JP4969847B2 - Method for drying hydrogel granules - Google Patents

Description

  The present invention relates to a method for drying hydrogel granules.

A hydrogel that is a gel-like material containing a large amount of water is produced, for example, as follows. That is, when a paste-like product obtained by mixing a water-soluble polymer compound and water is irradiated with radiation, the polymer compound is crosslinked in a network form to form a hydrogel. The dried product obtained by removing moisture from the hydrogel has extremely excellent water absorption and can absorb water several hundred times as large as its own volume. In addition, the retention of absorbed water is excellent, and water does not escape from the hydrogel even if some pressure is applied.
Since it has such a property, hydrogel and its dried product are used as a water-absorbing material, a water retaining material, and the like. For example, it is also used as a medical product in addition to a disposable diaper water-absorbing material, a soil conditioner in the agricultural field, and a treatment for manure from livestock.

JP 2001-329070 A JP 2003-48997 A JP 2004-59926 A

When the hydrogel is produced by the method as described above, a large mass of the hydrogel is usually obtained. Therefore, the hydrogel is crushed into fine particles and further dried for use in the above-described applications.
However, since hydrogel has excellent water absorption, it has not been easy to dry efficiently in a short time. Moreover, since hydrogel has adhesiveness, there existed a problem that a granular material was easy to adhere | attach between drying.
Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a method for easily drying a hydrogel granule without adhering it.

In order to solve the above problems, the present invention has the following configuration. That is, the method for drying a hydrogel granule according to claim 1 according to the present invention is a method for drying a hydrogel granule in which a polymer compound crosslinked in a network form contains a large amount of water, The granular material is obtained by pre-chopping the hydrogel lump into a large number of fine pieces and then pulverizing them into particles by putting them into a screw extruder and extruding them. The particulate matter is heated while being blown up and stirred by the airflow , and this heating is performed by placing the particulate matter in a container having a vent at the bottom and continuously moving a plurality of the containers in a row, It heats, sending the said airflow from the downward direction of the said container .
Moreover, the drying method of the hydrogel granule of Claim 2 which concerns on this invention is a drying method of the hydrogel granule of Claim 1, In the drying method of the hydrogel granule of Claim 1, a several air-feeding port is said along the row | line | column of the said container. Provided on the lower side of the container, the plurality of air supply ports are alternately arranged on the left and right of the row of the containers, and the direction of the airflow hitting the granular material from the air supply port is the movement of the granular material. It is characterized by being repeated alternately left and right along .

Furthermore, the method for drying a hydrogel granule according to claim 3 of the present invention is a method for drying a hydrogel granule in which a polymer compound crosslinked in a network form contains a large amount of water, An air stream is blown up from below the granular material, and the granular material is heated while being stirred by the air flow. This heating is performed by placing the granular material in a container having a vent at the bottom and arranging a plurality of the containers in a row. While continuously moving, heating is performed while feeding the airflow from below the container.
Furthermore, the drying method of the hydrogel granule according to claim 4 of the present invention is the method of drying a hydrogel granule according to claim 3, wherein a plurality of air supply ports are arranged along the row of the containers. Provided on the lower side of the container, the plurality of air supply ports are alternately arranged on the left and right of the row of the containers, and the direction of the airflow hitting the granular material from the air supply port is the movement of the granular material. It is characterized by being repeated alternately left and right along.

  According to the method for drying a hydrogel granule of the present invention, the hydrogel granule can be easily dried without adhering the hydrogel granule.

Embodiments of the method for drying a hydrogel granule according to the present invention will be described in detail with reference to the drawings.
First, the manufacturing method of hydrogel is demonstrated. Carboxymethylcellulose (with the hydrogen of the carboxyl group replaced with sodium) and water (pure water, ion-exchanged water, and distilled water are preferred) are charged into a stirrer and mixed well to obtain a paste. When this paste-like material is poured into a plate-like mold (for example, width 300 mm, length 450 mm, thickness 40 mm) and irradiated with radiation at room temperature, the linear polymer compound carboxymethylcellulose undergoes a crosslinking reaction to form a network. It forms a structure and becomes a water-insoluble hydrogel. Hydrogel contains a large amount of water, and this water does not escape even if a certain pressure is applied.

