JP2001335645A - Absorbing sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an absorbing sheet which is thin, but strong in sheet strength, capable of displaying a good absorption even in repeatedly absorbing a liquid. SOLUTION: The absorbing sheet is characterized by composing of at least a hydrophilic fiber and a high water absorbing polymer, wherein this high water absorbing polymer is blended by 50 to 95 wt.%, and also composed of at least two kinds of polymers with 3 times or more different ratio of water absorbing rate of a physiological saline, and by having the density of 0.2 to 0.7 g/cm3 measured by a method conforming to JIS L-1906 when the sheet is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to absorbent sheets, and more particularly to drip sheets, kitchen absorbent sheets, household cleaning sheets and pet undersheets, as well as for babies or incontinent persons. The present invention relates to an absorbent sheet used as an absorbent pad used as an absorbent article for absorbent articles such as diapers.

[0002]

2. Description of the Related Art In recent years, not only liquid absorbing capacity but also strength and thinness of a sheet have become important characteristics in an absorbent sheet. As means for satisfying this requirement, for example, in U.S. Pat. No. 3,070,095, a superabsorbent polymer is sprayed on a tissue, another tissue is laminated, and then pressure-bonded by a roller. A technique of a thin absorbent sheet in which a superabsorbent polymer is fixed in a tissue is disclosed. However, according to this method, the superabsorbent polymer is merely sandwiched and fixed between the tissue layers in a layered manner, so that not only can it be easily detached from the tissue but also a large amount of the superabsorbent polymer cannot be fixed. Therefore, when such an absorbent sheet is used, for example, for an absorbent body of an absorbent article, by the movement of the wearer,
In particular, when the superabsorbent polymer absorbs urine or the like and swells, it separates from the tissue to create a space. Furthermore, when a superabsorbent polymer is present in a layered form and absorbs liquid, it swells in a layered form and causes absorption inhibition such as gel blocking, which is unsuitable as an absorber.

Further, there is disclosed a technique in which a hot melt adhesive is applied to the entire surface of a tissue or the like, and the superabsorbent polymer is fixed by the adhesive. According to this method, the superabsorbent polymer can be reliably fixed. However, since most of the surface of the superabsorbent polymer is covered with the hot melt adhesive, swelling inhibition of the superabsorbent polymer and absorption inhibition of the liquid occur, which is unsuitable as an absorbent sheet.

On the other hand, a method for obtaining an absorbent sheet using wood pulp produced by a dry method is also well known. Wood pulp produced by the dry method in such an absorbent sheet is very bulky, resulting in a low sheet strength and a large sheet thickness. Therefore, if the sheet is strongly compressed by a roller or the like in order to improve the sheet strength and reduce the thickness, the liquid absorbing speed is reduced, and the sheet becomes unsuitable as an absorbent sheet. In order to increase the sheet strength of the absorbent sheet by using a chemical binder, a high-composite synthetic pulp, a low-melting point synthetic fiber, or the like in order to improve the sheet strength, the absorbent sheet becomes hydrophobic and the absorption rate decreases. descend. Further, when the absorbent sheet containing the low melting point synthetic fiber or the like is strongly compressed by a roller or the like, the liquid absorption rate is significantly reduced, and the liquid absorbent becomes unsuitable as an absorbent sheet.

[0005] Further, US Patent Nos. 5,866,242 and 5,916,670 disclose a wood pulp layer in which a superabsorbent polymer is dispersed by using an alkali-treated wood pulp. There is disclosed a technique in which layers of only wood pulp are laminated on the upper and lower sides and strongly compressed by a heating roll to obtain a thin absorbent sheet. However, in this method,
Wood pulp-only layers are required on both sides of the layer containing the superabsorbent polymer, and as a result, the thickness of the absorbent sheet is not sufficiently reduced, and the cost of using alkali-treated wood pulp is low. Is high and is unsuitable.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional absorbent sheet, and the superabsorbent polymer does not cause gel blocking even when the liquid is repeatedly absorbed, thereby achieving high water absorption. Another object of the present invention is to provide an absorbent sheet capable of exhibiting the inherent absorption characteristics of a conductive polymer, and further having a thin sheet and strong sheet strength.

