Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
  • B01J20/26—Synthetic macromolecular compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
  • B01J20/30—Processes for preparing, regenerating, or reactivating
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/04—Acids; Metal salts or ammonium salts thereof
  • C08F220/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/12—Powdering or granulating

Definitions

• the present invention relates to a method for producing water-absorbent resin particles.
• a polymerization method such as an aqueous solution polymerization method in which water is used at the time of polymerization to obtain a lumpy hydrogel (for example, Patent Document 1).
• the lumpy hydrogel contains a large amount of water used during the polymerization, and therefore needs to be dried.
• the hydrogel when the hydrous gel is dried using a drying device, the hydrogel may adhere to the metal surface of the drying device, and it may be difficult to peel off even after the drying is completed.
• a resin-processed metal such as fluororesin
• a metal coated with a resin such as fluororesin has problems such as a lower heat transfer rate, lower heat resistance, and easy deterioration than the original metal. Therefore, in order to improve the peelability of the resin coating or the like. It is desirable that the crosslinked polymer has high peelability after drying even on a general unprocessed metal surface.
• An object of the present invention is to provide a method for producing water-absorbent resin particles having excellent peelability from a metal surface of a crosslinked polymer after drying.
• controlling the degree of drying particularly at the initial stage of the drying step (15 minutes from the start of the drying step) improves the peelability of the crosslinked polymer after the drying step. I found it important.
• the present invention is a method for producing water-absorbent resin particles containing a crosslinked polymer, which comprises a drying step of drying the crosslinked polymer, and has a dry content standard moisture content of 100% by mass or more before the drying step of the crosslinked polymer.
• the present invention provides a method in which the drying step is carried out so that the initial rate of change of the dry content-based water content represented by the following formula is 6.0% / min or less.
• Initial rate of change of dry content standard moisture content Rate (% / min) [ ⁇ (Dry content standard moisture content before the drying process-Dry content standard moisture content 15 minutes after the drying process) / Dry content standard moisture content before the drying process) Rate ⁇ x 100] / 15
• the drying step is performed so that the initial rate of change of the dry content-based moisture content is 5.6% / min or less.
• the drying step is performed so that the initial rate of change of the dry content-based moisture content is 3.0% / min or more.
• the crosslinked polymer may be further pulverized.
• Water-soluble means that it exhibits a solubility in water of 5% by mass or more at 25 ° C.
• the materials exemplified in the present specification may be used alone or in combination of two or more.
• the content of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified.
• “content of (meth) acrylic acid compound” means acrylic acid, acrylic acid salt, methacrylic acid and methacrylic acid. It means the total amount of acid salt.
• Room temperature means 25 ° C ⁇ 2 ° C.
• the method for producing water-absorbent resin particles containing the crosslinked polymer according to the present embodiment includes a drying step of drying the crosslinked polymer.
• the crosslinked polymer can be obtained by polymerizing, for example, a monomer.
• Polymerization of the monomer can be carried out using, for example, an aqueous monomer solution containing the monomer.
• the production method according to the present embodiment is suitable when the crosslinked polymer obtained by polymerization is in the form of a water-containing gel and a polymerization method that needs to be dried, for example, an aqueous solution polymerization method is used.
• an aqueous solution polymerization method is used.
• the monomer may contain an ethylenically unsaturated monomer and may contain a water-soluble ethylenically unsaturated monomer.
• the ethylenically unsaturated monomer include unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, maleic anhydride and fumaric acid, and carboxylic acid-based monomers such as salts thereof; (meth) acrylamide, Nonionic monomers such as N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate; N, N-diethylaminoethyl ( Amino group-containing unsaturated monomers such as meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylamide, and quaternary products thereof; vinyl
• the ethylenically unsaturated monomer can contain at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and salts thereof.
• the ethylenically unsaturated monomer may contain both (meth) acrylic acid and a salt of (meth) acrylic acid.
• Examples of the salt of unsaturated carboxylic acid ((meth) acrylic acid, etc.) include alkali metal salts (sodium salt, potassium salt, etc.), ammonium salts, and the like.
• the ethylenically unsaturated monomer having an acid group may have an acid group neutralized in advance with an alkaline neutralizing agent.
• alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; ammonia and the like.
• the alkaline neutralizer may be used in the form of an aqueous solution in order to simplify the neutralization operation.
