JP2006205071A - Dissolution method of powder - Google Patents

Abstract

In a method of dissolving a granular material in a solvent, the dissolution time is shortened and foaming is completed at the completion of dissolution in dissolving the granular material that easily forms lumps (for example, dissolution of PVA granular material in water). And a dissolution method in which no undissolved material remains.
A liquid in which a powder and a solvent are mixed is circulated between a tank provided with a stirring device and a pulverizer to dissolve the powder, and the circulated liquid is transferred from the pulverizer to the tank. The discharge port of the liquid feed pipe for returning to the tank is immersed in the liquid in the tank, and the discharge direction of the liquid discharged from the discharge port is substantially the same direction as the swirl flow direction of the liquid in the tank by the stirring device To.
[Selection] FIG.

Description

  The present invention relates to a method for dissolving powder particles in a solvent, and more particularly to a dissolution method for dissolving a water-soluble polymer such as polyvinyl alcohol in an aqueous solvent.

  It is widely used in various fields to dissolve a polymer or other granular material in a solvent such as water. It is desirable to shorten the melting time for the melting operation of these powder particles in order to improve industrial production efficiency, and the melting equipment and the melting method are improved.

  In the case of dissolving powder particles such as polymers that are relatively difficult to dissolve, it is necessary to first uniformly disperse the powder particles in the solvent. When the dissolution is promoted by heating in a non-uniform dispersion state, problems such as undissolved matters remain easily. Therefore, the time required to obtain a sufficiently dispersed state is long, which is an obstacle to improving the dissolution efficiency.

  Further, if the stirring for dispersion / dissolution is strengthened, bubbles are likely to be generated in the solution. In particular, in the case of a polymer solution, since the viscosity is high, it took a considerable time to remove bubbles once generated. If air bubbles remain in the solution, problems such as poor liquid feeding due to the generation of voids in the liquid feeding mechanism in the liquid feeding process, an increase in the size of the dissolving equipment accompanying an increase in apparent volume, and a decrease in production efficiency occur.

  On the other hand, ink jet recording paper is generally provided with an ink receiving layer made of inorganic fine particles such as a water-soluble polymer or silica on a support. In particular, polyvinyl alcohol (hereinafter abbreviated as PVA) is preferably used as a binder for the ink receiving layer. However, PVA is difficult to dissolve in water, and in particular, it took a considerable amount of time to dissolve PVA having a high degree of polymerization at a high concentration.

  In order to suppress the occurrence of lumps when dissolving PVA, a general method is to fill the tank with cold water or room temperature water, gradually add and disperse PVA in a stirred state, and dissolve by stirring and heating. Has been done. This method has a low dissolution efficiency because the time required for charging the powder and the dispersion time before the temperature rise must be increased.

  Here, “dama” means a lump of agglomerated particles, and when the particles are not sufficiently dispersed in the solvent when the particles come into contact with the solvent, only the surface of the dama dissolves. As a result, a gel-like film was formed, and the granular material inside the mass remained undissolved, which contributed to dissolution inhibition.

For these problems, the following Patent Documents 1 to 3 disclose melting equipment, a method for adding granular materials, or a melting method, but from the aspect of the foaming of the solution at the time of equipment scale and cost, and completion of dissolution. It was not enough.
JP 2002-302551 A JP 2003-53170 A JP 2003-113596 A

  Therefore, the object of the present invention is to reduce the time required for dissolution in the dissolution process of the granular material that is likely to form lumps, suppress foaming at the completion of dissolution, and retain undissolved matter when dissolving the granular material in the solvent. It is to provide a dissolution method without any.

The above object of the present invention has been achieved by the following invention.
1) A method in which a liquid in which a powder and a solvent are mixed is circulated between a tank equipped with a stirring device and a pulverizer to dissolve the powder, and the circulated liquid is removed from the pulverizer. The discharge port of the liquid feed pipe for returning to the tank is immersed in the liquid in the tank, and the discharge direction of the liquid discharged from the discharge port is roughly the swirl flow direction of the liquid in the tank by the stirring device Keep in the same direction.
2) The method for dissolving a granular material according to 1) above, wherein the granular material is polyvinyl alcohol having an average degree of polymerization of 2000 to 5000, and the solvent is water.

  By carrying out the dissolution method of the present invention, it was possible to achieve dissolution without shortening the required dissolution time and suppressing foaming at the completion of dissolution and without remaining undissolved substances.

  Hereinafter, the present invention will be described in detail. Examples of the powder applied to the dissolution method of the present invention include natural and synthetic water-soluble polymers. Among these, water-soluble polymers that are difficult to dissolve, such as PVA and modified products thereof, polyacrylamide, celluloses, polysaccharides, and the like are preferably applied to the dissolution method of the present invention. In particular, PVA having an average degree of polymerization of 2000 to 5000 and a modified product thereof can be preferably applied. These water-soluble polymers can also be preferably applied when dissolved alone or in combination.

  The dissolution method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a melting apparatus used in the melting method of the present invention. The tank 1 and the pulverizer 4 are connected by a liquid feeding pipe 2 so that the liquid 5 in the tank circulates between the tank 1 and the pulverizer 4 installed outside the tank 1. In the middle of the liquid feeding pipe 2, a liquid feeding mechanism 3 comprising a pump or the like is installed. When the pulverizer itself also serves as a liquid feeding mechanism, the liquid feeding mechanism 3 can be omitted.

