JPH07100329B2 - Method for producing water-absorbent sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a water-absorbing sheet having a large water absorption amount and a large water-retaining power which does not easily release water even by an operation such as draining.

[0002]

2. Description of the Related Art Conventionally, water-absorbent sheets made of synthetic resin sponges have been used in many fields including sheets for sick people, cosmetics, cleaning products, and culture media for hydroponics, but they have not yet been used. I haven't found anything that can meet that demand. For example, a water-absorbent sheet made of polyvinyl alcohol sponge is widely used as a cleaning sheet, but when the water content evaporates, it loses elasticity or flexibility and becomes hard, so it must be kept in a wet state. Any of the water-absorbent sheets made of synthetic resin sponge imparting hydrophilicity has a small water absorption amount. For example, even a relatively large water-absorbent sheet made of hydrophilic polyurethane sponge has a water absorption amount of about 0.2 g / drycc. In addition to these, these water-absorbent sheets easily release water by simply shaking off the water-absorbent sheet several times as a draining operation, and their water retention capacity is extremely small, for example, even those with relatively water retention. The drainage test of the present invention (the test method is described later) shows only about 70% residual water, and The use of art for La nature was also limited naturally.

The present inventor has conducted various studies to improve the drawbacks of these conventional water-absorbent sheets and to produce a novel water-absorbent sheet having a large water absorption amount and a large water retention ability. It was found that the one obtained by compression molding has an extremely large water absorption amount and water retention property, and has completed the present invention. The object of the present invention is to provide a large water absorption amount and a large water retention property of a novel water absorbent sheet. It is to provide a manufacturing method.

[0004]

That is, according to the present invention, a hydrophilic polyurethane sponge is thermocompression molded to have an apparent specific gravity of 0.08 to 0.3 and a water absorption of about 0.5 to 2.50 g / d.
It is ry cc and the residual water content in the drainage test is 8
A method for producing a water-absorbent sheet, which comprises using a hydrophilic polyurethane sponge having a water retention capacity of 0% or more. Normally, a soft hydrophilic polyurethane sponge consisting of open cells absorbs water even in the state as it is,
It releases water easily when it is shocked and has poor water retention. However, when a soft hydrophilic polyurethane sponge having open cells is heat-compressed and its volume is compressed to a fraction, for example, the water absorption of the compressed polyurethane sponge exceeds the water absorption of the sponge body before compression. The water absorption amount is about 1.4 to 2.0 times, and the water retention capacity is remarkably improved.

The water absorption amount in the present invention means the weight of water absorbed (g / dry c) after the sample sheet is immersed at room temperature for 10 minutes or more and the free water adhering to the surface is wiped off.
It is a value obtained by dividing c) by the volume of the sample sheet when dried, and the drainage test is that the sample sheet is put in a plastic canister having a diameter of 25 cm and a depth of about 3 cm and stopped at a drop of about 70 cm. These are the measured values of residual water after repeating this operation 115 times. The relationship between the number of draining operations and the residual water content is shown in FIG. 2 in comparison with commercially available water absorbing sheets and polyurethane sheets. Here, the residual water content is a value in which the weight reduction rate corresponding to the number of drainages is shown as%, with the total weight when absorbing water being 100.

Table 1 shows how the water absorption capacity and water retention capacity of the hydrophilic polyurethane sponge are changed by thermal compression. In Table 1, Experiment No. 1 is a urethane sponge having a thickness of 15 mm (specific gravity 0.03), Experiment No. 2 has a thickness of 3 mm, and Experiment No. 3 has a thickness of 10 m /
m urethane sponge (specific gravity 0.03) with a thickness of 3.25
This is the case when compressed to mm.

[0007]

[Table 1]

Remarks ... Water absorption amount = (sheet weight after water absorption) −
(Weight of sheet before water absorption) / volume of sheet before water absorption

In this table, the water absorption of the uncompressed sample (Experiment No. 1) (specific gravity 0.03) is 0.16 to 0.19.
g / Dry cc, but thickness of 15 mm to 3 m
When compressed to m (Experiment No. 2) (compression ratio ⅕ (specific gravity is 0.15 which is 5 times), theoretically, the water absorption amount is about 5 times the water absorption amount of the non-compressed product [that is, (0 .16 to 0.19) × 5
= 0.80-0.95 g / Drycc], but the experimental result shows that the experimental result is 1.7-
The value was 1.82 g / Dry cc, which was about twice or more the theoretical value. Similarly, in the case of experiment number 3, the compression ratio is about 1 /
Since it is 3.08, the theoretical water absorption is 0.49 to 0.59.
[(0.16-0.19) × 3.08≈0.49-0.
59] should actually be 0.8-1.0 g /
It shows an increase in water absorption of Dry cc and about 1.6 to 1.7 times the theoretical value.

