Apparatus and method for manufacturing superabsorbent resin particles

Abstract

This water-absorbent resin particle production device is provided with a dryer, a classifier, and a sorter. The dryer is for drying a water-absorbent resin composition to obtain water-absorbent resin precursors. The classifier is for classifying the water-absorbent resin precursors to obtain water-absorbent resin particles. The sorter is disposed on a pathway connecting the dryer and the classifier. The sorter is configured to select water-absorbent resin precursors having a water content of 20% or more.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and a method for producing water-absorbent resin particles. [Background Art]

[0002] The production process of water-absorbent resin particles includes a step of polymerizing a raw material monomer to obtain a water-absorbent resin composition, and a subsequent step of drying the water-absorbent resin composition to obtain a water-absorbent resin precursor. By classifying the water-absorbent resin precursor obtained through these steps with a classifier, water-absorbent resin particles having a target particle size distribution can be produced.

[0003] Patent Document 1 discloses an apparatus for producing a water-absorbent resin, comprising a dryer for drying a water-absorbent resin composition to obtain a powder, a powder flow path member forming a flow path for the powder, a powder flow rate adjusting and discharging member discharging the powder at a predetermined flow rate, and a collector. According to Patent Document 1, among the powder passing through the flow path, powder agglomerates larger than a predetermined size are collected by the collector, thereby suppressing an increase in the driving load on the driving unit of the powder flow rate adjusting and discharging member caused by the powder agglomerates, and enabling production of the water-absorbent resin with high production efficiency. [Prior Art Document] [Patent Document]

[0004] [Patent Document 1] Japanese Patent No. 6738979 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] According to Patent Document 1, large powder agglomerates sometimes have inferior properties as a water-absorbent resin. Therefore, by collecting and removing large powder agglomerates with the collector, production efficiency can be improved and a water-absorbent resin with excellent quality can be produced. However, even with the production apparatus disclosed in Patent Document 1, variations in the quality of water-absorbent resin particles still occur.

[0006] Generally, various properties such as water absorption performance (water absorption rate, water absorption capacity under pressure (pressurized water absorption capacity)), impact resistance, and fluidity are used as indicators of the quality of superabsorbent polymer particles. The inventors' research revealed that variations are particularly likely to occur in pressurized water absorption capacity and water absorption rate. Therefore, there has been a need for an apparatus that can produce superabsorbent polymer particles with even greater quality variations, such as pressurized water absorption capacity and water absorption rate.

[0007] The present invention aims to provide an apparatus and method for producing superabsorbent resin particles that can produce superabsorbent resin particles in which variations in pressurized water absorption capacity and water absorption rate are suppressed. [Means for solving the problem]

[0008] The apparatus for producing superabsorbent resin particles according to the first aspect comprises a dryer, a classifier, and a sorter. The dryer dries the superabsorbent resin composition to obtain a superabsorbent resin precursor. The classifier classifies the superabsorbent resin precursor to obtain superabsorbent resin particles. The sorter is positioned on a path connecting the dryer and the classifier. The sorter is configured to sort the superabsorbent resin precursor having a water content of 20% or more.

[0009] According to the inventors' studies, the water-absorbent resin precursors dried in the dryer still contain a relatively high amount of moisture. When such water-absorbent resin precursors are fed into a classifier, variations in the quality of the resulting water-absorbent resin particles, particularly in their pressurized water absorption capacity and water absorption rate, tend to occur. In the water-absorbent resin particle manufacturing apparatus according to the above viewpoint, water-absorbent resin precursors with a moisture content of 20% or more are separated in the path connecting the dryer and the classifier. This allows the separated water-absorbent resin precursors with a moisture content of 20% or more to be removed from the path leading to the classifier, thereby reducing variations in the pressurized water absorption capacity and water absorption rate of the water-absorbent resin particles.

[0010] The apparatus for producing water-absorbent resin particles according to the second aspect is the apparatus for producing water-absorbent resin particles according to the first aspect, wherein the sorting machine is configured to sort water-absorbent resin precursors having a surface temperature of 50°C to 100°C and exceeding a predetermined size as water-absorbent resin precursors with a water content of 20% or more.

[0011] The apparatus for producing water-absorbent resin particles according to the third aspect is the apparatus for producing water-absorbent resin particles according to the second aspect, wherein the sorting machine includes an input port formed therein into which the water-absorbent resin precursor discharged from the dryer is introduced, and a sorting member connected to the input port and having an opening of a predetermined size. The sorting machine is configured to send the water-absorbent resin precursor that has passed through the opening from the water-absorbent resin precursor introduced into the input port to a path connected to the classifier.

[0012] The apparatus for producing water-absorbent resin particles according to the fourth aspect is the apparatus for producing water-absorbent resin particles according to the third aspect, wherein the sorting member is composed of a mesh member having a plurality of openings of a predetermined size.

[0013] The apparatus for producing water-absorbent resin particles according to the fifth aspect is an apparatus for producing water-absorbent resin particles according to the third or fourth aspect, wherein the sorting member is configured to impart movement to the water-absorbent resin precursor introduced into the input port.

[0014] The apparatus for producing water-absorbent resin particles according to the sixth viewpoint is an apparatus for producing water-absorbent resin particles according to any of the second viewpoint to the fifth viewpoint, wherein the predetermined size is 7 mm to 15 mm.

[0015] The apparatus for producing water-absorbent resin particles according to the seventh aspect is an apparatus for producing water-absorbent resin particles according to any of the first to sixth aspects, further comprising a cooler positioned on the path connecting the sorting machine and the classifier. The cooler is configured to cool the water-absorbent resin precursor sent to the path connecting the sorting machine to the classifier.

[0016] A method for producing water-absorbent resin particles according to the eighth aspect includes the following steps. · A step of drying a water-absorbent resin composition to obtain a water-absorbent resin precursor. · A step of sorting and removing the water-absorbent resin precursor having a water content of 20% or more from the water-absorbent resin precursor. · A step of classifying the remaining water-absorbent resin precursor to obtain classified water-absorbent resin particles. Effects of the Invention

[0017] The water-absorbent resin precursor after being dried by a dryer still includes particles that contain a relatively large amount of moisture, and such water-absorbent resin precursor is one cause of variations in the pressurized water absorption capacity and water absorption rate of the water-absorbent resin particles after classification by a classifier. According to the above aspect, the water-absorbent resin precursor having a water content of 20% or more is sorted from the water-absorbent resin precursor on the path connecting the dryer and the classifier. This makes it possible to remove the sorted water-absorbent resin precursor from the path leading to the classifier, thereby suppressing variations in the pressurized water absorption capacity and water absorption rate of the water-absorbent resin particles obtained by the classifier. Brief Description of the Drawings

[0018] [Figure 1] Overall configuration diagram of an apparatus for producing water-absorbent resin particles according to one embodiment. [Figure 2A] An example of a mesh member. [Figure 2B] An example of a mesh member. [Figure 2C] An example of a mesh member. [Figure 2D] An example of a mesh member. [Figure 3A] An example of a plate-shaped member. [Figure 3B] An example of a plate-shaped member. [Figure 4] A diagram for explaining the calculation method of opening ratio. [Figure 5A] Configuration example of a sorter. [Figure 5B] Configuration example of a sorter. [Figure 5C] Configuration example of a sorter. [Figure 5D]Example configuration of a sorting machine. [Figure 6] A diagram illustrating a method for determining the size of a water-absorbent polymer precursor. [Figure 7] A flowchart showing the process for manufacturing water-absorbent resin particles according to one embodiment. [Figure 8] A diagram showing the configuration of the experimental apparatus. [Figure 9A] A graph showing the amount of water absorbed under pressure, obtained from the experiment. [Figure 9B] A graph showing the evaluation index of water absorption rate obtained from experiments. [Modes for carrying out the invention]

[0019] The following describes, with reference to the drawings, an apparatus for producing water-absorbent resin particles and a method for producing water-absorbent resin particles according to one embodiment of the present invention. In this specification, "selecting" means not only "extracting only a specific subgroup a from a large group X," but also "extracting a specific subgroup a from a large group X, including other subgroups b (however, such that the proportion of subgroup a included in the large group X is higher (by mass))."