• the acid group may be neutralized before the polymerization of the ethylenically unsaturated monomer as a raw material, or may be performed during or after the polymerization.
• the degree of neutralization of the ethylenically unsaturated monomer by the alkaline neutralizer is from the viewpoint that good water absorption performance can be easily obtained by increasing the osmotic pressure, from the viewpoint of enhancing safety, and from the viewpoint of increasing the excess alkaline neutralizer. From the viewpoint of suppressing defects due to existence, 10 to 100 mol%, 30 to 90 mol%, 40 to 85 mol%, or 50 to 80 mol% is preferable.
• the "neutralization degree” is the neutralization degree for all the acid groups of the ethylenically unsaturated monomer.
• the content of the monomer is 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, and 30% by mass based on the total mass of the aqueous monomer solution. % Or more, or 35% by mass or more.
• the content of the monomer may be 60% by mass or less, 55% by mass or less, 50% by mass or less, less than 50% by mass, 45% by mass or less, less than 45% by mass, or 40% by mass or less. From the viewpoint of facilitating the adjustment of the dry content standard moisture content before the drying step, which will be described later, to an appropriate range, the monomer content in the aqueous monomer solution is preferably 40% by mass or less.
• the water content of the monomer aqueous solution is preferably 60% by mass or more.
• the water content of the monomer aqueous solution can be calculated by the following formula.
• Moisture content of monomeric aqueous solution (%) 100-Solid content of monomeric aqueous solution (%)
• the solid content ratio of the monomer aqueous solution is the ratio of the compound converted into the solid content constituting the crosslinked polymer to the total amount of the monomer aqueous solution. Since the amount of components other than the monomer (for example, a cross-linking agent and a polymerization initiator) contained in the monomer aqueous solution is smaller than the amount of the monomer, the monomer content in the monomer aqueous solution May be a substantial solid content.
• the water content of the aqueous monomer solution may be, for example, 70% by mass or less, or 65% by mass or less.
• the content of the (meth) acrylic acid compound is based on the total amount of monomers contained in the aqueous monomer solution and / or the total amount of ethylenically unsaturated monomers contained in the aqueous monomer solution. It may be 50 mol% or more, 70 mol% or more, 90 mol% or more, 95 mol% or more, 97 mol% or more, or 99 mol% or more.
• the monomer contained in the aqueous monomer solution is substantially composed of a (meth) acrylic acid compound, that is, 100 mol% of the monomer contained in the aqueous monomer solution is a (meth) acrylic acid compound. It may be in a certain aspect.
• the monomer aqueous solution may contain a polymerization initiator.
• the polymerization of the monomer contained in the aqueous monomer solution may be started by adding a polymerization initiator to the aqueous monomer solution and, if necessary, heating, irradiating with light or the like.
• the polymerization initiator include a photopolymerization initiator, a radical polymerization initiator and the like, and a water-soluble radical polymerization initiator is preferable.
• the polymerization initiator preferably contains at least one selected from the group consisting of azo compounds and peroxides from the viewpoint of easily enhancing water absorption performance.
• Examples of the azo compound include 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride and 2,2'-azobis ⁇ 2- [N- (4-chlorophenyl) amidino] propane ⁇ dihydrochloride.
• the azo compounds are 2,2'-azobis (2-methylpropionamide) dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2 from the viewpoint that good water absorption performance can be easily obtained.
• Peroxides include persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl. Examples thereof include organic peroxides such as peroxyacetate, t-butylperoxyisobutyrate, and t-butylperoxypivalate.
• the peroxide is composed of potassium persulfate, ammonium persulfate, and sodium persulfate from the viewpoint of easily obtaining good water absorption performance and easily reducing unreacted monomers contained in the water-absorbent resin particles. It is preferable to include at least one selected from the group.
• the content of the polymerization initiator is an ethylenically unsaturated monomer (for example, (meth)) from the viewpoint of easily enhancing the water absorption performance and easily reducing the amount of unreacted monomers contained in the water-absorbent resin particles.
• Acrylic acid compound 0.001 mmol or more, 0.005 mmol or more, 0.01 mmol or more, 0.05 mmol or more, 0.1 mmol or more, or 0.15 mmol or more is preferable with respect to 1 mol.
