the present invention can be any one of the following 1-3.
1. A water-absorbing agent having an absorption capacity of 30 (g / g) or more under no pressure and an absorption capacity (1) of 20 (g / g) or more under static deterioration.
2. A water-absorbing agent having an absorption capacity of 30 (g / g) or more under no pressure and an absorption capacity of 20 (g / g) or more under dynamic deterioration.
3. A water-absorbing agent having an absorption capacity of 30 (g / g) or more under no pressure and an absorption capacity (4) of 30 (g / g) or more under static deterioration.

The absorbent body of the present invention is an absorbent body comprising the water-absorbing agent of the present invention and a fiber substrate, wherein the weight ratio of the water-absorbing agent to the total amount of both is 0.4 or more.
The absorbent article of the present invention comprises an absorbent layer containing the absorbent body of the present invention, a top sheet having liquid permeability, and a back sheet having liquid impermeability.
The method for measuring the absorption characteristics of the present invention includes the absorption characteristics under pressure of the water absorbent, the absorption characteristics of the absorber in which the weight ratio of the water absorbent to the total amount of the water absorbent and the fiber substrate is 0.4 or more, and the water absorption In a method for measuring at least one absorption characteristic of an absorbent article including an absorbent having a weight ratio of the water-absorbing agent to the total amount of the agent and the fiber substrate of 0.4 or more, reduction as an absorbed liquid A characteristic substance-containing liquid is used.

Absorption capacity under no pressure, absorption capacity under static degradation and absorption capacity under dynamic degradation, the water absorption agent satisfying the value of the present invention is always stable to any urine composition and has little absorption change over time. Therefore, it is also suitably used for absorbent articles having a high resin concentration.
Since the absorbent article of the present invention is specified by the static deterioration concentration absorption index and the dynamic deterioration concentration absorption index considering the resin concentration, it always shows a stable and high absorption amount, which is also practically used. The amount of absorption until the formation of a mole in a very close use form is high.
According to the method for measuring absorption characteristics of the present invention, it is possible to easily and accurately predict the absorption behavior of water absorbents and absorbent articles during actual use, and therefore, water absorbents and absorbent articles exhibiting excellent absorption characteristics are manufactured. Very useful to.

Hereinafter, the present invention will be described in detail.
<Water absorbing agent>
The water-absorbing agent of the present invention has an absorption ratio under no pressure exceeding a specific value, and the new physical properties such as an absorption ratio under static deterioration and pressurization, an absorption ratio under dynamic deterioration and an absorption index under deterioration pressurization are also over a specific value. It has a value.
The absorption capacity without pressure in the present invention means that 0.2 g of a water-absorbing agent is uniformly placed in a non-woven bag (60 mm × 60 mm) and immersed in a 0.9 wt% aqueous sodium chloride solution (saline). After a minute, the bag is pulled up, drained at 250 G for 3 minutes using a centrifuge, and then the weight W ₁ (g) of the bag is measured. On the other hand, the same operation is performed without using a water absorbing agent. W ₀ (g) is measured, and from these two weights W ₁ and W ₀ and the weight of the water absorbing agent (g),
Absorption capacity (g / g) = [(weight W ₁ −weight W ₀ ) / weight of water absorbing agent] −1
It is a numerical value calculated according to

Absorption capacity under static deterioration pressure in the present invention means that a water-absorbing agent (resin) is first swollen 15 times using a physiological saline containing a predetermined concentration of L-ascorbic acid as a liquid to be absorbed and left for a predetermined time. This is the absorption capacity measured under load, and is a novel evaluation item for water-absorbing agents.
So far, absorption capacity, absorption capacity under pressure, liquid permeability, suction power, absorption speed, etc. are known as absorption characteristics of water-absorbent resin (water-absorbing agent). Generally, comparison is made using a liquid with an electrolyte concentration close to that of urine. Measurement is performed in a short time. However, the actual diaper is often worn for a long time. Especially when used at night, it is often worn for 6 hours or more. Therefore, the water-absorbent resin excellent in the evaluation results according to the above-described normal evaluation items that have been advocated so far does not show excellent performance even in actual use. Urine contains compounds that change (deteriorate) the physical properties of the resin over time, and the presence of these compounds greatly affects the absorption behavior of the water-absorbent resin during actual use.

The present inventors diligently developed an evaluation method that can correctly evaluate the absorption capacity of the water-absorbent resin during actual use, and as a result, using a physiological saline containing a predetermined concentration of L-ascorbic acid in the liquid to be absorbed. It was found that the absorption behavior under actual use can be easily and accurately predicted by measuring the absorption capacity under pressure after standing for a relatively long time.
So far, a method for solubilizing a water-absorbent resin using L-ascorbic acid or a salt thereof or measuring the amount of the solubilized soluble component is known (Japanese Patent Laid-Open No. 5-472221, special feature). (Kaihei 7-59813, JP-A-8-337726, JP-A-10-67805, etc.). However, these technologies are to solubilize the water-absorbent resin under saturated swelling conditions. What is the point of how the ability of the water-absorbent resin to absorb the liquid changes during use? It is not considered. On the other hand, the absorption capacity under static deterioration and pressure in the present invention determines how the original absorption capacity left in the resin during urine absorption after the first urine absorption changes due to urine. It is a new evaluation item that can be done.
Absorption capacity under static deterioration (1) (also referred to as absorption capacity under deterioration (2)) in the present invention is 15 (g / g) with physiological saline containing 0.005% by weight of L-ascorbic acid. A swollen water-absorbing agent is formed, left in that state for 6 hours, and then loaded with a load of 50 g / cm ² and further absorbed with physiological saline for 1 hour. Absorption magnification.
The water-absorbing agent of the present invention is characterized in that the absorption capacity under no pressure is 30 (g / g) or more and the value of the absorption capacity (1) under static deterioration and pressure is 20 (g / g) or more. When the absorption capacity under no pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of the absorption capacity under static deterioration pressure (1) is less than 20 (g / g), the absorbent composition of the absorbent article is similarly insufficient, and the liquid composition is likely to leak or absorb. The absorption behavior varies greatly due to fluctuations in the pressure, and stable absorption characteristics cannot be obtained. Absorption capacity (1) under static deterioration pressure is preferably 23 (g / g) or more.
Absorption capacity under static deterioration (2) (also referred to as absorption capacity under deterioration (1)) in the present invention is 15 (g / g) with physiological saline containing 0.005% by weight of L-ascorbic acid. A swollen water-absorbing agent is formed, left in that state for 2 hours, and then loaded with a load of 50 g / cm ² and further absorbed with physiological saline for 1 hour. Absorption magnification.

The water-absorbing agent of the present invention is characterized in that the absorption capacity under no pressure is 30 (g / g) or more and the value of the absorption capacity (2) under static deterioration and pressure is 23 (g / g) or more. When the absorption capacity under no pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of absorption capacity (2) under static deterioration pressure is less than 23 (g / g), the absorbent composition of the absorbent article is similarly insufficient, and leakage is likely to occur or the liquid composition is absorbed. The absorption behavior fluctuates greatly due to fluctuations in the pressure, and stable absorption characteristics cannot be obtained. Absorption capacity (2) under static deterioration pressure is preferably 25 (g / g) or more.
Absorption capacity under static deterioration (3) in the present invention (also referred to as absorption capacity under deterioration (3)) is 15 (g / g) with physiological saline containing 0.05% by weight of L-ascorbic acid. A swollen water-absorbing agent is formed, left in that state for 2 hours, and then loaded with a load of 50 g / cm ² and further absorbed with physiological saline for 1 hour. Absorption magnification.

The water-absorbing agent of the present invention is characterized in that the absorption capacity under no pressure is 30 (g / g) or more and the value of the absorption capacity (3) under static deterioration and pressure is 20 (g / g) or more. When the absorption capacity under no pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of absorption capacity under static deterioration pressure (3) is less than 20 (g / g), the absorbent composition of the absorbent article is similarly insufficient, and the liquid composition is liable to leak or absorb. The absorption behavior fluctuates greatly due to fluctuations in the pressure, and stable absorption characteristics cannot be obtained. The absorption capacity (3) under static deterioration pressure is preferably 23 (g / g) or more.
The absorption capacity (4) under static deterioration pressure in the present invention is such that a water-absorbing agent swollen to 15 (g / g) with physiological saline containing 0.05% by weight of L-ascorbic acid is formed, and 6 The absorption capacity of the water-absorbing agent is determined from the weight of the swollen gel after standing for a period of time and then placing a load of 20 g / cm ² and absorbing physiological saline for another hour.

The water-absorbing agent of the present invention is characterized in that the absorption capacity under no pressure is 30 (g / g) or more and the value of the absorption capacity (4) under static deterioration and pressure is 30 (g / g) or more. When the absorption capacity under no pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of absorption capacity (4) under static deterioration pressure is less than 30 (g / g), the absorbent composition of the absorbent article is similarly insufficient, and leakage is likely to occur or the liquid composition to absorb The absorption behavior fluctuates greatly due to fluctuations in the pressure, and stable absorption characteristics cannot be obtained. The absorption capacity (4) under static deterioration pressure is preferably 32 (g / g) or more, more preferably 34 (g / g) or more.
In the present invention, the absorption capacity under no pressure and the absorption capacity under static deterioration (1), (2), (3), (4) provide an unprecedented water-absorbing agent having a specific value or more. The paper diaper is suitably used for paper diapers having a high resin concentration accompanying a reduction in the thickness of the paper diaper and a low usage rate of the fiber substrate, and leakage during actual use can be reduced.
In the present invention, in particular, the measured value of the absorption capacity under static deterioration (1) or the measured value of the absorption capacity under static deterioration (4) is found to be important. It provides an unprecedented water-absorbing agent having an absorption capacity under static deterioration (1) or an absorption capacity under no pressure and an absorption capacity under static deterioration (4) above a specific value. The used absorbent article (for example, paper diapers) can reduce leakage during actual use.

In the case of paper diapers with a high resin concentration accompanying the recent thinning of paper diapers and a small percentage of fiber base material used, the measured value of the absorption capacity (1) under static deterioration and pressure of the water absorbent is preferable. is important.
Absorption capacity under dynamic deterioration and pressure in the present invention refers to the use of physiological saline containing a predetermined concentration of L-ascorbic acid in the liquid to be absorbed, and the water absorbing agent (resin) is first swollen 15 times and left for a predetermined time, Furthermore, it is an absorption magnification measured under load after applying dynamic damage assuming movement in actual use, and is a new evaluation item of a water absorbing agent.
So far, as absorption characteristics of a water-absorbent resin (water-absorbing agent), absorption capacity, absorption capacity under pressure, liquid permeability, suction force, absorption speed, and the like are known. In addition, there is known a method of measuring the reabsorption ability of a gel after absorbing the physiological saline in the water-absorbent resin, gelling and applying shear (US Pat. No. 5,453,323). However, since these are generally measured in a relatively short time using a liquid with an electrolyte concentration close to that of urine, a water-absorbent resin excellent in this evaluation result does not necessarily exhibit excellent performance even in actual use. I didn't. Urine contains compounds that change (deteriorate) the physical properties of the resin over time, and the presence of these compounds greatly affects the absorption behavior of the water-absorbent resin during actual use. Furthermore, since the user moves during actual use, not only a load but also a dynamic force acts on the resin.

The present inventors diligently developed an evaluation method capable of correctly evaluating the absorption capacity of the water-absorbent resin during actual use, and as a result, using a physiological saline containing a predetermined concentration of L-ascorbic acid in the liquid to be absorbed. It has been found that the absorption behavior under actual use can be easily and accurately predicted by allowing the sample to stand for a relatively long time and measuring the absorption capacity under pressure after applying a dynamic force.
So far, a method for solubilizing a water-absorbent resin using L-ascorbic acid or a salt thereof or measuring the amount of the solubilized soluble component is known (Japanese Patent Laid-Open No. 5-472221, special feature). (Kaihei 7-59813, JP-A-8-337726, JP-A-10-67805, etc.). However, these technologies are to solubilize the water-absorbent resin under saturated swelling conditions. What is the point of how the ability of the water-absorbent resin to absorb the liquid changes during use? It is not considered. On the other hand, the absorption capacity under dynamic deterioration and pressure in the present invention is that the original absorption capacity left in the resin between the time when urine is once absorbed and then further absorbed is added to the urine and the resin. It is a new evaluation item that can judge how it changes due to the dynamic force.

The absorption capacity under dynamic deterioration and pressure in the present invention is such that a water-absorbing agent swollen to 15 (g / g) is formed with physiological saline containing 0.005% by weight of L-ascorbic acid and left in that state for 4 hours. This is the absorption capacity of the water-absorbing agent determined from the weight of the swollen gel after placing a load of 50 g / cm ² after dynamic damage and further absorbing physiological saline for 1 hour.
The water-absorbing agent of the present invention is characterized in that the absorption capacity under no pressure is 30 (g / g) or more and the value of the absorption capacity under dynamic degradation and pressurization is 20 (g / g) or more. When the absorption capacity under no pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of the absorption capacity under dynamic deterioration pressurization is less than 20 (g / g), the absorption capacity of the absorbent article is similarly insufficient, and leakage or the like is likely to occur, or fluctuations in the liquid composition to be absorbed and Absorption behavior fluctuates greatly due to dynamic force applied to the resin, and stable absorption characteristics cannot be obtained. The absorption capacity under dynamic deterioration pressure is preferably 23 (g / g) or more.

The present invention provides an unprecedented water-absorbing agent having an absorption capacity under no pressure and an absorption capacity under dynamic deterioration under a specific value, and has a high resin concentration accompanying the recent thinning of paper diapers. It is also suitable for paper diapers with a small percentage of material used, and leakage during actual use can be reduced.
The absorption index under deterioration pressure in the present invention is the absorption capacity under static deterioration pressurization (1), absorption capacity under static deterioration pressurization (2), absorption capacity under static deterioration pressurization (3), Absorption capacity (4) is the total of absorption capacity under dynamic deterioration and pressure. The absorption index under deterioration pressure is an evaluation that assumes damage in actual use. The larger the sum of the values obtained by these evaluations, the higher the value of the various damage that occurs when actually used. It is considered to show performance.

