Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
1998-12-09
2001-02-13
Acquah, Samuel A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C526S088000, C526S317100, C526S318400, C528S499000, C528S50200C
Reexamination Certificate
active
06187902
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Technical Field
The present invention relates to: a production process of a hydrophilic crosslinked polymer, more particularly, a production process in which hydrophilic crosslinked polymers such as water-absorbent resins can be dried uniformly with good efficiency.
B. Background Art
Generally, a hydrophilic crosslinked polymer is produced by polymerizing a solution including a hydrophilic monomer and a crosslinking agent, and then drying the resultant polymer. As a drying method, various methods such as static drying, stirring drying, and pneumatic drying are known, and these methods are properly employed according to natures and usages of polymers.
In the case where the hydrophilic crosslinked polymer is, for example, a water-absorbent resin, it is difficult to apply the stirring drying and the pneumatic drying, and the drying needs to be carried out in a static state, because the obtained polymer is usually a hydrogel and has strong tackiness and aggregates in the midway of drying.
However, though a surface portion is fast dried by the drying in a static state, there is a problem that an internal potion with which a hot wind is difficult to touch is hardly dried and the drying becomes non-uniform. Also, when the water content is dried to about 1~8 weight % by the static drying, there is a problem that partly excessively dried portions occur and these portions are deteriorated and have much soluble content. For the purpose of solving this problem, it is carried out to grind dried products in the midway of drying and then further dry them (Japanese Patent Publication (Kohyo) 08-506363 and so on), but it is still insufficient.
SUMMARY OF THE INVENTION
A. Object of the Invention
It is an object of the present invention to provide a production process, in which hydrophilic crosslinked polymers can be dried uniformly with good efficiency, and the deterioration during the drying is little.
B. Disclosure of the Invention
To solve the above problems, the present invention provides the below production processes of a hydrophilic crosslinked polymer.
(1) A production process of a hydrophilic crosslinked polymer , comprising the steps of polymerizing an aqueous solution including a hydrophilic monomer and a crosslinking agent to obtain a hydrogel crosslinked polymer, and drying the hydrogel crosslinked polymer, thus obtaining the hydrophilic crosslinked polymer,
with the process being characterized in that: the hydrogel crosslinked polymer is dried in a static state until it becomes possible to disintegrate an aggregate of the hydrogel crosslinked polymer; the dried hydrogel crosslinked polymer is disintegrated into a particle size of 20 mm or less; and the disintegrated hydrogel crosslinked polymer is dried in a stirred state and/or a fluidized state.
(2) A production process of a hydrophilic crosslinked polymer according to process (1) above, wherein the drying in a static state is carried out until the water content of the hydrogel crosslinked polymer becomes 10~20 weight %.
(3) A production process of a hydrophilic crosslinked polymer according to process (1) or (2) above, wherein the drying in a static state is carried out by a drying method in which the hydrogel crosslinked polymer is brought into contact with a hot wind of 120~220° C.
(4) A production process of a hydrophilic crosslinked polymer according to any one of processes (1) to (3) above, wherein the drying in a stirred state and/or a fluidized state is carried out by a drying method in which the hydrogel crosslinked polymer is dried while stirred by rotation of a rotor.
(5) A production process of a hydrophilic crosslinked polymer according to any one of processes (1) to (3) above, wherein the drying in a stirred state and/or a fluidized state is carried out using a fluidized bed.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.
DETAILED DESCRIPTION OF THE INVENTION
Examples of the hydrophilic monomer in the present invention are water-soluble monomers including an ethylenically unsaturated group as follows: anionic monomers and their salts such as (meth)acrylic acid, maleic acid (anhydride), fumaric acid, crotonic acid, itaconic acid, 2-(meth)acryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, and styrenesulfonic acid; nonionic monomers including a hydrophilic group such as (meth)acrylamide, N-substituted (meth)acrylamide, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; and unsaturated monomers including an amino group and their quaternization products such as N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate and N,N-dimethylaminopropyl(meth)acrylamide. Particularly, (meth)acrylic acid and their salts are preferable.
The hydrophilic crosslinked polymer is obtained by polymerizing a solution including the above hydrophilic monomer and a crosslinking agent. The concentration of the hydrophilic monomer during the polymerization is preferably in the range of 20~50 weight % from a viewpoint of the polymerizability of the monomer or the control of the polymerization. The above crosslinking agent is not especially limited if it is a crosslinking agent which forms a crosslinking structure when or after polymerizing, and its examples are as follows: compounds having 2 or more polymerizable unsaturated double bonds per molecule; compounds having 2 or more groups, reactable with a functional group of the hydrophilic monomer such as an acid group, a hydroxyl group, and an amino group, per molecule; compounds having 1 or more unsaturated bonds as well as 1 or more groups reactable with the functional group of the monomer per molecule: compounds having 2 or more sites reactable with the functional group of the monomer per molecule: and hydrophilic polymers which can form a crosslinking structure by graft bonding and so on when monomer components are polymerized. Among the hydrophilic crosslinked polymers, particularly, the water-absorbent resin is usually obtained as a hydrogel polymer derived from its crosslinking structure, so it is effective to carry out two-step drying according to the present invention. The water-absorbent resin in the present invention is a hydrophilic crosslinked polymer with an absorption capacity of 10 g/g or more for aqueous liquids such as water and urine.
In the present invention, drying (first-step drying) of the hydrogel crosslinked polymer obtained by the polymerization is carried out in a static state until it becomes possible to disintegrate an aggregate as formed by aggregation of the polymer due to the drying, and then, after disintegrating the aggregate into a particle size of 20 mm or less, further drying (second-step drying) is carried out in a stirred state and/or a fluidized state.
The water content of the hydrogel crosslinked polymer, obtained by the polymerization and provided to the first-step drying, is usually in the range of 50~80 weight %, and such a hydrogel crosslinked polymer has strong tackiness and aggregates in the midway of drying, so the drying in a stirred state and/or a fluidized state is difficult and it is necessary to carry out the drying in a static state. The method for the drying in a static state is not especially limited if it can dry materials in a static state, and any conventional drying method of batch or continuous type or direct and/or indirect heating types can be used. Examples are as follows: parallel flow band or tunnel drying machine; through-flow band or tunnel drying machine; vacuum drying machine of static type; and drum drying machine. The through-flow band drying machine is especially preferable.
The particle diameter of the above hydrogel crosslinked polymer provided to the first-step drying is generally in the range of 0.1~50 mm, preferably in the range of 0.5~20 mm. Especially, it is preferable that 90% or more of the hydrogel
Hatsuda Takumi
Miyake Koji
Yanase Toru
Yano Akito
Acquah Samuel A.
Nippon Shokubai Co. , Ltd.
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