• the content of the polymerization initiator is 5 mmol or less, 4 mmol or less, 2 mmol or less, 1 mmol or less, 0.9 mmol or less, from the viewpoint of easily improving the water absorption performance and avoiding a rapid polymerization reaction. It is preferably 0.7 mmol or less, 0.5 mmol or less, 0.4 mmol or less, or 0.3 mmol or less. From these viewpoints, the content of the polymerization initiator is preferably 0.001 to 5 mmol.
• the monomer aqueous solution may contain a reducing agent.
• a reducing agent examples include sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, L-ascorbic acid and the like.
• a polymerization initiator and a reducing agent may be used in combination.
• the monomer aqueous solution may contain an oxidizing agent.
• the oxidizing agent include hydrogen peroxide, sodium perborate, perphosphate and salts thereof, potassium permanganate and the like.
• the monomer aqueous solution may contain an internal cross-linking agent.
• the obtained cross-linking polymer can have a cross-linking structure by the internal cross-linking agent in addition to the self-cross-linking structure by the polymerization reaction as the internal cross-linking structure.
• Examples of the internal cross-linking agent include compounds having two or more reactive functional groups (for example, polymerizable unsaturated groups).
• Examples of the internal cross-linking agent include di or tri (meth) acrylic acid esters of polyols such as (poly) ethylene glycol, (poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and (poly) glycerin.
• unsaturated polyesters obtained by reacting the above polyol with unsaturated acids (maleic acid, fumaric acid, etc.); (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin.
• Glycidyl group-containing compounds such as diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) glycerin polyglycidyl ether, and glycidyl (meth) acrylate; bisacrylamides such as N, N'-methylenebis (meth) acrylamide; Di or tri (meth) acrylic acid esters obtained by reacting with (meth) acrylic acid; obtained by reacting polyisocyanate (tolylene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth) acrylic acid.
• bisacrylamides such as N, N'-methylenebis (meth) acrylamide
• Di or tri (meth) acrylic acid esters obtained by reacting with (meth) acrylic acid
• polyisocyanate tolylene diisocyanate, hexamethylene diisocyanate, etc.
• the internal cross-linking agent is (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) from the viewpoint of easily enhancing water absorption performance and excellent reactivity.
• the content of the internal cross-linking agent is 0.001 mmol or more and 0.005 per 1 mol of ethylenically unsaturated monomer (for example, (meth) acrylic acid compound) from the viewpoint that good water absorption performance can be easily obtained. It is preferably mmol or more, 0.01 mmol or more, 0.05 mmol or more, 0.07 mmol or more, 0.09 mmol or more, 0.1 mmol or more, 0.11 mmol or more, or 0.13 mmol or more.
• the content of the internal cross-linking agent is 5 mmol or less, 4.5 mmol or less, 4 mmol or less, 3.5 mmol or less, 3 mmol or less, 2.5 mmol or less, 2 from the viewpoint that good water absorption performance can be easily obtained. Millimole or less, 1.5 mmol or less, 1 mmol or less, 0.9 mmol or less, 0.8 mmol or less, 0.7 mmol or less, 0.5 mmol or less, 0.4 mmol or less, or 0.3 mmol or less preferable. From these viewpoints, the content of the internal cross-linking agent is preferably 0.001 to 5 mmol.
• the monomer aqueous solution may contain additives such as a chain transfer agent, a thickener, and an inorganic filler as components different from the above-mentioned components.
• a chain transfer agent include thiols, thiol acids, secondary alcohols, hypophosphorous acid, phosphorous acid, achlorine and the like.
• the thickener include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyethylene glycol, polyacrylic acid, polyacrylic acid neutralized product, polyacrylamide and the like.
• the inorganic filler include metal oxides, ceramics, and viscous minerals.
• a polymerization method for aqueous solution polymerization there is a static polymerization method in which the monomer aqueous solution is polymerized without stirring (for example, a static state); a stirring polymerization method in which the monomer aqueous solution is polymerized while being stirred in a reaction device, or the like. Can be mentioned.
• a static polymerization method when the polymerization is completed, a single block-shaped gel occupying substantially the same volume as the monomer aqueous solution existing in the reaction vessel can be obtained.
• the form of polymerization may be batch, semi-continuous, continuous or the like.
• the polymerization reaction can be carried out while continuously supplying the monomer aqueous solution to the continuous polymerization apparatus to continuously obtain a gel.
