JP2008264672A - Granulation method of powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a granulation method of powder which is excellent in production efficiency and does not spoil an original performance of the powder. <P>SOLUTION: The granulation method of the powder has (1) a mixing step for obtaining a powder composition by mixing the powder, a radical polymeric compound and water of 10 mass parts or more for the powder of 100 mass parts, and (2) an irradiation step for irradiating an active energy ray to the powder composition. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for granulating powder.

  Particles generated by the polymerization reaction are known to easily generate fine particles, and the generation of fine particles in such a production process causes various problems. For example, dust is likely to be generated during handling, and the work environment is likely to deteriorate or lose, health problems such as pneumoconiosis, the fluidity of the powder, and hopper bridging, flash phenomenon And the like are likely to occur. Moreover, discarding the generated fine powder greatly reduces the yield and is disadvantageous in terms of disposal cost.

  When the powder is a water-absorbing resin, the generation of fine powder becomes a particularly significant problem. In general, the water-absorbing resin is preferably as low as the content of fine particles of less than 150 μm. This is because, when a water-absorbing article such as a diaper is used, the fine powder reduces liquid permeability due to clogging in the water-absorbing article and causes liquid leakage.

Therefore, various attempts have been made to solve the above problems by granulating fine powder, which is inevitably generated in the production process of various powders such as these water-absorbent resins, using a liquid binder. For example, a technique using a water-soluble polymer as the liquid binder (for example, Patent Document 1), a technique using water glass (for example, Patent Document 2), a technique using an oil-in-water modified wax emulsion (for example, Patent Document 3). )
JP-A-63-154766 JP-A-7-70328 JP-A-6-263881

  However, in the case of a conventionally used binder, the original performance of the powder may be impaired due to the addition thereof, for example, in the case of a water absorbent resin, the water absorption performance such as the water absorption speed is impaired. In addition, in the conventional method by adding a binder, it may be difficult to obtain a granulated product having a uniform particle size.

  In particular, when the powder is a water absorbent resin, there are the following problems. The water-absorbent resin is required to have a high absorption capacity, an excellent absorption rate, a high gel strength, an excellent suction force for sucking water from the substrate, and the like. However, since the water absorption property is affected by the crosslink density, the relationship between the properties does not necessarily show a positive correlation, for example, the gel strength increases but the water absorption amount decreases as the crosslink density increases. In particular, the absorption magnification and the absorption rate, gel strength, suction force, and the like are in a contradictory relationship. For this reason, in the water-absorbent resin having improved absorption capacity, when the particles come into contact with the liquid, water absorption is not performed uniformly, and a part of the water-absorbent resin is formed or water is absorbed in the entire water-absorbent resin particles. Since it does not diffuse, the absorption rate may be drastically reduced.

  In order to alleviate this phenomenon and obtain a water-absorbent resin having a high absorption capacity and a relatively good absorption rate, the surface of the water-absorbent resin is treated with a crosslinking agent, Frequently, some surface treatment such as a surface treatment for increasing the crosslinking density is performed. The conventional method for granulating a water-absorbent resin has a problem in terms of production efficiency because such an operation is further required.

  Under such circumstances, the present invention is a powder granulation method that is excellent in production efficiency and does not impair the original performance of the powder, and a powder in which the remaining monomer (radical polymerizable compound) is reduced. The purpose is to provide a granulated product.

  The present invention includes (1) a mixing step of obtaining a water-containing powder composition by mixing powder, a radical polymerizable compound, and 10 parts by mass or more of water with respect to 100 parts by mass of the powder; (2) An irradiation step of irradiating the powder composition with active energy rays.

  The granulation method of the powder of the present invention is very simple and can be widely applied to various powders. Moreover, when applied to a water-absorbing resin, a water-absorbing resin excellent in water-absorbing characteristics, in particular, the water-absorbing capacity under pressure can be obtained.

  The present invention includes (1) a mixing step of obtaining a water-containing powder composition by mixing powder, a radical polymerizable compound, and 10 parts by mass or more of water with respect to 100 parts by mass of the powder; (2) A powder granulation method comprising an irradiation step of irradiating the powder composition with active energy rays.

  Hereinafter, each process is explained in full detail.

(1) Mixing step In this step, the powder, the radical polymerizable compound, and 10 parts by mass or more of water are mixed with respect to 100 parts by mass of the powder. You may mix the radical polymerization initiator mentioned later in this mixing process. There is no limitation on the mixing order when mixing the powder, the radical polymerizable compound, water and, in some cases, the polymerization initiator. Therefore, each may be mixed with the powder alone, or an aqueous solution containing a radical polymerization initiator and a radical polymerizable compound may be prepared in advance and mixed with the powder. However, in order for the radically polymerizable compound to be uniformly dispersed on the surface of the powder, an aqueous solution containing the radically polymerizable compound and optionally a radical polymerization initiator is prepared in advance, and this is mixed with the powder. Is preferred. In addition, after mixing a radical polymerization initiator, a radically polymerizable compound, and powder, you may mix with water. The aqueous solution in which the radical polymerization initiator and the radical polymerizable compound are dissolved may contain other solvents in addition to water as long as the solubility thereof is not impaired, but preferably only water is used.

  The amount of water used in this step is not particularly limited, but is 10 parts by mass or more, 10 to 150 parts by mass, 10 to 120 parts by mass with respect to 100 parts by mass of the powder (converted to a solid content of 100% by mass). It is preferable in order of 15-100 mass parts, 15-50 mass parts, and 30-50 mass parts. If it is such a range, granulation is performed effectively, and much energy is not required for drying in the drying process after irradiating an active energy ray.

  In order to improve the mixing property of the powder composition, it is preferable to add a mixing aid to the powder, the radical polymerizable compound, water, or a mixture thereof. At this time, water is not included as a mixing aid. Further, the timing of adding the mixing aid is not particularly limited, but it is preferable to add the mixing aid simultaneously with the step (1) or before the step (1).

  These mixing aids may be used alone or in the form of a mixture of two or more. Further, the amount of the mixing aid is not particularly limited as long as it can suppress aggregation of the powder by water and can improve the mixing property of the aqueous solution and the powder, but for example, with respect to 100 parts by mass of the powder 0.01 to 40 parts by mass, more preferably 0.1 to 5 parts by mass. Alternatively, in the present invention, the mixing aid is used in an amount of preferably 0 to 40% by mass, more preferably 0.01 to 30% by mass, and still more preferably 0.1 to 10% by mass with respect to the total amount of the aqueous solution. May be.

  In the step (1), the mixing conditions are particularly limited as long as the powder, the radical polymerizable compound, and 10 parts by mass or more of water are uniformly mixed with respect to 100 parts by mass of the powder. Although not intended, preferred conditions will be exemplified below.

  The temperature of the powder and water before the step (1) is not particularly limited. For example, the temperature of the powder before the mixing step is 0 to 150 ° C, 10 to 120 ° C, 20 to 100 ° C, 50 to 100 ° C. It is preferable in this order. At this time, if the temperature of the powder before step (1) exceeds 150 ° C., the powder may be deteriorated by heat, and conversely, if it is less than 0 ° C., water is condensed and operation is stabilized. May not be possible. Moreover, the temperature of the water before a process (1) becomes like this. Preferably it is 5-80 degreeC, More preferably, it is 10-60 degreeC, Most preferably, it is 20-50 degreeC. In such a temperature range, it is unlikely that water will evaporate excessively before step (1) and sufficient granulation is not performed, and water will condense and operation can be performed stably. There is also a low possibility of not.

  The mixing temperature in the step (1) is preferably in the order of 0 to 150 ° C, 10 to 120 ° C, 20 to 100 ° C, 30 to 90 ° C, and 40 to 70 ° C. At this time, if the mixing temperature exceeds 150 ° C., the powder may be deteriorated by heat. On the other hand, if the mixing temperature is less than 0 ° C., water may condense and the operation may not be performed stably. In addition, it is preferable to perform a mixing process at high temperature, when adding a radical polymerization initiator, since a radically polymerizable compound is superposed | polymerized with a small amount of active energy ray irradiation with a heat | fever.

