JP4545448B2 - Method for producing water-absorbent molded body - Google Patents

Description

  The present invention relates to a production method for producing a water-absorbent molded article by polymerizing a water-soluble ethylenically unsaturated monomer, and more specifically, a water-absorbent mold for polymerization using a photopolymerization initiator. The present invention relates to a method for manufacturing a body.

  In recent years, hygroscopic materials such as paper diapers, sanitary napkins, so-called incontinence pads, and the like have been widely used as hydrophilic materials for the purpose of absorbing body fluids. Examples of the water-absorbing resin include a cross-linked polyacrylic acid partially neutralized product, a hydrolyzate of starch-acrylonitrile graft polymer, a neutralized product of starch-acrylic acid graft polymer, and a vinyl acetate-acrylic acid ester copolymer. Known are saponified polymers, hydrolysates of acrylonitrile copolymers or acrylamide copolymers or cross-linked products thereof, and cross-linked products of cationic monomers.

  As a method for producing a water-absorbing resin from a water-soluble ethylenically unsaturated monomer, for example, the reverse of polymerization in which a water-soluble ethylenically unsaturated monomer or an aqueous solution thereof is suspended and dispersed in a hydrophobic organic solvent. A phase suspension polymerization method and the like are known.

And as a method for obtaining a water-absorbent molded body that is a molded body of the water-absorbent resin, for example, in Patent Documents 1 to 6, a thickener is added to the monomer solution to obtain a predetermined viscosity, and then light The structure which obtains a polymer by irradiating is disclosed.
Patent No. 3009574 (Registration date; December 3, 1999) JP 9-51912 A (publication date; February 25, 1997) Japanese Patent Laid-Open No. 10-5583 (Date of publication; January 1, 1998) Japanese Patent Laid-Open No. 10-18125 (Publication Date; January 20, 1998) JP 62-156102 A (publication date; July 11, 1987) US Pat. No. 6,222,610 (registration date February 8, 2000)

  However, in the methods disclosed in Patent Documents 1 to 6, a thickener is added to the monomer solution in advance in order to form a predetermined shape. Since this thickener has a high viscosity, it is difficult to handle. Therefore, labor is required to mix the thickener with the monomer solution. Moreover, depending on the kind of thickener, the performance of the water-absorbent molded article as a product may be lowered.

  This invention is made | formed in view of the said conventional problem, The objective is to provide the manufacturing method of the water-absorbing molded object which manufacture is simpler, without adding a thickener.

  In order to solve the above problems, the method for producing a water-absorbent molded body according to the present invention intermittently irradiates light to an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer. It is characterized by carrying out polymerization.

  In the method for producing a water-absorbent molded body according to the present invention, a structure in which polymerization is performed on the surface of another substrate or in another substrate is more preferable.

  In order to solve the above problems, a method for producing a water-absorbent molded body according to the present invention is a method for producing a water-absorbent molded body in which an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer is polymerized. A first polymerization step in which a part of the water-soluble ethylenically unsaturated monomer is polymerized by irradiating the aqueous solution with light, and the aqueous solution containing a part of the polymer by stopping the light irradiation. A molding step for molding, and a second polymerization step for polymerizing the remaining water-soluble ethylenically unsaturated monomer by irradiating the aqueous solution partially containing the polymer molded by the molding step with light. It is characterized by including.

  In the method for producing a water-absorbent molded body according to the present invention, it is more preferable that the aqueous solution before light irradiation includes a crosslinking agent in advance.

  In the method for producing a water-absorbent molded body according to the present invention, it is more preferable that the aqueous solution further includes a radical polymerization initiator other than the photopolymerization initiator.

  The method for producing a water-absorbent molded body according to the present invention preferably has a configuration in which polymerization is performed by heating after light irradiation.

  In the method for producing a water-absorbent molded body according to the present invention, a configuration in which the second polymerization step is performed on the aqueous solution partially including a polymer in the middle of molding is more preferable.

  As for the manufacturing method of the water-absorbing molded object concerning this invention, the structure which performs the said shaping | molding process on a fiber base material or in a fiber base material is more preferable.

  In the method for producing a water-absorbent molded body according to the present invention, a configuration in which the first polymerization step and the molding step are continuously performed is more preferable.

  In the method for producing a water-absorbent molded body according to the present invention, a configuration in which the first polymerization step and the molding step are performed on a continuous belt is more preferable.

  The method for producing a water-absorbent molded body according to the present invention has a configuration in which it is molded into at least one shape selected from the group consisting of a string shape, a fiber shape, a foam shape, a sheet shape, a film shape, a cubic shape and a spherical shape. preferable.

  According to said structure, light is intermittently irradiated with respect to the aqueous solution containing a photoinitiator and a water-soluble ethylenically unsaturated monomer. Therefore, the aqueous solution can be partially polymerized by light irradiation temporarily to increase the viscosity of the aqueous solution to a viscosity necessary for molding. Thereby, it becomes possible to mold easily without using a thickener. And after that, by irradiating light again and completing superposition | polymerization, the water absorptive molded object shape | molded in the desired shape can be manufactured easily.

  In addition, when polymerization is performed using a photopolymerization initiator, by controlling the light irradiation, for example, compared with a configuration in which a monomer is polymerized using a thermal decomposition type or redox type polymerization initiator. Control can be performed more easily.

  As described above, the method for producing a water-absorbent molded body according to the present invention performs polymerization by intermittently irradiating light to an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer. It is the structure to perform.

  In addition, as described above, the method for producing a water-absorbent molded body according to the present invention comprises irradiating an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer with light, and A first polymerization step for polymerizing a part of the unsaturated monomer, a molding step for stopping the light irradiation, and forming the aqueous solution, and irradiating the aqueous solution formed by the molding step with light. And a second polymerization step for polymerizing the remaining water-soluble ethylenically unsaturated monomer.