  The water-absorbing agent of the present invention has an absorption capacity under no pressure of 30 (g / g) or more and an absorption index value under deteriorated pressure of 110 (g / g) or more. When the absorption capacity without pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used for an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of the absorption index under deteriorated pressure is less than 110 (g / g), the absorbent article does not have sufficient absorption capacity, and leakage or the like is likely to occur or the liquid composition to be absorbed varies and / or Absorption behavior fluctuates greatly due to dynamic force applied to the resin, and stable absorption characteristics cannot be obtained. The absorption index under deteriorated pressure is preferably 120 (g / g) or more, more preferably 130 (g / g) or more.

The present invention provides an unprecedented water-absorbing agent having an absorption ratio under no pressure and an absorption index under deterioration under pressure exceeding a specific value, and has a high resin concentration accompanying the recent thinning of paper diapers. It is also suitable for paper diapers with a low usage rate, and leakage during actual use can be reduced.
As described above, as a result of diligent efforts to develop an evaluation method capable of correctly evaluating the absorption capacity of the water-absorbent resin during actual use, the present inventors have obtained the above-mentioned static deterioration pressure absorption capacity, dynamic deterioration pressure absorption capacity. In addition, we found a new physical property called an absorption index under deteriorated pressure. In addition to this, the resin was swollen with physiological saline and allowed to stand for a long time, and then the absorption capacity (ie, absorption capacity under real pressure) was measured under load. By doing so, it was also found that the absorption behavior during actual use can be easily predicted with a certain degree of accuracy.

That is, it is possible to evaluate the absorption capacity of the water absorbent resin when there are few components that cause deterioration of the water absorbent resin during actual use or when urine fluctuations do not occur much. However, considering that there are many cases where the components to be deteriorated and fluctuations in urine often occur during actual use, this new physical property of absorption capacity under real pressure seems to be the absorption capacity of the water-absorbent resin that is required at the minimum in actual use. It is.
The absorption capacity under substantial pressure is the absorption capacity measured under load after first swelling the water absorbent (resin) 15 times with physiological saline and leaving it for a predetermined time. It is. Depending on the length of the standing time, there are two absorption capacities (1) and (2) under substantial pressure which will be described later. According to the absorption ratio under substantial pressure, it can be determined how the original absorption capacity left in the resin during urine absorption once and then further urine change due to urine.

First, the absorption capacity under substantial pressure (1) was determined by forming a water-absorbing agent swollen to 15 (g / g) with physiological saline, leaving it in that state for 2 hours, and then placing a load of 50 g / cm ² on it. Furthermore, the absorption capacity of the water-absorbing agent is determined from the weight of the swollen gel after the physiological saline is absorbed for 1 hour.
In the present invention, the water-absorbing agent preferably has an absorption capacity under no pressure of 30 (g / g) or more and a value of the absorption capacity under substantial pressure (1) of 23 (g / g) or more. In this case, the water-absorbing agent has any one of the new physical properties of the above-mentioned specific values, such as absorption capacity under static deterioration (1) to (4), absorption capacity under dynamic deterioration pressure and absorption index under deterioration pressure. Or you may have two or more. When the absorption capacity under no pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration, leakage or the like is likely to occur. The absorption capacity without pressure is more preferably 33 (g / g) or more, and still more preferably 35 (g / g) or more. In addition, when the value of the absorption capacity under actual pressure (1) is less than 23 (g / g), the absorbent article is similarly insufficient in absorption capacity, and leaks are likely to occur, and stable absorption characteristics cannot be obtained. . The absorption capacity (1) under substantial pressure is preferably 24 (g / g) or more, more preferably 25 (g / g) or more.

Next, the absorption capacity under substantial pressure (2) was determined by forming a water-absorbing agent swollen to 15 (g / g) with physiological saline, leaving it in that state for 6 hours, and then applying a load of 50 g / cm ^2. This is the absorption capacity of the water-absorbing agent determined from the weight of the swollen gel after the physiological saline has been absorbed for another hour.
In the present invention, the water-absorbing agent preferably has an absorption capacity under no pressure of 30 (g / g) or more and a value of the absorption capacity under substantial pressure (2) of 20 (g / g) or more. In this case as well, the water-absorbing agent has one of the new physical properties of the above-mentioned specific values, the absorption capacity under static deterioration pressure (1) to (4), the absorption capacity under dynamic deterioration pressure and the absorption index under deterioration pressure. You may have one or two or more. When the absorption capacity under no pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of the absorption capacity under substantial pressure (2) is less than 20 (g / g), the absorbent article is similarly insufficient in absorption capacity and is liable to leak, and stable absorption characteristics cannot be obtained. . Absorption capacity (2) under substantial pressure is preferably 23 (g / g) or more.

In the present invention, it is possible to provide an unprecedented water-absorbing agent in which the absorption capacity under no pressure and the absorption capacity under substantial pressure (1), (2) are not less than a specific value, and accompanying the recent thinning of paper diapers It is also suitably used for paper diapers with a high resin concentration and a low usage rate of the fiber base material, and leakage during actual use can be reduced.
The water-absorbing agent of the present invention preferably has an absorption rate of 20 to 80 (sec) and a water-soluble component amount of 1 to 15% by weight. The amount of the water-soluble component is more preferably 2 to 15% by weight, and further preferably 2 to 10% by weight. When the absorption rate exceeds 80 (sec), absorption of liquid up to 60 minutes tends to be slow when the absorbent body or absorbent article is made, and the return amount tends to increase. If the absorption rate is less than 20 (sec), the absorption of the liquid is too fast when the absorbent body or absorbent article is made, and gel block is likely to occur. Such a phenomenon becomes remarkable particularly in an absorbent body or absorbent article having a high weight ratio (resin concentration) of the water absorbing agent to the total amount of the water absorbing agent and the fiber base material. In addition, a water-absorbing agent having a water-soluble component amount of less than 1% by weight is very expensive to manufacture, and is substantially difficult to manufacture. The magnification tends to decrease. If the amount of water-soluble component exceeds 15% by weight, it becomes difficult to obtain a water-absorbing agent that has an absorption capacity under static deterioration pressure, an absorption capacity under dynamic deterioration pressure, and an absorption index under deterioration pressure that satisfies the scope of the present invention. Alternatively, it becomes difficult to obtain a water-absorbing agent having an absorption capacity under substantial pressure that satisfies the above range.

As a structure of the water absorbing agent of the present invention, those having a water absorbing resin as an essential component are preferably employed.
The water-absorbing agent having the specific parameter of the present invention is, for example,
1. A specific amino polyvalent carboxylic acid and a surface cross-linking agent capable of reacting with a carboxyl group of the water-absorbent resin are mixed with the water-absorbent resin, or subjected to a crosslinking treatment, or
2. A specific amino polyvalent carboxylic acid is added to a surface-crosslinked specific water-absorbing resin having an absorption capacity of 23 (g / g) or more under pressure,
It is obtained by the method.

The method for obtaining the water-absorbing agent of the present invention is not limited to the above method.
Hereinafter, the manufacturing method of the water absorbing agent of the present invention will be described in detail.
The water-absorbing resin used in the production of the water-absorbing agent of the present invention is a conventionally known resin that absorbs a large amount of water of 50 to 1000 times in ion-exchanged water and forms a hydrogel. Examples of such water-absorbing resins include polyacrylic acid partially neutralized crosslinked products, starch-acrylonitrile graft polymer hydrolysates, starch-acrylic acid graft polymer hydrolysates, vinyl acetate-acrylic acid ester copolymer Examples thereof include a saponified product of a polymer, a hydrolyzate of an acrylonitrile copolymer or an acrylamide copolymer, or a crosslinked product thereof, a saponified product of a carboxyl group-containing crosslinked polyvinyl alcohol, and a crosslinked isobutylene-maleic anhydride copolymer. Among them, those having a carboxyl group are preferable, and typically, the polymer is obtained by polymerizing and crosslinking a monomer having acrylic acid and / or a salt thereof (neutralized product) as a main component. As the water absorbent resin, those having an uncrosslinked water-soluble component in the water absorbent resin of 25% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less are used.

  Examples of the acrylate include alkali metal salts such as sodium, potassium and lithium of acrylic acid, ammonium salts and amine salts. The water-absorbent resin has a constitutional unit in the range of 0 mol% to 50 mol% acrylic acid and 100 mol% to 50 mol% acrylate (however, the total amount of both is 100 mol%). Preferably, those in the range of 10 mol% to 40 mol% acrylic acid and 90 mol% to 60 mol% acrylate (however, the total amount of both is 100 mol%) are more preferable. This neutralization may be performed in the monomer state before the polymerization, or may be performed in the polymer state during the polymerization or after the polymerization. Since a considerably long time is required, it is preferable to perform neutralization in a monomer state before polymerization from the viewpoint of production cost.

  In obtaining the water-absorbent resin of the present invention, a monomer other than the acrylic acid (salt) may be contained as necessary. Although it does not specifically limit as monomers other than acrylic acid (salt), Specifically, for example, methacrylic acid, maleic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide- Anionic unsaturated monomers such as 2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid and their salts; acrylamide, methacrylamide, N-ethyl (meth) Acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene Glycol (meth) acrylate, polyester Nonionic hydrophilic group-containing unsaturated monomers such as lenglycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate , N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and cationic unsaturated monomers such as quaternary salts thereof Examples include the body. These monomers may be used alone or as a mixture of two or more.

In the present invention, when a monomer other than acrylic acid is used, the monomer other than acrylic acid is preferably 30 mol% or less based on the total amount of acrylic acid and its salt used as the main component. More preferably, the proportion is 10 mol% or less. By using the monomer other than the acrylic acid in the above ratio, the water absorbing property of the obtained water absorbing resin can be further improved and the water absorbing resin can be obtained at a lower cost.
When polymerizing the above-described monomer to obtain the water-absorbent resin used in the present invention, bulk polymerization or precipitation polymerization can be performed. However, from the viewpoint of performance and ease of control of polymerization, It is preferable to perform aqueous solution polymerization or reverse phase suspension polymerization by making the monomer into an aqueous solution. In addition, the concentration of the monomer in the aqueous solution (hereinafter referred to as a monomer aqueous solution) when the monomer is an aqueous solution is not particularly limited, but is 10 wt% to 70 wt%. The range is preferable, and the range of 20% by weight to 40% by weight is more preferable. Moreover, when performing the said aqueous solution polymerization or reverse phase suspension polymerization, you may use together solvents other than water as needed, and the kind of solvent used together is not specifically limited.

When starting the above polymerization, for example, potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-aminodipropane) dihydrochloride, etc. These radical polymerization initiators can be used.
Further, a reducing agent that promotes the decomposition of the polymerization initiator may be used in combination, and a redox initiator may be obtained by combining the two. Examples of the reducing agent include (bi) sulfurous acid (salt) such as sodium sulfite and sodium bisulfite, L-ascorbic acid (salt), reducing metal (salt) such as ferrous salt, amines, and the like. Although it is mentioned, it is not particularly limited.

The amount of these polymerization initiators used is usually 0.001 mol% to 2 mol%, preferably 0.01 mol% to 0.1 mol%. When the amount of the polymerization initiator used is less than 0.001 mol%, the amount of unreacted monomer increases, and therefore the amount of residual monomer in the resulting water-absorbent resin increases, which is not preferable. On the other hand, when the usage-amount of these polymerization initiators exceeds 2 mol%, since the amount of water-soluble components in the obtained water-absorbent resin increases, it may not be preferable.
Moreover, you may start a polymerization reaction by irradiating active energy rays, such as a radiation, an electron beam, and an ultraviolet-ray, to a reaction system instead of using a polymerization initiator. In addition, the reaction temperature in the said polymerization reaction is although it does not specifically limit, The inside of the range of 20 to 90 degreeC is preferable. Further, the reaction time is not particularly limited, and may be appropriately set according to the kind of the monomer or polymerization initiator, the reaction temperature, and the like.

The water-absorbing resin used in the present invention may be a self-crosslinking type that does not use a crosslinking agent, but two or more polymerizable unsaturated groups or two or more reactive groups in one molecule. Those obtained by copolymerizing or reacting an internal crosslinking agent having a group are more preferred.
Specific examples of these internal crosslinking agents include, for example, N, N-methylenebis (meth) acrylamide, (poly) ethylene glycol (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth). Acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, Poly (meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene Glycol, propylene glycol, glycerol, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethylenimine, and glycidyl (meth) acrylate.

These internal cross-linking agents may be used alone or in combination of two or more. These internal cross-linking agents may be added to the reaction system all at once or in divided portions. When two or more types of internal crosslinking agents are used, it is preferable to essentially use a compound having two or more polymerizable unsaturated groups in consideration of the water absorption characteristics of the resulting water absorbent resin. By using the internal cross-linking agent, it is possible to suppress a decrease in gel absorption capacity when the swollen gel is exposed to a deteriorated atmosphere.
The amount of these internal crosslinking agents used is preferably in the range of 0.005 mol% to 2 mol%, preferably in the range of 0.02 mol% to 0.5 mol%, relative to the hydrophilic monomer. More preferably, it is inside. More preferably, it exists in the range of 0.03 mol%-0.3 mol%. When the amount of the internal cross-linking agent used is less than 0.005 mol% and more than 2 mol%, the desired static deterioration pressurization absorption capacity, dynamic deterioration pressurization absorption capacity, deterioration addition There is a possibility that a water-absorbing agent having a reduced absorption index or absorption capacity under substantial pressure and a water-absorbing agent exhibiting excellent urine resistance may not be obtained.