  In addition, the mixing time in step (1) is not particularly limited as long as each component can be mixed uniformly. Specifically, the mixing time is preferably 0.1 second to 60 minutes, more preferably 1 second to 30 minutes, even more preferably 2 seconds to 20 minutes, and most preferably 5 seconds to 10 minutes. At this time, if the mixing time is less than the lower limit, the respective components may not be mixed uniformly, and conversely, if the mixing time exceeds the upper limit and becomes longer than necessary, excess water penetrates into the water absorbent resin. Therefore, granulation by irradiation with active energy rays may not easily proceed.

  In order to improve the granulation effect, it is preferable to suppress excessive leakage of water vapor by sealing the mixing / irradiation system.

  The equipment used for the mixing process is not particularly limited, and is an ordinary mixer such as a V-type mixer, a ribbon-type mixer, a screw-type mixer, a rotating disk-type mixer, a paddle-type mixer, and an airflow type. There are methods using a mixer, a batch kneader, a continuous kneader, a high-speed fluid mixer, a floating fluid mixer, and the like.

(2) Irradiation step In this step, the powder composition obtained in the step (1) described above is irradiated with active energy rays simultaneously or separately.

  Active energy rays are used as a polymerization initiator, and radically polymerizable compounds existing between powders are polymerized by irradiation with the active energy rays. By this polymerization, the adhesion between the powders increases and the powders are granulated. Also in the mixing step, water becomes a binder and granulation proceeds to some extent, but granulation is performed efficiently and uniformly by irradiation with active energy rays. In the present invention, the amount of water and the radical polymerizable compound that contributes to the adhesion between the powders is controlled, and preferably a radical polymerization initiator is added to balance the granulation properties and powder physical properties. By optimizing in this way, it was possible to find a useful granulation technique capable of reducing the remaining radical polymerizable compound in a short time.

  The active energy ray may be irradiated during the mixing of the powder, water, and the radical polymerizable compound, or may be irradiated after mixing two or more of these. That is, step (1) and step (2) may be performed simultaneously, and step (2) may be performed after step (1). However, the step (2) is preferably performed after the step (1) in that granulation can be uniformly formed.

Examples of active energy rays include one or more of ultraviolet rays, electron beams, and gamma rays. Of these, ultraviolet rays and electron beams are preferable. Considering the influence of active energy rays on the human body, ultraviolet rays are more preferable. When a polymerization initiator is not used, an ultraviolet ray having a wavelength of preferably 300 nm or less, more preferably a wavelength of 200 nm or less, particularly preferably a wavelength of 100 to 200 nm is used. Moreover, when using a polymerization initiator, Preferably it uses the wavelength of 300 nm or less, More preferably, the ultraviolet ray of 180-290 nm is used. Irradiation conditions, when ultraviolet rays are used, preferably, irradiation intensity 3~1000mW / cm ^2, irradiation amount is 100~10000mJ / cm ^2.

  Examples of the apparatus for irradiating ultraviolet rays include a high pressure mercury lamp, a low pressure mercury lamp, a metal halide lamp, a xenon lamp, and a halogen lamp. As long as ultraviolet rays are irradiated, preferably, other ultraviolet rays and wavelengths may be included as long as ultraviolet rays having a wavelength of 300 nm or less are irradiated, and the method is not particularly limited. In the case of using an electron beam, preferably the acceleration voltage is 50 to 800 kV and the absorbed dose is 0.1 to 100 Mrad.

  In general, the irradiation time of active energy rays may be preferably 0.1 minutes or more and less than 60 minutes, more preferably 0.2 minutes or more and less than 30 minutes, and further preferably 1 minute or more and less than 15 minutes.

  In the present invention, when granulating by irradiating active energy rays, it is not necessary to heat. However, the irradiation with the active energy ray can also be performed under heating. When the powder is a water-absorbing resin, a water-absorbing resin excellent in water-absorbing characteristics can be obtained. The temperature during irradiation with active energy rays is preferably in the range of 0 to 150 ° C, more preferably 10 to 120 ° C, still more preferably 20 to 100 ° C, and particularly preferably 50 to 100 ° C. In addition, radiant heat may be generated when active energy rays are irradiated. In this case, irradiation with active energy rays is performed under heating.

  In addition, although the radical polymerization initiator mentioned later is activated by heating, in this invention, since a radical polymerization initiator is activated by irradiation of an active energy ray, heating is auxiliary. In addition, as a heating method, a method of introducing a heated gas into the active energy ray irradiation device, a method of heating around the active energy ray irradiation device with a jacket or the like, or radiant heat when irradiating the active energy ray is used. Examples thereof include a method of heating, and a method of irradiating a preheated powder with an active energy irradiation beam.

  At the time of irradiation with active energy rays, the powder may be fluidized by stirring or the like, or the powder may be allowed to stand still. In the granulation method of the present invention, a preferred embodiment includes the above-described step (1) and the step (2) of leaving the powder composition and irradiating active energy rays. It is. By standing and irradiating, there is an effect that a massive coarse granulated product can be obtained.

  Although the specific method of a process (2) will not be specifically limited if an active energy ray can be uniformly irradiated to a powder composition, For example, performing in a fluid state is preferable. The flow state is a concept including partial flow by gentle stirring. By flowing the powder composition, the active energy ray can be uniformly irradiated to the mixture of the radical polymerization initiator and the powder, the particle diameter of the resulting granulated product can be easily controlled, and the effect of granulation Becomes even more prominent. The apparatus capable of stirring the powder during irradiation with active energy rays is not particularly limited, and is a vibration type mixer, a vibration feeder, a ribbon type mixer, a conical ribbon type mixer, a screw type mixing extruder, and an air flow type. Mixers, batch kneaders, continuous kneaders, paddle type mixers, high-speed fluid mixers, floating fluid mixers, cylindrical vertical mixers, high-speed agitator mixers, V-shaped mixers, ribbon mixers And double-arm kneaders, pulverizing kneaders, rotary mixers, turbulizers, batch-type Redige mixers, continuous-type Redige mixers, and the like. Alternatively, the water-absorbent resin composition may be flowed in a device having a cylindrical shape or a box shape, and active energy rays may be irradiated from the periphery of the device. At this time, in order to cause the mixture to flow, the pressure of a gas such as air may be used as used for pneumatic transportation of the powder. When air is used, it is preferable to humidify the air to prevent the powder from drying. Irradiation of active energy rays can be uniformly surface-treated in a short time when performed from multiple directions. In addition, the material which comprises the said apparatus will not be restrict | limited especially if it is a material which does not largely inhibit irradiation of the active energy ray to a water absorbing resin composition, For example, quartz glass etc. are illustrated.

  In general, it is known that a reaction using radical as an active species is inhibited by oxygen. However, in the production method of the present invention, it is necessary to make the atmosphere inert when irradiating with active energy rays. There is no.

  After irradiation with active energy rays, the powder may be heat-treated at a temperature of 50 to 250 ° C. as necessary for drying and the like.

  From the viewpoint of production efficiency, the production equipment used in the step (1) and the step (2) is preferably the same, and a stirring granulator using a stirring and mixing granulation mechanism is preferable. The stirring granulator is an apparatus having a rotating stirring bar (stirring blade, stirring blade) and capable of mixing and granulating by stirring the stirring bar. Examples of the agitation granulator include Pagmill, Henschel, and Eirich (Revised 5th edition, Chemical Engineering Handbook 18/12 (issued March 18, 1988)). A suitable agitation granulator is an agitation granulator provided with a stirring blade (horizontal axis type, vertical axis type) rotatably arranged in a mixing tank (for example, a separable flask) into which raw materials are charged. The stirring rod having a blade at the end is preferably installed in a direction perpendicular to the bottom surface of the mixing tank (vertical shaft shape). The shape of the selected stirring blade is not particularly limited, and examples thereof include a shovel such as a Roedige mixer, a paddle, a turbine, and a curved blade. Since the effect of granulation becomes more prominent, the shape of the stirring blade is preferably a paddle, an inclined paddle, a curved blade fan turbine, an arrow blade turbine, a propeller, a fiddler type, or a bull margin type. Further, in a stirring granulator having a paddle, an inclined paddle, a fouler type, and a propeller stirring blade, the powder is put into the mixing tank by rotating at an appropriate rotation speed (usually 300 to 600 rpm, preferably 400 to 500 rpm). From the viewpoint of improving the granulation effect, it is preferable to carry out the turbulent flow so that at least part of the laminar flow of the composition is generated. More preferably, the stirring bar is installed in a direction perpendicular to the bottom surface of the mixing tank, and the powder is pressurized by gravity and rotation of the stirring blade.

