JP4379071B2 - Method for producing water-absorbing material - Google Patents

Description

  This patent relates to a method for producing an absorbent material comprising a water absorbent resin and fibers. More specifically, the present invention relates to a method for producing a water-absorbing material in which a water-absorbing resin is fixed to a fiber with high density and high strength and also has flexibility. The water-absorbing material of the present invention can be suitably used as an absorbent core for industrial materials such as sanitary materials such as disposable diapers and sanitary products, absorbent materials such as waste water, and holding materials.

  Absorbent materials used as absorbent cores in absorbent articles such as disposable diapers and sanitary products are capable of quickly absorbing liquids such as body fluids and diffusing them throughout the absorbent material, as well as holding them in the absorbent material It is required to have. Moreover, this kind of absorptive material is calculated | required to have a softness | flexibility, in order to ensure the wearer's comfort. Furthermore, in order to reduce transportation and handling costs, the absorbent material is required to be thinner.

  Absorbent cores composed of a water-absorbent resin and fibers such as pulp are widely known as satisfying these requirements regarding absorption characteristics and flexibility. In general, a water-absorbing resin can absorb and retain a large amount of liquid, but its absorption rate is not so fast. On the other hand, fibers such as pulp do not have a large liquid absorption capacity, but their absorption rate and diffusion rate are relatively high. Therefore, when the liquid is released to the absorbent article, the liquid is first absorbed and diffused by the pulp having a high absorption rate, and then the water absorbent resin slowly absorbs and holds the liquid absorbed and diffused by the pulp. The absorbent core is designed.

  On the other hand, in order to satisfy the demand for thinning, in order to secure the liquid absorption capacity of the water absorbent core, the pulp content is reduced while maintaining the content of the absorbent resin that determines the absorption capacity (that is, the water absorbent resin). Higher concentration) is required. However, when the amount of the pulp is reduced, the initial absorbability and diffusibility of the liquid, which are functions that the pulp should bear, are reduced, and the flexibility of the absorbent article is also impaired. Therefore, in reality, the absorbent core is designed at a compromise between these conflicting requirements.

  As a method for producing a water-absorbing material comprising a water-absorbing resin and pulp, an air-laid method in which mixed phase air in which the water-absorbing resin and pulp are mixed is widely known. However, in the absorptive material obtained by this method, the water-absorbing resin is only present dispersed in the pulp. For this reason, the water-absorbing resin is easy to drop off from the water-absorbing material, and the water-absorbing resin leaks from the water-absorbing material when force is applied to the water-absorbing material after the water-absorbing resin absorbs the liquid. There was a problem with fixability in the water-absorbing material.

  As a method for improving the fixing property of the water absorbent resin in the water absorbent material, a method of bonding the water absorbent resin to a substrate with a binder is known. However, the water-absorbing material obtained by this method has problems such as the binder adhering to the surface of the water-absorbing resin impairs the water-absorbing property of the water-absorbing resin, and the water-absorbing resin is not sufficiently fixed after water absorption. The performance that the water-absorbing material should have was insufficient. There was also a problem in terms of manufacturing cost.

  As another method, JP-A-62-262829 and JP-A-3-287870 are methods in which a monomer solution comprising acrylic acid and acrylate is directly applied or dispersed on a substrate and then the monomer is polymerized on the substrate. And JP-A-4-218502. However, in this method, the water-absorbing resin can be fixed only on the surface of the base material, and when a large amount of monomer is applied to the base material, the flexibility of the water-absorbing material is impaired.

  Further, Japanese Patent Publication No. 5-58030 includes a fibrous base material at least partly composed of hydrophobic fibers and a water absorbent resin attached to the base material, and at least part of the water absorbent resin is based on the base material. There is described a water-absorbing article characterized by wrapping a material in a substantially spherical shape and adhering discontinuously. According to this technique, since the water absorbent resin is discontinuously fixed to the fiber base material, the flexibility of the composite can be secured, and the water absorbent resin can also be sufficiently fixed. However, in this technique, since the water-absorbent resin needs to be fixed on the fiber surface discontinuously, there is a limit to the amount of the water-absorbent resin supported on the fiber. Furthermore, since the water-absorbent resin wraps the fiber, the inhibition of the swelling of the water-absorbent resin by the fiber is inevitable. Moreover, in order to control the adhesion form of a water absorbing resin and a fiber, there also exists a restriction | limiting that the base material used must be a hydrophobic fiber.

  Furthermore, in JP-A-63-275355, JP-A-61-62463, and JP-A-63-63723, the water-absorbent resin is kneaded and dispersed with fibers in a state where water or a water-containing solvent is absorbed and swollen. There has been proposed a water-absorbent composite in which at least a part of the fiber length is post-dried and pulverized and embedded in a water-absorbent resin, and a method for producing the same. In this method, in order to obtain a composite having a certain size, a pulverization treatment is required after kneading and drying. For this reason, generation | occurrence | production of a crushed product cannot be avoided, but problems, such as generation | occurrence | production of fiber waste and a water-absorbing-resin fine particle, generation | occurrence | production of non-fixed water-absorbing-resin, will arise.

  JP-A-11-93073 discloses a composite of a water absorbent resin and a fiber in which a substantially spherical water absorbent resin is discontinuously fixed on the surface of a non-molded fiber and the non-molded fiber is deposited, or A composite body in which non-molded fibers are bonded via the water absorbent resin is disclosed. From the point that the water-absorbing resin and the fiber are adhered, it can be said that the immobilization of the water-absorbing resin has been realized. However, as long as the adhesion is on the surface of the fiber, the adhesion form must be point adhesion or wire adhesion, and the adhesive strength of the water-absorbent resin to the fiber in the dry state and the fixability after water absorption cannot be said to be sufficient. . On the other hand, there is a description of the case where the fibers are encased in the water-absorbent resin, but there are the same drawbacks as in Japanese Patent Publication No. 5-58030. In addition, when the water absorbent resin absorbs water and the surface swells and expands, there is a problem that the peeled water absorbent resin can be easily moved. Furthermore, since the fibers are bonded via a water-absorbent resin, it is difficult to open the composite. If the fiber is opened forcibly, the water-absorbent resin itself is damaged, resulting in a decrease in water absorption performance. It causes problems such as occurrence. Therefore, it is difficult to uniformly mix this composite with other materials after opening.

JP-A-62-62829 JP-A-3-287870 JP-A-4-218502 Japanese Patent Publication No. 5-58030 JP-A 63-275355 Japanese Patent Laid-Open No. 61-62463 JP-A 63-63723 Japanese Patent Laid-Open No. 11-93073

  An object of the present invention is to provide a method for producing an absorbent material capable of rapidly absorbing a sufficient amount of liquid to diffuse and hold the liquid. It is another object of the present invention to provide a method capable of producing a flexible and thin absorbent material by a simple method. Furthermore, it is an object of the present invention to provide a method for producing a water-absorbing material having good fixability of the water-absorbing resin without generating fiber waste and water-absorbing resin fine particles.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by the production method of the present invention described below.

That is, this invention provides the manufacturing method of the water absorbing material which consists of a water absorbing resin and a fiber including the following process (A)-(D).
(A) A droplet containing a polymerizable monomer that gives a water-absorbing resin and / or a polymerized product of the polymerizable monomer and a fiber that has been previously opened at a plurality of positions where the monomer conversion rate of the polymerizable monomer is different. A composite step (B) for obtaining a composite comprising a water-absorbent resin and a fiber having a structure in which the water-absorbent resin adheres to the fiber by causing collision and further polymerization of the polymerizable monomer (B) Recovery step for collecting (C) Drying step for drying the aggregate (D) Molding step for molding the aggregate

  Each of the above steps is preferably performed in the order of a compounding step, a recovery step, a forming step, and a drying step. Moreover, it is also preferable to perform in order of a composite process, a collection | recovery process, a drying process, and a formation process. Between the drying step and the molding step, it is possible to preferably include a fiber opening step of opening the aggregate obtained in the drying step and obtaining an aggregate composed of the opened water absorbent resin and fibers. Moreover, the sieving process which isolate | separates the fiber which has not adhered the water absorbing resin can be preferably included between the opening process and the molding process. The fibers separated in the sieving step can be used in the compounding step. In the molding step, the aggregate composed of the water-absorbing resin and the fiber and the water-absorbing resin and / or the fiber may be mixed. At this time, the fibers separated in the sieving step may be used in the molding step. All the steps of the present invention are preferably carried out in a continuous operation.

