JPS59229322A - Manufacture of water-absorbing sheet - Google Patents

Abstract

PURPOSE:To manufacture a sheet excellent in water-absorbing and water-holding properties by a method wherein high water-absorbing polymer particles are prepared by degrees and in layers according to particle diameters and fixedly stuck securely on the surface of the reticulate foamed sheet of base material and in continuous foams of said base material. CONSTITUTION:Synthetic resin with foaming agent is extruded by an extruder 3 through a T-die 1 to obtain a reticulate foamed sheet A having water permeability. Fine particles of high water-absorbing polymer is scattered uniformly by a scattering device 4 on the surface of said sheet A, heated by a heater 9 between feed rolls 5, 5' and stretching rolls 6, 6', stretched at a suitable magnification, sucked by a vacuum device 10 from the back to prepare high water-absorbing polymer 7 in stepped layers in the foams of reticulate foamed sheet A according to particle diameters and adsorbed and held. Then, the coated sheet B is welded by the T-die 2 to above reticulate foamed sheet A to obtain water-absorbing sheet 8.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a water absorbent sheet.

Traditionally, water-absorbent sheets have been used for items that require high water absorption capacity and are water-based, such as disposable diapers, sanitary napkins, paper towels, medical bats, disposable rags, etc., as well as fruits and vegetables, leafy vegetables, fresh fish, etc. For inner packaging of meat, etc. (
Packaging materials that absorb water or liquid in advance (including underlays), or those that require water retention, such as moisture (liquid) control sheets that are used as they are when dry. There is. In order to meet these demands, we have conventionally developed water absorbent sheets that utilize the physical water absorption properties of fibers such as valves, rayon, nonwoven fabrics, and paper, or water absorbent sheets that use superabsorbent polymers.
A sheet made by simply adding and kneading a super absorbent polymer to a synthetic resin such as polyethylene or polyvinyl chloride, or applying the super absorbent polymer to a base material using an adhesive or a binder such as a thermoplastic resin. There are many types in which the polymer is fixed by pressure bonding, spraying, etc., and in which the polymer is dispersed and held between fibrous base materials such as woven fabrics, nonwoven fabrics, and paper.

However, in both the fixing method and the dispersion holding method described above, if the binder used is particularly a hydrophobic binder, most of the surface area of the superabsorbent polymer is broken by the binder and becomes highly absorbent. Water-absorbing polymers are difficult to fully demonstrate their original water-absorbing function, and those that are dispersed and retained between fibrous base materials are subject to stress such as bending, stretching, compression, and restoration during use. Problems such as non-uniform dispersion or falling off of the superabsorbent polymer occurred, and sufficient performance could not be exhibited in practical use.

Therefore, although the water-absorbing sheets produced by the conventional method use relatively expensive super-absorbent polymers, they are not necessarily sufficient in terms of the substantial effect of the added amount.

The present invention has been made against the above-mentioned technical background, and involves forming superabsorbent polymer particles in a stepwise layered manner according to the particle size on the surface of a reticulated foam sheet as a base material and on the open cells of the base material. It is an object of the present invention to provide a method for manufacturing a water-absorbing sheet that can be reliably adhered to the interior of the water-absorbing sheet to fully exhibit its water-absorbing or water-retaining functions.

Hereinafter, embodiments of the first and second inventions of the present application will be described in more detail based on the drawings.

A regular reticulated foam sheet with open cells or a mixture of open cells and closed cells extruded with the main No. 1 T die/
(hereinafter referred to as a reticulated foamed sheet) (A) is obtained, heated with a heater between feed rolls s, s' and stretching rolls 2, t', and stretched to an appropriate magnification using a suction blower or vacuum suction from the back side. Vacuum device 10 for rooms etc.
By suctioning, the super absorbent polymer is adsorbed and retained by forming a stepwise layer in the cells of the reticulated foam sheet (A) according to the particle size, and is further coated with a second T die (see below). B) is fused to the reticulated foam sheet (A) to obtain a water absorbent sheet K.

