JP2005036100A - Method for producing water-absorbing resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a high-quality water-absorbing resin at low cost. <P>SOLUTION: The method for producing the water-absorbing resin comprises the step(a) of feeding a monomer-containing aqueous solution 102 onto an endless belt 106, the step(b) of polymerizing the monomer while evaporating the water in the aqueous solution 102 in a boiling condition and expanding the resultant hydrous polymer 108, the step(c) of irregularly peeling the hydrous polymer 108 off the endless belt 106 owing to the expansion, and the step(d) of contracting the expanded hydrous polymer 108 and collecting it. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for continuously producing a water absorbent resin. More specifically, the present invention relates to a method for producing a water-absorbing resin by continuous polymerization of monomers contained in an aqueous solution. The water-absorbent resin produced by the method of the present invention is effectively used for sanitary products such as disposable diapers and sanitary napkins, and water retention agents for soil.

  The water-absorbing resin is a resin having an excellent water-absorbing power, and has been applied to a wide range of uses by making use of its characteristics. For example, the water-absorbing resin is applied to sanitary goods such as paper diapers and sanitary napkins, soil water retention agents, and the like.

  Such a water-absorbing resin (also referred to as a highly water-absorbing resin or a water-absorbing polymer) is described in, for example, Japanese Industrial Standard (JIS) K7223-1996 and is already known. Examples of the water-absorbing resin include a crosslinked polyacrylic acid partially neutralized product, a hydrolyzate of starch-acrylic acid graft polymer, a saponified vinyl acetate-acrylic ester copolymer, an acrylonitrile copolymer, or an acrylamide. A hydrolyzate of a copolymer or a crosslinked product thereof, and a crosslinked product of a cationic monomer are known.

  Since the water-absorbing resin is relatively used in sanitary products and soil water retention agents, it has a great influence on the cost competitiveness of products using the water-absorbing resin. Therefore, development of a technique for reducing the manufacturing cost of the water absorbent resin is desired.

  When manufacturing a water absorbing resin by aqueous solution polymerization, the aqueous solution containing a monomer and a polymerization initiator is prepared. Aqueous polymerization proceeds in the aqueous solution to obtain a gel-like hydrated polymer. After crushing the water-containing polymer, the particulate water-containing polymer is dried to obtain a particulate base polymer. Subsequently, the base polymer is surface-crosslinked to obtain a water absorbent resin.

  In such a process, a large amount of energy is required to dry the hydropolymer. Therefore, a method for producing a water-containing polymer having a low water content using an aqueous solution containing a high concentration of monomer has been proposed (see, for example, Patent Document 1 and Patent Document 2). However, the water-absorbent resin produced according to the proposed method has a problem with respect to the water-absorbing property, such as a large amount of soluble component for the absorption capacity of the produced water-absorbent resin. Although the reason is not clear, it is considered that a high molecular weight component generated at the initial stage of high concentration polymerization adversely affects the water absorption characteristics.

  Therefore, in order to improve the water absorption characteristics of the produced water absorbent resin, a technique for polymerizing while using an aqueous solution having a low monomer concentration while controlling the temperature below a certain temperature has been developed (for example, Patent Document 3). And Patent Document 4). By adopting mild polymerization conditions, it is possible to obtain a water-absorbing resin having excellent water absorption characteristics. However, since heat of polymerization is generated during the polymerization reaction, it is necessary to remove heat from the polymerization reaction solution. Further, a large amount of heat is required to dry the water-containing polymer having a high water content. That is, the techniques disclosed in Patent Document 3 and Patent Document 4 contribute to the improvement of the water absorption characteristics of the water absorbent resin, but leave room for improvement in terms of manufacturing cost.

  As a technique that satisfies both the manufacturing cost and quality, a method is disclosed in which an aqueous solution containing acrylic acid or its sodium salt at a high concentration is polymerized while the polymerization initiation temperature is set high and water is evaporated (Patent Document). 5). If such a method is used, heat removal during polymerization is unnecessary, and therefore the cost required for heat removal can be reduced. Moreover, since the water content of the formed water-containing polymer is small, the cost required for drying can be reduced. In addition, the water-absorbing properties of the produced water-absorbing resin are also excellent. However, in Patent Document 5, the technology for producing a water-absorbing resin in a continuous process is only briefly described.

As a technique related to continuous polymerization of monomers contained in an aqueous solution, for example, a technique that facilitates peeling of a formed polymer by controlling the shape of an endless belt to which an aqueous solution is supplied has been proposed. (See Patent Document 6). The endless belt disclosed in Patent Document 6 is provided with a support roll, and an aqueous solution is supplied to a recess formed in a concave shape by the support roll. The polymerization reaction proceeds in this state, and the formed polymer is solidified along the shape of the recess. The endless belt becomes flat as it approaches the end, and the polymer solidified along the shape of the recess gradually peels from the side end of the endless belt.
JP 58-71907 A US Pat. No. 4,985,518 JP-A-4-175319 JP-A-11-228604 JP 2002-212204 A Japanese Unexamined Patent Publication No. 62-156102

  An object of the present invention is to provide a means for producing a high-quality water-absorbing resin at a low cost.

  The present invention includes a step (a) of supplying an aqueous solution containing a monomer onto an endless belt, and expanding the hydrous polymer by polymerizing the monomer while evaporating water contained in the aqueous solution in a boiling state. A step (b) of causing the water-containing polymer to be irregularly separated from the endless belt by expansion, and a step (d) for continuously recovering the expanded water-containing polymer by contraction. And a method for producing a water-absorbent resin.

  By using the production method of the present invention, a high-quality water-absorbing resin can be produced at a low cost.

  First, a method for producing a water absorbent resin using acrylic acid or a salt thereof as a monomer will be described with reference to the drawings. However, the manufacturing method of the present invention is not limited to the illustrated embodiment. For example, the production method of the present invention can be applied to embodiments using other compounds as monomers. Further, it does not preclude improvement as necessary when the production method of the present invention is carried out.

  FIG. 1 is a process diagram of a method for producing a water absorbent resin. First, an aqueous solution 102 containing acrylic acid or a salt thereof (hereinafter abbreviated as “acrylic acid component”) is supplied onto an endless belt 106 provided in the polymerization apparatus 104. The endless belt 106 is movable, and the supplied aqueous solution 102 is conveyed as the endless belt 106 moves. The aqueous solution 102 contains other components as required in addition to the acrylic acid component. For example, the aqueous solution 102 includes a crosslinking agent, a polymerization initiator, and the like. When using an acrylate as a monomer, an aqueous sodium hydroxide solution that neutralizes acrylic acid may be added to the aqueous solution 102 in advance.

