JP4454735B2 - Method for producing water-absorbing polymer - Google Patents

Description

【０１０８】
上記の表１によれば、実施例１〜３で得られた吸水性微細粒子Ａ，Ｃ，Ｄは、比較例１で得られた吸水性微細粒子Ｂと比較して、１）含水ゲルの状態での光の透過率が高い。すなわち、残存する気泡の量が低減されていることが判る。そして、空気輸送を想定した機械的ダメージを与えた場合でも、２）微粉（鱗片状の断片の一部も含む）の発生量が少なく、３）加圧下吸収倍率；吸収倍率；が良好である。
【０１０９】
【発明の効果】
以上のように、本発明にかかる吸水性重合体の製造方法、及び製造装置によれば、最終的に得られる吸水性重合体に残存する気泡（不活性ガス等）の量は、従来の製造方法によるものと比較して少なくなる（または、０となる）。これにより、優れた取扱い性と良好な諸物性とを有する吸水性重合体を製造することができるという効果を奏する。
【０１１０】
例えば、吸水性重合体の一形態としての含水ゲルを乾燥した後に（微）粉砕処理して吸水性微細粒子（吸水性重合体の他の形態）とする場合、副産物として発生する微粉や鱗片状の断片の量を従来と比較して極めて少なくすることができる。それ故、上記の吸水性微細粒子等に対し、例えば、表面処理剤により表面処理を均一に施すことが容易となり、また、該吸水性物質に表面処理剤を混合した後の加熱処理を良好に行うことができる。加えて、上記の吸水性微細粒子は、その表面に気泡に由来する凹凸が少なく、従来のものと比較して、１）プロセスダメージを受けて表面処理剤が施された表面処理層が壊れる虞が少ない。また、２）加圧下吸収倍率；通液性；等の諸物性が良好である。
【図面の簡単な説明】
【図１】 本発明にかかる吸水性重合体の製造装置の一例を示す概略の構成図である。
【図２】 図１に示す製造装置に設けられた混合塔（サイクロン室を兼ねる）の概略構成を示す拡大図である。
【図３】 本発明にかかる吸水性重合体の製造装置の他の例を示す概略の構成図である。
【符号の説明】
１２ エジェクタ（ガス供給手段）
１５ 混合塔（サイクロン室；ガス除去手段）
１８ 重合機（重合部）
２４ 超音波照射槽[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water-absorbing polymer (a water-absorbing resin or a hydrophilic polymer), which uses an inert gas to remove oxygen from a solution containing a hydrophilic monomer and then subject the solution to a polymerization reaction. Synonymous).
[0002]
[Prior art]
The water-absorbing polymer is applied to a wide range of applications such as absorbent materials for sanitary products such as sanitary products and disposable diapers; drip absorbents; These water-absorbing polymers are produced by polymerizing a hydrophilic monomer (hereinafter simply referred to as a monomer) as a raw material in a batch system or a continuous system. When the monomer is subjected to a polymerization reaction as a solution containing the monomer (hereinafter referred to as a monomer solution), an inert gas such as nitrogen gas is supplied to the monomer solution and is contained in the monomer solution. It is common to remove oxygen.
[0003]
This is intended to reduce the influence of oxygen (mainly dissolved oxygen) contained in the monomer solution on the polymerization reaction, and after removing oxygen contained in the monomer solution as described above. By using the polymerization reaction, inhibition of the polymerization reaction due to oxygen is reduced, and a water-absorbing polymer having good physical properties can be produced with high productivity.
[0004]
[Problems to be solved by the invention]
By the way, according to the method of supplying an inert gas such as nitrogen gas to the monomer solution and removing the oxygen from the monomer solution before subjecting it to the polymerization reaction, a hydrous gel (water absorbing weight) in which bubbles are dispersed is provided. One form of coalescence is produced. This is presumably because the polymerization reaction occurs in a state where a large amount of inert gas is contained in the monomer solution, and the bubbles are dispersed. The hydrogel in which bubbles such as inert gas are dispersed has the following problems.
[0005]
For example, when the water-containing gel is dried and then pulverized to produce water-absorbing particles (one form of water-absorbing polymer) as one processed form of the water-containing gel, fine powder and scale pieces are added to the water-absorbing particles. There is a risk that a large amount of the fragments will be generated as a by-product. This is because the peripheral part of the space derived from bubbles such as inert gas is crushed.
[0006]
Since these fine powders and scaly fragments have a large surface area relative to their volume, the liquid absorption rate is faster than that of the water-absorbing particles. Therefore, for example, when the surface treatment agent is uniformly mixed, the fine powder and the scaly fragments absorb the surface treatment agent quickly, and uniformly apply the surface treatment agent to the surfaces of the water-absorbing particles. May be difficult. In addition, the fine powder and scale-like fragments that have absorbed the surface treatment agent aggregate to form a lump, and heat treatment after mixing the surface treatment agent may not be performed satisfactorily.
[0007]
Further, as a result of the pulverization treatment, irregularities derived from the bubbles of the inert gas are exposed on the surfaces of the water-absorbing particles. The unevenness exposed on the surface is easy to be scraped off, which may cause fine powder to be generated in processes other than the pulverization process, and may cause various physical properties of the water-absorbing particles to deteriorate. More specifically, for example, in a process for producing water-absorbing particles (including a transporting process) and a process for processing the water-absorbing particles (or hydrous gel) into a water-absorbing material used for diapers or the like 1) Upon processing damage, the surface is shaved and fine powder is generated, or the surface treatment layer to which the surface treatment agent is applied is broken. Fake Problems occur. Further, this may cause problems such as deterioration in various physical properties such as 2) absorption capacity under pressure; liquid permeability of swollen gel (water-absorbing water-absorbing particles); Furthermore, it is also conceivable that the fine powder generated in the pulverization step or other steps may reduce workability. Suppressing the occurrence of such a problem is particularly important when, for example, a monomer solution is supplied to the upper surface of the belt to be driven and the monomer is continuously polymerized on the belt.
[0008]
The present invention has been made in order to solve the above-mentioned problems, and its purpose is to reduce the amount of remaining bubbles (inert gas, etc.) compared to the conventional one, and to provide excellent handling properties and goodness. Another object of the present invention is to provide a method for producing a water-absorbing polymer having various physical properties and an apparatus for producing the polymer.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the method for producing a water-absorbing polymer according to the present invention polymerizes the hydrophilic monomer continuously using a solution containing the hydrophilic monomer and a crosslinking agent. A process for continuously supplying an inert gas to the solution before the solution is subjected to a polymerization reaction; and Degas the inert gas present as bubbles in the inside or remove the dissolved inert gas And a process.
[0010]
In order to solve the above problems, the method for producing a water-absorbing polymer according to the present invention is a continuous static polymerization in which the polymerization reaction is performed while continuously supplying the solution to a conveying means. Degas the inert gas present as bubbles, or remove dissolved inert gas The step is performed before the solution is supplied to a conveying means for continuous stationary polymerization.
[0011]
In order to solve the above-described problems, the method for producing a water-absorbing polymer according to the present invention further comprises an aqueous solution of the hydrophilic monomer and the crosslinking agent, and the aqueous solution has a liquid thickness of 1 to 50 mm. The water-containing gel obtained by the above-described polymerization reaction is dried within a range of 100 to 240 ° C. by a dryer.
[0012]
In order to solve the above-mentioned problem, the method for producing a water-absorbing polymer according to the present invention further comprises a solution containing a hydrophilic monomer and a cross-linking agent, and the final solution is a hydrous gel. The above solution so that the transmittance of light having a wavelength of 700 nm is 10% or more. Degas the inert gas present as bubbles in the inside or remove the dissolved inert gas It is characterized by that.