  In the production method of the present invention, a partially neutralized acrylic acid polymer crosslinked product can be preferably used as the water absorbent resin. Preferably, a compound having two or more reactive groups capable of reacting with a carboxyl group in a molecule is imparted to the aggregate between the recovery step and the drying step, and the aggregate is dried and absorbs water in the drying step. The surface of the resin can be crosslinked. A glycidyl group can be preferably employed as the reactive group here.

  In the production method of the present invention, the composite step is performed in the reactor, and the aggregate of the composite deposited on the bottom of the reactor in the recovery step can be recovered. Further, in the compounding process, the fibers are supplied into the reactor as a mixed phase flow with air, and in the recovery process, the lower part of the mesh installed at the bottom of the reactor is in a reduced pressure state in the reactor so that the aggregate is placed on the mesh. It can be deposited and recovered. At this time, it is preferable to use the air sucked downward through the mesh to be mixed with fibers in the compounding step to form a multiphase flow.

  The composite formed by the production method of the present invention includes one water-absorbing resin particle and two or more fibers, and the water-absorbing resin particles are substantially spherical, and among the two or more fibers One or more of the fibers are partially embedded in the resin particles and partially exposed from the resin particles, and at least one of the two or more fibers is the fiber. It is preferable that a part of the fiber is bonded to the surface of the resin particle without being embedded in the resin particle (composite A). The composite formed by the production method of the present invention includes one or more water-absorbing resin particles and one or more fibers, and the water-absorbing resin particles are substantially spherical, The fibers are partly embedded in the resin particles, partly exposed from the resin particles, and none of the fibers are bonded to the surface of the resin particles. Is also preferred (complex B). Further, the composite formed by the production method of the present invention includes one or more water-absorbing resin particles and one or more fibers, and the water-absorbing resin particles are substantially spherical, It is also preferred that the fiber has a part of the fiber adhered to the surface of the resin particle, and none of the fiber is embedded in the resin particle (composite C).

  According to the production method of the present invention, it is possible to easily produce an absorptive material that can rapidly absorb a sufficient amount of liquid to diffuse and retain the liquid. Since the water-absorbing material produced by the production method of the present invention is flexible and can be formed into a thin shape, it can be widely used in water-absorbing articles such as diapers and sanitary products. Further, according to the production method of the present invention, it is possible to produce a water-absorbing material having good fixability of the water-absorbent resin without generating fiber waste and water-absorbent resin fine particles.

BEST MODE FOR CARRYING OUT THE INVENTION

  Below, the manufacturing method of the water absorbing material of this invention is demonstrated in detail. In the production method of the present invention, the compounding step, the recovery step, the drying step, and the molding step are essential steps. First, these essential steps will be described in order, then optional steps will be described, and a general manufacturing method combining these steps will be described. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[I] Essential Step (I-1) Compounding Step In the compounding step, droplets containing a polymerizable monomer that gives a water-absorbent resin and / or a polymerized product of the polymerizable monomer are dispersed in the gas phase. While performing the polymerization, a fiber that has been previously opened so as to collide with the dispersed droplets is supplied. This compounding step is usually performed in a reactor such as a polymerization tank. Usually, a polymerizable monomer aqueous solution containing a polymerization initiator is supplied to a monomer supply nozzle installed in the upper part of the polymerization tank, and the polymerizable monomer aqueous solution is discharged in droplets from the nozzle. While being dropped, the polymerization is carried out while bringing it into contact with the fibers supplied into the polymerization tank to carry out the compounding.

(Polymerizable monomer)
As the polymerizable monomer used for polymerization, any monomer can be used as long as it gives a water-absorbing resin by polymerization. Usually, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid and itaconic acid are used. If desired, some of these may be used in combination, or other monomers such as (meth) acrylamide and 2-hydroxyethyl (meth) acrylate may be used in combination. Among these, it is preferable to use acrylic acid or methacrylic acid. Particularly preferred is acrylic acid, and it is usually preferred to use acrylic acid alone or a monomer mixture in which acrylic acid accounts for 50 mol% or more, particularly 80 mol% or more.

  In addition, it is preferable to use at least a part of these unsaturated carboxylic acids as water-soluble salts such as alkali metal salts and ammonium salts. By carrying out like this, the water absorption ability of the water-absorbing resin obtained can be improved. For example, in the case of acrylic acid, the water-absorbing ability of the resulting water-absorbent resin can be remarkably improved by subjecting the polymerization to 20% or more, preferably 20 to 90%, as an alkali metal salt or ammonium salt.

  In the present invention, a small amount of a crosslinking agent can be contained in the solution of the polymerizable monomer to be subjected to polymerization, if desired. As the crosslinking agent, for example, N, N′-methylenebis (meth) acrylamide or (poly) ethylene glycol diglycidyl ether can be used, and the amount of the crosslinking agent used is usually 0.001 to 1 wt. %, Preferably 0.01 to 0.5% by weight. When there is too much quantity of a crosslinking agent, there exists a tendency for the water absorption ability of the water absorbing resin particle to produce | generate to fall.

  The concentration of the polymerizable monomer in the monomer solution is generally 20% by weight or more, and preferably 25% by weight or more in total of the weights of the free form and the salt form. If the concentration of the monomer is too small, it is difficult to form droplets having an appropriate viscosity, and when the resin particles collide with the fibers, the shape thereof is liable to break down. As a result, the properties of the water-absorbing composite finally obtained are It tends to be inferior. The upper limit of the monomer concentration is about 80% by weight from the viewpoint of handleability.

(Polymerization initiator)
As the polymerization initiator, it is preferable to use a redox polymerization initiator comprising a combination of an oxidizing radical generator and a reducing agent. Hydrogen peroxide is preferably used as the radical generator, but persulfates such as ammonium persulfate and potassium persulfate, hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide, etc. Cerium salts, permanganates, chlorites, hypochlorites and the like can be used. These radical generators are preferably used in an amount of usually 0.01 to 10% by weight, particularly 0.1 to 2% by weight, based on the polymerizable monomer.

  As the reducing agent, it is preferable to use L-ascorbic acid or an alkali metal salt thereof. In addition, sulfites such as sodium sulfite and sodium hydrogen sulfite, sodium thiosulfate, cobalt acetate, copper sulfate, ferrous sulfate and the like can be used. It can also be used. These reducing agents are preferably used in an amount of usually 0.001 to 10% by weight, particularly 0.01 to 2% by weight, based on the polymerizable monomer.

(fiber)
As the fiber, synthetic fiber, natural fiber, semi-synthetic fiber, inorganic fiber and the like can be used.
The fibers used are preferably hydrophilic fibers such as pulp, rayon, cotton, regenerated cellulose and other cellulose fibers, and are those that enjoy the benefits of the present invention. Those having hydrophilic fibers as the main component are particularly preferred fibers in the present invention. On the other hand, from the viewpoint of improving the diffusibility of water, hydrophobic fibers can also be used, for example, polyester-based, polyethylene-based, polypropylene-based, polystyrene-based, polyamide-based, polyvinyl alcohol-based, polyvinyl chloride-based, Polyvinylidene chloride-based, polyacrylonitrile-based, polyurea-based, polyurethane-based, polyfluoroethylene-based, and polycyanide vinylidene-based fibers can be exemplified. Of course, it is also possible to use a combination of hydrophilic fibers and hydrophobic fibers.

  Preferred fibers for use in the present invention are those having a fiber length of 50 to 50,000 μm. More preferably, it is 100-30,000 micrometers, More preferably, it is 500-10,000 micrometers. When a fiber having a fiber length longer than 50,000 μm is used, the fiber tends to adhere to a plurality of water absorbent resin particles, so that the independence of the plurality of water absorbent resin particles cannot be ensured, and the composite is difficult to open. There is. On the other hand, when a fiber having a fiber length shorter than 50 μm is used, it tends to be difficult to embed or bond the fiber to the water absorbent resin.

  The fiber diameter of the fiber used in the present invention is preferably 0.1 to 500 dtex, more preferably 0.1 to 100 dtex, still more preferably 1 to 50 dtex, and particularly preferably 1 to 10 dtex. When the fiber diameter is larger than 500 dtex, not only is the rigidity of the fiber too large, it becomes difficult to embed or adhere to the water-absorbent resin, but compression molding becomes difficult, which may be undesirable for thinning. In addition, it may be stiff or tingling for uses such as sanitary products, and the touch may not be preferable. On the other hand, if the fiber diameter is smaller than 0.1 dtex, the above-mentioned water conductivity and diffusibility tend not to be ensured because the fiber is too thin. In addition, since the rigidity is insufficient, the blocking phenomenon that the water-absorbing resins come into contact with each other to impair the water conductivity may not be prevented.

