Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Effecting a change in a polymerization process in response...
Reexamination Certificate
2000-10-31
2003-12-23
Harlan, Robert (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Effecting a change in a polymerization process in response...
C526S071000, C526S930000
Reexamination Certificate
active
06667372
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a manufacturing method of a water-absorbent polymer (water-absorbent resin, high water-absorbent polymer, high water-absorbent resin, water-swelling/water-insoluble resin, water-absorbent agent, water-absorbent particles) by performing a polymerization of a hydrophilic monomer in a continuous manner, and more particularly relates to a continuous manufacturing method of a water-absorbent polymer which includes at least one of the steps of 1) subjecting a solution containing a hydrophilic monomer such as water-soluble ethylenically unsaturated monomer to a polymerization reaction after removing therefrom oxygen dissolved therein; 2) placing the solution containing a hydrophilic monomer to an inert gas deaerator, a mixer for mixing the solution with a polymerization initiator, a polymerization section, or the like; 3) detecting reaction temperatures of the polymerization reaction using a plurality of temperature detection means provided in the polymerization section (polymerization zone); and 4) transporting a water-containing gel (hydrogel) resulting from the polymerization of the hydrophilic monomer.
BACKGROUND OF THE INVENTION
Water-absorbent polymers have been used in various applications: for example, absorbing materials for sanitary materials such as sanitary napkins, paper diapers (disposable diapers), etc.; drip absorbing materials; water retentive material for soil, or the like. These water-absorbent polymers are manufactured by performing a polymerization of a raw material of hydrophilic monomer (hereinafter may simply referred to as a monomer) in a batch manner or a continuous manner. The monomer is usually used in the polymerization reaction in a form of solution (hereinafter, referred to as a monomer solution). In this case; however, before carrying out the polymerization reaction, is performed the process of introducing an inert gas such as nitrogen gas, etc., into the monomer solution so as to remove therefrom oxygen dissolved therein.
The purpose of performing the above process is to suppress the adverse effects of oxygen (mainly oxygen dissolved in the solution) contained in the monomer solution on the polymerization reaction. By carrying out the polymerization reaction after removing oxygen contained in the monomer solution in the foregoing manner, the adverse effects of dissolved oxygen on the polymerization reaction can be suppressed, thereby permitting water-absorbent polymers having desirable properties to be manufactured at high yield.
In the case of polymerizing a monomer in a continuous manner, generally, an initiator of a polymerization reaction (hereinafter referred to as a polymerization initiator) is mixed with a monomer solution beforehand, and thus this continuous polymerization is performed by 1) mixing the monomer solution with a polymerization initiator in a mixing column (mixing vessel), and subsequently 2) supplying the monomer solution having the polymerization initiator mixed therewith on an upper surface of a transport belt polymerization device provided in a polymerization section via an inlet tube which constitutes a lower end part of the mixing column. In this way, the monomer in a form of a monomer solution can be supplied continuously, and a static polymerization (polymerization without stirring) can be performed on the belt in a continuous manner, thereby manufacturing water-absorbent polymers at high yield.
On the other hand, in the case of polymerizing a monomer in a batch manner, a polymerization initiator is mixed in a polymerization reaction container, and thus this batch-wise polymerization is performed by a) supplying a monomer solution in the polymerization reaction container such as a stainless tray or a kneader provided in the polymerization section, and subsequently mixing the monomer solution with a polymerization initiator in the polymerization reaction container. Alternately, the polymerization initiator can be mixed beforehand, and in this case, b) after the monomer solution is mixed with the polymerization initiator in the mixing column, the resulting mixture is supplied into the polymerization reaction container via the inlet tube which constitutes the lower end part of the mixing column, thereby polymerizing the monomer in a batch manner.
However, when manufacturing a water-absorbent polymer by performing a polymerization of a monomer, a temperature of the monomer (reaction temperature of the polymerization reaction) greatly vales due to heat generated in the polymerization reaction as will be explained in details below in reference to FIG.
8
. Here, a monomer in the polymerization reaction indicates a mixture gel (reaction system) of the monomer and a water-absorbent polymer produced from the monomer.
As indicated by (A) in
FIG. 8
, at the beginning of the first half, reaction temperature increases gradually as the polymerization reaction proceeds smoothly, and then the reaction temperature starts increasing sharply towards a peak of the polymerization reaction (hereinafter referred to as a polymerization peak). For the second half of the polymerization reaction, i.e., the reaction after the polymerization peak, the reaction temperature drops sharply at the beginning, and starts decreasing gradually as time passes.
It is known that the described changes in reaction temperature in the polymerization reaction affect the properties of the resulting water-absorbent polymers or the yields thereof. For example, an excessive increase in reaction temperature (peak temperature) in the polymerization reaction causes the problems of: 1) an increase in ratio of unwanted secondary reaction; 2) an increase in soluble component in the water-absorbent polymer; 3) a reduction in absorbency with and without an applied pressure, and 4) a reduction in durability (gel stability against urine). On the other hand, an excessive reduction in reaction temperature in the second half of the polymerization reaction results in incomplete polymerization reaction, and this causes the problems of, for example, 1) an increase in an amount of monomer remaining in the water-absorbent polymer, 2) the resulting water-absorbent polymer is difficult to be handled due to an increase in viscosity, etc.
As a solution to the above problem, a device for use in producing water-absorbent polymers has been proposed by European Patent No. 922717A wherein the monomer is subjected to cooling for a predetermined time (reaction time from 0 to t in FIG.
8
), and thereafter the monomer is subjected to heating for a predetermined time (reaction time after t in
FIG. 8
) when necessary. In the manufacturing device, a monomer to be polymerized is transported within the polymerization device by a transport belt, and first, a polymerization reaction of a monomer is performed while suppressing an excessive increase in the temperature of the monomer (reaction temperature) (i.e., under cooling for a predetermined time). Subsequently, a polymerization reaction is performed while suppressing an excessive decrease in temperature of the monomer (i.e., under heating for a predetermined time). As a result, variations in reaction temperature of the polymerization reaction as indicated by (B) in
FIG. 8
can be achieved, and water-absorbent polymers having desirable properties can be produced at high yield.
The above water-absorbent polymers are initially produced in a form of a water-containing gel (water-containing gel-like crosslinked polymer). Then, the resulting water-containing gel is transported from the polymerization device to a gel granulator, for example, as disclosed in European Patent No. 925836A, to be granulated into granules of a predetermined size. The resulting granulated water-containing gel having a diameter of several tens cm square is then transported to, for example, a gel pulverizer such as meat chopper as disclosed in U.S. Pat. No. 5,275,773 to be pulverized into gel particles (one type of water-absorbent polymer) of a predetermined size (for example, a particle diameter of not more than 5 mm square). A
Fujita Sachio
Hatsuda Takumi
Ishizaki Kunihiko
Kajikawa Katsuhiro
Miyake Koji
Harlan Robert
Nippon Shokubai Co. , Ltd.
Nixon & Vanderhye P.C.
Presta Frank P.
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