[0020] <1. Equipment for manufacturing water-absorbent resin particles> Figure 1 shows an overall configuration diagram of the water-absorbent resin particle manufacturing apparatus 100 used in the implementation of the water-absorbent resin particle manufacturing method according to this embodiment. Water-absorbent resin particles are widely used in various applications, such as sanitary materials like disposable diapers and sanitary napkins, daily necessities like pet sheets, industrial materials such as absorbent sheets for food, waterproofing materials for cables, and condensation prevention materials, and water-retaining agents and soil conditioners for greening, agriculture, and horticulture. Water-absorbent resin particles are manufactured by polymerizing monomers, which are used as raw materials, to produce polymers.

[0021] As shown in Figure 1, the water-absorbent resin particle manufacturing apparatus 100 comprises a polymerizer 1 and a concentrator 2. The polymerizer 1 polymerizes monomers that will be used as raw materials for water-absorbent resin particles to produce a slurry (a liquid containing a water-containing gel-like polymer) containing a water-containing gel-like polymer. The concentrator 2 concentrates the slurry by distilling off the liquid component from the slurry sent from the polymerizer 1 to produce a water-absorbent resin composition A1, which is a concentrated polymer solution. The manufacturing apparatus 100 further comprises a dryer 3, which dries the water-absorbent resin composition A1 sent from the concentrator 2 (i.e., volatilizes the liquid component). This yields a water-absorbent resin precursor A2, which is a stage before it becomes the water-absorbent resin particle P1 product. When a water-containing gel-like polymer is produced by reverse-phase suspension polymerization, the liquid component mainly consists of a hydrocarbon dispersion medium and water, and when a water-containing gel-like polymer is produced by aqueous solution polymerization, it mainly consists of water.

[0022] As shown in Figure 1, the manufacturing apparatus 100 further comprises a sorter 4, a cooler 5, and a classifier 6. The sorter 4 sorts the water-absorbent resin precursor A2 with a moisture content of 20% or more from the water-absorbent resin precursor A2 sent from the dryer 3 and discharges it from the first discharge port 43. The sorter 4 also discharges the remaining water-absorbent resin precursor A3 from another second discharge port 44 in order to send it to the cooler 5. The cooler 5 cools the water-absorbent resin precursor A3 discharged from the second discharge port 44, removes the heat applied by the dryer 3, and then sends the water-absorbent resin precursor A3 to the classifier 6. The classifier 6 classifies the water-absorbent resin precursor A3 into several classes. Of the water-absorbent resin precursor A3, those classified into classes that meet the product specifications are called water-absorbent resin particles P1.

[0023] Furthermore, as shown in Figure 1, the manufacturing apparatus 100 further includes a control device 7 that controls the manufacturing process of the water-absorbent resin by controlling the operation of each of the devices 1 to 6. The control device 7 is typically implemented as a computer controlled by a program. In addition to controlling the operation of each of the devices 1 to 6, the control device 7 may also be configured to control the operation of the piping and the first to fourth passage members L1 to L4 that constitute the path connecting each of the devices 1 to 6, as well as the valves that may be installed therein.

[0024] <2. Configuration of each device> The following will provide a detailed explanation of each of the devices 1 through 6, along with appropriate references to the various devices connected to them.

[0025] [polymerizer] Polymerizer 1 has a polymerization tank (not shown). The polymerization tank is a container that holds monomers, such as water-soluble ethylenically unsaturated monomers, which are the raw materials for water-absorbent resin particles, and liquid components, such that a gaseous phase component is formed at the top. Inside the polymerization tank, the monomers and liquid components are stirred as appropriate by a stirrer (not shown) and heated by a heating device (not shown), thereby promoting the polymerization reaction of the monomers and producing a water-containing gel-like polymer. These stirrers and heating devices are connected to a control device 7, and their operation is controlled. As a result, a slurry containing the water-containing gel-like polymer is contained inside the polymerization tank. The slurry is discharged from the polymerization tank 1 through a lower opening formed at the bottom of the polymerization tank to be sent to the concentrator 2.

[0026] One end of a pipe is connected to the lower opening of the polymerization tank. The other end of this pipe is connected to an opening formed at the top of the concentrator 2. Slurry discharged from the polymerization tank 1 passes through the pipe and is introduced into the concentrator 2 through the opening at the top of the concentrator 2. A valve is attached to the pipe, and the opening and closing of the valve is controlled by the control device 7 to control the flow of slurry through the pipe.

[0027] [Concentrator] The concentrator 2 has a concentrating tank (not shown). The slurry discharged from the polymerizer 1 flows into the concentrating tank through an upper opening formed at the top of the concentrator 2, and is contained such that a gaseous phase component is formed in the upper part of the concentrating tank. Inside the concentrating tank, the slurry is stirred as appropriate by a stirrer (not shown) and heated by a heating device (not shown), thereby distilling off the liquid components contained therein and concentrating the slurry. These stirrers and heating devices are connected to a control device 7, and their operation is controlled. As a result, the concentrating tank contains a concentrated liquid containing a water-containing gel-like polymer. The concentrated liquid containing the water-containing gel-like polymer is discharged from the concentrator 2 through a lower opening formed at the bottom of the concentrating tank to be sent to the dryer 3 as a water-absorbent resin composition A1.

[0028] One end of a pipe is connected to the lower opening of the concentration tank. The other end of this pipe is connected to the upper opening formed at the top of the dryer 3. The superabsorbent resin composition A1 discharged from the concentrator 2 passes through the pipe and is introduced into the dryer 3 through the upper opening of the dryer 3. A valve is attached to the pipe, and the opening and closing of the valve is controlled by the control device 7 to control the communication of the superabsorbent resin composition A1 through the pipe.

[0029] [Dryer] The dryer 3 has a drying chamber (not shown). The superabsorbent resin composition A1 discharged from the concentrator 2 flows into the drying chamber through the upper opening of the dryer 3. The dryer 3 heats the superabsorbent resin composition A1 in the drying chamber with a heating device (not shown) to remove the water contained therein. This produces a superabsorbent resin precursor A2 obtained by drying the superabsorbent resin composition A1. The heating device is connected to a control device 7, and its operation is controlled. The heating device dries the superabsorbent resin composition A1 so that the overall water content (mass%) of the superabsorbent resin composition A1 contained in the drying chamber is preferably 20% or less, more preferably 10% or less. The superabsorbent resin precursor A2 obtained after drying is discharged from the dryer 3 through a lower opening formed at the bottom of the drying chamber to be sent into the first passage member L1, which will be described later.

[0030] The dryer 3 may be configured to dry the slurry discharged from the polymerizer 1 as the water-absorbent resin composition A1. That is, the manufacturing apparatus 100 may omit the concentrator 2, and the polymerizer 1 may be directly connected to the dryer 3. In this case, the slurry discharged from the polymerizer 1 corresponds to the water-absorbent resin composition A1. The dryer 3 will then concentrate and dry the water-absorbent resin composition A1 simultaneously.

[0031] [First passage member] The first passage member L1 is a member that defines a passage for the water-absorbent resin precursor A2 to move in a predetermined direction, and together with the second passage member L2, third passage member L3, and fourth passage member L4, which will be described later, it constitutes a path connecting the dryer 3 and the classifier 6. One end of the first passage member L1 is connected to the lower opening of the drying chamber. The first passage member L1 is composed of piping, although not limited to this, and the water-absorbent resin precursor A2 can move inside the first passage member L1 by gravity, for example. Inside the first passage member L1, a collector 30 is arranged so as to intersect with the direction of movement of the water-absorbent resin precursor A2. More specifically, the collector 30 is installed in the first passage member L1 such that its outer peripheral edge is in contact with the inner surface of the first passage member L1. As a result, the internal space of the first passage member L1 is divided into an upstream passage located on the dryer 3 side with the collector 30 in between, and a downstream passage located on the sorting machine 4 side with the collector 30 in between.