[0007]

The present invention for solving the problems of the above-mentioned conventional absorbent sheet includes the following inventions. (1) In an absorbent sheet comprising at least a hydrophilic fiber and a superabsorbent polymer, in the absorbent sheet,
50-95% by weight of superabsorbent polymer is blended,
The superabsorbent polymer was measured by the following method,
A water absorption rate of a first superabsorbent polymer having the fastest water absorption rate and a second superabsorbent polymer having the slowest water absorption rate, comprising at least two types of physiological saline having different absorption rates. Is 3 times or more, and
An absorbent sheet, wherein the density of the absorbent sheet measured by a method according to JIS L-1906 is 0.2 to 0.7 g / cm ³ . Measuring method of water absorption rate: (1) In a 100 ml beaker, 50 ml of 0.9% aqueous sodium chloride solution is added, and the liquid temperature is adjusted to 25 ° C. (2) A Teflon rotator (diameter 8 mm, length 30 mm, weight 3.8 g) is put into the above-mentioned beaker, and stirred with a magnetic stirrer at 600 rpm. (3) Add 2 g of the superabsorbent polymer into the vortex, and measure the time (second) from the time of addition to the time when the vortex disappears and the liquid level becomes horizontal.

(2) The first superabsorbent polymer has a water absorption rate of 0.5 to 15 seconds, measured by the above method,
The absorbent sheet according to (1), wherein the second super absorbent polymer has a water absorption rate of 45 to 90 seconds.

(3) The compounding ratio of the first superabsorbent polymer and the second superabsorbent polymer is as follows:
The absorbent sheet according to the above (1) or (2), wherein the ratio is from 5:95 to 50:50.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The absorbent sheet of the present invention contains at least two kinds of superabsorbent polymers constituting the absorbent sheet, which have different absorption rates of physiological saline as measured by the above method. Wherein the ratio of the water absorption rate of the first superabsorbent polymer having the fastest water absorption rate to the second superabsorbent polymer having the slowest water absorption rate is 3 times or more, and 0.2 to 0. It has a density of 0.7 g / cm ³ .

In the absorbent sheet of the present invention having such a structure, when it comes into contact with a liquid, first, the first superabsorbent polymer having a high water absorption rate absorbs the liquid, and the first superabsorbent polymer together therewith. When the polymer swells to form voids for diffusing the liquid in the absorbent sheet, and then the absorbent sheet comes into contact with the liquid again, the liquid diffuses into the absorbent sheet through the voids, and the liquid having a low water absorption rate. Two superabsorbent polymers absorb the liquid. Thus, the absorbent sheet of the present invention, even when a thin sheet is formed, shows good absorption performance without causing blocking due to swelling of the superabsorbent polymer when absorbing liquid, and It has excellent sheet strength.

In this case, the first superabsorbent polymer having a water absorption rate of 0.5 to 15 seconds is used, and the second superabsorbent polymer having a water absorption rate of 45 to 90 seconds is used. The mixing ratio of both is first: second = 5: 95-
By setting the ratio to 50:50, the effect of the present invention described above can be further enhanced.

The absorbent sheet of the present invention is basically constituted as a composite comprising a hydrophilic fiber and a superabsorbent polymer. If necessary, the composite may be formed of a natural fiber such as tissue or non-woven fabric and / or a non-woven fabric. Alternatively, it may be wrapped by a sheet member made of a synthetic fiber, or may be a laminated structure sandwiched between a plurality of sheet members. Further, for the purpose of maintaining the strength of the sheet, a long fiber or a heat-fusible synthetic fiber can be blended.

In the present invention, natural fibers such as cotton, hemp, wool and silk, rayon fibers and the like can be used as the hydrophilic fibers in addition to pulp fibers. Among them, pulp fibers are advantageously used. Can be The pulp fiber preferably has a fiber length of 5 mm or less obtained by defibrating a chemical pulp sheet or a mechanical pulp sheet with a crusher. The raw material for the pulp is not limited to conifers, but hardwood, straw, bamboo, kenaf, and used paper pulp can also be used.

In the present invention, the superabsorbent polymer is incorporated in the absorbent sheet in an amount of 50 to 95% by weight. If the blending ratio of the superabsorbent polymer is less than 50% by weight, the blending ratio of the hydrophilic fibers increases, and the absorption performance decreases.
On the other hand, when the compounding ratio of the superabsorbent polymer exceeds 95% by weight, the compounding ratio of the hydrophilic fibers for fixing and holding the superabsorbent polymer decreases, and the superabsorbent polymer is easily dropped off and absorbed. It becomes difficult to form a conductive sheet.