Coating sheet) (B) is a synthetic resin sheet, paper, cloth, etc., or a combination thereof, which is fixed and integrated with the reticulated foam sheet to improve the adhesion retention of the superabsorbent polymer and,
This serves to improve the strength of the water absorbent sheet.

At this time, as shown in Figures 2, 3, and J, relatively large-diameter particles of the superabsorbent polymer are placed near the surface layer of the reticulated foam sheet (A), and fine particles are placed deep in the inner layer. enter,
The polymer is distributed in a favorable manner in terms of water absorption and water retention performance, forming a graded layer according to the particle size and fixing. As a result of exhibiting strong adhesion due to expansion, a water-absorbing sheet with extremely excellent water absorption and water retention functions can be obtained.

In addition, each of the water-absorbing sheets g shown in these FIGS.
) can increase the amount of superabsorbent polymer that adheres to the surface. The thus obtained products implemented by the method of each invention of the present application (the ones shown in FIGS. 2, 3, and 4) are similar to the conventional water absorbent sheets g shown in FIGS. In other words, a reticulated foam sheet is impregnated with a superabsorbent polymer dispersion and dried (Fig. J), a superabsorbent polymer is kneaded into a thermoplastic resin (Fig. 4), and a superabsorbent polymer is used as a binder. −
The water retention properties are even better than those bonded to a reticulated foam sheet (Fig. 7) and those in which a super absorbent polymer is kneaded into a water-absorbing binder and applied to a reticulated foam sheet (Fig. 7). .

The water-absorbent sheet exhibits excellent functions such as quick-acting water absorption and water retention! The J1 superabsorbent polymer must be uniformly spread on the reticulated foam sheet, and must be sucked and fixed inside the sheet.

The reason for this is that if the superabsorbent polymer becomes uneven due to agglomeration or drop-off, the water-absorbent sheet will not be able to perform its full function. This is because the fusion properties between (B) and the reticulated foam sheet (A) are inhibited.

Therefore, methods for uniformly distributing the superabsorbent polymer include, for example, known mechanical methods, such as dropping the superabsorbent polymer onto a vibrating wire screen (screen) through predetermined slits and sieving it off. A method is used in which the material is dropped through a slit onto a rotating brush and splashed by the brush.

Next, as shown in claim 2, it is preferably 7.2 to
A reticulated foamed sheet stretched 3 to 3 J times, or a reticulated foamed sheet stretched under the above stretching conditions while superabsorbent polymer is being spread using a stretching device (not shown) between feed rolls O and T', the air bubbles are stretched and expanded. In addition to improving the infiltration rate of the superabsorbent polymer, stretching also produces a molecular orientation effect in the reticulated foam sheet, improving mechanical strength, which improves not only water absorption but also the adhesion of the polymer. and has excellent handling properties.

Note that when the stretching ratio is 42 times or less, the cellular portions of the foamed sheet as a base material are slightly deformed but are not substantially stretched, so that the cellular portions of the foamed sheet are hardly stretched.

Therefore, the penetration rate of the superabsorbent polymer into the cells of the foamed sheet is not significantly improved, and the mechanical strength of the foamed sheet itself cannot be improved due to the molecular orientation effect. On the other hand, when the stretching ratio is 5 times or more, most of the superabsorbent polymer particles cannot stay in the surface layer of the foam sheet and are buried in the air bubbles, or the fine particles are absorbed into the air bubbles of the foam sheet. Practical water absorption to pass between
This is undesirable as it causes a decline in water retention and other functions.

In addition, by providing a heating heater on the superabsorbent polymer adsorption surface side between the feed roll J1 and the stretching rolls B and O', the superabsorbent polymer 7 and the reticulated foam sheet) (A
) (B) and reticulated foam sheet) (A)
It is possible to further increase the fusion strength with.

In carrying out the second invention of the present application, the method for coating the superabsorbent polymer adsorption surface is not limited to the extrusion method, but may also be carried out by a curtain flow coater method, an airless coating method, a lamination method, or the like.