  Hereinafter, each component used at a process (1) and a process (2) is explained in full detail.

(A) Powder The powder used in the present invention is not particularly limited, and specifically, for example, grains such as wheat flour, ceramics, clay, plastics, carbon black, detergent, and water-soluble resin And hydrophilic resins such as water-absorbing resins. The particle diameter is not particularly limited, but a powder having a mass average particle diameter of 300 μm or less is preferable. The powder may be, for example, only fine powder (for example, powder having a particle diameter of less than 150 μm), a mixture of fine powder and particles larger than the fine powder, or a powder excluding the fine powder. Good. The water-absorbing resin may be subjected to surface cross-linking, but preferably uses a water-absorbing resin that is not surface cross-linked.

  The powder suitably used in the present invention is a water absorbent resin. As the water-absorbent resin, those obtained by polymerization using a conventionally known method using a monomer component essentially containing an ethylenically unsaturated monomer are preferable.

  The ethylenically unsaturated monomer is not particularly limited and is preferably a monomer having an unsaturated double bond at the terminal, such as (meth) acrylic acid, 2- (meth) acryloylethanesulfonic acid, 2- Anionic monomers such as (meth) acryloylpropane sulfonic acid, 2- (meth) acrylamide-2-methylpropane sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid and salts thereof; (meth) acrylamide, N-substituted (meta ) Nonionic hydrophilic group-containing monomers such as acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate; N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (Meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, N, N- Methylamino propyl (meth) acrylamide, amino group-containing unsaturated monomers and their quaternized products and the like; or the like can be cited, and may be used alone or two or more selected from these. Preferably, (meth) acrylic acid, 2- (meth) acryloylethanesulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, salts thereof, N, N-dimethylaminoethyl (meth) acrylate, N , N-dimethylaminoethyl (meth) acrylate quaternized product, (meth) acrylamide, particularly preferably acrylic acid and / or a salt thereof.

  When acrylate is used as the monomer, a monovalent salt of acrylic acid selected from alkali metal salts, ammonium salts, and amine salts of acrylic acid is preferable from the viewpoint of water absorption performance of the water absorbent resin. More preferred are alkali metal acrylates, and particularly preferred are metal salts selected from sodium salts, lithium salts and potassium salts.

  When producing the water-absorbent resin, other monomer components other than the above-mentioned monomers can be used within a range not impairing the effects of the present invention. For example, an aromatic ethylenically unsaturated monomer having 8 to 30 carbon atoms, an aliphatic ethylenically unsaturated monomer having 2 to 20 carbon atoms, and an alicyclic ethylenically unsaturated monomer having 5 to 15 carbon atoms And hydrophobic monomers such as alkyl group (meth) acrylic acid alkyl ester having 4 to 50 carbon atoms. Generally the ratio of these hydrophobic monomers is the range of 0-20 mass parts with respect to 100 mass parts of said ethylenically unsaturated monomers. If the hydrophobic monomer exceeds 20 parts by mass, the water absorption performance of the resulting water absorbent resin may be reduced.

  The water absorbent resin used in the present invention becomes insoluble due to the formation of internal crosslinks. Such internal crosslinking may be a self-crosslinking type that does not use a crosslinking agent, but uses an internal crosslinking agent having two or more polymerizable unsaturated groups and / or two or more reactive functional groups in one molecule. Can be formed.

  Such an internal cross-linking agent is not particularly limited. For example, N, N′-methylenebis (meth) acrylamide, N-methylol (meth) acrylamide, glycidyl (meth) acrylate, (poly) ethylene glycol di (meth) Acrylate, (poly) propylene glycol di (meth) acrylate, glycerol tri (meth) acrylate, glycerol acrylate methacrylate, (meth) acrylic acid polyvalent metal salt, trimethylolpropane tri (meth) acrylate, triallylamine, triallyl cyanurate , Triallyl isocyanurate, triallyl phosphate, ethylene glycol diglycidyl ether, (poly) glycerol glycidyl ether, polyethylene glycol diglycidyl ether, and the like. Two or more of these internal cross-linking agents may be used in combination.

  The amount of the internal crosslinking agent used is preferably 0.0001 to 1 mol%, more preferably 0.001 to 0.5 mol%, based on the total amount of monomer components used in producing the water absorbent resin. More preferably, it is 0.005-0.2 mol%. When the amount is less than 0.0001 mol%, internal crosslinking is not introduced into the resin. On the other hand, when the amount exceeds 1 mol%, the gel strength of the water-absorbent resin becomes too high, and the water absorption ratio may be lowered. When a crosslinked structure is introduced into the polymer using the internal cross-linking agent, the internal cross-linking agent is added to the reaction system before, during or after the polymerization of the monomer, or after the polymerization or neutralization. What should I do?

  In order to obtain a water-absorbing resin, the monomer component including the monomer and the internal crosslinking agent may be polymerized in an aqueous solution. In this case, usable polymerization initiators include persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; potassium peracetate, sodium peracetate, potassium percarbonate, sodium percarbonate, t-butyl hydroperoxide; Hydrogen peroxide; azo compounds such as 2,2′-azobis (2-amidinopropane) dihydrochloride, water-soluble radical polymerization initiators such as 2-hydroxy-2-methyl-1-phenyl-propane-1- There are photopolymerization initiators such as ON. Further, for example, a reducing agent such as sulfite, L-ascorbic acid or ferric salt may be combined with the radical polymerization initiator and used as a redox initiator.

  The amount of the polymerization initiator used is preferably in the range of 0.01 to 20 parts by mass, more preferably in the range of 0.1 to 15 parts by mass, particularly preferably 1 to 10 parts by mass with respect to 100 parts by mass of the water absorbent resin. Range. When the mixing amount of the polymerization initiator is less than 0.01 parts by mass, the water-absorbent resin may not be sufficiently granulated even when irradiated with active energy rays. On the other hand, when the mixing amount of the polymerization initiator is more than 20 parts by mass, the water absorption performance of the granulated water absorbent resin may be lowered.

  Although there is no restriction | limiting in particular in the density | concentration of the monomer in the said monomer aqueous solution, Preferably it is 15-90 mass%, More preferably, it is 35-80 mass%. If it is less than 15% by mass, the obtained hydrogel has a large amount of water, which requires a heat amount and time for drying, which is disadvantageous.

  The polymerization method is not particularly limited, and well-known methods such as aqueous solution polymerization, reverse phase suspension polymerization, precipitation polymerization, bulk polymerization and the like can be employed. Among these methods, aqueous solution polymerization in which a monomer is dissolved in an aqueous solution for polymerization and reverse phase suspension polymerization are preferable from the viewpoint of ease of control of the polymerization reaction and performance of the obtained water-absorbent resin.

  When starting the above polymerization, the above polymerization initiator is used. In addition to the polymerization initiator, active energy rays such as ultraviolet rays, electron beams, and γ rays may be used alone or in combination with the polymerization initiator. The temperature at the start of polymerization depends on the type of polymerization initiator used, but is preferably in the range of 15 to 130 ° C, more preferably in the range of 20 to 120 ° C. If the temperature at the start of polymerization is out of the above range, there may be an increase in the residual monomer of the resulting water-absorbent resin or an excessive self-crosslinking reaction to deteriorate the water-absorbing performance of the water-absorbent resin.