[0013]
In order to solve the above problems, the method for producing a water-absorbing polymer according to the present invention further provides: Degas the inert gas present as bubbles, or remove dissolved inert gas The above process the above A method of irradiating the solution with ultrasonic waves, the above A method of forming a swirl of solution, the above A method of placing the solution in a vacuum environment; the above Heating the solution just before the polymerization reaction starts, the above It is characterized by being carried out by at least one method selected from the group consisting of a method of adding an antifoaming agent to the solution.
[0014]
In order to solve the above problems, the method for producing a water-absorbing polymer according to the present invention further provides: Degas the inert gas present as bubbles, or remove dissolved inert gas The above process irradiates the solution with ultrasonic waves Done by way It is characterized by that.
[0015]
In order to solve the above problems, the method for producing a water-absorbing polymer according to the present invention is characterized in that the frequency of the ultrasonic wave is 25 kHz or more.
[0016]
In order to solve the above problems, the method for producing a water-absorbing polymer according to the present invention further provides: Degas the inert gas present as bubbles, or remove dissolved inert gas The process forms a swirl of the solution Done by way It is characterized by that.
[0017]
In order to solve the above problems, the method for producing a water-absorbing polymer according to the present invention further includes a step of introducing a polymerization reaction initiator into the swirling flow of the solution. Yes.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described as follows. Note that the present invention is not limited thereby.
[0019]
[Method for producing water-absorbing polymer]
A method for producing a water-absorbing polymer according to the present invention is a method for producing a water-absorbing polymer in which a hydrophilic monomer is polymerized in a continuous manner using a solution containing the hydrophilic monomer, Before subjecting the solution to a polymerization reaction, in other words, before the polymerization reaction of the hydrophilic monomer is started, continuously supplying an inert gas to the solution; Degassing the inert gas present as bubbles in the solution or removing the dissolved inert gas (hereinafter referred to as “ Removing the inert gas supplied to the solution ") A method comprising:
[0020]
A method for producing a water-absorbing polymer according to the present invention is a method for producing a water-absorbing polymer in which a hydrophilic monomer is used to polymerize the hydrophilic monomer. A) supplying an inert gas to the solution before subjecting the solution to a polymerization reaction; and 2) irradiating the solution with ultrasonic waves and / or forming a swirl of the solution, Removing the inert gas supplied to the solution. Unless otherwise specified, the water-absorbing polymer is a hydrogel produced by polymerizing a “hydrophilic monomer” described below, and the hydrogel is subjected to pulverization and / or drying treatment. It is a general term for granular gels, water-absorbing fine particles, and the like obtained in this way.
[0021]
In the present invention, the “hydrophilic monomer” is not particularly limited as long as it is a monomer that can be used as a raw material for the water-absorbing polymer. Specifically, for example, acrylic acid, methacrylic acid, maleic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamido-2-methylpropane sulfonic acid, 2- (meth) acryloylethane sulfonic acid, 2- Anionic unsaturated monomers such as (meth) acryloylpropanesulfonic acid and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) Acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinyl pyri N, N-vinylpyrrolidone, N-vinylacetamide, N-acryloylpiperidine, N-acryloylpyrrolidine, and other nonionic hydrophilic group-containing unsaturated monomers; N, N-dimethylaminoethyl (meth) acrylate, N, Cationic unsaturated monomers such as N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide and quaternary salts thereof; be able to. Among the above-exemplified monomers, acrylic acid and salts thereof (more specifically, alkali metal salts such as Li, Na and K, ammonium salts and the like) are preferably used as the main raw material. These hydrophilic monomers may be used alone in the polymerization reaction, or two or more types may be mixed and used. Hereinafter, the hydrophilic monomer is simply referred to as a monomer.
[0022]
When acrylic acid and its alkali metal salt (or ammonium salt) are used as the monomer, the neutralization rate (namely, alkali metal salt (or ammonium salt of acrylic acid) in the finally produced water-absorbing polymer. ) / Mol of all monomers × 100 (%)) is not particularly limited, but is preferably in the range of 0% to 90%, and in the range of 0% to 80%. It is more preferable that The neutralization rate in the water-absorbing polymer is adjusted after the polymerization reaction, in addition to the mixing ratio of acrylic acid as a monomer to be subjected to the polymerization reaction and its alkali metal salt (or ammonium salt). It is also possible. Specifically, for example, when using a monomer with a neutralization rate of 0% to 50%, the water-absorbing polymer (hydrous gel) obtained by the polymerization reaction is converted to an alkali metal (or ammonium) carbonate or water. By treating with an oxide, the neutralization rate in the water-absorbing polymer can be, for example, 55% to 80%.
[0023]
The monomer is subjected to a polymerization reaction as a solution containing the monomer (hereinafter referred to as a monomer solution). As the monomer solution, an aqueous monomer solution is more preferable. The concentration of the aqueous monomer solution is not particularly limited, but is preferably 20% by weight (mass percentage) to 50% by weight, and more preferably 30% to 45% by weight. If said density | concentration is 20 weight% or more, the intensity | strength of the water-absorbing polymer obtained can be reliably made into a practical value. Moreover, if it is 50 weight% or less, the reaction heat generated by the polymerization reaction can be easily removed, and the polymerization reaction can be reliably controlled.
[0024]
An inert gas is supplied to the monomer solution before being subjected to the polymerization reaction, so that dissolved oxygen contained in the monomer solution is removed. This is intended to reduce the influence of dissolved oxygen on the polymerization reaction. The inert gas supplied to the monomer solution is not particularly limited as long as it is not reactive with the monomer described above. Specifically, for example, nitrogen, argon, helium, and in some cases Carbon dioxide gas or the like is preferably used.
[0025]
Also, the method for supplying the inert gas to the monomer solution is not particularly limited. Specifically, for example, 1) an inert gas (or monomer solution) is ejected from a nozzle by an ejector or an aspirator, and the monomer is A method in which an inert gas is continuously blown into the flow of the solution (or inert gas) (continuous supply), 2) an inert gas introduction pipe is placed in the monomer solution stored in the monomer tank, and the inert gas is inactive Examples thereof include a method of introducing a gas. The above exemplified methods may be used alone or in combination. The degree of removal of dissolved oxygen in the monomer solution is not particularly limited, but the amount of dissolved oxygen in the monomer solution is more preferably 2 mg / l or less, and even more preferably 1 mg / l.
[0026]
The monomer solution to which the inert gas is supplied by the method described above contains an inert gas instead of dissolved oxygen. Hereinafter, the process of removing the inert gas contained in the monomer solution will be described.
[0027]
The step of removing the inert gas is a step of removing the inert gas present as bubbles in the monomer solution or removing the dissolved inert gas. The degree of removal of the inert gas in the step is not particularly limited as long as the inert gas is positively removed as compared with the case where the monomer solution is left in a natural state. Further, in the step of removing the inert gas, there is an effect that the dissolved oxygen remaining without being removed can be removed together.
[0028]
The amount of the inert gas contained in the monomer solution may be directly measured. For example, as described in the following examples, the final water-absorbing polymer (hydrous gel) It can also be measured indirectly by measuring the light transmittance. When the light transmittance is used as a reference, the transmittance is preferably 10% or more, more preferably 20% or more, and further preferably 50% or more.
[0029]
More specifically, the inert gas is removed from the monomer solution by 1) a method of irradiating the monomer solution with ultrasonic waves, 2) a method of forming a swirling flow of the monomer solution, and 3) depressurizing the monomer solution. 4) At least one method selected from a method of placing in an environment, 4) a method of heating the monomer solution to such an extent that a polymerization reaction does not occur, 5) a method of adding an antifoaming agent to the monomer solution, and the like. Is performed by a combination of these methods.
[0030]
More specifically, the method 1) is a method of irradiating the monomer solution with ultrasonic waves using an ultrasonic generator (gas removing means) or the like. The frequency of the ultrasonic wave is not particularly limited as long as it is 20 kHz or more, but is more preferably in the range of 25 kHz to 60 kHz. By setting the frequency to 25 kHz or more, it is possible to prevent the inert gas present as bubbles in the monomer solution from being finely dispersed. Thereby, it is possible to prevent finely dispersed bubbles from remaining in the finally obtained water-absorbing polymer. It is known that bubbles are finely dispersed when using a sound wave having a frequency of less than 20 kHz. The upper limit of the frequency is not particularly limited, but generally ultrasonic waves up to 60 kHz can be used industrially.
