Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-01-11
2002-02-19
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S262000, C525S333300, C525S331200, C525S332400
Reexamination Certificate
active
06348545
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a water absorbing resin obtained on modifying a high-molecular material, and a manufacturing method therefor.
2. Description of the Related Art
Among acrylonitrile-containing resins, there are a polystyrene-based resin, exemplified by an acrylonitrile-butadiene-styrene (ABS) resin, a styrene-acrylonitrile (SAN) resin, and an acrylonitrile-acryl-styrene (AAS) resin, and a synthetic rubber of acrylonitrile-butadiene (NBR) rubber. These resins are relatively inexpensive and, in particular, the former resin, that is polystyrene resin, is superior in toughness, dimensional stability and workability, and hence is used as a resin material for casing of an electric appliances or materials for various parts. The latter resin, that is the synthetic rubber, is used as a tube, hose or a variety of shock-absorbing material.
In these circumstances, the high-molecular weight materials are finding a wider field of use and expectations are made for researches towards a product with a higher added value. The products formed of these high-molecular materials yield a large quantity of waste materials with increase in outputs. Recently, waste materials from the high-molecular materials tend to be increased in quantity such that it is nowadays a desideratum to make effective use of the waste materials in keeping with rise in general interest in maintenance of global environment.
The water-absorbing resin is being used in a wide field of use, such as hygienic material, horticultural usage, food servicing, civil engineering, cosmetics and toiletry application, medical application, electronic or paint/adhesives, and is treated as necessaries of life.
The researches into use of the water-absorbing resin for afforestation of deserts are also proceeding briskly.
With increased usage of the high-molecular materials, a demand for the properties required of them is also becoming stringent. That is, simply high water-absorbing properties are not sufficient. In the field of sanitary products, increase in so-called dry-touch and reduction in a leakage ratio are required, while high gelation factor is preferred to water-absorbing factor.
Thus, water-absorbing resins are being developed positively.
Meanwhile, the water-absorbing resin is mainly used for sanitation products, such as paper diaper or physiological articles. In addition, the water-absorbing resin is expected to be used in construction, horticulture, fire extinguisher or sealants, and investigations are going on briskly in these fields.
Under these circumstances, hydrolyzates of polyacrylonitrile or acrylonitrile/styrene copolymers are proposed. However, for these hydrolyzates to be used as water-absorbing resin, nitrile group containing polymers need to be produced. There are also raised problems such as time consuming reaction or insufficient water-absorbing properties of the water-absorbing resin.
Since the water-absorbing resin for horticulture or civil engineering is used outdoors, the water-absorbing resin is required to accommodate hostile conditions, such changes in lighting or temperature.
Also, in keeping up with general interest in upkeep of global environment, needs for water-absorbing resin that can be used for desert afforestation are increasing, so that it has become necessary to furnish these water-absorbing resins at reduced cost and in large quantities.
The waste materials, mainly composed of the high-molecular materials are disposed of in three different methods, that is by land-filling, incineration and re-melting. Of these, land-filling and incineration account for approximately 90%, that is, the waste materials are hardly put to recycling.
For recycling, the waste materials are usually heat-melted and re-molded, although the waste materials that can be disposed by this method are limited to thermoplastic resins. There are, however, a number of problems presented due to thermal deterioration, such as lowering in molecular weight or oxidation of resins, mixing of foreign mater, such as dust and dirt, or mixing of coloring agents, inorganic pigments, as reinforcements, or resins containing powdered metal pigments, thus necessitating color matching. In this manner, recycling of the waste materials by melting on heating has met significant impediments in connection with the processing technique and cost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a water-absorbing resin superior in water-absorbing properties in a short time, and a manufacturing method thereof.
It is another object of the present invention to provide a water-absorbing resin that is able to utilize the waste materials effectively, and a manufacturing method thereof.
It is another object of the present invention to provide a water-absorbing resin superior in stability outdoors with lapse of time, and a manufacturing method thereof.
The present invention has been fulfilled on the basis of the above information.
In one aspect, the present invention provides a water-absorbing resin obtained on introducing an ionic group into a high-molecular material containing acrylonitrile, styrene and a conjugated diene as constituent units.
The conjugated dienes form a rubber phase in the high-molecular material and is susceptible to chemical modification. Thus, it is the conjugated dienes that undergo the reaction first of all in processing with an acid and/or an alkali. That is, with the progress in the reaction, the rubber phase of the high-molecular material containing the conjugated dienes is swollen to produce cracks in the surface of the material. The result is that the high-molecular material containing the conjugated dienes becomes porous in its surface due to erosion with the acid and/or alkali to increase the surface area participating in the reaction.
Thus, the reaction of the high-molecular material containing the conjugated dienes is completed in a shorter time due to the increased surface area participating in the reaction. Moreover, the material has superior water-absorbing properties due to increased surface area.
Meanwhile, in order for the conjugated dienes to be more susceptible to reactions, the rubber phase needs to be formed in the high-molecular material. Therefore, the conjugated dienes are desirably contained in the block-copolymerized state in the material.
On processing with acid and/or alkali, hydrophilic amid groups, carboxylic groups or acids thereof are introduced into the acrylonitrile part of the high-molecular material, thus improving the water-absorbing properties of the produced water-absorbing resin.
On acid processing in particular, strong acid groups, such as sulfonic acid groups, are introduced into the styrene part of the high-molecular material, thus improving the water-absorbing effect of the produced water-absorbing resin.
By the above reason, it is desirable that 10 to 50 mol %, preferably 25 to 40 mol %, of acrylonitrile, 30 to 70%, preferably 40 to 60 mol %, of styrene, 5 to 50 mol %, preferably 10 to 30 mol %, of conjugated dienes, be contained as constituent units in the high-molecular material.
In the water-absorbing resin of the first aspect of the present invention, the high-molecular material, as the main starting material, forms a two-phase structure of a rubber phase mainly composed of conjugated dienes and a vitreous phase composed of the styrene part and the acrylonitrile part. Thus, if the resin is processed with an acid and/or an alkali, the vitreous phase is first reacted so that the surface of the material becomes porous to increase the reaction surface to permit the reaction to proceed deep into the vitreous phase of the styrene part or the acrylonitrile part.
By the above reason, in the water-absorbing resin of the first aspect of the present invention, the conjugated dienes operate effectively so that the water-absorbing resin superior in water-absorbing properties can be produced in a shorter time than conventionally.
If the above three constituent units are contained in the above-mentioned pre-set
Inagaki Yasuhito
Noguchi Tsutomu
Watanabe Haruo
Cain Edward J.
Lee Katarzyna W.
Sonnenschein Nath & Rosenthal
Sony Corporation
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