• the polymerization temperature varies depending on the polymerization initiator used, but from the viewpoint of rapidly advancing the polymerization, increasing the productivity by shortening the polymerization time, and removing the heat of polymerization to facilitate the smooth reaction, 0 to 0 to It is preferably 130 ° C or 10 to 110 ° C.
• the polymerization time is appropriately set depending on the type and amount of the polymerization initiator used, the reaction temperature and the like, but is preferably 1 to 200 minutes or 5 to 100 minutes.
• the drying step may be performed. You may provide it.
• the hydrous gel may be placed in an environment of 25 ° C. or higher and lower than the drying temperature (for example, 75 ° C. or lower) until it is subjected to the drying step.
• the crosslinked polymer is preferably coarsely ground in advance before the drying step. That is, it is preferable that the production method according to the present embodiment includes a step of coarsely crushing the crosslinked polymer before the step of drying the crosslinked polymer. By coarsely crushing the crosslinked polymer before the drying step, drying can be performed more efficiently. In the coarse crushing step, for example, the massive hydrogel obtained by polymerization can be coarsely crushed.
• a kneader pressurized kneader, double-armed kneader, etc.
• a meat chopper, a cutter mill, a pharma mill, or the like can be used.
• the lumpy hydrogel may be cut in advance into, for example, about 5 cm square, and the cut hydrogel may be subjected to coarse crushing.
• the polymerization step is carried out by stirring polymerization with an apparatus such as a kneader, the polymerization step and the coarse crushing step may be carried out substantially at the same time.
• the crosslinked polymer (crude gel, coarsely crushed polymer) after coarse crushing may be in the form of particles, or may have an elongated shape such that particles are connected.
• the size of the minimum side of the coarsely crushed gel may be, for example, about 0.1 to 15 mm, preferably about 1.0 to 10 mm.
• the size of the maximum side of the coarsely crushed gel may be about 0.1 to 200 mm, preferably about 1.0 to 150 mm.
• the drying step is performed so that the initial rate of change of the dry content-based water content represented by the following formula is 6.0% / min or less.
• the dry content standard moisture content before the drying step shall be 100% by mass or more.
• Initial rate of change of dry content standard moisture content Rate (% / min) [ ⁇ (Dry content standard moisture content before the drying process-Dry content standard moisture content 15 minutes after the drying process) / Dry content standard moisture content before the drying process) Rate ⁇ x 100] / 15
• drying means removing at least a part of the water contained in the crosslinked polymer by placing the crosslinked polymer in an environment of 80 ° C. or higher.
• the dry content standard moisture content is the ratio (mass%) of the water content in the crosslinked polymer to the solid content (dry amount) in the crosslinked polymer. Therefore, when the dry content standard moisture content is 100% by mass, the moisture content and the solid content content in the crosslinked polymer are the same.
• the initial rate of change of the dry content-based moisture content represented by the above formula means the average value per minute of the dry-weight-based moisture content change rate in 15 minutes from the start of the drying process.
• the crosslinked polymer is applied to the metal surface of the drying device after the drying step. It is possible to prevent sticking and improve the peelability.
• the crosslinked polymer after the drying step is completed, can be peeled off from the metal surface by natural dropping, for example, without applying a force to the crosslinked polymer from the outside.
• the crosslinked polymer is dried by placing the crosslinked polymer on a metal surface.
• the metal surface may be, for example, a wire mesh, a metal plate having holes, or the like.
• Metals that have undergone resin processing such as fluororesin processing tend to have a lower heat transfer rate than the original unprocessed metal, so the metal surface of the drying device is resin-processed for efficient drying. It is preferable not to do so. According to the production method according to the present embodiment, even if a metal that has not been resin-processed is used for at least a part of the metal surface of the drying device, the peelability of the crosslinked polymer from the drying device is excellent.
• the dry content standard moisture content before the drying step is the dry content standard moisture content immediately before the crosslinked polymer is subjected to the drying step.
• Immediately before being subjected to the drying step is, for example, immediately before installing the crosslinked polymer at a predetermined place in the drying apparatus when the drying is performed using the drying apparatus.
• the production method includes a rough crushing step of the crosslinked polymer
• the dry content-based water content of the crosslinked polymer immediately after the rough crushing may be used as the dry content-based water content before the drying step.