The mixing ratio of the polymer compound is not particularly limited, but is preferably 10 to 60% by mass, and more preferably 50 to 60% by mass. If the mixing ratio of the polymer compound is too large, the water is difficult to disperse uniformly. Conversely, if the mixing ratio is too small, the crosslinking reaction is difficult to occur or water cannot be retained in the hydrogel.
The type of polymer compound is not limited to carboxymethylcellulose as long as it is a water-soluble polymer compound capable of forming a hydrogel, but is not limited to carboxymethylcellulose, sodium acrylate, acrylamide, polyvinyl alcohol, polyethylene oxide, Polyvinyl pyrrolidone or the like can also be used. However, since carboxymethylcellulose and carboxymethyl starch are biodegradable, they have the advantage that they do not decompose and remain in the soil when embedded in soil.

Furthermore, the molecular weight (molecular weight before crosslinking) of the polymer compound is not particularly limited, but usually several hundred to several tens of thousands are used.
Furthermore, if desired, additives such as starch may be mixed into the hydrogel. When mixing the additive, the polymer compound, the additive, and water are mixed to form a paste, and irradiated with radiation to form a hydrogel. In addition, when using starch together with carboxymethylcellulose or carboxymethyl starch, it is preferable to use 20 to 400 parts by weight of starch, more preferably 100 parts by weight, based on 100 parts by weight of carboxymethylcellulose or carboxymethyl starch. preferable.

Furthermore, the type of radiation is not particularly limited, but gamma rays, electron beams, X-rays and the like are preferable. In consideration of industrial production of hydrogel, gamma rays using cobalt 60 as a radiation source and electron beams using an accelerator as a radiation source are particularly preferable.
Further, the irradiation amount of radiation is not particularly limited as long as a crosslinking reaction occurs to form a hydrogel, but is usually 0.1 to 1000 kGy, preferably 5 to 10 kGy. If the irradiation amount is small, the crosslinking reaction may be insufficient and water retention may be insufficient. On the other hand, when there is too much irradiation amount, a crosslinking reaction may become excess.
The cross-linking reaction is preferably caused by radiation, but it can also be caused by heat or chemicals depending on the type of polymer compound.

  Next, the hydrogel granulation method will be described. Granulation of the hydrogel is performed by a screw extruder as shown in FIG. The type and size of the screw extruder are not particularly limited, and for example, a single screw extruder or a twin screw extruder may be used. Moreover, the shape of the screw is not particularly limited, and a screw that can be crushed into a size corresponding to the use of the hydrogel or a dried product thereof may be selected.

  When the hydrogel is charged into the extruder, the plate-shaped hydrogel (lumps) taken out from the mold is shredded in advance so that the hydrogel is stably supplied to the extruder. It is preferable to add hydrogel. Depending on the type of the extruder and the properties of the hydrogel, it may be supplied to the extruder to some extent even if it is not shredded, but to ensure that the hydrogel is stably supplied to the extruder. In general, it is preferable to perform preliminary shredding.

  In preliminary shredding, the width of the spiral groove formed in the screw (the portion of the spiral groove formed in the portion exposed to the opening of the cylinder to which the hopper is attached, that is, the portion into which the hydrogel is introduced). It is preferable to chop the hydrogel smaller than (width). Usually, it shreds into a rectangular parallelepiped having a side of about 15 to 20 mm. Then, since the hydrogel fine piece enters the spiral groove of the screw, the hydrogel fine piece is stably fed into the extruder by the screw.

  The hydrogel shredding method is not particularly limited, but since hydrogel has high toughness, high elasticity, and high adhesiveness, a strong shearing force seems to act on the hydrogel for efficient shredding. Is preferred. For example, a guillotine type, a rotary blade type, or a scissor type that moves the blade up and down is preferable. The cutter type that moves the blade back and forth is difficult to shred because the hydrogel is sticky.

It should be noted that the shape and size of the hydrogel fine pieces are not necessarily uniform. In addition, the smaller the hydrogel finer piece, the better the biting into the screw and the shorter the extrusion time, but it is not easy to cut the hydrogel finely by the usual cutting method. The size of the gel subsection may be determined.
A large number of the hydrogel fine pieces 40 chopped in this manner are put into a hopper 32 of an extruder 31 and extruded. In that case, it is not necessary to heat or cool. The hydrogel fine pieces 40 are sequentially fed from the hopper 32 into the extruder 31, fed into the cylinder 34 by the screw 33, and crushed by receiving shearing force and compressive force between the screw 33 and the inner wall of the cylinder 34. , Further refined.