  The reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended in a hydrophobic organic solvent. For example, U.S. Pat. Nos. 4,093,764, 4,367,323, 4,446,261, 4,683,274, and 5,244,735. In US patents such as The aqueous solution polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. For example, U.S. Pat. Nos. 4,462,001, 4,873,299, 4,286,682, 4,973,632, 4,985,518, 5,124,416, 5,250,640 are used. No. 5,264,495, US Pat. No. 5,145,906, US Pat. No. 5,380,808, and European patents such as European Patent Nos. 081636, 09555086, and 0922717. Monomers and initiators exemplified in these polymerization methods can also be applied in the present invention.

  When aqueous solution polymerization is performed, a partially neutralized product such as acrylic acid is polymerized, or an acid group-containing monomer such as acrylic acid is polymerized and then polymerized with an alkali compound such as sodium hydroxide or sodium carbonate. Can also be neutralized. Therefore, the water-absorbing resin used in the present invention preferably contains an acid group and has a predetermined neutralization rate (mol% of neutralized acid groups in all acid groups). Under the present circumstances, the neutralization rate (mol% of the neutralized acid group in all the acid groups) of the water absorbing resin obtained is the range of 25-100 mol%, Preferably it is the range of 50-90 mol%, More preferably, it is 50-75 mol%, Most preferably, it is the range of 60-70 mol%.

  After polymerization, it is usually a hydrogel crosslinked polymer. In the present invention, the water-containing gel-like crosslinked polymer can be used as it is as a water-absorbing resin, but is preferably dried to have a water content (%) (100-solid content (%)) described later.

  On the other hand, the water-absorbent resin used in the present invention is preferably a powdery water-absorbent resin obtained by polymerizing a monomer mainly composed of acrylic acid (salt). The water-containing gel-like product obtained by polymerization is preferably pulverized after drying to obtain a water-absorbing resin. The drying may be performed, for example, using a dryer such as a hot air dryer, preferably at 100 to 220 ° C, more preferably at 120 to 200 ° C.

  As a pulverizer that can be used for such pulverization, for example, among the pulverization model names classified in Table 1.10 of the Powder Engineering Handbook (Edition of the Powder Engineering Society, first edition), a shear pulverizer, It is classified into an impact crusher and a high-speed rotary crusher, and those having one or more crushing mechanisms such as cutting, shearing, impact, and friction can be preferably used. Among crushers corresponding to these models, cutting and shearing A crusher whose mechanism is the main mechanism can be used particularly preferably. For example, a roll mill (roll rotary type) pulverizer is preferable.

  In addition to or instead of the above, the water-absorbent resin used in the present invention can be obtained by obtaining a water-absorbent resin precursor having a low neutralization rate and adding a base to the water-absorbent resin precursor. preferable. Conventionally, polyfunctional surface treatment agents have been used for surface treatment (surface crosslinking). This polyfunctional surface treating agent has a property of reacting with a carboxyl group (—COOH) in a water absorbent resin but not reacting with a salt thereof (for example, —COONa). For this reason, by polymerizing an ethylenically unsaturated monomer mixture (for example, a mixture of acrylic acid and sodium acrylate) that has been adjusted so that the abundance ratio of -COOH / -COONa is in an appropriate range, When a water-absorbing resin in which COOH and -COONa are uniformly distributed is produced and used for surface crosslinking with a polyfunctional surface treating agent, uniform crosslinking is obtained. On the other hand, a water-absorbent resin obtained by polymerizing an acid-type ethylenically unsaturated monomer such as acrylic acid as a main component and then neutralizing the polymer with an alkali compound such as sodium hydroxide or sodium carbonate Has a low soluble content and high gel strength. However, when the surface is crosslinked with a polyfunctional surface treatment agent, -COOH and -COONa are not uniformly distributed, so that the water absorption property is deteriorated. For this reason, it is not desirable to subject the water-absorbent resin obtained by the latter method to surface cross-linking with a conventional polyfunctional surface treating agent. According to the method of the present invention, once a monomer / monomer mixture mainly composed of an acid-type ethylenically unsaturated monomer such as acrylic acid is polymerized, water absorption with a low neutralization rate is achieved. After obtaining the resin precursor, it becomes possible to modify the water-absorbent resin obtained by neutralizing the water-absorbent resin precursor with an alkali compound such as sodium hydroxide or sodium carbonate. The modified water-absorbing resin thus obtained can exhibit high gel strength and excellent water absorption characteristics.

  As described above, the water-absorbing resin is polymerized with a monomer / monomer mixture containing an acid-type ethylenically unsaturated monomer as a main component to form a water-absorbing resin precursor having a low neutralization rate. In the case where the base is obtained by adding a base to the water absorbent resin precursor after being obtained, the base may be added in any form of a solid or a liquid. Preferably, the base is added in the form of a liquid, in particular an aqueous solution. When the base is added in the form of an aqueous solution in this manner, the obtained water-absorbing resin is in a water-containing state, and therefore the step of adding the base to the water-absorbing resin precursor and the step of obtaining the water-absorbing resin composition are performed simultaneously. Can do. The base that can be used in the above embodiment is not particularly limited as long as it can neutralize the water-absorbing resin precursor having a low neutralization rate to a desired neutralization rate, and is a conventionally known inorganic or organic salt or acid. Can be used. Specifically, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, sodium phosphate, potassium phosphate, Examples thereof include ammonium phosphate, sodium borate, potassium borate, ammonium borate, sodium acetate, potassium acetate, ammonium acetate, sodium lactate, potassium lactate, ammonium lactate, sodium propionate, potassium propionate, and ammonium propionate. These bases may be used alone or in a suitable mixture of two or more. Among the above bases, a low neutralization water-absorbing resin precursor obtained by polymerizing a monomer / monomer mixture mainly composed of an acid-type ethylenically unsaturated monomer such as acrylic acid When neutralizing, monovalent cation hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide; sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, Monovalent cation carbonates such as ammonium hydrogen carbonate are preferred because they are easily available industrially, have high physical properties, and can be efficiently adjusted to a desired neutralization rate. In addition, the addition amount of the base in the said embodiment is not restrict | limited in particular, The water absorbing resin used by the mixing process (1) is suitably selected for the desired neutralization rate of the above preferable ranges.

  In the present invention, the “low neutralization rate water-absorbing resin precursor” means that the neutralization rate (mol% of neutralized acid groups in all acid groups) is low or the acid groups are not neutralized. It refers to a water-absorbing resin precursor (neutralization rate is 0). Specifically, the neutralization rate (mol% of neutralized acid groups in all acid groups) is preferably 0 to 50 mol%, more preferably Means about 0 to 20 mol%. Such a low neutralization rate water-absorbing resin precursor is a monomer mainly composed of a monomer having an acid group such as acrylic acid so as to achieve the neutralization rate in the above method. Since it is obtained by the same method as described above by using the mixture, the detailed description is omitted here.

(B) Radical polymerizable compound The radical polymerizable compound used in the present invention contributes to the granulation of powder by polymerizing by ultraviolet irradiation described later and increasing the adhesion between the powders. Moreover, the residual radically polymerizable compound contained in the powder granulated product can be controlled to 300 ppm or less, more preferably 100 ppm or less with respect to the powder by the production method of the present invention.

  The radically polymerizable compound to be mixed with the powder in the present invention is preferably the above-mentioned ethylenically unsaturated monomer and crosslinkable unsaturated monomer. In the present specification, “ethylenically unsaturated monomer” is a monomer having one vinyl group in one molecule, and “crosslinkable unsaturated monomer” is 2 in one molecule. It is a monomer having the above vinyl group. The ethylenically unsaturated monomer and the crosslinkable unsaturated monomer may be used alone or in combination. Preferably, the ethylenically unsaturated monomer and the crosslinkable unsaturated monomer used for producing the water-absorbent resin are used in combination. When the granulated powder is a water absorbent resin, the molar composition ratio may be the same as or different from that of the water absorbent resin as the base polymer, but preferably compared with the composition of the water absorbent resin as the base polymer. Thus, a relatively large amount of crosslinkable monomer is included with respect to the ethylenically unsaturated monomer. In particular, it is preferable to use acrylic acid (salt) as a main component as an ethylenically unsaturated monomer and to use a crosslinkable unsaturated monomer in combination with this in view of excellent water absorption characteristics. In addition, said base polymer refers to the water absorbing resin before a granulation process.