In the present invention, as the superabsorbent polymer, a superabsorbent polymer having a different absorption rate of physiological saline as measured by the following method is used. At least two types of superabsorbent polymers are used, a first superabsorbent polymer having a fast rate and a second superabsorbent polymer having a slow absorption rate. Measuring method of water absorption rate: (1) In a 100 ml beaker, 50 ml of 0.9% aqueous sodium chloride solution is added, and the liquid temperature is adjusted to 25 ° C. (2) A Teflon rotator (diameter 8 mm, length 30 mm, weight 3.8 g) is put into the above-mentioned beaker, and stirred with a magnetic stirrer at 600 rpm. (3) Add 2 g of the superabsorbent polymer into the vortex, and measure the time (second) from the time of addition to the time when the vortex disappears and the liquid level becomes horizontal.

In this case, it is necessary that the ratio of the water absorption rate between the first superabsorbent polymer and the second superabsorbent polymer is three times or more. That is, the water absorption rate of the first superabsorbent polymer measured by the above method is 0.5 to 15 seconds, preferably 1 to 10 seconds, and the water absorption rate of the second superabsorbent polymer. Is 45 to 90 seconds, preferably 50 to 80 seconds. If the water absorption rate of the first superabsorbent polymer is less than 0.5 seconds, the particle size of the superabsorbent polymer will be too small, and it will be difficult to produce stably and gel blocks will easily occur, It is not suitable for the production of absorbent sheets. On the other hand, if the water absorption rate exceeds 15 seconds, the ratio of the water absorption rate to the second superabsorbent polymer becomes small, and the effect of blending the superabsorbent polymers having different water absorption rates is not preferable. Further, when the water absorption rate of the second superabsorbent polymer is slower than 90 seconds, the absorption rate cannot catch up when a large amount of urine or the like is excreted, and on the other hand, leakage tends to occur. On the other hand, if the water absorption rate is less than 45 seconds, the ratio of the water absorption rate to the first superabsorbent polymer becomes small, and the effect of blending the superabsorbent polymers having different water absorption rates is not preferable.

In the present invention, both the first superabsorbent polymer and the second superabsorbent polymer can be selected from superabsorbent polymers used in ordinary absorbents. Any of these can be used as long as they have a crosslinked structure and are superabsorbents having a carboxyl group and / or a carboxylate group as a component of the polymer, and the type and polymerization method of the polymer are not limited. Among them, polyacrylate crosslinked product, starch-acrylic acid graft copolymer crosslinked product,
Hydrolysates of starch-acrylonitrile graft copolymer cross-linked products, acrylate-vinyl acetate copolymer hydrolysates, acrylate-acrylamide copolymer cross-linked products and polyacrylonitrile cross-linked hydrolysates are preferred. An example is given. Other than the above, polyethylene oxide cross-linked with acrylic acid, cross-linked product of sodium carboxycellulose, maleic anhydride-isobutylene, maleic acid salt of acrylic acid, itaconic acid salt, 2-acrylamide-2-methylsulfonic acid salt, 2-acrylic acid Examples thereof include those obtained by copolymerizing a comonomer such as ilethanesulfonic acid and 2-hydroxyethyl acrylate. The shape is not particularly limited, and a sphere, a grape-like in which a plurality of spheres are combined, an irregular shape, a fibrous shape, or the like can be used. For the first superabsorbent polymer that requires liquid permeability, amorphous is more preferred.

In the present invention, the mixing ratio of the first superabsorbent polymer and the second superabsorbent polymer is as follows:
5:95 to 50:50. That is, the first superabsorbent polymer is 5 to 50 parts, and the second superabsorbent polymer is 9 parts.
It is composed by mixing 5 to 50 parts. If the blending ratio of the first superabsorbent polymer is less than 5 (the blending ratio of the second superabsorbent polymer is more than 95), sufficient voids are not formed in the absorbent sheet, and a gel blocking phenomenon occurs. Therefore, it is inappropriate. On the other hand, when the blending ratio of the second superabsorbent polymer is less than 50 (the blending ratio of the first superabsorbent polymer is more than 50), no void is formed when the first superabsorbent polymer swells, Rather, since a blocking phenomenon occurs, the effect of improving the absorption rate is hardly observed, which is inappropriate.