  More specifically, the hydrogel sub-section 40 becomes denser as it approaches the tip of the screw 33, so between the screw 33 and the hydro-gel sub-section 40, between the cylinder 34 and the hydro-gel sub-section 40, and Due to the pressure and frictional force generated between the hydrogel fine pieces 40, the hydrogel fine pieces 40 receive a strong shearing force and a compressive force, and are gradually crushed and sent to the chamber 36 in front of the die 35. Simultaneously with the crushing, many fine cracks are generated on the surface.

  The hydrogel fine piece 40 sent to the chamber 36 in front of the die 35 is further compressed and squeezed by the subsequent hydrogel fine piece 40, and the generation and crushing of the cracks proceed. In this state, the hydrogel fine piece 40 passes through the die hole 35a. Is issued. The hydrogel fine piece 40 is almost fully crushed when it passes through the screw 33 to the chamber 36 in front of the die 35, but it is hydrogel larger than the diameter of the die hole 35a even in a compressed state. The fine piece 40 is further crushed and made finer when passing through the die hole 35a. And when it comes out of the die hole 35a, most things do not become a string-like continuous shape, but naturally cut into an appropriate length to become granular (hydrogel granular material 41), and a part thereof is about 20 mm. Some are long, but because they have many cracks on the surface, they break apart and become fine.

  A high pressure is acting on the hydrogel in the extruder 31, but when the pressure is released from the die hole 35a, the hydrogel expands, and the surface is raised due to the cracks. Become. Thus, the hydrogel granular material 41 crushed by the extruder 31 has an irregular shape with various sizes. In addition, since the surface is shaped like a raised surface, the surface area is large. Therefore, it is easy to dry in the subsequent drying step. Further, when water is absorbed by the dried hydrogel, the surface area is large, which facilitates water absorption and is advantageous.

The diameter of the die hole 35a is not particularly limited, and may be appropriately set depending on the size of the target hydrogel granular material 41. Usually, it is about 1.8 to 3 mm. Further, when the rotational speed of the screw 33 is increased, the crushing speed is also improved, but the extruded state in the die hole 35a is hardly changed.
Furthermore, an extruder is optimal for granulating the hydrogel, but other devices can be used as long as they can be crushed to the required size by applying a strong shearing force and compressive force to the hydrogel. Examples include a Henschel mixer and a ball mill.

Next, a method of drying the hydrogel granules using the hot air drying device 2 will be described with reference to FIGS.
FIG. 2 is a diagram showing the hot air drying device 2 in a sectional plan view, and FIG. 3 is a diagram showing the hot air drying device 2 in a side view. The hot air drying device 2 is a rectangular parallelepiped device, and the conveyor 4 passes from one end side to the other end side in the longitudinal direction of the device. It moves at speed.

  The hot air drying device 2 is composed of drying chambers D1, D2, D3, D4, D5,. As shown in FIG. 4, the first first drying chamber D <b> 1 from the left side has a heater 6 that heats indoor air to a set temperature, and hot air that is generated below the indoor space where the conveyor 4 is disposed. A blower fan 8 to be sent out, a wind guide part 20 for guiding the hot air emitted from the blower fan 8 downward in the width direction of the conveyor 4, and a rectifying part for rectifying the hot air flowing below the conveyor 4 so as to blow up toward the conveyor 4 12. In addition, the code | symbol 8a is a fan motor, the code | symbol 4a is a conveyor of a return direction, and the code | symbol 14 shown with a dashed-two dotted line covers the circumference | surroundings of the box which forms the drying room D1, and maintains the temperature in the drying room D1 It is a heat insulation panel.