  Moreover, various properties such as hydrophilicity, hydrophobicity, adhesiveness, and biocompatibility can be imparted to the powder surface by appropriately selecting a radical polymerizable compound to be mixed with the powder. Examples of the ethylenically unsaturated monomer that imparts hydrophilicity to the powder surface include hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate, and polyethylene glycol (meth) acrylate. Examples include polyethylene glycol-containing monomers such as polyethylene glycol methyl ether (meth) acrylate. Examples of ethylenically unsaturated monomers that impart hydrophobicity to the powder surface include alkyl (meth) acrylates such as methyl methacrylate and stearyl (meth) acrylate, aromatic group-containing monomers such as styrene, and 2,2. Examples include fluorine-containing monomers such as 2-trifluoroethyl methacrylate. Examples of the ethylenically unsaturated monomer that imparts adhesiveness to the surface of the water-absorbent resin particles include monomers that form a polymer having a glass transition temperature of 25 ° C. or lower, such as butyl acrylate and 2-ethylhexyl acrylate, vinylamine, allylamine, Examples include cationic monomers such as dimethylaminoethyl (meth) acrylate and (meth) acryloyloxyethyltrimethylammonium chloride, and monomers containing a silane group such as 3-methacryloyloxypropyltrimethoxysilane. Among them, a monomer containing a silane group is preferably used because it can improve not only the adhesion between particles but also the adhesion of particles to a substrate such as metal, glass and pulp. Furthermore, when the powder is a water-absorbing resin, the liquid permeability is greater when 3-methacryloyloxypropyltrimethoxysilane is added to an aqueous solution containing partially neutralized acrylic acid and persulfate than when not added. Can obtain an excellent water-absorbing resin. Examples of the ethylenically unsaturated monomer that imparts biocompatibility to the powder surface include monomers having a phospholipid-like structure such as 2-methacryloyloxyethyl phosphorylcholine.

When the powder is a water absorbent resin, the radical polymerizable compound is used to produce the water absorbent resin described in (a) above in order to achieve the purpose of modifying the properties of the water absorbent resin particle surface. It is desirable to include a compound different from the ethylenically unsaturated monomer and the internal crosslinking agent. At this time, the ethylenically unsaturated monomer having a neutralization rate different from that of the ethylenically unsaturated monomer used to produce the water-absorbent resin described in (a) above is described in “(a) above”. And a radically polymerizable compound different from the ethylenically unsaturated monomer and the internal cross-linking agent used to produce the water absorbent resin. In particular, it is preferable that the radically polymerizable compound contains an ethylenically unsaturated monomer containing at least one hetero atom other than oxygen selected from the group consisting of nitrogen, sulfur, phosphorus, silicon, and boron. Thereby, the property of the water-absorbent resin particles can be greatly modified. More preferably, silicon, especially silane group _{(X n Si (OR) 4} -n, where, R represents, independently, represent methyl, ethyl, phenyl or acetoxy radical, n is an integer from 1 to 3 ), Ethylenically unsaturated monomers containing phosphorus are used. In addition, when an ethylenically unsaturated monomer containing a hetero atom other than oxygen is used as the radical polymerizable compound, the amount of the ethylenically unsaturated monomer containing a hetero atom other than oxygen is appropriately determined depending on the desired properties. Although it can select, it is preferable that it is 50 mass parts or less with respect to 100 mass parts of whole quantity of a radically polymerizable compound, More preferably, it is 0.01-20 mass parts, Most preferably, it is 0.1-10 mass parts.

  Among the above-mentioned ethylenically unsaturated monomers, the compound having low water solubility is dispersed in an aqueous solution containing a radical polymerization initiator and other radical polymerizable compound as necessary, or dissolved in a hydrophilic organic solvent. After mixing with the aqueous solution, it may be added to the water absorbent resin. Alternatively, if necessary, it may be dissolved in an organic solvent and added separately from the aqueous solution. At this time, the addition order of the ethylenically unsaturated monomer is not particularly limited, and may be added before or after the aqueous solution.

  In addition, from the viewpoint of powder characteristics and economical viewpoint, the radical polymerizable compound preferably contains acrylic acid and / or an alkali metal salt of acrylic acid. At this time, the amount of acrylic acid and / or alkali metal salt of acrylic acid can be appropriately selected depending on the desired performance, and is not particularly limited. The acid (salt) is preferably used in an amount of 50 parts by mass or more, more preferably 70 to 95 parts by mass.

  In addition, the crosslinkable unsaturated monomer that can be used in the present invention is not particularly limited. For example, monomers exemplified as an internal crosslinking agent used in the production of a water-absorbent resin and 2-hydroxy-1-acryloxy -3-methacryloxypropane and the like. Of these, polyethylene glycol diacrylate and 2-hydroxy-1-acryloxy-3-methacryloxypropane are preferably used. The amount of the crosslinkable unsaturated monomer in such a case can be appropriately selected depending on the desired properties, but is 0.05 to 20 mol%, more preferably 0.1 to 0.1%, based on the total amount of the radical polymerizable compound. It is preferably 10 mol%, most preferably 0.3 to 5 mol%. The crosslinkable unsaturated monomer is 50 parts by mass or less, preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, with respect to 100 parts by mass of the ethylenically unsaturated monomer. Part range. By using a crosslinkable unsaturated monomer in combination, the absorption capacity under pressure can be further improved. The reason why the absorption capacity under pressure is improved by using a crosslinkable unsaturated monomer is not clear, but the water-soluble ethylenically unsaturated monomer is crosslinked by a crosslinkable unsaturated monomer during polymerization. This is presumably because this is introduced into the surface of the water-absorbent resin.

  The radical polymerizable compound may be used alone or in a mixture of two or more, and the combination in the latter case can be appropriately selected depending on the properties to be imparted and is particularly limited. It is not something.

  The amount of the radical polymerizable compound to be used is preferably in the range of 1 to 50 parts by mass, more preferably 1 to 30 parts by mass, and further preferably 1 to 10 parts by mass with respect to 100 parts by mass of the water absorbent resin. Within such a range, the granulation of the powder can be performed satisfactorily and the characteristics of the powder can be maintained.

(D) Radical polymerization initiator By simultaneously or separately adding radical polymerization initiators, the polymerization reactivity of the polymerizable compound by irradiation with active energy rays is further improved. Examples of the radical polymerization initiator that can be used in the present invention include photodegradable polymerization initiators such as benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds. In addition, persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; hydroperoxides such as hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide; azonitrile compounds, azoamidine compounds, cyclic azoamidine compounds, azoamides Thermal decomposition polymerization initiators such as compounds, alkylazo compounds, azo compounds such as 2,2′-azobis-2-amidinopropane hydrochloride; Furthermore, these polymerization initiators may be used in combination with a reducing agent such as sulfite and L-ascorbic acid (salt).

  When the powder is a water-absorbing resin, it can be easily and uniformly dispersed on the surface of the water-absorbing resin having excellent hydrophilicity and water-absorbing property. Preferably it is an initiator. Specifically, persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate; hydrogen peroxide; 2,2′-azobis-2-amidinopropane dihydrochloride, 2,2′-azobis [2-2 And water-soluble azo compounds such as (-imidazolin-2-yl) propane] dihydrochloride. Among these, the use of persulfate is particularly preferable in that the absorption capacity under pressure, liquid permeability, and free swelling ratio of the water-absorbent resin after the surface treatment are all excellent. In addition, a water-soluble radical polymerization initiator refers to what melt | dissolves 1 mass part or more in water (25 degreeC), Preferably it is 5 mass parts or more, More preferably, it is 10 mass parts or more.

  Although there is no restriction | limiting in the usage-amount of a radical polymerization initiator, In this invention, the range of 0.01-20 mass parts is preferable with respect to 100 mass parts of powder, More preferably, it is the range of 0.1-15 mass parts, Especially preferably, it is the range of 1-10 mass parts. If it is such a range, since the performance of a powder is maintained and granulation is performed effectively, it is preferable.

