JP3222064B2 - Method for producing water-absorbing and water-retaining rigid polyurethane foam having moderate brittleness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbing and water-retaining material which has a required strength, is suitably brittle, has good air permeability, is easy to absorb water, and has a moderate brittleness which is excellent in water retention. The present invention relates to a method for producing a rigid polyurethane foam (hereinafter, referred to as a moderately brittle water-absorbing and water-retaining foam). The moderately brittle water-absorbent and water-retentive foam produced by the method of the present invention can be used for agricultural and horticultural purposes, particularly as a nursery bed in hydroponic cultivation, a support for live flowers, and the like.

[0002]

2. Description of the Related Art Conventionally, phenolic resin foam has been used as a nursery bed in agriculture, horticulture, etc., or as a support for live flowers, and especially as a nursery bed in hydroponics for fruits and vegetables such as onions. It is heavily used. This nursery is provided with a number of holes for sowing. And
After laying the seedlings in a nursery box and irrigating the seedlings, tens of seeds of green onions are sown in each hole. After that, the plants are kept warm while appropriately supplying water and liquid fertilizer. After the onions have grown sufficiently, high-pressure air and water are blown around the roots to remove the foam by blowing it off. Then, one outermost skin is peeled off before shipping as a product.

[0003] The nursery bed is required to be excellent in water absorbency and water retention, good in germination and rooting, and that roots and the like grow smoothly. Also, after growing, when high-pressure air and water are blown around the root, at a pressure that does not cause all the roots of the onion to be blown off, it has moderate brittleness so that all foams are easily blown off It is necessary to be. This onion root is indispensable for keeping freshness after shipping. In addition, the nursery bed must have the above-mentioned required characteristics and must not contain components that inhibit the growth of various fruits and vegetables, flowers and the like.

[0004] On the other hand, various attempts have been made to use polyurethane foam in agricultural and horticultural applications. For example, JP
JP-A-2-39478 discloses a simple living flower support made of a hydrophilic open-celled rigid polyurethane foam. Japanese Patent Publication No. 60-52115 describes a mat obtained by cutting a semi-rigid hydrophilic polyurethane foam into a required shape and suitable for raising seedlings and transplanting. Further, JP-A-2-14209 discloses a method for producing an open-cell hydrophilic polyurethane foam used as a support for cut flowers, and JP-A-6-25374 discloses a method for producing the same.
A method for producing a hydrophilic / water-absorbing rigid urethane foam used as a soil substitute or the like is disclosed.

[0005]

At present, phenol resin foams mainly used at present are excellent in required properties such as brittleness and water absorption. However, at the time of manufacture, the temperature must be strictly controlled because the influence of the ambient temperature on the foam generation rate is large. Further, there is a problem that the viscosity is rapidly increased when solidifying from a liquid state, and furthermore, the heat generation during the formation of the foam is severe, so that cracks or internal burning easily occur. For this reason, there are many problems in actual production, such as difficulty in foaming a large molded product and a large change in the raw material with time.

Further, phenol resin foam is difficult to handle and dangerous because a strong acid such as concentrated hydrochloric acid, concentrated sulfuric acid, phosphoric acid or the like is used as a foam-forming catalyst. Further, due to the effect of the acid remaining in the foam, the pH of the water becomes acidic,
Fruits and vegetables, flowers, etc. may be adversely affected. Others
Phenolic resin foam cannot be incinerated, is difficult to treat after use, and has environmental problems.

As described above, the use of a polyurethane foam has been proposed in place of the phenol resin foam having various problems as described above. In particular, there is no problem with germination, rooting, root growth, and the like, especially with open-celled polyurethane foam. However, conventional polyurethane foam does not have moderate brittleness.Before shipping, the foam attached to the roots is blown off by pressurized air, etc., and when removing, all of the roots are blown off together with the foam. Problem.

The present invention solves the problems of the above-mentioned polyurethane foams, in which four specific polyols are used in combination, a predetermined amount of an inorganic filler is compounded, and the isocyanate index is set to a specific low value. Set to range. Accordingly, it is an object of the present invention to provide a foam having appropriate brittleness and good water absorption and water retention. Also, specify the composition of the foam stabilizer,
It is another object of the present invention to provide a moderately brittle water-absorbing and water-retaining foam having excellent properties.