When using the internal cross-linking agent to introduce a cross-linked structure into the water-absorbent resin, the internal cross-linking agent is added to the reaction system during or after polymerization of the hydrophilic monomer, or after polymerization and neutralization. You just have to do it.
In the polymerization, the reaction system includes various foaming agents such as carbonate (hydrogen) salt, carbon dioxide, azo compound, inert organic solvent; starch / cellulose, starch / cellulose derivatives, polyvinyl alcohol, polyacrylic acid ( Salt), hydrophilic polymers such as crosslinked polyacrylic acid (salt); various surfactants; chain transfer agents such as hypophosphorous acid (salt) may be added.
When the water absorbent resin obtained by the polymerization reaction is in a gel form, the water absorbent resin is usually dried and pulverized as necessary.

  The water content of the water-absorbent resin that can be used in the present invention is not particularly limited, but preferably the water content (wet basis) is 1% or more and less than 40%, preferably 1% or more and 20% or less, more preferably 1%. More than 10%. The particle size of the water-absorbent resin that can be used in the production method of the present invention is usually an average particle size of 10 μm to 1000 μm, preferably 50 μm to 800 μm, more preferably more than 75 μm to 600 μm or less, particularly preferably more than 150 μm. 500 μm or less. The particle shape of the water-absorbent resin thus obtained is not particularly limited to a spherical shape, a crushed shape, an indeterminate shape, etc., but an indeterminate crushed shape obtained through a pulverization step can be preferably used. .

As the water-absorbent resin before surface crosslinking obtained through the above polymerization, drying, and pulverization steps, it is possible to use one having an absorption capacity of 30 g / g or more, further 35 g / g or more under no pressure. Although the effect of the invention is remarkably expressed, it is preferable. Of course, the above-mentioned absorption ratio is appropriately adjusted according to the purpose.
-Addition of amino polycarboxylic acid-
The water-absorbing agent having the parameters of the present invention includes, for example, the following specific amino polyvalent carboxylic acid and the carboxyl group possessed by the water-absorbing resin with respect to the water-absorbing resin before surface crosslinking obtained as described above. It is obtained by mixing a surface cross-linking agent capable of reacting with and cross-linking.

  Specific amino polyvalent carboxylic acids used in the present invention are aminocarboxylic acids having 3 or more carboxyl groups and salts thereof. These amino polyvalent carboxylic acids have high sequestering ability and chelating ability with respect to Fe and Cu, and stability constants with respect to Fe ions are 10 or more, preferably 20 or more. Specifically, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl etherdiaminetetraacetic acid, ethylenediaminetetrapropionic acid, N-alkyl -N'-carboxymethylaspartic acid, N-alkenyl-N'-carboxymethylaspartic acid, and alkali metal salts, alkaline earth metal salts, ammonium salts or amine salts thereof. Of these, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, N-hydroxyethylethylenediaminetriacetic acid and salts thereof are most preferable.

The amount of the specific amino polycarboxylic acid used in the present invention varies depending on the surface crosslinking agent used for crosslinking in the vicinity of the surface, but is usually 0.00001 to 10 parts by weight with respect to 100 parts by weight of the solid content of the water absorbent resin. Preferably it is the range of 0.0001-1 weight part. When the amount used exceeds 10 parts by weight, not only the effect suitable for use cannot be obtained and the economy becomes uneconomical, but also the amount of absorption decreases. On the other hand, if the amount is less than 0.00001 parts by weight, it is difficult to improve the absorption capacity under static deterioration or substantial absorption under pressure.
Examples of the surface crosslinking agent that can be used in the present invention include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4. -Trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, , 6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block Polyhydric alcohol compounds such as copolymers, pentaerythritol, sorbitol; ethylene glycol diglycidyl ether, polyethylene diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene Epoxy compounds such as glycol diglycidyl ether and glycidol; polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine, and inorganic or organic salts thereof (for example, aditinium salts) Etc.); multivalent compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate Polyacid oxazoline compounds such as 1,2-ethylenebisoxazoline; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl-1,3 -Dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxymethyl-1,3-dioxolane-2- ON, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxan-2-one, 1,3-dioxopan-2- Alkylene carbonate compounds such as ON; haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, and polyvalent amine adducts thereof (for example, -Cures sponge (registered trademark); silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane; hydroxides or chlorides such as zinc, calcium, magnesium, aluminum, iron, zirconium And polyvalent metal compounds such as products. Of these, polyhydric alcohols and alkylene carbonate compounds are preferred in view of safety when an unreacted surface cross-linking agent remains.

These surface cross-linking agents may be used alone or in combination of two or more. When two or more types of surface cross-linking agents are used in combination, a water-absorbing agent having even more excellent water absorption characteristics is obtained by combining the first surface cross-linking agent and the second surface cross-linking agent having different solubility parameters (SP values). be able to. The above solubility parameter is a value generally used as a factor representing the polarity of a compound.
The first surface cross-linking agent is a compound having a solubility parameter of 12.5 (cal / cm ³ ) ^1/2 or more that can react with the carboxyl group of the water-absorbent resin, such as ethylene glycol, propylene glycol, glycerin. , Ethylene carbonate, propylene carbonate and the like. The second surface cross-linking agent is a compound having a solubility parameter of less than 12.5 (cal / cm ³ ) ^1/2 that can react with the carboxyl group of the water-absorbent resin, such as glycerol polyglycidyl ether, (poly ) Glycerol polyglycidyl ether, ethylene glycol diglycidyl ether, 1,3-butanediol, trimethylolpropane, 1,3-propanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,4 -Butanediol, etc.

  The amount of the surface cross-linking agent used for the water-absorbent resin depends on the combination of the water-absorbent resin and the surface cross-linker, but is more preferably within the range of 0.005 to 10 parts by weight with respect to 100 parts by weight of the water-absorbent resin in the dry state. May be in the range of 0.05 to 5 parts by weight. By using the surface cross-linking agent within the above range, it is possible to further improve the water absorption characteristics for body fluids (aqueous liquids) such as urine, sweat and menstrual blood. When the amount of the surface cross-linking agent used is less than 0.005 parts by weight, the cross-linking density near the surface of the water-absorbent resin can hardly be increased, and the absorption capacity under static deterioration pressure, the absorption capacity under dynamic deterioration pressure, the absorption under deterioration pressure. In some cases, the index or the absorption capacity under substantial pressure does not improve. In addition, when the amount of the surface cross-linking agent used is more than 10 parts by weight, the surface cross-linking agent becomes excessive, which is uneconomical and it is difficult to control the cross-linking density to an appropriate value. There is a possibility that the absorption ratio, the absorption ratio under dynamic deterioration under pressure, the absorption index under deterioration under pressure, or the absorption ratio under substantial pressure may not be improved.

  In the present invention, it is preferable to use water when mixing the water-absorbent resin with the specific amino polyvalent carboxylic acid and the surface cross-linking agent. In the present invention, the amount of water used varies depending on the type, particle size, and water content of the water-absorbent resin, but is 0.5 to 10 parts by weight, preferably 100 parts by weight based on the solid content of the water-absorbent resin. The range is 0.5 to 3 parts by weight. If the amount of water used exceeds 10 parts by weight, the absorption capacity may decrease. If the amount is less than 0.5 parts by weight, it is difficult to fix the specific amino polyvalent carboxylic acid on the surface of the water-absorbent resin, the absorption capacity under static deterioration pressure, the absorption capacity under dynamic deterioration pressure, the absorption index under deterioration pressure. Alternatively, the absorption capacity under substantial pressure may not be improved.

  In the present invention, a hydrophilic organic solvent may be used when the water-absorbent resin is mixed with the specific amino polyvalent carboxylic acid and the surface cross-linking agent. Examples of the hydrophilic organic solvent used include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol, t-butyl alcohol, propylene glycol; ketones such as acetone; dioxane, alkoxy (poly) And ethers such as ethylene glycol and tetrahydrofuran; amides such as N, N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. The amount of the organic solvent to be used varies depending on the type and particle size of the water absorbent resin, but is usually in the range of 0 to 10 parts by weight, preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the water absorbent resin.

In the present invention, the water-absorbing resin, the specific amino polyvalent carboxylic acid, and the surface cross-linking agent may be mixed in a state where the water-absorbing resin is dispersed in an organic solvent such as cyclohexane or pentane. In order to maximize the features, the following methods (1) to (5) can be preferably exemplified.
(1) A method in which a specific amino polyvalent carboxylic acid containing water and / or a hydrophilic organic solvent and a surface cross-linking agent are mixed in advance, if necessary, and then the mixture is sprayed or dropped and mixed with a water-absorbent resin.
(2) A specific amino polyvalent carboxylic acid or a specific amino polyvalent carboxylic acid aqueous solution is mixed with the water-absorbing resin in advance, and then a surface cross-linking agent containing water and / or a hydrophilic organic solvent is sprayed or dropped as necessary. Method.

(3) If necessary, a surface cross-linking agent containing water and / or a hydrophilic organic solvent is sprayed or dropped on the water-absorbent resin, and then a specific amino polyvalent carboxylic acid or a specific amino polyvalent carboxylic acid aqueous solution is mixed. Method.
(4) A method in which a surface cross-linking agent containing water and / or a hydrophilic organic solvent and a specific amino polyvalent carboxylic acid are simultaneously sprayed or dripped into a water-absorbent resin with two nozzles, if necessary.
(5) A method in which a specific amine polycarboxylic acid is added in advance to a water-containing resin hydrogel, followed by drying or dehydration, and then spraying or mixing a surface cross-linking agent containing water and / or a hydrophilic organic solvent as necessary. (In this case, the aminopolycarboxylic acid can be added in the course of drying or dehydrating the hydrogel.)

Further, as described above, for mixing the specific amino polyvalent carboxylic acid or the surface cross-linking agent into the water-absorbing resin, it is preferable to mix as a solution using water or a hydrophilic organic solvent. By mixing the specific amino polyvalent carboxylic acid and the water-absorbing resin in the presence of water, it is possible to improve the value of the absorption capacity under static deterioration or the absorption capacity under substantial pressure. In addition, when using water for mixing, you may coexist water-insoluble fine particle powder and surfactant.
A suitable mixing device used for the mixing needs to be able to generate a large mixing force to ensure uniform mixing. Examples of the mixing apparatus that can be used in the present invention include a cylindrical mixer, a double wall conical mixer, a high-speed stirring mixer, a V-shaped mixer, a ribbon mixer, a screw mixer, and a fluidizer. A mold furnace rotary desk mixer, an airflow mixer, a double-arm kneader, an internal mixer, a pulverizer kneader, a rotary mixer, a screw extruder, and the like are suitable.

In the present invention, the specific amino polyvalent carboxylic acid and the surface cross-linking agent are mixed with the water-absorbent resin, and then the specific amino polyvalent carboxylic acid and the surface cross-linker are preferably mixed in advance and then added to the water-absorbent resin. Thereafter, the surface of the water-absorbent resin is cross-linked by further heat treatment.
When performing heat processing by this invention, the processing temperature has the preferable range of 80-250 degreeC. When the heating temperature is less than 80 ° C., the heat treatment takes time, causing not only a reduction in productivity, but also a uniform cross-linking is not achieved, and the water-absorbing agent excellent in the absorption capacity under static degradation and pressure, which is the object of the present invention May not be obtained. Also, when the processing temperature exceeds 250 ° C, the water-absorbent resin is damaged and has excellent absorption capacity under static deterioration pressure, absorption capacity under dynamic deterioration pressure, absorption index under deterioration pressure, or absorption capacity under substantial pressure. May be difficult to obtain.

The heat treatment can be performed using a normal dryer or a heating furnace, and examples include a grooved mixed dryer, a rotary dryer, a desk dryer, a fluidized bed dryer, an airflow dryer, and an infrared dryer. .
Further, a different method for producing the water-absorbing agent of the present invention is to add the specific amino polyvalent carboxylic acid described above to a surface-crosslinked water-absorbing resin having an absorption capacity under pressure of 23 (g / g) or more.
The surface-crosslinked water-absorbing resin used in this case is generally obtained by mixing the water-absorbing resin before surface cross-linking obtained by the above-described method with the above-described surface cross-linking agent and performing a cross-linking treatment.

This surface-crosslinked water-absorbent resin needs to have an absorption capacity under pressure of 23 (g / g) or more. If the absorption capacity under pressure is lower than 23 (g / g), the absorption capacity under static deterioration does not fall within the scope of the present invention, or the absorption capacity under static deterioration pressure, the absorption capacity under dynamic deterioration pressure and The absolute value of the absorption capacity under substantial pressure is low, and the water absorption performance cannot be sufficiently exhibited in the diaper even if long-term use is considered. The absorption capacity under pressure is preferably 24 (g / g) or more, more preferably 25 (g / g) or more.
In the present invention, the specific amino polyvalent carboxylic acid is added to a water-absorbing resin having an absorption capacity of 23 (g / g) or more under pressure subjected to surface crosslinking treatment. A method of combining the water-absorbent resin particles with water as a binder and granulating is preferable. Granulation increases the average particle size of the water-absorbent resin, improves the hygroscopic fluidity and facilitates handling. The amount of water added is in the range of 0.1 to 20 parts by weight, preferably 0.1 to 10 parts by weight, more preferably 0.5 to 4 parts by weight with respect to 100 parts by weight of the water absorbent resin. It is a range.