The reticulated foam sheet (A) used in each invention of the present application has open cells or a mixture of open cells and closed cells, has water permeability, has appropriate elasticity and restoring force,
Moreover, since the super absorbent polymer is suctioned and fixed within the open cells within the reticulated foam, the drawbacks of water absorbent sheets produced by conventional methods, namely, the super absorbent properties due to external forces such as bending, stretching, compression, and restoring force. It has features such as very little polymer shedding.

Further, the covering sheet (B) used in the second invention of the present application is usually preferably a water-permeable sheet, paper and cloth, or a composite sheet thereof, and a water-impermeable sheet may be used depending on the application. In some cases, it may be.

(Reticular foamed sheet) Materials of (A) include, for example, high density polyethylene, low density polyethylene, linear low density polyethylene, ethylene vinyl acetate copolymer polypropylene, polybutene, ethylene propylene copolymer, ethylene-butene copolymer, ethylene acrylic. acid ester copolymer,
There are polyvinyl chloride, polyamide, polyethylene terephthalate, and their copolymers, etc. Among them, polyolefin resins, polyvinyl chloride resins, A reticulated foam sheet that is a copolymer of these and has excellent flexibility is preferred.

In addition, the material of (B) is the reticulated foamed seam)
The same material as (A), paper cloth made of natural fibers, or a composite material thereof can be used.

The foaming agent and crosslinking agent used in the molding of the reticulated foam sheet for the invention of the present application include azosica-bonamide, dinito-p
Foaming agents such as sopentamethylenetetramine, goo≠oxybisbenzenesulfonyl hydrazide, azobisisobutyronitrile, paratoluenesulfonyl hydrazide, and ditert-butyl peroxide, /-3bis(tert-butylperoxypropyl) A chemical crosslinking agent such as benzene or dicumyl peroxide is used, and a foaming aid may also be used in combination.

Further, the inventions of the present application can be carried out not only by chemical crosslinking but also by electron beam irradiation crosslinking.

The superabsorbent polymers used in each invention of the present application include synthetic resin-based polyvinyl alcohol-based products, polyacrylate-based products, polyethylene oxide-based products, polyacrylonitrile-based products, starch-based acrylonitrile-grafted hydrolysates, There are acrylic butyrate grafted products, cellulose-based graft polymerized products, carboxymethylated products, etc.
One type or a combination of two or more of these can also be used.

These superabsorbent polymers are usually granular powders or fine powders, and the average particle size of the polymer particles used in the inventions of this application is 700 microns or less, preferably 7 to 700 microns.

The water absorbent sheets obtained by the methods of the inventions of the present application can be used, for example, in disposable diapers, fragrance adsorption and preservation materials, freshness preservation agents for fresh foods, dew condensation prevention temperature control materials for agricultural greenhouses, walls for building materials, etc.
It is suitably used as a material for preventing condensation on ceilings, etc., and as a curing sheet for mortar, concrete, etc.

Each invention of the present application will be explained below with reference to Examples and Comparative Examples.
The methods of each invention of the present application are not limited to these examples.

Example I (first invention of the present application) Low density polyethylene (F201-8 specific gravity 0.
92 MI/, t) To 100 parts by weight, 5 parts by weight of a blowing agent (Vinihole AC-3M manufactured by Hydraulic Chemical Co., Ltd.) and 0.2 parts by weight of dicumyl peroxide as a crosslinking agent were added and kneaded in a pressure kneader. After that, the thickness is 6mm and the width is 3mm using the SOd extruder.
A normal reticulated foam sheet containing a mixture of closed cells and open cells of 0011H is extruded, and then passed through a feed roll and a stretching roller.
The super absorbent polymer "Sumikagel 5-
30'' (vinyl alcohol/acrylic acid copolymer manufactured by Jumin Chemical Co., Ltd.) Amount of application/θ,! It was uniformly spread using a rotating brush method at a ratio of i'/m', and vacuum suction was performed from the back side using a vacuum device at a pressure of 30QMMAf to obtain a water absorbent sheet with a thickness of 4 Atp x width of 300 M.