[0031]
When the monomer solution is not flowing, specifically, for example, when the monomer solution is stored in a container; in the irradiation of ultrasonic waves, When once introduced into the irradiation tank; etc., or B) When the monomer solution is flowing, specifically, for example, when the monomer solution is continuously supplied to the polymerization reaction, etc. It can carry out without being limited to either case.
[0032]
The ultrasonic irradiation time in the case of A) is not particularly limited, but is preferably in the range of 1 second to 10 minutes, more preferably in the range of 2 seconds to 5 minutes. Preferably, it is in the range of 1 minute or more and 3 minutes or less. By setting the irradiation time to 1 second or longer, it is possible to suitably remove the inert gas bubbles contained in the monomer solution. In addition, by setting the irradiation time to 10 minutes or less, it is possible to eliminate the possibility that the temperature of the monomer solution is increased by the energy of ultrasonic irradiation and the polymerization reaction is induced.
[0033]
The ultrasonic irradiation time in the case of B) may be the same as the example in the description of A). However, in order to secure the ultrasonic irradiation time, the flow rate of the monomer solution may be moderated in some cases. It is desirable to take measures such as providing a plurality of ultrasonic generators along the flow direction of the monomer solution.
[0034]
The timing of ultrasonic irradiation to the monomer solution is not particularly limited as long as the inert gas can be removed from the monomer solution (or the reaction system after the start of the polymerization reaction including the monomer solution). . The timing is from immediately after the inert gas is supplied to the monomer solution until the polymerization reaction is started (in the case of using the polymerization reaction initiator, the initiator (in the case of the redox initiator described below) Is a mixture of an oxidative initiator and a reducing agent), and any timing until the polymerization solution is mixed with the monomer solution is more suitable. Is preferred.
[0035]
More specifically, the method 2) is a method in which the monomer solution is introduced into, for example, a cyclone chamber (gas removal means) shown in FIG. 2 to form a swirling flow of the monomer solution. . According to this method, a swirl flow is formed by the monomer solution flowing along a spiral line 15b in a cyclone chamber or the like, and the inert gas bubbles are generated by the centrifugal force generated by the swirl flow. Can be separated from the monomer solution. In addition, since the monomer solution becomes a thin film on the line 15b, defoaming of the bubbles is promoted. In addition, as long as it has the structure which can form the swirl | vortex flow of a monomer solution, gas removal means other than the said cyclone chamber of the illustration can also be used for execution of the method of said 2).
[0036]
The timing for forming the swirl flow of the monomer solution is not particularly limited as long as the inert gas can be removed from the monomer solution (or the reaction system after the start of the polymerization reaction including the monomer solution). The timing is more preferably an arbitrary timing from immediately after the inert gas is supplied to the monomer solution until the polymerization reaction is started. For example, the cyclone chamber starts the polymerization reaction with the monomer solution. In the case where it also serves as a mixing tower for mixing the agent, the swirl flow may be formed in the initial stage of the polymerization reaction.
[0037]
The above method 3) is, for example, a method in which the monomer solution introduced into a closed system or a system equivalent thereto (hereinafter referred to as a closed system) is placed under a reduced pressure environment. As the above-mentioned closed system or the like, usually, a part of the water-absorbing polymer production apparatus can be used as it is, but if necessary, it is separately attached to perform a step of removing bubbles of the inert gas. You can also use things. The above-described reduced pressure environment refers to an environment in which the pressure of the gas in contact with the monomer solution in a closed system or the like is equal to or lower than atmospheric pressure. The atmospheric pressure is preferably within a range of 0.1 kPa to 50 kPa, and more preferably within a range of 0.5 kPa to 10 kPa. Specifically, such a reduced pressure environment is, for example, using a method of exhausting the gas inside the sealed system or the like using a vacuum pump or the like, a method of cooling the gas inside the sealed system, or the like. Although it is formed, the method for forming the reduced pressure environment is not particularly limited.
[0038]
When the monomer solution containing an inert gas is placed in the reduced pressure environment, the inert gas dissolved in the monomer solution or present as bubbles is removed from the monomer solution, and is put into an internal space such as a closed system. Released. This is because equilibrium movement occurs in order to compensate for a loss of atmospheric pressure in the above-described closed system or the like when forming a reduced pressure environment.
[0039]
When the gas inside the closed system or the like is cooled, the monomer solution in contact with the gas may be cooled. Depending on the degree of cooling of the monomer solution, the solubility of the inert gas in the monomer solution may be increased. Therefore, among the above-described methods for forming the reduced pressure environment, a method of discharging the gas inside the closed system or the like outside the system using a vacuum pump or the like is more preferable than usual.
[0040]
The timing of placing the monomer solution in a reduced pressure environment is not particularly limited as long as the inert gas can be removed from the monomer solution (or the reaction system after the start of the polymerization reaction including the monomer solution). The timing is more preferably an arbitrary timing immediately after the inert gas is supplied to the monomer solution until the polymerization reaction is started, and more preferably a timing immediately before the polymerization reaction is started. is there.
[0041]
The method 4) is a method in which the monomer solution is heated to such an extent that a polymerization reaction does not occur. When the monomer solution containing the inert gas is heated as described above, the inert gas dissolved in the monomer solution or present as bubbles is removed from the monomer solution and released into the internal space such as a closed system. . This is because the solubility of the inert gas in the monomer solution is reduced by heating.
[0042]
The heating of the monomer solution can be performed at any timing immediately after the inert gas is supplied to the monomer solution and until the polymerization reaction is started, but is performed immediately before the polymerization reaction is started. Is more preferable.
[0043]
When the monomer solution is heated, for example, an internal gas such as a closed system is indirectly heated, and the atmospheric pressure rises. In this case, there is a possibility that the gas dissolves in the monomer solution, but this problem can usually be ignored as long as the heating does not cause a polymerization reaction.
[0044]
The method 5) is more specifically a method of adding an antifoaming agent such as a surfactant to the monomer solution to erase the bubbles of the inert gas.
[0045]
In the present invention, the monomer polymerization reaction is usually carried out (continuously) while continuously supplying the monomer solution. Moreover, it is more preferable that it is stationary polymerization. That is, the polymerization reaction is particularly preferably continuous stationary polymerization. In addition, when the step of removing the inert gas is performed by a method of irradiating the monomer solution with ultrasonic waves and / or a method of forming a swirling flow of the monomer solution, the above polymerization reaction is performed with a certain amount of monomer. It may be performed for each solution (batch mode). In addition, the monomer solution immediately before being subjected to the polymerization reaction may or may not be removed as described above.
[0046]
The continuous static polymerization is performed, for example, using a conveying means such as a conveying belt (more preferably an endless type) or a drum dryer while continuously supplying the monomer solution to the conveying means (the upper surface thereof). Is called. The thickness of the monomer solution supplied to the conveying means is not particularly limited, but is preferably in the range of 1 mm to 50 mm, more preferably in the range of 10 mm to 40 mm, and 20 mm to 30 mm. More preferably, it is in the range. If the said liquid thickness is 1 mm or more, production of a water-absorbing polymer can be performed on an industrial level. Further, if the liquid thickness is 50 mm or less, it is easy to remove reaction heat generated by the polymerization reaction, bumping during the polymerization reaction, increase in soluble content contained in the resulting water-absorbing polymer, A decrease in the strength of the polymer can be prevented.