There are no particular restrictions on the method of adding the specific amino polyvalent carboxylic acid and water. For example, a method in which an aqueous solution of the specific amino polyvalent carboxylic acid is added to the water-absorbing resin for granulation, or the specific amino polyvalent carboxylic acid is absorbed in water. Examples of the method include adding water to the resin and then adding water to granulate. A specific organic polyvalent carboxylic acid and a hydrophilic organic solvent such as methanol, ethanol, isopropyl alcohol, and propylene glycol can be used in combination in order to improve the mixing property between water and the water-absorbent resin. Furthermore, a surfactant, inorganic fine particles such as silica and titanium oxide can be added in advance or simultaneously.
The water-absorbing agent obtained as described above has an excellent absorption capacity under no pressure and absorption capacity under static deterioration, absorption capacity under dynamic deterioration and pressure, water absorption index under deterioration and pressure, or absorption capacity under substantial pressure. It is a water-absorbing agent that has unprecedented superior properties, and it is also suitable for paper diapers with a high resin concentration accompanying the recent thinning of paper diapers and a small percentage of fiber base material used. Leakage can also be reduced.
<Absorber>
The water-absorbing agent of the present invention can be used in the form of an absorber. This absorber includes a water absorbing agent and a fiber base material such as a hydrophilic fiber. The weight ratio of the water absorbing agent to the total amount of the water absorbing agent and the fiber base material is 0.4 or more. In the case where the absorbent body is composed of, for example, a water absorbent and hydrophilic fibers, the structure of the absorbent body, for example, a structure including a uniform mixture of the water absorbent and hydrophilic fibers exhibits the effects of the present invention sufficiently. This is preferable. For example, a structure in which a water-absorbing agent and a hydrophilic fiber are uniformly mixed; a water-absorbing agent and a hydrophilic fiber are uniformly mixed to form a layer, and a hydrophilic fiber formed in a layer on this is formed. A laminated structure: a structure in which a water-absorbing agent and hydrophilic fibers are uniformly mixed to form a layer, and a water-absorbing agent is sandwiched between the layered hydrophilic fiber and the like can be exemplified. In addition, a configuration in which a water-absorbing agent is sandwiched between hydrophilic fibers formed in layers may be used. Further, the absorbent body may have a structure in which the water absorbing agent is formed into a sheet by blending a specific amount of water with the water absorbing agent. In addition, the structure of an absorber is not limited to the structure of the said illustration.

As a water-absorbing agent used in the absorber, the absorption capacity under no pressure is 30 (g / g) or more and the absorption capacity under static deterioration (1) is 20 (for reasons of improving the absorption capacity in actual use. g / g) Absorbent capacity with no pressure applied is 30 (g / g) or higher, Absorbent capacity with dynamic degradation is 20 (g / g) or higher, Absorbent capacity without pressure is Any water-absorbing agent having an absorption capacity (4) of 30 (g / g) or more under static deterioration and pressure is preferably 30 (g / g) or more.
The reason why it is preferable to use a water-absorbing agent having an absorption capacity under no pressure of 30 (g / g) or more and a value of the absorption capacity under static deterioration pressure (1) of 20 (g / g) or more is as follows. It is as follows. When the absorption capacity without pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when the absorbent is used for an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of the absorption capacity under static deterioration pressure (1) is less than 20 (g / g), the absorbent composition of the absorbent article is similarly insufficient, and the liquid composition is likely to leak or absorb. The absorption behavior varies greatly due to fluctuations in the pressure, and stable absorption characteristics cannot be obtained. Absorption capacity (1) under static deterioration pressure is preferably 23 (g / g) or more.

  The reason why it is preferable to use a water-absorbing agent having an absorption capacity under no pressure of 30 (g / g) or more and a value of the above-mentioned dynamic deterioration pressure absorption capacity of 20 (g / g) or more is as follows. . When the absorption capacity without pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when the absorbent is used for an absorbent article having a high resin concentration, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of the absorption capacity under dynamic deterioration pressurization is less than 20 (g / g), the absorption capacity of the absorbent article is similarly insufficient, and leakage or the like is likely to occur, or fluctuations in the liquid composition to be absorbed and Absorption behavior fluctuates greatly due to dynamic force applied to the resin, and stable absorption characteristics cannot be obtained. The absorption capacity under dynamic deterioration pressure is preferably 23 (g / g) or more.

  The reason why it is preferable to use a water-absorbing agent having an absorption capacity under no pressure of 30 (g / g) or more and an absorption capacity under static deterioration pressure (4) of 30 (g / g) or more is as follows. It is as follows. When the absorption capacity without pressure is lower than 30 (g / g), the absorption capacity is insufficient, and particularly when used in an absorbent article having a high resin concentration using the absorber, leakage or the like is likely to occur. Absorption capacity without pressure is preferably 33 (g / g) or more, more preferably 35 (g / g) or more. In addition, when the value of absorption capacity (4) under static deterioration pressure is less than 30 (g / g), the absorbent composition of the absorbent article is similarly insufficient, and the liquid composition is liable to leak or absorb. The absorption behavior fluctuates greatly due to fluctuations in the pressure, and stable absorption characteristics cannot be obtained. The absorption capacity (4) under static deterioration pressure is preferably 32 (g / g) or more, more preferably 34 (g / g) or more.

Examples of the fiber substrate include hydrophilic fibers such as cellulose fibers such as mechanical pulp, chemical pulp, semi-chemical pulp and dissolving pulp obtained from wood, and artificial cellulose fibers such as rayon and acetate. Among the above-exemplified fibers, cellulose fibers are preferable. The hydrophilic fiber may contain a synthetic fiber such as polyamide, polyester, or polyolefin. The fiber base material is not limited to the above-exemplified fibers. If the fiber substrate is in the form of a sheet or tape such as a mat or web, it can be easily used as an absorbent layer to be described later.
Moreover, when the ratio of fiber base materials, such as a hydrophilic fiber, in an absorber is comparatively small, you may adhere an absorber, ie, hydrophilic fiber, using an adhesive binder. By adhering the hydrophilic fibers together, it is possible to increase the strength and shape retention of the absorbent body before and during use of the absorbent body.

Examples of the adhesive binder include heat-bonded fibers such as polyolefin fibers such as polyethylene, polypropylene, ethylene-propylene copolymer, and 1-butene-ethylene copolymer, and adhesive emulsions. These adhesive binders may be used alone or in combination of two or more. The weight ratio between the hydrophilic fiber and the adhesive binder is preferably within the range of 50/50 to 99/1, more preferably within the range of 70/30 to 95/5, and within the range of 80/20 to 95/5. Is more preferable.
The absorber using the water-absorbing agent of the present invention preferably satisfies a static deterioration concentration absorption index represented by the following formula (1).

Static degradation concentration absorption index = X (1−α) + Yα ≧ 23 (1)
(In the formula, X is the absorption capacity (g / g) of the above water-absorbing agent under no pressure, Y is the absorption capacity (1) (g / g) of static absorption of the water-absorbing agent, and α is the water-absorbing agent and fiber. (The weight ratio of the water-absorbing agent to the total amount with the base material (α ≧ 0.4).)
The static deterioration concentration absorption index is the product of the absorption capacity X (g / g) of the water-absorbing agent under no pressure and the weight ratio of the fiber substrate in the absorbent, and the absorption capacity under static deterioration pressure (1) Y (g / g) is the sum of the product of the weight ratio of the water-absorbing agent in the absorber, and is a measure newly discovered by the present inventors as an index for predicting the absorption capacity in actual use of the absorber. is there.

  The weight ratio α of the water absorbing agent to the total amount of the water absorbing agent and the fiber substrate is selected so that the static deterioration concentration absorption index represented by the above formula (1) is 23 or more, and the water absorbing agent is selected. Thus, the amount of absorption in a state close to the actual use of the obtained absorber can be improved. Furthermore, if you select a water-absorbing agent that has an absorption ratio X under no pressure at which the static deterioration concentration absorption index values are equal and an absorption ratio (1) Y under static deterioration and pressure, each absorption capacity value Even if they are different from each other, it is possible to manufacture an absorbent body having an absorption amount almost in the same state as actual use. In this case, the absorption capacity (1) under static deterioration and pressure is a measured value using a specific novel evaluation method as described above. As described above, there are many prior literatures that evaluate the absorption capacity under pressure. In general, measurement is performed in a relatively short time using a liquid having an electrolyte concentration close to that of urine. However, the actual diaper is often worn for a long time. In particular, it is often worn for 6 hours or more when used at night. Therefore, the water-absorbing resin (water-absorbing agent) excellent in the evaluation results according to the above-described normal evaluation items that have been advocated so far does not always exhibit excellent performance even in actual use. Urine contains compounds that change (deteriorate) the physical properties of the resin over time, and the presence of these compounds greatly affects the absorption behavior of the water-absorbent resin during actual use. Furthermore, the present inventors have clarified that the importance of this characteristic varies depending on the weight ratio α of the water absorbing agent to the total amount of the water absorbing agent and the fiber base material. That is, even if only the value of the absorption capacity under pressure is pursued, the amount of absorption in a state close to the actual use of the absorbent body in a paper diaper or the like containing a fiber base material cannot be improved. It is necessary to select the resin so that the static degradation concentration absorption index satisfies a value of 23 or more.

  In the absorbent body of the present invention, the smaller the weight ratio α of the water-absorbing agent to the total amount of the water-absorbing agent and the fiber base material, the more the absorption capacity X under no pressure tends to be regarded as more important as the water-absorbing agent that can be used. Considering the value of the static deterioration concentration absorption index, a resin with a high absorption capacity (1) Y under static deterioration pressure can be used. In addition, as α increases, the absorption capacity under static deterioration and pressure as a usable water absorbing agent (1) Y tends to be more important, but the absorption capacity under no pressure in consideration of the value of static deterioration concentration absorption index Resins with high X can also be used. The effect of the present invention appears remarkably when α is 0.4 or more. Α is preferably 0.6 or more. When α is less than 0.4, depending on the type of the water-absorbing agent, the physical property difference does not appear as a significant difference in the performance of the absorber.

In the present invention, the weight ratio α of the water absorbing agent to the total amount of the water absorbing agent and the water absorbing agent and the fiber base material is determined so that the static deterioration concentration absorption index value represented by the formula (1) is 23 or more. When the static degradation concentration absorption index value is less than 23, the amount of absorption in a state close to actual use of the absorber is low. For example, in the case of paper diapers using the absorber, the rate of occurrence of leakage increases. Preferably, the static deterioration concentration absorption index value is 26 or more.
Even when the static deterioration concentration absorption index is 23 or more, the amount of water-absorbing agent used is preferably 8 (g) or more. Absorbent articles in which the amount of water-absorbing agent used is less than 8 (g) may lack a dry feeling as a product and may have a very high return amount. More preferably, it is 10-20 (g). The basis weight of the water-absorbing agent in the absorber is preferably 100 (g / m ² ) or more.

The absorber using the water-absorbing agent of the present invention preferably satisfies a dynamic deterioration concentration absorption index represented by the following formula (2).
Dynamic degradation concentration absorption index = X (1-γ) + Aγ ≧ 23 (2)
(In the formula, X is the absorption capacity (g / g) of the water-absorbing agent under no pressure, A is the absorption capacity (g / g) of the water-absorbing agent under dynamic deterioration and pressure, and γ is the water-absorbing agent and the fiber substrate. The weight ratio of the water-absorbing agent to the total amount (γ ≧ 0.4).)
The dynamic degradation concentration absorption index is the product of the absorption capacity X (g / g) of the water-absorbing agent under no pressure and the weight ratio of the fiber base material in the absorbent, and the absorption capacity A (g / g of dynamic degradation pressure). This is the sum of the product of g) and the weight ratio of the water-absorbing agent in the absorber, and is a measure newly found by the present inventors as an index for predicting the absorption capacity in actual use of the absorber.

  The weight ratio γ of the water absorbing agent with respect to the total amount of the water absorbing agent and the fiber base material is selected so that the dynamic deterioration concentration absorption index represented by the above formula (2) is 23 or more, and the water absorbing agent is selected. Thus, the amount of absorption in a state close to the actual use of the obtained absorber can be improved. Furthermore, if a water-absorbing agent having a value of the absorption ratio X under no pressure so that the values of the dynamic deterioration concentration absorption index are equal and the absorption ratio A under the dynamic deterioration pressurization is selected, the values of the respective absorption ratios are different. Even so, it is possible to manufacture an absorbent body having an absorption amount in a state almost similar to actual use. Further, the absorption capacity under dynamic deterioration and pressure in this case is a measured value using a specific novel evaluation method as described above. As described above, there are many prior literatures that evaluate the absorption capacity under pressure. In general, measurement is performed in a relatively short time using a liquid having an electrolyte concentration close to that of urine. However, the actual diaper is often worn for a long time. In particular, it is often worn for 6 hours or more when used at night. Therefore, the water-absorbing resin (water-absorbing agent) excellent in the evaluation results according to the above-described normal evaluation items that have been advocated so far does not always exhibit excellent performance even in actual use. Urine contains compounds that change (deteriorate) the physical properties of the resin over time, and the presence of these compounds greatly affects the absorption behavior of the water-absorbent resin during actual use. Further, since the user moves during actual use, not only a load but also a dynamic force acts on the resin. Furthermore, the present inventors have clarified that the importance of this characteristic varies depending on the weight ratio γ of the water absorbing agent with respect to the total amount of the water absorbing agent and the fiber base material. That is, even if only the value of the absorption capacity under pressure is pursued, the amount of absorption in a state close to the actual use of the absorbent body in a paper diaper or the like containing a fiber base material cannot be improved. It is necessary to select the resin so that the dynamic deterioration concentration absorption index satisfies a value of 23 or more.

  In the absorbent body of the present invention, the smaller the weight ratio γ of the water-absorbing agent with respect to the total amount of the water-absorbing agent and the fiber substrate, the more important is the absorption capacity X under no pressure as a usable water-absorbing agent. In view of the value of the dynamic deterioration concentration absorption index, a resin having a high absorption ratio A under dynamic deterioration pressure can also be used. Further, as γ is larger, the absorption capacity A under dynamic deterioration and pressurization is more important as a usable water absorbing agent, but the absorption capacity X under no pressure is higher in consideration of the value of the dynamic deterioration concentration absorption index. Resin can also be used. The effect of the present invention appears remarkably when γ is 0.4 or more. Preferably γ is 0.6 or more. When γ is less than 0.4, depending on the type of the water-absorbing agent, the physical property difference does not appear as a significant difference in the performance of the absorber.

In the present invention, the weight ratio γ of the water absorbing agent with respect to the total amount of the water absorbing agent and the water absorbing agent and the fiber base material is determined so that the dynamic deterioration concentration absorption index value represented by the formula (2) becomes 23 or more. When the dynamic degradation concentration absorption index value is less than 23, the amount of absorption in a state close to the actual use of the absorber is low. For example, in the case of paper diapers using the absorber, the rate of occurrence of leakage increases. Preferably, the dynamic deterioration concentration absorption index value is 26 or more.
Even when the value of the dynamic deterioration concentration absorption index is 23 or more, the amount of the water-absorbing agent used is preferably 8 (g) or more. Absorbent articles in which the amount of water-absorbing agent used is less than 8 (g) may lack a dry feeling as a product and may have a very high return amount. More preferably, it is 10-20 (g). The basis weight of the water-absorbing agent in the absorber is preferably 100 (g / m ² ) or more.

