JP3402764B2 - Method for producing water-absorbing polyurethane foam - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a water-absorbent polyurethane foam (hereinafter referred to as a water-absorbent foam) which is excellent in mechanical strength and water absorption, and particularly has a high water absorption rate. The water-absorbent foam obtained by the method of the present invention is used for cosmetic puffs, water-absorbing rolls and the like.

[0002]

2. Description of the Related Art In applications such as the above-mentioned cosmetic puffs, a polyurethane foam formed by chemical foaming using water, methyl chloride, flon, etc. as a foaming agent usually has insufficient mechanical strength such as tensile strength. , Mechanical foam is used. However, in the case of mechanical foaming, the foam will have high self-foaming property, so in order to impart water absorbency, the foam itself should be formed from a water-absorbing material or a raw material containing a water-absorbing material, or surface-treated with a surfactant. The method of improving the wettability of the foam surface is adopted.

However, when the foam itself is formed of a water-absorbing material or a raw material containing it,
Since water is absorbed by the resin forming the foam itself, there is no escape route for the absorbed water, the foam swells, and the absolute amount of water absorbed is not always sufficient. In addition, since its water absorption rate is particularly low, it becomes inconvenient to use in applications such as cosmetic puffs. On the other hand, when the foam surface is treated with a surfactant, only the wettability of the foam surface is improved and the water absorption is not so improved.

[0004]

DISCLOSURE OF THE INVENTION The present invention is to solve the problems of the conventional water-absorbent foams described above.
Excellent mechanical strength and water absorption, especially high water absorption speed,
Another object of the present invention is to provide a water-absorbent foam that maintains excellent water absorption for a long period of time.

[0005]

Means for Solving the Problems The inventors of the present invention have made earnest studies on the correlation between the water absorption of a foam obtained by mechanical foaming and the raw material composition of the foam. As a result, a specific low isocyanate index (hereinafter referred to simply as "index") has been obtained. .), It was found that a foam excellent in mechanical strength and water absorbency can be obtained when the foam is formed substantially using only a metal catalyst, and the present invention has been completed.

The method for producing a water absorbent foam of the first invention is
In a method for producing a water-absorbent foam by mixing a polyisocyanate and a polyol component and mechanically foaming, the index is in the range of 35 to 50, the polyol component contains a polyol, water and a catalyst, and the water is the polyol. 1.0 to 3.0 parts by weight with respect to 100 parts by weight, the catalyst is substantially only a metal catalyst, and the reaction curing temperature is in the range of 50 to 180 ° C. . The second invention is characterized in that the water is 1.0 to 2.0 parts by weight with respect to 100 parts by weight of the polyol, and the third invention is such that the polyol component is added to 100 parts by weight of the polyol. On the other hand, it is characterized by containing 8 to 12 parts by weight of a foam stabilizer.

As the above-mentioned "polyisocyanate", those generally used in the production of polyurethane foam can be used without particular limitation, but among them, MDI, T
DI or a mixture thereof and modified products of TDI and MDI are preferable. The "polyol" is also not particularly limited in kind, but is preferably a polymer polyol, that is, a polyol obtained by graft-polymerizing an ethylenically unsaturated compound such as acrylonitrile, styrene, or methyl methacrylate to a polyether polyol, and these are It is used in the form of a soluble and highly stable suspension.

A feature of the present invention is that the "index" is significantly lower than that of ordinary flexible foams, such as 80-115. In the present invention, the index is "35-
50 ", and a range of about 40 to 50 is particularly preferable for stable production of foam. The index is 3
When it is less than 5, the amount of polyisocyanate with respect to the polyol is insufficient, and unreacted polyol remains in the water-absorbent foam, and the surface of the water-absorbent foam becomes sticky. In addition, the unreacted polyol weakens the resin strength, and the foam shrinks, causing defective molding. On the other hand, when the index exceeds 50, the amount of polyisocyanate is sufficient, so that in addition to the reaction between the polyol and polyisocyanate (resinification reaction), the reaction between water and polyisocyanate (foaming reaction) occurs. , The bubbles become coarse, and urea is generated, so that the mechanical strength decreases.

The above "water" is used in an amount of 1.0 to 3.0 parts by weight based on 100 parts by weight of the polyol. Particularly, as in the second invention, 1.0 to
It is preferable to use 2.0 parts by weight. Within this range, a water-absorbent foam having more excellent mechanical strength and water absorption can be obtained. If this amount is less than 1.0 part by weight, the formation of the communication structure will be insufficient and water absorption will decrease, and if it exceeds 3.0 parts by weight, the reaction between water and isocyanate (foaming reaction) will occur. As with the above, problems such as coarse bubbles occur.

As the "catalyst", substantially only "metal catalyst" is used. As the metal catalyst, a suitable catalyst for polyurethane foam such as stannas octoate, dibutyltin diacetate, dibutyltin dilaurate can be used, and the amount thereof is preferably about 1 to 3 parts by weight based on 100 parts by weight of the polyol. Using substantially only the above metal catalyst, before the reaction curing step, a resinification reaction to the extent that the formation of a continuous structure is inhibited, and a foaming reaction to generate carbon dioxide by the reaction of water and isocyanate, This means that the amine catalyst is not allowed to coexist in such an amount that it can proceed at a practical speed.