[0032] The collecting body 30 is a component for collecting powdery lumps B1 larger than a predetermined size from the water-absorbent resin precursor A2 that has flowed into the first passage member L1 and removing them from the manufacturing apparatus 100. The powdery lumps B1 are, for example, water-containing gel-like polymers adhering to the inner walls of the polymerization tank, concentration tank and drying chamber, lumps that have grown into clumps with the water-absorbent resin composition A1 acting as a nucleus, and lumps that have formed when the water-absorbent resin composition A1 has aggregated. Depending on their size, the powdery lumps B1 cannot pass through the gap defined by the collecting body 30 and do not reach the downstream passage. On the other hand, the remaining water-absorbent resin precursor A2 passes through the gap defined by the collecting body 30 and reaches the downstream passage, and then moves further down the downstream passage. The specific configuration of the collecting body 30 is disclosed in Patent Document 1, so it is considered to be as described herein, and a detailed explanation is omitted here. The powdery clumps B1 removed by the collection body 30 are larger water-absorbent resin precursors than the water-absorbent resin precursors B2 separated by the sorting member 42 of the sorting machine 4 described later. The particle size of the powdery clumps B1 is, for example, 30 mm or more, preferably 50 mm or more.

[0033] The first passage member L1 has an extraction opening 31 that communicates with the upstream passage. The extraction opening 31 defines an opening for extracting the powdery lumps B1 collected by the collecting body 30 to the outside of the first passage member L1. The collecting body 30 is positioned inside the first passage member L1 so that the collected powdery lumps B1 move towards the extraction opening 31, for example, by gravity. In this way, the powdery lumps B1 are extracted to the outside of the first passage member L1 via the extraction opening 31 without blocking the gaps in the collecting body 30 or the upstream passage.

[0034] The water-absorbing resin precursor A2 that flows into the downstream passage of the first passage member L1 is sent to the sorting machine 4 via the second passage member L2 connected to the first passage member L1. The first passage member L1 and the second passage member L2 may be connected via a relay member 32 that relays the path of the water-absorbing resin precursor A2, such as a hopper for temporarily storing the water-absorbing resin precursor A2.

[0035] [Second passage member] The second passage member L2 is a member that defines a passage for sending the water-absorbent resin precursor A2 from the first passage member L1 to the sorting machine 4, and constitutes a path connecting the dryer 3 and the classifier 6. The method of transporting the water-absorbent resin precursor A2 from the first passage member L1 to the sorting machine 4 is not particularly limited, and a transport method by gravity, a transport method by an inert gas flow, a transport method by a transport mechanism such as a conveyor can be appropriately selected. The second passage member L2 is not particularly limited in its form as long as it is configured to introduce the water-absorbent resin precursor A2 into the inlet 40 of the sorting machine 4 according to the transport method of the water-absorbent resin precursor A2. For example, the second passage member L2 can be constructed using piping, transport piping in which airflow is generated, a conveyor, a feeder, etc. A valve whose operation is controlled by a control device 7 to adjust the flow rate of the water-absorbent resin precursor A2 may be attached to the second passage member L2. Furthermore, a surface temperature adjustment device may be provided in the second passage member L2 to adjust the surface temperature of the water-absorbent resin precursor A2 that is fed into the sorting machine 4. The surface temperature adjustment device is a device that heats the second passage member L2 from the outside and / or the inside (heater) and / or cools it (cooler). For example, the surface temperature adjustment device has a tubular member wound around the outside of the second passage member L2, and the second passage member L2 can be heated and / or cooled by passing a heat transfer medium such as water vapor inside the tubular member. The lower limit of the surface temperature of the superabsorbent polymer precursor A2 introduced into the sorting machine is 50°C or higher, preferably 55°C or higher, and more preferably 60°C or higher. The upper limit is 100°C or lower, preferably 95°C or lower, more preferably 90°C or lower, even more preferably 85°C or lower, and particularly preferably 80°C or lower. In summary, the surface temperature of the superabsorbent polymer precursor A2 introduced into the sorting machine may be between 50°C and 100°C, and more preferably between 60°C and 80°C. According to the inventors' findings, if the surface temperature of the water-absorbing resin precursor A2 is within the above range, the sorting machine can efficiently sort out water-absorbing resin precursor A2 with a water content of 20% or more (and keep the inclusion rate of water-absorbing resin precursor A2 with a water content of less than 20% in the sorted water-absorbing resin precursor B2 low).

[0036] [Sorting machine] The sorting machine 4 can consist of, for example, a vibrating sorter, a trommel (rotary sorter), or other sieving devices. The sorting machine 4 is positioned on the path connecting the dryer 3 and the classifier 6 to sort out the water-absorbent resin precursor A2 with a moisture content of 20% or more after it has been discharged from the dryer 3. The sorting machine 4 comprises an input port section 41 with an input port 40 formed therein, and a sorting member 42. The input port 40 is an opening for inputting the water-absorbent resin precursor A2 that has been discharged from the dryer 3 and sent through the second passage member L2. In this embodiment, the input port section 41 is a casing that houses the sorting member 42. Inside the input port section 41, the sorting member 42 is connected so as to define a sorting region 45 (see Figures 5A to 5D) for sorting the water-absorbent resin precursor A2. As will be described later, the sorting member 42 may be connected to the input port 41 via other members connected to the input port 41, and the sorting region 45 may be defined by the sorting member 42 and at least one of the input port 41 and the other members. As will be described later, the sorting member 42 may be configured to be movable in order to impart movement to the water-absorbing resin precursor A2 in the sorting region 45, and its operation may be controlled by the control device 7.

[0037] The water-absorbent resin precursor A2, after being discharged from the dryer 3, is fed into the sorting machine 4 with a surface temperature of 50°C to 100°C. The water-absorbent resin precursor A2 fed into the sorting machine 4 first enters the sorting area 45. The casing has a first discharge port 43 and a second discharge port 44 that connect the inside and outside of it. The water-absorbent resin precursor A2 that has entered the sorting area 45 is separated in two ways by the sorting member 42 and discharged outside the sorting machine 4 from either discharge port 43 or 44.

[0038] [Selection materials] The overall shape of the sorting member 42 can be appropriately selected from a planar shape, cylindrical shape, truncated cone shape, rectangular tube shape, etc. Multiple openings of a predetermined size are formed in the sorting member 42, connecting the inside and outside of the sorting area 45. As a result, among the water-absorbing resin precursor A2 that enters the sorting area 45, those that are larger than the size of the openings of the sorting member 42 cannot pass through the openings of the sorting member 42, and are sorted into those that are large enough to pass through the openings of the sorting member 42. The sorted water-absorbing resin precursor A2 is removed from the path connecting the sorting machine 4 and the classifier 6 for reasons to be described later. Hereinafter, water-absorbing resin precursor A2 that cannot pass through the openings of the sorting member 42 will be referred to as water-absorbing resin precursor B2, and those that can pass through the openings of the sorting member 42 will be referred to as water-absorbing resin precursor A3.

[0039] The sorting member 42 of this embodiment is composed of a mesh member 42a having numerous openings (commonly referred to as "eyes"). The mesh member 42a is formed by weaving linear members made of metal or the like into a square grid, as shown in Figure 2A, for example. In the example shown in Figure 2A, the weaving method of the linear members is not particularly limited and may be plain weave including flat-top weave or twill weave. However, the components constituting the sorting member 42 are not limited to the square grid-like mesh member 42a shown in Figure 2A, and can be changed as appropriate. The shape of the sorting member 42 will be described in detail below.

[0040] <When the members constituting the sorting member 42 are square grid-shaped mesh members 42a> If the members constituting the sorting member 42 are the square grid-like mesh members 42a shown in Figure 2A, the size of the openings of the mesh members 42a is defined by the mesh opening E, which depends on the number of openings per inch and the wire diameter of the linear members. Specifically, the mesh opening E of the sorting member 2 is defined by the following formula (1). Equation (1)...E(mm)=(25.4 / M)-d(mm) In equation (1), M represents the number of apertures per inch (25.4 mm), and d represents the wire diameter of the linear member.

