JP2001171027A - Highly water-absorbable composite sheet and surface processing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly water-absorbable composite sheet certainly holding a highly water-absorbable resin in a dry state so as not to separate the same from a base material even if the resin absorbs water to expand in its volume. SOLUTION: In a highly water-absorbable composite sheet wherein a highly water-absorbable resin is distributed on the single surface of a nonwoven fabric base material in such a state a part thereof is infiltrated in the gaps of the base material and the other part thereof is exposed to the surface of the base material, the surface of the exposed highly water-absorbable resin is coated with a fiber net-like double hot melt layer consisting of a first dense mesh fiber net-like hot melt layer and a second relatively coarse mesh fiber net-like hot melt layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbing composite, a method for producing the same, and an absorbent article, and more particularly, to a water-absorbing composite coated with a net of a hot-melt adhesive, a method for producing the same, and a method for using the same. Absorbent article.

[0002]

2. Description of the Related Art Conventionally, a superabsorbent polymer (hereinafter sometimes referred to as "SAP") has been fixed to a substrate by utilizing the tackiness of a hot melt adhesive.
Further, in a superabsorbent resin system or a superabsorbent resin / pulp mixed system, a superabsorbent resin or a superabsorbent resin / pulp has been fixed to a substrate using an emulsion binder, respectively. Furthermore, in a superabsorbent resin system or a superabsorbent resin / pulp mixed system, in the presence of a heat-soluble binder fiber (bicomponent fiber),
By heating and then cooling, the superabsorbent resin or superabsorbent resin / pulp has been fixed to the substrate. Furthermore, the highly heat-fusible fibers or the fiber web containing the same are covered with the superabsorbent resin, and the fibers constituting the fibrous web are fused by heat treatment, and the superabsorbent resin is fixed to the base material. I've been.

[0003]

However, in the prior art, it is difficult to greatly increase the superabsorbent resin / pulp ratio (referred to as SAP ratio), particularly in a superabsorbent resin / pulp mixture system. There was a limit around 50% by weight. Also,
In a system in which a superabsorbent resin is fixed to a substrate with a binder, the swelling force of the superabsorbent resin and the binding force of the superabsorbent resin act in an antagonistic manner. That is, as the binding force of the superabsorbent resin increases, the swelling of the superabsorbent resin is inhibited, and conversely, if the swelling of the superabsorbent resin is not inhibited, it becomes difficult to restrain the superabsorbent resin.

Accordingly, the present invention is directed to a structure in which the base material simultaneously expands as the superabsorbent resin swells, that is, while maintaining a loosely bonded state that can maintain the degree of freedom of the superabsorbent resin, It is an object of the present invention to provide a structure that swells a superabsorbent resin so as not to be detached from a substrate.

[0005]

According to the present invention, a superabsorbent resin is provided on one surface side of a nonwoven fabric base material in such a manner that part of the superabsorbent resin is present in the voids of the nonwoven fabric and part of the other is exposed to the surface from the nonwoven fabric. The exposed surface of the superabsorbent resin layer is located on the first hot melt layer in the form of a fiber net having a dense mesh and the first hot melt layer on the first hot melt layer. And coated with a fiber net-like hot melt layer composed of a double hot melt layer with a second fiber-like hot-melt layer having a coarse mesh relative to the first hot-melt layer. The highly water-absorbent composite sheet is characterized in that the highly water-absorbent resin is less likely to fall off.

The first hot-melt layer having a dense mesh of mesh and the second hot-melt layer having a coarse mesh of mesh may be upside down.

[0007] The present invention also relates to a non-woven fabric based on a portion in which the superabsorbent resin is partially distributed in the voids of the non-woven fabric on one surface side and the other portion is distributed in the form of a layer exposed from the non-woven fabric to the surface. It can also be applied to a superabsorbent sheet composed of a material-only part.

The present invention further provides a method for processing the surface of a superabsorbent composite sheet in which the superabsorbent resin is distributed in a layer on one surface side of the nonwoven fabric substrate, wherein the superabsorbent resin is distributed. A first-stage hot-melt processing step of performing hot-melt processing by a hot-melt adding device (A) for forming a first hot-melt layer in the form of a dense fiber net on a surface having a mesh; Surface treatment in combination with a second-stage hot-melt processing step of performing hot-melt processing with a hot-melt addition device (B) for obtaining a second hot-melt layer having a coarse mesh net relative to the melt layer And a method for processing the surface of the superabsorbent composite sheet.

Preferably, the first stage hot melt processing is
Mesh coating amount is carried out in the range of 0.3g / m ² ~2g / m ² to form a first hot-melt layer of dense, a second stage hot-melt processing, the coating amount is 1g / m ² ~10g / The ^second step is performed in the range of m ² to form a second hot melt layer having a coarse mesh relative to the first-stage hot melt processing. Alternatively, the order of the first-stage hot-melt processing and the second-stage hot-melt processing can be reversed.