• the dry content standard moisture content before the drying step is 100% by mass or more, and may be 110% by mass or more, 120% by mass or more, 130% by mass or more, or 135% by mass or more.
• the dry content standard moisture content before the drying step is preferably 233% by mass or less from the viewpoint of suppressing elution of the monomers constituting the crosslinked polymer during the drying step and improving the peelability. Even if the dry content standard moisture content before the drying step is 220% by mass or less, 210% by mass or less, 200% by mass or less, 190% by mass or less, 180% by mass or less, 170% by mass or less, or 160% by mass or less. good.
• the dry content-based water content before the drying step can be adjusted, for example, by adjusting the water content of the monomer aqueous solution used for the polymerization of the crosslinked polymer. This is because the water content of the monomer aqueous solution affects the water content of the massive hydrogel obtained by polymerization and the dry content-based water content of the crosslinked polymer after coarse crushing.
• the polymerization step is carried out under a nitrogen stream, the gel becomes hot due to the heat of reaction during the polymerization step and the generated vapor is distilled off, and / or the massive hydrous gel obtained by the polymerization is subjected to a nitrogen stream. By subjecting to the coarse crushing step below, the dry content-based moisture content before the drying step may be reduced.
• the drying temperature for 15 minutes from the start of the drying process and after 15 minutes has passed is 80 ° C. or higher, 90 ° C. or higher, 100 ° C. or higher, 120 ° C. or higher, 140 ° C. or higher, 160 ° C. or higher, 170 ° C. or higher, 180 ° C. or higher. , 190 ° C. or higher, or 195 ° C. or higher.
• the drying temperature may be a temperature equal to or higher than the boiling point of water.
• the drying temperature may be 220 ° C. or lower, 210 ° C. or lower, or 200 ° C. or lower.
• the drying temperature may be the set temperature of the drying device or the exposure atmosphere temperature of the hydrogel in the drying step.
• the drying step may be performed at normal pressure or reduced pressure.
• the environmental temperature may be temporarily below the predetermined drying temperature or below 80 ° C.
• the drying device for drying the crosslinked polymer is set to 80 ° C. or higher, preferably a predetermined drying temperature in advance, and the drying is started at the same time as the crosslinked polymer is installed in the drying device.
• the cumulative time of the drying process may be set so that the dry content standard moisture content after drying is in an appropriate range according to the conditions such as the drying temperature.
• the total time of the drying step may be, for example, 15 minutes or more, 20 minutes or more, 25 minutes or more, or 30 minutes or more, and may be 120 minutes or less, 90 minutes or less, or 60 minutes or less.
• Drying of the crosslinked polymer is performed, for example, by hot air dryer, vacuum dryer, ventilation belt type dryer, ventilation band type dryer, rotary ventilation dryer, stirring dryer, fluidized layer dryer, vibration fluid dryer, vacuum drying. This can be done using a drying device such as a machine.
• the initial rate of change of the dry content standard moisture content is 6.0% / min or less, 5.8% / min or less, 5.6% / min or less, 5.3% / min or less, 5.0%. It may be less than / min, 4.5% / min or less, 4.2% / min or less, 4.0% / min or less, 3.8% / min or less, or 3.5% / min or less.
• the initial rate of change of the dry content standard moisture content may be 3.0% / min or more, preferably 3.5% / min or more. When the initial rate of change is 3.5% / min or more, the peelability of the crosslinked polymer after drying can be further improved.
• the initial rate of change may be 4.5% / min or higher, or 5.0% / min or higher.
• the initial rate of change of the dry content standard moisture content can be adjusted, for example, by adjusting the drying temperature, the amount of water volatilized from the crosslinked polymer released to the outside of the system, etc. within 15 minutes from the start of the drying step. ..
• the dry content standard moisture content 15 minutes after the drying step means the dry content standard moisture content 15 minutes after the start of the drying process.
• the dry content standard water content after 15 minutes of the drying step may be, for example, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40. It may be mass% or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, or 60% by mass or more.
• the dry content standard water content after 15 minutes of the drying step is, for example, 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, It may be 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less.
• the mode of drying after 15 minutes from the start of the drying process is not particularly limited, and for example, in order to perform more efficient drying, the drying conditions may be stronger than those at the initial stage of the drying process. good.