[0041] The lower limit of the wire diameter d may be 0.8 mm or more, preferably 1.0 mm or more, more preferably 1.3 mm or more, and particularly preferably 1.5 mm or more. The upper limit may be 2.2 mm or less, preferably 2.0 mm or less, more preferably 1.8 mm or less, and particularly preferably 1.7 mm or less. In summary, the wire diameter d may be 0.8 mm to 2.2 mm, preferably 1.0 mm to 2.0 mm, more preferably 1.3 mm to 1.8 mm, and particularly preferably 1.5 mm to 1.7 mm. If the wire diameter d is within this range, the adhesion of the water-absorbent resin precursor A2 to the sorting member 42 can be suppressed, and water-absorbent resin particles can be produced with good yield. Furthermore, the lower limit of the mesh opening E may be 7 mm or more, 8 mm or more, preferably 9 mm or more, 9.5 mm or more, and more preferably 9.8 mm or more. The upper limit may be 15 mm or less, 14 mm or less, 13 mm or less, 12 mm or less, or 11 mm or less, preferably 10.5 mm or less, and more preferably 10.2 mm or less. In summary, the mesh opening E may be between 7 mm and 15 mm, preferably between 9 mm and 11 mm, more preferably between 9.5 mm and 10.5 mm, and even more preferably between 9.8 mm and 10.2 mm. If the mesh opening E is within the above range, water-absorbing resin precursor A2 with a water content of 20% or more can be efficiently sorted.

[0042] Furthermore, if the sorting member 42 is in the shape of a square grid as shown in Figure 2A, the opening ratio defined by the following formula (2) may be 55% or more, preferably 60% or more, more preferably 65% ​​or more, and particularly preferably 70% or more. The upper limit may be 90% or less, preferably 85% or less, more preferably 80% or less, and particularly preferably 77% or less. Formula (2)...Aperture ratio (%)=(E / E+d) 2 ×100 If the opening ratio is within the above range, water-absorbing resin precursor A2 with a water content of 20% or more can be efficiently sorted.

[0043] <When the members constituting the sorting member are mesh members 42a other than square grid members> Furthermore, as shown in Figures 2B to 2D, for example, if the shape of the opening in the mesh member 42a is, for example, a rectangle, parallelogram, hexagon, etc., the smallest interval E among the intervals between parallel linear members that define one opening is taken as the size of that opening. In this case, the average value Em of E measured for 10 different openings randomly selected in the mesh member 42a is taken as the size of the opening in the mesh member 42a.

[0044] Other embodiments of the members constituting the sorting member 42 include, for example, a plate-shaped member 42b having multiple openings (also referred to as "mesh" similar to the mesh member 42a), as shown in Figures 3A and 3B. The plate-shaped member 42b is, for example, a metal plate with multiple through holes formed by punching. For example, as shown in Figure 3A, if the shape of the openings of the plate-shaped member 42b when it is laid flat is circular, the diameter E of the circle is defined as the size of one opening. Also, as shown in Figure 3B, if the shape of the openings of the plate-shaped member 42b is oval, the spacing E between the parallel edges defining the opening is defined as the size of one opening. Furthermore, if the shape of the openings of the plate-shaped member 42b is, for example, rectangular, parallelogram, hexagon, etc., the smallest spacing E among the parallel edges defining the opening is defined as the size of one opening, in the same manner as with the mesh member 42a. For the plate-shaped member 42b, similar to the mesh-like member 42a, the average value Em of E measured at 10 different openings randomly selected is used as the size of the openings in the plate-shaped member 42b.

[0045] Even when the sorting member 42 is composed of a mesh member 42a or a plate member 42b as illustrated in Figures 2B to 3B, it is preferable that the size of the opening (mesh opening) of the sorting member 42 is within the range described above.

[0046] Furthermore, when the sorting member 42 is composed of a mesh member 42a or a plate member 42b as illustrated in Figures 2B to 3B, the opening ratio of the sorting member 42 can be appropriately selected depending on the overall shape of the sorting member 42. Figure 4 is a diagram illustrating the method for calculating the opening ratio of the sorting member 42. The opening ratio can be defined as the ratio of the area SA occupied by the opening within the region enclosed by rectangle R to the area SR of rectangle R, where R is the smallest rectangle formed by connecting the centers of the opening shapes in the sorting member 42 when it is laid out on a plane. In Figure 4, the case where the opening of the sorting member 42 is a regular hexagon is illustrated, but the above method for calculating the opening ratio can also be applied to sorting members 42 with openings of other shapes. Even when the sorting member 42 is composed of a mesh member 42a or a plate-shaped member 42b as illustrated in Figures 2B to 3B, it is preferable that its opening ratio is within the range described above.

[0047] [Example of sorting machine configuration] Figures 5A to 5D show examples of the configuration of the sorting machine 4. As shown in Figures 5A to 5D, the orientation of the input port 40 and the positional relationship between the input port 41 and the sorting member 42 are not particularly limited and can be selected as appropriate. In addition, the shape of the input port 41 and the orientation of the input port 40 can be selected as appropriate according to the overall shape of the sorting member 42. The first discharge port 43 formed in the sorting machine 4 is an opening for removing the water-absorbing resin precursor B2 from within the sorting area 45 in order to prevent clogging of the sorting member 42. The second discharge port 44 formed in the sorting machine 4 is an opening for discharging the water-absorbing resin precursor A3 from the sorting machine 4 and sending it to the third passage member L3, which defines the path leading to the classifier 6, and subsequently to the cooler 5 and the fourth passage member L4.

[0048] Figure 5A shows an example where the sorting member 42 is flat. In this example, the sorting member 42 is connected to the input port 41 via a passage member 46 that defines a passage connected to the input port 40. The passage member 46 is connected to the input port 41 and, together with the sorting member 42, defines a sorting region 45. Of the water-absorbing resin precursor A2 introduced from the input port 40, the water-absorbing resin precursor A3 passes through multiple openings in the sorting member 42, exits the sorting region 45, and is discharged from the second discharge port 44. On the other hand, the water-absorbing resin precursor B2 is discharged from the first discharge port 43. The sorting member 42 may be inclined with respect to the horizontal direction in order to move the water-absorbing resin precursor B2 to the first discharge port 43 more quickly. Furthermore, the sorting member 42 may be configured to vibrate by a vibration mechanism (not shown) to prevent the openings from becoming blocked and clogged, thereby imparting movement to the water-absorbing resin precursor A2.

[0049] Figure 5B shows an example where the sorting member 42 is cylindrical or rectangular. In this example, both ends of the sorting member 42 in the direction of the cylindrical axis are open. The sorting member 42 is oriented horizontally at both ends and connected to the input port 41 so that each end is connected to the input port 40 and the first output port 43. Of the water-absorbing resin precursor A2 introduced from the input port 40, the water-absorbing resin precursor A3 passes through multiple openings in the sorting member 42, exits the sorting area 45, and is discharged from the second output port 44. On the other hand, the water-absorbing resin precursor B2 is discharged from the first output port 43 via one end of the sorting member 42. The sorting member 42 may be configured to rotate around the cylindrical axis by a rotating mechanism (not shown) to prevent clogging caused by the openings becoming blocked, thereby imparting movement to the water-absorbing resin precursor A2. Furthermore, the sorting machine 4 may be equipped with a blade member inside the sorting member 42 that can move from the end on the input side 40 to the end on the first discharge port 43 in order to move the water-absorbing resin precursor B2 to the first discharge port 43 more quickly. In addition, the sorting member 42 may be frustoconical in shape.