  When a thermal polymerization initiator is used as the polymerization initiator, the polymerization may start before the aqueous solution 102 is supplied onto the endless belt 106, and the piping may be blocked. Therefore, the thermal polymerization initiator may be added immediately before the aqueous solution 102 is supplied onto the endless belt 106. In order to achieve uniform polymerization, the aqueous solution 102 is preferably stirred before being supplied to the endless belt 106. The stirring means is not particularly limited in the present invention.

  In the present invention, the aqueous solution supplied to the endless belt 106 is heated, and the polymerization reaction proceeds while water is vigorously evaporated. Therefore, it is preferable that the aqueous solution 102 supplied to the endless belt 106 is heated to a certain temperature in advance. The aqueous solution 102 may be heated using a heating device such as a heater, or the neutralization heat and / or dissolution heat of acrylic acid may be used. Considering the production cost, it is preferable to use the heat of neutralization and / or the heat of dissolution of acrylic acid.

  Here, for reference, a schematic diagram of an embodiment of a water-absorbing resin polymerization apparatus is shown in FIG. The polymerization apparatus includes a rotating body 202 at one end, another rotating body 204 provided at the other end, and a movable endless belt 106 stretched between the rotating body 202 and the rotating body 204. The rotating body is connected to a power source such as a motor, if necessary, via a transmission or the like (both not shown). It is sufficient that at least one of the rotating bodies is connected to the power source.

  A monomer supply means 206 for supplying an aqueous solution containing a monomer is disposed at one end of the upper surface of the endless belt 106, and a water-containing polymer discharging device 208 for discharging the water-containing polymer 108 is disposed at the other end. Known techniques can be applied to specific materials and improvements constituting the polymerization apparatus. For example, known techniques described in JP 2000-17004 A can be appropriately referred to.

  The monomer in the aqueous solution is polymerized while being conveyed on the endless belt 106, and the temperature of the polymerization system rises due to the polymerization heat accompanying the polymerization. The monomer polymerization reaction proceeds in an aqueous solution in which water heated to the boiling point is evaporated in a boiling state. As a result, the produced hydropolymer 108 expands in the process of being conveyed on the endless belt 106, and the hydropolymer 108 is in a foamed state. In the process where the hydrous polymer becomes a foam by expansion, the hydropolymer 108 peels irregularly from the endless belt 106. The water contained in the water-containing polymer 108 gradually evaporates as the endless belt 106 advances. Therefore, the water content in the water-containing polymer gradually decreases as the endless belt 106 advances. As the endless belt 106 advances, water from the water-containing polymer 108 also evaporates gradually, and the foamed water-containing polymer gradually contracts. In order to prevent the back flow of the aqueous solution 102 supplied onto the endless belt 106, the polymerization apparatus may be low on the side where the hydropolymer 108 is conveyed.

  When a foamed water-containing polymer is produced by advancing the polymerization reaction while evaporating water, the finally obtained water-absorbent resin is excellent in water absorption characteristics. Although it was thought that when the polymerization reaction was allowed to proceed under severe reaction conditions, the water absorption characteristics were lowered, the water absorption having the same quality as the water absorbent resin produced under mild reaction conditions was obtained using the production method of the present invention. Resin can be manufactured. The reason is not clear, but it is possible to suppress the formation of a high-molecular-weight water-containing polymer that adversely affects the water-absorbing properties if a polymerization reaction is started at a certain high temperature and a method for producing a foamed water-containing polymer is adopted. Guessed.

  In the methods described in Patent Document 3 and Patent Document 4, the temperature of the aqueous solution in which the polymerization reaction proceeds and the concentration of the monomer are controlled to be low so that the polymerization reaction proceeds slowly. That is, it is necessary to remove heat from the aqueous solution as necessary so that the temperature of the aqueous solution does not increase more than necessary due to the generated heat of polymerization. On the other hand, the method of the present invention utilizes the heat of polymerization to raise the temperature of the aqueous solution. Therefore, the method of the present invention is excellent in energy efficiency.

  In addition, when the aqueous solution is at a high temperature, the polymerization reaction proceeds at a sufficient rate. Continuous polymerization using an endless belt is inherently excellent in productivity. However, before the water-containing polymer is recovered from the endless belt, the polymerization reaction needs to proceed sufficiently. For this reason, the productivity of continuous polymerization using an endless belt is greatly influenced by the polymerization reaction rate. For example, in order to ensure a sufficient supply amount of the aqueous solution to the endless belt, it is necessary to use a wide endless belt or lengthen the endless belt to increase the transport speed of the endless belt. However, in any case, the polymerization apparatus is increased in size, and the production cost of the water absorbent resin is increased. In the method for producing a water absorbent resin of the present invention, the polymerization reaction proceeds at such a high temperature that the aqueous solution supplied to the endless belt evaporates violently, and the reaction rate of the polymerization reaction is very high. For this reason, polymerization in a short time that cannot be imagined by continuous polymerization using a conventional endless belt is possible, and the productivity of the water-absorbent resin is greatly improved. In terms of the size of the polymerization apparatus, a large amount of water-absorbing resin can be processed by a polymerization apparatus having a scale similar to that of a conventionally used polymerization apparatus, so that the equipment cost can be greatly reduced. On the contrary, if the supply amount of the water-absorbing resin is kept constant, the polymerization apparatus can be downsized. However, the size of the polymerization apparatus should be determined with care that the volume of the foamed hydropolymer is greatly increased.

  Further, when foam polymerization is performed using an endless belt, a gel sheet made of a gel-like water-containing polymer can be made thick. When performing foam polymerization by batch polymerization, since it expands freely in all directions, it is difficult to obtain a thick gel sheet. On the other hand, in the case of continuous polymerization while moving on the endless belt, since expansion in the traveling direction is restricted, the gel expands upward and a thick gel sheet can be obtained. For this reason, productivity improves further. Specifically, the thickness of the gel sheet made of the gel-like water-containing polymer is preferably 2 to 20 mm in the portion where the wrinkles are stretched and flattened.

