Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-02-14
2002-05-14
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S064000, C521S143000
Reexamination Certificate
active
06387970
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a porous moisture-absorbing and desorbing polymer having high moisture-absorbing and desorbing properties and good moisture-absorbing and desorbing rates and also relates to a method for manufacturing the same.
2. Prior Art
As a means for the removal of moisture in air, moisture absorbers such as lithium chloride, calcium chloride, magnesium chloride and phosphorus pentaoxide have been used so far. Those moisture absorbers have much moisture absorbing capacity and high moisture absorbing rate but, due to their deliquescent property, they have disadvantages that they are liquefied after moisture absorption to contaminate others and that they are hardly molded and difficult to reactivate. Besides them, various kinds of moisture absorbers of an inorganic type such as silica gel, zeolite, sodium sulfate, activated alumina and activated carbon have been used as well. When moisture is absorbed with those moisture absorbers of an inorganic type, the shape is stable, no stickiness is resulted and the processing property is good. However, they have practical problems that their saturated moisture-absorbing capacity itself is small and, in some uses, their moisture-absorbing property is insufficient and that, when high moisture-absorbing property is required, they are to be added too much resulting in inconvenience.
Against the above, super water-absorbing resins represented by a polyacrylate type are sometimes used with regard to a moisture-absorber of an organic type. However, in the case of such super water-absorbing resins, their water-absorbing ability is very good but their moisture-absorbing property is not satisfactory. One of the specific problems is that their saturated moisture-absorbing capacity under low humidity is small and another is that their moisture-absorbing rate is slow. In addition, it is pointed out as a disadvantage of them that, once moisture is absorbed, the absorbed water is hardly desorbed.
Those problems are pointed out in the Japanese Laid-Open Patent Publication Hei-05/105,704 for example and, as a countermeasure therefor, a method in which an acrylate and a deliquescent inorganic salt are combined has been proposed. It is mentioned in said method that moisture-absorbing property under low humidity can be improved and an absorber having a high moisture-absorbing capacity without dripping of the liquid can be prepared. With regard to a moisture-absorbing rate however, time required for moisture absorption is in an order of hours (in the examples, a significant increase in a moisture-absorbing amount is available during ten hours) and they are not satisfactory in the use where moisture-absorbing rate in an order of minutes or seconds is required such as a rotary moisture removing device.
Particularly with regard to a moisture-absorbing rate, it is pointed out, as mentioned in
Kogyo Zairyo
, volume 29, no. 8, page 18, that a highly hydrophilic polymer such as a highly water-absorbing resin has a slow moisture-absorbing rate as a whole. The reason therefor is mentioned to be that, due to an interaction among polar groups, molecular movement of the polymer itself is suppressed and diffusion of water hardly takes place. With regard to a high saturated moisture-absorbing capacity under high humidity, it is mentioned that, with a progress of absorption of moisture, said interaction is gradually deteriorated and plasticization proceeds so that diffusion of water is apt to take place whereupon relatively high saturated moisture-absorbing amount is finally achieved.
PROBLEMS TO BE SOLVED BY THE INVENTION
An object of the present invention is to offer, by utilizing a high affinity of organic high-molecular substance having polar groups with water, an organic polymer having good moisture-absorbing and desorbing properties and being able to express said moisture-absorbing and desorbing properties within a short period or, in other words, having a good moisture-absorbing and desorbing rates.
MEANS TO SOLVE THE PROBLEMS
The present inventor has carried out an intensive study for hydrophilic polymers and for the method for manufacturing the same. As a result, it has been found that, when an organic polymer having polar groups and high affinity with water is made into a porous substance having pores of a specific size, it is now possible to give an organic polymer having high moisture-absorbing and desorbing properties and also having good moisture-absorbing and desorbing rates whereby the present invention has been accomplished. Thus, the above-mentioned object of the present invention can be achieved by:
a porous moisture-absorbing and desorbing polymer, characterized in that, said polymer is an organic polymer containing 2.0-12.0 meq/g of carboxyl groups of a salt type, having a cross-linking structure and having macropores of not less than 1 m
2
/g of specific surface area and 0.005-1.0 &mgr;m of average pore size; and
the following two manufacturing methods, i.e.
(1) a method for the manufacture of a porous moisture-absorbing and desorbing polymer, characterized in that, a polymer solution prepared from an acrylonitrile polymer and a solvent therefor is coagulated in a solvent which is a non-solvent for said polymer to give a porous acrylonitrile polymer, then cross-links are introduced thereinto by the reaction with a hydrazine compound, and a hydrolysis of the residual nitrile group is conducted to introduce 2.0-12.0 meq/g of carboxyl groups of a salt type thereinto whereby the resulting polymer has macropores of not less than 1 m
2
/g of specific surface area and 0.005-1.0 &mgr;m of average pore size; and
(2) a method for the manufacture of a porous moisture-absorbing and desorbing polymer, characterized in that, a monomer mixture containing not less than 50% by weight of acrylonitrile is subjected to an aqueous precipitation polymerization to give a porous acrylonitrile polymer, then cross-links are introduced by the reaction with a hydrazine compound, and a hydrolysis of the residual nitrile group is conducted to introduce 2.0-12.0 meq/g of carboxyl groups of a salt type therein whereby the resulting polymer has macropores of not less than 1 m
2
/g of specific surface area and 0.005-1.0 &mgr;m of average pore size.
The present invention will now be further illustrated as hereunder.
BEST MODE FOR CARRYING OUT THE INVENTION
Firstly, it is necessary that the organic polymer in the present invention contains 2.0-12.0 meq/g of carboxyl groups of a salt type and has a cross-linking structure. Said carboxyl group of a salt type is a highly hydrophilic polar group for resulting in hygroscopicity and it is preferred to contain said group as many as possible in achieving a high moisture-absorbing property. However, in order to make the moisture-absorbing rate higher together with a high moisture-absorbing capacity, they are to be well-balanced in view of the ratio with the cross-linking structure. To be more specific, when the amount of the carboxyl group of a salt type is too much or, in other words, when it is more than 12.0 meq/g, the ratio of the cross-linking structure which can be introduced thereinto becomes too small whereby the porosity of the polymer is unable to be maintained and a sufficient moisture-absorbing rate is unable to be achieved. In an extreme case where only the carboxyl group of a salt type is increased, the product is as if a super water-absorbing resin and, as mentioned already, an extreme reduction in a rate is resulted whereby an object of the present invention cannot be achieved.
On the other hand, in case the amount of a carboxyl group of a salt type is small, the moisture-absorbing property reduces and, particularly when it is lower than 2.0 meq/g, the resulting moisture-absorbing property is inferior to that of the above-mentioned moisture-absorbing inorganic materials whereby that has no practical value. Actually, when the amount of the carboxyl group of a salt type is 6.0 meq/g or more, there are many cases where its superiority in
Foelak Morton
Womble Carlyle Sandridge & Rice PLLC
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