The above "reaction curing temperature" is "100 to 180.
The range is "° C." If this temperature is less than 100 ° C., it takes a relatively long time for reaction curing, which is not practical.
Since the evaporation of water is not always sufficient, it is difficult to form the communication holes, and the water absorption is reduced. If the reaction curing temperature exceeds 180 ° C., the temperature will be higher than the decomposition temperature of the urethane compound, and foam will not be formed. Reaction curing temperature is especially 1
The temperature is preferably in the range of 20 to 160 ° C. In this range, the reaction curing proceeds rapidly, and water evaporates at an appropriate rate to form an open cell structure.

Further, in the present invention, as compared with the amount of the foam stabilizer usually used in the flexible foam as in the third invention (about 1 to 4 parts by weight with respect to 100 parts by weight of polyol),
Remarkably large amount (8-12 per 100 parts by weight of polyol)
It is preferable to use (part by weight) foam stabilizer. As the foam stabilizer, a reactive foam stabilizer having a hydroxyl group at the terminal is particularly suitable. By using a large amount of the foam stabilizer as described above, the foam stabilizing effect is improved, the foamability is improved, and the moldability is improved. In addition, it is effective in improving the wettability of the foam surface and increases the water absorption rate.

[0013]

The mechanical foaming is a method in which foaming is carried out in a state where the viscosity is low before the reaction is started, uniform and micro foams are produced, and then the reaction is cured at a high temperature. The amine catalyst promotes both the resinification reaction and the foaming reaction even at room temperature, and the chemical foaming proceeds due to the reaction with the water in the polyol even at the foaming time. Therefore, a metal catalyst is usually used in the mechanical foaming. Further, in the present invention, the purpose is to cure only the resin without adding a foaming agent, and in this sense also, it is necessary to use a metal catalyst that accelerates the resinification reaction. The metal catalyst used is temperature-sensitive, does not work at a practical reaction rate when foaming at room temperature, and works industrially when the temperature rises.

The foam obtained by mechanical foaming is excellent in mechanical strength, but has high foaming property and is inferior in water absorption as it is. However, in the present invention, since the index is very low and substantially only the metal catalyst is used, the water in the polyol component does not substantially participate in the curing reaction, and the water is kept at a high temperature during the reaction. It is considered that the gas is vaporized and diffuses from the foam to the outside of the foam while forming communication holes between the single cells in the foam, and as a result, the water-absorbent foam of the present invention is mechanically foamed, It has an open cell structure, and it is considered that water contacting the surface is easily absorbed into the foam. Therefore, it is considered that, while maintaining the original high mechanical strength of the foam due to mechanical foaming, it is also excellent in water absorption, and in particular, has a high water absorption rate.

[0015]

EXAMPLES Hereinafter, a method for producing a water-absorbent foam of the present invention will be described.
This will be described more specifically by way of examples. Example 1 The following were prepared as solutions A and B. Liquid A (polyol component): Polymer polyol (manufactured by Mitsui Toatsu Co., Ltd., trade name “POP34 / 28”) 100 parts by weight, water 1.5 parts by weight, foam stabilizer (Toray Silicon Co., trade name “SF2910”) ) 10 parts by weight and 2 parts by weight of a resin-forming catalyst (Stanas octoate, manufactured by Johoku Chemical Co., Ltd.) were mixed to prepare a polyol component. Liquid B: polyisocyanate (manufactured by Nippon Polyurethane Company, trade name "Millionate MTL")

The solution A having the above composition and the solution B having an index of 40 were premixed for 30 seconds and then foamed for 10 minutes. After that, the reaction is cured at 160 ° C. for 30 minutes, and the water remaining in the raw material is vaporized as the reaction is cured.
The obtained foam was after-cured at 110 ° C. for 4 hours to obtain a water-absorbent foam. The tensile strength of the water-absorbent foam obtained as described above was measured according to JIS K 6301. Moreover, one drop of 0.1-0.2 cc of water was dripped on the surface of the foam by a spoid, and the water drop was completely removed. It was visually confirmed that the foam was absorbed in the foam, and the time was measured.

Example 2 A water absorbent foam was produced in the same manner as in Example 1 except that the index was set to 50, and the tensile strength and the water drop absorption time were measured in the same manner as in Example 1. Example 3 A water-absorbent foam was produced in the same manner as in Example 1 except that the amount of the foam stabilizer was 4 parts by weight, and the tensile strength and the water droplet absorption time were measured in the same manner as in Example 1.

Comparative Example 1 A foam was produced in the same manner as in Example 1 except that the index was 30, and the absorption time of water droplets was measured in the same manner as in Example 1. Comparative Example 2 A foam was produced in the same manner as in Example 1 except that the index was set to 55, and the tensile strength and the water droplet absorption time were measured in the same manner as in Example 1. Comparative Example 3 A foam was produced in the same manner as in Example 1 except that water was not used, and the tensile strength and the water droplet absorption time were measured in the same manner as in Example 1.