  Therefore, there is an effect that molding can be easily performed without using a thickener. In addition, when polymerization is performed using a photopolymerization initiator, by controlling the light irradiation, for example, compared with a configuration in which a monomer is polymerized using a thermal decomposition type or redox type polymerization initiator. There is also an effect that the control can be performed more easily.

  The present invention is described in detail below.

  The method for producing a water-absorbent molded body according to the present embodiment is a method of performing polymerization by intermittently irradiating light to an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer. is there.

(Water-soluble ethylenically unsaturated monomer)
Specific examples of the water-soluble ethylenically unsaturated monomer constituting the water-absorbent molded body include acrylic acid, methacrylic acid, crotonic acid, (anhydrous) maleic acid, fumaric acid, itaconic acid, and vinyl sulfonic acid. Anionic unsaturated monomers such as styrenesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, and salts thereof Acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate , 2-hydroxypropyl (meth) acrylate, methoxypo Nonionic hydrophilic group-containing unsaturated monomers such as ethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine; N, N- Dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof A cationic unsaturated monomer; and the like. These monomers may be used alone or in combination of two or more as appropriate. Among the water-soluble ethylenically unsaturated monomers exemplified above, it is more preferable to use acrylic acid and / or a salt thereof (hereinafter referred to as acrylic acid (salt)) in terms of performance and cost. Moreover, it is more preferable to use acrylic acid (salt) as a main component (50 mol% or more) as a water-soluble ethylenically unsaturated monomer, it is more preferable to use 80 mol% or more, and 95 mol% or more is used. Is particularly preferred.

  Moreover, in this invention, when using acrylic acid (salt) and another monomer, monomers other than acrylic acid (salt) are with respect to the total amount of acrylic acid and its salt. The ratio is preferably 30 mol% or less, more preferably 10 mol% or less. By using a monomer other than the acrylic acid (salt) in the above ratio, the water-absorbing property of the obtained water-absorbing resin can be further improved, and the water-absorbing resin can be obtained at a lower cost.

(Photopolymerization initiator)
In the present embodiment, the water-soluble ethylenically unsaturated monomer is polymerized using a photopolymerization initiator. Examples of the photopolymerization initiator include acetophenone, benzoin, benzophenone, benzyl, and derivatives thereof. Specific examples of these derivatives and other photopolymerization initiators include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 4- (2 -Hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 2-methyl-2-morpholino (4-thiomethylphenyl) propan-1-one, 2-benzyl-2 Acetophenone derivatives such as dimethylamino-1- (4-morpholinophenyl) -butanone; benzoin alkyl ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether; ο-methyl benzoylbenzoate, 4- Phenyl Nzophenone, 4-benzoyl-4′-methyl-diphenyl sulfide, 3,3 ′, 4,4′-tetra (t-butylperoxylcarbonyl) benzophenone, 2,4,6-trimethylbenzophenone, 4-benzoyl-N, Benzophenone derivatives such as N-dimethyl-N- [2- (1-oxo-2-propenyloxy) ethyl] benzeneammonium chloride, (4-benzoylbenzyl) trimethylammonium chloride; thioxanthone compounds; bis (2,4,6 -Trimethylbenzoyl) -phenylphosphine oxide, bis (2,6-dimethoxybenzoyl) 2,4,4-trimethyl-pentylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoyl Fe Acylphosphine oxide derivatives such as nylethoxyphosphine oxide; 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis (N, N′-dimethyleneisobutylamidine) and its salts, 2, 2'-azobis (2-methylpropionamidine) and its salt, 2,2'-azobis (2-methylpropionitrile), 4,4'-azobis (4-cyanovaleric acid) and its salt, 2,2 '-Azobis [2-hydroxymethyl (propionitrile)], 2,2'-azobis {2-methyl N- [1,1'-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2, 2′-azobis {2-methyl-N- [1,1′-bis (hydroxymethyl) ethylpropionamide]} 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) ) Propionamide], 2,2'-azobis (2-methylpropionamide) azo compounds such; and the like. The azo compound can also act as a thermally decomposable radical initiator. These photopolymerization initiators may be used alone or in combination of two or more. Of the photopolymerization initiators exemplified above, it is more preferable to use an acetophenone derivative, an acylphosphine oxide derivative, or an azo compound in terms of cost and reactivity.

  The amount of the photopolymerization initiator used may be an amount that can start the polymerization reaction, and depends on the intensity of light used, but with respect to the water-soluble ethylenically unsaturated monomer. The range of 0.001 to 5 mass% is more preferable, and the range of 0.01 to 3 mass% is more preferable. When the usage-amount of the said photoinitiator is less than 0.001 mass%, a polymerization reaction may not occur. On the other hand, when the usage-amount of the said photoinitiator is more than 5 mass%, it is not economical.

(Monomer concentration)
In view of performance and ease of polymerization control, the water-soluble ethylenically unsaturated monomer is preferably polymerized in the form of an aqueous solution. In this case, the concentration of the water-soluble ethylenically unsaturated monomer in the aqueous solution is more preferably in the range of 10% by mass to 95% by mass, and in the range of 20% by mass to 60% by mass with respect to the total amount of the aqueous solution. Is more preferable. Further, a solvent other than water may be used in combination as necessary, and the type of the solvent used in combination is not particularly limited.

(Crosslinking agent)
Moreover, in this Embodiment, although the said water-soluble ethylenically unsaturated monomer is polymerized using the photoinitiator, you may superpose | polymerize by adding a crosslinking agent as needed. By adding the crosslinking agent, it is possible to further improve the degree of polymerization (crosslinking degree) of the resulting water-absorbent molded article.