[0047]
In order to start the polymerization reaction, a polymerization reaction initiator (polymerization initiator) is usually used. Examples of the polymerization initiator include, but are not limited to, a redox initiator comprising a combination of an oxidizing initiator and a reducing agent; a thermal decomposition initiator; a photopolymerization initiator; and the like. is not. By using these polymerization initiators, for example, a polymerization reaction of monomers such as radical thermal polymerization and radical photopolymerization is started. In addition, the said polymerization initiator may be used independently and may be used in combination of multiple types. These polymerization initiators may be used in the form of a solution such as an aqueous solution.
[0048]
Among the polymerization initiators exemplified above, a redox initiator is more preferable. The oxidizing initiator contained in the redox initiator is not particularly limited, and examples thereof include persulfate, hydrogen peroxide, benzoyl peroxide, and the like. Further, the reducing agent contained in the redox initiator is not particularly limited. For example, L-ascorbic acid (salt), isoascorbic acid (salt), sulfite (including its hydrogen salt), thio, Examples thereof include sulfates, amines, iron (II) ions, molle salts, and the like. One oxidizing initiator (or reducing agent) may be used, or a plurality may be used in combination. As a combination of the oxidizing initiator and the reducing agent, specifically, a combination of persulfate such as sodium persulfate (NaPs) and L-ascorbic acid (salt); persulfate, hydrogen peroxide, L -Ascorbic acid (salt) combinations; etc. are preferred.
[0049]
Although the usage-amount of an oxidizing initiator is not specifically limited, It is preferable to exist in the range of 0.0001g-1g with respect to 1mol of monomers, and it exists in the range of 0.001g-0.5g. It is more preferable. By setting the amount of the oxidizing initiator used to be 0.0001 g or more with respect to 1 mol of the monomer, the polymerization reaction can be reliably started, and the amount of the monomer remaining unreacted can be reduced. it can. Further, by making the amount used 1 g or less with respect to 1 mol of the monomer, it is possible to reliably prevent the polymerization reaction from proceeding rapidly and making it difficult to remove the reaction heat (polymerization heat). . In addition, it is possible to reliably prevent a decrease in various physical properties such as an increase in soluble content contained in the obtained water-absorbing polymer and a decrease in the absorption capacity of the polymer.
[0050]
Although the usage-amount of a reducing agent is not specifically limited, Usually, it is preferable to exist in the range of 0.0001 mol-2 mol with respect to 1 mol of oxidizing initiators. By setting the amount of the reducing agent used to 0.0001 mol or more with respect to 1 mol of the oxidizing initiator, the polymerization reaction can be reliably started and completed. In addition, when the amount used is 2 mol or less with respect to 1 mol of the oxidizable initiator, it is possible to reliably prevent the monomer from remaining unreacted due to the rapid progress of the polymerization reaction.
[0051]
The above redox initiator can be used in combination with a pyrolytic initiator. In this way, the redox initiator functions exclusively at the stage where the temperature of the monomer solution subjected to the polymerization reaction is low, and the pyrolysis-type initiator is present at the stage where the temperature of the monomer solution increases as the polymerization reaction proceeds. Function. That is, since the polymerization reaction can be carried out stably, it is possible to obtain a water-absorbing polymer having excellent water absorption performance and low water-soluble content (soluble content). The above thermal decomposition type initiator is not particularly limited. For example, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobisisobutyronitrile, 2,2 And azo initiators such as' -azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobisisobutyramide dihydrate; and the like. Only one kind of these pyrolytic initiators may be used, or a plurality of them may be used in combination.
[0052]
Although the usage-amount of a thermal decomposition type initiator is not specifically limited, It is preferable to exist in the range of 0.0001g-1g with respect to 1mol of monomers, and within the range of 0.001g-0.5g. More preferably. By making the use amount of the oxidizing initiator 0.0001 g or more with respect to 1 mol of the monomer, it is possible to reliably obtain the effect of addition. Moreover, it can prevent reliably that a polymerization reaction advances rapidly and the removal of the polymerization heat becomes difficult by making this usage-amount into 1 g or less with respect to 1 mol of monomers. In addition, it is possible to reliably prevent a decrease in various physical properties such as an increase in soluble content contained in the obtained water-absorbing polymer and a decrease in the absorption capacity of the polymer.
[0053]
The combination of the redox initiator and the pyrolytic initiator is not particularly limited, but at least one oxidizing initiator selected from persulfate; hydrogen peroxide; and L-ascorbic acid ( Salt); isoascorbic acid (salt); sulfite (including its hydrogen salt); thiosulfate; at least one reducing agent selected from amines and 2,2′-azobis (2-amidinopropane) dihydrochloride A combination with at least one pyrolytic initiator selected from azo initiators such as salts is preferably used. More specifically, a combination of persulfate, hydrogen peroxide, azo initiator, L-ascorbic acid (salt), etc. is more preferably used, and persulfate, hydrogen peroxide, 2,2 ′ − A combination of azobis (2-amidinopropane) dihydrochloride (azo initiator) and L-ascorbic acid (salt) is particularly preferably used.
[0054]
By the way, when a redox initiator is used (including the case where it is used in combination with another polymerization initiator), it is more preferable to add the oxidizing initiator and the reducing agent to the monomer solution at different timings. Since the redox initiator functions only when the oxidizing initiator and the reducing agent are mixed, according to such a charging method, it is possible to arbitrarily control the timing of starting the polymerization reaction. Further, when a redox initiator and a pyrolytic initiator are used as the polymerization initiator, a first mixing step of mixing the oxidizing initiator and the pyrolytic initiator into the monomer solution, and a reducing agent It is performed in two steps, the second mixing step to be mixed with the monomer solution, or the first mixing step in which the oxidizing initiator is mixed with the monomer solution, the reducing agent and the thermal decomposition type initiator. It is more preferable to carry out in two steps, the second mixing step of mixing the monomer solution with the monomer solution. In this case, the execution order of the first mixing step and the second mixing step is not particularly limited. The details of the polymerization reaction using the redox initiator and the thermal decomposition initiator will be described in the description of the water-absorbing polymer production apparatus below.
[0055]
In the said polymerization reaction, you may use a crosslinking agent as needed. The crosslinking agent is not particularly limited as long as it has two or more functional groups in the molecule and contributes to the formation of a crosslinked structure. By performing the polymerization reaction in the presence of a crosslinking agent, a water-absorbing polymer having excellent durability can be obtained. Moreover, depending on the case, a crosslinked structure can also be formed by adding a crosslinking agent to the hydrogel (one form of a water-absorbing polymer) obtained by the polymerization reaction. In this case, a cross-linking agent having two or more epoxy groups, amino groups, hydroxyl groups, etc. in the molecule, which is reactive with a functional group such as a carboxyl group of the hydrous gel is preferably used.
[0056]
As described above, any of the methods for producing a water-absorbing polymer according to the present invention includes a “step of removing the inert gas contained in the monomer solution”. Therefore, the amount of bubbles (inert gas or the like) contained in the finally obtained water-absorbing polymer is reduced (or becomes 0) as compared with the conventional production method. That is, the occurrence of unevenness due to the inert gas bubbles is reduced in the water-absorbing polymer. As a result, a water-absorbing polymer having excellent handleability and good physical properties is produced.
[0057]
The water-absorbing polymer (hydrous gel) thus obtained is subjected to a crushing process using a gel crusher; a granulating process using a gel granulator; a drying process using a dryer; (Fine) pulverization by a machine; When all of the above-described roughing treatment, granulating treatment, drying treatment, and grinding treatment are performed, they are usually performed in this order.
[0058]
The granulation treatment is, for example, using a gel granulator such as a kneader, a meat chopper, a hard crusher, a shredder, a pelletizer, a screw extruder, etc. It is the process made into the granular gel (one form of a water-absorbing polymer).
[0059]
The said drying process is a process which dries the said granular gel etc. using drying machines, such as a hot air dryer, a fluidized bed dryer, a stirring dryer, a rotary kiln, a Nauta mixer, for example. Although the drying temperature in a drying process is not specifically limited, It is preferable to exist in the range of 100 to 240 degreeC, and it is more preferable to exist in the range of 150 to 220 degreeC.