As the water-absorbing agent used in the absorbent body of the present invention, those having an absorption rate of 20 to 80 (sec) and a water-soluble component amount of 1 to 15% by weight are preferable for the reason described in the description of the water-absorbing agent. .
In addition, a deodorant, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a fertilizer, an oxidizing agent, a reducing agent, water, salts, and the like are further added to the absorber, You may give various functions to an absorber or an absorbent article using the same.
<Absorbent article>
The water-absorbing agent of the present invention can be used for absorbent articles. This absorbent article is composed of an absorbent layer including an absorber, a top sheet having liquid permeability, and a back sheet having liquid permeability. The absorption layer is sandwiched between a top sheet having liquid permeability and a back sheet having liquid permeability. Since the absorbent article has an absorption layer including the absorber having the above-described configuration, it has excellent water absorption characteristics as described above. Specific examples of the absorbent article include paper diapers, sanitary napkins, and sanitary materials such as so-called incontinence pads, but are not particularly limited. Since the absorbent article has excellent water absorption characteristics, for example, when the absorbent article is a paper diaper, it is possible to prevent leakage of urine and to impart a so-called dry feeling. If necessary, a diffusion layer made of a nonwoven fabric, cellulose, crosslinked cellulose, or the like can be disposed on the upper surface of the absorbent layer, the back surface of the top sheet, or the top surface of the top sheet.

The structure of an absorption layer is not specifically limited, What is necessary is just to have said absorber. Moreover, the manufacturing method of an absorption layer is not specifically limited. Furthermore, the method for sandwiching the absorbent layer between the liquid-permeable sheet and the liquid-impermeable sheet, that is, the method for producing the absorbent article is not particularly limited.
The absorber included in the absorbent layer includes the water-absorbing agent of the present invention and a fiber base material. Since the material, configuration, weight ratio, and other physical properties of the water-absorbing agent and the fiber base material are the same as those described in the description of the absorbent body, description thereof is omitted here.
The liquid-permeable sheet (hereinafter referred to as a liquid-permeable sheet) is made of a material having a property of transmitting an aqueous liquid. Examples of the material of the liquid permeable sheet include nonwoven fabrics, woven fabrics, and porous synthetic resin films made of polyethylene, polypropylene, polyester, polyamide, and the like. The liquid-impermeable sheet (hereinafter referred to as a liquid-impermeable sheet) is made of a material having a property of not transmitting an aqueous liquid. Examples of the material of the liquid-impermeable sheet include synthetic resin films made of polyethylene, polypropylene, ethylene vinyl acetate, polyvinyl chloride, etc .; films made of composite materials of these synthetic resins and nonwoven fabrics; And a film made of a composite material. Note that the liquid-impermeable sheet may have a property of allowing vapor to pass therethrough.

In addition, a deodorant, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a fertilizer, an oxidizing agent, a reducing agent, water, salts, and the like are further added to the absorber, Various functions may be imparted to the absorbent body or absorbent article.
The absorbent article of the present invention uses a water-absorbing agent having an absorption capacity under no pressure of 30 (g / g) or more and an absorption capacity under substantial pressure (2) of 20 (g / g) or more. The absorption ratio under no pressure is X (g / g), the absorption capacity under substantial pressure (2) is Z (g / g), and the weight ratio of the water absorbent to the total amount of the water absorbent and the fiber substrate is β. In some cases, the real concentration absorption index represented by the following formula (2) is 23 or more.

Real concentration absorption index = X (1-β) + Zβ (2)
The real concentration absorption index in the present invention is the sum of the absorption rate X (g / g) of the water-absorbing agent under no pressure and the value obtained by multiplying the absorption rate under real pressure (2) Z (g / g) by a specific ratio. The specific ratio is obtained from the weight ratio β of the water absorbing agent to the total amount of the water absorbing agent and the fiber base material.
By selecting the weight ratio β of the water-absorbing agent to the total amount of the water-absorbing agent and the fiber base so that the real concentration absorption index represented by the above formula (2) is 23 or more, and selecting the water-absorbing agent, The amount of absorption in a state close to actual use of the resulting absorbent article can be improved. Furthermore, if a water-absorbing agent having a value of absorption factor X under no pressure and a value of absorption factor under substantial pressure (2) Z that makes the value of the real concentration absorption index equal, the value of each absorption factor is different. However, the absorbent article which has the absorption amount in the state close | similar to the substantially same actual use can be manufactured. Further, the absorption capacity under substantial pressure (2) in this case needs to be a measured value using a specific novel evaluation method as described above. As described above, there are many prior literatures that evaluate the absorption capacity under pressure, but in general, measurement is performed in a relatively short time using a liquid having an electrolyte concentration close to that of urine. However, the actual diaper is often worn for a long time. In particular, it is often worn for 6 hours or more when used at night. Therefore, the water-absorbing resin (water-absorbing agent) excellent in the evaluation results according to the normal evaluation items as described above has not always exhibited excellent performance even in actual use. Furthermore, the present inventors have clarified that the importance of this characteristic varies depending on the weight ratio β of the water absorbing agent to the total amount of the water absorbing agent and the fiber base material. That is, even if only the value of the absorption capacity under pressure is pursued, the amount of absorption in a state close to the actual use of the absorbent article in a paper diaper or the like containing a fiber base material cannot be improved. It is necessary to select the resin so that the actual concentration absorption index to be satisfied satisfies the range of the present invention.

  The absorbent article of this invention contains the absorber whose weight ratio of a water absorbing agent with respect to the total amount of a water absorbing agent and a fiber base material is (beta). When β is small, absorption capacity X under no pressure tends to be regarded as more important as a water-absorbing agent that can be used. However, in consideration of the value of the real concentration absorption index, the absorption capacity under real pressure (2) is high. Resin can also be used. In addition, when β is large, the absorption capacity under real pressure as a water-absorbing agent (2) Although Z tends to be more important, the absorption capacity X under no pressure is high considering the value of the real concentration absorption index. Resin can also be used. The effect of the present invention appears remarkably when β is 0.4 or more. Preferably β is 0.6 or more. When β is less than 0.4, depending on the type of water-absorbing agent, the physical property difference does not appear as a performance difference of the absorbent article.

In the present invention, the weight ratio β of the water absorbing agent to the total amount of the water absorbing agent and the water absorbing agent and the fiber base material is determined so that the substantial concentration absorption index value represented by the formula (2) becomes 23 or more. When it is less than 23, the amount of absorption in a state close to actual use of the absorbent article is low. For example, when the absorbent article is a paper diaper, the rate of leakage increases. Preferably, the substantial concentration absorption index value is 26 or more.
Even when the value of the substantial concentration absorption index is 23 or more, the amount of the water-absorbing agent used is preferably 8 (g) or more. Absorbent articles in which the amount of water-absorbing agent used is less than 8 (g) may lack a dry feeling as a product and may have a very high return amount. More preferably, it is 10-20 (g). The basis weight of the water-absorbing agent in the absorber is preferably 100 (g / m ² ) or more.

Such an absorbent article of the present invention can be easily obtained by using the water-absorbing agent of the present invention that satisfies the above-described absorption capacity under no pressure, absorption capacity under deterioration pressure, absorption capacity under deterioration shear pressure, and absorption capacity under substantial pressure. Can be manufactured.
The absorbent article of the present invention sandwiches an absorbent layer containing such an absorbent body between a liquid-permeable surface sheet and a liquid-impervious back sheet. A diffusion layer made of non-woven fabric, cellulose, crosslinked cellulose, or the like that assists liquid diffusion can also be disposed on the back surface and the top surface of the top sheet.
The absorbent article according to the present invention is formed by sandwiching an absorbent layer including an absorbent body having the above structure between a liquid-permeable sheet and a liquid-impermeable sheet. And since this absorbent article has an absorption layer containing the absorber of the said structure, it is equipped with the outstanding water absorption characteristic as mentioned above. Specific examples of the absorbent article include paper diapers, sanitary napkins, and sanitary materials such as so-called incontinence pads, but are not particularly limited. Since the absorbent article has excellent water absorption characteristics, for example, when the absorbent article is a paper diaper, it is possible to prevent leakage of urine and to impart a so-called dry feeling.

  The liquid-permeable sheet (hereinafter referred to as a liquid-permeable sheet) is made of a material having a property of transmitting an aqueous liquid. Examples of the material of the liquid permeable sheet include nonwoven fabrics, woven fabrics, and porous synthetic resin films made of polyethylene, polypropylene, polyester, polyamide, and the like. The liquid-impermeable sheet (hereinafter referred to as a liquid-impermeable sheet) is made of a material having a property of not transmitting an aqueous liquid. Examples of the material of the liquid-impermeable sheet include synthetic resin films made of polyethylene, polypropylene, ethylene vinyl acetate, polyvinyl chloride, etc .; films made of composite materials of these synthetic resins and nonwoven fabrics; And a film made of a composite material. Note that the liquid-impermeable sheet may have a property of allowing vapor to pass therethrough.

The structure of an absorption layer is not specifically limited, What is necessary is just to have said absorber. Moreover, the manufacturing method of an absorption layer is not specifically limited. Furthermore, the method for sandwiching the absorbent layer between the liquid-permeable sheet and the liquid-impermeable sheet, that is, the method for producing the absorbent article is not particularly limited.
In addition, a deodorant, a fragrance, various inorganic powders, a foaming agent, a pigment, a dye, a hydrophilic short fiber, a fertilizer, an oxidizing agent, a reducing agent, water, salts, and the like are further added to the absorber, Various functions may be imparted to the absorbent body or absorbent article.
<Measurement method of absorption characteristics>
The method for measuring the absorption characteristics of the present invention includes the absorption characteristics under pressure of the water-absorbing agent, the absorption characteristics of the absorber in which the weight ratio of the water-absorbing agent to the total amount of the water-absorbing agent and the fiber substrate is 0.4 or more, and the water-absorbing agent and In a method for measuring at least one absorption characteristic of an absorbent article including an absorbent having a weight ratio of the water-absorbing agent to the total amount with respect to the fiber substrate of 0.4 or more, a reducing substance-containing liquid is used as the liquid to be absorbed. It is a novel evaluation method characterized by using.

As a reducing substance used here, L-ascorbic acid, ascorbate such as sodium L-ascorbate, (bi) sulfurous acid (salt) such as isoascorbic acid, isoascorbate, sodium sulfite, sodium bisulfite, Although reducing metals (salt), such as ferrous salt, amines, etc. are mentioned, L-ascorbic acid (salt) and isoascorbic acid (salt) are preferable. The concentration of the reducing substance-containing liquid varies depending on the type of reducing substance to be used and the intended usage, but for example, when L-ascorbic acid is used as the reducing substance, it is about 0.001 wt% to 0.5 wt%.
The liquid to be absorbed is not particularly limited as long as it contains a reducing substance, and examples thereof include artificial urine, physiological saline, and human urine.

The conditions for measuring the absorption characteristics of the water-absorbing agent, absorber and absorbent article are, for example, 34 to 42 ° C., preferably 35 to 39 ° C., for the purpose of predicting the absorption behavior during actual use of the absorbent article. It is preferable to measure at the temperature of this, and oxygen presence.
Examples of the absorption characteristics under pressure of the water-absorbing agent measured by the measurement method of the present invention include all absorption characteristics under pressure, and examples include absorption capacity under pressure and liquid permeability under pressure. In particular, the present invention is effective for measuring the absorption capacity under pressure.
The conditions for measuring the absorption capacity under pressure include the process of absorbing the above-mentioned reducing substance-containing liquid as essential, and based on the intended usage, European Patent No. 339,461, European Patent No. 605,150, European Patent No. No. 640,330, European Patent No. 712,659, etc., the ordinary absorption capacity under pressure, and the method of measuring the diffusion absorption capacity under pressure, loading conditions, resin basis weight, resin particle size, presence / absence of liquid diffusion conditions, etc. Should be optimized. Preferably, the absorption behavior in actual use can be more correctly determined by allowing the resin to stand for a predetermined time after absorbing the reducing substance-containing liquid, preferably for about 1 to 12 hours, and then measuring the absorption capacity under pressure. preferable.

Examples of the measurement of liquid permeability under pressure include measurement of liquid permeability of a gel under pressure as disclosed in International Application Publication No. WO95 / 26209.
Examples of the absorption characteristics of the absorber measured by the measurement method of the present invention include all absorption characteristics under no pressure and under pressure, for example, International Application Publication WO95 / 26209, European Patent No. 339,461, European Patent. Examples include absorption characteristics (absorption amount) of the absorber under pressure as disclosed in No. 712,659, absorption rate under pressure of the absorber and wet back as disclosed in European Patent No. 761,241.
Examples of the absorption characteristics of the absorbent article measured by the measurement method of the present invention include all absorption characteristics under no pressure and under pressure, for example, an absorbent article as disclosed in European Patent No. 339,461. Absorption rate and absorption amount, and absorption characteristics (absorption amount) of absorbent articles as disclosed in EP 712,659.

  According to the measurement method of the present invention, it is possible to design, select, and select a water-absorbing agent, an absorbent body, and an absorbent article that always exhibit a stable absorption behavior despite variations in the liquid to be absorbed. Moreover, the measuring method of the present invention can be preferably used for quality control on the production side of the water-absorbent resin.

Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to these examples. Various performances of the water absorbing agent were measured by the following methods.
(A) Absorption capacity under no pressure 0.2 g of a water-absorbing agent (water-absorbing resin) was uniformly placed in a non-woven bag (60 mm × 60 mm) and immersed in a 0.9 wt% aqueous sodium chloride solution (physiological saline). After 60 minutes, the bag was pulled up, drained at 250 G for 3 minutes using a centrifuge, and the weight W ₁ (g) of the bag was measured. Moreover, the same operation was performed without using a water absorbing agent, and the weight W ₀ (g) at that time was measured. From these weights W ₁ and W ₀ ,
Absorption capacity (g / g) =
(Weight W ₁ (g) −weight W ₀ (g)) / weight of water-absorbing agent (g) −1
The absorption capacity without load (g / g) was calculated according to
(B) Absorption capacity under pressure Absorption capacity under pressure was measured under 50 g / cm ² according to ABSORBENCY AGAINST PRESSURE of EDANA, ABSORBENCY III 442.1-99 (October 1997). That is, 0.9 g of a water-absorbing agent (water-absorbing resin) is uniformly sprayed on the bottom net of a plastic support cylinder having an inner diameter of 60 mm, in which a stainless steel 400 mesh wire mesh (mesh size 38 μm) is welded to the bottom. A piston (cover plate) with an outer diameter slightly smaller than 60 mm and no gap between the support cylinder and the vertical movement is not hindered, and the weight of the support cylinder, the water absorbent and the piston is measured ( Wa (g)). On this piston, a load adjusted so that a load of 50 g / cm ² including the piston can be uniformly applied to the water-absorbing agent is placed, and the measuring device set is completed. Place a 90 mm diameter glass filter inside a 150 mm diameter petri dish and add 0.9 wt% aqueous sodium chloride solution to the same level as the upper surface of the glass filter. A filter paper (Toyo Filter Paper No. 2) with a diameter of 9 cm is placed on it so that the entire surface is wetted, and excess liquid is removed.

The measuring device set is placed on the wet filter paper and the liquid is absorbed under load. When the liquid level drops from the top of the glass filter, add liquid to keep the liquid level constant. One hour later, the measuring device set is lifted and removed, and the weight (weight of the support cylinder, swollen water absorbing agent and piston) from which the load is removed is measured again (Wb (g)). And from these weights Wa and Wb, the following formula: Absorption capacity under pressure (g / g) = (Wb (g) −Wa (g)) / weight of water-absorbing agent (g)
The absorption capacity under pressure (g / g) was calculated according to
(C) Absorption capacity under static deterioration pressure (1)
The absorption capacity under static deterioration pressure (1) was measured using the same measuring apparatus as described in the section of absorption capacity under pressure. The measurement method will be described below. First, 0.9 g of a water-absorbing agent (water-absorbing resin) is uniformly spread on the inside of the support cylinder, that is, on a stainless steel 400 mesh wire net, and the weight obtained by adding the above piston (cover plate) to this is defined as W ₁ (g). . Add 13.5 g of 0.9 wt% sodium chloride aqueous solution containing 0.005 wt% L-ascorbic acid in a petri dish with a diameter of 90 mm, and spray the water absorbent resin onto the bottom wire mesh without applying any load. A support cylinder is placed, and a 0.9 wt% sodium chloride aqueous solution containing 0.005 wt% L-ascorbic acid in a petri dish is uniformly absorbed by the resin to form a 15-fold swollen gel and allowed to stand at 37 ° C. for 6 hours.

After 6 hours, place the piston (cover plate) and load in this order, adjusted so that a load of 50 g / cm ² can be uniformly applied to the swollen water absorbent. . Next, a 90 mm diameter glass filter is placed inside a 150 mm diameter petri dish, and 0.9 wt% sodium chloride aqueous solution is added to the same level as the surface of the glass filter. A 9 cm diameter filter paper (Toyo Filter Paper Co., Ltd. No. 2) is placed on the top so that the upper surface is completely wetted, and excess liquid is removed.
Then, the set of measuring devices pressurized with 15-fold swelling gel is placed on the wet filter paper, and the liquid is absorbed under load. When the liquid level drops from the top of the glass filter, add liquid to keep the liquid level constant. After 1 hour, lift up the measuring device set, remove it from the filter paper, remove the load, and re-measure its weight (W ₂ (g)). And, from these weights W ₁ and W ₂ , the following formula Static capacity deterioration absorption capacity (1) = (W ₂ (g) −W ₁ (g)) / weight of water absorbing agent (g)
Thus, the absorption capacity (1) under static deterioration and pressure was calculated.
(D) Absorption capacity under static deterioration pressure (2)
In the above measurement of the absorption capacity under static deterioration (1), the same procedure was followed except that the time for forming and leaving the gel with 15 times swelling was changed from 6 hours to 2 hours. (2) was calculated.
(E) Absorption capacity under static deterioration pressure (3)
In the above measurement of the absorption capacity under static deterioration pressure (2), the same operation was performed except that the amount of L-ascorbic acid contained in physiological saline was changed from 0.005 wt% to 0.05 wt%. Absorption capacity (3) was calculated.
(F) Absorption capacity under static deterioration pressure (4)
In the measurement of absorption capacity (1) under static deterioration and pressure, the amount of L-ascorbic acid contained in physiological saline may be changed from 0.005% by weight to 0.05% by weight and added uniformly to the water-absorbing agent. The same operation was performed except that the load that could be changed from 50 g / cm ² to 20 g / cm ² , and the absorption capacity (4) under static deterioration and pressure was calculated.
(G) Absorption capacity under dynamic deterioration and pressure 0.9 g of a water-absorbing agent (water-absorbing resin) is put in a 5 cm × 10 cm polyethylene bag, and 0.9 wt% sodium chloride aqueous solution (wt% is based on the weight of the solution). )) Was added 13.5 g of a solution in which L-ascorbic acid was dissolved at a concentration of 0.005% by weight to prepare a 15-fold swollen gel and sealed. The sealed product was kept at 37 ° C. for 4 hours. After incubating for 4 hours, the air inside the bag was removed and sealed again, and the gel was subjected to dynamic damage with a roller (diameter 9 cm, width 20 cm) having a weight of 5 kg together with the bag. At this time, the roller made 50 reciprocations at 5 seconds / rotation.

The gel that gave dynamic damage was taken out of the bag, and the absorption capacity under pressure measured using the same measuring apparatus as described in the above-mentioned absorption capacity under pressure (b) was defined as the absorption capacity under dynamic deterioration pressure. . This measuring method was as follows. The weight of the dynamically damaged gel taken out of the bag, spread on the inside of the support cylinder, that is, on the stainless steel 400 mesh wire net, and added with the piston (cover plate) (W _A (g)) Was measured. On this piston, the load adjusted so that the load of 50 g / cm < ² > including a piston was uniformly added with respect to the gel was mounted. Next, a glass filter having a diameter of 90 mm was placed inside a petri dish having a diameter of 150 mm, and a 0.9 wt% sodium chloride aqueous solution was added so as to be at the same level as the surface of the glass filter. A filter paper having a diameter of 9 cm (Toyo Filter Paper Co., Ltd. No. 2) was placed thereon, so that the upper surface of the filter paper was completely wetted, and excess liquid was removed.

And the said measuring device set which pressurized 15 times swelling gel was mounted on the said wet filter paper, and the liquid was absorbed under load. When the liquid level dropped from the top of the glass filter, the liquid was added to keep the liquid level constant. After 1 hour, the set of measuring apparatus was lifted and separated from the filter paper, the load was removed, and the weight (W _B (g)) was measured again. From the above weights W _A and W _B ,
(W _B (g) −W _A (g) +13.5) g / weight of water absorbing agent g
Thus, the absorption capacity under dynamic deterioration and pressure was calculated.
(H) Absorption capacity under dynamic pressure 0.9% by weight sodium chloride without adding L-ascorbic acid as a solution used for swelling before giving dynamic damage in the measurement (g) of absorption capacity under dynamic deterioration and pressure aqueous solution (wt% is based on the weight of the solution.) for the use of, performs the same operation other that the sealing of the 15 times swollen gel was kept at 37 ° C. 30 min, the above weight W _a And W _B , the following equation: Absorption capacity under dynamic pressure =
(W _B (g) −W _A (g) +13.5) g / weight of water absorbing agent g
Thus, the absorption capacity under dynamic pressure was calculated.
(I) Absorption capacity under substantial pressure (1)
Absorption capacity under substantial pressure (1) was measured using the same measuring apparatus as described in the section of absorption capacity under pressure. The measurement method will be described below. First, 0.9 g of a water-absorbing agent (water-absorbing resin) is uniformly spread on the inside of the support cylinder, that is, on a stainless steel 400 mesh wire net, and the weight obtained by adding the above piston (cover plate) to this is defined as W ₁ (g). . In a petri dish with a diameter of 90 mm, add 13.5 g of 0.9 wt% sodium chloride aqueous solution and place a support cylinder on which the above water-absorbing resin is dispersed on the bottom metal mesh without applying a load. A 15% swelled gel is formed by uniformly absorbing a weight% sodium chloride aqueous solution into the resin and allowed to stand at 37 ° C. for 2 hours.

After 2 hours, place the piston (cover plate) and the load in this order, adjusted so that a load of 50 g / cm ² can be uniformly applied to the swollen water absorbent. . Next, a 90 mm diameter glass filter is placed inside a 150 mm diameter petri dish, and 0.9 wt% sodium chloride aqueous solution is added to the same level as the surface of the glass filter. A 9 cm diameter filter paper (Toyo Filter Paper Co., Ltd. No. 2) is placed on the top so that the upper surface is completely wetted, and excess liquid is removed.
Then, the set of measuring devices pressurized with 15-fold swelling gel is placed on the wet filter paper, and the liquid is absorbed under load. When the liquid level drops from the top of the glass filter, add liquid to keep the liquid level constant. After 1 hour, lift up the measuring device set, remove it from the filter paper, remove the load, and re-measure its weight (W ₂ (g)). And, from these weights W ₁ and W ₂ , the following formula substantially absorbs capacity under pressure (1) = (W ₂ (g) −W ₁ (g)) / weight of water absorbent (g)
Thus, the absorption capacity (1) under substantial pressure was calculated.
(J) Absorption capacity under substantial pressure (2)
In the above measurement of the absorption capacity under substantial pressure (1), the same operation was carried out except that the time for forming and leaving a 15-fold swollen gel was changed from 2 hours to 6 hours. Calculated.
(K) Absorption rate The absorption rate was measured according to JIS K7224. Next, the measurement method is described. In a 100 ml beaker with a flat bottom as defined in JIS R3503, 50.0 g of physiological saline (0.9% by weight sodium chloride aqueous solution) previously adjusted to 30 ° C. and a stirrer chip (center diameter is 8 mm, diameters at both ends) 7 mm, 30 mm in length and coated with fluororesin), and stirred with a magnetic stirrer at a speed of 600 rpm. The end point was the time when gelation occurred, the fluidity decreased, and the water vortex at the center of stirring disappeared, that is, the stirrer chip disappeared. The time required from disappearance of the sample to the disappearance of the vortex was measured, and this was taken as the absorption rate.
(L) Water-soluble component amount 0.500 g of the water-absorbing resin was dispersed in 1000 ml of deionized water, stirred for 16 hours, and then filtered through a filter paper. Next, 50 g of the obtained filtrate was put into a 100 ml beaker, and 1 ml of 0.1N sodium hydroxide aqueous solution, 10.00 ml N / 200-methylglycol chitosan aqueous solution, and 4 drops of 0.1 wt% toluidine blue aqueous solution were added to the filtrate. Was added. Next, the solution of the beaker was colloidally titrated with an N / 400-polyvinyl potassium sulfate aqueous solution, and the titration Y (ml) was determined with the time when the color of the solution changed from blue to reddish purple as the end point of titration. Further, the same operation was performed using 50 g of deionized water instead of 50 g of the filtrate, and a titration Z (ml) was obtained by performing a blank titration. And from these titration amounts Y and Z and the neutralization rate W (mol%) of acrylic acid used for the production of the water-absorbent resin, the following formula

The amount of water-soluble components (% by weight) was calculated according to
(M) Moisture content (humidity standard)
About 1 g of water absorbent resin is heated in an oven at 105 ° C. for 3 hours, and the weight of the water absorbent resin before and after heating is measured.

The moisture content (weight%) based on the moisture content was calculated according to
[Example 1]
9.25 g of polyethylene glycol diacrylate (average added mole number of ethylene oxide 8) was dissolved in 5500 g of an aqueous solution of sodium acrylate having a neutralization rate of 65 mol% (monomer concentration 30 wt%) to prepare a reaction solution. Next, this reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with a 10 L inner volume and having two sigma-shaped blades. The gas was replaced. Subsequently, 1.91 g of 2,2′-azobis (2-amidinopropane) dihydrochloride, 0.96 g of sodium persulfate and 0.10 g of L-ascorbic acid were added while stirring the reaction solution. Started. Then, polymerization was performed at 30 ° C. to 80 ° C., and the hydrogel polymer was taken out 60 minutes after the start of the polymerization.