  Examples of the crosslinking agent include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, Glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly ( (Meth) allyloxyalkane, (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, ethylene glycol, polyethylene glycol Propylene glycol, glycerin, pentaerythritol, ethylenediamine, ethylene carbonate, propylene carbonate, polyethylenimine, and glycidyl (meth) acrylate.

  These crosslinking agents may be used alone, or two or more kinds may be appropriately mixed and used. Moreover, these crosslinking agents may be added all at once to the reaction system, or may be added in divided portions. The amount of the crosslinking agent used is more preferably in the range of 0.005 mol% to 2 mol%, preferably 0.01 mol% to 1 mol%, relative to the water-soluble ethylenically unsaturated monomer. It is more preferable that it is within the range, particularly preferably within the range of 0.03 to 0.5 mol%, and most preferably within the range of 0.06 to 0.3 mol%. When the amount of the crosslinking agent used is less than 0.005 mol% and more than 2 mol%, a water absorbent resin having desired water absorption characteristics may not be obtained.

(Initiator)
In the present embodiment, the polymerization is carried out using a photopolymerization initiator. However, in addition to the photopolymerization initiator, another polymerization initiator may be added to promote the polymerization.

  Examples of such other polymerization initiators include potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, and 2,2′-azobis (2-amidinopropane) dihydrochloride. And thermal decomposable radical polymerization initiators. In addition, 2,2'-azobis (2-amidinopropane) dihydrochloride can also act as a photopolymerization initiator. Furthermore, you may use the redox type | system | group initiator which combined the said radical polymerization initiator and the reducing agent which accelerates | stimulates decomposition | disassembly of this radical polymerization initiator. Examples of the reducing agent include (bi) sulfurous acid (salt) such as sodium sulfite and sodium bisulfite, L-ascorbic acid (salt), reducing metal (salt) such as ferrous salt, amines, and the like. Can be mentioned.

  The amount of the other polymerization initiator used is about 0.001 mol% to 2 mol%, more preferably 0.01 mol% to 0.1 mol%, based on the water-soluble ethylenically unsaturated monomer. It is. When the amount of the polymerization initiator used is less than 0.001 mol%, the amount of unreacted monomers increases, and the amount of monomers remaining in the resulting water-absorbent resin may increase. On the other hand, when the usage-amount of these polymerization initiators exceeds 2 mol%, there exists a possibility that the amount of water-soluble components in the water-absorbing resin obtained may increase.

  As the addition form of the other polymerization initiator, for example, it may be added when preparing an aqueous solution containing the water-soluble ethylenically unsaturated monomer, or the polymerization is initiated by a photopolymerization initiator. The aqueous solution may be added in a state where it has a certain viscosity.

(Water absorbent resin)
By polymerizing an aqueous solution containing the water-soluble ethylenically unsaturated monomer, a water-absorbing resin (water-absorbing molded article) is obtained. This water-absorbent resin absorbs a large amount of water from 50 times to 1000 times in ion-exchanged water under no pressure to form a hydrogel. The water-absorbing resin preferably has a carboxyl group, and is obtained, for example, by polymerizing / crosslinking the water-soluble ethylenically unsaturated monomer mainly composed of acrylic acid (salt) (neutralized product). It is done. The water-absorbent resin is more preferably 25% by mass or less, further preferably 15% by mass or less, and particularly preferably 10% by mass or less as an uncrosslinked water-soluble component in the water-absorbent resin. Further, when the water-soluble ethylenically unsaturated monomer containing the acrylic acid (salt) is polymerized, as the acrylate, an alkali metal salt of acrylic acid (for example, Li salt, Na salt, K salt), Examples thereof include ammonium salts and amine salts. The water-absorbent resin has a constitutional unit in the range of 10 mol% to 100 mol% of acrylic acid and 90 mol% to 0 mol% of acrylate (however, the total amount of both is 100 mol%). More preferred are those in the range of 20 mol% to 100 mol% acrylic acid and 80 mol% to 0 mol% acrylate, and 25 mol% to 60 mol% acrylic acid and 75 mol% to 40 mol acrylate. It is particularly preferable to be in the range of mol%. When obtaining a water-absorbing resin by polymerizing a water-soluble ethylenically unsaturated monomer mainly composed of acrylic acid (salt), it can be used in combination with acrylic acid (salt), if necessary. The monomer may be contained.

(Method for producing water-absorbent molded article)
In the present embodiment, polymerization is performed by intermittently (intermittently) irradiating light to an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer. More specifically, in the method for producing a water-absorbent molded article that polymerizes a water-soluble ethylenically unsaturated monomer containing a photopolymerization initiator, the photopolymerization initiator and the water-soluble ethylenically unsaturated monomer are included. Irradiating the aqueous solution with light to polymerize a part of the monomer, a first polymerization step for obtaining a thickened thickened aqueous solution, and stopping the light irradiation, It is a method including a molding step of molding into a desired shape, and a second polymerization step of polymerizing the remaining water-soluble ethylenically unsaturated monomer by irradiating the molded thickened aqueous solution with light. That is, the water-absorbent resin obtained by photopolymerizing the aqueous solution is formed into a desired shape by stopping the light irradiation in the middle of the photopolymerization to increase the viscosity, and then further polymerizing. The water-absorbent molded article according to the present invention is obtained. Below, a specific manufacturing method is explained in full detail.

  The water-absorbent molded body as used in the present invention is not particularly limited as long as it has a certain shape, and may be formed into a certain shape in the process of polymerizing the monomer aqueous solution. Examples of the fixed shape include a sheet shape, a film shape, a string shape, a fiber shape, a cubic shape, and a spherical shape. Further, the water-absorbent molded article of the present invention means a hydropolymer (hydrogel) obtained after being molded into a certain shape as described above or a dried product thereof (molded dry product). The water-absorbent resin powder obtained from a dried and pulverized polymer gel that is generally manufactured is indefinite and has a certain shape (or obtained by molding or processing the water-absorbent resin powder). Water-absorbent molded article).