[0060]
In addition, the pulverization treatment may be performed by, for example, drying the granular gel using, for example, a fine granulator such as a pin mill, a roll mill, a hammer mill, or the like to form water-absorbing fine particles (one form of water-absorbing polymer). This is a process of crushing (fine). The particle diameter of the water-absorbing fine particles is not particularly limited, but is preferably such that it passes through an 850 μm sieve. The water-absorbing fine particles are preferably classified with a sieve having a mesh size of 100 μm to 200 μm, and particles having a particle size of 150 μm or less are preferably adjusted to 5% or less. The average particle diameter of the water-absorbing fine particles is usually in the range of 250 μm to 500 μm.
[0061]
Surface treatment with a surface cross-linking agent (surface treatment agent) is applied to the above water-containing gel, granular gel (including those obtained by drying them) and water-absorbing fine particles (that is, water-absorbing polymer) as necessary. It can also be applied. More specifically, it refers to crosslinking by applying a surface cross-linking agent that can react with a functional group such as a carboxyl group that the water-absorbing polymer usually has on the vicinity of the surface of the water-absorbing polymer. For example, after mixing the surface cross-linking agent and the water-absorbing polymer, heating can be performed at 80 ° C. to 220 ° C. to react the carboxyl group near the surface with the surface cross-linking agent. This surface treatment increases the gel strength and improves the absorption capacity under pressure (absorption capacity under pressure).
[0062]
In addition, when said drying process, a grinding | pulverization process, etc. are performed, generally a fine powder and scale-like fragment generate | occur | produce as a by-product. Since these fine powders and scaly fragments have a large surface area for their volume, for example, it is difficult to absorb the surface treatment agent quickly and uniformly apply the surface treatment agent to the surface of water-absorbing fine particles and the like. Cause. In addition, if the fine powder and scale-like fragments that have absorbed the surface treatment agent are aggregated into a lump, the heat treatment of the water-absorbing fine particles after mixing the surface treatment agent cannot be performed satisfactorily. Become.
[0063]
However, the water-absorbing polymer (hydrous gel) produced by the production method of the present invention has a small amount (or 0) of remaining bubbles (inert gas or the like) as compared with the conventional production method. . Therefore, the amount of fine powder and scale-like fragments generated as a by-product during the production of the water-absorbing fine particles (one form of water-absorbing polymer) can be extremely reduced as compared with the conventional case. Therefore, it becomes easy to uniformly treat the water-absorbing fine particles and the like with the surface treatment agent, for example, and the heat treatment after mixing the surface treatment agent with the water-absorbing substance is favorably performed. There is an effect that can be. In addition, the water-absorbing fine particles and the like have less irregularities due to bubbles on their surfaces, and 1) process treatment damages the surface treatment layer that has been subjected to a surface treatment agent as compared with conventional ones. There is little fear. In addition, various physical properties such as 2) absorption capacity under pressure; liquid permeability;
[0064]
[Production equipment for water-absorbing polymer]
The apparatus for producing a water-absorbing polymer according to the present invention comprises a gas supply means for continuously supplying an inert gas to a solution containing a hydrophilic monomer, and a polymerization for continuously polymerizing the hydrophilic monomer. The apparatus for producing a water-absorbing polymer provided with a part further comprises a gas removing means for removing the inert gas supplied to the solution. That is, the inert gas contained in the above solution is removed by the gas removing means, and the water-absorbing polymer having a small amount (or no) of remaining bubbles (inert gas, etc.) is compared with the conventional one. It is the manufacturing apparatus which can be manufactured with a formula.
[0065]
For example, as shown in FIG. 1, the manufacturing apparatus includes a monomer tank 11 for storing a monomer as a raw material for a water-absorbing polymer as an aqueous solution, an ejector (gas supply means) 12 for supplying an inert gas, a polymerization reaction An initiator tank 13 for storing the initiator, a reducing agent tank 14 for storing the reducing agent, a mixing tower (also serving as a cyclone chamber as a gas removing means) 15 for mixing the monomer, the initiator, and the reducing agent, It has a conveyor belt (conveying means) 16 that continuously conveys the monomer supplied into the polymerization machine 18 from the nozzle port 15a provided in the mixing tower 15 in the conveyance direction, and further, the upper wall of the polymerization machine 18 Infrared radiation thermometer T as a plurality of temperature detecting means 27 ₁ ~ T ₆ Is provided. In the production apparatus shown in FIG. 1, the polymerization portion refers to the polymerization machine 18.
[0066]
The monomer is stored in the monomer tank 11 as, for example, an aqueous solution (hereinafter referred to as a monomer aqueous solution). The monomer aqueous solution removes dissolved oxygen by an inert gas (nitrogen gas) supplied from the ejector 12. Then, it is introduced into the mixing tower 15 via the monomer supply path 17.
[0067]
As shown in FIG. 2, the mixing tower 15 includes 1) a first mixing section (also serving as a cyclone chamber) through which the aqueous monomer solution flows along a line 15 b shown in a spiral shape, and 2) a first mixing section. It is the structure provided with the 2nd mixing part which follows. For example, the first mixing portion is configured such that an inner surface formed in a columnar shape and an inner surface formed in a truncated cone shape are combined, and its cross-sectional area decreases as it goes downward. Further, the second mixing portion has, for example, a thin tube shape having a constant cross-sectional area.
[0068]
In the first mixing section, the monomer aqueous solution introduced from the monomer supply path 17 flows along the line 15b, and a swirling flow of the monomer aqueous solution is formed. Thereby, the bubble of an inert gas can be removed (deaerated) from the monomer aqueous solution. In parallel with the removal of the inert gas, an oxidizing initiator such as NaPs is supplied / mixed to the monomer aqueous solution via the initiator supply path 13a.
[0069]
Subsequently, the monomer aqueous solution in which the inert gas is removed and the oxidizing initiator is mixed is introduced into the second mixing section. In the second mixing portion, for example, a reducing agent such as L-ascorbic acid (LA) is supplied and mixed with the monomer aqueous solution via the reducing agent supply path 14a. Thereby, a monomer, an oxidizing initiator, and a reducing agent are mixed, and a polymerization reaction is started. As described above, when a redox initiator containing an oxidizing initiator and a reducing agent is used as a polymerization initiator, the reducing agent is supplied and mixed in the first mixing section to start oxidizing. The agent supply and line mixing may be performed in the second mixing section. Since the redox initiator functions only when the oxidizing initiator and the reducing agent are mixed, one of them is mixed from the cyclone chamber (first mixing portion), and the other is mixed with the cyclone chamber and the polymerization machine 18. It is possible to arbitrarily control the start timing of the polymerization reaction by performing line mixing between the two (second mixing portion).
[0070]
In the production apparatus shown in FIG. 1, for example, a redox initiator composed of a combination of persulfate, hydrogen peroxide, and L-ascorbic acid, and an azo initiator (for example, V- 50; trade name of Wako Pure Chemical Industries, Ltd.) as a polymerization initiator, an oxidizing initiator (persulfate and hydrogen peroxide) and a thermal decomposition initiator (azo-based initiator) Is preferably mixed with the monomer aqueous solution in the first mixing portion, and the reducing agent (L-ascorbic acid) is mixed with the monomer aqueous solution in the second mixing portion subsequent to the first mixing portion. If the four components are mixed in the monomer aqueous solution in this way, the possibility that the polymerization reaction starts in the first mixing portion that also serves as the cyclone chamber can be eliminated.