[0009]

According to a first aspect of the present invention, there is provided a method for producing a moderately brittle water-absorbing and water-retaining foam, which comprises producing a rigid polyurethane foam using a raw material containing a polyol component, a polyisocyanate and an inorganic filler. The polyol component contains a polyol, a foaming agent, a catalyst, and a foam stabilizer. The polyol includes the following polyols (a), (b), (c), and (d), and the total amount of the polyol is When the amount is 100 parts by weight, the polyol (a) is 30 to 50 parts by weight, and the polyol (b) is 5-2.
5 parts by weight, 5 to 15 parts by weight of polyol (c) and 20 to 40 parts by weight of polyol (d), and the inorganic filler is 15 parts by weight based on 100 parts by weight of the total amount of the polyol.
To 55 parts by weight and an isocyanate index of 35 to 75.

Polyol (a): polyoxyalkylene triol (polyoxyalkylene moiety is 90 to 10
It consists of 0 mol% of oxypropylene groups and 0 to 10 mol% of oxyethylene groups. ), Hydroxyl value; 140 to 19
0 polyol (b): polyoxyalkylene triol,
Oxyethylene group content; 70 to 90 mol%, hydroxyl value; 28 to 42 Polyol (c): oxyalkylated product of ethylenediamine (the oxyalkylated portion contains 0 to 25 mol% oxyethylene groups) , Hydroxyl value; 600 to 85
0 polyol (d): polyoxyalkylene glycol monoalkyl ether, oxyethylene group content;
100 mol%, hydroxyl value; 56 to 187

The above "polyols (a), (b), (c)
And (d) are used together in a specific ratio, whereby a moderately brittle water-absorbing and water-retaining foam having good flyability, water-absorbing property and water-retaining property can be obtained. The polyol (a) is trifunctional and has a high hydroxyl value, and the polyol (c) is tetrafunctional and has a particularly high hydroxyl value. These polyols make the foam moderately brittle. In addition, the polyols (b) and (d) have a high content of oxyethylene groups, which increases the hydrophilicity of the foam and improves water absorption and water retention. Further, the polyol (c) is a tertiary amino group-containing polyol, and has an effect of improving the compatibility of the mixed polyol.

As the above-mentioned "polyisocyanate", those generally used for rigid polyurethane foams (hereinafter, referred to as rigid foams) can be used. Examples include crude or polymeric diphenylmethane diisocyanate (MDI), crude tolylene diisocyanate (TDI), and prepolymers thereof. Also, a mixture of crude MDI and crude TDI can be used. The polyol and the polyisocyanate have an “isocyanate index (hereinafter, referred to as an index)” of “35 to 7”.
5 ", especially in the range of 40-60. When the index is less than 35, the number of cells is large, but the air permeability is good probably because of the high open cell property. However, the flyability is greatly reduced and cannot be put to practical use. On the other hand, when the index exceeds 75, the air permeability of the foam is extremely reduced, and the water absorption is also greatly reduced.

The above-mentioned "inorganic filler" includes calcium carbonate, clay, aluminum hydroxide, barium sulfate and the like. These are used in the form of powder, and preferably have a particle size of 500 to 2000 mesh. If the particle size is less than 500 mesh, the dispersibility of the inorganic filler in the polyol mixture is poor, and the inorganic filler may settle. This inorganic filler imparts brittleness to the foam, and if the amount is less than 15 parts by weight, the brittleness of the foam becomes insufficient (it has toughness). Also, 5
If the amount exceeds 5 parts by weight, the density of the foam increases, the open-cell properties decrease, and the air permeability and water absorption of the foam decrease.

The inorganic filler is usually blended in advance with the polyol and then mixed with the polyisocyanate. If the compounding amount exceeds 55 parts by weight, in addition to the above problems, the viscosity of the polyol component may become too high, the workability may be reduced, and the mass production may be hindered. The amount of the inorganic filler is particularly preferably about 20 to 50 parts by weight, and within this range, a foam having appropriate brittleness and excellent water absorption and water retention properties can be obtained.

As the above-mentioned "blowing agent", water is usually used. Actually, carbon dioxide generated by the reaction between water and polyisocyanate is used, but for convenience, water is referred to as a blowing agent. In the present invention, the water is used in an amount of 5 to 15 parts by weight, particularly 8 to 100 parts by weight of the polyol.
Use about 12 parts by weight. Further, as the "catalyst", is mainly used in the production of rigid foam,
For example, amine derivatives and morpholine derivatives can be used. This catalyst is added in an amount of about 0.5 to 3 parts by weight based on 100 parts by weight of the polyol.