  In addition, when a water-absorbing resin is produced by continuous polymerization using an endless belt, surprisingly, an effect of improving the quality of the obtained water-absorbing resin is also obtained. When manufacturing a water-absorbing resin by batch polymerization, the walls of the polymerization equipment are on all sides, so there are many monomers adhering to the walls, and they are reattached to the gel on which the monomers are formed and remain in the hydrous polymer. Many monomers are used. On the other hand, if the production method of the present invention is used, there are walls on both sides of the polymerization apparatus, but there are no walls in the traveling direction. For this reason, it is estimated that the residual monomer which adheres again to a water-containing polymer decreases.

  The hydropolymer transported on the endless belt 106 is continuously collected at the end of the endless belt and transported to the crusher 110. The means for recovering the water-containing polymer from the endless belt is not particularly limited. For example, the sheet-like water-containing polymer is taken up using a take-up roller and conveyed to the crusher 110. The produced hydropolymer may be continuously supplied to the crusher using a conveyance roller or the like.

  If a polymerization method in which water in an aqueous solution containing a monomer is evaporated is used for foaming, the water-containing polymer formed on the endless belt 106 is a foam, and the endless belt 106 and the foam The contact area is small. Therefore, the water-containing polymer 108 can be easily peeled from the endless belt 106, and the labor required for recovery can be reduced. Such advantages are great in continuously producing a hydrous polymer. Further, it is possible to prevent the water-containing polymer that has not been recovered from remaining on the endless belt 106 and deteriorating the quality of the product.

  Patent Document 6 discloses a technique in which the endless belt itself is used as a recess to peel off the polymer attached to the endless belt, but the peeling mechanism is fundamentally different from that of the present application. The technique disclosed in Patent Document 6 is a technique applied to a polymer that adheres firmly to an endless belt, and it is assumed that the polymer is solidified along the endless belt. On the other hand, in the present invention, the formed water-containing polymer becomes a foam, and the adhesion between the water-containing polymer and the endless belt is naturally weakened during the polymerization process. Therefore, even if the endless belt of the present invention is flat, the water-containing polymer can be easily peeled off from the endless belt. Further, the water-containing polymer is not continuously peeled from the side end portion, but the adhesive force between the endless belt and the water-containing polymer is weakened as a whole during the foaming process, and peels irregularly. Here, “peeling irregularly” means that many parts peel irregularly. For example, the form in which peeling gradually proceeds from the side as the endless belt progresses does not correspond to “irregular peeling”. On the other hand, a form in which a large number of peeling portions of the endless belt and the water-containing polymer appear irregularly with the progress of the endless belt corresponds to “irregular peeling”. However, in some cases, the endless belt may be bent on the recess. For example, the endless belt may be bent on the recess by its own weight.

  The recovered water-containing polymer is crushed to a size suitable for drying in the crusher 110 and conveyed to the dryer 112. In the present invention, since the water-containing polymer is formed while water is evaporated, the water content of the water-containing polymer is low. In other words, the solid content concentration of the water-containing polymer is high. For this reason, the energy required for drying the water-containing polymer can be reduced. In the conventional continuous process, since the processing capacity of the dryer is lower than the processing capacity of other equipment, in some cases, it was necessary to take measures such as preparing multiple dryers and making the drying process into multiple series . If the manufacturing method of this invention is employ | adopted, it is also possible to unify a drying process in one series, and reduction of installation cost and uniformization of product quality can be promoted by this invention.

  The base polymer generated by drying the water-containing polymer is conveyed to the classifier 114. The base polymer means a polymer produced by drying the hydropolymer. When surface cross-linking is performed in a subsequent step, it means a polymer before surface cross-linking. The base polymer having a predetermined size is conveyed to the surface crosslinking device 116. A base polymer having an excessively large particle size is pulverized using a pulverizer 118 such as a roll mill, and conveyed to the classifier 114 again. A finely powdered base polymer having a particle size that is too small is conveyed to the granulator 120. The base polymer is granulated using the aqueous liquid sprayed from the spray 122, and is transported to the crusher 110 again as a water-containing polymer.

  In the surface crosslinking device 116, the surface polymer is surface-crosslinked with a surface crosslinking agent to obtain a surface-crosslinked water-absorbing resin. The surface-crosslinked water-absorbent resin is subjected to a necessary treatment such as sizing, and then becomes a product 124.

  The water-absorbing resin produced in the present invention has, for example, a load-absorbing capacity (GV) with respect to 0.90% by mass physiological saline of 10 to 90 g / g, preferably 20 to 55 g / g, and more preferably 25. It is resin which shows the water absorption which is the range of -50g / g. Furthermore, the water-absorbent resin produced in the present invention has a water absorption capacity (AAP) of, for example, 4.83 kPa against 0.90% by mass physiological saline under a pressure of 60 minutes, preferably 10 g / g or more. It is a resin exhibiting water absorption in a range of 15 g / g or more, more preferably 20 g / g or more.

  Subsequently, compounds that can be used, reaction conditions, and the like will be described in detail.

  As a monomer used as a raw material for the water absorbent resin in the present invention, (meth) acrylic acid, (anhydrous) maleic acid, itaconic acid, cinnamic acid, vinyl sulfonic acid, allyl toluene sulfonic acid, vinyl toluene sulfonic acid, Such as styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, 2-hydroxyethyl (meth) acryloyl phosphate, etc. Anionic unsaturated monomers and salts thereof; mercaptan group-containing unsaturated monomers; phenolic hydroxyl group-containing unsaturated monomers; (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meta) ) Amide group-containing unsaturated monomer such as acrylamide; N, N-dimethylaminoethyl (Meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) amino group-containing unsaturated monomer acrylamide. A monomer may be used independently and 2 or more types may be used together.

  Considering the water absorption performance and cost of the water absorbent resin, it is preferable to use acrylic acid and / or a salt thereof as a monomer. Specific examples of the salt include sodium salt, lithium salt, potassium salt, ammonium salt and amine salt of acrylic acid. In view of cost, a sodium salt of acrylic acid is preferably used. Although other monomers may be contained, the amount of acrylic acid and / or its salt used is preferably 70 mol% or more, more preferably 80 mol% or more, and more preferably 80 mol% or more, based on the total number of moles of monomers. Preferably it is 90 mol% or more, Most preferably, it is 95 mol% or more.