• the drying temperature after 15 minutes from the start of the drying process may be higher or lower than that at the initial stage of the drying process.
• the final dry content standard moisture content is the dry content standard moisture content immediately after the drying step of the crosslinked polymer is completed.
• Immediately after the completion of the drying step is, for example, immediately after the crosslinked polymer is taken out from the drying device when drying using a drying device.
• the crosslinked polymer is pulverized after the drying step, for example, the water content of the crosslinked polymer immediately before pulverization may be used as the final dry content-based water content.
• the water content of the crosslinked polymer before adding water is used as the final dry amount standard.
• the final dry content standard moisture content can be reduced, for example, by increasing the drying temperature, extending the drying time, or the like.
• the final dry content standard moisture content may be 15% by mass or less, 10% by mass or less, 8% by mass or less, 6% by mass or less, or 5% by mass or less.
• the final dry content standard water content is from the viewpoint of reducing the adhesion of the crosslinked polymer to the crusher and reducing the load on the crusher to suppress machine failure when the crosslinked polymer is crushed after the drying step. Therefore, it is preferably 15% by mass or less.
• the final dry content standard moisture content may be, for example, 1% by mass or more, 2% by mass or more, 3% by mass or more, 3.5% by mass or more, or 4% by mass or more.
• the dried crosslinked polymer can be taken out from the drying apparatus. If the crosslinked polymer is placed on a metal surface during the drying step, the crosslinked polymer is stripped from the metal surface. According to the production method according to the present embodiment, the crosslinked polymer can be peeled off from the metal surface of the drying apparatus by, for example, free fall, without applying an external force.
• the crosslinked polymer (coarsely crushed and dried polymer) after the coarse crushing and drying steps is preferably further pulverized. That is, the production method according to the present embodiment preferably includes a step of pulverizing the crosslinked polymer after the drying step. By pulverization, a particulate crosslinked polymer (polymer particles) having a smaller particle size can be obtained.
• roller mill roller mill
• stamp mill stamp mill
• jet mill high-speed rotary crusher
• hammer mill pin mill, rotor beater mill, etc.
• container-driven mill rotary mill, vibration mill, planetary mill, etc.
• the crusher may have an opening on the outlet side, such as a perforated plate, a screen, or a grid, for controlling the maximum particle size of the crushed particles.
• the shape of the opening may be polygonal, circular, or the like, and the maximum diameter of the opening may be 0.1 to 5 mm, 0.3 to 3.0 mm, or 0.5 to 1.5 mm.
• the particulate crosslinked polymer obtained by pulverization may be further classified.
• the production method according to the present embodiment may include a step of classifying the crosslinked polymer after pulverization.
• Classification refers to an operation of dividing a certain particle group into two or more particle groups having different particle size distributions according to the particle size. Further, a plurality of classification steps may be performed, such as crushing the classified particles again and repeating the crushing step and the classification step, or the classification step may be performed after the surface cross-linking step described later.
• the particle classification can be performed by, for example, a screen classification, a wind power classification, or the like.
• the particles may be granulated as needed.
• the particle size may be adjusted so as to have a desired particle size distribution by remixing the crosslinked polymer of each particle size obtained by the classification, if necessary.
• the method for producing water-absorbent resin particles according to the present embodiment may include a step of performing surface cross-linking of the polymer particles.
• Surface cross-linking can be performed, for example, by adding a cross-linking agent (surface cross-linking agent) for performing surface cross-linking to the polymer particles and reacting them.
• a cross-linking agent surface cross-linking agent
• the surface cross-linking agent may contain, for example, two or more functional groups (reactive functional groups) having reactivity with a functional group derived from an ethylenically unsaturated monomer.
• functional groups reactive functional groups
• examples of the surface cross-linking agent include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly) ethylene glycol di.
• Polyglycidyl compounds such as glycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, epibromhydrin, ⁇ - Haloepoxy compounds such as methylepicrolhydrin; compounds having two or more reactive functional groups such as isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3- Oxetane compounds such as oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetan ethanol, 3-butyl-3-oxet
• the water-absorbent resin particles obtained by the production method according to the present embodiment include the above-mentioned particulate crosslinked polymer (polymer particles).