As the above-mentioned "foam stabilizer", a foam stabilizer suitable for making open cells of a rigid foam can be used. For example, it has a pendant structure generally used in the production of a flexible polyurethane foam, and its polyether part has 40 to 60 mol% of oxypropylene groups and 60
A block copolymer of dimethylpolysiloxane having ジ メ チ ル 40 mol% of oxyethylene groups and polyether is preferred. When the content of the block copolymer is 100% by weight, the foam stabilizer of the second invention in which the dimethylpolysiloxane portion is 7 to 25% by weight is particularly preferable. Although the amount ratio of the dimethylpolysiloxane part is lower than usual, in the present invention, such a foam stabilizer is used in a large amount of 3 to 7 parts by weight, particularly about 5 parts by weight, based on 100 parts by weight of the polyol. This improves the wettability of water on the surface of the foam obtained.

If the dimethylpolysiloxane content is less than 7% by weight, the foam may be inferior in stability during foaming and may collapse. In addition, the number of cells is small, in other words, a foam having a large cell diameter is formed, and the water retention is reduced. On the other hand, if the dimethylpolysiloxane portion exceeds 25% by weight, the air permeability of the foam is reduced, and the wettability of water on the surface of the obtained foam is significantly reduced.
The foam has poor water absorption (negative capillary action). The content of the dimethylpolysiloxane part is more preferably in the range of 10 to 20% by weight. By using such a foam stabilizer, a foam having more excellent water absorbability can be obtained.

Further, as the foam stabilizer, those having an inert group to an isocyanate group such as an alkoxy group at the terminal of the polyether portion are more preferable. Thereby, the foaming of the foam is increased, and the wettability of the surface is further improved. When a foam stabilizer having an active group for an isocyanate group such as a hydroxyl group or an amino group at the end of the polyether portion is used, the air permeability of the foam is reduced, and the wettability of water to the foam surface is reduced. And water absorption becomes insufficient.

The openness of the foam can be further improved by using a cell opener together with the above foam stabilizer. As the bubble communicating agent, a foam stabilizer having a foam breaking property such as dimethylpolysiloxane is usually used. The compounding amount of the cell communication agent is 0.1 to 1.0 part by weight, particularly 0.5 to 1.0 part by weight, when the polyol is 100 parts by weight.

The moderately brittle water-absorbent and water-retentive foam of the present invention can be used as a nursery for various fruits and vegetables, flowers and the like. May be. For example, when used as a nursery bed in hydroponic cultivation of onions, brown foams are preferred and used.

The moderately brittle water-absorbing and water-retaining foam of the present invention comprises a rigid foam having a three-dimensional network structure. Then, as in the third invention, by the following method
The measured cell number is 20 to 40 cells / inch, the flyability is 50% or more, and the air permeability is 50 to
Foams having 200 cm ³ / cm ² / sec, a water absorption time of 60 seconds or less, and a water retention of 50% or more are particularly preferred. still,
The air permeability is 50 to 70 cm ³ / cm ² / sec, and the water absorption time is 40
If it is less than seconds and the water retention is 70% or more, it is possible to obtain a more preferable foam excellent in the balance of each property. Even if the flyability is 100%, the required form can be obtained. However, if this flyability is set to 99% or less, especially about 97% or less,
A foam having more appropriate brittleness can be obtained. Number of cells; JIS K6402 air permeability; JIS L1096 water absorption time by method A ; 115 × 110 × 80 mm specimen at 25 ° C.
Allow the sample to stand on water and completely wet the specimen
Is measured. Water retention: Weight of a sample of 115 × 110 × 80 mm
(W _F ) is measured. Then, the specimen was placed in water at 25 ° C for 1 hour.
After soaking for a while, take it out gently and measure its weight (W _A )
I do. Then, the sample was allowed to stand on a wire mesh at 21 ° C. and 65%
Was allowed to stand in an atmosphere of RH 7 days, the weight again (W _T)
Is measured. Water retention rate _{(%) = (W T -W} F) / (W A -W F) × 100 friability; ASTM C421-61

When the number of cells is less than 20 cells / inch, the cell diameter is large and the air permeability and water absorption are improved, but the water retention tends to be reduced. When the number of cells exceeds 40 cells / inch, water retention is improved, but rooting and growth of the seedlings are poor. When the number of cells is within the above range, a foam having good balance between water absorption and water retention and good rooting and growing properties of seedlings is easily obtained. However, the number of cells is obtained by observing the foam on one surface, and in order to form a foam having excellent water absorption and water retention over the inside, the air permeability needs to be within the above range. .