  The concentration of the monomer in the aqueous solution supplied to the endless belt is not particularly limited, but is preferably 30% by mass or more, more preferably 35% by mass or more, further preferably 40% by mass or more, and even more preferably 45% by mass. % Or more, particularly preferably 50% by mass or more, and most preferably 55% by mass or more. By increasing the monomer concentration, the productivity of the water absorbent resin is improved. In the present invention, the polymerization reaction can be advanced using an aqueous solution containing a high concentration of monomer. A high-quality water-absorbing resin can be produced without suppressing an increase in polymerization temperature due to polymerization heat as in conventional continuous polymerization. The upper limit of the monomer concentration is not particularly limited, but is preferably 70% by mass or less, and more preferably 60% by mass or less. If the concentration of the monomer is too high, the absorption capacity may be lowered.

  When using a monomer containing an acid group as a raw material, it may be neutralized before polymerization. For example, when acrylic acid is used as a monomer, acrylic acid may be neutralized with sodium hydroxide or the like to form an acrylate. By neutralizing the acid group, it can be applied to sanitary goods such as paper diapers and sanitary napkins without being neutralized after polymerization.

  The neutralization rate of the monomer containing an acid group is not particularly limited, but is preferably 50 mol% or more and less than 100 mol%, more preferably 55 mol% or more and 80 mol% or less, and further preferably 60 mol% or more and 75 mol%. It is less than mol%.

  In the aqueous solution supplied on an endless belt, a crosslinking agent is suitably contained as needed. The crosslinking agent is a compound having a plurality of vinyl groups in the molecule; a compound having a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule, and the performance required for the monomer or water-absorbing resin used. It is appropriately selected depending on.

  Specific examples of the compound having a plurality of vinyl groups in the molecule include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, and (poly) propylene glycol di (meth). Examples include acrylate, trimethylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, and the like.

  Examples of the compound having a plurality of functional groups capable of reacting with a carboxyl group or a sulfonic acid group in the molecule include a polyhydric alcohol compound, an epoxy compound, a polyvalent amine compound, a condensate of a polyvalent amine and a haloepoxy compound, Examples include isocyanate compounds, polyvalent oxazoline compounds, alkylene carbonate compounds, haloepoxy compounds, polyhydric metal hydroxides and chlorides, and the like. For example, (poly) ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, (Poly) glycerin, 2-butene-1,4-diol, 1,4-butanediol, (poly) ethylene glycol diglycidyl ether, (poly) glycerol polyglycidyl ether, diglycerol polyglycidyl ether, (poly) propylene glycol Diglycidyl ether, glycidol and the like can be used.

  However, the crosslinking agent is not limited to the exemplified crosslinking agent, and a known crosslinking agent can be used as appropriate. For example, Japanese Patent Application Laid-Open No. 11-188727 is incorporated in this application as a reference. This publication can be referred to for other components that can be contained in the aqueous solution. You may refer to other literature.

  Although the usage-amount of a crosslinking agent is not specifically limited, Preferably it is 0.0001-10 mol% with respect to the total amount of a monomer, More preferably, it exists in the range of 0.001 mol%-1 mol%.

  The polymerization initiator is not particularly limited, and a thermal decomposition initiator or a photodecomposition initiator can be used. Thermal decomposition initiators include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide and methyl ethyl ketone peroxide; azonitrile compounds, azoamidine compounds, cyclic Azoamidine compounds, azoamide compounds, alkylazo compounds, azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride Is mentioned. Examples of the photolytic initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, azo compounds, and the like. These polymerization initiators may be used alone or in appropriate combination. Considering the residual monomer reducing ability, it is preferable to use a thermal decomposition initiator and a photodecomposition initiator in combination.

  Other components may be included in the aqueous solution supplied to the endless belt. For example, starch, starch derivatives, cellulose, cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), hydrophilic polymers such as polyacrylic acid (salt) cross-linked products; chain transfer agents such as hypophosphorous acid (salt); chelate Agents and the like can be added to the aqueous solution.

  It is preferable that the temperature of the aqueous solution supplied onto the endless belt is previously increased. By increasing the temperature of the aqueous solution, dissolved oxygen in the aqueous solution is removed. Moreover, when the temperature of aqueous solution is high, it is convenient when applying the polymerization method of this invention superposed | polymerized, evaporating water at high temperature.

  Specifically, the temperature of the aqueous solution supplied onto the endless belt is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, further preferably 70 ° C. or higher, particularly preferably 80 ° C. or higher, and most preferably 90 ° C. or higher. It is. Although the upper limit of the temperature of aqueous solution is not specifically limited, The temperature of aqueous solution becomes like this. Preferably it is 105 degrees C or less, More preferably, it is 100 degrees C or less. If the temperature of the aqueous solution is too low, it takes time for the temperature of the aqueous solution to rise to the boiling point of water in the aqueous solution, and productivity is lowered. Further, the physical properties of the water absorbent resin are lowered.

  When a monomer containing an acid group such as acrylic acid is used, the temperature of the aqueous solution supplied onto the endless belt is adjusted using the heat of neutralization generated when the acid group is neutralized with an alkali. It is preferable to increase. The temperature of the aqueous solution supplied onto the endless belt may be increased by the heat of dissolution of the monomer and alkali. Both heat of neutralization and heat of dissolution may be used. Further, dissolved oxygen in the aqueous solution can be volatilized by the heat of neutralization and / or the heat of dissolution.

  The size of the polymerization apparatus and the size of the endless belt are determined according to the water absorbent resin to be produced. The size of the polymerization apparatus and the endless belt is not particularly limited, but it should be noted that the water-containing polymer expands greatly as the foam formed. The basic design of the polymerization apparatus and the endless belt may also be referred to as appropriate from known techniques, and is not particularly limited in the present invention. The material of the endless belt is not particularly limited, but considering the features of the present invention in which the aqueous solution supplied onto the endless belt is heated to a high temperature and the polymerization reaction proceeds while water is evaporated, the endless belt is heat resistant. It is preferable that it consists of material excellent in. The endless belt is preferably made of a material that is excellent in releasability from the water-containing polymer. However, in the present invention, the water-containing polymer that is a foam is easily peeled off from the endless belt, so that it can be said that the range of material selection is relatively wide. For example, the endless belt is formed from a fluororesin. Alternatively, an endless belt whose surface is coated with a fluororesin may be used.

  The polymerization reaction is usually allowed to proceed under normal pressure, but may be performed under reduced pressure in order to lower the boiling temperature of the polymerization system. Preferably, from the viewpoint of workability, the polymerization reaction is allowed to proceed under normal pressure.