[0050] Figure 5C shows another example where the sorting member 42 is cylindrical or rectangular. In this example, the sorting member 42 is connected to the input port 41 such that one end of the sorting member 42 in the axial direction of the cylinder points vertically upward and the other end points vertically downward. The downward end (lower end) of the sorting member 42 is not open and is continuous with the side circumference of the sorting member 42. That is, multiple openings of a predetermined size are also formed at the lower end of the sorting member 42. Of the water-absorbing resin precursor A2 introduced from the input port 40, the water-absorbing resin precursor A3 passes through the multiple openings of the sorting member 42, exits the sorting region 45, and is discharged from the second discharge port 44. The sorting member 42 is connected to a passage member 47 that defines a passage connecting the sorting region 45 and the first discharge port 43 near its lower end. The inner diameter of the passage of the passage member 47 is larger than the size of the water-absorbing resin precursor B2. As a result, the water-absorbing resin precursor B2 passes through the passage of the passage member 47 and is discharged from the first discharge port 43. The sorting member 42 may be configured to vibrate by a vibration mechanism (not shown) to prevent the opening from being blocked and causing clogging, thereby imparting movement to the water-absorbing resin precursor A2. Furthermore, the lower end of the sorting member 42 may be inclined with respect to the horizontal direction to move the water-absorbing resin precursor B2 to the passage member 47 more quickly. In addition, the sorting member 42 may be frustoconical in shape.

[0051] Figure 5D shows yet another example of the sorting machine 4, where the sorting member 42 is cylindrical or rectangular. This example differs from the example in Figure 5B in that the sorting member 42 is positioned so that its cylindrical axis is inclined with respect to the horizontal. The sorting machine 4 may be configured so that the inclination angle of the sorting member 42 can be varied within a certain range. Other points are described in the example in Figure 5B and will therefore not be explained further.

[0052] As described above, the sorting machine 4 is configured to sort absorbent resin precursor A2 based on the size (particle diameter) of the absorbent resin precursor A2 having a surface temperature of 50°C to 100°C. For convenience, in this specification, the size of the absorbent resin precursor A2 used as the sorting criterion is assumed to be a value specified as shown in Figure 6. Specifically, three mutually orthogonal planes are defined to form circumscribed rectangles Rx, Ry, and Rz representing the projection shape of the absorbent resin precursor A2, and the average of the longer sides of these circumscribed rectangles Rx, Ry, and Rz is taken as the size (particle diameter) of the absorbent resin precursor A2. In this embodiment, absorbent resin precursor A2 having a surface temperature of 50°C to 100°C and whose specified size exceeds the size of the opening (predetermined size) of the sorting member 42 is sorted as absorbent resin precursor B2. Furthermore, in this embodiment, water-absorbing resin precursor A2 having a surface temperature of 50°C to 100°C and a size such that is less than or equal to the opening size of the sorting member 42 is sent to the classifier 6 as water-absorbing resin precursor A3.

[0053] [Reasons for selecting water-absorbent polymer precursors] The following explains the reason for selecting water-absorbing resin precursor A2 with a water content of 20% or more, and why water-absorbing resin precursor B2, which has a surface temperature of 50°C to 100°C and exceeds the size of the opening of the sorting member 42, is efficiently selected as water-absorbing resin precursor A2 with a water content of 20% or more.

[0054] The water-absorbing resin precursor A2 is dried in the dryer 3 so that its overall moisture content is at least 20% or less. However, due to the temperature distribution in the drying chamber, there is variation in the degree of drying of individual water-absorbing resin precursors A2. As a result, some of the water-absorbing resin precursor A2 as a solid contains particles that are not sufficiently dried. According to the inventors' investigation, such water-absorbing resin precursors A2 contain a relatively large amount of moisture even at relatively high temperatures after drying, which affects the quality of the water-absorbing resin particles P1, such as pressurized water absorption capacity and water absorption rate. In other words, the presence of water-absorbing resin precursors A2 with a moisture content of 20% or more increases the variation in the pressurized water absorption capacity and water absorption rate of the water-absorbing resin particles P1 after classification, making it more difficult to control the pressurized water absorption capacity and water absorption rate of the water-absorbing resin particles P1.

[0055] The inventors confirmed through experiments described later that when superabsorbent polymer precursor A2 with a surface temperature of 50°C to 100°C after drying is sorted by a sorting machine 4, superabsorbent polymer precursor A2 with a moisture content of 20% or more is efficiently sorted. The predetermined size is determined by the size of the opening of the sorting member 42 provided in the sorting machine 4. Therefore, the predetermined size of the superabsorbent polymer precursor A2 that serves as the sorting standard may be 7 mm to 15 mm or less, preferably 9 mm to 11 mm, more preferably 9.5 mm to 10.5 mm, and even more preferably 9.8 mm to 10.2 mm, as described above regarding the size of the opening of the sorting member 42. According to experiments described later, it was confirmed that the moisture content of superabsorbent polymer precursor B2 sorted using a sorting machine 4 having a sorting member 42 with an opening of 10 mm was 60% or more. Thus, when the water-absorbing resin precursor A2 discharged from the dryer 3 is sorted by the sorter 4, those with a relatively high water content are selected as water-absorbing resin precursor B2.

[0056] The water content of the selected superabsorbent polymer precursor B2 may be 20% or more, may be 30% or more or 40% or more, preferably 50% or more, and more preferably 60% or more. Furthermore, the upper limit may be 85% or less, preferably 75% or less or 70% or less, and more preferably 65% ​​or less.

[0057] Furthermore, the inventors experimentally confirmed that when the water-absorbent resin precursor A2 is separated while the surface temperature is relatively high after drying, and the remaining water-absorbent resin precursor A3 is classified in the classifier 6, the variation in the pressurized water absorption capacity and water absorption rate of the classified water-absorbent resin particles P1 becomes smaller. Based on the above, it can be said that by removing the water-absorbent resin precursor B2 from the path connecting the dryer 3 and the classifier 6, water-absorbent resin particles P1 with more suppressed variation in pressurized water absorption capacity and water absorption rate can be obtained.

[0058] [Third passage member] The third passage member L3 is a member connected to the second outlet 44 and the upper opening formed at the top of the cooler 5. The third passage member L3 defines a passage for sending the water-absorbent resin precursor A3 discharged from the second outlet 44 to the cooler 5, and constitutes a path connecting the dryer 3 and the classifier 6. The method of transporting the water-absorbent resin precursor A3 to the cooler 5 is not particularly limited, and a method of transport by gravity, a method of transport by an inert gas flow, a method of transport by a transport mechanism such as a conveyor can be appropriately selected. The third passage member L3 is not particularly limited in its form as long as it is configured to introduce the water-absorbent resin precursor A3 into the upper opening formed at the top of the cooler 5, depending on the method of transporting the water-absorbent resin precursor A3. For example, the third passage member L3 can be constructed using piping, transport piping in which an inert gas flow is generated, a conveyor, a feeder, etc. A valve whose operation is controlled by a control device 7 to adjust the flow rate of the water-absorbent resin precursor A2 may be attached to the third passage member L3.

[0059] [Cooler] The cooler 5 is positioned on the path connecting the dryer 3 and the classifier 6, and has a cooling chamber (not shown). The water-absorbent resin precursor A3 discharged from the second discharge port 44 of the sorting machine 4 flows into the cooling chamber through the upper opening of the cooler 5. The cooler 5 cools the water-absorbent resin precursor A3 in the cooling chamber with a cooling device (not shown), removing the heat imparted to the water-absorbent resin precursor A3 by the dryer 3. The cooling device is connected to a control device 7, and its operation is controlled. After cooling, the water-absorbent resin precursor A3 is discharged from the cooler 5 through a lower opening formed at the bottom of the cooler 5, which is in communication with the cooling chamber, in order to be sent to the classifier 6.

