Aqueous polyurethane gel, process for producing the same,...

Details Aqueous polyurethane gel, process for producing the same,... Aqueous polyurethane gel, process for producing the same,...

2001-12-19

2003-03-04

Niland, Patrick D. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S839000, C524S840000

Reexamination Certificate

active

06528577

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a novel polyurethane hydrogel, a production process and use of the polyurethane hydrogel.
BACKGROUND OF THE INVENTION
Hydrophilic polyurethane resins can be obtained by crosslinking and curing an isocyanate-containing polyurethane resin, i.e., a reaction product of polyol and polyisocyanate, in the presence of water. The hydrophilic polyurethane resins thus obtained are known as hydrogels useful as microorganism carriers, etc. (e.g., Advances in Biochemical Engineering/Biotechnology, Vol. 29).
The above hydrophilic polyurethane resins, however, have drawbacks. Since polyol, one of the starting materials, is a mixture of hydrophilic polyethylene glycol and hydrophobic polypropylene glycol, a solid or highly viscous resin tends to form and it is difficult to mix such resin with water. In addition, since the hydrophilic polyurethane resin lacks uniformity between the hydrophilic and hydrophobic portions, the ability of a hydrogel of the resin to carry microorganisms is insufficient.
Japanese Unexamined Patent Publication No. 51794/1997 discloses a porous carrier suitable for use in bioreactors, which comprises a polyurethane hydrogel having communicating pores. This polyurethane hydrogel is produced by reacting a polyol, e.g., a copolymer of ethylene oxide and propylene oxide, with an isocyanate compound, then reacting the resulting isocyanate-containing polyurethane resin with water at a high concentration of the resin, i.e., at a water:resin weight ratio of about 0.5:1 to 5:1 and adding water to allow the hydrogel to swell with water.
This polyurethane hydrogel, however, has drawbacks. Since the polyurethane hydrogel has a large number of isolated holes and communicating pores, the hydrogel has a specific gravity of less than 1.0. When used as a microorganism carrier, the hydrogel floats in water and can not be efficiently dispersed by stirring, etc. The hydrogel with such a large number of communicating pores and air holes has low strength and the maximum possible volume by swelling with water is 1,000%. In addition, a high concentration is required for the reaction of an isocyanate-containing polyurethane resin with water to produce such porous hydrogel. In this case, pot life after mixing the resin and water is 20 to 30 seconds, and it is difficult to handle the mixture.
DISCLOSURE OF THE INVENTION
An object of the invention is to provide a polyurethane hydrogel free of the problems of the prior art, a production process and use of the polyurethane hydrogel.
Another object of the invention is to provide a polyurethane hydrogel whose volume swelling percentage can be more than 1,000% and which has substantially no voids such as air bubbles or pores, a specific gravity of 1 or more, and high strength and which is suitable as a microorganism carrier or a water retention material, a production process and use of the polyurethane hydrogel.
Other objects and features of the invention will become apparent from the following description.
The present invention provides the following polyurethane hydrogel, production process and use thereof.
1. A polyurethane hydrogel prepared by crosslinking and curing a terminal isocyanate-containing polyurethane resin (C) in the presence of water at a water:resin (C) weight ratio of more than 9:1,
the resin (C) being a reaction product of a polyisocyanate (A) and a liquid polyol (B), and
the polyol (B) containing 70 wt. % or more of a random copolymer prepared by copolymerization of ethylene oxide (a) and propylene oxide (b) at an ethylene oxide (a): propylene oxide (b) weight ratio of 50:50 to 90:10.
2. The polyurethane hydrogel according to item 1 wherein the terminal isocyanate-containing polyurethane resin (C) has a number average molecular weight of about 1,000 to 100,000.