By using a foam having the cell number and air permeability in the above ranges, a foam having the above-mentioned water absorption time and water retention can be stably obtained. And
The foam of the third invention is excellent in air permeability, absorbs water promptly, has high water retention ability, and has good rooting and growth properties, and is suitable as a nursery bed. In addition, it has moderate brittleness, maintains a predetermined shape during the growing process of seedlings, and has a pressure sufficient to prevent all roots from being blown off before being blown with compressed air before shipping. And can be easily removed.

The density of the foam is 0.02 to 0.0
It is about 4 g / cm ³ . This density does not significantly affect the flyability of the foam and the water absorption and water retention. However, if the density is 0.025-0.0
It is particularly preferable to use a foam in the range of 35 g / cm ³ because a foam having more excellent performance and the like described above can be obtained.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples. (1) Manufacture of foam The following were used as a polyol, a foaming agent, a catalyst, a foam stabilizer, an inorganic filler, a cell communication agent, and a polyisocyanate.

1) Polyol Polyol (a): polyoxypropylene triol, hydroxyl value: 158, oxyethylene group content: 0 mol%, compounding amount: 45 parts by weight Polyol (b): polyoxyalkylene triol, hydroxyl value; 33.7, oxyethylene group content; 8
0 mol%, compounding amount: 15 parts by weight Polyol (c): oxypropylated product of ethylenediamine, hydroxyl value: 760, oxyethylene group content: 0 mol%, compounding amount: 12 parts by weight Polyol (d): polyethylene Glycol monomethyl ether, hydroxyl value; 100, oxyethylene group; 1
00 mol%, compounding amount: 28 parts by weight

2) Polyisocyanate; crude MDI
(Manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Millionate MR-400"), isocyanate content: 30% 3) Inorganic filler: heavy calcium carbonate (manufactured by Dowa Calfine Co., Ltd., trade name "KS-1300")

4) Blowing agent: water, blended amount: 9 parts by weight 5) Catalyst: 2- (2-dimethylaminoethoxy) ethanol which is an amine derivative, blended amount: 1 part by weight 6) Foam stabilizer: flexible polyurethane foam A dimethylpolysiloxane-polyether block copolymer and a block copolymer having a pendant structure and having a polyether moiety having 50 mol% of oxypropylene groups and oxyethylene groups used in the production of 5, 10, 15, 20, and 30% by weight of the dimethylpolysiloxane part therein; blending amount: 5 parts by weight; a methoxy group is bonded to the terminal of the polyether part. 7) Bubble communication agent: dimethyl polysiloxane (trade name “L-45” manufactured by Nippon Unicar Co., Ltd.), viscosity: 1000
cps, compounding amount: 0.7 parts by weight

Experimental Example 1 A predetermined amount of each polyol, water, catalyst, foam stabilizer and inorganic filler were weighed and placed in a 2 liter polyethylene beaker. Thereafter, the mixture was mixed while maintaining the temperature at 21 ° C. to prepare a polyol component. Then, the temperature was set to 21 ° C.
, A predetermined amount of the polyisocyanate and the cell opener were weighed and added to the above beaker. afterwards,
The mixture was stirred at high speed for 5 seconds to prepare a mixture of a polyol component and a polyisocyanate, and the mixture was poured into a polyethylene bag placed in a 37 cm square cardboard box to allow free foaming. The density, cell number, air permeability, water absorption time, water retention and flyability of the obtained foam were measured. Table 1 shows the results.

Experimental Examples 2 to 11 Foams were obtained in the same manner as in Example 1 except that the isocyanate index, the content of dimethylpolysiloxane as a foam stabilizer and the amount of the inorganic filler were changed as shown in Table 1. . The air permeability and others were measured in the same manner.

Experimental Examples 12 to 15 As the polyol, the polyol (a) was not used (Experimental Example 12), the polyol (b) was not used (Experimental Example 13), and the polyol (c) was not used. A foam was obtained in the same manner as in Example 1 except that (Experimental Example 14) and polyol (d) were not used (Experimental Example 15). In addition, the air permeability and others were measured in the same manner. As described above, the results of Experimental Examples 2 to 8 are also shown in Table 1, and the results of Experimental Examples 9 to 15 are shown in Table 2. In Tables 1 and 2, * indicates the first
In the scope of the invention, ** indicates that the scope is out of the scope of the second invention. *** indicates that the properties of the foam are outside the scope of the third invention.