Comparative Example 4 Except that water was not used, the stannas octoate was replaced with an amine catalyst (a mixture of 33% by weight of tolylenediamine and 67% by weight of propylene glycol, manufactured by Chukyo Yushi Co., Ltd., trade name "LV33"). A foam was produced in the same manner as in Example 1. In this case, since water was substantially absent, even when the amine catalyst was used, a reaction in which significant bubbles were generated during premixing did not occur. However, along with the foaming reaction, the resinification reaction proceeded even at room temperature, and the strength of the foam produced was extremely weak as compared with the case where a metal catalyst was used, and a completely solidified foam could not be obtained. Comparative Example 5 A foam was produced in the same manner as in Example 1 except that water was not used instead of amine catalyst (N-methylmorpholine, manufactured by Kao Corporation) in place of stannas octoate, but in the same manner as in Comparative Example 4. No fully solidified foam was obtained.

Table 1 shows the compositions of the above Examples and Comparative Examples and the moldability, tensile strength and water absorption time of the resulting water absorbent foams. In addition, each numerical value of a composition represents a weight part when a polyol is 100 weight part. Moldability evaluation criteria are: Good: Moldability is good, Poor: Rough cells are poor molding, and tensile strength cannot be measured. Meaning that the water absorption time cannot be measured means that the water was not completely absorbed even 5 minutes after the dropping of the water drop.

[0021]

[Table 1]

According to the results shown in Table 1, the water-absorbent foam of Example 1 has excellent moldability, sufficient tensile strength, and a water-absorption time of only 3 seconds. It can be seen that it is an extremely excellent foam in. Further, in Example 2 having an index of 50, both the tensile strength and the water absorption are the same as in Example 1, and in Example 3 with a small amount of the foam stabilizer, the water absorption time is slightly longer at 15 seconds. As a result, a water-absorbent foam having satisfactory performance is obtained.

On the other hand, Comparative Example 1 in which the index is less than the lower limit
Then, the surface of the obtained foam had a sticky feeling, and although the water absorbency was apparently excellent, the foam shrank, resulting in poor molding. Further, in Comparative Example 2 in which the index exceeds the upper limit, although the foam can be molded, the influence of the foaming reaction between water and isocyanate becomes large, so that the cell structure is rough and the tensile strength is lowered. Fine cell structured foams suitable for cosmetic puffs are not available. Furthermore, in Comparative Example 3 in which water was not added to the polyol component at all, although there was no problem in moldability and tensile strength, since a continuous structure was not formed, the water absorption time was 60 seconds, which is much higher than that of the foams of Examples. It is very long and is not suitable for applications such as cosmetic puffs. Comparative Example 4 in which an amine catalyst was used in place of the metal catalyst and water was not mixed
In Nos. 5 and 5, foaming was not sufficient, and neither resinification progressed nor solidification was sufficient, so that neither tensile strength nor water absorption time could be measured.

The present invention is not limited to the specific examples described above, but various modifications may be made within the scope of the present invention depending on the purpose and application. For example, the amount of water is 1.5 to 100 parts by weight of polyol.
When the amount of the foam stabilizer is changed to 2.0 parts by weight and the foam stabilizer is changed to 10 to 15 parts by weight, the water absorption time becomes about 5 to 10 seconds, and a desired water absorbent foam can be obtained.

[0025]

According to the method for producing a water-absorbent foam of the first invention, since the index is low and substantially only the metal catalyst is used, chemical foaming is suppressed and a foam having high strength is obtained, and at the same time, foam is obtained. It is possible to obtain a water-absorbent foam which is excellent in strength and water-absorbing property, and particularly has a high water-absorbing speed, without causing molding defects such as roughness. Further, if the amount of water specified in the second aspect of the invention is satisfied, the foaming reaction can be more reliably suppressed, sufficient communication holes can be formed, and a foam having even more excellent water absorption can be obtained. Furthermore, the third
When a specific large amount of foam stabilizer is used as in the invention, foam roughness is suppressed and the moldability is improved, the wettability of the foam surface is also improved, and a foam having more excellent water absorption is obtained. .

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C08G 18/06-18/08 C08G 18/22-18/26

Claims (3)

(57) [Claims] 1. A method for producing a water-absorbing polyurethane foam by mixing a polyisocyanate and a polyol component and mechanically foaming the same, wherein the isocyanate index is in the range of 35 to 50, and the polyol component comprises a polyol, water and a catalyst. And the water is 1.0 to 100 parts by weight of the polyol.
3.0 parts by weight, the catalyst is substantially only a metal catalyst, and the reaction curing temperature is in the range of 100 to 180 ° C. 2. The method for producing a water-absorbent polyurethane foam according to claim 1, wherein the water is 1.0 to 2.0 parts by weight with respect to 100 parts by weight of the polyol. 3. The method for producing a water-absorbent polyurethane foam according to claim 1, wherein the polyol component contains 8 to 12 parts by weight of a foam stabilizer with respect to 100 parts by weight of the polyol.