  The polymerization initiation temperature is usually 50 ° C. or higher, preferably 60 ° C. or higher, more preferably 70 ° C. or higher, still more preferably 80 ° C. or higher, and particularly preferably 90 ° C. or higher. When the polymerization start temperature is too low, the productivity of the polymerization is lowered. Moreover, there exists a possibility that the physical property of a water absorbing resin may fall. Further, the polymerization initiation temperature is preferably 105 ° C. or lower, more preferably 100 ° C. or lower. If the polymerization start temperature is too high, foaming and stretching do not occur sufficiently, and the water absorption properties of the water absorbent resin may be deteriorated. The polymerization initiation temperature can be observed by the cloudiness of the aqueous monomer solution, the increase in viscosity, the increase in temperature, and the like. In order to ensure the temperature of the aqueous monomer solution and initiate polymerization, as described above, the heat of neutralization of the aqueous monomer solution and / or the heat of dissolution (of acrylic acid and alkali) should be used. Is preferred.

  The polymerization start is controlled according to the polymerization initiator used. When a photopolymerization initiator is blended, polymerization is initiated by light irradiation. When a thermal polymerization initiator is blended, the polymerization reaction is induced by the temperature rise of the aqueous solution.

  The maximum temperature reached during the polymerization is not particularly limited, but is preferably 150 ° C. or lower, more preferably 140 ° C. or lower, still more preferably 130 ° C. or lower, particularly preferably 120 ° C. or lower, and most preferably 115 ° C. or lower. If it exceeds 150 ° C., the water absorption of the resulting water absorbent resin may be greatly reduced.

  In the present invention, the difference ΔT between the polymerization initiation temperature and the highest temperature reached during polymerization is preferably 70 ° C. or less, more preferably 60 ° C. or less, still more preferably 50 ° C. or less, even more preferably 40 ° C. or less, particularly Preferably it is 30 degrees C or less, Most preferably, it is 25 degrees C or less. There exists a tendency for the water absorption characteristic of the water absorbent resin obtained to improve, so that (DELTA) T is small.

  The polymerization time is not particularly limited, but is preferably 5 minutes or less, more preferably 3 minutes or less, still more preferably 2 minutes or less, and particularly preferably 1 minute or less. The shorter the polymerization time, the higher the productivity of the polymerization reaction. Here, the polymerization time refers to the time from when the aqueous monomer solution with the polymerization initiator added is supplied to the polymerization apparatus until the water-containing polymer is recovered from the polymerization apparatus.

  According to a preferred embodiment of the present invention, the temperature of the system rapidly increases after the start of polymerization, and the temperature of the system reaches the boiling point of water at a low polymerization rate of about 10 to 20 mol%. And water vapor | steam is emitted and superposition | polymerization advances, solid content concentration rising. The solid content concentration increases by effectively using the heat of polymerization.

  The water-containing polymer becomes a foam during the polymerization, but the shape of the foam is not particularly limited. In order to produce a water-absorbent resin having excellent quality, the expansion ratio during polymerization is preferably 2 times or more, more preferably 3 times or more, more preferably 5 times or more, more preferably 10 times or more, more preferably 20 times or more. The expansion ratio during the polymerization can be measured by the method described in the examples.

  The water vapor generated from the polymerization reaction system may contain a monomer. The water vapor containing the monomer may be recovered and reused. As an example of an embodiment for recovering and reusing, water vapor containing monomer is concentrated by a condenser to obtain an aqueous solution containing monomer. This aqueous solution is supplied to a pipe for supplying the aqueous solution to the polymerization apparatus (not shown).

  As the polymerization reaction proceeds, the solid content concentration of the hydropolymer gradually increases. Since the water-containing polymer of the present invention has a high solid content concentration, less energy is required to dry the water-containing polymer in the subsequent drying step. In order to enhance this effect, the solid content concentration of the hydropolymer is preferably 50% by mass or more, more preferably 55% by mass or more, still more preferably 60% by mass or more, and particularly preferably 66% by mass or more. On the other hand, if the solid content concentration is too high, it becomes difficult to handle the hydropolymer. Moreover, there exists a tendency for the water absorption performance of the water absorbent resin finally obtained to fall, and for the soluble content to increase. Therefore, the solid content concentration of the hydropolymer is preferably controlled to 82% by mass or less, more preferably 80% by mass or less, and still more preferably 75% by mass or less.

  The hydropolymer continuously formed on the endless belt is recovered after shrinking. The term “shrinkage” in the present invention means that after the hydrous polymer exhibits the maximum expansion ratio, its volume is reduced as compared with the maximum expansion due to the temperature decrease of the system. At the stage where the hydrated polymer shrinks, most of the polymerization reaction is completed, and in some cases, the hydrated polymer during shrinkage may be recovered. However, from the viewpoint of workability, the water-containing polymer is preferably recovered after shrinking to the above-mentioned preferable sheet thickness. The term “recovery” used herein means that the hydropolymer is taken out from the polymerization apparatus and used for the next step such as winding or crushing.

  Since the water-containing polymer formed according to the method of the present invention is partially peeled from the endless belt during the foaming process, it can be easily recovered.

  The recovered water-containing polymer is crushed using a pulverizer. The crusher is not particularly limited. Moreover, as long as crushing is possible, means other than the crusher may be used. Examples of the crusher include screw type extruders such as meat chopper (manufactured by Hiraga Corporation) and Dome Gran (manufactured by Fuji Powdal Co., Ltd.), and solid type crushers such as Rotoplex (manufactured by Hosokawa Micron Corporation). Etc. can be used. However, the crusher used is not limited to these.

  The weight average particle size of the hydropolymer after crushing is preferably 100 mm or less, more preferably 10 mm or less, still more preferably 3 mm or less, and particularly preferably 1 mm or less. Ideally, it can be crushed to the final product particle size in the state of a hydrous polymer.

  The amount of residual monomer contained in the hydropolymer after pulverization is not particularly limited, but it is preferably as small as possible to prevent scattering of the residual monomer during drying in the subsequent step. Specifically, the amount of residual monomer contained in the hydropolymer after crushing is preferably 3000 ppm or less. Depending on the application, the amount of residual monomer contained in the hydropolymer after crushing is preferably 1000 ppm or less, more preferably 500 ppm or less, and even more preferably 300 ppm or less. In particular, when it is used as a particulate hydrous polymer for sanitary goods such as paper diapers, it is preferably 1000 ppm or less, and more preferably 500 ppm or less.