  First, partial polymerization is performed by irradiating light to an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer (first polymerization step).

  The light used for irradiation may be any light that includes a wavelength at which the photopolymerization initiator is decomposed, and light containing ultraviolet light or visible light is preferably used. As the wavelength of the light to be irradiated, 200 nm or more is more preferable, 300 nm or more is more preferable, and a light containing more light components of 300 to 400 nm is preferably used. In particular, from the viewpoint of light transmission and degradation of the produced polymer (water-absorbing resin), absorption of the monomer used (monomer component containing a water-soluble ethylenically unsaturated monomer) and its polymer (water-absorbing resin) It is preferable to irradiate light mainly having a wavelength larger than the wavelength.

  As the light source for irradiating the light, a commercially available lamp may be used, and examples thereof include a mercury lamp, a metal halide lamp, a xenon lamp, a tungsten lamp, and a fluorescent lamp.

The illuminance and irradiation time of the light to be used are not particularly limited as long as the aqueous solution containing the monomer is adjusted to such a degree that the aqueous solution containing the monomer is thickened to a viscosity suitable for molding by partial polymerization. A range of 0.0001 to 100 mW / cm ² is more preferable, and a range of 0.001 to 50 mW / cm ² is more preferable. The irradiation time is more preferably about 0.1 seconds to 30 minutes. As a method of irradiation, the illuminance may be constant or may be changed, or may be irradiated intermittently. In addition, for example, when a thermal decomposable polymerization initiator is included, it is particularly possible to easily control the temperature of the monomer aqueous solution to be thickened by adjusting the polymerization, in other words, by adjusting the heating value of the polymerization. In addition, intermittent irradiation is preferably used.

  In this first polymerization step, a monomer component containing a water-soluble ethylenically unsaturated monomer may be polymerized until a desired viscosity is obtained. The desired viscosity may be a viscosity that can suitably form an aqueous solution of a thickening monomer (a water-soluble ethylenically unsaturated monomer partially containing a polymer) obtained by partial polymerization.

  That is, the viscosity of the thickening monomer thickened by partial polymerization is not particularly limited as long as it is suitable for the intended molding, but is usually in the range of 10 mPa · s to 20,000,000 mPa · s. Is more preferably in the range of 50 mPa · s to 10,000,000 mPa · s, and particularly preferably in the range of 100 mPa · s to 1,000,000 mPa · s. If it is less than 10 mPa · s, deformation is easily caused by its own weight or slight external force except when casting is not preferable. On the other hand, when the viscosity is larger than 20,000,000 mPa · s, the viscosity is too high and molding becomes difficult.

  The reaction temperature in the polymerization reaction is preferably −5 ° C. or more and 150 ° C. or less, and more preferably 20 ° C. or more and 120 ° C. or less in terms of prevention of bumping and the like and performance. Further, the reaction time is not particularly limited, and may be set as appropriate according to the type and amount of the monomer and the polymerization initiator, the reaction temperature, and the like.

  Next, a thickening monomer having a viscosity within the above range is molded into a desired shape (molding step). When this molding process is performed, light irradiation is temporarily stopped. In addition, you may restart irradiation of light in the middle of shaping | molding.

  In the molding step, for example, when the water-absorbent molded body is molded into a string shape, the thickening monomer can be extruded from a nozzle to be molded into a string shape. Further, for example, when the water-absorbing molded body is formed into a sheet or film, it can be formed into a sheet or film by pouring the thickening monomer onto a continuous belt.

  In the molding step, the thickening monomer is selected from the group consisting of a string-like, fibrous, foam-like, sheet-like, film-like, cubic-like, and spherical shape. It is more preferable to mold so as to obtain at least one shape.

  Then, the thickened monomer that has been molded / mould be molded is irradiated again with light to complete the polymerization and obtain the water-absorbent molded body of the present invention (second polymerization step).

  The thickening monomer is polymerized in various forms depending on the purpose. For example, a fiber-like or string-like polymer gel (water-absorbent molded article) having a diameter of several tens of μm to several hundreds of mm can be obtained by polymerizing while discharging from a plurality of nozzles (strings). Alternatively, by polymerizing while dropping from a plurality of nozzles or the like, a spherical polymer gel having a shape of several tens of μm to several hundreds of mm can be obtained. These can be performed in a liquid phase or in a gas phase, and can be performed on a metal or resin plate or a conveyor belt. In particular, when it is desired to obtain a spherical gel having a large diameter, it is advantageous to carry out in an organic solvent.

  In addition, for example, a water-absorbing composite in which a water-absorbing resin and a fiber base material are integrated by forming the above thickening monomer on a fiber base material such as a non-woven fabric or by performing polymerization after the forming. You can also get a body. The obtained water-absorbent molded article or the water-absorbent composite containing the water-absorbent molded article may be used as it is as a water-containing polymer (hydrated gel), and is dried until a desired water content is obtained. May be used. It can also be dried and pulverized and used as a water-absorbent resin powder (indefinite shape powder).

  In addition, when a thermally decomposable radical polymerization initiator is mixed in an aqueous solution containing a water-soluble ethylenically unsaturated monomer, or when the polymerization initiator is added to a thickening monomer, the second polymerization is performed. In the process, polymerization may be accelerated by applying heat. In the second step, the polymerization reaction may be advanced by irradiating light, and then the polymerization reaction may be completed by heating.