  The fibers are preferably in a state where they are dispersed as evenly as possible. In general, a technique called opening is used to ensure uniformity. As specific methods, “Fiber Handbook (Processing Edition)” (Fiber Society of Japan, Maruzen, 1969) introduced on page 18 and below, cotton spinning type, eyelash type, woolen type, hemp type, silk spinning type, etc. It can be used as appropriate. It is also possible to charge fibers known as flocking and uniformly disperse them using electrostatic repulsion between the fibers. In the present specification, “opening” includes the concept of both defibration and fiberization. Defibration includes tearing a sheet-like material such as nylon into strips or fibers. In addition, the fiberization includes cutting the base paper-like cellulose into pulp.

(Polymerization method)
Polymerization can be carried out by various known methods. According to the method described in JP-A-2000-198805, each of the nozzles in which a polymerizable monomer aqueous solution containing a radical generator and a polymerizable monomer aqueous solution containing a reducing agent are installed opposite to each other on the upper part of the polymerization tank. It is preferable that the liquid is ejected in a liquid column form, and both liquids collide with each other in the air to be mixed and dispersed into droplets (FIG. 2). For example, a first liquid containing an oxidizing agent and a polymerizable monomer aqueous solution constituting a redox polymerization initiator, and a second liquid containing a reducing agent and a polymerizable monomer aqueous solution constituting a redox polymerization initiator are vapor-phased. The method of mixing in can be illustrated as a preferable method. The size of the droplet is usually 5 to 3000 μm, particularly preferably 50 to 1000 μm. As soon as the two liquids are mixed, the polymerization starts, and the polymerization proceeds in the droplets and falls in the polymerization tank. The atmosphere in the polymerization tank is arbitrary as long as it does not interfere with the polymerization reaction. Usually, nitrogen, helium, carbon dioxide, or the like is used as the atmospheric gas, but air or water vapor can also be used. The temperature of the atmosphere is usually room temperature to 150 ° C, preferably room temperature to 100 ° C. In addition, what is necessary is just to set the amount of water vapor | steam in the case of sending water vapor | steam in atmosphere from the point of how much the amount of water evaporation from monomer aqueous solution shall be made. The amount of water evaporated from the monomer aqueous solution can be determined based on the concentration of the monomer aqueous solution used for the reaction, the moisture content desired for the water-absorbing resin particles to be generated, and the like.

(Combination of water absorbent resin and fiber)
In the present invention, a fiber composed of a water-absorbing resin and a fiber is fed by supplying pre-opened fibers into the polymerization tank, colliding the falling monomer droplets with the fibers and causing the polymerization of the monomers to proceed. Form the body. The adhesion form of the water-absorbent resin and the fiber can be controlled by the monomer conversion rate at the time of collision between the droplet and the fiber, the fiber type used, and the like.
In the form status of the complex consisting of the water-absorbing resin and the fiber, composite A described below, the complex B, mention may be made of composites C. The composite A is composed of one water-absorbing resin particle and two or more fibers, the water-absorbing resin particles are substantially spherical, and one or more of the two or more fibers are part of the fibers. While being embedded in the resin particles, a part is exposed from the resin particles, and at least one of the two or more fibers is not embedded in the resin particles. , A part of the fiber has a structure adhered to the surface of the resin particle. The composite B is composed of one or more water-absorbing resin particles and one or more fibers, and the water-absorbing resin particles are substantially spherical, and one or more of the fibers of the one or more fibers are in the resin particles. It is embedded and partly exposed from the resin particles, and all the fibers have a structure not adhered to the surface of the resin particles. The composite C is composed of one or more water-absorbing resin particles and one or more fibers, and the water-absorbing resin particles are substantially spherical, and one or more of the fibers are part of the surface of the resin particles. The fibers have a structure in which none of the fibers are embedded in the resin particles.

Further, in the composite A, at least one fiber is embedded in the inside of the substantially spherical water-absorbent resin particle in the same composite, and a part of the fiber is exposed from the particle. In addition, at least one fiber is not embedded in the inside of the substantially spherical water-absorbent resin particle, and a part of the fiber is on the surface of the particle. It has a structure that adheres along. For this reason, the composite has excellent water conductivity to the water absorbent resin described above, diffusibility in the water absorbent material, and fixability of the water absorbent resin in the water absorbent material before and after water absorption. A water-absorbing material may be provided. The composite A is most desirable when used for sanitary materials such as disposable diapers where the water absorption rate and diffusion rate are fast and the water absorbent resin particles are required to be strongly fixed in the water absorbent material.
In the composite B, the fibers embedded in the water-absorbing resin particles increase the water conductivity of the water-absorbing resin particles and improve the fixability of the water-absorbing resin particles in the water-absorbing material before and after water absorption. Has an effect. That is, the composite B can provide a water-absorbing material having a high water absorption rate and excellent fixability of the water-absorbing resin in the water-absorbing material.
In the composite C, the fibers adhered to the surface of the water-absorbent resin particles improve the diffusibility of water in the water-absorbent material, and the water-absorbent resin particles come into contact with each other by swelling during water absorption. Has the effect of preventing the so-called gel blocking phenomenon that interferes. That is, the composite C can provide a water-absorbing material excellent in water diffusibility.
In the production method of the present invention, only one of the composites A to C may be selectively produced, or a mixture thereof may be produced. When manufacturing a mixture, you may select a manufacturing condition suitably and produce | generate a mixture, and you may obtain a mixture by manufacturing and mixing 2 or more types of composite_body | complex separately.

  The dry weight ratio between the fibers and the water-absorbent resin particles in each composite is preferably 1: 1 to 1: 1,000,000, more preferably 1: 2 to 1: 100,000. Even more preferably, it is 1: 3 to 1: 10,000.

  The conversion rate at the time when the droplets undergoing polymerization collide with the gas phase or the fibers is usually in the range of 0 to 90%, preferably 5 to 80%, more preferably 10 to 70%. If the conversion rate is higher than 90%, the fibers used may not be embedded or adhered to the water-absorbent resin.

  In general, if a droplet collides with a fiber in a state where the monomer conversion rate is low, it is easy to obtain a composite B in which the fiber is embedded in the water-absorbent resin, and the droplet is converted into a fiber in a state where the monomer conversion rate is high. If the fibers collide, it is easy to obtain the composite C in which the fibers are bonded to the surface of the water-absorbent resin, and if the fibers collide with the liquid droplets at a plurality of positions having different monomer conversion rates, some of the fibers are absorbed in the water-absorbent resin. It is easy to obtain a composite A in which other fibers are bonded to the surface of the water-absorbent resin while being embedded in the interior of the resin. In order to obtain a composite having a desired structure, the monomer conversion rate of the droplets when colliding with the fibers is appropriately determined in consideration of the fiber type and the like. When the fibers collide with the droplets at a plurality of positions having different monomer conversion rates, it is desirable to select any monomer conversion rate from the above range.

(Fiber transport method)
The method for supplying the fibers to contact the droplets during polymerization can be selected from generally known transport methods. The spatial density of the fibers in the polymerization tank is preferably set so as to be in the range of 0.005 to 1000 g / m ³ . If this upper limit is exceeded, fibers that are not embedded in the water-absorbent resin particles are generated, and if the lower limit is not reached, water-absorbing resin particles that do not embed fibers are generated, and the yield of the composite tends to be relatively lowered. .
In order to supply the fibers in the finest and uniform state possible, it is preferable to supply the fibers as a multiphase flow with the gas. As the gas used at that time, those mentioned above as the gas phase gas that gives the reaction field can be used. Among these, it is preferable to use air from an economical viewpoint and a viewpoint of reducing environmental load.

The weight mixing ratio of the supplied fiber and gas is set to 1:20 or less, and the linear velocity of the gas in the supplied pipe is preferably set to 1 to 50 m / s, desirably 5 to 20 m / s. If the linear velocity of the gas exceeds 50 m / s, the trajectory of the progress of polymerization in the reaction field may be disturbed, and adhesion to the inner surface of the polymerization tank may become a problem. On the other hand, if the gas linear velocity is less than 1 m / s, fiber uniformity may not be ensured.
It is desirable to select the temperature of the gas supplied as a multiphase flow within a range that does not significantly impair the polymerization. Specifically, it is room temperature to 150 ° C, desirably room temperature to 100 ° C. From the viewpoint of fiber conveyance, it is preferable that the humidity in the gas is low, but if the humidity is too low, the humidity in the polymerization tank is lowered, and before the polymerization proceeds, the water in the monomer aqueous solution evaporates and the monomer is removed. As a result, the polymerization rate may be significantly reduced, or the polymerization may be stopped in the middle.