  The crushed water-containing polymer is dried to become a base polymer. The dryer is not particularly limited. An appropriate dryer may be selected according to the solid content concentration and the particle size of the water-containing polymer. The drying method is not particularly limited, but a drying method that makes good contact with the hot air or the heat transfer surface while moving the water-containing polymer, such as a stirring drying method, a fluidized bed drying method, and an airflow drying method, is preferably used. As a medium used for drying, hot air, infrared rays, microwaves, or the like can be used. A ventilator or the like may be used as long as sufficient drying can be achieved without heating. “Drying” in the present invention is a concept widely including a step of increasing the solid content concentration of the hydrous polymer. The water content of the base polymer after drying is not particularly limited, but it is preferably dried so that the solid content is 90% by mass or more.

  The hydropolymer produced according to the method of the present invention has a high solid content concentration. Therefore, the drying process can be greatly simplified. It takes a long time to dry a water-containing polymer having a low solid content and a high water content. For this reason, a drying process will become a rate-limiting process. In order to solve this problem, it is necessary to prepare a plurality of dryers so that a plurality of drying processes are performed or a large dryer is prepared. However, these methods increase the equipment cost and waste energy, and adversely affect the production cost of the final product. Moreover, the dryer which can be used is also limited.

  On the other hand, if this invention is applied, the solid content concentration of the hydropolymer conveyed to a dryer will be high. For this reason, drying can be completed in a short time, and the equipment required for drying can be simplified. For example, depending on the dryer to be selected, it is possible to make the drying process one line.

  The dried base polymer is classified, and a base polymer having a suitable particle size is conveyed to a surface crosslinking apparatus and surface crosslinked. However, surface cross-linking is optional in the present invention. In the present application, the base polymer is included in the concept of the water-absorbent resin when sufficient characteristics can be obtained without surface crosslinking. The classifier is not particularly limited. As the particle size distribution of the base polymer after classification is narrower, various characteristics such as absorption performance are improved. The particle size of the base polymer is preferably in the range of 20 to 2000 μm, more preferably 50 to 1000 μm, still more preferably 150 to 850 μm, and most preferably 300 to 600 μm. The shape of the base polymer is not particularly limited, and may be any shape such as a spherical shape, a scale shape, an irregularly crushed shape, and a granular shape. The same applies to the water-absorbent resin formed by surface crosslinking of the base polymer.

  The base polymer having a particle size outside the range is preferably reused after the particle size is controlled in order to improve the productivity of the water absorbent resin. The base polymer having an excessively large particle size is pulverized using a pulverizer such as a roll mill, and is again charged into a classifier. The finely powdered base polymer is granulated and then charged into a crusher. The granulator is not particularly limited, and various known techniques can be applied. For example, Japanese Patent Laid-Open No. 11-106514 is incorporated in this application as a reference. Although FIG. 1 shows a granulator for spraying an aqueous liquid using a spray, the granulator used in the present invention is not limited to such an embodiment.

  The classified base polymer is preferably cross-linked with a surface cross-linking agent to increase the cross-linking density in the vicinity of the surface of the hydrophilic resin particles. By treating the base polymer with a surface cross-linking agent, liquid permeability, water absorption speed, water absorption magnification under pressure, liquid permeability, and the like are improved. The form of the surface cross-linking device used for cross-linking the surface of the base polymer is not particularly limited. Generally, an apparatus capable of continuously producing a water absorbent resin while mixing is used.

  The surface cross-linking agent may be a compound that has a plurality of reactive groups and reacts with a functional group such as a carboxyl group that the base polymer has. The surface cross-linking agent is not particularly limited, and one or more known surface cross-linking agents may be employed. For example, a polyhydric alcohol; a polyvalent epoxy compound; a polyvalent amine compound; a polyvalent isocyanate compound; a polyvalent oxazoline compound; an alkylene carbonate compound; a haloepoxy compound; Specifically, (poly) ethylene glycol, diethylene glycol, (poly) propylene glycol, triethylene glycol, tetraethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3- Pentanediol, (poly) glycerin, 2-butene-1,4-diol, and the like can be used. For example, Japanese Patent Application Laid-Open No. 11-188727 is incorporated in this application as a reference.

  By introducing secondary crosslinking into the hydrophilic resin using a surface crosslinking agent, the water absorption capacity under pressure is further improved. Moreover, the amount of a component that elutes into the aqueous liquid when it comes into contact with the aqueous liquid, that is, a so-called water-soluble component can be reduced.

  The amount of the surface crosslinking agent used is preferably in the range of 0.001 to 5 parts by mass with respect to 100 parts by mass of the water absorbent resin. Water may be used for mixing the surface cross-linking agent and the water absorbent resin. Generally the usage-amount of water becomes like this. Preferably it is 0.5-10 mass parts with respect to 100 mass parts of solid content of a water absorbing resin, More preferably, it is the range of 1-5 mass parts. Moreover, when mixing a surface crosslinking agent and its aqueous solution, a hydrophilic organic solvent and a 3rd substance may be used. Examples of the hydrophilic organic solvent include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol and other lower alcohols; acetone and other ketones; dioxane, tetrahydrofuran , Ethers such as methoxy (poly) ethylene glycol; amides such as ε-caprolactam and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, Polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol Glycerol, polyglycerol, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexane Examples include dimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymers, polyhydric alcohols such as pentaerythritol, sorbitol, and the like. The amount of the hydrophilic organic solvent used is preferably 50 parts by mass or less, more preferably 100 parts by mass or less, based on the solid content of 100 parts by mass of the water absorbent resin, although it depends on the type, particle size, water content, etc. of the water absorbent resin. Is 0.1 to 10 parts by mass. In addition, inorganic acids, organic acids, polyamino acids and the like disclosed in European Patent No. 0668080 may be present as the third substance.

  A mixing method for mixing the water absorbent resin and the surface cross-linking agent is not particularly limited. For example, a method in which a water-absorbing resin is immersed in a hydrophilic organic solvent and a surface cross-linking agent dissolved in water and / or a hydrophilic organic solvent is mixed as necessary, water and / or hydrophilicity directly in the water-absorbing resin Examples thereof include a method in which a surface cross-linking agent dissolved in an organic solvent is mixed by spraying or dropping.