(E) Mixing aid The mixing aid is a water-soluble or water-dispersible compound other than the ethylenically unsaturated monomer or the water-soluble radical polymerization initiator, suppresses aggregation of the powder by water, Improves mixing with powder. At this time, water is not included as a mixing aid. The mixing aid is not particularly limited, but is preferably a water-soluble or water-dispersible compound. Specific examples of such water-soluble or water-dispersible compounds include surfactants, water-soluble polymers, hydrophilic organic solvents, water-soluble inorganic compounds, inorganic acids, inorganic acid salts, organic acids, and organic acids. Salt can be used. In the present specification, the water-soluble compound means a compound having a solubility in 100 g of water of 1 g or more at room temperature, preferably 10 g or more. By adding a mixing aid other than water, agglomeration of the powder with water can be suppressed and the aqueous solution and the powder can be mixed uniformly. Therefore, when the active energy ray is irradiated in the next step, the active energy ray Can be evenly and evenly applied to the powder, and the entire powder can be uniformly granulated. The mixing aid that can be used in this case is not particularly limited as long as it can suppress aggregation of the powder by water and can improve the mixing property of the aqueous solution and the water absorbent resin. Specifically, surfactants, water-soluble polymers, hydrophilic organic solvents, water-soluble inorganic compounds, inorganic acids, inorganic acid salts, organic acids and organic acid salts can be used.

  In the case of using a mixing aid, the usage form of the mixing aid is not particularly limited, and it may be used in the form of a powder or may be used by dissolving, dispersing or suspending in a solution. Used in the form of an aqueous solution.

  In addition, the order of addition of the mixing aid when using the mixing aid is not particularly limited, and a method of adding an aqueous solution to the powder in advance and then adding an aqueous solution thereto and mixing, and mixing aid A method such as a method in which an agent is dissolved in an aqueous solution and mixed with the powder can also be used.

  As such a surfactant, at least one surfactant selected from the group consisting of a nonionic surfactant having an HLB of 7 or more or an anionic surfactant can be used. For example, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, polyoxyethylene acyl ester, sucrose fatty acid ester, higher alcohol sulfate ester salt, alkylnaphthalene sulfone Examples thereof include acid salts, alkyl polyoxyethylene sulfate salts, and dialkyl sulfosuccinates. Among these, polyoxyethylene alkyl ether is preferable. The number average molecular weight of the polyoxyethylene alkyl ether is preferably 200 to 100,000, and more preferably 500 to 10,000. If the number average molecular weight is too large, the solubility in water decreases, the amount added cannot be increased, and the viscosity of the solution also increases, so the mixing with the powder is not good. On the other hand, when the number average molecular weight is too small, the effect as a mixing aid is inferior.

  Examples of the water-soluble polymer include polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polypropylene glycol, polyacrylamide, polyacrylic acid, sodium polyacrylate, polyethyleneimine, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, dextrin, Examples include sodium alginate and starch. Among these, polyethylene glycol is preferable. Similar to polyoxyethylene alkyl ether, the number average molecular weight is preferably 200 to 100,000, more preferably 500 to 10,000.

  Examples of hydrophilic organic solvents include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, isobutyl alcohol and t-butyl alcohol; ketones such as acetone and methyl ethyl ketone; dioxane and alkoxy (poly) ethylene glycol , Ethers such as tetrahydrofuran; amides such as ε-caprolactam and N, N-dimethylformamide; sulfoxides such as dimethyl sulfoxide; ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, 1,3 -Propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, glycerin, 2-butene-1,4-dioe 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, And polyhydric alcohols such as triethanolamine, polyoxypropylene, pentaerythritol, and sorbitol; and one or more of these can be used.

  Examples of water-soluble inorganic compounds include alkali metal salts such as sodium chloride, sodium hydrogen sulfate, and sodium sulfate other than the polymerization initiator, ammonium salts such as ammonium chloride, ammonium hydrogen sulfate, and ammonium sulfate, and alkalis such as sodium hydroxide and potassium hydroxide. Metal hydroxides, polyvalent metal salts such as aluminum chloride, polyaluminum chloride, aluminum sulfate, potassium alum, calcium chloride, alkoxy titanium, ammonium zirconium carbonate, zirconium acetate, and bicarbonates, dihydrogen phosphates, phosphorus Non-reducing alkali metal salt pH buffering agents such as oxyhydrogen salts are exemplified.

  Examples of inorganic acids (salts) include hydrochloric acid, sulfuric acid, phosphoric acid, carbonic acid, boric acid, and salts thereof, such as alkali metal salts and alkaline earth metal salts, and examples of organic acids (salts) include Representative examples include acetic acid, propionic acid, lactic acid, citric acid, succinic acid, malic acid, tartaric acid and salts thereof, for example, alkali metal salts and alkaline earth metal salts.

  Of the above examples, polyoxyethylene alkyl ether, polyethylene glycol, water-soluble polyvalent metal salt, sodium chloride, ammonium hydrogen sulfate, ammonium sulfate, sulfuric acid, and hydrochloric acid are preferably used as mixing aids.

  Since the first of the present invention relates to a granulation method, the present invention can be used as a method of granulating particles having a particle diameter less than a desired particle diameter to obtain an appropriate particle diameter. According to the granulation method of the present invention, what has conventionally been a waste loss such as fine powder can be used without waste. For example, after classification into particles (fine particles) having a desired particle size (target particles), particles having a desired particle size (target particles), and particles (coarse particles) having a larger particle size than desired by classification, By granulating by the granulation method of the invention, the fine particles can be recycled. The particle size of the target particle is appropriately set according to the use of the powder used.

  Moreover, instead of granulating only the fine particles as described above, the entire powder may be granulated by the first method of the present invention. Even in such a form, the generated fine particles can be granulated, and the amount of fine particles contained is reduced. Specifically, the powder having a particle diameter of less than 500 μm is preferably 20% or less, preferably 10% or less, with respect to 100 parts by mass of the powder obtained by the first granulation method of the present invention. Is more preferable. The particle size distribution of the powder after granulation shifts to a higher particle size side as compared with the particle size distribution of the powder before granulation. The ratio of the shift is changed by appropriately setting the type and amount of the radical polymerization agent, the ratio of water, the irradiation condition of the active energy ray, the flow method during irradiation, and the like. When the powder is a water-absorbent resin, the final powder is preferably 20 parts by mass with respect to 100 parts by mass of the powder having a particle size in the range of less than 500 μm (specified by sieve classification). Hereinafter, it is more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less. Further, the particles having a particle diameter in the range of less than 150 μm are preferably 3 parts by mass or less, more preferably 1 part by mass or less with respect to 100 parts by mass of the powder.

  When the powder is a water-absorbent resin, the final particle size is preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 95% by mass or more, more preferably 150 μm or more based on the required properties. It is 98 mass% or more, Most preferably, it is 100 mass%. A water-absorbent resin having a particle diameter of 150 μm or more is less likely to cause clogging during use or to reduce water absorption performance. In order to adjust the particle size to 150 μm or more, after manufacturing the water absorbent resin, the water absorbent resin (1) of less than 150 μm and the water absorbent resin (2) of 150 μm or more are classified to obtain the water absorbent resin (1). After the granulation by the first granulation method of the present invention, classification is performed again, and the obtained water-absorbing resin (3) having a size of 150 μm or more is returned to the water-absorbing resin (2), thereby obtaining a desired particle diameter (150 μm Many particles of the above are obtained. The step (1) and the step (2) may be further performed on the water-absorbent resin thus sized, or another surface cross-linking step may be performed. In addition, as a numerical value of the said particle diameter, the value measured with the measuring method of the particle size distribution described in the following Examples shall be employ | adopted.

  A second aspect of the present invention is a powder sizing method in which at least one of classification and pulverization is performed on the powder obtained in the first aspect.

  The powder obtained by the first granulation method may contain aggregates (coarse particles) in which a plurality of particles are aggregated, in addition to particles (target particles) having a desired particle size. In addition, there may be a case where the amount of fine particles is smaller than that before granulation. By performing classification and / or pulverization (pulverization), a powder having a narrow particle size distribution can be obtained.