The obtained hydrogel polymer was subdivided into about 5 mm in diameter. The finely divided hydrogel polymer was spread on a 50 mesh wire net and dried with hot air at 150 ° C. for 90 minutes. Next, the dried product was pulverized using a vibration mill, and further classified with a 20-mesh wire mesh to obtain an irregularly crushed water-absorbent resin precursor (a) having an average particle size of 300 μm.
To 100 parts by weight of the obtained water-absorbing resin precursor (a), 0.005 part by weight of diethylenetriaminepentaacetic acid pentasodium, 1 part by weight of propylene glycol, 0.05 part by weight of ethylene glycol diglycidyl ether, and 3 parts by weight of water A surface cross-linking agent consisting of 1 part by weight of isopropyl alcohol was mixed. The above mixture was heat-treated at 210 ° C. for 45 minutes to obtain a water absorbing agent (1). Absorption capacity under no pressure, absorption capacity under pressure, absorption capacity under static deterioration pressure (1), absorption capacity under static deterioration pressure (2), absorption capacity under static deterioration pressure (3) , Absorption capacity under static deterioration (4), Absorption capacity under dynamic pressure, Absorption capacity under dynamic deterioration, Absorption capacity under real pressure (1), Absorption capacity under real pressure (2), Absorption rate, Water acceptable The results of measuring the amount of dissolved components are shown in Table 1.
[Example 2]
A reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 liters with two sigma-shaped blades, 720 g of acrylic acid, and 3.08 g of N, N'-methylenebisacrylamide as an internal cross-linking agent Then, 2718 g of deionized water as a solvent was charged to prepare a reaction solution. Next, the system was purged with nitrogen gas while maintaining the temperature of the reaction solution at 15 ° C. Subsequently, while stirring the reaction solution, 21.6 g of 10 wt% 2,2'-azobis (2-amidinopropane) dihydrochloride aqueous solution, 18.0 g of 1 wt% L-ascorbic acid aqueous solution, and 3.5 wt% aqueous peroxide solution 20.6 g was added to initiate the polymerization. Stirring was stopped simultaneously with the start of polymerization. Then, polymerization was performed while appropriately raising the temperature of the jacket following the temperature rise of the reaction solution so that the temperature of the reaction solution and the temperature of the jacket were substantially equal. Then, after the temperature of the reaction solution reaches the maximum temperature, the temperature of the jacket is controlled to maintain the temperature of the reaction solution at 55 ° C or higher, and after 3 hours, the blades of the double-arm kneader are rotated to form a hydrogel bridge. The polymer was crushed into particles. Further, 750 g of 40 wt% sodium hydroxide aqueous solution was dropped and mixed while rotating the blades of the double arm type kneader to obtain a hydrogel polymer having a neutralization rate of 75 mol%. At this time, the time required for neutralization was 6 hours. The hydrogel polymer was spread on a 50 mesh wire net and dried with hot air at 60 ° C. for 16 hours. Next, the dried product was pulverized using a vibration mill, and further classified with a 20-mesh wire mesh to obtain an irregularly crushed water-absorbent resin precursor (b) having an average particle size of 300 μm.

A surface cross-linking agent comprising 1 part by weight of propylene glycol, 0.05 part by weight of ethylene glycol diglycidyl ether, 3 parts by weight of water and 1 part by weight of isopropyl alcohol to 100 parts by weight of the obtained water-absorbent resin precursor (b). Were mixed. The above mixture was heat-treated at 205 ° C. for 50 minutes to obtain a water absorbent resin b. The absorption capacity of the water absorbent resin b under pressure was 26.9 (g / g), and the water content (wet basis) was 1% by weight or less. Further, after spraying a mixed liquid consisting of 0.005 parts by weight of diethylenetriaminepentaacetic acid pentasodium and 3 parts by weight of water on 100 parts by weight of this water-absorbent resin b, the mixture was dried at 80 ° C. to obtain the water-absorbing agent (2) of the present invention. . Absorption capacity without pressure, absorption capacity under pressure, absorption capacity under static deterioration (1), absorption capacity under static deterioration (2), absorption capacity under static deterioration (3) , Absorption capacity under static deterioration (4), Absorption capacity under dynamic pressure, Absorption capacity under dynamic deterioration, Absorption capacity under real pressure (1), Absorption capacity under real pressure (2), Absorption rate, Water acceptable The results of measuring the amount of dissolved components are shown in Table 1.
[Comparative Example 1]
A reaction solution was prepared by dissolving 1.52 parts by weight of trimethylolpropane triacrylate in 5500 parts by weight of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% (monomer concentration: 33% by weight). Next, this reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with a 10 L inner volume and having two sigma-shaped blades. The gas was replaced. Subsequently, 2.46 parts by weight of sodium persulfate and 0.10 parts by weight of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. Then, polymerization was performed at 30 ° C. to 80 ° C., and the hydrogel polymer was taken out 60 minutes after the start of the polymerization. The obtained hydrogel polymer was subdivided into about 5 mm in diameter. The finely divided hydrogel polymer was spread on a 50 mesh wire net and dried with hot air at 150 ° C. for 90 minutes. Next, the dried product was pulverized using a vibration mill, and further classified with a 20-mesh wire mesh to obtain an irregularly crushed water-absorbent resin precursor (c) having an average particle size of 350 μm.

A surface cross-linking agent consisting of 1 part by weight of glycerin, 0.05 part by weight of ethylene glycol diglycidyl ether, 3 parts by weight of water and 1 part by weight of isopropyl alcohol is added to 100 parts by weight of the obtained water-absorbing resin precursor (c). Mixed. The above mixture was heat treated at 195 ° C. for 40 minutes to obtain a water absorbent resin c. The absorption capacity of the water absorbent resin c under pressure was 22.3 (g / g), and the water content (wet basis) was 1% by weight or less. Further, a mixed liquid consisting of 0.005 parts by weight of diethylenetriaminepentaacetic acid pentasodium and 3 parts by weight of water was sprayed on 100 parts by weight of this water-absorbing resin c and then dried at 80 ° C. to obtain a comparative water-absorbing agent (1). Absorption capacity under no pressure, Absorption capacity under pressure, Absorption capacity under static deterioration (1), Absorption capacity under static deterioration (2), Absorption capacity under static deterioration (3) ), Absorption capacity under static degradation (4), Absorption capacity under dynamic pressure, Absorption capacity under dynamic degradation, Absorption capacity under real pressure (1), Absorption capacity under real pressure (2), Absorption rate, Water The results of measuring the amount of soluble components are shown in Table 1.
[Comparative Example 2]
In 5500 parts by weight of an aqueous solution of sodium acrylate having a neutralization rate of 75% by mole (monomer concentration 33% by weight), 4.5 parts by weight of polyethylene glycol diacrylate (average number of moles of ethylene oxide added 8) was dissolved in a reaction solution. did. Next, this reaction solution was degassed for 30 minutes under a nitrogen gas atmosphere. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with a 10 L inner volume and having two sigma-shaped blades. The gas was replaced. Subsequently, 2.46 parts by weight of sodium persulfate and 0.10 parts by weight of L-ascorbic acid were added while stirring the reaction solution, and polymerization started about 1 minute later. Then, polymerization was performed at 30 ° C. to 80 ° C., and the hydrogel polymer was taken out 60 minutes after the start of the polymerization. The obtained hydrogel polymer was subdivided into about 5 mm in diameter. The finely divided hydrogel polymer was spread on a 50 mesh wire net and dried with hot air at 150 ° C. for 90 minutes. Next, the dried product was pulverized using a vibration mill, and further classified with a 20-mesh wire mesh to obtain an irregularly crushed water-absorbent resin precursor (d) having an average particle size of 280 μm.

A surface crosslinking agent comprising 100 parts by weight of the obtained water-absorbent resin precursor (d), 1 part by weight of propylene glycol, 0.05 part by weight of ethylene glycol diglycidyl ether, 3 parts by weight of water, and 1 part by weight of isopropyl alcohol. Were mixed. The above mixture was heat treated at 210 ° C. for 40 minutes to obtain a comparative water-absorbing agent (2). Absorption capacity under no pressure, Absorption capacity under pressure, Absorption capacity under static deterioration (1), Absorption capacity under static deterioration (2), Absorption capacity under static deterioration (3) ), Absorption capacity under static degradation (4), Absorption capacity under dynamic pressure, Absorption capacity under dynamic degradation, Absorption capacity under real pressure (1), Absorption capacity under real pressure (2), Absorption rate, Water The results of measuring the amount of soluble components are shown in Table 1.
[Example 3]
A monomer containing 67.0 parts by weight of a 37% by weight aqueous sodium acrylate solution, 10.2 parts by weight of acrylic acid, 0.097 parts by weight of polyethylene glycol diacrylate (average number of polyethylene oxide units 8) and 22.0 parts by weight of water were mixed. An aqueous solution was prepared. Nitrogen was blown into the aqueous solution in a bat to make dissolved oxygen in the aqueous solution 0.1 ppm or less. Subsequently, the temperature of the aqueous solution was adjusted to 18 ° C. under a nitrogen atmosphere, and then 0.16 part by weight of 5% by weight aqueous sodium persulfate solution and 5% by weight 2,2′-azobis (2-amidinopropane) hydrochloride aqueous solution 0 .16 parts by weight, 0.15 parts by weight of 0.5% by weight L-ascorbic acid aqueous solution and 0.17 parts by weight of 0.35% by weight aqueous hydrogen peroxide solution were added dropwise with stirring in this order.

Polymerization started immediately after the dropwise addition of the hydrogen peroxide solution, and the monomer temperature reached the peak temperature after 10 minutes. The peak temperature was 85 ° C. Subsequently, the vat was immersed in an 80 ° C. water bath and aged for 15 minutes.
The obtained transparent hydrogel polymer was crushed with a meat chopper, and this finely divided hydrogel polymer was spread on a 50 mesh wire net and dried with hot air at 160 ° C. for 65 minutes. Next, the dried product was pulverized by a pulverizer, and further classified into what passed through an 850 μm sieve and remained on the 106 μm sieve to obtain an irregularly crushed water-absorbing resin precursor (e) having an average particle diameter of 320 μm. .
100 parts by weight of the obtained water-absorbent resin precursor (e) is composed of 1 part by weight of propylene glycol, 0.5 part by weight of 1,4-butanediol, 3 parts by weight of water, and 1 part by weight of isopropyl alcohol. A surface cross-linking agent was mixed. The above mixture was heat-treated at 210 ° C. for 40 minutes to obtain a water absorbent resin e. The absorption capacity of the water absorbent resin e under pressure was 26.6 (g / g), and the water content (wet basis) was 1% by weight or less. Furthermore, after spraying a mixed liquid consisting of 0.005 parts by weight of diethylenetriaminepentaacetic acid pentasodium and 3 parts by weight of water to 100 parts by weight of this water-absorbent resin e, the mixture was dried at 80 ° C. to obtain the water-absorbing agent (3) of the present invention. It was. Absorption capacity under no pressure, absorption capacity under pressure, absorption capacity under static deterioration (1), absorption capacity under static deterioration (2), absorption capacity under static deterioration (3) , Absorption capacity under static deterioration (4), Absorption capacity under dynamic pressure, Absorption capacity under dynamic deterioration, Absorption capacity under real pressure (1), Absorption capacity under real pressure (2), Absorption rate, Water acceptable The results of measuring the amount of dissolved components are shown in Table 1.
[Comparative Example 3]
Stainless steel with jacket having 10.6 g of polyethylene glycol diacrylate dissolved in 6570 g of 30 wt% aqueous solution of partially neutralized sodium acrylate with a neutralization rate of 75 mol%, and having two sigma type blades with an internal volume of 10 liters In a reactor with a lid on a double-arm kneader made of nitrogen, nitrogen was substituted while maintaining the liquid temperature at 30 ° C. with a jacket in which water at 30 ° C. was circulated. Next, while stirring the kneader blade at 40 rpm, 15.6 g of 20 wt% sodium persulfate and 14.9 g of 0.1 wt% L-ascorbic acid aqueous solution were added as polymerization initiators to initiate the polymerization. When the start of polymerization was confirmed by white turbidity, the blade was stopped, and the temperature was maintained until the internal temperature reached 60 ° C. while removing heat from the jacket. When the internal temperature became less than 60 ° C, the blade was rotated to break up the gel, and further polymerization was performed so that the maximum internal temperature was 75 ° C. Subsequently, the jacket temperature was raised to 60 ° C., and the polymerization system was maintained at 65 ° C. or higher while crushing the gel for 20 minutes to complete the polymerization.

The obtained hydrogel polymer was dried with hot air at 160 ° C. for 65 minutes. Furthermore, the dried product was pulverized using a vibration mill to obtain an irregularly crushed water-absorbent resin precursor (f) having an average particle diameter of 450 μm.
To 100 parts by weight of the obtained water absorbent resin precursor (f), 0.5 part by weight of glycerin, 0.05 part by weight of ethylene glycol diglycidyl ether, 3 parts by weight of water, and 0.75 part by weight of isopropyl alcohol A surface cross-linking agent consisting of A comparative water-absorbing agent (3) was obtained by heat-treating the above mixture at 200 ° C. for 50 minutes. Absorption capacity under no pressure, absorption capacity under pressure, absorption capacity under static deterioration (1), absorption capacity under static deterioration (2), absorption capacity under static deterioration (3) ), Absorption capacity under static degradation (4), Absorption capacity under dynamic pressure, Absorption capacity under dynamic degradation, Absorption capacity under real pressure (1), Absorption capacity under real pressure (2), Absorption rate, Water The results of measuring the amount of soluble components are shown in Table 1.

[Example 4]
50 parts by weight of the water-absorbing agent (1) obtained in Example 1 and 50 parts by weight of wood pulverized pulp were dry-mixed using a mixer. Next, the resulting mixture was formed into a web having a size of 120 mm × 380 mm by air-making on a wire screen formed to 400 mesh (mesh size: 38 μm) using a batch type air-making machine. . Further, this web was pressed at a pressure of 2 kg / cm ² for 5 seconds to obtain an absorbent having a basis weight of about 526 g / m ² .
Subsequently, a back sheet (liquid-impermeable sheet) made of liquid-impermeable polypropylene and having a so-called leg gather, the absorber, and a top sheet (liquid-permeable sheet) made of liquid-permeable polypropylene. The absorbent article (that is, a paper diaper) was obtained by sticking each other in this order using a double-sided tape and attaching two so-called tape fasteners to the sticking. The weight of this absorbent article was 47 g.

Each of the above absorbent articles was mounted on a so-called cupy doll (three bodies with a body length of 55 cm and a weight of 5 kg, one body with a body length of 65 cm and a weight of 6 kg), and the doll was placed in a prone state at a room temperature of 37 ° C. After that, a tube is inserted between the absorbent article and the doll, and 50 g of physiological saline containing 0.005% by weight L-ascorbic acid per time is provided at a position corresponding to the position where urination is performed in the human body at intervals of 90 minutes. Sequential injections were made. And when the inject | poured physiological saline was absorbed by the absorbent article and leaked, said injection | pouring operation | movement was complete | finished and the quantity of the physiological saline inject | poured by this time was measured. The amount of absorption of the absorbent article in the prone state was defined as the average value of the amount of physiological saline obtained by the measurement of the four cupy dolls. Table 2 shows the results of the absorption amount (g) in the prone state together with the values of the absorption index under deterioration pressure, the real concentration absorption index, the static deterioration concentration absorption index, and the dynamic deterioration concentration absorption index.
[Examples 5 and 6]
In Example 4, an absorbent article was obtained in the same manner as in Example 4 except that the water absorbing agents (2) and (3) obtained in Examples 2 and 3 were used instead of the water absorbing agent (1). It was. All of these absorbent articles weighed 47 g.