  After mixing the water-absorbent resin and the surface cross-linking agent, heat treatment is usually performed to carry out the cross-linking reaction. Although the said heat processing temperature is based also on the surface crosslinking agent to be used, Preferably it is 40-250 degreeC. When the treatment temperature is less than 40 ° C., there is a possibility that water absorption characteristics such as water absorption magnification under pressure are not sufficiently improved. If the treatment temperature exceeds 250 ° C., the water absorbent resin may be deteriorated and the performance may be lowered. The heat treatment time is about 1 minute to 2 hours, preferably about 5 minutes to 1 hour.

  The present invention will be described in more detail using examples. The expansion ratio, gel sheet thickness, residual monomer, and absorption capacity under no load were measured according to the following methods.

<Measurement of expansion ratio>
(In the case of continuous polymerization)
The gel during polymerization is photographed by video, and the cross-sectional area in the belt width direction at the time of maximum expansion is read from the photographed image, and the value is divided by the charged cross-sectional area of the aqueous monomer solution in the belt width direction. That is,

である。

It is.

(In the case of batch polymerization)
A scale in units of cm was provided in the polymerization vessel in the vertical and horizontal directions, and the size when it expanded the largest during the polymerization was visually measured to determine its volume. Divide that value by the volume of the aqueous monomer solution. That is,

である。

It is.

<Measurement of gel sheet thickness>
The wrinkles produced by the shrinkage of the collected gel sheet were stretched, and the thickness of the flattened portion was measured with calipers. The thickness measurement was performed 5 times per polymerization condition, and the maximum value and the minimum value were recorded.

<Measurement of residual monomer>
After adding 0.5 g of water-absorbing resin to 1000 g of deionized water and extracting with stirring for 2 hours, the water-absorbing resin swollen and gelled using filter paper is filtered off, and the amount of residual monomer in the filtrate is determined by liquid chromatography. analyzed. On the other hand, a calibration curve obtained by analyzing a monomer standard solution having a known concentration in the same manner was used as an external standard, and the amount of residual monomer in the water-absorbent resin was determined in consideration of the dilution rate of the filtrate.

<Measurement of absorption capacity under no load>
0.2 g of the water-absorbent resin was uniformly placed in a non-woven bag (60 mm × 60 mm) and immersed in a 0.9 mass% sodium chloride aqueous solution (physiological saline). After 30 minutes, the bag was pulled up, drained at 250 × 9.81 m / s ² (250 G) for 3 minutes using a centrifuge, and then the mass W1 (g) of the bag was measured. Further, the same operation was performed without using the water absorbent resin, and the mass W0 (g) at that time was measured. From these masses W1 and W0,

に従って、ＧＶ（無荷重下吸収倍率）を算出した。

Thus, GV (absorption capacity under no load) was calculated.

<Measurement of soluble content>
In a 250 ml plastic container with a lid, weigh out 184.3 g of 0.9 mass% NaCl aqueous solution (saline), add 1.00 g of water absorbent resin to the aqueous solution, and stir for 16 hours. The soluble amount of was extracted. 50.0 g of the filtrate obtained by filtering this extract using a filter paper was measured and used as a measurement solution.

  First, physiological saline alone was titrated to pH 10 with a 0.1N aqueous NaOH solution, and then titrated to pH 2.7 with a 0.1N aqueous HCl solution, followed by empty titration ([bNaOH] ml, [bHCl] ml).

  By performing the same titration operation on the measurement solution, titration amounts ([NaOH] ml, [HCl] ml) were obtained.

  For example, in the case of a water-absorbing resin composed of acrylic acid and its sodium salt, based on the weight average molecular weight and the titration amount obtained by the above operation, the soluble content in the water-absorbing resin is calculated by the following formula: Can be calculated.

Soluble content (mass%) = 0.1 × Mw × 184.3 × 100 × ([HCl] − [bHCl]) / 1000 / 1.0 / 50.0
However,
Mw = 72.06 × (1−neutralization rate / 100) + 94.04 × neutralization rate / 100
Neutralization rate (mol%) = {1 − ([NaOH] − [bNaOH]) / ([HCl] − [bHCl])} × 100
<GEX value>
When the GV value of the base polymer is represented by y (g / g) and the soluble content is represented by x (mass%), the GEX value is defined by the following formula.

GEX value = (y−15) / ln (x)
ln (x): natural logarithm of x In the relationship between the GV value and the soluble amount, the GEX value is evaluated based on the evaluation that the smaller soluble amount is better for the GV value, and the lower is the larger one. It is an evaluation value for expressing with a parameter, and the higher this value, the higher the performance.

<Measurement of UV light intensity>
UVD-S365 (manufactured by USHIO INC.) Is attached to UV-integrated light meter UIT-150 (manufactured by USHIO ELECTRIC CO., LTD.), And the amount of UV light at the same irradiation position and irradiation time as in the polymerization of the water-absorbing resin is measured. did.

(Example 1)
48.5% by mass of caustic soda aqueous solution 4.95 g / second, acrylic acid 6.12 g / second, 30% by weight polyethylene glycol diacrylate (number average molecular weight 523) aqueous solution (I) 0.0672 g / second, 20% by weight 0.0758 g / sec of a solution (II) in which 0.989 parts by mass of 2-hydroxymethyl-2-methylpropiophenone and 1.08 parts by mass of trisodium diethylenetriaminepentaacetate were dissolved in 97.9 parts by mass of an aqueous acrylic acid solution The water was set to a flow rate of 5.23 g / second, and was continuously supplied to the mixer for mixing. The monomer aqueous solution temperature at this time was 95 degreeC.

Further, after adding 3 mass% sodium persulfate aqueous solution at a flow rate of 0.223 g / sec, the vehicle runs at a speed of 1.7 m / min kept at about 100 ° C. It was continuously fed to a thickness of 4.9 mm on an endless belt having a defined effective length of 3.2 m and having a glass fiber substrate surface coated with a fluororesin. The aqueous monomer solution supplied on the belt rapidly polymerized and expanded while emitting water vapor. The expansion ratio at the time of maximum expansion was 35 times. In this expansion process, the water-containing polymer peeled irregularly from the belt and contracted about 1 minute after the start of polymerization. The contracted water-containing polymer was irradiated with ultraviolet rays having a light quantity of 210 mJ / cm ² using an ultraviolet irradiation device VB15201BY (manufactured by Ushio Inc.).