[0071]
In other words, when the redox initiator and the thermal decomposition initiator are continuously mixed in the monomer aqueous solution, the oxidizing initiator and the thermal decomposition initiator are mixed from the first mixing portion, and then the reducing agent is added. It is more preferable to perform line mixing between the first mixing unit and the polymerization machine 18 (second mixing unit). The oxidizing initiator, the reducing agent, and the thermal decomposition initiator can be mixed in line with each other. Even in this case, the reducing agent is preferably mixed at the end (more preferably, the timing immediately before reaching the polymerization machine 18). In particular, as a polymerization reaction initiator, persulfate, hydrogen peroxide (all are oxidizing initiators), L-ascorbic acid (salt) as a reducing agent, 2,2′-azobis (2-amidinopropane) 2 When using a hydrochloride (azo initiator), it becomes easy to continuously produce a water-absorbing polymer at an industrial level by using the above mixing method.
[0072]
The monomer aqueous solution introduced into the mixing tower 15 is then supplied to the upper surface of the conveyor belt 16 provided in the polymerization machine 18 via the nozzle port 15a. A nozzle port 15 a provided at one end of the mixing tower 15 is bent in the same direction as the conveying direction of the aqueous monomer solution by the conveying belt 16. This bent structure is a structure for 1) to smoothly supply the monomer aqueous solution to the upper surface of the conveyor belt 16, and 2) to make the supply amount of the monomer aqueous solution to the upper surface of the conveyor belt 16 constant. The structure is not particularly limited to this. The supply amount of the monomer aqueous solution to the upper surface of the conveyance belt 16 (feed amount: when the width of the nozzle port 15a is fixed) is not particularly limited.
[0073]
More specifically, the conveyor belt 16 is an endless belt conveyor supported and driven by drive shafts 20 and 20 that rotate at the same speed in the same direction, and is covered with a hood 41 provided above the conveyor belt 16. Nitrogen substitution. In addition, the upper surface of the transport belt 16 is cooled by a constant region (cooling zone 18a) located on the front side in the transport direction, and a constant region (heating zone 18b) located on the rear side in the transport direction is heated. Yes. Here, “heating” and “cooling” are based on the temperature of the reaction system.
[0074]
The method of cooling and heating the upper surface of the conveyor belt 16 is not particularly limited. For example, a method of cooling and heating the upper surface from the back side using a cooler / heater, a cold water shower / hot water shower, etc. A method of cooling and heating the upper surface from the back side can be mentioned. When cooling the upper surface from the back side using a cold water shower, the temperature of the cold water is not particularly limited, but is more preferably in the range of 0 ° C to 30 ° C. In addition, when the upper surface is heated from the back side using a hot water shower or a heater, the temperature of the upper surface after heating is not particularly limited, but is preferably 50 ° C. or higher, preferably 60 ° C. or higher. More preferably.
[0075]
The monomer supplied (introduced) to the upper surface of the conveying belt 16 via the nozzle port 15a is continuously statically polymerized on the upper surface. The polymerization reaction on the upper surface of the conveyor belt 16 is performed under a cooling condition for a certain period in the cooling zone 18a, and is subsequently performed under a heating condition for a certain period in the heating zone 18b. Thereby, the monomer aqueous solution subjected to the polymerization reaction is transported through the polymerization machine 18 by the transport belt 16, and the polymerization reaction is first performed while suppressing an excessive increase in the reaction temperature. Subsequently, a polymerization reaction and aging are performed while suppressing an excessive decrease in the reaction temperature, and a hydrous gel (one form of a water-absorbing polymer) 19 is produced.
[0076]
In addition, the above polymerization reaction is performed using an infrared radiation thermometer T attached to the upper wall of the polymerization machine 18. ₁ ~ T ₆ Thus, the reaction temperature is measured in a non-contact manner. Above infrared radiation thermometer T ₁ ~ T ₆ As shown in FIG. 1, the reaction temperature is measured at a plurality of points at different distances in the monomer transport direction. This makes it possible to measure the reaction temperature over time and easily monitor the change pattern.
[0077]
The gas removing means is not particularly limited to the cyclone chamber. Specifically, for example, an ultrasonic generator may be provided in the monomer supply path 17 from the ejector 12 to the mixing tower 15 as a gas removing means. In addition, as shown in FIG. 3, an ultrasonic irradiation tank 24 containing an ultrasonic generator (gas removal means) may be provided in the middle of the monomer supply path 17 from the ejector 12 to the mixing tower 15. . The mixing tower 15c shown in FIG. 3 may or may not serve as a cyclone chamber.
[0078]
Moreover, the manufacturing apparatus of the water absorbing polymer concerning this invention is not limited to the thing illustrated in FIG. 1 or FIG. For example, the manufacturing apparatus which does not have the cooling zone 18a and / or the heating zone 18b may be sufficient.
[0079]
The produced hydrogel 19 is carried out of the polymerization machine 18 by the conveyor belt 16. The unloaded hydrogel 19 is transported by a roller conveyor composed of a plurality of rotating rolls 40 provided between the polymerization machine 18 and the gel crusher 21, and is carried into the gel crusher 21. And it is roughly crushed by the gel crusher 21 to a size of about 10 cm square, for example. Subsequently, the crushed hydrated gel 19 is granulated by a gel finer 22 and is, for example, a granular gel having an average particle size of 0.5 mm to 3.0 mm (one form of a water-absorbing polymer). . If necessary, the granular gel is further dried by a drier (not shown) and then finely pulverized by a mill-type pulverizer. For example, water-absorbing fine particles having an average particle size of 250 μm to 500 μm (one form of water-absorbing polymer) It is said.
[0080]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these. First, physical property tests performed in Examples and Comparative Examples will be described.
[0081]
(Measurement of light transmittance)
The absorption spectrum of the water-absorbing polymer (hydrous gel) is measured, and the transmittance of light having a wavelength of 700 nm is measured. As a measuring device, UV3100PC (manufactured by Shimadzu Corporation) was used. By measuring the transmittance, the “amount of inert gas contained in the monomer solution” can be indirectly measured.
[0082]
(Measurement of absorption ratio)
Measured using water-absorbing fine particles (one form of water-absorbing polymer) obtained by subjecting a water-absorbing polymer (hydrous gel) to crushing, granulating, heating, and (fine) grinding. Is done. 0.2 g of the water-absorbing fine particles were uniformly placed in a non-woven bag (60 mm × 60 mm) and immersed in 0.9 wt% physiological saline. After 20 minutes, the bag was pulled up from physiological saline, drained at 250 G for 3 minutes using a centrifuge, and the weight W1 (g) of the bag was measured.
[0083]
The same operation was performed with a non-woven bag (60 mm × 60 mm) without water-absorbing fine particles, and the weight W0 (g) of the bag was measured. The absorption rate (g / g) was determined according to the following formula.
[0084]
Absorption capacity (g / g) = (W1-W0) / weight of water-absorbing fine particles (0.2 g)
(Measurement of absorption capacity under pressure)
The same as the above “Measurement of Absorption Capacity” except that the non-woven bag was immersed in 0.9 wt% physiological saline under a load of 0.7 psi (under pressure) for 60 minutes. W1 (g) and W0 (g) were measured, and the above-mentioned absorption ratio was determined. And this absorption capacity was used as an absorption capacity under pressure.
[0085]
(Measurement of fine powder amount)
After mechanical damage (described in Example 1 below) was applied to the water-absorbing fine particles having a weight of W2, this was passed through a sieve having a 150 μm sieve, and the crushed pieces passing through the sieve were collected as fine powder. Then, the weight (W3) of the fine powder was divided by the weight (W2) of the water-absorbing fine particles, and the proportion of the fine powder was determined. That is, the fine powder amount is represented by the following formula.
[0086]
Fine powder amount (%) = (W3 / W2) × 100
[Example 1]
A water-absorbing polymer was produced using the production apparatus shown in FIG. In this embodiment, the conveyor belt 16 is a stainless endless belt having a width of 60 cm and a length (that is, a distance between the centers of the drive shafts 20 and 20) of 24 m. Moreover, the conveyance speed of the conveyance belt 16 is 1 m / min, the length of the cooling zone 18a is 15 m, and the length of the heating zone 18b is 9 m. The cooling zone is cooled to 15 ° C. by a cooler, and the heating zone is heated to 70 ° C. by a heater.