The air guide unit 20 includes an intake port 20a for taking in hot air from the blower fan 8 and a delivery port 20b opened below the conveyor 4 (corresponding to an air supply port which is a component of the present invention). Inside the box, a laminar flow plate 20c is disposed inside the box to change the turbulent hot air from the blower fan 8 into a laminar flow and flow it to the delivery port 20b.
The rectifying unit 12 includes a wind speed control plate in which a plurality of slits are formed in parallel to each other in a direction orthogonal to the moving direction of the conveyor 4, and a plurality of wind receiving plates 18a ... 18f fixed to the lower surface of the wind speed control plate. It is a member. The plurality of wind receiving plates 18a... 18f are made of an angle material, and the height of the wind receiving plate 18a closest to the wind guide portion 20 is low, and the height of the wind receiving plate 18f farthest from the wind guide portion 20 is high. The heights of the other wind receiving plates 18b... 18e between them are gradually lowered toward the wind guide portion 20.

  Here, the hot air flowing from the air guide portion 20 rises and flows after hitting each wind receiving plate 18a... 18f, but the wind receiving area of the rising portion of each wind receiving plate 18a. The area is set such that an amount of hot air that is optimal for drying the hydrogel particulates flows uniformly toward the portion of the conveyor 4 thereover. The shape of the plurality of slits formed in the wind speed control plate is also set so that the hot air flowing upward through these slits has an optimum wind speed for drying the hydrogel granular material. For example, if a slit plate having a slit width of 29.2% with linear slits having a width of 6 mm provided at an interval of 20 mm is used, the hydrogel particles are dried with an air volume of about 1/3 that when not used. Therefore, drying can be performed at low cost.

  And each drying chamber D1-D5 shown in FIG.2 and FIG.3 is equipped with the structure similar to this 1st drying chamber D1. However, the drying chambers D <b> 1 to D <b> 5 are alternately symmetrical in the longitudinal direction of the conveyor 4. The drying chambers D3 and D5 are the same as in FIG. 4, but the drying chambers D2 and D4 are symmetrical with respect to the drying chamber D1. That is, the delivery ports 20b are alternately arranged on the left and right of the conveyor 4 (that is, the row of containers that is a constituent of the present invention). Thereby, the hot air from the delivery port 20b can be sent from the left and right to the moving hydrogel particles, and the hot air can be sent alternately left and right along the movement of the hydrogel particles.

  Here, as shown in FIG. 5, the conveyor 4 covers the basket 4b (for example, 270 mm long, 325 mm wide, 100 mm high) containing the hydrogel particles therein and the upper opening of the basket 4b. The lid 4c is connected to both ends in the longitudinal direction of the plurality of baskets 4b, and the transport chain 4d is moved from one end side to the other end side in the longitudinal direction of the hot air drying device 2. In the case of the basket 4b having the above dimensions, the amount of the hydrogel particles is preferably about 1 to 1.5 kg. The basket 4b and the lid 4c are provided with a large number of hot air passage holes 4e and 4f. In order to form the hot air passage holes 4e and 4f, the bottom of the basket 4b and the lid 4c are made of a stainless steel net. If any of these is coated with a fluororesin such as tetrafluoroethylene, the adhesion of the hydrogel particles is suppressed.

  Next, a drying method using the hot air drying device 2 having the above configuration will be described below. When the granular material carried on the conveyor 4 enters the first drying chamber D1, the heated air generated by the heater 6 of the first drying chamber D1 is heated as hot air through the blower fan 8 in the room. It is sent out downward. Then, the hot air sent into the air guide section 20 is rectified into the first laminar flow state therein, and then sent out below the conveyor 4. The hot air sent out below the conveyor 4 hits the plurality of wind receiving plates 18a... 18f of the rectifying unit 12 and flows over the entire lower surface of the wind speed control plate with a uniform air density while the air volume is controlled. Then, the hot air passes through the plurality of slits of the wind speed control plate, the wind speed is controlled, and the hot air is blown from below onto the granular material in the conveyor 4 while being rectified into the second laminar flow state. Thus, even if the hot air sent out from the blower fan 8 is in a turbulent state, the air is rectified into the first laminar flow state by passing through the air guide unit 20 and passes through the rectifying unit 12. The air flow is controlled to an optimal air volume and speed and rectified into a second laminar flow state, and the rectified hot air is uniformly blown from below to the granular material stored in the conveyor 4 for drying.