[0060] [Fourth passage member] The fourth passage member L4 is a member connected to the lower opening of the cooler 5 and the upper opening formed at the top of the classifier 6. The fourth passage member L4 defines a passage for sending the water-absorbing resin precursor A3 discharged from the lower opening of the cooler 5 to the classifier 6, and constitutes a path connecting the dryer 3 and the classifier 6. The method of transporting the cooled water-absorbing resin precursor A2 to the classifier 6 is not particularly limited, and a transport method by gravity, a transport method by an inert gas flow, a transport method by a transport mechanism such as a conveyor can be appropriately selected. The fourth passage member L4 is not particularly limited in its form as long as it is configured to introduce the water-absorbing resin precursor A3 into the classifier 6 from the upper opening, depending on the method of transporting the water-absorbing resin precursor A3. For example, the fourth passage member L4 can be constructed using a pipe with one end connected to the lower opening of the cooler 5 and the other end connected to the upper opening of the classifier 6, a transport pipe in which an inert gas flow is generated, a conveyor, a feeder, etc. A valve may be attached to the fourth passage member L4, the operation of which is controlled by the control device 7 in order to adjust the flow rate of the water-absorbing resin precursor A3.

[0061] [Classifier] The classifier 6 is a device that separates the water-absorbent resin precursor A3 into groups of water-absorbent resin particles having a desired particle size distribution. Examples of classifiers 6 include vibrating screens (unbalanced weight driven type, resonant type, vibration motor type, electromagnetic type, circular vibration type, etc.), in-plane motion screens (horizontal motion type, horizontal circular-linear motion type, three-dimensional circular motion type, etc.), movable mesh screens, forced stirring screens, mesh surface vibrating screens, wind screens, and sonic screens. The classifier 6 in this embodiment has multiple in-plane motion screens. The multiple in-plane motion screens are combined in an order such that those with larger mesh sizes are on top and those with smaller mesh sizes are on the bottom. As a result, the water-absorbent resin precursor A3 sent to the classifier 6 and fed into the in-plane motion screens is classified into classes defined by the in-plane motion screens. Of these, those classified into classes that conform to product standards are obtained as water-absorbent resin particles P1.

[0062] <3. Method for producing water-absorbent resin particles> A method for manufacturing water-absorbent resin particles according to one embodiment of the present invention will be described below with reference to the drawings. Figure 7 is a flowchart showing the flow of each step performed when manufacturing water-absorbent resin particles using the manufacturing apparatus 100. Each step S1 to S7 is mainly controlled by the control device 7.

[0063] In step S1, polymerization is carried out in polymerizer 1. The polymerization tank of polymerizer 1 contains monomers, which are the raw materials for water-absorbent resin particles, and a liquid component (hydrocarbon dispersion medium). These are stirred and heated in the polymerization tank, which promotes the polymerization reaction of the monomers and produces a slurry containing a water-containing gel polymer. The produced slurry is sent to concentrator 2.

[0064] In step S2, the concentrator 2 performs concentration. The slurry sent from the polymerizer 1 is placed in the concentration tank of the concentrator 2. The slurry is concentrated by being stirred and heated in the concentration tank. This yields a concentrated liquid containing a water-containing gel-like polymer, i.e., the superabsorbent resin composition A1. The superabsorbent resin composition A1 is sent to the dryer 3.

[0065] In step S3, the dryer 3 performs drying. The superabsorbent resin composition A1 sent from the concentrator 2 is placed in the drying chamber of the dryer 3. The superabsorbent resin composition A1 is dried in the drying chamber to remove moisture and become a superabsorbent resin precursor A2. Step S3 is an example of the "step of drying a superabsorbent resin composition to obtain a superabsorbent resin precursor" of the present invention. The obtained superabsorbent resin precursor A2 is sent to the first passage member L1 connected to the sorting machine 4.

[0066] In step S4, the powdery clumps B1 are collected by the collector 30 installed in the first passage member L1 and removed from the first passage member L1. The remaining water-absorbing resin precursor A2 is sent to the sorting machine 4 with a surface temperature of 50°C to 100°C.

[0067] In step S5, the sorting machine 4 separates the water-absorbent resin precursor A2 into water-absorbent resin precursor B2 and water-absorbent resin precursor A3. Water-absorbent resin precursor B2 is removed as water-absorbent resin precursor A2 with a water content of 20% or more. The remaining water-absorbent resin precursor A3 is sent to the cooler 5. Step S5 is an example of the "step of sorting and removing water-absorbent resin precursors with a water content of 20% or more from water-absorbent resin precursors" of the present invention.

[0068] In step S6, the cooler 5 performs cooling. The water-absorbent resin precursor A3 sent from the sorting machine 4 is placed in the cooling chamber of the cooler 5 and cooled to remove the heat supplied to the dryer 3. After cooling, the water-absorbent resin precursor A3 is sent to the classifier 6.

[0069] In step S7, the classifier 6 classifies the water-absorbent resin precursor A3. This yields water-absorbent resin particles P1 that are classified and conform to product specifications. Step S7 is an example of the "step of classifying the remaining water-absorbent resin precursor to obtain classified water-absorbent resin particles" of the present invention. Note that the water-absorbent resin particles P1 also include water-absorbent resin particles to which additives have been added as needed after classification by the classifier 6.

[0070] <4. Features> According to the manufacturing apparatus 100 and the method for producing superabsorbent polymer particles using the manufacturing apparatus 100 as described above, the sorting machine 4, which is located in the path connecting the dryer 3 and the classifier 6, sorts the superabsorbent polymer precursor A2. This allows superabsorbent polymer precursor A2 with a relatively high moisture content of 20% or more, even after drying, to be sorted as superabsorbent polymer precursor B2 and removed from the manufacturing apparatus 100. Then, by classifying the superabsorbent polymer precursor A3 after removing the superabsorbent polymer precursor B2 in the classifier 6, it is possible to suppress variations in quality, such as the pressurized water absorption capacity and water absorption rate according to size, of the resulting superabsorbent polymer particles P1.

[0071] <5. Variation> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. For example, the following modifications are possible.

[0072] (1) The collecting body 30 and step S4 may be omitted. In other words, the first passage member L1 may be constructed without providing the collecting body 30.

[0073] (2) The cooler 5 and step S6 may be omitted. In other words, the manufacturing apparatus 100 does not need to have a cooler 5, and the sorter 4 and classifier 6 may be configured to be directly connected.

[0074] (3) The opening of the sorting member 42 may be slit-shaped. In this case, the average value of the slit spacing corresponds to the size of the opening of the sorting member 42.

[0075] (4) The relay member 32 and the second passage member L2 may be omitted. That is, the first passage member L1 may also serve as the second passage member L2, and the other end of the first passage member L1 may be connected to the input port 40 of the sorting machine 4. [Examples]

[0076] The following describes embodiments of the present invention, but the present invention is not limited to the following embodiments.

[0077] <Experiment 1> A manufacturing apparatus similar to the manufacturing apparatus 100 according to the above embodiment was prepared, and superabsorbent resin particles were produced using the manufacturing method according to the above embodiment. The water content of the superabsorbent resin precursor selected to be removed from the manufacturing apparatus 100 and the superabsorbent resin precursor sent to the classifier was measured using the method described later. The detailed manufacturing method of superabsorbent resin particles is described below.

[0078] [1. Preparation of the monomer aqueous solution in the first step] In a container for preparing the first-stage monomer, 28.8 parts by mass of an 80% by mass aqueous solution of acrylic acid was added as a water-soluble ethylenically unsaturated monomer. While cooling, 31.9 parts by mass of a 30% by mass aqueous solution of sodium hydroxide was added dropwise as an alkaline neutralizing agent, and the mixture was neutralized to a degree of neutralization of 76 mol% of the acid groups of the water-soluble ethylenically unsaturated monomer. Next, 1.15 parts by mass of a 2% by mass aqueous solution of potassium persulfate was added as a radical polymerization initiator, 0.14 parts by mass of a 3% by mass aqueous solution of ethylene glycol diglycidyl ether was added as a crosslinking agent, and 11.0 parts by mass of water was added and dissolved to prepare the first-stage monomer aqueous solution, which was then maintained at a temperature of 20-21°C.