Example No. (Second invention of the present application) 5 parts by weight of a blowing agent (manufactured by Hydraulic Chemical Co., Ltd. Viny Hall AC-3M>
01.2 parts by weight of dicumyl peroxide was added as a crosslinking agent, and after kneading with a pressure kneader, a normal reticulated foam sheet with a thickness of 3H width of 300ff and a mixture of closed cells and open cells was produced using a jOφ extruder. extrude, then feed roll j1
The super absorbent polymer [Sumikagel 5-
So] was uniformly spread using a rotating brush method at a ratio of the amount/(01/rrf), and 23-0 was coated from the back side using a vacuum device 10 to obtain a water absorbent sheet with a thickness of 3 ff.

Example 3 Evatate D20, an ethylene-vinyl acetate copolymer resin with acetic acid content of Swt% (manufactured by Sumitomo Chemical) 700
Foaming agent (Excela Q2!r manufactured by Hydration Kasei) based on parts by weight
10 parts by weight and crosslinking agent dicumyl peroxide, 0.3
After adding part by weight and kneading with a pressure kneader, it was mixed with a jOφ extruder to a thickness of 3 mm and a width of 30 mm. A normal foam sheet of OWIM is extruded, and then vibrated between feed roll j15' and stretching roll O, 6', and stretched 45 times in the longitudinal direction. Spread the mixture uniformly using a rotating brush method at the amount of d, then vacuum suction from the back side at 3θ0jIjlA-pressure using a vacuum device, and cover the superabsorbent polymer adsorption surface with a coating sheet (B) made of ethylene-vinyl acetate copolymer film. Thickness, 2. /Ml water absorbent sheet was obtained.

Example G In Example λ, a reticulated foam sheet (A
) was not stretched, but a water absorbent sheet was obtained in the same manner as in Example No.

Example j A water absorbent sheet was obtained in the same manner as in Example 3, except that the reticulated foam sheet (A) having a thickness of 211rII was not stretched.

Comparative Example/Reticular foam seam in Example λ) From the back side of (A),
A water absorbent sheet was obtained in the same manner as in Example 2, except that suction was not performed using a vacuum device.

Comparative Example 2 A water-absorbing sheet was obtained in the same manner as in Example 3, except that suction was not performed from the back side of the reticulated foam sheet (A) using a vacuum device in Example 3.

Comparative Example 3 Low-density polyethylene (Sumirikisen F ＼20g manufactured by Juju Chemical Co., Ltd.
-/, specific gravity 0. 'P, 2, MI/, j) 100 parts by weight of the super absorbent polymer "Sumikagel S-30,"
Parts by weight of JjT were added, and a kneaded type water absorbent sheet having a thickness of Q, , l raw and a width of 300111M was obtained using a jθφT die extrusion molding machine.

Comparative example≠ Vinyl acetate emulsion adhesive (Chuo Rika Kogyobu AW-/) was applied to kraft paper with a basis weight of 609/rrf at 20 (H//).
d, and then the superabsorbent polymer "Sumikagel 5-30" was spread and adhered to the surface at a ratio of 7 (H1/rrf) to obtain a binder-adhesive type water-absorbent sheet.

The water absorption and water retention properties of the samples obtained in the above Examples and Comparative Examples,
Table 1 shows a comparison of fragrance retention, water-absorbing polymer retention, and sheet strength.

Table/77-Evaluation Test Method Water absorption capacity is determined by immersing a super absorbent sheet sample cut into a size of 300 x 300 m in water at 20°C for 70 minutes, then dehydrating the adhering water in a washing machine dehydration tank for 75 seconds. ) was used to determine the water absorption capacity.

The water retention rate is determined by measuring the above dehydrated sample at a temperature of 23°C and a humidity of JO%.
Equation (2) is used to express the results after 50 hours under the following environment.

Polymer retention was determined by immersing a super absorbent sheet sample cut into 300 x 300 squares in water at 20°C for 10 minutes, washing with stirring in a washing machine for 70 minutes, dehydrating, and drying in a gear open at gO°C for 5 hours. was carried out, and the polymer retention rate was expressed by equation (3).