Here, since hot air blows up from the bottom of the conveyor 4, the internal hydrogel particles are caused to rise, move like dancing in the air, and are dried with stirring. The lid 4c prevents the particulate matter from leaking out. Thus, since the hydrogel particles are constantly stirred in the conveyor during drying, adhesion between the particles is unlikely to occur.
The hot air is circulated as shown by the arrows in FIG. 4, and some of the hot air is discharged to the outside through a path (not shown) and new air is introduced. And like this embodiment, since the delivery port 20b is alternately arranged by right and left of the conveyor 4 sequentially, and the flow of the wind is alternated right and left along the advancing direction of a conveyor, Inconveniences such as drying unevenness can be prevented.

  That is, for example, when hot air from the right delivery port 20b blows up the hydrogel particles, the direction of the air flow is apt to be inclined obliquely upward to the left. Therefore, if the delivery port 20b is arranged only on the right side or the left side of the conveyor 4, the hydrogel particulates are biased to the right side or the left side of the basket 4b due to the air flow, and there is a possibility that sufficient drying cannot be performed. In addition, since the wind speed may be different between the right end portion and the left end portion of the basket 4b, if the delivery port 20b is disposed only on the right side or the left side of the conveyor 4, it is uniform with respect to all the hydrogel particles in the basket 4b. Hot air cannot be sent and drying unevenness may occur. However, if the delivery ports 20b are alternately arranged on the left and right of the conveyor 4, the above-described disadvantages are less likely to occur.

  The temperature of the hot air varies depending on the type and amount of the hydrogel particles, but is preferably 70 ° C or higher and 130 ° C or lower. Moreover, although the wind speed of the hot air at the time of spraying on a granular material also changes with kinds and quantity of granular material, 12 m / s or more and 20 m / s or less are preferable. Here, the hot air is set to 70 ° C., and the wind speed at the time of blowing to the granular material is 20 m / s in the drying chamber D1, 17 m / s in the drying chamber D2, 15 m / s in the drying chamber D3, and 12.5 m / s in the drying chamber D4 and below. s. This is because the moisture content in the first drying chamber D1 is high and the moisture content gradually decreases, so even if the wind speed is lowered, the particulate matter can be blown up and moved in the air. The granular material thus dried has a water content of 10% by mass or less and shrinks to a size of about 3 to 6 mm. Although the time required for drying varies depending on the conditions, it is 5 to 30 minutes.

It is sectional drawing of the extruder explaining the granulation method of hydrogel. It is the figure which showed the hot air drying apparatus which dries the granular material of hydrogel with the plane sectional view. It is the figure which showed the hot air drying apparatus of FIG. 2 by the side view. It is AA sectional drawing of the hot air drying apparatus of FIG. It is a perspective view which shows the structure of a conveyor.

Explanation of symbols

2 Hot Air Dryer 4 Conveyor 4b Basket 20b Delivery Port 31 Extruder 33 Screw 40 Hydrogel Fine Piece 41 Hydrogel Granules

Claims (4)

A method of drying a hydrogel granule in which a polymer compound cross-linked in a network contains a large amount of water, wherein the granule is pre-chopped into a mass of the hydrogel and a plurality of fine fragments. In addition, it is crushed into granules by being put into a screw extruder and extruded, and heated while stirring the particulates with the air stream by blowing up an air stream from below the particulates . A hydrogel characterized in that the granular material is placed in a container having a vent hole at the bottom, and the plurality of the containers are arranged in a row and continuously moved, and heated while sending the airflow from below the container . Drying method for granular materials. A plurality of air supply ports are provided on the lower side of the container along the row of the containers, and the plurality of air supply ports are alternately arranged on the left and right of the row of the containers, and the granularity is formed from the air supply ports. The method for drying a hydrogel granule according to claim 1 , wherein the direction of the airflow hitting the object is alternately repeated left and right along the movement of the granule. A method of drying a hydrogel granule in which a polymer compound crosslinked in a network form contains a large amount of water, while blowing an air stream from below the granule and stirring the granule with the air stream The heating is performed by putting the granular material in a container having a vent at the bottom, and heating the air flow from below the container while continuously moving a plurality of the containers in a row. A method for drying a hydrogel granule. A plurality of air supply ports are provided on the lower side of the container along the row of the containers, and the plurality of air supply ports are alternately arranged on the left and right of the row of the containers, and the granularity is formed from the air supply ports. The method of drying a hydrogel granule according to claim 3, wherein the direction of the airflow hitting the object is alternately repeated left and right along the movement of the granule.

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