(I-2) Recovery step The recovery step is a step of recovering the composite made of the water-absorbent resin and fibers obtained in the composite step as an aggregate. Preferred is an embodiment in which the aggregate is deposited on the bottom of the polymerization tank and the aggregate is recovered as a deposit. Specifically, a mesh or the like is installed at the bottom of the polymerization tank, and the assembly is efficiently deposited and recovered on the mesh by setting the area under the mesh to be in a slightly reduced pressure state than in the polymerization tank. The degree of vacuum under the mesh is usually about −100 to −10000 Pa with respect to the inside of the polymerization tank.

  The recovery can be performed in batch operation or continuous operation, but continuous operation is desirable. In the continuous operation, aggregates are continuously deposited on a mesh belt installed at the bottom of the polymerization tank, and the aggregates are continuously collected as deposits. For example, specifically, a vacuum conveyor having a mesh belt capable of accumulating aggregates is installed at the bottom of the polymerization tank, and fibers are fed into the polymerization tank in a multiphase flow with air, and from the polymerization tank bottom by the vacuum conveyor. Air is sucked downward, the composite is deposited on the mesh belt, and the aggregate of the composite composed of the water-absorbent resin and fibers is continuously collected as a deposit. At this time, since the air sucked and collected by the vacuum conveyor contains some fine fibers and monomer vapor, it is desirable to recycle as air for supplying fibers in the compounding step.

(I-3) Drying step The drying step is a step of reducing the moisture content of the aggregate obtained through the compounding step and the recovery step. Usually, it dries until the water content becomes 10% by weight or less. The drying temperature is preferably set within a range of 100 to 150 ° C. If the drying temperature is too low, drying takes a long time and the efficiency becomes poor. On the other hand, when the drying temperature is too high, the polymer chain is cleaved, the residual monomer in the aggregate is increased, and the quality of the water is increased.
In addition, although the drying efficiency is lowered, by performing the drying process in a state where the relative humidity is 50% or more, it is possible to perform the residual monomer process described later simultaneously with the drying.

(I-4) Molding step The molding step is a step of forming an aggregate composed of the water-absorbent resin and fibers obtained through the compounding step and the recovery step into a desired shape. Molding can be performed while appropriately adjusting conditions such as pressure, temperature, and humidity.
Before or during molding, depending on the performance required for the water-absorbing material to be manufactured, fibers such as pulp and water-absorbing resin are further added to the aggregate to adjust the content ratio of the water-absorbing resin and fibers. May be. Usually, the dry weight ratio of the fibers that are not embedded or adhered to the water absorbent resin and the water absorbent resin is preferably in the range of 95: 5 to 5:95. More preferably, it is 90: 10-7: 93, and still more preferably 85: 15-10: 90. If the ratio of the water-absorbing resin is too large, gel blocking is likely to occur, and conversely if the ratio of the water-absorbing resin is too small, the water-absorbing capacity becomes insufficient.

In the molding step, the density of the molded body obtained after molding is usually 0.20 to 0.85 g / cm ³ , preferably 0.3 to 0.85 g / cm ³ , more preferably 0.4 to 0.85 g / cm ³ . ^Mold to be ³ . Moreover, it shape | molds so that the thickness of a molded object may be 0.2-20 mm normally, Preferably it is 0.2-10 mm, More preferably, it is 0.2-5 mm.
When pressurizing in the forming step, for example, a flat press or a roll press can be used as the press. The pressure is not particularly limited as long as the water absorbent resin particles do not break. If the water-absorbent resin particles break, the broken particle pieces will detach from the fibers and leak from the absorbent article, or the water-absorbing gel may leak from the fibers and leak or move during swelling, thereby reducing the performance of the absorbent article. It will be.
When heating in a shaping | molding process, it can heat to the temperature below the melting point of the fiber to be used. When heated above the melting point, the fibers bind to form a network, and the function of the composite is impaired.
When humidifying in the molding process, it is usually humidified using steam. Depending on the humidification conditions, the density of the molded body can be improved, and the fixing property of the water absorbent resin particles to the fibers can be improved.

[II] Arbitrary Step (II-1) Opening Step The opening step is to open an aggregate composed of the water-absorbent resin and fibers obtained through the composite step and the recovery step, and to make a smaller aggregate or composite It is a process of making a body.
Since the composites obtained by the present invention are independent of each other, they can be easily opened. Opening can be performed using the opening method shown in the above-mentioned fiber section, but an apparatus and conditions that do not damage the water-absorbent resin particles due to mechanical impact must be selected. In the fiber opening process, it is not necessary to open all the components of the aggregate to a composite.

(II-2) Sieving step A part of the fibers loosely adhered to the surface of the water absorbent resin is removed from the water absorbent resin by the opening process. In the sieving step, fibers that have not been combined in the combining step and independent fibers that are not attached to the resin, such as fibers that have been removed from the composite in the opening step, are separated from the composite. The separated fibers can be recycled to the compounding process or molding process. The sieving can be performed by employing a commonly used sieving means.

(II-3) Surface cross-linking step The surface cross-linking step is a step of cross-linking the surface of the water-absorbent resin particles with a cross-linking agent in order to improve water absorption performance. The surface cross-linking agent is applied to the composite, assembly, or molded body in any step after the compounding step and the recovery step and before the drying step. And usually, a crosslinking reaction is allowed to proceed simultaneously with drying by heat treatment in the drying step, and a crosslinked structure is selectively introduced on the surface of the water-absorbent resin particles.
In general, it is known to improve the properties of resin particles by applying a crosslinking agent to the surface of powdered water-absorbent resin particles and then heating to crosslink the surface, forming a crosslinked structure selectively on the surface. As a result, it is considered that the shape can be maintained without inhibiting the swelling when water is absorbed and swollen.

(Surface cross-linking agent)
Examples of the surface cross-linking agent include polyfunctional compounds that can be copolymerized with polymerizable monomers such as N, N′-methylenebis (meth) acrylamide and (poly) ethylene glycol bis (meth) acrylate, and polyfunctional compounds having two or more glycidyl groups. A compound having a plurality of functional groups capable of reacting with a carboxylic acid group such as a valent glycidyl compound is preferably used. Among the latter, aliphatic polyhydric alcohol polyglycidyl ether is particularly preferable. Specifically, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, polyglycerin polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, pentaerythritol polyglycidyl ether Etc. are preferably used. Some of these may be used in combination if desired. Among these, ethylene glycol diglycidyl ether and glycerin (di, tri) glycidyl ether are preferable.

(Applying surface cross-linking agent)
The amount of these surface cross-linking agents used is usually 0.005 to 1% by weight, preferably 0.1 to 0.5% by weight, more preferably 0.2 to 0.5% by weight, based on the composite. . When using a surface crosslinking agent, it is preferable to spray as a solution diluted with water, ethanol, methanol or the like so as to be uniformly applied to the entire composite. The concentration of the surface crosslinking agent solution is usually 0.1 to 10% by weight, preferably 0.1 to 1% by weight, more preferably 0.2 to 0.5% by weight. The surface cross-linking agent solution improves the solubility and dispersibility of the cross-linking agent and further promotes diffusion on the particle surface when applied to the water-absorbent resin particle precursor. May be included.
The surface cross-linking agent solution can usually be sprayed onto the composite, assembly or molded body using a sprayer. Also, a method of applying by rotating a roll brush whose lower part is immersed in a tank containing a surface cross-linking agent solution and bringing the surface with the surface cross-linking agent solution attached into contact with the surface of the molded article having water-absorbing resin particles. It may be used. At this time, the surface cross-linking agent solution is once applied excessively, and thereafter, the water-absorbent resin particles are lightly squeezed to such an extent that the water-absorbent resin particles are not crushed or wind is blown to remove the surplus surface cross-linking agent solution. It may be. The application of the surface crosslinking agent solution can be performed at room temperature.

(heating)
The composite to which the surface cross-linking agent solution is applied usually proceeds with the cross-linking reaction by heating. Heating may be performed immediately after applying the surface cross-linking agent, or may be performed simultaneously with drying in a drying step performed later. Preferably, heating is performed within 2 minutes after the application of the surface cross-linking agent solution. Thereby, the cross-linking agent can be reacted substantially only on the surface of the water-absorbent resin particles, and the formation of cross-links inside can be easily suppressed.
The heating conditions need to be appropriately selected depending on the type of the surface cross-linking agent to be used, but usually the cross-linking reaction is advanced by heating at a temperature of 100 ° C. or higher for 10 minutes or longer. At this time, since water evaporates from the water absorbent resin particles simultaneously with heating, it is possible to prevent the crosslinking agent from penetrating into the water absorbent resin particles during the heating. Preferably, the heating conditions are controlled so that the water content of the water-absorbent resin particles is 15% by weight or less within 10 minutes from the start of heating. More preferably, the water content is 15% by weight or less within 7 minutes, particularly within 5 minutes from the start of heating.