[0087]
70% neutralized sodium acrylate (monomer) was used as a raw material for the water-absorbing polymer. First, a 39% by weight aqueous solution of sodium acrylate was prepared, and a monomer obtained by adding polyethylene glycol diacrylate as a cross-linking agent to the aqueous solution in an amount of 0.1 mol per 1 mol of sodium acrylate It supplied to the monomer tank 11 as aqueous solution. Subsequently, nitrogen gas (inert gas) is supplied from the nozzle by the ejector 12 at a rate of 3 L / min, and the nitrogen gas is continuously supplied into the flow of the monomer aqueous solution (0.95 L / min) supplied from the monomer tank 11. Infused into. Thus, the dissolved oxygen contained in the aqueous monomer solution was continuously removed. As a result, the dissolved oxygen amount in the monomer aqueous solution was 0.3 mg / L.
[0088]
Subsequently, the monomer aqueous solution was supplied to the ultrasonic irradiation tank 24 where ultrasonic waves having a frequency of 38 kHz were irradiated. The average residence time of the monomer aqueous solution in the ultrasonic irradiation tank (equal to the average ultrasonic irradiation time) was 2.4 minutes. The temperature of the aqueous monomer solution at this time was 18 ° C.
[0089]
The monomer aqueous solution from which nitrogen gas was removed by ultrasonic waves was then supplied to a mixing tower (which also serves as a cyclone chamber) 15c. In the mixing tower 15 c, 0.12 g of sodium persulfate and 0.0015 g of hydrogen peroxide (both oxidizing initiators) are supplied from different initiator tanks 13. Subsequently, 0.0018 g of L-ascorbic acid (reducing agent) was supplied from the reducing agent tank 14 with respect to 1 mol of the sodium acrylate and mixed with the aqueous monomer solution.
[0090]
Subsequently, the monomer aqueous solution was continuously supplied (continuously charged) to the upper surface of the conveyor belt 16 through the nozzle port 15a so that the liquid thickness was 23 mm, and a polymerization reaction was performed. On the conveyor belt 16, polymerization of sodium acrylate was started about 30 seconds after the monomer aqueous solution was charged, and a polymerization peak was reached after 9 minutes. The peak temperature at this time was 98 ° C. As a result of continuing the polymerization reaction for 15 minutes after the polymerization peak, a hydrous gel (one form of a water-absorbing polymer) 19 was produced. The water-containing gel 19 was scraped off from the upper surface of the conveyor belt 16, and the light transmittance was measured as described above.
[0091]
The hydrogel 19 scraped from the upper surface of the conveyor belt 16 is crushed to a size of 10 cm square by a gel crusher 21, and then a screw type extruder (gel refinement) in which a spiral projection is provided inside the body. Equivalent to apparatus 22). And the water-containing gel 19 was extruded from the perforated plate of the hole diameter 16mm provided in this screw type extruder, and this water-containing gel 19 was used as the granular gel (not shown). The average particle diameter of the obtained granular gel was 1.5 mm.
[0092]
The granular gel was dried with hot air at 170 ° C. for 43 minutes, and then subjected to a roll mill (corresponding to a mill-type pulverizer not shown) to obtain water-absorbing fine particles having a particle size of 850 μm or less. Subsequently, the water-absorbing fine particles were classified with a sieve having a 150 μm mesh, and particles having a particle size of 150 μm or less were removed. The average particle diameter of the water-absorbing fine particles obtained by classification was about 400 μm.
[0093]
Subsequently, a surface cross-linking agent comprising 0.5 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, 1 part by weight of isopropyl alcohol and 3 parts by weight of water with respect to 100 parts by weight of the above water-absorbing fine particles. The water-absorbing fine particles A as one embodiment of the water-absorbing polymer according to the present invention were obtained by mixing the above solution and heat-treating at 210 ° C.
[0094]
Then, after giving the mechanical damage shown below to said water-absorbing fine particle A, the absorption capacity | capacitance, the absorption capacity | capacitance under pressure, and the amount of fine powder were measured. Thereby, the physical properties of the water-absorbing polymer according to the present invention were evaluated. In addition, the measurement result of each physical property was shown in the following Table 1 with the measurement result of the light transmittance.
[0095]
(Mechanical damage)
In a glass container (mayonnaise bottle manufactured by Yamamura Glass Co., Ltd., trade name: A-29), 30 g of water-absorbing fine particles A and 30 g of glass beads (soda lime glass beads for precise fractional filling with a diameter of about 6 mm) are placed. I put it in. This was sandwiched between clamps provided in a disperser (manufactured by Toyo Seiki Seisakusho, No488 test disperser) and fixed at 100 V / 60 Hz with a vibration speed of 750 cpm for 30 minutes. As a result, the glass container is tilted 12.5 ° to the left and right with respect to the mounting surface of the clamp, and vibrates by 8 mm in the front and rear directions. Can give the same mechanical damage.
[0096]
[Comparative Example 1]
In Example 1, except that ultrasonic irradiation was not performed, production of water-absorbing fine particles (referred to as water-absorbing fine particles B) and measurement of light transmittance of the hydrogel 19 were performed under the same conditions. It was. Subsequently, the water-absorbing fine particles B were mechanically damaged in the same manner as in Example 1, and then the absorption ratio, the absorption ratio under pressure, and the amount of fine powder were measured. In addition, the measurement result of each physical property was shown in the following Table 1 with the measurement result of the light transmittance.
[0097]
[Example 2]
In Example 1 above, the production of water-absorbing fine particles (referred to as water-absorbing fine particles C) under the same conditions except that nitrogen gas (inert gas) was supplied from the nozzle at 9 L / min, and the hydrogel 19 The light transmittance was measured. Subsequently, after mechanically damaging the water-absorbing fine particles C in the same manner as in Example 1, the absorption ratio, the absorption ratio under pressure, and the amount of fine powder were measured. Thereby, the physical properties of the water-absorbing polymer according to the present invention were evaluated. In addition, the measurement result of each physical property was shown in the following Table 1 with the measurement result of the light transmittance.
[0098]
Example 3
The water-absorbing polymer was produced using the water-absorbing polymer production apparatus shown in FIG. In this embodiment, the conditions regarding the conveyor belt 16, the cooling zone 18a, and the heating zone 18b are the same as those in the first embodiment.
[0099]
65% neutralized sodium acrylate (monomer) was used as a raw material for the water-absorbing polymer. First, a 35 wt% aqueous solution of sodium acrylate was prepared, and a monomer obtained by adding polyethylene glycol diacrylate as a cross-linking agent to the aqueous solution so that the amount was 0.04 mol with respect to 1 mol of the sodium acrylate. It supplied to the monomer tank 11 as aqueous solution. Subsequently, nitrogen gas (inert gas) is supplied from the nozzle by the ejector 12 at a rate of 1 L / min, and the nitrogen gas is continuously fed into the monomer aqueous solution flow (0.95 L / min) supplied from the monomer tank 11. Infused into. Thus, the dissolved oxygen contained in the aqueous monomer solution was continuously removed. As a result, the dissolved oxygen amount in the monomer aqueous solution was 0.3 mg / L.
[0100]
The monomer aqueous solution was then supplied to the mixing tower 15. As shown in FIG. 2, the mixing tower 15 is provided with a Teflon coating. 1) A first mixing section in which a monomer aqueous solution flows along a line 15b shown in a spiral shape (also serves as a cyclone chamber). And 2) a second mixing unit subsequent to the first mixing unit.