  Moreover, in the manufacturing method of the water absorbing molded object concerning this Embodiment, it is more preferable that the said aqueous solution contains a crosslinking agent. The addition of the crosslinking agent to the aqueous solution may be performed before or after the first polymerization step, but is preferably added to the aqueous solution before the first polymerization step. In this case, the aqueous solution is in a state in which a photopolymerization initiator, a water-soluble ethylenically unsaturated monomer, and a crosslinking agent are mixed in advance. For this reason, a thickening monomer and a water absorbing molded object can be directly manufactured only by irradiating light intermittently to aqueous solution. Moreover, since the crosslinking agent is added to the aqueous solution before the first polymerization step, it is possible to uniformly disperse the crosslinking agent as compared with the case where it is added to the thickening monomer.

  Moreover, when adding a crosslinking agent to the aqueous solution before performing a 1st polymerization process, it becomes possible to perform the said 1st polymerization process and a shaping | molding process continuously. That is, since the crosslinking agent is added to the aqueous solution in advance, the thickening monomer that has undergone the first polymerization step is also mixed with the crosslinking agent. For this reason, it is not necessary to add a crosslinking agent to the thickening monomer, and after the aqueous solution is thickened, it can be molded as it is.

  In addition, when adding a crosslinking agent to the aqueous solution after performing a 1st polymerization process, after adding a crosslinking agent to a thickening monomer, a shaping | molding process will be performed. For this reason, a 1st superposition | polymerization process and a shaping | molding process cannot be performed continuously.

  In the case where the first polymerization step and the molding step are performed continuously, a method of continuously injecting an aqueous solution into an apparatus that performs these steps may be used. Although it will not specifically limit as said apparatus if it is an apparatus which can perform a 1st superposition | polymerization process and a shaping | molding process, For example, a continuous belt, a cylindrical apparatus, etc. can be used. The continuous belt is a rotatable endless belt. In the case of using a continuous belt, the aqueous solution may be continuously poured onto the continuous belt, and thickening and molding may be performed while the aqueous solution is conveyed. In this case, in order to prevent the aqueous solution from dropping from the continuous belt, it is preferable to perform the first polymerization step simultaneously with the injection of the aqueous solution onto the continuous belt. Moreover, when using a cylindrical apparatus, aqueous solution should be continuously inject | poured into this apparatus, and it should just thicken and shape | mold.

  And the water-absorbing molded object of this invention can be obtained by performing a 2nd superposition | polymerization process after the said shaping | molding. In addition, a 2nd superposition | polymerization process can be performed continuously after a formation process. Therefore, when the crosslinking agent is added to the aqueous solution in advance, the first polymerization step, the molding step, and the second polymerization step can be performed continuously.

  As described above, the method for producing a water-absorbent molded body according to the present embodiment is a method for performing polymerization while intermittently irradiating light. More specifically, in a method for producing a water-absorbent molded article by irradiating light and polymerizing an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated monomer, Is a method including a step of temporarily interrupting the irradiation to form a thickening monomer.

  In other words, when the aqueous solution containing the water-soluble ethylenically unsaturated monomer is thickened by irradiating light to a viscosity that enables molding, temporary polymerization is stopped and molding is performed. It has become. Thereby, it is not necessary to shape | mold the aqueous solution containing the said water-soluble ethylenically unsaturated monomer using a thickener like before.

  Moreover, since light is used for the polymerization, the polymerization can be easily controlled. That is, since the polymerization is performed using the photopolymerization initiator, the polymerization can be temporarily interrupted by interrupting the light irradiation. Therefore, a thickening monomer having a viscosity suitable for molding can be easily produced by intermittently irradiating light to an aqueous solution containing a water-soluble ethylenically unsaturated monomer.

  In the first polymerization step and the second polymerization step, the wavelength of light to be irradiated may be changed. In the first polymerization step, polymerization may be performed to such an extent that the aqueous solution is thickened. Therefore, light having a relatively long wavelength, that is, light having low energy may be irradiated. On the other hand, since it is necessary to complete the polymerization in the second polymerization step, it is sufficient to irradiate light having a relatively short wavelength, that is, high energy. Thus, the thickening monomer which has a suitable viscosity can be produced more easily by changing the wavelength of the light to irradiate with the 1st polymerization process and the 2nd polymerization process.

  Further, in the method for producing a water-absorbent molded body according to the present embodiment, an aqueous solution containing a photopolymerization initiator and a water-soluble ethylenically unsaturated polymer was irradiated with light to obtain a desired viscosity. It may be a method of completing the polymerization by stopping the light irradiation at the time, forming the above thickened aqueous solution into a desired shape, and then irradiating the light again.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these. In addition, about the evaluation of the water absorbing molded object finally obtained, it evaluated by the absorptive capacity under no pressure, a soluble content, and solid content. Below, the method of each evaluation is demonstrated.

[Absorption capacity under no pressure]
Absorption capacity under no pressure was measured by the following method.

First, about 0.2 g of the water-absorbent resin powder and about 0.4 g of the water-containing polymer (water-containing polymer gel) before drying are accurately weighed (accurately with 3 digits after the decimal point) Were uniformly placed in a bag (60 mm × 60 mm) and immersed in a 0.9 mass% sodium chloride aqueous solution (physiological saline). In the case of water-absorbent resin powder, the bag is pulled up after 30 minutes in the case of a water-containing polymer before drying, and drained at 250 × 9.81 m / s ² (250 G) for 3 minutes using a centrifuge. After that, the weight W1 (g) of the bag was measured. Next, the same operation as described above was performed without using the water absorbent resin, and the weight W0 (g) at that time was measured. Then, the absorption capacity under no load (GV) was calculated by the following formula (1) using the weights W0 and W1.