Using the above absorbent article, the amount of absorption of the absorbent article in the prone state was determined by the same operation as in Example 4. Table 2 shows the results of the absorption amount (g) in the prone state together with the values of the absorption index under deterioration pressure, the real concentration absorption index, the static deterioration concentration absorption index, and the dynamic deterioration concentration absorption index.
[Comparative Examples 4, 5, 6]
In Example 4, it replaced with the water absorbing agent (1), and it was the same as that of Example 4 except having used the comparative water absorbing agent (1), (2), (3) obtained in Comparative Examples 1, 2, and 3. Thus, a comparative absorbent article was obtained. All of these absorbent articles weighed 47 g.
Using the above absorbent article, the amount of absorption of the absorbent article in the prone state was determined by the same operation as in Example 4. Table 2 shows the results of the absorption amount (g) in the prone state together with the values of the absorption index under deterioration pressure, the real concentration absorption index, the static deterioration concentration absorption index, and the dynamic deterioration concentration absorption index.

[Example 7]
75 parts by weight of the water-absorbing agent (1) obtained in Example 1 and 25 parts by weight of wood pulverized pulp were dry-mixed using a mixer. Next, the obtained mixture was formed into a web having a size of 120 mm × 350 mm by air-making on a wire screen formed to 400 mesh (mesh size: 38 μm) using a batch type air-making machine. . Further, this web was pressed at a pressure of 2 kg / cm ² for 5 seconds to obtain an absorbent having a basis weight of about 500 g / m ² .
Subsequently, a back sheet (liquid-impermeable sheet) made of liquid-impermeable polypropylene and having a so-called leg gather, the absorber, and a top sheet (liquid-permeable sheet) made of liquid-permeable polypropylene. The absorbent article (that is, a paper diaper) was obtained by sticking each other in this order using a double-sided tape and attaching two so-called tape fasteners to the sticking. The weight of this absorbent article was 44 g.

Each of the above absorbent articles was mounted on a so-called cupy doll (three bodies with a body length of 55 cm and a weight of 5 kg, one body with a body length of 65 cm and a weight of 6 kg), and the doll was placed in a prone state at a room temperature of 37 ° C. After that, a tube is inserted between the absorbent article and the doll, and 50 g of physiological saline containing 0.005% by weight L-ascorbic acid per time is provided at a position corresponding to the position where urination is performed in the human body at intervals of 90 minutes. Sequential injections were made. And when the inject | poured physiological saline was absorbed by the absorbent article and leaked, said injection | pouring operation | movement was complete | finished and the quantity of the physiological saline inject | poured by this time was measured. The amount of absorption of the absorbent article in the prone state was defined as the average value of the amount of physiological saline obtained by the measurement of the four cupy dolls. Table 3 shows the results of the absorption amount (g) in the prone state along with the values of the absorption index under deterioration pressure, the real concentration absorption index, the static deterioration concentration absorption index, and the dynamic deterioration concentration absorption index.
[Examples 8 and 9]
In Example 7, an absorbent article was obtained in the same manner as in Example 7 except that the water absorbing agents (2) and (3) obtained in Examples 2 and 3 were used instead of the water absorbing agent (1). It was. All of these absorbent articles weighed 44 g.

Using the above absorbent article, the amount of absorption of the absorbent article in the prone state was determined in the same manner as in Example 7. Table 3 shows the results of the absorption amount (g) in the prone state along with the values of the absorption index under deterioration pressure, the real concentration absorption index, the static deterioration concentration absorption index, and the dynamic deterioration concentration absorption index.
[Comparative Examples 7, 8, 9]
In Example 7, it replaced with the water absorbing agent (1), and it was the same as that of Example 7 except having used the comparative water absorbing agent (1), (2), (3) obtained in Comparative Examples 1, 2, and 3. Thus, a comparative absorbent article was obtained. All of these comparative absorbent articles weighed 44 g.
Using the above comparative absorbent article, the amount of absorption of the absorbent article in the prone state was determined by the same operation as in Example 7. Table 3 shows the results of the absorption amount (g) in the prone state along with the values of the absorption index under deterioration pressure, the real concentration absorption index, the static deterioration concentration absorption index, and the dynamic deterioration concentration absorption index.

[Example 10]
60 parts by weight of the water-absorbing agent (1) obtained in Example 1 and 40 parts by weight of wood pulverized pulp were dry-mixed using a mixer. Next, the resulting mixture was formed into a web having a size of 120 mm × 380 mm by air-making on a wire screen formed to 400 mesh (mesh size: 38 μm) using a batch type air-making machine. . Further, this web was pressed at a pressure of 2 kg / cm ² for 5 seconds to obtain an absorbent having a basis weight of about 530 g / m ² .
Subsequently, a back sheet (liquid-impermeable sheet) made of liquid-impermeable polypropylene and having a so-called leg gather, the absorber, and a top sheet (liquid-permeable sheet) made of liquid-permeable polypropylene. The absorbent article (that is, a paper diaper) was obtained by sticking each other in this order using a double-sided tape and attaching two so-called tape fasteners to the sticking. The absorbent article weighed about 47 g.
[Comparative Example 10]
In Example 10, a comparative absorbent article was obtained in the same manner as in Example 10 except that instead of the water absorbing agent (1), the comparative water absorbing agent (2) obtained in Comparative Example 2 was used. The comparative absorbent article weighed about 47 g.

Tested on 5 children ranging in age from 1 year 8 months to 2 years 4 months. In the test, 10 absorbent articles (obtained in Example 10) and 10 comparative absorbent articles (obtained in Comparative Example 10) were distributed to one child, and one sheet was used overnight. After collection, the amount of urine absorbed in the diaper and the presence of leakage during use were examined. In order to eliminate leakage caused by misalignment or the like when wearing diapers, data processing was calculated for absorbent articles that absorbed 150 g or more of urine. The results are shown in Table 4.
The average urine volume is a value obtained by dividing the total amount of urine absorbed by the paper diaper by the number of paper diapers absorbing 150 g or more of urine in a paper diaper that absorbs 150 g or more of urine.

The average urine volume at the time of leakage is the total amount of urine absorbed by the diaper when leakage occurred in a paper diaper that absorbed urine of 150 g or more, divided by the number of paper diapers that caused the leakage. Value.
The leakage rate indicates a ratio (percentage) of the number of cases where leakage occurred among the number of paper diapers that absorbed 150 g or more of urine with respect to the number of paper diapers that absorbed 150 g or more of urine.

For the five commercially available diapers shown in Table 5 (purchased during the period from April to September 1998), the weight ratio of the water absorbent resin (water absorbent resin concentration) to the total amount of the water absorbent resin and the fiber material, water absorbency Absorption capacity under no pressure, Absorption capacity under pressure, Absorption rate, Amount of water-soluble component, Absorption capacity under real pressure (1), Absorption capacity under real pressure (2), Absorption capacity under static deterioration (1) Absorption capacity under static deterioration (2) Absorption capacity under static deterioration (3) Absorption capacity under static deterioration (4) Absorption capacity under dynamic pressure, Absorption capacity under dynamic deterioration, deterioration Table 5 shows the absorption index under pressure, the real concentration absorption index of the absorber, the static deterioration concentration absorption index, and the dynamic deterioration concentration absorption index.
Each measuring method followed the following.
(1) Water-absorbing resin concentration Each commercially available diaper was dried under reduced pressure at 60 ° C. for 16 hours. Back sheets, top sheets, non-woven sheets, paper, and some diapers have an acquisition layer made of only fiber materials, but all of these are removed, and the main components are water-absorbing resin and fiber materials. The weight X (g) of the resulting absorbent layer was measured. The weight Y (g) of the water absorbent resin contained in the absorption layer was quantified.

Water-absorbing resin concentration = Y / X
According to the calculation, the water-absorbing resin concentration was calculated.
(2) Various physical properties of water-absorbent resin The water-absorbent resin and the fiber material are separated from each commercially available diaper absorber and dried under reduced pressure at 60 ° C. for 16 hours. Absorption rate, absorption rate, amount of water-soluble component, absorption factor under real pressure (1), absorption factor under real pressure (2), absorption factor under static deterioration pressure (1), absorption factor under static deterioration pressure (2 ) Absorption capacity under static degradation pressure (3), Absorption capacity under static degradation pressure (4), Absorption capacity under dynamic pressure, Absorption capacity under dynamic degradation pressure. In addition, the absorption index under deterioration pressure is the absorption capacity under static deterioration pressure (2), absorption capacity under static deterioration pressure (3), absorption capacity under static deterioration pressure (4), absorption capacity under dynamic deterioration pressure. It is the total value of each measurement value.
(3) Various physical properties of the absorbent The water-absorbent resin and the fiber material are separated from each commercially available diaper absorbent and dried under reduced pressure at 60 ° C. for 16 hours. Absorption index and dynamic degradation concentration absorption index were calculated.

  The water-absorbing agent, absorbent, and absorbent article of the present invention are excellent in urine resistance and have little deterioration over time, and are suitable for sanitary materials such as paper diapers, sanitary napkins, and so-called incontinence pads.

Claims (15)

A water-absorbing agent having an absorption capacity under non-pressure of 30 (g / g) or more, and an absorption capacity (1) of static deterioration under pressure as defined below of 20 (g / g) or more.
Absorption capacity under static deterioration pressure (1): The water-absorbing agent is swollen to 15 (g / g) with physiological saline containing 0.005% by weight of L-ascorbic acid, and left in that state for 6 hours. is absorption capacity of the water-absorbing agent obtained from the swollen gel weight after allowed to absorb physiological saline for a further 1 hour by placing the load of 50 g / cm ^2. A water-absorbing agent having an absorption capacity of 30 (g / g) or more under no pressure and an absorption capacity of 20 (g / g) or more under dynamic deterioration and pressure as defined below.
Absorption capacity under dynamic deterioration and pressure: Swell the water-absorbing agent to 15 (g / g) with physiological saline containing 0.005% by weight of L-ascorbic acid. Is the absorption rate of the water-absorbing agent determined from the weight of the swollen gel after placing a load of 50 g / cm ² and absorbing physiological saline for 1 hour. A water-absorbing agent having an absorption capacity under non-pressure of 30 (g / g) or more and an absorption capacity (4) of static deterioration under pressure as defined below of 30 (g / g) or more.
Absorption capacity under static deterioration pressure (4): The water-absorbing agent is swollen to 15 (g / g) with physiological saline containing 0.05% by weight of L-ascorbic acid, and left in that state for 6 hours. The absorption capacity of the water-absorbing agent is determined from the weight of the swollen gel after placing a load of 20 g / cm ² and absorbing physiological saline for another hour.   The water-absorbing agent according to any one of claims 1 to 3, having an absorption rate of 20 to 80 (sec) and a water-soluble component amount of 1 to 15% by weight.   An absorbent body comprising the water-absorbing agent according to claim 1 and a fiber base material, wherein the weight ratio of the water-absorbing agent to the total amount of both is 0.4 or more. The absorber according to claim 5, wherein the water-absorbing agent has a static deterioration concentration absorption index of 23 or more represented by the following formula (1).
Static deterioration concentration absorption index = X (1−α) + Yα (1)
(In the formula, X is the absorption capacity (g / g) of the water-absorbing agent under no pressure, Y is the absorption capacity (1) (g / g) of static water-absorbing pressure defined in claim 1 of the water-absorbing agent, α Is the weight ratio of the water absorbing agent to the total amount of the water absorbing agent and the fiber substrate.)   The absorbent according to claim 5 or 6, wherein the water-absorbing agent has an absorption rate of 20 to 80 (sec) and a water-soluble component amount of 1 to 15% by weight.   The absorber which contains the water absorbing agent of Claim 2, and a fiber base material, and the weight ratio of the said water absorbing agent with respect to the total amount of both is 0.4 or more. The absorbent according to claim 8, wherein the water-absorbing agent has a dynamic deterioration concentration absorption index represented by the following formula (2) of 23 or more.
Dynamic degradation concentration absorption index = X (1-γ) + Aγ (2)
(Wherein X is the absorption capacity (g / g) of the water-absorbing agent under no pressure, A is the absorption capacity (g / g) of dynamic water-absorbing pressure as defined in claim 2 of the water-absorbing agent, and γ is the water-absorbing agent) And the weight ratio of the water-absorbing agent to the total amount of the fiber base material.)   The absorbent according to claim 8 or 9, wherein the water-absorbing agent has an absorption rate of 20 to 80 (sec) and a water-soluble component amount of 1 to 15% by weight.   The absorber which contains the water absorbing agent of Claim 3, and a fiber base material, and the weight ratio of the said water absorbing agent with respect to the total amount of both is 0.4 or more.   The absorber according to claim 11, wherein the water-absorbing agent has an absorption rate of 20 to 80 (sec) and a water-soluble component amount of 1 to 15% by weight.   An absorbent article comprising an absorbent layer comprising the absorber according to any one of claims 5 to 12, a top sheet having liquid permeability, and a back sheet having liquid impermeability.   Absorption characteristics under pressure of the water-absorbing agent, absorption characteristics of the absorbent body in which the weight ratio of the water-absorbing agent to the total amount of the water-absorbing agent and the fiber base material is 0.4 or more, and the total amount of the water-absorbing agent and the fiber base material In a method for measuring at least one absorption characteristic of an absorbent article including an absorbent having a weight ratio of water absorbing agent of 0.4 or more, a reducing substance-containing liquid is used as the liquid to be absorbed. To measure absorption characteristics. The method for measuring absorption characteristics according to claim 14, wherein the reducing substance is ascorbic acid or a salt thereof.