As a hot melt adding device, a curtain spray type, a spiral coat type or a line coat type device is used in an appropriate combination according to the required density of the hot melt layer or the thickness of the fiber. be able to.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In one embodiment of the present invention, the structure of a superabsorbent sheet to be covered with a hot melt layer is such that a layer of a superabsorbent resin is compounded on one surface of a nonwoven fabric substrate. Things. In the present invention, the nonwoven fabric substrate is
Made of natural fiber, synthetic fiber, wood pulp, foamed foam, etc., for example, synthetic fiber spunbond, composite nonwoven of spunbond and meltblown, card method air-through nonwoven, spunlace nonwoven, needle punched nonwoven, flocked nonwoven , Non-woven fabric by dry pulp method, etc.
Preferably the basis weight ^{10g / m 2 ~100g / m 2} , aiming at a specific gravity 0.2 g / m
A nonwoven fabric with a relatively low basis weight of ² or less and a high bulk is desirable.

Examples of the superabsorbent resin include carboxymethylcellulose, polyacrylic acid and salts thereof, acrylate polymer crosslinked product, starch-acrylic acid graft copolymer, starch-acrylonitrile graft copolymer hydrolyzate, Formation of hydrated gels such as crosslinked polyoxyethylene, crosslinked carboxymethylcellulose, polysulfonic acid-based compounds, polyethylene oxide, polyacrylamide and other partially crosslinked water-swellable polymers, or copolymers of isobutylene and maleic acid High-performance resin. By drying these resins, a polymer resin serving as a base is obtained. Next, generally, a post-treatment is performed to further increase the crosslinking density on the surface of the particulate resin, and at the same time, an anti-blocking agent is added to suppress the blocking property of the particles due to moisture absorption.

In addition, the present invention also relates to a superabsorbent polymer resin derived from microorganisms, which is a biodegradable crosslinked product of amino acid of polyaspartic acid or a culture product from Alcaligenes Latus. Can be used as a superabsorbent resin. Examples of the shape of the superabsorbent resin include particles, granules, films, and nonwoven fabrics. More preferable shapes include particles, granules, flakes, pellets, and short needles that can be uniformly dispersed in a dispersion medium. The equivalent diameter of the superabsorbent resin is usually 100 to 1000 μm.

In recent years, with respect to the superabsorbent resin, a so-called dry polymer resin having high gel stability has been regarded as important, and the evaluation is based on the absorption under load (AUL), the capacity under load (PUP) or the swelling. Liquid permeability of gel (SF
With the measurement C), the function of the SAP is discussed (US Pat. No. 5,599,335, Goldman et al.). However, from the application scope of the present invention, if it is stable against human urine, animal urine, and blood, even a normal high-absorbency resin having a low degree of cross-linking can sufficiently perform its function, and can be converted to an AUL equivalent of 15 g / g. Anything above is sufficient.

It is desirable that all the superabsorbent resin be contained in the bulky structure of the nonwoven fabric substrate, that is, in the voids of the fibers. However, although it depends on the amount of the superabsorbent resin to be added and the bulkiness of the web used, it does not hinder that part of the resin is exposed on the surface of the nonwoven fabric substrate.
Such an exposed superabsorbent resin causes dusting due to friction and bending during processing such as slit processing and combination processing with a product even if it is seemingly stable in a dry state or a standing state. In addition, when wet swelling, it is easily detached from the composite. In order to stabilize such a dry state and a wet state by the wrapping effect of only the nonwoven fabric substrate, the bulk of the nonwoven fabric substrate should be increased, and SA to be wrapped
The amount of P itself is greatly restricted. That is, generally speaking, it is difficult to enclose more than 70% of SAP added only with nonwoven fabric, and the amount of SAP added is 200 g / m ^2.
It is difficult to exceed.

By using a double hot-melt layer as in the present invention, a nonwoven fabric substrate, such as a polypropylene spunbond (abbreviated as SB) or a spunbond, which could not be used until now because of a large amount of desorption. The / melt blown / spunbond composite (abbreviated as SMS) can also be used as an absorbent substrate.

The superabsorbent composite sheet of the present invention has a form in which a layer of a superabsorbent resin is composited on one surface of a nonwoven fabric substrate as described above, and its structure has two models. I do. FIG. 1 shows an example of a model of a support form of an SAP on a nonwoven fabric substrate applied to the present invention. <Model 1> In Model 1 shown in FIG. 1 (A), most of the SAP is wrapped in the fiber gap of the nonwoven fabric, and some of the fibers constituting the fiber layer of the nonwoven fabric base material have a surface. And a part of the SAP is also exposed on the surface. In the case of such a bulky nonwoven fabric substrate, generally,
More than 50% of the SAP is encapsulated between the fibers.

<Model 2> On the other hand, in Model 2 shown in FIG. 1 (B), most of the SAP is exposed on the surface of the nonwoven fabric, and the SAP layer and the portion of only the nonwoven fabric without SAP coexist. . Such a nonwoven fabric substrate is relatively flat, and generally the amount of SAP held between fibers is
Less than 50%.

In the structural models of the superabsorbent sheets such as Model 1 and Model 2, in the case of Model 1, the fiberized hot melt material is stably bonded to the existing fiber surface while covering the SAP particles. I do. On the other hand, in the case of Model 2, while covering the exposed SAP particles,
It is necessary that the non-woven fabric portion free of AP and the hot melt layer be stably bonded. Therefore, the stability of the coating state is affected by the bonding property between the hot melt layer and the nonwoven fabric substrate.

The present invention is applicable to any of these two models. The surface of the nonwoven fabric substrate on the side where the SAP is present is a first hot-melt layer having a mesh-like dense fiber net shape. And the second hot-melt layer having a coarse mesh with respect to the first hot-melt layer.