(II-4) Pre-drying step The pre-drying step is a step performed to increase the processing efficiency of the subsequent steps by preliminarily lowering the moisture content of the aggregate obtained in the compounding step. For example, in a manufacturing process of a water-absorbing material including a compounding process, a recovery process, a fiber opening process, a sieving process, a surface crosslinking process, a molding process, and a drying process, the water absorbent resin obtained through the compounding process and the recovery process And an assembly of fibers are preliminarily dried to a moisture content level at which fiber opening treatment is possible. The aggregate composed of the preliminarily dried water-absorbent resin and fibers can be easily separated into a composite in which the fibers are attached to the water-absorbent resin and fibers that are not attached to the water-absorbent resin by opening and sieving. . The composite composed of the separated water-absorbing resin and fibers is, for example, when subjected to the surface cross-linking step, the surface of the water-absorbing resin particles is effectively removed from the surface cross-linking material because no extra fibers are attached to the surface. Can be applied.

The water content of the water-absorbing resin particles constituting the composite obtained by preliminary drying is usually 10 to 30% by weight (based on the water-containing water-absorbing resin). If the water content is too low, the surface cross-linking agent only reaches the surface of the particles, and the desired water absorption performance cannot be obtained. If the moisture content is too high, the fiber opening process becomes difficult. The preliminary drying temperature is usually 100 to 150 ° C. as in the drying step. If the drying temperature is too low, the drying takes a long time and the efficiency is poor. On the other hand, when the drying temperature is too high, the polymer chain is cleaved, the residual monomer in the complex is increased, and the water-soluble content is increased.
In addition, although the drying efficiency is lowered, the residual monomer can be processed simultaneously with the preliminary drying by performing the preliminary drying process at a relative humidity of 50% or more.

(II-5) Residual monomer treatment step The residual monomer treatment step is a step of reducing the residual amount of monomer contained in the composite. Examples of the method for treating the residual monomer include 1) a method for allowing the polymerization of the monomer to proceed, 2) a method for leading the monomer to another derivative, and 3) a method for removing the monomer.

(Method of advancing monomer polymerization)
Examples of the method of proceeding the polymerization of the monomer of 1) include, for example, a method of further heating the composite, a method of heating after adding a catalyst or a catalyst component for promoting polymerization of the monomer to the composite, a method of irradiating with ultraviolet rays, an electromagnetic Examples include a method of irradiating radiation or fine particle ionizing radiation.

In the method of further heating the composite, the composite is heat-treated at 100 to 250 ° C. to polymerize monomers remaining in the composite.
The method of adding a catalyst or catalyst component that promotes the polymerization of the monomer to the composite is, for example, when the polymerization is performed using a redox polymerization initiator, since the radical generator often remains, What is necessary is just to give a reducing agent solution to a body. As the reducing agent, sodium sulfite, sodium hydrogen sulfite, L-ascorbic acid or the like used as a redox-based initiator may be used, and these are usually imparted to the composite as a 0.5 to 5% by weight aqueous solution. The amount of the reducing agent applied is preferably 0.1 to 2% by weight based on the dry resin. Application | coating of a reducing agent solution can be performed by arbitrary methods, such as spraying using an atomizer and immersing in a reducing agent solution. The composite provided with the reducing agent is then heated to polymerize the polymerizable monomer. Heating may be performed, for example, at 100 to 150 ° C. for about 10 to 30 minutes. Although the moisture content of the composite is reduced by this heating, if the moisture content is not sufficiently reduced, it may be further dried with a dryer or the like.

  In the method of irradiating the composite with ultraviolet rays, an ordinary ultraviolet lamp may be used. Irradiation intensity, irradiation time, and the like vary depending on the type of fiber used, the amount of residual monomer impregnation, and the like. In general, an ultraviolet lamp of 10 to 200 w / cm, preferably 30 to 120 w / cm is used. 1 second to 30 minutes, with a ramp-complex spacing of 2 to 30 cm. The water content in the composite at this time is generally 0.01 to 40 parts by weight, preferably 0.1 to 1.0 parts by weight, relative to 1 part by weight of the polymer. Less than 0.01 parts by weight or more than 40 parts by weight is not preferable because it significantly affects the reduction of residual monomers. As an atmosphere when irradiating with ultraviolet rays, any of vacuum, presence of an inorganic gas such as nitrogen, argon and helium, or air can be used. Moreover, there is no restriction | limiting in particular about irradiation temperature, The objective can fully be achieved at room temperature. There is no restriction | limiting in particular also about the ultraviolet irradiation device to be used, Arbitrary methods, such as the method of irradiating for a fixed time for a fixed time, or the method of irradiating continuously with a belt conveyor, can be used.

  High energy radiation such as accelerated electrons and gamma rays is used for the method of irradiating the composite. The amount of radiation to be irradiated varies depending on the amount of residual monomer in the complex, the amount of water, and the like, but is generally 0.01 to 100 megarads, preferably 0.1 to 50 megarads. When the dose exceeds 100 megarads, the amount of water absorption becomes extremely small. When the dose is less than 0.01 megarad, the water absorption capacity and the water absorption rate are large, and it is difficult to obtain a particularly small residual monomer. Further, the water content of the composite at this time is generally 40 parts by weight or less, preferably 10 parts by weight or less, relative to 1 part by weight of the polymer. An amount of water exceeding 40 parts by weight is not preferable because the effect of improving the water absorption rate is small and particularly has a significant effect on the reduction of unpolymerized monomers. As the atmosphere when the composite is irradiated with high-energy radiation, any of vacuum, inorganic gas such as nitrogen, argon and helium, or air can be used. A preferable atmosphere is air. When irradiation is performed in the air, the water absorption capacity and the water absorption speed are large and the residual monomer is particularly small. Moreover, there is no restriction | limiting in particular in irradiation concentration, The objective can fully be achieved at room temperature.

(Method to lead monomer to other derivatives)
Examples of the method of deriving the monomer 2) to other derivatives include a method of adding amine, ammonia and the like to the complex, and a method of adding a reducing agent such as bisulfite, sulfite and pyrosulfite to the complex.

(Method for removing monomer)
Examples of the method 3) for removing the monomer include extraction with an organic solvent and distillation. In the method of extracting with an organic solvent, the composite is immersed in a water-containing organic solvent to extract and remove residual monomers. As the water-containing organic solvent, ethanol, methanol, acetone or the like can be used, and the water content is preferably 10 to 99% by weight, particularly preferably 30 to 60% by weight. Generally, the higher the water content, the higher the ability to remove the residual monomer. However, when a water-containing organic solvent having a high water content is used, the energy consumption in the subsequent drying step increases. The time for immersing the complex in the water-containing organic solvent is usually about 5 to 30 minutes, and it is also preferable to adopt a means for promoting the extraction of the residual monomer such as shaking the complex. After the immersion treatment, it is usually dried with a dryer or the like.

  Moreover, as a method of distilling off a residual monomer, the method of processing a composite_body | complex with superheated steam or water vapor containing gas can be mentioned. For example, the amount of residual monomers in the composite can be reduced by heating saturated steam at 110 ° C. to 120 to 150 ° C. and bringing it into contact with the composite as superheated steam. In this method, it is considered that when the water in the complex evaporates as water vapor, the remaining monomer is also vaporized and escapes from the complex. According to this method, the removal of the residual monomer and the drying of the composite can be performed together.

(II-6) Additive Addition Step Various additives can be added to the composite to give a desired function depending on the intended use. Examples of these additives include a stabilizer that prevents the water-absorbing resin from being decomposed and altered by the liquid to be absorbed, an antibacterial agent, a deodorant, a deodorant, a fragrance, and a foaming agent.