[0079] [2. Transfer to the polymerization reactor and addition of additives] 90.0 parts by mass of n-heptane as a hydrocarbon dispersion medium and 2.02 parts by mass of a 10% by mass n-heptane solution of maleic anhydride-ethylene-propylene copolymer as a dispersion stabilizer were charged into the polymerizer, and these were stirred using the stirring device attached to the polymerizer. Next, the entire volume of the first stage monomer aqueous solution was added to the polymerizer. Furthermore, while heating the contents of the polymerizer, 2.02 parts by mass of a 10% by mass n-heptane solution of sucrose fatty acid ester was added to the polymerizer. Nitrogen was blown into the polymerizer body, and the inside of the polymerizer was purged with nitrogen.

[0080] [3.1st Polymerization Reaction] Next, the contents of the polymerization chamber were heated to 64°C to initiate the first stage polymerization reaction, and the first stage reaction mixture was obtained.

[0081] [4.2 Preparation of monomer aqueous solution] Meanwhile, a second monomer aqueous solution was prepared in a separate container. Specifically, 41.3 parts by mass of an 80% by mass acrylic acid aqueous solution was added to a separate container as a water-soluble ethylenically unsaturated monomer. While cooling, 45.7 parts by mass of a 30% by mass sodium hydroxide aqueous solution was added dropwise as an alkaline neutralizing agent to neutralize the mixture to a degree of neutralization of 76 mol% of the acid groups of the water-soluble ethylenically unsaturated monomer. Next, 1.45 parts by mass of a 2% by mass aqueous solution of potassium persulfate was added as a radical polymerization initiator, 0.12 parts by mass of a 3% by mass aqueous solution of ethylene glycol diglycidyl ether was added as a crosslinking agent, and 1.51 parts by mass of water was added and dissolved to prepare the second monomer aqueous solution.

[0082] [5.2 Addition of monomer aqueous solution] Next, the entirety of the second stage monomer aqueous solution was added to the polymerizer. Nitrogen was then blown into the polymerizer, purging the inside of the polymerizer with nitrogen.

[0083] [6.2nd Polymerization Reaction] Next, the contents of the polymerization chamber were heated to 57°C to initiate the second stage of polymerization. After the polymerization reaction was completed, the second stage reaction mixture (a slurry containing a water-containing gel-like polymer) was obtained.

[0084] [7. Concentration process] The second-stage reaction mixture was transferred to a concentrator equipped with a stirring device. The second-stage reaction mixture was heated to 80-90°C while being stirred by the stirring device. n-heptane and water were separated by azeotropic distillation of n-heptane and water. The n-heptane was returned to the concentrator, and a predetermined amount of water was removed from the system.

[0085] [8. Drying process] The water-absorbent resin composition obtained after concentration was transferred to a dryer equipped with a stirring device. The water-absorbent resin composition was heated in the dryer to a temperature of 80-110°C while being stirred with the stirring device, and n-heptane and water were removed from the system by azeotropic distillation of n-heptane and water. After removing a predetermined amount of water from the system, 1.4 parts by mass of a 3% by mass aqueous solution of ethylene glycol diglycidyl ether was added as a post-crosslinking agent, and the mixture was further heated and dehydrated to obtain a post-crosslinked water-absorbent resin (water-absorbent resin precursor).

[0086] [9. Transfer of water-absorbent resin precursor and adjustment of surface temperature] The water-absorbing resin precursor discharged from the dryer was transferred to the sorting machine through piping, which is the first and second flow channel component. At this time, the piping was heated to approximately 80°C using a heater (surface temperature control device) to adjust the surface temperature of the water-absorbing resin precursor moving inside the piping to 60°C or higher.

[0087] A portion of the water-absorbing resin precursor passing through the second channel member was sampled four times, and the surface temperature of each sample was measured using a waterproof digital thermometer (SK-1260, manufactured by Sato Keiryoki Mfg. Co., Ltd.). The temperatures were 63.1°C, 68.2°C, 77.4°C, and 78.2°C, respectively.

[0088] [10. Sorting Process] The water-absorbing resin precursors transferred from the dryer were processed using a sorting machine (trommel sorting machine) to remove lumps larger than 10 mm. Specifically, the trommel sorting machine has the configuration shown in Figure 5B. The trommel-type sorting machine has a casing and a rotatable sorting member. The sorting member is a mesh member having the shape of Figure 2A (square grid, wire diameter 1.6 mm, mesh opening 10 mm, opening ratio 74%), and is composed of a cylindrical mesh member with an inner diameter of 42 cm and a length of 66 cm. The sorting member is positioned so that the cylindrical axis and the horizontal plane are approximately parallel. The sorting member is configured so that the water-absorbing resin precursor introduced from its first opening (the opening closest to the sorting machine's input port) moves toward the second opening (the opening closest to the sorting machine's first discharge port). Specifically, a blade member is provided inside the sorting member, and the water-absorbing resin precursor is propelled from the first opening toward the second opening as the sorting member rotates. The water-absorbing resin precursor introduced through the first opening of the sorting member was sorted as it moved toward the second opening. In other words, smaller particles of the water-absorbing resin precursor passed through the mesh of the sorting member and moved toward the second discharge port of the sorting machine, while larger particles (clumps) did not pass through the mesh of the sorting member and moved toward the first discharge port of the sorting machine.

[0089] [11. Classification process] The superabsorbent resin precursor that had moved to the second discharge port of the sorting machine was transferred to a classifier and classified using a classifier equipped with a sieve with a mesh size of 298 to 805 μm to obtain superabsorbent resin particles with a median particle size of 380 μm. The method for measuring the median particle size will be described later. To 100 parts by mass of these superabsorbent resin particles, 0.5 parts by mass of silica was mixed as an additive to obtain the final product, which is superabsorbent resin particles.

[0090] [Method for measuring moisture content] 2.0 g of the water-absorbent polymer precursor was weighed accurately (Wb(g)) in a stainless steel petri dish that had been pre-weighted to a constant weight (Wa(g)). The precursor was dried for 2 hours in a hot air dryer (manufactured by ADVANTEC) with an internal temperature set to 105°C, and then cooled in a desiccator. The mass after drying (Wc(g)) was measured. The water content of the water-absorbent polymer precursor was calculated using the following formula. Moisture content (mass%) = [(Wb-Wa)-(Wc-Wa)] / (Wb-Wa)×100

[0091] [Method for measuring medium particle size] JIS standard sieves were arranged from top to bottom in the following order: sieve with a mesh size of 850 μm, sieve with a mesh size of 600 μm, sieve with a mesh size of 500 μm, sieve with a mesh size of 400 μm, sieve with a mesh size of 300 μm, sieve with a mesh size of 250 μm, sieve with a mesh size of 150 μm, and a receiving tray. 100 g of the water-absorbent polymer particles before silica was added were placed in the topmost sieve of the assembled sieve, and the mixture was shaken for 10 minutes using a rotary shaker to classify the particles. After classification, the mass of the water-absorbent polymer particles remaining on each sieve was calculated as a mass percentage of the total amount, and the cumulative mass percentages were calculated by accumulating the cumulative mass percentages in order from the largest particle size. The relationship between the sieve mesh size and the cumulative mass percentage of the water-absorbent polymer particles remaining on the sieve was plotted on logarithmic probability paper. By connecting the plots on probability paper with straight lines, the particle size corresponding to a cumulative mass percentage of 50% was defined as the median particle size (μm) of the superabsorbent polymer particles.

[0092] <Result> In the [10. Sorting Process], a portion of the superabsorbent polymer precursor that had moved to the first discharge port was sampled twice, and the moisture content of each sample was measured. The results were 60.1% by mass and 64.8% by mass, respectively. Similarly, the moisture content of the superabsorbent polymer precursor that had moved to the second discharge port was measured, and since the moisture content was less than 20% by mass, it was confirmed that the sorting process effectively sorted out superabsorbent polymer precursors with high moisture content.

[0093] <Experiment 2> Superabsorbent polymer particles P2 (Example), which were the final product manufactured using the method described in Experiment 1, and superabsorbent polymer particles P3 (Comparative Example), which were manufactured using the same method as in Experiment 1 except that the sorting process was omitted, and had a medium particle size of 365 μm, were prepared. Three samples were taken of each. For each sample, the pressurized water absorption amount and water absorption rate, which indicate pressurized water absorption capacity, were measured.