GV (g / g) = [(W1-W0) / weight of water-absorbing resin] -1 (1)
(Measurement of soluble content)
Weigh out 184.3 g of 0.9 mass% sodium chloride aqueous solution (physiological saline) in a plastic container with a cap of 250 ml capacity, add 1.00 g of water-absorbing resin to the aqueous solution, and then stir for 16 hours. Thus, the soluble component in the resin was extracted. The extract was filtered using a filter paper, and 50.0 g of the obtained filtrate was weighed to obtain a measurement solution. Then, the physiological saline alone was titrated with a 0.1N NaOH aqueous solution until the pH reached 10, and then titrated with a 0.1N HCl aqueous solution until the pH reached 2.7. At this time, the titration amounts required for the titration are [bNaOH] ml and [bHCl] ml. Next, the same titration operation as described above was performed on the measurement solution, and the titration amounts required for each titration were [NaOH] ml and [HCl] ml. And the soluble content in a water absorbing resin was computed by the weight average molecular weight (Mw) of the water absorbing resin used for the measurement, and the said titration.

  Below, the calculation method of the soluble content about the water absorbing resin which consists of acrylic acid and its sodium salt is illustrated. The soluble content was calculated based on the following formula (2).

Soluble content (mass%) = 0.1 × Mw × 184.3 × 100 × ([HCl]-[bHCl]) / 1000 / 1.0 / 50.0 (2)
However, Mw = 72.06 × (1−neutralization rate / 100) + 94.04 × neutralization rate / 100
Neutralization rate (mol%) = (1-([NaOH]-[bNaOH]) / ([HCl]-[bHCl])) × 100
In addition, said Formula (2) is a case of the water absorbing resin which consists of acrylic acid and its sodium salt, and the value used for a formula will differ if materials differ.

[Solid content]
In the case of a water-containing polymer before drying: About 2 g of the polymer was taken in a petri dish, dried in a dryer at 180 ° C. for 16 hours, and calculated from loss on drying.

  In the case of a water-containing polymer after drying: About 1 g of the polymer was taken in a petri dish, dried in a dryer at 180 ° C. for 3 hours, and calculated from loss on drying.

  The solid content was calculated by ((weight after drying) / (weight before drying)) × 100.

[Example 1]
431 g of 37 mass% sodium acrylate aqueous solution, 40.7 g of acrylic acid, 0.22 g of polyethylene glycol diacrylate (n = 8), 0.20 g of 2-hydroxy-2-methylpropiophenone and 28.3 g of pure water are mixed. Thus, an aqueous monomer solution for polymerization was prepared. This aqueous monomer solution was degassed at room temperature for 30 minutes under a nitrogen stream. The monomer aqueous solution is taken in a glass syringe with a nozzle having a diameter of about 1.0 mm at the tip, and a UV light having a strength of about 1 mW / cm ² is used using a black light fluorescent lamp (FL6BLB, manufactured by Toshiba Lighting & Technology Corp.). A glass syringe was irradiated with (main wavelength 352 nm). Then, when a part of the monomer aqueous solution in the syringe was polymerized and thickened, UV irradiation was once stopped. Subsequently, a monomer aqueous solution (thickening monomer) thickened by partial polymerization is extruded from the nozzle tip at room temperature, and a black light mercury lamp (H400BL, manufactured by Toshiba Lighting & Technology Co., Ltd.) is used around the monomer aqueous solution in the middle of dropping. By irradiating ultraviolet rays (main wavelength: 352 nm) having an intensity of 30 mW / cm ² , a water-absorbent molded article (1) molded into a flexible string (about 0.8 mm in diameter) was obtained. . When this water-absorbent molded body (1) was cut with scissors about 1 mm in length and measured for physical properties, the absorption capacity under no pressure was 17.7 g / g, the soluble content was 1.2% by mass, the solid content Was 44.0% by mass. In addition, when the absorption capacity | capacitance under this non-pressurization and the value of a soluble part were converted into solid content 100%, they were set to 40.3 g / g and 2.7 mass%. Further, the string-like water-absorbent molded body (1) was dried in a hot air dryer at 170 ° C. for 10 minutes, and then pulverized with a desktop pulverizer. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a water absorbent resin powder (2) having a particle size of 600 to 300 μm. The absorption capacity of the water absorbent resin powder (2) under no pressure was 36.2 g / g, the soluble content was 7.5% by mass, and the solid content was 90.5% by mass.

[Example 2]
A monomer aqueous solution for polymerization was prepared in a conical beaker by mixing 431 g of 37% by mass sodium acrylate aqueous solution, 40.7 g of acrylic acid, 0.20 g of 2-hydroxy-2-methylpropiophenone and 28.3 g of pure water. . This aqueous solution was deaerated at room temperature for 30 minutes under a nitrogen stream, and then irradiated with ultraviolet rays from the top of the glass beaker under the same conditions as in Example 1 using a black light fluorescent lamp (FL6BLB, manufactured by Toshiba Lighting & Technology Corp.). Then, when a part of the monomer aqueous solution was polymerized and thickened, ultraviolet irradiation was once stopped. The viscosity of this aqueous monomer solution was about 2000 mPa · s as measured with a Brookfield viscometer. Next, 0.22 g of polyethylene glycol diacrylate (n = 8) was added as a crosslinking agent to the aqueous solution thickened by this partial polymerization (aqueous solution of thickening monomer), and mixed and dissolved. A part of the aqueous solution of the thickening monomer was taken in a syringe with a nozzle having a diameter of about 1.0 mm attached to the tip, and extruded from the tip of the nozzle at room temperature. At that time, by using a black light mercury lamp (manufactured by Toshiba Lighting & Technology Co., Ltd., H400BL) from around the monomer aqueous solution that is falling from the tip of the nozzle, ultraviolet rays are irradiated under the same conditions as in Example 1, thereby allowing flexibility. A water-absorbent molded body (3) molded into a string with a diameter (about 0.8 mm in diameter) was obtained. When this water-absorbing molded article (3) was cut into scissors with a length of about 1 mm and measured for physical properties, the absorption capacity under no pressure was 19.5 g / g, the soluble content was 1.6% by mass, The solid content was 43.4% by mass. In addition, when the absorption capacity | capacitance under this non-pressurization and the value of a soluble part are converted into solid content 100%, they will be 45.0 g / g and 3.8 mass%. Further, the string-like water-absorbent molded body (3) was dried in a hot air dryer at 170 ° C. for 10 minutes, and then pulverized with a desktop pulverizer. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a water-absorbent resin powder (4) having a particle size in the range of 600 to 300 μm. The absorption capacity of the water absorbent resin powder (4) under no pressure was 37.6 g / g, the soluble content was 6.9% by mass, and the solid content was 90.1% by mass.