(Stabilizer)
Among these, as stabilizers for preventing decomposition and alteration of the water-absorbent resin due to the liquid to be absorbed, the water-absorbent resin due to excrement (ie, human urine, feces), body fluid (body fluid such as human blood, menstrual blood, secretory fluid) Stabilizers that prevent decomposition and alteration are listed. JP-A-63-118375 discloses a method for containing an oxygen-containing reducing inorganic salt and / or organic antioxidant in a water-absorbing resin, JP-A-63-153060 discloses a method for containing an oxidizing agent, JP-A-63-127754 discloses a method of containing an antioxidant, JP-A-63-272349 discloses a method of containing a sulfur-containing reducing agent, and JP-A-63-146964 discloses a metal chelating agent. JP-A 63-15266 discloses a method containing a radical chain inhibitor, JP-A 1-275661 discloses a phosphinic acid group- or phosphonic acid group-containing amine compound or a salt thereof. JP-A-64-29257 discloses a method of containing a polyvalent metal oxide, JP-A-2-255804, JP-A-3-179008 discloses a method of adding a polyvalent metal oxide. A method for at coexistence of a water-soluble chain transfer agents have been proposed. In addition, JP-A-6-306202, JP-A-7-53884, JP-A-7-62252, JP-A-7-113048, JP-A-7-145326, JP-A-7-145263, The materials and methods described in JP-A-7-228788 and JP-A-7-228790 can also be used. Specific examples include potassium oxalate titanate, tannic acid, titanium oxide, phosphinic acid amine (or salt thereof), phosphonic acid amine (or salt thereof), metal chelate and the like. Of these, stabilizers against human urine, human blood, and menstrual blood are sometimes referred to as human urine stabilizer, human blood stabilizer, and menstrual blood stabilizer, respectively.

(Antimicrobial agent)
Antibacterial agents are used in order to prevent spoilage due to the absorbed liquid. As antibacterial agents, for example, “New development of bactericidal / antibacterial technology”, pages 17-80 (Toray Research Center (1994)), “Testing / evaluation methods and product design of antibacterial / antifungal agents”, pages 128-344 (NTT) S (1997)), Japanese Patent No. 2760814, Japanese Unexamined Patent Publication No. 39-179114, Japanese Unexamined Patent Publication No. 56-31425, Japanese Unexamined Patent Publication No. 57-25813, Japanese Unexamined Patent Publication No. 59-189854, JP 59-105448, JP 60-158861, JP 61-181532, JP 63-135501, JP 63-139556, JP 63-156540. JP-A-64-5546, JP-A-64-5547, JP-A-1-153748, JP-A-1-221242, JP-A-2-253. No. 47, JP-A-3-59075, JP-A-3-103254, JP-A-3-221141, JP-A-4-11948, JP-A-4-92664, JP-A-4-138165. JP-A-4-266947, JP-A-5-9344, JP-A-5-68694, JP-A-5-161671, JP-A-5-179053, JP-A-5-269164, Those introduced in JP-A-7-165981 can be appropriately selected.

  Examples of the antibacterial agent include alkyl pyridinium salts, benzalkonium chloride, chlorhexidine gluconate, pyridione zinc, and silver-based inorganic powders. Representative examples of quaternary nitrogen-based antibacterial reagents include methylbenzethonium chloride, benzalkonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide Can do. Examples of heterocyclic quaternary nitrogen-based antibacterial reagents include dodecylpyridinium chloride, tetradecylpyridinium chloride, cetylpyridinium chloride (CPC), tetradecyl-4-ethylpyridinium chloride, and tetradecyl-4-methylpyridinium chloride.

  Other preferred antibacterial reagents include bis-biguanides. These bis-biguanides are also known as antibacterial reagents. These are described in detail, for example, in US Pat. Nos. 2,684,924, 2,990,425, 2,830,006 and 2,863,019. It is described in. The most preferred bis-biguanide is 1,6-bis (4-chlorophenyl) diguanide hexane, known as chlorhexidine and its water-soluble salts. Particularly preferred are chlorohexidine hydrochloride, acetate and gluconate.

  Several other types of antibacterial reagents are also useful. For example, carbanilides, substituted phenols, metal compounds, and rare earth salts of surfactants can be exemplified. The carbanilide includes 3,4,4′-trichlorocarbanilide (TCC, triclocarban) and 3- (trifluoromethyl-4,4′-dichlorocarbanilide (IRGASAN). Mention may be made of 5-chloro-2- (2,4-dichlorophenoxy) phenol (IRGASAN DP-300), which include graphite and tin salts such as zinc chloride, zinc sulfide and tin chloride. A rare earth salt of a surfactant is disclosed in European Patent Publication No. 10819. Examples of this type of rare earth salt include a lanthanum salt of a linear C10-18 alkylbenzene sulfonate.

(Deodorant, deodorant, fragrance)
Further, deodorizers, deodorizers and fragrances are used to prevent or alleviate the unpleasant odor of the absorbed liquid. Examples of the deodorant, deodorant, and fragrance are “new deodorant / deodorant and technology and prospect” (Toray Research Center (1994)), JP-A-59-105448, JP-A-60-158861, JP-A-61-118132, JP-A-1-153748, JP-A-1-221242, JP-A-1-265156, JP-A-2-41155, JP-A-2-253847, Those introduced in Japanese Laid-Open Patent Publication No. 3-103254, Japanese Laid-Open Patent Publication No. 5-269164, and Japanese Laid-Open Patent Publication No. 5-277143 can be appropriately selected. Specifically, examples of the deodorizer and deodorizer include iron complexes, tea extraction components, and activated carbon. Examples of fragrances include fragrances (citral, cinnamic aldehyde, heliotopine, camphor, bornyl acetate) wood vinegar, paradichlorobenzene, surfactants, higher alcohols, terpene compounds (limonene, pinene, camphor, borneol, eucalyptol, Eugenol).

(Foaming agent, foaming aid)
Further, a foaming agent and a foaming aid can be used in combination for increasing the water absorption performance of the water-absorbent resin to increase the porosity and the surface area. As the foaming agent and foaming aid, for example, those introduced in “Rubber / Plastic Compounding Chemicals” (Rubber Digest, 1989, pages 259 to 267) can be appropriately selected. Examples include sodium bicarbonate, nitroso compounds, azo compounds, sulfonyl hydrazides and the like.

(Additional time)
These additives are appropriately added according to the purpose and action mechanism in any step of the production method of the present invention. For example, the foaming agent is suitably added before or during the polymerization of the water absorbent resin. Human urine stabilizer, human blood stabilizer, antibacterial agent, deodorant and fragrance can be added in the compounding process, molding process and the like. Of course, it can also be applied to the fibers in advance.

(II-7) Other steps In the production method of the present invention, JP-A 63-267370, JP-A 63-10667, JP-A 63-295251, JP-A 63-270801. JP-A-63-294716, JP-A-64-64602, JP-A-1-231940, JP-A-1-243927, JP-A-2-30522, JP-A-2-153373. The purpose of applying the technique used for the sheet-shaped water-absorbing material proposed in JP-A-3-21385, JP-A-4-133728, JP-A-11-156188, etc. It can be adopted according to the situation.

[III] Order of steps The production method of the present invention includes a compounding step, a recovery step, a drying step, and a forming step as essential steps. The order in which the essential steps are performed is preferably the order of the compounding process, the recovery process, the drying process, and the molding process, or the order of the compounding process, the recovery process, the molding process, and the drying process. In the present invention, at least one of these essential steps may be performed a plurality of times. For example, the drying process may be performed twice by performing the composite process, the recovery process, the drying process, the molding process, and the drying process in this order. Further, the composite process, the recovery process, the drying process, the molding process, the drying process, and the molding process may be performed in this order, and the drying process and the molding process may be performed twice.

In the present invention, two or more of the essential steps may be performed simultaneously. For example, the molding process and the drying process may be performed simultaneously by performing drying while molding. Moreover, you may implement simultaneously a collection | recovery process and a drying process by also drying while collect | recovering. Further, by performing the molding while collecting, the collecting process and the molding process may be continuously performed without any separation. Furthermore, the recovery process, the molding process, and the drying process may be performed simultaneously by performing drying while continuously performing molding while collecting.
Such a combination of essential steps can be appropriately determined in consideration of the type and amount of the water-absorbing material to be manufactured, the manufacturing environment, usable equipment, and the like.

  The production method of the present invention may include optional steps such as a fiber opening step, a sieving step, a surface cross-linking step, a preliminary drying step, a residual monomer treatment step, and an additive addition step. These optional steps may be performed before or after the essential step, or may be performed simultaneously with the essential step.

  Of the optional steps, the fiber opening step can be performed on an aggregate composed of a water-absorbent resin and fibers obtained through at least the composite step and the recovery step. Therefore, the fiber opening process may be performed after passing through the composite process and the recovery process, or may be performed after passing through the composite process and the recovery process and further through a drying process or a molding process.

  Of the optional steps, the sieving step is performed after at least the compounding step. For example, after the compounding step, the compounding step and the recovery step, and then the compounding step, the recovery step, and the drying step can be performed. Preferred is an embodiment in which the sieving step is performed after the above-described opening step.