Next, various conditions of the hot melt layer applied to the present invention will be examined. About the mesh size of the fiber net-like hot melt layer. In the present invention, the term "fibrous net shape" is not to cover the entire film like a general hot melt process, but to form the hot melt layer into a fibrous shape and cover the entire net shape. Means a state in which coating is performed uniformly without impeding liquid permeation and SAP swelling. The required degree of density depends on the size and state of the SAP particles. That is, the type of the SAP used and the SA
It depends on whether P is in a dry state or a wet state. The particle size of the SAP at the time of drying is small in the case of a spherical SAP or a particle obtained by pulverizing a gel by reverse phase suspension polymerization, and is usually about 50 to 300 μm
In the case of flake SAP and granulated SAP, 30
It is about 0 μ to 1000 μ. When this swells by absorbing, for example, urine, the diameter increases about three times. Therefore the spherical S
AP has a diameter of 150 μ to 1000 μ, flake, granulated SA
P becomes 1000 μ to 3000 μ.

Therefore, in order to stabilize the surface when dry, that is, to prevent the surface SAP from falling off due to friction and refraction of the sheet, the fiber net has a finer mesh and a denser mesh than the strength of the fiber in the hot melt layer. The structure is more important. On the other hand, in order to prevent the swelling SAP from falling off when wet, the mesh of the fiber net-like hot melt layer is roughened in order to prevent the fiber of the hot melt layer from being broken by the swelling force of the SAP. But thicker fibers are more important.

It is difficult to achieve these two different requirements in one hot melt process. Therefore, in the present invention, by combining a hot melt adding device (A) for processing thin fibers into a dense mesh and a hot melt adding device (B) for processing thick fibers into a coarse mesh, Requirements are cleared,
This enables surface processing with less falling off during both dry and wet conditions. The fineness (thickness) of the fibers in the fiber net-like hot melt layer and the density of the mesh structure are determined by the diameter of nozzles for discharging the hot melt material, their intervals, and the discharge amount. If the nozzle diameter and the interval are the same, it depends on the discharge amount (application amount) and the supply air amount.

An adding device for obtaining fine fibers with a dense mesh
In the case of (A), the application amount is 0.3 g / m ^Two~ 2g / m^Two, Preferred
0.5g / m^Two~ 1g / m^TwoIt is about. 0.3g / m^TwoLower
Can not apply evenly, 2g / m^TwoBeyond
It is easy to become a net shape. Need a coarse and thick fiber mesh
In the case of the addition device (B), the coating amount is 1 g / m^Two~ 10g / m
 ^Two, Preferably 1 g / m^Two~ 5g / m^TwoIt is. 10g / m^TwoOver
The amount of hot melt material becomes too large,
May inhibit swelling.

FIG. 2 is a graph obtained by plotting the measured values of the relationship between the coating amount of the hot melt material and the average thickness of the obtained hot melt fiber when the same hot melt material is added under the same conditions. The vertical axis represents the frequency (%), and the horizontal axis represents the HM fiber diameter (mμ) at each application amount. From the measured values, it can be seen that the thickness of the obtained hot melt fiber increases as the application amount of the hot melt material increases. The thin fibrous net in the present invention is 3 mμ to 10 m in diameter when measured under a microscope.
μ, and a thick fibrous net refers to a diameter of about 10 μm to 50 μm. However, unlike the spun synthetic fiber, the net-shaped fiber does not have a uniform diameter, has a wide diameter distribution, and must be regarded as an average fiber.

The role of the first- and second-stage hot-melt surface processing The effects of the hot-melt surface processing by the combination of the addition devices (A) and (B) have been described. Further, by performing multi-step processing more than that, more perfection can be expected. However, in view of economic efficiency, two-stage processing is often sufficient. In the combination of the adding devices (A) and (B), in the first stage processing, whether the fibers are fine and the mesh has a dense fiber net-like surface, or if the fibers are thick and the mesh has a coarse fiber net-like surface The order of the coarse and dense combinations depends on the conditions of the nonwoven fabric substrate, the properties of the hot melt, and the like, and which combination is better is appropriately selected in consideration of these conditions.

Hot Melt Material Used One of the conditions required for the hot melt material used is that fiber netting is easy, the second is tackiness, and the third is nonwoven fabric. The bondability with the base material and its constituent components. The ease of fiberization depends on the degree of polymerization of the polymer, the melt index, and the like. The choice of an appropriate polymer is important. The problem of tackiness is a problem peculiar to this process. If tackiness is present, when it is overlapped, it is bonded to the back surface of the nonwoven fabric substrate, causing so-called blocking. Therefore, a hot melt material having low tackiness is preferably selected. However, in the combination of the first-stage processing and the second-stage processing, it is desired that the second-stage hot-melt layer has less tackiness, but the first-stage hot-melt layer is formed by the second-stage hot-melt layer. Since the surface is covered, there is no problem even if there is slight tackiness.

A typical hot melt material having low tackiness is EVA (ethylene-vinyl acetate copolymer).
belongs to. The vinyl acetate content is important for spinnability and fibrosis, and the molecular weight of vinyl acetate greatly affects ejection properties and fibrosis. It is preferable that the vinyl acetate content in the ethylene-vinyl acetate copolymer is high, for example, 15%.
% Or more, preferably 20 to 40% by weight. The molecular weight is determined by the coefficient of thermal fluidity (MFR (g / 10
Min)), it is 200 to 400 g / 10 min for a normal ethylene-vinyl acetate copolymer hot melt material, but in the present invention, 200 g / 10 min or less, preferably 50 to 150 g / 10 min. Are suitable.