Example 3
In the same manner as in Example 2, after preparing an aqueous solution of a thickening monomer in which a crosslinking agent was dissolved, the aqueous solution of the thickening monomer was intermittently extruded from a syringe onto a moving belt to form a polka dot, and further By irradiating ultraviolet rays under the same conditions as in Example 1 using a black light mercury lamp (H400BL, manufactured by Toshiba Lighting & Technology Co., Ltd.) from above, a pellet-shaped polymer gel (water absorbent molded body) was obtained.

Example 4
In the same manner as in Example 2, after preparing an aqueous solution of a thickening monomer in which a crosslinking agent was dissolved, when the aqueous solution of the thickening monomer was dropped from a syringe into a glass column containing liquid paraffin, black was added from the outside. Ultraviolet rays were irradiated under the same conditions as in Example 1 using a light mercury lamp (manufactured by Toshiba Lighting & Technology Corp., H400BL). The monomer solution became spherical in paraffin and slowly settled during polymerization. From the bottom of the column, there was obtained a polymer gel having a uniform spherical shape and a clean spherical shape without adhesion or aggregation between the gels.

Example 5
In the same manner as in Example 2, after preparing an aqueous solution of the thickening monomer in which the crosslinking agent was dissolved, the aqueous solution of the thickening monomer was string-like from the syringe on the fiber substrate (nonwoven fabric), and irregular. Were continuously extruded so as to have a laminated form. At that time, polymerization was performed by irradiating UV light from the periphery of the aqueous solution of the thickening monomer falling from the tip of the nozzle under the same conditions as in Example 1 using a black light mercury lamp (H400BL, manufactured by Toshiba Lighting & Technology Co., Ltd.). Made progress. The composite thus obtained was dried at 80 ° C. until the moisture content of the laminated string polymer (water-absorbent molded body) was 20%, thereby obtaining a flexible water-absorbent composite. Although depending on the diameter of the nozzle to be extruded, flexibility is lost when the moisture content is dried to 10% or less.

Example 6
431 parts by weight of a 37% by weight aqueous sodium acrylate solution, 40.7 parts by weight of acrylic acid, 0.32 parts by weight of polyethylene glycol diacrylate (n = 8), 0.20 parts by weight of 2-hydroxy-2-methylpropiophenone and A monomer aqueous solution for polymerization was prepared by mixing 28.3 parts by mass of pure water. This aqueous monomer solution was degassed at 20 ° C. under a nitrogen stream until the dissolved oxygen became 1 ppm or less. The monomer aqueous solution was poured onto a stainless steel conveyor belt having a width of 0.5 m and a length of 3.5 m at a flow rate of 30 kg / h using a pump. Immediately before pouring the monomer aqueous solution into the pump, a 3.0 mass% sodium persulfate aqueous solution was merged with the monomer aqueous solution at a flow rate of 0.183 kg / h and mixed.

Further, at the upper part of the conveyor belt, 0.3 m, 1.5 m and 3 m from the injection port for injecting the monomer aqueous solution onto the conveyor belt from the pump toward the conveyor belt length direction (downstream direction). A black light mercury lamp (Toshiba Lighting & Technology Corp., H400BL) is installed at a position of 0.0 m. In addition, the lower surface of the conveyor belt is cooled with 20 ° C. water from the liquid injection port to a position of 1 m in the length direction of the conveyor belt. For this reason, the monomer aqueous solution is injected onto the conveyor belt, and at the same time, the monomer aqueous solution is irradiated with ultraviolet rays having a strength of about 3.9 mW / cm ² (main wavelength: 352 nm), and the viscosity is increased by polymerization. It did not fall in the width direction. Further, when the monomer aqueous solution was thickened and lost its fluidity, the ultraviolet irradiation was interrupted and cooled. Then, the thickened monomer aqueous solution is transported by a transport belt and irradiated again with ultraviolet rays. Finally, a water-absorbent molded body (5) molded into a flexible plate (thickness of about 2 mm) was obtained from the exit of the conveyor belt. This water-absorbent molded body (5) was cut with scissors about 1 mm in length and measured for physical properties. Absorption capacity under no pressure was 14.7 g / g, soluble content was 1.8% by mass, solid content Was 42.3 mass%. In addition, when the absorption capacity | capacitance under this non-pressurization and the value of a soluble part were converted into solid content 100%, they were set to 34.8 g / g and 4.3 mass%. Further, the plate-like water-absorbent molded body (5) cut with scissors was dried in a hot air drier at 170 ° C. for 10 minutes, and then pulverized with a table crusher. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a water absorbent resin powder (6) having a particle size of 600 to 300 μm. The absorption capacity of the water absorbent resin powder (6) under no pressure was 31.6 g / g, the soluble content was 6.1% by mass, and the solid content was 89.5% by mass.