Further, the absorption capacity of physiological saline as measured by the following method is 3 for the first superabsorbent polymer.
0 to 70 g / g, preferably 35 to 65 g / g, and 35 to 70 g for the second superabsorbent polymer.
/ G, preferably 40 to 65 g / g. Measurement method of absorption capacity: The superabsorbent polymer was precisely weighed, placed in a nylon bag, immersed in a 0.9% aqueous sodium chloride solution for 30 minutes, pulled up, drained for 15 minutes, and weighed. The absorption capacity was calculated by the following equation. Absorption ratio = (weight after absorption−weight of superabsorbent polymer) /
Super absorbent polymer weight

The absorption capacity of the first superabsorbent polymer is 30.
If it is less than g / g, very good liquid permeability can be obtained, but since the absorption performance is reduced and the voids formed in the absorbent sheet are small, even if the absorbent sheet absorbs the liquid again, Liquid is not suitable because it cannot diffuse into the absorbent sheet through the voids. On the other hand, the absorption capacity is 70 g / g
If it exceeds, the liquid permeability deteriorates, and as a result, blocking tends to occur, which is inappropriate. When the absorption capacity of the second superabsorbent polymer is less than 35 g / g,
On the other hand, when the absorption capacity exceeds 70 g / g, the liquid permeability deteriorates, and as a result, blocking tends to occur, which is inappropriate.

The absorbent sheet of the present invention is JIS L-1
The density measured by a method according to 906 is 0.2 to 0.7 g.
/ Cm ³ . When the density is less than 0.2 g / cm ³ , the sheet becomes bulky, and as a result, the sheet strength is reduced and the sheet thickness is increased, which is not suitable. On the other hand, if the density is higher than 0.7 g / cm ³ , the absorption rate will be low, making the sheet unsuitable as an absorbent sheet.

[0023]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. Example 1 As a first superabsorbent polymer, a superabsorbent polymer having a water absorption rate of 10 seconds and an absorption capacity of 50 g / g measured by the above method was used, and a second superabsorbent polymer having a water absorption rate of 60 seconds was used. , A high water-absorbing polymer having an absorption capacity of 60 g / g was used, and both were mixed at a ratio of first: second = 10: 90, and the mixed pulp fiber comprising the high water-absorbing polymer and NBKP was 65:35. 500g /
A rectangular absorbent mat having a width of 100 mm and a length of 400 mm having a width of m ² was formed. The obtained rectangular absorbent mat was heated and pressed to produce an absorbent sheet having a density of 0.6 g / cm ³ .

Using the obtained absorbent sheet, the liquid absorption rate, the amount of liquid reversion, and the liquid diffusion length were evaluated. Each evaluation method is as follows. Liquid absorption speed: 10c with a 1-inch diameter hole in the center
An mx 10 cm stainless steel plate (weighing about 600 g) was placed at the center of the absorbent sheet, and 50 ml of artificial urine was injected into this hole, and the time (second) required for this to be absorbed was measured. The measurement was repeated three times every minute. In addition,
The composition of the artificial urine used is as follows. Urea 1.94% Sodium chloride 0.80% Calcium chloride 0.08% Magnesium sulfate 0.20% Deionized water 96.97%

Liquid reversal amount: After the absorbent sheet for which the liquid absorption rate was measured was left for 5 minutes, 5% was placed at the center of the absorbent sheet.
Ten layers of 0 mm × 50 mm filter paper (Advantech No. 63, manufactured by Toyo Filter Paper Co., Ltd.) were stacked, and a 5 kg load was left thereon for 5 minutes. Then, the weight increase of the filter paper was measured to determine the amount of liquid reversion ( g). Liquid diffusion length: Using an absorbent sheet whose liquid absorption rate was measured,
The maximum diffusion length (mm) of artificial urine in the longitudinal direction of the absorbent sheet was measured.