Examples of those which may have tackiness include olefins such as amorphous polyethylene and polypropylene, SEBS (styrene, ethylene, butadiene styrene block copolymer) and SIS (styrene, isoprene, styrene block copolymer). And the like.

Affinity between base nonwoven fabric and hot melt layer In the present invention, the conditions to be targeted for surface processing by the hot melt layer are as follows. First, the surface of the superabsorbent sheet is made uniform by the fibrillated hot melt layer. Second, good bonding between the coated hot melt layer and the surface of the base nonwoven fabric or the fibers constituting the nonwoven fabric.

To achieve the first goal, as described above, a double network structure consisting of a fine mesh and a coarse mesh may be formed. To achieve the second goal, the affinity between the hot melt layer and the nonwoven fabric substrate or the fibers constituting the substrate is important. In order to obtain an ideal bonding state, the components of the hot melt material and the fiber components are preferably the same. For example, there is a case where a polypropylene-based hot melt material is used for a polypropylene nonwoven fabric substrate.

However, since the components of the hot melt material are generally different from the fiber components, it is desirable to select a compatible combination from various combinations. For example, in the case of an EVA-based hot melt material, polyester fiber, nylon fiber, etc. are well bonded. Combination with polypropylene fibers also maintains some strength, but tends to be very weak when joined with polyethylene fibers or cellulose fibers. In this case, it is desirable to take measures to stabilize the bonding state by mixing polyester fibers with polyethylene fibers or cellulose fibers.

Next, specific examples of combinations of hot melt fiber patterns will be described. Examples of the combination of the first and second hot melt layers and the state of the surface covering of the superabsorbent sheet with the combination are shown in Examples 1, 2 and 3 of FIG. 3, respectively. In Example 1, the first stage and the second stage both used curtain spray, and the first stage densely filled thin hot melt fibers,
The second stage is an example in which surface processing is performed by roughly combining thick hot melt fibers. Example 2 is an example in which the first stage combines a fine and dense curtain spray, and the second stage combines a thick and coarse spiral coat. In Example 3, the first stage firstly forms a hot-melt fiber reinforcing line with a linear coat,
Then, the second stage is an example in which a fine and dense curtain spray is combined.

Hereinafter, the effect of the combination of the two-stage processing will be demonstrated. As described above, the effect of the combination of the two-step processing is performed in two directions, that is, the stability evaluation when dry and the stability evaluation when wet. Method for evaluating desorption of granular SAP from sheet during dry, and SA during wet
The method of measuring the retention rate indicating the degree of P desorption is shown below.

The stability of the SAP in a dry state is evaluated using a stability tester as shown in FIG. In FIG. 4, reference numeral 1 denotes a motor, 2 denotes a sample of a highly absorbent sheet to be evaluated, 3 denotes a drive belt, 4 denotes a drive roller, 5 denotes a tape,
Reference numeral 6 denotes a surface of the sample to which the coating liquid is applied, 7 denotes a back surface thereof, and 8 denotes a tension roller.

1. Preparation of sample 1) Sample size Cut to a basic size of 10 cm width x 80 cm length.
The width is a repeating unit such as a stripe pattern according to the sample. The width is about 10 to 30 cm. 2) Pre-drying In order to keep the water content at the time of evaluation constant, pre-drying is performed until the water content becomes 10% by weight or less. However, the drying temperature is set to 60 ° C. or lower in order to prevent deterioration of the sample. 3) Seasoning At least one temperature and humidity condition at which the water content is 10% by weight.
Leave for 2 hours. Open the application surface in a constant temperature / humidity chamber or container.

2. Evaluation of SAP sticking property by tester 1) Sample weight measurement (using an electronic balance with a sensitivity of 1 mg) The amount of SAP applied to the sample is calculated by subtracting the substrate weight from the sample weight (W0). 2) Attach the sample to the tester. With the application surface facing outward, the substrate surfaces at both ends of the sample are connected with an adhesive tape (FIG. 4D). 3) Apply a load with a tension roller. The load is 1kg /
The width is 10 cm. 4) Start-up In order to collect the dropped SAPs, spread black paper under the sample traveling point in advance and switch on the motor. The running speed is set to 30 m / min. 5) Check the amount of SAP dropped out after 1 minute. As the amount of the SAP that is insufficiently adhered (A zone), the amount of the SAP falling off for one minute after the start is checked (W1). FIG. 5 is a diagram showing the relationship between the running time and the amount of dropout. As the amount of SAP with insufficient adhesion (A zone), the amount of SAP falling off for one minute after startup is examined (W1). 6) Check the SAP dropout amount 4 minutes after restart. As the amount of SAP falling off over time due to bending friction (B zone), the amount of SAP falling off for 4 minutes after restart is examined (W
2). 7) Calculation of SAP dropout amount Dropout amount for one minute after startup (SAP amount with insufficient adhesion)
= (W1 / W0) × 100 Amount dropped for 5 minutes after startup (total amount of SAP dropped out) = [(W
1 + W2) / W0] × 100