[Comparative Example 1]
A monomer aqueous solution for polymerization was prepared in a conical beaker by mixing 431 g of 37% by mass sodium acrylate aqueous solution, 40.7 g of acrylic acid, 0.20 g of 2-hydroxy-2-methylpropiophenone and 28.3 g of pure water. . Hydroxyethyl cellulose as a thickener was dissolved in this solution so that the viscosity measured with a Brookfield viscometer was about 2000 mPa · s (about 1.8% by mass of monomer solid content). It took a long time to completely dissolve the thickener in the aqueous solution. Subsequently, 0.22 g of polyethylene glycol diacrylate (n = 8) was added to the aqueous solution thickened with hydroxyethylcellulose and mixed and dissolved. A part of the monomer aqueous solution was taken in a syringe having a nozzle having a diameter of about 1.0 mm attached to the tip, and extruded from the nozzle tip at room temperature. At that time, it is formed into a flexible string (about 0.8 mm in diameter) by irradiating UV light from the periphery of the monomer aqueous solution that is falling from the tip of the nozzle with a black light mercury lamp (Toshiba Lighting & Technology Corp., H400BL). Further, a comparative water-absorbent molded body (1) was obtained. When this comparative water-absorbent molded body (1) was cut with scissors about 1 mm in length and measured for physical properties, the absorption capacity under no pressure was 18.0 g / g and the soluble content was 2.0% by mass. The solid content was 44.1% by mass. In addition, when the absorption capacity | capacitance under this non-pressurization and the value of soluble part are converted into solid content 100%, they will be 40.8 g / g and 4.5 mass%. Furthermore, the string-like comparative water-absorbent molded body (1) was dried in a hot air drier at 170 ° C. for 10 minutes, and then pulverized with a table crusher. Subsequently, the pulverized product was classified with a sieve screen having openings of 600 μm and 300 μm to obtain a comparative water-absorbent resin powder (2) having a particle size of 600 to 300 μm. The absorption capacity of the comparative water absorbent resin powder (2) under no pressure was 35.2 g / g, the soluble content was 9.3 mass%, and the solid content was 90.4 mass%.

  The water-absorbent molded article of the present invention is directly molded by a polymerization process, and does not require a complicated molding process from a conventional water-absorbent resin powder. Such a water-absorbent molded body can be produced inexpensively and easily, has high physical properties, and can absorb various liquids such as water, body fluid, physiological saline, urine, blood, cement water, and fertilizer-containing water. It can be used as an absorbent article containing. Such absorbent articles are used in contact with the human body such as disposable diapers, sanitary napkins, incontinence pads, etc .; separators for water in oil; other dehydration or desiccants; water retention materials such as plants and soil; coagulants such as sludge; It is useful for various industrial applications that require water absorption, water retention, swelling, and gelation, such as water-proofing agents for electric wires or optical fibers; As a configuration of such an absorbent article, for example, a configuration in which an absorbent layer including the water-absorbent molded article of the present invention or a dry pulverized product thereof is sandwiched between a sheet having liquid permeability and a sheet having impermeability. Is mentioned.

Claims (10)

Photopolymerization initiator and acrylic acid, methacrylic acid, crotonic acid, (anhydrous) maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, 2 -(Meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate Rate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (Meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and a quaternary salt thereof , an aqueous solution containing one or more water-soluble ethylenically unsaturated monomers selected from A method for producing a water-absorbent molded article, characterized in that the aqueous solution before the light irradiation is polymerized by intermittently irradiating and containing a crosslinking agent in advance . 2. The production method according to claim 1, wherein the polymerization is carried out on or in the fiber substrate . Photopolymerization initiator and acrylic acid, methacrylic acid, crotonic acid, (anhydrous) maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, 2 -(Meth) acryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, and salts thereof; acrylamide, methacrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (Meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol mono (meth) acrylate Rate, vinylpyridine, N-vinylpyrrolidone, N-acryloylpiperidine, N-acryloylpyrrolidine; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl Water absorption for polymerizing an aqueous solution containing one or more water-soluble ethylenically unsaturated monomers selected from (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and quaternary salts thereof. In the method for producing a molded body,
A first polymerization step of irradiating the aqueous solution with light to polymerize a part of the water-soluble ethylenically unsaturated monomer;
A molding step of stopping the light irradiation and molding the aqueous solution containing a part of the polymer,
A second polymerization step of polymerizing the remaining water-soluble ethylenically unsaturated monomer by irradiating the aqueous solution partially containing the polymer formed by the molding step with light ;
The said aqueous solution before performing light irradiation contains a crosslinking agent previously , The manufacturing method of the water absorbing molded object characterized by the above-mentioned . The said aqueous solution further contains radical polymerization initiators other than a photoinitiator, The manufacturing method of any one of Claims 1-3 characterized by the above-mentioned. Polymerization is performed by heating after light irradiation, The manufacturing method of any one of Claims 1-4 characterized by the above-mentioned.   The manufacturing method according to claim 3, wherein the second polymerization step is performed on the aqueous solution partially including a polymer in the middle of molding. The manufacturing method according to claim 3 , wherein the forming step is performed on a fiber base material or in a fiber base material. The manufacturing method according to any one of claims 3 to 7 , wherein the first polymerization step and the molding step are continuously performed. The manufacturing method according to any one of claims 3 to 8 , wherein the first polymerization step and the molding step are performed on a continuous belt. It shape | molds in the shape of at least 1 sort (s) chosen from the group which consists of a string form, a fiber form, a foam form, a sheet form, a film form, a cubic form, and a spherical form in any one of Claims 1-9 characterized by the above-mentioned. The manufacturing method as described.