Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1991-04-22
1994-05-24
Zitomer, Fred
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525360, 525366, 525385, 526 73, 526207, 526241, 5263171, C08F 232, C08F 800, C08F 814, C08F 2006
Patent
active
053149521
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes for producing highly water absorptive resins having excellent water absorbency and saline solution absorbency. More particularly, it relates to processes for producing highly water absorptive resins having a high water absorption rate and water absorptive capacity, and an excellent gel-strength.
2. Description of the Prior Art
Various water absorbing materials such as sponge, pulp, paper and the like, are well known in the art. Also various synthetic products made by graft polymerization of materials containing a hydrophilic group, such as --OH, --NH.sub.2, --COOH, and the like, have been used conventionally. However, such water absorbing materials, e.g. a sponge, a pulp, and a paper, are characterized with physical mechanisms for absorbing water so that such materials have defects in that the majority of the absorbed water can be easily squeezed out by the application of external pressure. In recent years, in order to solve these defects, synthetic water-absorptive products having particular physical and chemical characteristics have been developed. The majority of such synthetic products are crosslinked polyacrylic acid salts, polymethacrylic acid salts, crosslinked polyacrylic acid-methacrylic acid copolymer salts, crosslinked saponification products of starch-acrylonitrile graft copolymer, and cellulose and acrylate-grafted copolymer. Such grafted products are on the market as sanitary napkins, sanitary pads, and diapers in the sanitary field, water absorbing containers in the civil and gardening field, and anti-dewdrop agents in the construction field.
However, although saponificated products of starch-acrylonitrile graft copolymer have a relatively high deionized water-absorbency, the saline-solution thereof is poor. Also, long-term storage is impossible due to the main component being starch.
On the other hand, partially crosslinked polyacrylic acid salts have high water absorption rates and capacity in saline solution as well as in deionized water, and they can be stored for a long period of time. Particularly, commercially available alkali metal acrylates are used as a starting material to prepare a water absorptive resin in the present invention.
Various processes are known for polymerizing acrylic acid and alkali acrylate, including bulk polymerization, aqueous solution polymerization, spray polymerization, inverse emulsion polymerization, inverse suspension polymerization, and the like. With the exception of inverse emulsion polymerization and inverse suspension polymerization, it is difficult to remove the heat of polymerization, and the viscosity of the polymerization mixture becomes too high to carry out general polymer production. Moreover, according to these processes it is difficult to obtain particulate polymers.
An example of the inverse emulsion polymerization process is disclosed in U.S. Pat. No. 3,284,393. When, for example, acrylic acid is used as the starting material, the obtained polymer is insoluble in water and does not have such an absorbency that the polymer can be called a water absorptive resin even if it is neutralized with an alkali such as sodium hydroxide or the like.
As a process for producing an acrylic acid-alkali metal acrylate polymer having a water absorbency, the inverse suspension polymerization process is mentioned in Japanese Patent Publication No. 79-30710. According to this process, a water absorptive polymer is prepared through a stable reaction by the use of a sorbitan fatty acid ester having a HLB (Hydrophilic-Lipophilic Balance) value of 3.about.6. The resin thus obtained has a high deionized water absorbency corresponding to 400.about.500 times its own weight; however, the saline solution-absorbency of said water absorptive resin is as low as 35.about.50 times its own weight.
In U.S. Pat. No. 4,497,930, there is disclosed a method for producing a water absorbent polymer comprising the steps of subjecting acrylic acid and sodium acrylate to polymerization in
REFERENCES:
patent: 4340706 (1982-07-01), Obayashi
patent: 4497930 (1985-02-01), Yamasaki
patent: 4806578 (1989-02-01), Kobayashi
Choi Su B.
Jang Tae H.
Kim Myung J.
Lee Huyng M.
Lucky Ltd.
Zitomer Fred
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