Next, a method for evaluating the stability of the SAP after absorption will be described. 1) Preparation of sample Cut to 10 cm width x 15 cm length. For line-coated products, the width is about 10 cm in repeating pattern units. 2) Evaluation procedure The weight of the sample is measured (W0). 2. 300 ml of physiological saline (0.9% by weight NaCl aqueous solution) is put into a stainless steel vat (17 cm × 22 cm). 3. Assemble the absorber evaluation unit. 6A and 6B are conceptual diagrams of the assembled absorber evaluation unit. FIG. 6A is a cross-sectional view of the absorber evaluation unit, and FIG. 6B is a plan view of the absorber evaluation unit. The sample 33 is wrapped with a filter paper 34 and sandwiched between a stainless steel wire mesh (10 cm × 15 cm, made by Nippon Filcon 316) on the upper surface and a stainless steel wire mesh (15 cm × 20 cm, made by Nippon Filcon 316) on the lower surface. In this case, the SAP attachment surface of the sample 33 is located on the lower side. Filter paper 34
The periphery is bent so as to enclose the sample 33,
The corners are fastened with needles. 4. The absorber evaluation unit is immersed in physiological saline in a stainless steel vat for 10 minutes. Immediately after the sample in the filter paper has sufficiently absorbed liquid and stabilized on the stainless steel for the underlay, the stainless steel mesh for preventing floating is removed, and the liquid is absorbed in a free swelling state. 5. The absorbent evaluation unit is taken out of the stainless steel vat and drained for 10 minutes. In order to remove free water remaining on the filter paper, the absorber evaluation unit is inclined at an inclination angle of 20 to 30 ° and drained for 1 minute. 6. Open the filter paper of the absorber evaluation unit, grasp the base part of the sample, pull it up vertically, and measure the weight (W
1). 7. The swollen SAP remaining on the filter paper is weighed together with the filter paper (W2). 8. The weight of the filter paper previously absorbed is measured (WF). 9. The absorption capacity of the sample and the retention of the swollen SAP to the substrate are calculated. Sample absorption capacity = [W1 + (W2-WF)]
/ W0 Retention rate of swollen SAP on substrate = ΔW1 / [W1 +
(W2-WF)]｝ × 100

[0039]

EXAMPLES (Example 1) <Preparation of nonwoven fabric substrate> A card web of 20 g / m ² using polyester fiber (6d × 51 mm) was used as an upper layer, and viscose rayon fiber (1.5d × 38 mm) was used. A two-layer nonwoven fabric obtained by treating a two-layer web having a 20 g / m ² card web as a lower layer with a high-pressure water stream was prepared as a base material. The upper layer was bulky and the lower layer was relatively dense, with an average apparent density of 0.06 g / cm ³ .

<Preparation of superabsorbent sheet> Tokushu Paper Co., Ltd.
MFC (S-MFC Super Micro Fibril Cell)
Water and ethanol to a 2.5% aqueous solution of
Aqueous ethanol dispersion with an MFC concentration of 0.67% (water / d
The weight ratio of tanol was 60/40). This minute
Sprayed particles S of average particle size 200mμ manufactured by Mitsubishi Chemical Corporation
AP (product name "Aqua Pearl AP-211D")
A slurry containing 25% by weight of AP was prepared. This slurry
It is composed of the polyester fiber as the base material of the nonwoven fabric having the two-layer structure.
The coat part is 7 mm on the upper layer
The line part is a 3 mm wide striped line coat
Coat with a coater so that the average SAP coating amount
And 200g / m ^TwoA highly water-absorbent sheet was prepared.

<Surface Processing by Hot Melt Layer> EVA-based hot melt material (trade name “Morescomelt S-
1396D ") was subjected to a surface treatment using a curtain spray method in both the first stage and the second stage while changing the amount of the hot melt material added. The amount of hot melt material added in the first and second stages is
0.5g / m ² , 1.0g / m ² combined, 3 kinds of sample 1,
A few were made. As a comparative example, a comparison sample of 3 g / m ² single-step processing was prepared, and comparison with the two-step processing was attempted.
The main composition of the hot melt material used in this example is as follows. EVA 45% Wax 5% Tackifier 50%

<Evaluation Results of Stability> The superabsorbent sheets having been subjected to the surface treatment of the first and second stages were evaluated for stability during drying and stability during absorption by the method described above. As for the stability at the time of drying, the dropout rate (%) was measured over time as shown in FIG. 3, and the change of the dropout rate over time was plotted in FIG. 7. The 1-minute value and 5-minute value are displayed. The stability at the time of wet absorption was shown by the retention (%). Table 1 shows the results.

[0043]

[Table 1]

Regarding the stability when dry, any of the two-stage processing shows better results than the one-stage processing. Among them, the combination of the first stage 0.5 g / m ² and the second stage 0.5 g / m ² Is the most excellent. The worst method is to use 3 g / m ² in one step. This means that a fine and dense mesh net that does not miss even the fine parts of the SAP particles is important for stability when dry.
This indicates that g / m ² results in a rather thick and coarse mesh. Regarding the stability at the time of absorbing moisture, the retention rate is higher in the two-stage processing, regardless of the amount of the hot-melt material added, as compared with the one-stage processing, but the first-stage 1 g / m ² , Two-step 1 g / m ² gives the best results. This means that the diameter of the SAP increases due to swelling, so that the fiber thickness of the fibrous hot melt fiber, which is not easily broken by swelling, as compared to the thin and dense structure, also has an effect on the stability after absorption. Indicates an important element.