3. The polyurethane hydrogel according to item 1 wherein the terminal isocyanate-containing polyurethane resin (C) is crosslinked and cured in the presence of water at a water:resin (C) weight ratio of 10:1 to 20:1.
4. The polyurethane hydrogel according to item 1 whose volume swelling percentage is more than 1,000%.
5. The polyurethane hydrogel according to item 1 which has substantially no voids and has a specific gravity of 1 or more.
6. The polyurethane hydrogel according to item 1 which has a compressive strength of 0.1 kg/cm
2
or more.
7. A process for preparing a polyurethane hydrogel comprising crosslinking and curing a terminal isocyanate-containing polyurethane resin (C) in the presence of water at a water:resin (C) weight ratio of more than 9:1,
the resin (C) being a reaction product of a polyisocyanate (A) and a liquid polyol (B), and
the polyol (B) containing 70 wt. % or more of a random copolymer prepared by copolymerization of ethylene oxide (a) and propylene oxide (b) at an ethylene oxide (a): propylene oxide (b) weight ratio of 50:50 to 90:10.
8. The process according to item 7 wherein the terminal isocyanate-containing polyurethane resin (C) is crosslinked and cured in the presence of water at a water:resin (C) weight ratio of 10:1 to 20:1.
9. A microorganism carrier comprising the polyurethane hydrogel of item 1.
10. A water retention material comprising the polyurethane hydrogel of item 1.
The present inventors carried out intensive research to achieve the above objects and found the following:
(1) The terminal isocyanate group-containing polyurethane resin (C) is liquid-like and easy to mix with water.
(2) When this polyurethane resin is crosslinked and cured in the presence of water at a water:resin weight ratio of more than 9:1, a polyurethane hydrogel whose volume swelling percentage is more than 1,000% can be produced.
(3) Since CO
2
generated during crosslinking evaporates out of the system due to the presence of a large amount of water in the system, the hydrogel has substantially no voids such as air bubbles or pores and thus has a specific gravity of 1 or more and high strength.
(4) Since the reaction of polyurethane resin and water occurs at a low concentration of the resin, pot life after mixing the resin and water is about 1 minute or longer. Therefore, it is easy to handle the mixture.
The present invention was accomplished based on these findings.
“Volume swelling percentage” as used herein is defined by the following equation:
Volume swelling percentage (%)=(
V/V
0
)×100
in which V
0
is the volume of terminal isocyanate-containing polyurethane resin (C) before addition of water; and V is the volume of polyurethane hydrogel formed by addition of water.
Examples of the polyisocyanate (A) of the present invention are compounds conventionally used for production of polyurethane resins and having an average of at least two isocyanate groups, preferably two to four isocyanate groups, per molecule, and a number average molecular weight of about 100 to 2,000.
Specific examples of such polyisocyanate (A) are organic diisocyanates such as hexamethylene diisocyanate, trimethyl hexamethylene diisocyanate and like aliphatic diisocyanates; hydrogenated xylylene diisocyanate, isophorone diisocyanate and like cycloaliphatic diisocyanates; tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate and like aromatic diisocyanates; adducts of such organic diisocyanate and polyalcohols, low molecular weight polyester resins, water or the like; cyclic polymers of two or more of such organic diisocyanates; and isocyanurates and biurets of these organic diisocyanates.
Representative commercially available products usable as polyisocyanate (A) are “Barnock D-750”, “Barnock-800”, “Barnock DN-950”, “Barnock-970” and “Barnock 15-455” (trade names; manufactured by Dainippon Ink & Chemicals, Inc.), “Desmodule L”, “Desmodule N”, “Desmodule HL”, “Desmodule IL” and “Desmodule N3390” (trade names; manufactured by Bayer AG); “Takenate D-102”, “Takenate-202”, “Takenate-110N” and “Takenate-123” (trade names; manufactured by Takeda Chemical Industries, Ltd.); “Coronate L”, “Coronate HL”, “Coronate EH” and “Coronate 203” (trade names; manufactured by Nippon Polyurethane Co., Ltd.); and “Duranate 24A-90CX” (t

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