[0032]

[Table 1]

[0033]

[Table 2]

(2) Evaluation of physical properties and the like In Tables 1 and 2, each physical property and the like were measured by the following methods. 1) Density: JIS K6401 2) Number of cells: JIS K6402 3) Air permeability: JIS L1096 A method 4) Water absorption time: A sample of 115 × 110 × 80 mm at 25 ° C.
And the time until the entire specimen is completely wetted is measured.

5) Water retention: The weight (W _F ) of a sample of 115 × 110 × 80 mm is measured. Thereafter, the sample is immersed in water at 25 ° C. for 1 hour, and then gently removed, and the weight (W _A ) is measured. Next, the specimen is allowed to stand on a wire mesh,
It is left in an atmosphere of 21 ° C. and 65% RH for 7 days, and its weight (W _T ) is measured again. Water retention rate _{(%) = (W T -W} F) / (W A -W F) × 10
06) Flyability; ASTM C421-61

(3) Growing onion In addition, when using the foams obtained in Experimental Examples 1 to 15 as a nursery bed and growing onion in the following manner, the germination, rooting and growth of The situation was observed. Furthermore, after the growth, pressurized air and water were sprayed on the foam to confirm the difficulty of removing the foam and to observe the root condition. 1) A foam having a thickness of 30 mm, which is formed by connecting a number of protrusions provided with depressions for sowing, is immersed in water. After absorbing the water sufficiently, remove it from the water and place it in a plastic tray. 2) Sow about 10 seeds of green onions per pit, sprinkle water evenly with joule, cover with newspaper, germinate,
Remove this newspaper immediately.

3) Water is absorbed into the foam at appropriate time intervals,
When the roots are formed in the foam and the length of the buds becomes about 10 cm, the foam is cut around each protrusion. Each cut block is fitted into a hole provided in a frame made of polystyrene foam placed on the water surface of the hydroponic cultivation pool for raising seedlings. 4) 40-50 days after sowing, root length is 10-1
At 5 cm, remove the blocks and blow high pressure air and water around the roots. If the foam has moderate brittleness, the foam will all blow off, leaving a root of about 1.5 cm in length.

(4) Consideration of Results According to the results of Tables 1 and 2, in Experimental Examples 1 to 5 included in the first and second inventions, each characteristic is within the scope of the third invention. It can be seen that the foam has moderate flyability and moderate air permeability, and is excellent in water absorption and water retention. In particular, in Experimental Examples 1 to 3 in which the isocyanate index is 50, it can be seen that the foam has a better performance with well-balanced properties. Also, there is no particular problem in growing onions, even when high-pressure air is blown, all foam is easily blown off,
And all the roots were not blown away, and the required length of roots remained.

On the other hand, although included in the first invention, the second invention
In the case of Experimental Examples 6 and 7, which are out of the scope of the present invention, in Experimental Example 6 using a foam stabilizer having a low dimethylpolysiloxane content, the number of cells is small (the cell diameter is large), so that the air permeability is high, and water absorption is high. It can be seen that the water retention is greatly reduced although the property is good. In Experimental Example 7 in which a foam stabilizer having a high content of dimethylpolysiloxane was used, it was found that the foam was insufficient in open cell formation and poor in air permeability and water absorption. In these forms, the green onions did not grow well and had no commercial value.

Further, the isocyanate index is the first
In Experimental Example 8, which is out of the range of the invention and low, the air permeability is high, but the water retention is excellent, probably because the number of cells is large and the cell diameter is small. However, it can be seen that the flyability is greatly reduced and cannot be put to practical use. With this foam, the green onions grew well, but the foam could not be removed without blowing enough high pressure air to blow off all the roots. On the other hand, in Experimental Example 9 in which the index was too high, the number of cells was small, the air permeability and water absorption were very poor, and the green onion was poorly grown.

In Experimental Example 10 in which the blending amount of the inorganic filler exceeds the upper limit of the first invention, both flyability and water retention are satisfactory, but the air permeability and water absorption are poor, and the green onions grow smoothly. Without any commercial value. On the other hand, the amount of the inorganic filler is less than the lower limit.
In this case, although the air permeability was not a problem, the foam was inferior in water absorbency and very low in flyability, and the foam could not be removed unless high pressure air was used to blow off all the roots.