(Example 2) <Preparation of nonwoven fabric base material> As a cellulosic nonwoven fabric, a product name of TCF404 (a unit weight of 40 g / m ² , apparent density 0.14 g / cm ³ ) manufactured by Nimura Chemical Industry Co., Ltd. was used as a base material. did.

<Preparation of superabsorbent sheet> Using the above-mentioned base material, a slurry (SAP 20%, S-MFC 0.6%, SAP-made by Mitsubishi Chemical Co., Ltd., trade name "Aqua Pearl 211D") was applied to the surface of the base material.
A dispersion having a weight ratio of ethanol / water of 70/30) was applied by a coater so that the coated portion became a stripe line coat having a width of 10 mm and the uncoated portion a width of 5 mm. A superabsorbent sheet having a SAP coating amount of 150 g./m ² was prepared.

<Surface Processing by Hot Melt Layer> In this embodiment, a cellulosic base material is used. Because the bondability between cellulosic substrate and EVA is not very good,
Although it is sticky, it has relatively good adhesion to cellulose.
A hot melt material (“Morescomelt ME-125”) containing polypropylene (PP) was used as the first stage.
As the second-stage hot melt material, as in Example 1, EV
A. We used "Morescomelt S". The main components of “Morescommelt ME-125” are as follows.・ 48 copies of EVA ・ 40 copies of tackifier ・ 12 copies of PP

The first stage aims at the anchor effect for increasing the affinity of the base material, and at the time of thick rough hot melt processing,
The hot melt material was added linearly at intervals of 7 m / m. Care was taken to add the hot melt material to the non-coated part. The second stage was processed by a curtain spray method to obtain a sample 4 with the aim of covering with a fine and dense net.

<Evaluation Results of Stability> In order to compare the combined effects of the first-stage processing and the second-stage processing, only the comparative sample 1 of the first-stage linear processing and the second-stage curtain spray processing were used. Comparative Sample 2 was added. Table 2 shows the results.

[0050]

[Table 2]

In the case of linear processing alone, most of the SAP is not covered with the hot melt layer, and therefore, of course, the dropout property in dry state and the retention property after absorption of moisture are extremely poor. In the case of curtain spray alone, the drop-off property and the retention property are worse than expected. This is because even if the net fiber is thin and the mesh is dense, the affinity between the hot melt layer and the cellulose is poor, so the bonding is poor, and the hot melt layer separates from the bonding surface with the base material together with water absorption and swelling. It is speculated that this is the result.

On the other hand, when the first and second hot melt layers are combined as in this embodiment, the first linear hot melt layer acts as an anchor, and the hot melt layer and the second hot melt layer are combined. Are stably bonded, so that a material which is excellent in the amount of falling off in the dry state and the holding property in the wet state can be obtained.

(Example 3) <Preparation of nonwoven fabric for base material> Rayon cold gauze (net-like woven fabric)
50 g / m ² polyester fiber (5d × 65m / m) 50 % of polyethylene, polyester sheath-core shaped composite fibers (3d X 41m
/ m) were prepared and bound brushed shaped nonwoven by needle punching by 50% was uniformly mixed superimposed webs 40 g / m ² was obtained. This non-woven fabric has a basis weight of 80 g / m ² and an apparent density of 0.1 g / c.
m ³ was very bulky.

<Preparation of superabsorbent sheet> SAP to be supported
As two types. SAP1 is a particulate SAP (trade name “Aqua Pearl 211D”) with an average particle size of 200 mμ manufactured by Mitsubishi Chemical, and SAP2 is an average particle size manufactured by Sanyo Chemical Industries.
400mμ flake SAP (trade name “Sunwet IM-5
000 "). While oscillating the base material on the diaphragm, SAP1 was added as uniformly as possible at an amount of 150 g / m ² , and then SAP2 was placed on top of SAP1 so as to overlap it.
It was added 0 g / m ² equivalent, was super absorbent sheet carrying SAP350g / m ^2. Most of the SAP was buried in the brushed web, but most of the SAP fell off when the SAP carrying surface was turned downward. They were immersed in physiological saline to evaluate the stability upon absorption, and as soon as they began to swell, most of the SAP fell off and could not be used for standard method measurements. This was designated as Comparative Sample 3.

<Surface processing by hot melt material> Same as in Example 1 on the side of the SAP on which the superabsorbent sheet was carried.
EVA-based hot melt materials ("Morescomelt S1396
Sample No. 5) obtained by performing surface processing by using a curtain spray type hot melt addition device in two stages using “0”). For comparison, a comparative sample 4 subjected to only the first-stage processing (curtain spray method) was prepared and similarly tested. These samples and comparative samples were subjected to the same stability test as in Example 1, and the results are shown in Table 3. As a result, compared to the first stage processing, the combination of the first stage and the second stage shows a much better stability effect, despite the small amount of hot melt material used in total. Was.

[0056]

[Table 3]

(Example 4) <Preparation of nonwoven fabric substrate> Polyester fiber (3d x 51m / m)
60% and 40% viscose rayon fiber (1.5d x 35m / m)
A nonwoven fabric obtained by treating a 40% g / m ² card web with a high-pressure water stream was prepared as a base material. The apparent density of this nonwoven fabric was 0.08 g / cm ³ .