  The method of sizing by classification or pulverization is not particularly limited, and examples thereof include the following two preferred forms.

  (1) A step of classifying the powder obtained in the first aspect of the present invention to remove coarse particles to obtain a sized powder; and after pulverizing the coarse particles, classify the uncrushed coarse particles; A form including a step of coalescing the finely sized powder with fine particles.

  (2) A mode including a step of pulverizing and classifying the powder obtained in the first aspect of the present invention to obtain a sized powder.

  Although the amount of fine powder is reduced by the granulation method of the present invention, agglomerates larger than the desired particle size may be produced. Such agglomerates can be easily sized to an appropriate particle size by pulverization.

  As a pulverizer that can be used for such pulverization, for example, among the pulverization model names classified in Table 1.10 of the Powder Engineering Handbook (Edition of the Powder Engineering Society, first edition), a shear pulverizer, It is classified into an impact crusher and a high-speed rotary crusher, and those having one or more crushing mechanisms such as cutting, shearing, impact, and friction can be preferably used. Among crushers corresponding to these models, cutting and shearing A crusher whose mechanism is the main mechanism can be used particularly preferably. For example, a roll cutter (roll rotary type) crusher or a knife cutter type crusher of a type in which a knife rotates to crush an object is preferable.

  The classification operation itself can be performed using a conventionally known dry classifier or the like. Such devices include a sieving machine that uses a sieve screen to separate fine particles that pass through the mesh and coarse particles that do not pass through, a horizontal flow type, a rising flow type, etc. Gravity classifiers that classify particles and fine powders, centrifugal classifiers that use sedimentation of particles in a centrifugal field, and classify particles with large inertia by changing the direction of airflow containing particles suddenly. An inertia classifier or the like can be used.

  Furthermore, you may add the process of granulating the fine particle removed by classification further by 1st invention.

  The third of the present invention is at least one of the steps of producing a powder, and at least one of the steps of producing a powder by using the powder granulated product obtained by the first granulation method of the present invention. It is a manufacturing method of powder including the process added in a process. Since the performance of the first granulated product of the present invention is maintained or improved as a powder, the physical properties of the powder are maintained even after recycling.

  The step of adding the granulated product is not limited as long as it is one or more in the powder production step. When the powder is a water-absorbing resin, for example, a monomer aqueous solution preparation step, a polymerization step, a drying step, a pulverization / disintegration / classification step, a surface treatment step, a storage step and the like can be mentioned. It can also be added in the transport step of each step. A water absorbent resin granulated product can also be added to the water absorbent resin as the final product.

  Specifically, it can be added to the monomer aqueous solution before polymerization, added to the gel during polymerization or after polymerization, added in the pulverization step, or added to the mixing step of the surface cross-linking agent. . The water-absorbent resin granulated product for recycling does not necessarily need to be dried and pulverized, and can be added as a granulated product mixed with an aqueous liquid.

  As a recycling method, there is known a method in which fine powder of a water-absorbing resin is added as it is to an aqueous monomer solution or a gel during or after polymerization for recycling. However, in this method, when the fine powder is mixed with the monomer, the fine powder tends to generate mamako, and thus it is not easy to mix uniformly. In addition, when added to the polymer gel, there is also a problem that the generated water vapor adheres to the piping and the inner surface of the apparatus. On the other hand, when adding water-absorbent resin fine powder in the form of a granulated product to the monomer aqueous solution or polymer gel, it is possible to prevent the occurrence of such mako and adhesion to the piping and the inner surface of the device. The fine powder of the conductive resin can be industrially advantageously recycled.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these. Hereinafter, for convenience, “mass part” may be simply referred to as “part”, and “liter” may be simply referred to as “L”. Measurement methods and evaluation methods in Examples and Comparative Examples are shown below. Moreover, a mass part and mass% are synonymous with a weight part and weight%, respectively. Unless otherwise specified, work is performed at room temperature (23 ± 1 ° C.) and humidity of 30 RH%.

(1) Particle size distribution: mass average particle size (D50) and logarithmic standard deviation (σζ) of particle size distribution
A water-absorbing resin or a particulate water-absorbing agent 10.0 g was appropriately selected from room temperature (20 to 25 ° C.) and humidity 50 RH% with openings of 2000 μm, 1000 μm, 850 μm, 600 μm, 500 μm, 300 μm, 150 μm, and 45 μm. Charge into JIS standard sieve (THE IIDA TESTING SIVE: diameter 8 cm), perform classification for 5 minutes with vibration classifier (IIDA SIEVE SHAKER, TYPE: ES-65 type, SER. No. 0501), log residual percentage R logarithm Plotted on probability paper. Thereby, the particle diameter corresponding to R = 50 mass% was read as the mass average particle diameter (D50).

  Further, when X1 is R = 84.1% by mass and X2 is each particle size when R = 15.9% by mass, the logarithmic standard deviation (σζ) is expressed by the following equation. That is, the smaller the value of σζ, the narrower the particle size distribution.

(2) Centrifugal Retention Capacity (also referred to as “CRC”)
CRC indicates the absorption capacity for 30 minutes with no pressure applied to a 0.90 mass% sodium chloride aqueous solution (hereinafter also simply referred to as “physiological saline”).

  0.200 g of water-absorbent resin was uniformly put into a bag (85 mm × 60 mm) made of a nonwoven fabric (trade name: Heaton Paper, model: GSP-22, manufactured by Nankoku Pulp Industries Co., Ltd.) and heat sealed, and then at room temperature. It was immersed in a large excess (about 500 mL) of physiological saline. After 30 minutes, the bag was pulled up and drained for 3 minutes with a centrifugal force (250 G) described in edena ABSORBENCY II 441.1-99 using a centrifuge (manufactured by Kokusan Co., Ltd., model: H-122). The mass of the bag was measured. This mass was defined as W1 (g). Moreover, the same operation was performed without using a water absorbent resin, and the mass at that time was defined as W0 (g). And CRC (g / g) was computed from the value of these W1 and W0 according to the following numerical formula.

(3) Absorption capacity under pressure (AAP)
A stainless steel 400 mesh wire mesh (aperture size 38 μm) is fused to the bottom of a plastic support cylinder with an inner diameter of 60 mm, and water is absorbed on the wire mesh at room temperature (25 ± 2 ° C.) and humidity 50 RH%. 0.900 g of the water-soluble resin was uniformly sprayed, and the outer diameter was adjusted to be able to uniformly apply a load of 4.83 kPa to the water-absorbent resin. A piston and a load in which no gap was formed between the wall surface and the vertical movement was not hindered were placed in this order, and the mass Wa (g) of this measuring device set was measured.

  A glass filter with a diameter of 90 mm (manufactured by Mutual Riken Glass Co., Ltd., pore diameter: 100 to 120 μm) is placed inside a petri dish with a diameter of 150 mm, and a 0.9 mass% sodium chloride aqueous solution (physiological saline) (23 ± 1 ° C.) was added to the same level as the top surface of the glass filter. On top of that, a sheet of filter paper having a diameter of 90 mm (manufactured by ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) was placed so that the entire surface was wetted. Excess liquid was removed.

A set of measuring devices was placed on the wet filter paper, and the liquid was absorbed under load for a predetermined time. This absorption time was calculated from the start of measurement and was 1 hour later. Specifically, after 1 hour, the measuring device set was lifted and its mass W _b (g) was measured. This mass measurement must be performed as quickly as possible and without vibrations. Then, the absorption capacity under pressure (AAP) (g / g) was calculated from W _a and W _b by the following formula.

(4) Total moisture content 1.00 g of water absorbent resin is uniformly spread on the bottom of the aluminum bag cup in an aluminum cup having a bottom diameter of 4 cm and a height of 2 cm, and the weight of the aluminum cup containing the water absorbent resin [W4 (G)] was measured. This was left in a hot air dryer adjusted to 180 ° C. for 3 hours, and the weight [W5 (g)] of the water-absorbent resin-containing aluminum cup immediately after removal from the hot air dryer (within at least 1 minute) was measured. did. And from these W4 and W5, the whole moisture content (mass%) was computed according to following Formula.