  Of the optional steps, the surface cross-linking step can be performed on an aggregate composed of a water-absorbent resin and fibers obtained through at least the composite step and the recovery step. Therefore, the fiber opening process may be performed after passing through the composite process and the recovery process, or may be performed after passing through the molding process after the composite process and the recovery process. After the surface crosslinking step, a drying step is performed and the crosslinking reaction is advanced by heating. The drying step may be performed immediately after the surface cross-linking step, or may be performed after other steps are performed.

  Of the optional steps, the preliminary drying step is performed as necessary before performing the drying step on the aggregate composed of the water-absorbent resin and the fibers obtained through at least the composite step and the recovery step. For example, when the opening process is performed after the collection process, it is preferable to perform a preliminary drying process prior to the opening process.

  Of the optional steps, the residual monomer treatment step is performed after at least the composite step. For example, it can be performed after the compounding step, after the compounding step and the recovery step. Further, the residual monomer treatment step can be performed simultaneously with other steps. For example, the remaining monomer can be polymerized by heating while performing the recovery step. In addition, the polymerization of the residual monomer can be advanced by heating performed in the drying step or the preliminary drying step.

  Of the optional steps, the additive addition step can be performed at any stage as necessary. Moreover, you may perform in another process. For example, it may be carried out by mixing an additive in the material used in the compounding step, or when the surface cross-linking agent is sprayed in the surface cross-linking step, the additive is sprinkled simultaneously or before and after. May be.

Specific examples of the order of essential steps and optional steps in the production method of the present invention are described below. For example, when the essential steps are performed in the order of the composite step, the recovery step, the drying step, and the molding step, the surface crosslinking step can be preferably performed between the recovery step and the drying step as shown below.
Compounding step-Recovery step-A-Surface cross-linking step-B-Drying step-C-Molding step At this time, between the recovery step and the surface cross-linking step (above A), between the surface cross-linking step and the drying step (above B) The opening process can be preferably inserted at any one or more timings between the drying process and the molding process (C). Among the above A to C, it is more preferable to perform the opening process at the timing of A or C. Moreover, the sieving step can be preferably inserted after the opening step. Further, when the opening process is performed at the timing of A or B, it is preferable to perform a preliminary drying process before the opening process.

Moreover, when performing an essential process in order of a composite process, a collection | recovery process, a formation process, and a drying process, a fiber opening process can be preferably implemented between a collection process and a formation process as shown below.
Combining process-recovery process-D-opening process-E-molding process-F-drying process It is preferable to perform a preliminary drying process before the opening process. Moreover, the sieving step can be preferably inserted after the opening step. In addition, the surface cross-linking step is performed at any one or more timings between the recovery step and the opening step (above D), between the opening step and the forming step (above E), and between the forming step and the drying step (above F). Can be preferably inserted. Among D to F, it is more preferable to perform the surface crosslinking step at the timing E.

The following (1) to (3) can be mentioned as specific examples as a particularly preferable order of steps in the production method of the present invention.
(1) Compositing step-Recovering step-Surface cross-linking step-Drying step-Opening step-Sieving step-Molding step (2) Combining step-Recovering step-Predrying step-Opening step-Sieving step-Surface Crosslinking step-Drying step-Molding step (3) Compounding step-Recovery step-Pre-drying step-Fiber opening step-Sieving step-Surface crosslinking step-Molding step-Drying step

  In these specific examples, the residual monomer treatment step and the additive addition step can be inserted as necessary. Moreover, it is possible to insert steps other than these as necessary.

  The features of the present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

  A specific procedure of the manufacturing method of the present invention will be described with reference to the schematic diagram of FIG. The manufacturing method of Example 1 is carried out in accordance with the order of steps (1) above.

<1> Compounding Step A part having a monomer concentration of 50% by weight and a neutralization degree of 60% by mole by adding 133.3 parts by weight of a 25% by weight aqueous sodium hydroxide solution and 3.3 parts by weight of distilled water to 100 parts by weight of acrylic acid. A neutralized acrylic acid aqueous solution was prepared. To 100 parts by weight of the partially neutralized acrylic acid aqueous solution, 0.14 parts by weight of N, N′-methylenebisacrylamide as a crosslinking agent and 4.55 parts by weight of 31% by weight aqueous hydrogen peroxide solution as an oxidizing agent were added. Solution A was prepared.
Separately, 0.14 parts by weight of N, N′-methylenebisacrylamide as a crosslinking agent and 0.57 parts by weight of L-ascorbic acid as a reducing agent were added to 100 parts by weight of the partially neutralized acrylic acid aqueous solution. Solution B was prepared.
The prepared solution A and solution B were mixed using the nozzle installed in the upper part of the polymerization tank 1 of FIG. The nozzle has the structure shown in FIG. 2, the inner diameter of the nozzle is 0.13 mm, and five nozzles for each solution are arranged at an interval of 1 cm. The crossing angle between the solution A and the solution B flowing out from the nozzle was adjusted to 30 degrees, and the distance between the nozzle tips was adjusted to 4 mm. Solution A and solution B were each heated to a temperature of 40 ° C. and supplied with a pump at a flow rate of 5 m / sec.
The solution A and the solution B merge when they exit the nozzles of the respective nozzle pairs, form a liquid column about 10 mm each, and then form liquid droplets in the gas phase (in air, at a temperature of 50 C) was dropped. The space density of the droplets in the reactor estimated from the space volume of the reactor, the amount of monomer supplied, and the dropping speed of the droplets was 3 g / m ³ .

On the other hand, the fibers opened from the supply ports installed at 0.8 m and 1.6 m below the tip of the nozzle were supplied in a multiphase flow with air. At that time, the temperature of the air in the multiphase flow was room temperature, and the linear velocity was 10 m / sec. The monomer conversion rates at 0.8 m and 1.6 m below the nozzle tip were 15% and 40%, respectively. The fiber used was a pulp having a fiber diameter of 2.2 dtex, a length of 2.5 mm, and a water contact angle of 0 °. The amount supplied was 11.5 g / min. The spatial density of the fiber in the reaction field estimated from the space capacity of the reaction field, the amount of fiber supplied, and the falling speed of the fiber was 6 g / m ³ . The droplets falling in the gas phase collided with the fibers supplied in this manner and dropped while forming a composite.

<2> Collection step The composite was deposited on the vacuum conveyor 2 installed 3 m below the tip of the nozzle. The vacuum conveyor 2 has a mesh belt at the conveying portion. Since the degree of vacuum under the mesh was set to -1000 Pa with respect to the inside of the polymerization tank 1, the composite could be efficiently deposited on the vacuum conveyor 2 while suppressing scattering of the composite. The air sucked by the vacuum conveyor 2 was circulated and used as air for forming a multiphase flow when supplying the fibers into the polymerization tank 1.

<3> Surface cross-linking step The recovered material recovered in the recovery step was conveyed into the surface cross-linking agent spray tank 3 by the rotating vacuum conveyor 2, and the surface cross-linking agent was sprayed there. Ethylene glycol diglycidyl ether was used as the surface cross-linking agent, water was used as the solvent, and the concentration of the surface cross-linking agent was 0.5% by weight. The spraying of the surface cross-linking agent was performed at room temperature. The spray amount was sprayed so that ethylene glycol diglycidyl ether was 1000 ppm by weight on the water-absorbent resin particles. The crosslinking reaction was allowed to proceed in the next drying step.

<4> Drying Step The recovered material sprayed with the surface cross-linking agent was further transported out of the surface cross-linking agent spray tank 3 by the rotating vacuum conveyor 2 and dried with hot air from the dryer 4. The time from spraying the surface cross-linking agent to starting to apply hot air was 1 minute. The hot air temperature was 130 ° C., and the moisture content of the recovered material was reduced to 10% by weight or less by applying it for 2 minutes.

<5> Opening step The dried recovered material was opened using the opening device 5. The fiber opening was performed by an electric drum carder in which the fiber lump was lashed by passing the fiber lump between two large and small rotating drums to which a large number of needles were fixed. The recovered material obtained in this example could be easily opened because the composites were independent of each other.

<6> Sieving step The recovered material opened was guided to a sieving device 6 installed under the opening device 5 and subjected to sieving. The sieving by the sieving machine 6 was performed by a vibration sieving machine (1000 cpm) provided with a 20 mesh (mesh 850 μm) sieve screen. By sieving, fibers not attached to the composite were separated from the composite. The recovered fiber was reused as a fiber to be supplied into the polymerization tank 1.