• the water-absorbent resin particles may be composed of only polymer particles, and may be, for example, a gel stabilizer, a metal chelating agent (ethylenediamine 4 acetic acid and its salt, diethylenetriamine 5 acetic acid and its salt, for example, diethylenetriamine 5 acetate 5 sodium and the like, etc. ), An additional component such as a fluidity improver (lubricant) may be further contained. Additional components may be placed inside, on the surface, or both of the polymer particles.
• the water-absorbent resin particles may contain a plurality of inorganic particles arranged on the surface of the polymer particles.
• the production method according to the present embodiment may further include a step of adhering the inorganic particles to the surface of the polymer particles.
• the shape of the water-absorbent resin particles obtained by the production method according to the present embodiment may be, for example, a crushed shape or a shape formed by aggregating crushed particles.
• the medium particle size of the water-absorbent resin particles may be 130 to 800 ⁇ m, 200 to 850 ⁇ m, 250 to 700 ⁇ m, 300 to 600 ⁇ m, or 300 to 450 ⁇ m.
• the water-absorbent resin particles obtained by the production method according to the present embodiment have excellent water absorption, and are, for example, sanitary materials such as disposable diapers and sanitary products, agricultural and horticultural materials such as water-retaining agents and soil conditioners, water-stopping agents, and dew condensation prevention. It can be used in fields such as industrial materials such as agents.
• the polymerization reaction After dropping the L-ascorbic acid aqueous solution, the polymerization reaction started 3 minutes later. After the viscosity of the reaction solution increased with the progress of the polymerization reaction, the reaction solution gelled. At 14 minutes after the completion of dropping the L-ascorbic acid aqueous solution, the installed thermometer showed 86.0 ° C., and then the temperature began to decrease.
• a stainless steel vat containing a hydrogel (crosslinked polymer in the form of a hydrogel) formed by gelation of the reaction solution is immersed in a water bath at 75 ° C., and the hydrogel is heated for 20 minutes in that state to fully complete the polymerization reaction. I let you.
• ⁇ Manufacturing example 2> [Preparation of aqueous monomer solution] 340.60 g (4.73 mol) of acrylic acid was placed in a 2 L separable flask. 292.87 g of ion-exchanged water was added to the acrylic acid in the separable flask with stirring. Then, by dropping 295.98 g of a 48 mass% sodium hydroxide aqueous solution under an ice water bath at about 3 ° C., a partial neutralizing solution of acrylic acid having a monomer concentration of 45.0 mass% (neutralization rate 75. 1 mol%) was prepared.
• Example 1 (Drying process) 60 g of the coarsely crushed gel obtained in Production Example 1 was placed uniformly within a range of 15 cm ⁇ from the center of a JIS sieve (diameter 20 cm) having an opening of 1.7 mm. Then, a metal petri dish (167 g) having a diameter of 15 cm is placed on the coarsely crushed gel, a weight of 250 g is further placed on the crushed gel, and a uniform load is applied to the entire surface of the coarsely crushed gel to sieve the coarsely crushed gel. Pressed against for 10 seconds.
• the metal petri dish and the weight were removed, and the upper opening of the JIS sieve on which the coarsely crushed gel was placed was covered with aluminum foil (cooking foil manufactured by Toyo Aluminum Echo Products Co., Ltd.).
• a JIS sieve covered with aluminum foil was placed in a hot air dryer (FV-320 manufactured by ADVANTEC) previously set at 200 ° C., and a drying step was carried out for 30 minutes to obtain a coarsely crushed and dried polymer. After the drying step, the JIS sieve on which the coarsely crushed and dried polymer was placed was taken out from the dryer, and then the peeling rate test was carried out immediately.
• the moisture-based moisture content (final moisture-based moisture content C) of the coarsely crushed dried polymer was measured, and the dry-weight-based moisture content (final dry-weight-based moisture content c) was calculated.
• the final moisture content standard moisture content C was 5.1% by mass.
• the coarsely crushed gel was taken out 15 minutes after the start of the drying process at 200 ° C.
• the moisture-based moisture content of the coarsely crushed gel taken out was measured, and the dry-weight-based moisture content (dry-weight-based moisture content b after 15 minutes of the drying step) was calculated.
• the moisture content standard moisture content B was 41.0% by mass.
• Example 2 After covering the upper surface opening of the JIS sieve with aluminum foil, a drying step was carried out in the same manner as in Example 1 except that 24 ventilation holes having a diameter of 3 mm were opened in the aluminum foil at intervals of 2 to 3 cm.