  A gel sheet made of a gel-like water-containing polymer was collected at the belt end, and after the gel sheet thickness was measured, it was led to a meat chopper and continuously chopped. The chopped water-containing polymer was dried for 40 minutes with a hot air dryer adjusted to 180 ° C. and then pulverized with a roll mill. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm, so that a base polymer (1) having a particle size of 300 to 600 μm was obtained. Table 1 shows the gel sheet thickness and the physical properties of the base polymer.

(Example 2)
By installing a cooling device after the mixer and cooling, the monomer aqueous solution temperature before adding the sodium persulfate aqueous solution was set to 85 ° C. An aqueous body solution was supplied. The expansion ratio at the time of maximum expansion was 30 times, and contracted about 1 minute after the start of polymerization. The contracted water-containing polymer was irradiated with ultraviolet rays having a light quantity of 210 mJ / cm ² using an ultraviolet irradiation device VB15201BY (manufactured by Ushio Inc.).

  In accordance with the same procedure as in Example 1, the water-containing polymer was recovered, and thickness measurement, shredding, drying, and classification were performed to obtain a base polymer (2). Table 1 shows the gel sheet thickness and the physical properties of the base polymer.

(Comparative Example 1)
As an example in which the water contained in the monomer aqueous solution was polymerized without evaporating in a boiling state and without being expanded, polymerization was performed according to the following procedure. By installing a cooling device after the mixer and cooling, the monomer aqueous solution temperature before adding the sodium persulfate aqueous solution was set to 75 ° C. An aqueous body solution was supplied. The monomer aqueous solution supplied on the belt excessively polymerized and crosslinked before reaching the boiling point, and hardly expanded (expansion ratio of 1). The contracted water-containing polymer was irradiated with ultraviolet rays having a light quantity of 210 mJ / cm ² using an ultraviolet irradiation device VB15201BY (manufactured by Ushio Inc.). In accordance with the same procedure as in Example 1, the water-containing polymer was recovered at the belt end, and thickness measurement, shredding, drying, and classification were performed to obtain a base polymer (3). A portion of the water-containing polymer remained on the belt after the water-containing polymer was recovered. Table 1 shows the gel sheet thickness and the physical properties of the base polymer.

(Comparative Example 2)
In 132 g of acrylic acid, 0.438 g of polyethylene glycol diacrylate (number average molecular weight 523), 0.0163 g of 2-hydroxymethyl-2-methylpropiophenone, and 0.0081 g parts by mass of trisodium diethylenetriaminepentaacetate were dissolved. While stirring the solution (i) with a magnetic stirrer, a solution (ii) obtained by diluting 107 g of a 48.5% by mass aqueous sodium hydroxide solution with 104 g of water was added. The monomer aqueous solution temperature at this time was 95 degreeC. 14.9 g of a 1% by mass aqueous sodium persulfate solution was added thereto and poured into a container having a bottom surface of 250 × 250 mm kept at a temperature of about 100 ° C. The aqueous monomer solution poured into the container quickly polymerized and expanded while emitting water vapor. The expansion ratio at the time of maximum expansion was 13 times, and contracted about 1 minute after the start of polymerization. The contracted water-containing polymer was irradiated with ultraviolet rays having a light amount of 210 mJ / cm ² using an ultraviolet irradiation device VB15201BY (manufactured by Ushio Inc.). 1.9 minutes after pouring into the container, the hydropolymer was removed from the container and chopped with scissors. The chopped water-containing polymer was dried for 40 minutes with a hot air dryer adjusted to 180 ° C. and then pulverized with a roll mill. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a base polymer (4) having a particle size of 300 to 600 μm. Table 1 shows the gel sheet thickness and the physical properties of the base polymer.

表１に示すように、エンドレスベルト上で、単量体水溶液を沸騰状態で蒸発させながら連続重合すると、含水重合体製造の生産性がよい。また、ゲルシートを厚くさせうることも、生産性向上に寄与する。さらに、沸騰させながら含水重合体が形成され、その過程で含水重合体は、不規則状に剥離する。このため、回収作業が容易である。生産性や作業性の向上によって、製造コストが低減され、製造される吸水性樹脂の価格競争力が増加する。

As shown in Table 1, when the continuous polymerization is carried out while evaporating the monomer aqueous solution in a boiling state on the endless belt, the productivity of the production of the hydrous polymer is good. Moreover, it can contribute to productivity improvement that a gel sheet can be made thick. Furthermore, a water-containing polymer is formed while boiling, and in the process, the water-containing polymer peels irregularly. For this reason, collection work is easy. By improving productivity and workability, the manufacturing cost is reduced, and the price competitiveness of the manufactured water absorbent resin is increased.

  Further, the residual monomer content in the water-absorbent resin is small, and the water-absorbent resin formed using the production method of the present invention is of high quality.

  These remarkable effects are the effects brought out by using the production method of the present invention.

It is process drawing of the manufacturing method of a water absorbing resin. It is a schematic diagram of one Embodiment of the superposition | polymerization apparatus of a water absorbing resin.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 102 ... Aqueous solution, 104 ... Polymerization apparatus, 106 ... Endless belt, 108 ... Hydrous polymer, 110 ... Crusher, 112 ... Dryer, 114 ... Classifier, 116 ... Surface cross-linking apparatus, 118 ... Crusher, 120 ... Granulation Machine, 122 ... spray, 124 ... product, 202 ... rotating body, 204 ... rotating body, 206 ... monomer supply means, 208 ... water-containing polymer discharging device.

Claims (5)

Supplying an aqueous solution containing the monomer onto the endless belt (a);
(B) expanding the hydrous polymer by polymerizing the monomer while evaporating water contained in the aqueous solution in a boiling state;
A step (c) of irregularly peeling the hydropolymer from the endless belt by expansion;
And (d) a step of continuously recovering the expanded hydrous polymer by contraction.   The method for producing a water absorbent resin according to claim 1, wherein the monomer is acrylic acid and / or a salt thereof.   The manufacturing method of the water absorbing resin of Claim 1 or 2 whose density | concentration of the said monomer in the aqueous solution supplied to the said endless belt is 30-70 mass%.   The manufacturing method of the water absorbing resin of any one of Claims 1-3 whose temperature of the aqueous solution supplied to the said endless belt is 50-105 degreeC.   Further, the step (e) of crushing the recovered water-containing polymer, the step (f) of obtaining a base polymer by drying the crushed water-containing polymer, and the step (g) of surface-crosslinking the base polymer. The manufacturing method of the water absorbing resin of any one of Claims 1-4 containing this.

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