Further, in Experimental Example 12, when foamed, the foam was inferior in stability and collapsed. Experimental Examples 13 and 1
In No. 5, although the flyability and the water retention are not particularly problematic, it can be seen that the air permeability and the water absorption are greatly reduced. In Experimental Example 14, although water absorption and flyability were not particularly problematic, the air permeability was too large, and the water retention was greatly reduced. Experimental Example 14
In this case, the compatibility of the three kinds of polyols was reduced, and there was a problem in workability. When these are also used as nursery beds,
There was the same problem as in Experimental Example 10 above.

[0043]

According to the first aspect of the present invention, a specific four kinds of polyols are used in combination, a predetermined amount of an inorganic filler is blended, and the range of the index is limited, so that a suitable flyability is obtained, and Due to moderate air permeability, a foam having excellent water absorption and water retention can be obtained. Further, as in the second invention, by using a foam stabilizer having a dimethylpolysiloxane part content in a specific range, a foam having excellent performance such as flyability, air permeability, water absorption and water retention can be obtained. Can be obtained more stably.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification code FI C08L 75:04 C08L 75:04 (58) Field surveyed (Int.Cl. ⁷ , DB name) C08G 18/00-18/87 C08J 9/02

Claims (3)

(57) [Claims] 1. A method for producing a rigid polyurethane foam using a raw material containing a polyol component, a polyisocyanate and an inorganic filler, wherein the polyol component comprises:
It contains a polyol, a foaming agent, a catalyst and a foam stabilizer. The polyol contains the following polyols (a), (b), (c) and (d), and the total amount of the polyol is 100 parts by weight. The polyol (a) is 30 to 50 parts by weight, the polyol (b) is 5 to 25 parts by weight, the polyol (c) is 5 to 15 parts by weight, and the polyol (d) is 20 to 40 parts by weight. Filler is the total amount of the above polyol 1
A method for producing a water-absorbing and water-retaining rigid polyurethane foam having an appropriate brittleness, wherein the amount is 15 to 55 parts by weight based on 00 parts by weight and the isocyanate index is 35 to 75. Polyol (a): polyoxyalkylene triol (the polyoxyalkylene portion is composed of 90 to 100 mol% of oxypropylene groups and 0 to 10 mol% of oxyethylene groups), hydroxyl value; 140 to 190 polyol (b) ): Polyoxyalkylene triol,
Oxyethylene group content; 70 to 90 mol%, hydroxyl value; 28 to 42 polyol (c): oxyalkylated product of ethylenediamine (oxyalkylated portion contains 0 to 25 mol% of oxyethylene groups), Hydroxyl value; 600 to 850 polyol (d): polyoxyalkylene glycol monoalkyl ether, oxyethylene group content;
100 mol%, hydroxyl value; 56 to 187 2. The foam stabilizer comprises a dimethylpolysiloxane-polyether block copolymer, and when the block copolymer is 100% by weight, the dimethylpolysiloxane part is 7 to 25% by weight. 2. The method for producing a water-absorbing and water-retaining rigid polyurethane foam having a suitable brittleness according to claim 1. 3. The method according to claim 1 , wherein the number of cells measured by the following method is 20.
~ 40 pieces / inch, flyability 50%
And the air permeability is 50 to 200 cm ³ / cm ² /
3. The method for producing a water-absorbing and water-retaining rigid polyurethane foam having an appropriate brittleness according to claim 1 or 2, wherein the water absorption time is 60 seconds or less and the water retention is 50% or more. Number of cells; JIS K6402 air permeability; JIS L1096 water absorption time by method A ; 115 × 110 × 80 mm specimen at 25 ° C.
Allow the sample to stand on water and completely wet the specimen
Is measured. Water retention: Weight of a sample of 115 × 110 × 80 mm
(W _F ) is measured. Then, the specimen was placed in water at 25 ° C for 1 hour.
After soaking for a while, take it out gently and measure its weight (W _A )
I do. Then, the sample was allowed to stand on a wire mesh at 21 ° C. and 65%
Was allowed to stand in an atmosphere of RH 7 days, the weight again (W _T)
Is measured. Water retention rate _{(%) = (W T -W} F) / (W A -W F) × 100 friability; ASTM C421-61