<Preparation of superabsorbent sheet> 125 parts by weight of an aqueous solution of 80% by weight of acrylic acid, 57.3 parts by weight of a 48.5% by weight aqueous solution of sodium hydroxide, 6.4 parts by weight of water, and a crosslinking agent (N,
A solution A was prepared by adding 0.15 parts by weight of (N'-methylenebisacrylamide) and 5.0 parts by weight of a 30% by weight aqueous hydrogen peroxide solution as an oxidizing agent. The monomer concentration of solution A is
The content was 60% by weight and the degree of neutralization was 50 mol%. Aside from this,
125 parts by weight of an aqueous solution of 80% by weight of acrylic acid, 57.3 parts by weight of a 48.5% by weight aqueous solution of sodium hydroxide, 9.9 parts by weight of water, and a crosslinking agent (N, N'-methylenebisacrylamide) 0.
15 parts by weight and L-ascorbic acid 1.5 as a reducing agent
A solution B was prepared by adding parts by weight. The monomer concentration and the degree of neutralization of the solution B were the same as those of the solution A. Use two nozzles with an inner diameter of 0.13 mm manufactured by Ikeuchi Co., Ltd.
And the distance between the tips of the nozzles is 4 mm. The liquid A is heated from one nozzle to the liquid A and the liquid B is heated from the other nozzle to a liquid temperature of 40 ° C., and the pumps are controlled to flow at a flow rate of 5 m / sec. Supplied with The liquids A and B merged when they came out of the nozzle, formed a liquid column of about 10 mm, and then fell as droplets in the rising airflow of air (60 ° C.). The droplets are received on the nonwoven fabric substrate 100 cm below the tip of the nozzle, sprayed with saturated steam at 120 ° C. for 10 seconds, subjected to steam treatment, and dried until the water content becomes about 10%. A superabsorbent sheet carrying 220 g / m ^{2 of} SAP was obtained.

<Surface processing with hot melt material> A curtain spray type hot melt addition device (manufactured by Sun Tool Co., Ltd.) was used as the first stage on the SAP supporting side of the superabsorbent sheet.
After spraying 0.5g / m ² of EVA hot melt material (Morescomelt S), the same hot melt material is heated to 2g / m ² using a spiral coat type hot melt addition device (manufactured by Suntool). Melt processing was performed. The resulting super-absorbent composite sheet after hot-melt processing was observed with a surface photograph of an electron microscope.
Had the surface structure as shown in FIG. This sheet showed no dust scattering even in a dry test, and the SAP retention after absorption was 85% or more.

[0060]

As described above, the SAP particles on the non-woven fabric substrate are formed into two different fibers having different thicknesses and different mesh densities.
By combining and covering various types of hot melt layers, S particles having a small particle size in a dry state and having no tackiness can be obtained.
Not only can the AP particles be prevented from falling off, but even if the SAP particles absorb and swell, the hot melt layer also expands in accordance with the swelling force, securely holding the SAP particles and effectively preventing the falling off. Can be prevented. In addition, the hot melt layer does not hinder the original water absorption of the superabsorbent composite sheet, and exhibits sufficient water absorption performance for various uses.

Further, by using a combination of two types of hot-melt adding devices in accordance with the method of the present invention, it is possible to easily produce a superabsorbent composite sheet having the above-described performance. .

[Brief description of the drawings]

FIG. 1 shows S applied on a nonwoven fabric substrate applied to the present invention.
Explanatory drawing which shows the model example of the support form of AP.

Fig. 2 Frequency (%) and thickness of hot melt fiber (mμ)
Is a graph obtained by plotting actual measured values of the relationship.

FIG. 3 is a schematic diagram of an example of a combination of a first-stage and a second-stage hot melt layers and a surface covering state of a superabsorbent sheet using the combination.

4A and 4B show a tester for evaluating the stability of the SAP, wherein FIG. 4A is a front view of the tester, FIG. 4B is a side view of the tester, FIG. 4C is a plan view of the sample, and FIG. Is a perspective view of a sample.

FIG. 5 is a graph showing a relationship between a running time and a dropout amount.

6A and 6B are conceptual diagrams of an assembled absorber evaluation unit, wherein FIG. 6A is a cross-sectional view of the absorber evaluation unit, and FIG. 6B is a plan view of the absorber evaluation unit.

FIG. 7 is a graph plotting the change in the SAP dropout rate over time.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Motor 2 Sample of highly absorbent sheet to be evaluated 3 Drive belt 4 Drive roller 5 Tape 6 SAP application surface of sample 7 Back surface 8 Tension roller 33 Sample filter paper 34 Filter paper

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) A61F 13/15 (72) Inventor Ma Suzuki 2-26-5 Nihonbashi Hamacho, Chuo-ku, Tokyo Nippon Absorption Co., Ltd. Ryoichi Matsumoto, Inventor Ryoichi Matsumoto 2-26-5 Nihonbashi-Hamacho, Chuo-ku, Tokyo In-house Absorbent Technology Research Institute, Inc. (72) Inventor Yoshihiro Tanaka 2-26-5, Nihonbashi-Hamacho, Chuo-ku, Tokyo Within Japan Absorbent Technology Research Institute Co., Ltd. (72) Inventor Tajima Politics 4--12-10, Mitsumitsu, Higashiyodogawa-ku, Osaka-shi, Japan Suntool Co., Ltd. F-term in Matsumura Oil Research Co., Ltd. (reference) 4C003 AA22 AA27 FA01 4F100 AJ04 AJ05 AK01A AK01B AK04G AK07G AK41 AK68G AK73G AR00C AR00D BA04 BA07 BA10A BA10D BA26 CB03 DC16C DC16D DG15A EH462 EJ82A EJ822 GB07 GB90 JA12G JD05 JD05A JD05B JL00 JL12C JL12D 4G066 AB06D AB07A AB07D AB10D AC02B AC17B AC23C AC35B AE06B BA05 BA42 FA42