In the water retention test, the compression sheet absorbs a large amount of water, which is 1.5 to 2.0 times the theoretical water absorption, but the water retention after 115 draining tests. Is 59% of the experiment number 1 and 86 to 88 in the experiment number 2.
%, Experiment No. 3 shows an extremely high numerical value of 80%.

The hydrophilic polyurethane sponge constituting the water-absorbent sheet of the present invention is a product obtained by adding a foaming agent to a reaction component composed of polyisosonate and a polyol to cause a foaming reaction, and is usually used. Is a hydrophilic polyurethane sponge.

The thermal compression condition in the present invention is 19
It is about 30 seconds to 90 seconds at 0 ° C to 220 ° C. Next, the present invention will be described more specifically with reference to Examples.

[0013]

EXAMPLES Example 1 As a polyol component, a molecular weight of about 5000, f = 3, EO
A mixture of about 60% content and a molecular weight of 3500, f = 3, and about 60% EO content at a ratio of about 50:50 was used, and tolylene diisocyanate TDI-80 was used for 100 parts of this polyol component. (2,4 type 80
%) Add about 100 equivalents and mix and foam, width 1000-
Foam extrusion is continuously performed to a cross-sectional shape of 1100 mm and a height of about 450 to 500 mm. The resulting hydrophilic polyurethane foam has an apparent density of 0.03 to 0.028 g / c.
c, elongation 160%, hardness 9.5 ± 2kg / 314c
m ² , water absorption 0.17 g / Dry cc. This hydrophilic polyurethane foam has a thickness of 15 mm and a thickness of 3 m.
In order to perform heat compression molding to m, the upper and lower hot plates of a one-stage hot press (hot plate size 1000 mm × 1500 mm upper and lower hot plate co-heating medium circulation heating system) are heated to 210 ° C., respectively.
At the center thereof, the hydrophilic polyurethane sponge (sponge size: thickness 15 mm, width × length = 800 mm × 800 m
m) is set, and a steel spacer having a thickness of 2.8 mm, a width of 50 mm and a length of 1000 mm is installed at both ends in the width direction of the heating plate 1500 mm, the upper and lower heating plates are closed, and heat compression molding is performed for 40 seconds, and then the hot plate is taken out. . The obtained thermal compression urethane sheet had a thickness (average on a flat plate) of about 2.9 to 3.05 mm and a width of about 810.
mm, and a length of about 805 mm. A water absorption test of this heat-pressurized urethane sheet was carried out by the above-mentioned method, and it showed a water absorption of 1.76 g / Dry cc. Further, in the water retention test described above, it was 86.5% after 115 times.

[0014]

As described above, the water absorbent sheet obtained by thermally compressing the hydrophilic polyurethane sponge according to the present invention has an apparent specific gravity of 0.08 to 0.3 and a water absorption of about 0.5.
~ 2.50 g / Dry cc, the residual water content in the drainage test has a water retention capacity of 80% or more, so that it has a larger apparent specific gravity and a larger water absorption amount than the conventional sponge sheet, so that the medium for hydroponic culture, As a sheet for a sick person or a mat for a bath, it has excellent effects compared to conventional ones, and since it has a large water retention capacity, it does not release water even with a simple impact, and therefore absorbs water such as fish boxes. Not only is it suitable as a mat, etc., but also by having these characteristics, for example, insecticide bactericide, disinfectant, detergent,
It can be used in new fields such as absorption of solutions such as fragrances, fertilizers, and various salts, and the effect is remarkable.

[Brief description of drawings]

FIG. 1 is a perspective view of a water absorbent sheet according to the present invention.

FIG. 2 is a drawing showing the relationship between the number of draining operations of a water absorbing sheet and the residual water content, in which the horizontal axis represents the number of times and the vertical axis represents the residual water content.

[Explanation of symbols]

 1 Water absorbent sheet

Claims (1)

[Claims] 1. A hydrophilic polyurethane sponge is heat-compression molded to have an apparent specific gravity of 0.08 to 0.3 and a water absorption of about 0.
A hydrophilic polyurethane sponge having a water retention capacity of 5 to 2.50 g / dry cc and a residual water content of 80% or more in a drainage test.
Manufacturing method