Example 2 A superabsorbent polymer having a water absorption rate of 10 seconds and an absorption capacity of 50 g / g was used as the first superabsorbent polymer, and an absorption capacity was used as the second superabsorbent polymer having a water absorption rate of 60 seconds. Is 6
Using 0 g / g superabsorbent polymer, the two were mixed in a ratio of first: second = 40: 60, and the mixed pulp fiber comprising superabsorbent polymer and NBKP was 65:35.
To form a rectangular absorbent mat having a basis weight of 600 g / m ^{2 and} a width of 100 mm and a length of 400 mm. The obtained rectangular absorption mat is heated and pressed to have a density of 0.3 g / cm ^3.
Was produced.

Comparative Example 1 An absorbent sheet was produced in the same manner as in Example 1 except that the superabsorbent polymer and the pulp fiber were mixed at a ratio of 40:60. Comparative Example 2 Except that the obtained rectangular absorption mat was not heated and pressed,
An absorbent sheet was produced in the same manner as in Example 1. The density of the obtained absorbent sheet was 0.1 g / cm ³ .

Comparative Example 3 The obtained rectangular absorbent mat was heated and pressurized to a density of 0.8 g.
An absorbent sheet was produced in the same manner as in Example 1 except that the thickness was changed to / cm ³ . Comparative Example 4 A superabsorbent polymer having a water absorption rate of 20 g and an absorption capacity of 60 g / g was used as the first superabsorbent polymer, and a water absorption rate of 45 sec and an absorption capacity of 6 was used as the second superabsorbent polymer.
Example 2 except that 0 g / g superabsorbent polymer was used.
An absorbent sheet was produced in the same manner as described above.

Table 1 shows the results of evaluating the performance of the absorbent sheets obtained in each of the examples and comparative examples. As can be seen from Table 1, the absorbent sheet of each example, which is the absorbent sheet of the present invention, has a stable and fast liquid absorption speed from the first to third times, a small amount of liquid reversion, and a small liquid diffusion length. Are contained in the absorbent sheet, whereas the absorbent sheet of the comparative example is inferior in any of the liquid absorption rate and the amount of liquid reversion, the liquid diffusion length, and the effect of the present invention is not good. confirmed.

[0030]

[Table 1]

[0031]

The absorbent sheet of the present invention has a water absorption rate of 3
It is a mixture of two types of superabsorbent polymers that differ by a factor of two or more at a specific ratio, so that even when liquid is repeatedly absorbed, the superabsorbent polymer does not cause gel blocking and the original absorption of the superabsorbent polymer Since the characteristics are exhibited, it is possible to provide a thin absorbent sheet having high sheet strength.

Continued on the front page F term (reference) 3B029 BA05 BA18 4C098 AA09 CC02 DD02 DD23 4F072 AA02 AA06 AA08 AB03 AD01 AD03 AD04 AD08 AD09 AD42 AD52 AK05 AK14 AL01

Claims (3)

[Claims] 1. An absorbent sheet comprising at least a hydrophilic fiber and a superabsorbent polymer, wherein the absorbent sheet contains 50 to 9 superabsorbent polymers.
5% by weight, and the superabsorbent polymer was measured by the following method.
A water absorption rate of a first superabsorbent polymer having the fastest water absorption rate and a second superabsorbent polymer having the slowest water absorption rate, comprising at least two types of physiological saline having different absorption rates. Is 3 times or more, and the density of the absorbent sheet measured by a method according to JIS L-1906 is 0.2 to 0.7 g / cm ³ . Measuring method of water absorption rate: (1) In a 100 ml beaker, 50 ml of 0.9% aqueous sodium chloride solution is added, and the liquid temperature is adjusted to 25 ° C. (2) A Teflon (registered trademark) rotor (diameter: 8 mm, length: 30 mm, weight: 3.8 g) is put into the beaker, and the mixture is stirred with a magnetic stirrer at 600 rpm. (3) Add 2 g of the superabsorbent polymer into the vortex, and measure the time (second) from the time of addition to the time when the vortex disappears and the liquid level becomes horizontal. 2. The method according to claim 1, wherein the water absorption rate of the first superabsorbent polymer is 0.5 to 15 seconds, and the water absorption rate of the second superabsorbent polymer is 45 to 90 seconds. The absorbent sheet according to claim 1, wherein: 3. The compounding ratio of the first superabsorbent polymer and the second superabsorbent polymer is as follows: first: second = 5: 9.
The ratio is 5:50:50.
The absorbent sheet according to the above.