Claims (11)

[Claims] 1. A high-water-absorbing resin, which is partially distributed in voids of the nonwoven fabric on one surface side of the nonwoven fabric substrate and distributed in a layered manner over substantially the entire surface with the other partially exposed from the nonwoven fabric surface. In the water-absorbent sheet, the surface of the exposed highly water-absorbent resin layer is located on the first hot-melt layer having a mesh-like dense fiber net shape and the first hot-melt layer; High water absorption characterized by being covered with a fiber net-like hot melt layer comprising a double hot melt layer with a second mesh-like hot melt layer having a coarse mesh relative to the melt layer. Highly water-absorbent composite sheet with less detachability of conductive resin. 2. A high-water-absorbing resin which is partially distributed in the voids of the nonwoven fabric on one surface side of the nonwoven fabric substrate and distributed in a layered manner over the entire surface with the other partially exposed from the nonwoven fabric surface. In the water-absorbent sheet, the surface of the exposed highly water-absorbent resin layer is located on the first hot-melt layer having a mesh-like fiber net shape and the first hot-melt layer; High water absorption characterized by being covered by a fiber net-like hot melt layer comprising a double hot melt layer with a fiber net-like second hot melt layer whose mesh is relatively dense with respect to the melt layer. Highly water-absorbent composite sheet with less detachability of conductive resin. 3. The superabsorbent composite sheet according to claim 1, wherein the fibers of the dense hot melt layer of the mesh are finer than the fibers of the coarse hot melt layer of the mesh. 4. A method for processing the surface of a superabsorbent composite sheet in which a superabsorbent resin is distributed in a layer on one surface side of a nonwoven fabric substrate, wherein the superabsorbent resin is distributed. A first-stage hot-melt processing step in which hot-melt processing is performed by a hot-melt adding device (A) for forming a first hot-melt layer in the form of a dense mesh fiber net on the surface; On the other hand, a surface treatment is performed by combining with a second-stage hot-melt processing step of performing a hot-melt process by a hot-melt adding device (B) for obtaining a second hot-melt layer having a relatively coarse mesh fiber net shape. A surface treatment method for a superabsorbent composite sheet, comprising: 5. The hot melt processing said first stage, the first mesh is tightly coating amount is performed in the range of 0.3g / m ² ~2g / m ²
Crude hot-melt layer is formed, the second stage hot-melt processing, relatively mesh to said first stage hot-melt processing amount coated is done in a range of 1g / m ² ~10g / m ² is The method for processing a surface of a superabsorbent composite sheet according to claim 4, wherein a second hot melt layer is formed. 6. The hot melt processing said first stage, the mesh forms a first hot-melt layer of coarse coating amount is carried out in a range of ^{1g / m 2 ~10g / m 2} , the second stage hot melt processing, claims applied amount relatively mesh to form a dense second hot-melt layer to the first stage hot-melt processing carried out in the range of 0.3g / m ² ~2g / m ² 5. The surface processing method of the superabsorbent composite sheet according to 4. 7. The hot melt adding apparatus according to claim 4, wherein two curtain spray type hot melt adding apparatuses capable of obtaining a relatively dense mesh are combined in front and rear with respect to a moving direction of the nonwoven fabric substrate. Any one
Item 14. The surface processing method for a superabsorbent composite sheet according to item 6. 8. A dense mesh first hot-melt layer is formed by using a curtain-spray type hot-melt adding device as the first-stage hot-melt adding device, and the second-stage hot-melt adding device is formed. The method according to any one of claims 4 to 7, wherein a second hot melt layer having a mesh relatively coarse with respect to the first hot melt layer is formed using a spiral coat type hot melt addition device. The surface processing method of the superabsorbent composite sheet according to the above. 9. The method according to claim 9, wherein a first hot melt layer having a coarse mesh is formed by using a spiral coat type hot melt adding device as the first stage hot melt adding device. The method according to any one of claims 4 to 7, wherein the second hot melt layer having a mesh relatively dense with respect to the first hot melt layer is formed using a curtain spray type hot melt addition device. The surface processing method of the superabsorbent composite sheet according to the above. 10. A dense mesh first hot melt layer is formed by using a curtain spray type hot melt addition device as said first stage hot melt addition device, and said second stage hot melt addition device is provided. The method according to any one of claims 4 to 7, wherein the second hot melt layer having a mesh relatively coarse with respect to the first hot melt layer is formed using a line coat type hot melt addition device. The surface processing method of the superabsorbent composite sheet according to the above. 11. A first hot-melt adding device of a coarse mesh is formed by using a line-coat type hot-melt adding device as said first-stage hot-melt adding device, and said second-stage hot-melt adding device is formed. The method according to any one of claims 4 to 7, wherein the second hot melt layer having a mesh relatively dense with respect to the first hot melt layer is formed using a curtain spray type hot melt addition device. The surface processing method of the superabsorbent composite sheet according to the above.