<7> Molding Step The composite obtained in the sieving step was collected on the rotating vacuum conveyor 7 and conveyed to the crimping machine 8. Before collecting on the vacuum conveyor 7, the composite was further mixed with a water absorbent resin and / or fiber to adjust the weight ratio of the water absorbent resin and the fiber. The fibers to be mixed were set so that the fibers collected in the sieving step can be used as appropriate. The composite was molded into a desired shape by the crimping machine 8, and finally a water absorbent material composed of a water absorbent resin and fibers was obtained. Thereby, the dry weight ratio of the fibers not embedded or bonded to the water absorbent resin and the water absorbent resin is 30:70, the basis weight of the water absorbent resin is 300 g / m ² , and the density is 0.3 g. / Cm ³ , and a water-absorbing material having a thickness of 1.3 mm was obtained.
The water-absorbing material manufactured by the manufacturing method of the present invention is then used for manufacturing a water-absorbing article through a process such as cutting. The piece of water-absorbing material discharged by cutting or the like can be recycled to any of the above-described manufacturing steps of the water-absorbing material through processing such as opening.

<8> Structure confirmation of composite body The recovered material obtained in the recovery process is taken out for screening and screened to remove free fibers that did not come into contact with the water absorbent resin, and a composite composed of the water absorbent resin and fibers. Got. When this composite was observed with a microscope, the composite contained one water-absorbing resin particle and two or more fibers, and the water-absorbing resin particles were substantially spherical, and among the two or more fibers, One or more of the fibers are partially embedded in the resin particles and partially exposed from the resin particles, and at least one of the two or more fibers is the fiber. It was confirmed that a part of the fiber was bonded to the surface of the resin particle without being embedded in the resin particle (FIG. 3).

  In the above production method, [1] Instead of the pulp used as the fiber, polyethylene terephthalate (PET) having a fiber diameter of 1.7 dtex, a length of 0.9 mm, and a water contact angle of 80 ° is used. [2] When using nylon having a fiber diameter of 1.7 decitex, a length of 0.9 mm, and a water contact angle of 50 °, instead of the pulp used as the fiber, [3] fiber In place of the pulp used as the fiber, the fiber diameter is 1.7 dtex, the length is 0.9 mm, and the contact angle of water is 50 °, and the contact diameter of water is 0. When a fiber mixture having a rayon weight ratio of 1: 1 at a temperature of [4] is used, instead of the pulp used as the fiber, the fiber diameter is 1.7 decitex, the length is 0.9 mm, and water contact Polytetrafluoroethylene with an angle of 108 ° For the case of using the down (PTFE) also, the composite was obtained was confirmed to have a similar structure.

[Reference Example 1]
A water-absorbing material is produced in the same manner as in Example 1 except that in the compounding step of the production method of Example 1, the fiber is supplied only from the fiber supply port located 0.8 m below the tip of the nozzle. did. The structure of the composite was confirmed by the same method as in Example 1. As a result, the composite (30%) having the same structure as in Example 1, one or more water-absorbent resin particles, and one or more fibers were included. The water-absorbing resin particles are substantially spherical, and the one or more fibers are partially embedded in the resin particles and partially exposed from the resin particles, and the fibers Were confirmed to be a mixed composition with a composite (FIG. 4) (70%) not adhered to the surface of the resin particles.

[Reference Example 2]
A water-absorbing material is produced in the same manner as in Example 1 except that in the compounding step of the production method of Example 1, the fiber is supplied only from the fiber supply port located 1.6 m below the tip of the nozzle. did. When the structure of the composite was confirmed by the same method as in Example 1, the composite (20%) having the same structure as in Example 1, one or more water-absorbent resin particles, and one or more fibers were included. The water-absorbing resin particles are substantially spherical, one or more of the fibers are partially bonded to the surface of the resin particles, and all of the fibers are embedded in the resin particles. It was confirmed that it was a mixed composition with the composite (FIG. 5) (80%) not yet formed.

Industrial applicability

  In the water-absorbent material produced by the production method of the present invention, the water-absorbent resin is fixed to the fiber with high density and high strength. For this reason, liquids, such as a body fluid, can be absorbed rapidly, can be spread | diffused throughout the absorptive material, and can be hold | maintained in an absorptive material. Moreover, according to the manufacturing method of this invention, since the water absorbing material which has a softness | flexibility can be manufactured, if this is used, the diaper, sanitary goods, etc. which have comfortable wearability can be provided. Furthermore, according to the production method of the present invention, a thin water-absorbing material can be produced, so that transportation and handling costs can be reduced. Further, according to the production method of the present invention, it is possible to produce a water absorbent material without generating fiber waste and water absorbent resin fine particles, and the fixability of the water absorbent resin in the produced water absorbent material is good. is there. Since it has such excellent characteristics, the method for producing a water-absorbing material of the present invention can be widely used in various fields.

It is an example of a flow sheet in order to manufacture a water absorbing material continuously by the manufacturing method of this invention. It is an example of the nozzle for ejecting the polymerizable monomer aqueous solution used at the compounding process of this invention. 2 is a schematic view and a scanning electron micrograph of the composite produced in Example 1. 2 is a schematic view and a scanning electron micrograph of the composite produced in Reference Example 1 . It is the schematic of the composite_body | complex manufactured by the reference example 2 , and a scanning electron micrograph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polymerization tank 2 Vacuum conveyor 3 Surface crosslinking agent spray tank 4 Dryer 5 Opening device 6 Sieving device 7 Vacuum conveyor 8 Crimping machine

Claims (16)

A method for producing a water-absorbing material comprising a water-absorbing resin and fibers, comprising the following steps (A) to (D).
(A) A droplet containing a polymerizable monomer that gives a water-absorbing resin and / or a polymerized product of the polymerizable monomer and a fiber that has been previously opened at a plurality of positions where the monomer conversion rate of the polymerizable monomer is different. A composite step (B) for obtaining a composite comprising a water-absorbent resin and a fiber having a structure in which the water-absorbent resin adheres to the fiber by causing collision and further polymerization of the polymerizable monomer (B) Recovery step for collecting (C) Drying step for drying the aggregate (D) Molding step for molding the aggregate The composite includes one water-absorbing resin particle and two or more fibers, the water-absorbing resin particles are substantially spherical, and one or more of the two or more fibers are part of the fibers. Embedded in the resin particles and partly exposed from the resin particles, and at least one of the two or more fibers is embedded in the resin particles. The method for producing a water-absorbing material according to claim 1, wherein some of the fibers are adhered to the surface of the resin particles. The method for producing a water-absorbing material according to claim 1 or 2 , wherein the composite step, the recovery step, the molding step, and the drying step are sequentially performed. Composite step, recovery step, drying step, the production method of the water-absorbing material according to claim 1 or 2 sequentially perform forming process. The water absorbing property according to claim 4 , further comprising a fiber opening step of opening the aggregate obtained in the drying step and obtaining an aggregate composed of the opened water absorbent resin and fibers between the drying step and the molding step. Material manufacturing method. The method for producing a water-absorbent material according to claim 5 , further comprising a sieving step for separating fibers to which the water-absorbent resin is not attached between the opening step and the molding step. The method for producing a water-absorbing material according to claim 6 , wherein the fibers separated in the sieving step are used in the compounding step. The method for producing a water-absorbing material according to claim 6 , wherein the fibers separated in the sieving step are used in the molding step. The method for producing a water-absorbing material according to any one of claims 1 to 8 , wherein in the molding step, an aggregate composed of a water-absorbing resin and fibers, and the water-absorbing resin and / or fibers are mixed. The method for producing a water-absorbing material according to any one of claims 1 to 9 , wherein the water-absorbing resin comprises a partially neutralized acrylic acid polymer crosslinked product. Between the collection step and the drying step, a compound having two or more reactive groups capable of reacting with a carboxyl group is added to the aggregate, and the aggregate is dried in the drying step and the surface of the water absorbent resin The method for producing a water-absorbing material according to claim 10 , which is crosslinked. The method for producing an absorbent material according to claim 11 , wherein the reactive group is a glycidyl group. The method for producing a water-absorbing material according to any one of claims 1 to 12 , wherein the composite step is performed in the reactor, and the aggregate of the composite deposited on the bottom of the reactor in the recovery step is recovered. In the compounding process, the fibers are supplied into the reactor as a mixed phase flow with air, and in the recovery process, the lower part of the mesh installed at the bottom of the reactor is depressurized more than in the reactor to deposit the aggregate on the mesh. The method for producing a water-absorbing material according to claim 13 , wherein the water-absorbing material is collected. The method for producing a water-absorbing material according to claim 14 , wherein air sucked downward through the mesh is used to mix with fibers in the compounding step to form a multiphase flow. The method for producing a water-absorbing material according to any one of claims 1 to 15 , wherein all steps are performed in a continuous operation.