(Production Example 1)
5433 g of an aqueous solution of sodium acrylate having a neutralization rate of 70 mol% (monomer) in a reactor formed by attaching a lid to a stainless steel double arm type kneader with an internal volume of 10 L and having two sigma blades Concentration: 39% by mass) was charged, and 12.83 g of polyethylene glycol diacrylate (average number of ethylene oxide units: n = 9) as an internal crosslinking agent was dissolved in the aqueous solution to prepare a reaction solution. Subsequently, this reaction liquid was deaerated under a nitrogen gas atmosphere. Subsequently, 29.43 g of a 10% by mass aqueous solution of sodium persulfate as a polymerization initiator and 24.53 g of a 0.1% by mass aqueous solution of L-ascorbic acid were added to the reaction solution while stirring. As a result, polymerization started after about 1 minute. Then, polymerization was performed at 20 to 95 ° C. while pulverizing the generated gel, and a hydrous gel-like crosslinked polymer was taken out 30 minutes after the polymerization started. The obtained hydrogel crosslinked polymer had a particle size of 5 mm or less. The crushed water-containing gel-like crosslinked polymer was spread on a 50 mesh (mesh opening 300 μm) wire net and dried with hot air at 175 ° C. for 50 minutes. In this way, an agglomerated powdery aggregate that can be easily pulverized was obtained.

  The obtained powdery aggregate was pulverized using a roll mill, and further classified using a JIS standard sieve having an opening of 425 μm. Next, the particles that passed through the sieve having an opening of 425 μm by the above operation were classified using a JIS standard sieve having an opening of 125 μm, and the particles that passed through the sieve having an opening of 125 μm were removed. In this way, a water absorbent resin (A) was obtained.

  The particle size distribution of the obtained water-absorbent resin (A) is shown in Table 1 below. In Table 1 below, “2000 μm on” indicates the ratio (mass%) of the water-absorbing resin remaining on the sieve having an opening of 2000 μm after the classification operation. “45 (600, 500, 300) μm pass” indicates the ratio (mass%) of the water-absorbent resin that passed through a sieve having an opening of 45 (600, 500, 300) μm after the classification operation. “X to y μm” indicates the ratio (mass%) of the water-absorbent resin that passed through the sieve having an opening of x μm and remained on the sieve having an opening of y μm after the classification operation.

Example 1
10 g of water-absorbing resin (A) as a base polymer is added to a 500 mL quartz separable flask, 0.02 g of polyethylene glycol diacrylate (average number of ethylene oxide units: n = 9), 0.2 g of sodium acrylate, acrylic acid A processing solution in which 0.08 g, 1.6 g of water, and 0.1 g of ammonium persulfate were mixed in advance was added, and a stirring blade (an inclined four-paddle shown in FIGS. 2 and 3; FIG. 2 shows the bottom of the separable flask). A schematic view of the paddle as viewed from above, FIG. 3 is a schematic view of the paddle as viewed from the direction of III in FIG. 2) and is stirred at 500 rpm (room temperature (23 ± 1 ° C.), 10 minutes) to form a water absorbent resin composition Got.

Using an ultraviolet irradiation apparatus (UV-152 / 1MNSC3-AA06) equipped with a metal halide lamp (USHIO, UVL-1500M2-N1), at an irradiation intensity of 60 mW / cm ² for 10 minutes at room temperature (23 ± 1 ° C. ) Was irradiated from the side of the separable flask (FIG. 1) to obtain a granulated water-absorbing resin. The center of the lamp was installed so that the distance from the side surface (quartz surface) of the separable flask was 14 cm (FIG. 1), and the temperature in the system due to radiant heat was adjusted to 70 to 80 ° C. during irradiation. Table 1 shows the particle size distribution of the obtained water-absorbent resin, and Table 2 shows the results of various evaluations. In addition, “CRC after correction of total moisture content” and “AAP after correction of total moisture content” were calculated by the following formulas. In the following formula, “CRC before correction of total moisture content” is the centrifuge retention capacity (CRC) of the water-absorbent resin before measuring the total moisture content of (5) above. “AAP before moisture content correction” is the absorption capacity (AAP) under pressure of the water absorbent resin before measuring the total moisture content in (5) above.

(Example 2)
A water absorbent resin composition was obtained in the same manner as in Example 1 except that 1.6 g of water was changed to 3.2 g of water. Further, as in Example 1, the water-absorbent resin composition was irradiated with ultraviolet rays. Table 1 shows the particle size distribution of the obtained water-absorbent resin, and Table 2 shows the results of various evaluations.

(Comparative Example 1)
10 g of water-absorbing resin (A) as a base polymer is added to a 500 mL quartz separable flask, 0.02 g of polyethylene glycol diacrylate (average number of ethylene oxide units: n = 9), 0.2 g of sodium acrylate, acrylic acid A processing solution in which 0.08 g, 0.9 g of water, 0.1 g of ammonium persulfate, and 0.05 g of polyethylene glycol monomethyl ether (number average molecular weight of about 2,000) were mixed in advance was added, and a stirring blade (shown in FIGS. 2 and 3) was added. The mixture was stirred at 500 rpm (23 ± 1 ° C., 10 minutes) with an inclined four-sheet paddle to obtain a water-absorbent resin composition. Further, the water absorbent resin composition obtained in the same manner as in Example 1 was irradiated with ultraviolet rays. Table 1 shows the particle size distribution of the obtained water-absorbent resin, and Table 2 shows the results of various evaluations.

  From the above results, it was shown that the particle size distribution of the water-absorbent resins of Example 1 and Example 2 was shifted to the higher particle size side, and the granulation effect was improved. In addition, as shown in Table 2, the water-absorbent resins of the examples were superior in water absorption characteristics, particularly in water absorption capacity under pressure, as compared with conventional granulated products. In addition, the water-absorbent resin of Examples had a small amount of remaining monomer (radical polymerizable compound). Even if these granulated materials are classified or pulverized as appropriate and mixed with the powder as the final product, high water absorption characteristics can be maintained.

It is a figure which shows the outline of the ultraviolet irradiation apparatus and stirring apparatus which were used in the Example. It is the schematic of the paddle seen from the upper direction with respect to the separable flask bottom face of the stirring apparatus used in the Example. It is the schematic of the paddle seen from the III direction of FIG.

Explanation of symbols

1 UV irradiation equipment,
2 lamps,
3 Separable flask,
3a bottom of separable flask,
4 Paddles.

Claims (10)

(1) A mixing step of obtaining a powder composition containing water by mixing 10 parts by mass or more of water with respect to 100 parts by mass of the powder, radically polymerizable compound, and
(2) an irradiation step of irradiating the powder composition with active energy rays;
A method for granulating a powder.   The granulation method according to claim 1, wherein a mixing amount of the radical polymerizable compound is 1 to 50 parts by mass with respect to 100 parts by mass of the powder.   The granulation method according to claim 1 or 2, wherein, in the mixing step, a powder composition containing water by mixing radical polymerization initiators simultaneously or separately is obtained.   The granulation method according to claim 1, wherein the powder is a water absorbent resin.   The granulation method according to any one of claims 1 to 4, wherein the irradiation step includes a step of flowing the powder composition to irradiate the active energy ray.   The granulation method according to claim 5, wherein at least a part of the powder composition is fluidized in a laminar flow state.   The granulation method according to any one of claims 1 to 6, wherein the active energy rays are ultraviolet rays.   A powder granulated product obtained by the granulation method according to any one of claims 1 to 7, wherein a powder having a particle diameter of less than 500 µm is contained with respect to 100 parts by mass of the powder granulated product. Powder granulated product which is 20 parts by mass or less.   A powder sizing method in which at least one of classification and pulverization is performed on the powder granulated product obtained by the granulation method according to claim 1.   A method for producing a powder, comprising the step of adding the powder granulated product obtained by the granulation method according to any one of claims 1 to 7 in at least one step of producing a powder. .

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