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...
Patent
1995-09-05
1997-09-30
Schofer, Joseph L.
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...
524832, C08L 3326, C08L 3302
Patent
active
056726562
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a novel water absorbing resin having water absorbability that changes significantly at temperatures near room temperature and provides water absorption and discharge depending on ambient temperature.
BACKGROUND
Water absorbing resins have been used in various applications, for example, as sanitary materials such as menstrual articles, diapers and disposable napkins or as water retaining agents in agricultural or horticultural uses or for condensation prevention in building materials. As such water absorbing resins, hydrogels using carboxy-methyl cellulose crosslinking products, starch-acrylonitrile graft copolymers, polyvinyl alcohols and polyacrylates as the raw materials have been generally known. However, such hydrogels mentioned above have only one function of starting water absorption upon contact with water.
However, it has been attempted in recent years to further add other functions. For instance, as shown in Japanese Patent Laid-Open Sho 61-55180, a non-ionic hydrogel having a function of reversibly repeating water absorption and discharging, depending on the change of temperature, has been known. That is, the hydrogel scarcely shows water absorption if a water temperature is higher than a certain temperature and can absorb water if the temperature lowers to less than this certain temperature. However, since the hydrogel is non-ionic, it has small water absorbing amount at low temperatures and it is not practical. For increasing the water absorbing amount, a copolymerized hydrogel of n-isopropyl acrylamide and an ionic monomer such as sodium acrylate have been proposed, for example, in U.S. Pat. No. 4,732,930 and J. Chem. Phys. 1987, 87, 1392.
However, although the hydrogel with the ionic monomer described above is improved for water absorbing amount, it involves a drawback that the inherent temperature sensing point (a boundary temperature in which water absorbability exists below the temperature but is almost negligible at a higher temperature) changes greatly by merely copolymerizing the ionic monomer slightly. More specifically, there exits a drawback in that the temperature sensing point rises as the content of the ionic monomer is increased, making it difficult to obtain a composition possessing a temperature sensitivity near room temperature.
Further, various methods have been proposed for improving the water absorbing characteristic of a gel having a sensitive and reversible water absorbing and discharging performance relative to the change of temperature in water. For instance, there have been known, for example, a method of an mixing iron oxide in an aqueous solution of polyvinyl methyl ether under irradiating .gamma.-rays, thereby improving porosity and heat transfer rate resulting in increased water absorbing rate (J. Chem. Eng. Japan, 21, 10, 1988); a method of mixing hydroxyl propyl cellulose to synthesize a gel, cleaning the gel after polymerization to remove hydroxypropyl cellulose, thereby making the gel porous, which improves the water absorbing rate (J. Polym. Soc.: Part A, 30, 2121, 1992); and a method of synthesizing a gel having a nonhomogeneous crosslinking structure by polymerization at a temperature higher than a volume transition temperature (Polymer Communications, 32, 322, 1991). On the other hand, various improvements for increased water absorption have also been conducted on general highly absorbing resins having no water absorbing and discharging performance relative to the change of ambient temperature. For instance, there have been reported, for example, a method of mixing a water absorbing resin powder with hydrotalcite to improve the water absorbing rate (Japanese Patent Laid-Open Hei 2-215863), and a method of mixing a water absorbing resin powder with attapulgite to improve the water absorbing rate (Japanese Patent Laid-Open Sho 61-58657).
However, although conventional methods may improve the water absorbing rate, they involve problems in that the production process for the gel is extremely complicated
REFERENCES:
patent: 3927199 (1975-12-01), Micchelli et al.
patent: 4071650 (1978-01-01), Gross
patent: 5447970 (1995-09-01), Tomita et al.
"Vol.-Phase Transitions of Ionized N-Isopropylacrylamide Gels", by Hirotsu et al., J. Chem Phys., vol. 87, No. 2, 15 Jul., 1987, pp. 1392-1395.
"Effect of Salt Solution On Selling or Shrinking Behavior of Poly(Vinylmethylether) Gel (PVMEG)" by Huang et al., J. Chem Eng. of Japan, vol. 21, No. 1, 3 Apr., 1988, pp. 11-14.
"Synthesis and Characterization of Thermally Reversible Macroporous Poly(N-Isopropylacrylamide) Hydrogels", by Wu et al., J. POLYM. SOC., Part A: Polymer Chemistry vol. 30, 1992, pp. 2121-2129.
"Synthesis of Fast Response, Temperature-Sensitive Poly(N-Isopropylacrylamide) Gel", by Kabra et al., POLYMER COMMUNICATIONS, vol. 32, No. 11, 1991, pp. 322-323.
Maruyama Takashi
Murayama Teiichi
Cheng Wu C.
Kohjin Co., Ltd.
Schofer Joseph L.
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