W, total sheet weight before water absorption -F+P W, total sheet weight after water absorption -W, +S, 10 adsorbed water weight prefecture, total sheet electric lapse after a certain period of time, w, total sheet weight after drying for go℃j hours, S, Weight of attached water after 10 minutes of immersion F Weight of foam sheet P Super absorbent polymer weight formula (1) Water absorption capacity, w, -2 (M injury descent-PV V8-prefecture formula (2) Water retention rate H-■- (I + s, > X / 00
W, -F Formula (3) Polymer retention rate -We F, x 700 Fragrance retention is 5oxso'sya each sample with water 41j%
Each sample was immersed in a solution of 1 liter of 5% ethanol and 10% aromatic agent for 70 minutes, and the fragrance retention was observed after 10 days of normal indoor storage.

○: All of the 10 people sensed the fragrance.

△: More than JÅ out of 10 people sense the fragrance.

×: Less than μÅ out of 10 people perceived a slight aroma.

The strength of each sheet is JISZ/702.
Measured according to the method, and shows the strength ratio of the unstretched sample (Example ≠ and ≠) at break point strength.

[Brief explanation of the drawing]

FIG. 1: A schematic diagram showing an embodiment of the manufacturing method of the present invention. FIG. 2: An enlarged sectional view of a water absorbent sheet obtained according to the present invention. FIG. 3 is an enlarged cross-sectional view of a water-absorbent sheet obtained by covering the polymer adsorption surface of the water-absorbent sheet with a reticulated foam sheet according to the present invention. Figure μ: An enlarged cross-sectional view of a water-absorbent sheet obtained by covering the polymer adsorption surface of the water-absorbent sheet with a film-like material according to the present invention. FIG. 5 is an enlarged sectional view of a water absorbent sheet obtained by impregnating a reticulated foam sheet with a super absorbent polymer dispersion and then drying it. Figure 6: An enlarged sectional view of a water absorbent sheet obtained by the conventional method of kneading a super absorbent polymer into a thermoplastic resin. FIG. 7: An enlarged sectional view of a water absorbent sheet obtained by a conventional method of adhering a super absorbent polymer to a lJd-shaped foamed sheet using a binder. Fig. g: An enlarged sectional view of a water absorbent sheet obtained by a conventional method of kneading a super absorbent polymer into a water absorbent binder and applying it to a reticulated foam sheet. /・・・1st T die 2・・・・・2nd T die 3・・・Extruder≠・・・Polymer spreading device jS, 3″・・Feeding 4-rule z1”・...Stretching roll 7...Super absorbent polymer ♂...Water absorbent sheet g' according to the present invention...
・Water-absorbing sheet by conventional method...Heating heater IO...Vacuum device A...Reticular foam sheet B...Coating sheet

Claims (1)

[Scope of Claims] / A highly water-absorbent polymer powder is uniformly sprinkled on the surface of a water-permeable reticulated foamed sheet (A), and the reticulated foamed sheet (A) is then suctioned under reduced pressure from the back side. , the reticulated foamed sheet should have relatively large particles of super absorbent polymer in the surface layer and fine particles of super absorbent polymer in the inner layer to form a graded layer according to the particle size. (A)
A method for producing a water-absorbing sheet, characterized by suctioning and fixing a super-absorbent polymer to a sheet. 2. The method for producing a water-absorbing sheet according to claim 1, characterized in that the reticular foamed sheet (A) is stretched 7.2 to j times in the vertical or horizontal uniaxial direction, or in the vertical and horizontal biaxial directions. 3. Spread highly water-absorbent polymer powder uniformly on the surface of the water-permeable mesh foam sheet) (A), and then vacuum-suction the mesh foam sheet (A) from the back side, leaving a relatively large amount on the surface layer. The reticulated foamed sheet (A) has high water absorbency so that the super absorbent polymer particles are present in the inner layer, and the super absorbent polymer fine particles form a graded layer according to the particle size of each particle. The polymer is suctioned and fixed, then a reticulated foam sheet) (
A) (')i% water-absorbing polymer adsorption surface coated sheet)
A method for producing a water-absorbing sheet, characterized by coating it with (B).