[0101]
In the first mixing section, 0.02 g of 0.5 wt% sodium persulfate aqueous solution and 0.002 g of 0.1 wt% hydrogen peroxide solution (both oxidizing initiators) per 1 mol of sodium acrylate. ), And 0.02 g of 0.5 wt% 2,2′-azobis (2-amidinopropane) dihydrochloride aqueous solution (thermal decomposition type initiator) are simultaneously supplied dropwise from different initiator tanks 13. It was. Then, the degassing of nitrogen gas from the aqueous monomer solution by the formation of a swirl flow and the mixing of the oxidizing initiator and the thermal decomposition initiator into the aqueous monomer solution were simultaneously performed.
[0102]
The monomer aqueous solution exiting the first mixing section (also serving as a cyclone chamber) was introduced into the second mixing section. In the second mixing section, 0.0014 g of 0.005 wt% L-ascorbic acid (reducing agent) aqueous solution was supplied from the reducing agent tank 14 with respect to 1 mol of the sodium acrylate, and line-mixed with the monomer aqueous solution. .
[0103]
The monomer aqueous solution from which nitrogen gas has been removed (degassed) is continuously supplied (continuously charged) to the upper surface of the conveying belt 16 through the nozzle port 15a so that the liquid thickness becomes 25 mm, and a polymerization reaction is performed. It was. On the conveyor belt 16, polymerization of sodium acrylate started about 3 minutes after the monomer aqueous solution was charged, and reached a polymerization peak after 12 minutes. The peak temperature at this time was 85 ° C. As a result of continuing the polymerization reaction for 12 minutes after the polymerization peak, a hydrous gel (one form of a water-absorbing polymer) 19 was produced. The water-containing gel 19 was scraped from the upper surface of the conveyor belt 16, and the light transmittance was measured as described above.
[0104]
The hydrogel 19 scraped from the upper surface of the conveyor belt 16 is crushed to a size of 10 cm square by a gel crusher 21, and then a screw type extruder (gel refinement) in which a spiral projection is provided inside the body. Equivalent to apparatus 22). And the hydrogel 19 was extruded from the perforated plate of the hole diameter 9.5mm provided in this screw type extruder, and it was set as the granular gel (not shown). The average particle diameter of the obtained granular gel was 1.7 mm.
[0105]
The granular gel was dried with hot air at 170 ° C. for 43 minutes, and then subjected to a roll mill (corresponding to a mill-type pulverizer not shown) to obtain water-absorbing fine particles having a particle size of 850 μm or less. Subsequently, the water-absorbing fine particles were classified with a sieve having a 150 μm mesh, and particles having a particle size of 150 μm or less were removed. The average particle diameter of the water-absorbing fine particles obtained by classification was about 300 μm.
[0106]
A solution of a surface cross-linking agent consisting of 0.5 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, 1 part by weight of isopropyl alcohol and 3 parts by weight of water with respect to 100 parts by weight of the above water-absorbing fine particles. By mixing and heat-treating at 195 ° C., water-absorbing fine particles D as one embodiment of the water-absorbing polymer according to the present invention were obtained. Subsequently, mechanical damage was given to the water-absorbing fine particles D in the same manner as in Example 1, and then the absorption ratio, the absorption ratio under pressure, and the amount of fine powder were measured. Thereby, the physical properties of the water-absorbing polymer according to the present invention were evaluated. In addition, the measurement result of each physical property is put together in the following Table 1 with the measurement result of the light transmittance.
[0107]
[Table 1]

[0108]
According to Table 1 above, the water-absorbing fine particles A, C, and D obtained in Examples 1 to 3 were compared with the water-absorbing fine particles B obtained in Comparative Example 1 as follows: The light transmittance in the state is high. That is, it can be seen that the amount of remaining bubbles is reduced. Even when mechanical damage is assumed assuming pneumatic transportation, 2) the generation amount of fine powder (including part of the scale-like fragments) is small, and 3) absorption capacity under pressure; absorption capacity is good. .
[0109]
【The invention's effect】
As described above, according to the method and apparatus for producing a water-absorbing polymer according to the present invention, the amount of bubbles (inert gas, etc.) remaining in the finally obtained water-absorbing polymer is the same as in the conventional production. Less (or 0) than by the method. Thereby, there exists an effect that the water-absorbing polymer which has the outstanding handleability and favorable physical properties can be manufactured.
[0110]
For example, when the water-containing gel as one form of the water-absorbing polymer is dried and then finely pulverized to form water-absorbing fine particles (another form of the water-absorbing polymer), fine powder or scales generated as a by-product The amount of the fragments can be extremely reduced as compared with the prior art. Therefore, it becomes easy to uniformly treat the water-absorbing fine particles and the like with a surface treatment agent, for example, and the heat treatment after mixing the surface treatment agent with the water-absorbing substance is improved. It can be carried out. In addition, the water-absorbing fine particles described above have less irregularities due to bubbles on the surface, and compared with conventional ones, 1) there is a risk that the surface treatment layer to which the surface treatment agent has been applied is damaged due to process damage. Less is. In addition, various physical properties such as 2) absorption capacity under pressure; liquid permeability;
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a water-absorbing polymer production apparatus according to the present invention.
2 is an enlarged view showing a schematic configuration of a mixing tower (also serving as a cyclone chamber) provided in the manufacturing apparatus shown in FIG. 1;
FIG. 3 is a schematic configuration diagram showing another example of a water-absorbing polymer production apparatus according to the present invention.
[Explanation of symbols]
12 Ejector (gas supply means)
15 Mixing tower (cyclone chamber; gas removal means)
18 Polymerizer (Polymerization Department)
24 Ultrasonic irradiation tank

Claims (9)

A method for producing a water-absorbing polymer in which a hydrophilic monomer and a crosslinking agent are used to polymerize the hydrophilic monomer continuously.
A step of continuously supplying an inert gas to the solution before subjecting the solution to a polymerization reaction;
A method for producing a water-absorbing polymer, comprising : degassing an inert gas present as bubbles in the solution , or removing a dissolved inert gas . The polymerization reaction is continuous static polymerization performed while continuously supplying the solution to the conveying means,
The degassing of the inert gas existing as bubbles or the step of removing the dissolved inert gas is performed before the solution is supplied to the conveying means for continuous stationary polymerization. A method for producing a water-absorbing polymer. The solution comprising a hydrophilic monomer and a crosslinking agent is an aqueous solution;
The aqueous solution has a liquid thickness of 1 to 50 mm and is supplied to a conveying means for continuous stationary polymerization,
The method for producing a water-absorbing polymer according to claim 2, wherein the hydrogel obtained by the polymerization reaction is dried within a range of 100 to 240 ° C by a dryer. The solution comprising a hydrophilic monomer and a crosslinking agent is an aqueous solution;
The inert gas present as bubbles in the solution is degassed or the dissolved inert gas is added so that the light-containing gel finally obtained has a light transmittance of 700 nm at a wavelength of 10% or more. The method for producing a water-absorbing polymer according to claim 1 or 2, wherein the water-absorbing polymer is removed . Defoaming inert gas present as bubbles, or the step of removing the inert gas to be dissolved is a method of applying ultrasonic waves to the solution, a method of forming a swirling flow of the solution, the solution pressure environment the method of placing the underlying claims, characterized in that it is performed by at least one method methods is selected from the group consisting of a method of adding an antifoaming agent to the solution to heat just before the polymerization reaction the solution is started Item 5. The method for producing a water-absorbing polymer according to any one of Items 1 to 4. 6. The water absorbing weight according to claim 5, wherein the step of degassing the inert gas present as bubbles or removing the dissolved inert gas is performed by a method of irradiating the solution with ultrasonic waves. Manufacturing method of coalescence.   The method for producing a water-absorbing polymer according to claim 6, wherein the frequency of the ultrasonic wave is 25 kHz or more. 6. The water absorbing weight according to claim 5, wherein the step of degassing the inert gas present as bubbles or removing the dissolved inert gas is performed by a method of forming a swirling flow of the solution. Manufacturing method of coalescence.   9. The method for producing a water-absorbing polymer according to claim 8, further comprising a step of introducing a polymerization reaction initiator to the swirling flow of the solution.

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