• the wet content-based moisture content (final moisture-based moisture content C) of the coarsely crushed and dried polymer obtained after the drying step was 4.7% by mass.
• Example 3> (Drying process) Using the coarsely crushed gel obtained in Production Example 2, the coarsely crushed gel was pressed against the JIS sieve with a metal petri dish and a weight in the same manner as in Example 1 for 10 seconds. The metal petri dish and the weight were removed, and the JIS sieve on which the coarsely crushed gel was placed was placed in a hot air dryer (FV-320 manufactured by ADVANTEC) set in advance at 180 ° C. After 15 minutes, the JIS sieve on which the coarsely crushed gel was placed was taken out from the inside of the hot air dryer, immediately transferred to another hot air dryer (manufactured by ADVANTEC, FV-320) set at 200 ° C. in advance, and dried for another 15 minutes.
• a hot air dryer FV-320 manufactured by ADVANTEC
• moisture-based moisture content of the coarsely crushed gel taken out 15 minutes after the start of the drying step at 180 ° C. (15 minutes after the drying step, moisture-based moisture content B) was measured and found to be 19.7% by mass. there were.
• Example 4 The drying step was carried out in the same manner as in Example 1 except that the temperature of the drying step for 30 minutes was changed to 180 ° C. and the upper surface opening of the JIS sieve was not covered with aluminum foil.
• the moisture-based moisture content (final moisture-based moisture content C) of the obtained coarsely crushed dry polymer was 5.1% by mass.
• the moisture-based moisture content of the coarsely crushed gel taken out 15 minutes after the start of the drying step at 180 ° C. (15 minutes after the drying step, moisture-based moisture content B) was measured and found to be 19.5% by mass. there were.
• Example 5 Using the coarsely crushed gel obtained after the coarse crushing step in Production Example 3, the drying step was carried out in the same manner as in Example 3 except that the drying step temperature was changed to 160 ° C. for 15 minutes from the start of the drying step.
• the moisture-based moisture content (final moisture-based moisture content C) of the obtained coarsely crushed dry polymer was 3.6% by mass.
• the moisture-based moisture content of the coarsely crushed gel taken out 15 minutes after the start of the drying step at 160 ° C. (15 minutes after the drying step, moisture-based moisture content B) was measured and found to be 23.0% by mass. there were.
• Example 2 Same as Example 3 except that the order of the 180 ° C. hot air dryer and the 200 ° C. hot air dryer was changed, dried in the 200 ° C. hot air dryer for 15 minutes, and then quickly transferred to the 180 ° C. dryer. The drying process was carried out.
• the moisture-based moisture content (final moisture-based moisture content C) of the obtained coarsely crushed dry polymer was 3.7% by mass.
• the moisture-based moisture content of the coarsely crushed gel taken out 15 minutes after the start of the drying step at 200 ° C. (15 minutes after the drying step, moisture-based moisture content B) was measured and found to be 8.4% by mass. there were.
• the moisture content standard moisture content A before the drying step, the moisture content standard moisture content B 15 minutes after the drying step, and the final moisture content standard moisture content C of the measurement sample were measured by the following methods.
• a sample of 20.0 g of the coarsely crushed gel obtained in the coarse crushing step was used as a measurement sample.
• a sample of 20.0 g of the coarsely crushed gel taken out 15 minutes after the start of the drying step was used as a measurement sample.
• a sample of 20.0 g of the coarsely crushed and dried polymer obtained immediately after the total drying step 160 to 200 ° C., 30 minutes
• the above measurement sample is placed on a fluororesin-coated stainless steel vat (outer dimensions: 185 mm ⁇ 140 mm ⁇ height 30 mm) that has been preliminarily set to a constant amount (W1 (g)), and the total mass W2 (g) of the stainless steel vat and the measurement sample is refined. Weighed.
• the crosslinked polymer after an excellent drying step showed peelability.
• the crosslinked polymer after the drying step showed high peelability even if the drying conditions after 15 minutes from the start of the drying step were made stronger.
• the initial rate of change of the dry content standard moisture content exceeds 6.0% / min, it is shown that the peeling rate is low even if the drying conditions after 15 minutes have passed from the start of the drying step are milder. Was done.

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• 2021
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