[0094] [Method for measuring pressurized water absorption] Figure 8 shows a measuring device 9 for pressurized water absorption. The measuring device 9 comprises a burette section 90, a conduit 91, a measuring stand 92, and a measuring section 93. The burette section 90 includes a burette 900, a first cock 902 connected to the bottom of the burette 900, and an air inlet pipe 901. The tip of the air inlet pipe 901 is connected to a second cock 903. The burette section 90 and the measuring stand 92 are connected by a conduit 91. The measuring stand 92 has a through hole that communicates with the conduit 91. The measuring section 93 includes a cylindrical section 930 made of plexiglass, a nylon mesh 931 bonded to the bottom of the cylindrical section 930, and a weight 932.

[0095] The inner diameter of the through-hole in the measuring platform was 2 mm, and the inner diameter of the cylindrical part 930 was 20 mm. The mesh opening of the nylon mesh 931 used in the experiment was 57 μm (255 mesh). The weight 932 had a diameter of 19 mm and a mass of 60 g. The weight 932 was placed on a sample of water-absorbent resin particles P2 or P3, allowing a load of 0.3 PSI to be applied to the water-absorbent resin particles P2 and P3.

[0096] The measurement was performed in a room at 25°C. First, the first stopcock 902 and the second stopcock 903 were closed, and 0.9 mass% saline solution, adjusted to 25°C, was poured into the burette 900 through its upper opening. Then, the upper opening of the burette 900 was closed with a rubber stopper. Next, the first stopcock 902 and the second stopcock 903 were opened, and the height of the measuring platform 92 was adjusted so that the water level of the 0.9 mass% saline solution in the through-hole of the measuring platform 92 was the same as the height of the top surface of the measuring platform 92.

[0097] Separately, a measuring unit 93 was prepared for each sample of water-absorbent resin particles P2 and P3, and placed on the measuring stand 92. Specifically, 0.1000 ± 0.0002 g of water-absorbent resin particles P2 or P3 was uniformly scattered on a nylon mesh 931, and the measuring unit 93 with a weight 932 placed on top was placed on the measuring stand 92. The measuring unit 93 was positioned so that the cylindrical axis of the cylindrical part 930 passed through the through hole in the measuring stand 92.

[0098] The amount of 0.9% by mass saline solution (W) (ml) that decreased from the burette 900 represents the amount of 0.9% by mass saline solution absorbed by the superabsorbent polymer particle P2 or P3. W (ml) was read, and the pressurized water absorption amount AUL (ml / g) of the superabsorbent polymer particle P2 or P3 60 minutes after the start of absorption was calculated according to the following formula. AUL = W / 0.1000

[0099] [Method for measuring water absorption rate] 50±0.1g of physiological saline solution, adjusted to a temperature of 25±0.2℃ in a constant temperature water bath, was weighed into a 100mL beaker. Next, a vortex was generated by stirring at 600 rpm (conventional vortex method) using a magnetic stirrer bar (8mmφ×30mm, without ring). 2.0±0.002g of superabsorbent polymer particles P2 and P3 were added to the physiological saline solution simultaneously. The time [seconds] from the addition of superabsorbent polymer particles P2 and P3 until the vortex on the liquid surface converged was measured, and this time was obtained as the water absorption rate of superabsorbent polymer particles P2 and P3. Note that the water absorption rate is a parameter influenced by the particle size of the superabsorbent polymer particles (generally, the larger the particle size, the slower the water absorption rate). Therefore, for convenience, the value obtained by dividing the water absorption rate (V (seconds)) by the respective median particle size (MPS (μm)), V / MPS, was used as an evaluation index for the water absorption rate of the water-absorbing resin particles P2 and P3. The method for measuring the median particle size is as already described in Example 1.

[0100] <Result> The measurement results for the three samples of superabsorbent polymer particles P2 and P3 are shown in graphs 9A and 9B, respectively. Figure 9A is a graph of pressurized water absorption AUL (ml / g). As can be seen from Figure 9A, the variation in pressurized water absorption AUL was smaller for the superabsorbent polymer particles P2 in the example than for the superabsorbent polymer particles P3 in the comparative example. In addition, the values ​​of pressurized water absorption AUL were generally higher for the superabsorbent polymer particles P2 in the example. Specifically, the average value of pressurized water absorption AUL for the three samples of superabsorbent polymer particles P2 was 34.7, while the average value of pressurized water absorption AUL for the three samples of superabsorbent polymer particles P3 was 32. In other words, it was confirmed that the pressurized water absorption AUL of the superabsorbent polymer particles P2 in the example improved by 2.7 (ml / g) compared to the superabsorbent polymer particles P3 in the comparative example.

[0101] Figure 9B is a graph of the water absorption rate evaluation index V / MPS. As can be seen from Figure 9B, the variation in the water absorption rate evaluation index V / MPS was smaller for the water-absorbing resin particles P2 according to the example than for the water-absorbing resin particles P3 according to the comparative example. Specifically, the variance of the water absorption rate evaluation index V / MPS for three samples of water-absorbing resin particles P2 was 0.0003, while the variance of the water absorption rate evaluation index V / MPS for three samples of water-absorbing resin particles P3 was 0.004. This confirms that the variation in the water-absorbing resin particles P2 according to the example was reduced compared to the water-absorbing resin particles P3 according to the comparative example. [Explanation of symbols]

[0102] 1. Polymerizer 2 Concentrator 3 Dryer 4. Sorting machine 5 Cooler 6 Classifier 40 Inlet 41 Inlet part 42 sorting components 42a Mesh member 42b Plate-shaped member 100 Manufacturing equipment A1 Water-absorbing resin composition A2 Superabsorbent resin precursor A3 Superabsorbent resin precursor

Claims

1. A dryer for drying a water-absorbent resin composition to obtain a particulate water-absorbent resin precursor, A classifier for classifying the water-absorbing resin precursor to obtain water-absorbing resin particles, A sorting machine is positioned on the path connecting the dryer and the classifier, Equipped with, The sorting machine is configured to sort the water-absorbing resin precursors having a surface temperature of 50°C to 100°C and exceeding a predetermined size into water-absorbing resin precursors with a water content of 20% or more. A manufacturing apparatus for superabsorbent polymer particles.

2. The sorting machine includes an input port formed therein into which the water-absorbing resin precursor discharged from the dryer is fed, and a sorting member connected to the input port and having an opening of a predetermined size. The sorting machine is configured to send the water-absorbing resin precursor that has passed through the opening, from the water-absorbing resin precursor introduced into the input port, to a path connected to the classifier. Apparatus for producing water-absorbent resin particles according to claim 1.

3. The sorting member is composed of a mesh-like member in which a plurality of openings of a predetermined size are formed. Apparatus for producing water-absorbent resin particles according to claim 2.

4. The sorting member is configured to impart movement to the water-absorbing resin precursor introduced into the input port. Apparatus for producing water-absorbent resin particles according to claim 2 or claim 3.

5. The predetermined size is 7 mm to 15 mm. An apparatus for producing water-absorbent resin particles according to any one of claims 1 to 4.

6. Cooling machine located on the path connecting the sorting machine and the classifier Furthermore, The cooling unit is configured to cool the water-absorbing resin precursor that is sent to the path connecting the sorting machine to the classifier. An apparatus for producing water-absorbent resin particles according to any one of claims 1 to 5.

7. The steps include drying the water-absorbent resin composition to obtain a particulate water-absorbent resin precursor, From the water-absorbing resin precursor, water-absorbing resin precursors having a surface temperature of 50°C to 100°C and exceeding a predetermined size are selected and removed as water-absorbing resin precursors with a water content of 20% or more. The steps include classifying the remaining water-absorbing resin precursor to obtain classified water-absorbing resin particles, including, A method for producing water-absorbent resin particles.

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