  The tank 1 is provided with a stirring device including a power mechanism 8 and a stirring blade 9. Furthermore, a heating means (for example, a heating jacket) 10 for raising the temperature of the liquid 5 is attached to the tank 1. This heating means may also serve as a means for cooling or adjusting the temperature of the liquid 5.

  In the dissolution method of the present invention, a lump of powder mixed in a solvent is melted by stirring and raising the temperature in a tank while crushing it with a pulverizer. In order to reduce the number, the discharge direction and discharge position of the mixture of powder and solvent (hereinafter referred to as liquid) that circulates back into the tank are specified. That is, the discharge port 7 of the liquid feeding pipe 2 for returning the circulating liquid from the pulverizer 4 to the tank 1 is immersed in the liquid 5 of the tank 1, and the discharge direction of the liquid discharged from the discharge port 7 is The direction of the swirl flow of the liquid generated by the stirring blade 9 is approximately the same. As a result, the circulation efficiency of the liquid 5 can be increased and the generation of bubbles can be suppressed.

  Here, “circulation efficiency” means that the liquid 5 in the tank 1 is evenly circulated to the pulverizing device 4, and the liquid 5 in the tank 1 stays locally and is not circulated or circulated. It is necessary to prevent the liquid returning to the tank 1 from being circulated as it is without mixing with other liquids in the tank.

  Specifically, the “short path phenomenon” between the discharge from the discharge port 7 to the tank 1 (return to the tank) and the discharge from the tank valve 6 to the pulverizer 4 (out of the tank). In a state where a short-circuit flow called “occurs, only a local portion of the liquid 5 circulates between the tank 1 and the pulverizer 4, which causes a reduction in circulation efficiency. In addition, agitation in which sedimentation of undissolved material due to insufficient agitation or local decrease in flow rate occurs also causes a reduction in circulation efficiency.

  FIG. 2 is a plan view of the tank 1. When the stirring blade 9 is driven to rotate, a swirl flow 21 of liquid is generated. The direction of the discharge port 7 is set so that the swirl flow 21 and the discharge direction 22 of the liquid from the discharge port 7 of the liquid feeding pipe 2 substantially coincide.

  The position (height) of the discharge port 7 in the tank 1 is preferably as high as the stirring blade 9. More preferably, the discharge port 7 is arranged in the vicinity of the stirring blade 9 and on the far side from the tank valve 6 (position slightly higher than the stirring blade 9).

  The pulverizer used in the present invention preferably has a mechanism for pulverizing a lump in the liquid by passing the liquid through the narrow gap, and more preferably the gap between the narrow gaps is 1 to 3 mm. It is good to use what has.

  Preferable examples of the pulverizer used in the present invention include a high-pressure emulsifier, a spiral pin mixer manufactured by Taiheiyo Kiko Co., Ltd., and a vibro reactor manufactured by PUC. The schematic configuration of these crushers will be described with reference to the drawings.

  FIG. 3 is a principle diagram of a high-pressure emulsifier. When the liquid 31 to which pressure is applied passes through the minute gap 32, it is sheared by friction with the gap walls forming the minute gap, and solids present in the liquid are crushed. In addition, there is a pulverizing action by causing the liquid 33 ejected from the minute gap 32 to collide with the wall surface 34, or a cavitation effect in the liquid in a high-speed flow in the ejection to effectively obtain the pulverizing action.

  FIG. 4 is a principle diagram of a spiral pin mixer. The spiral pin mixer is a device that continuously dissolves, disperses, and kneads powder and liquid. The liquid is introduced into the case 42 from the inlet 41 and provided on the upper surface of the rotor 44 that is rotated by the power mechanism 43. While being coarsely pulverized by the primary dispersion pin 45 and staying in the case body, the secondary dispersion pin 46 is further subjected to a shearing force and then discharged from the discharge port 47.

  FIG. 5 is a principle diagram of a vibro reactor. The liquid introduced from the suction port 51 is coarsely pulverized in the gap portion 55 between the blade 53 rotating by the power mechanism 52 and the casing 54, and then further shearing force is applied in the gap portion 57 between the rotating disk 56 and the casing 54. receive. Thereafter, the gas is discharged from the discharge port 59 by the discharging action accompanying the rotation of the rotor 58. This vibro reactor is an apparatus having both a pulverizing action and a liquid feeding mechanism.

  Here, as a liquid feeding mechanism that circulates between the tank 1 and the pulverizing device 4, a liquid feeding means such as a positive displacement type or a pressure pump, or a device having a liquid feeding function in the above pulverizing device may be substituted.

  Further, the gear pump is preferable as a liquid feeding mechanism in that the meshing portion of the gear brings about a crushing action in the crushing device.

  Examples of the stirring device attached to the tank 1 include a propeller blade, an anchor blade, and a sawtooth disk plate driven by a power mechanism, and a sawtooth disk plate having a high shearing force is more preferable. Examples of the stirring device having the above functions include a DS impeller manufactured by Satake Chemical Machinery Co., Ltd. and a homodispa manufactured by Tokushu Kika Kogyo Co., Ltd., but the present invention is not limited thereto.

  Examples of the means for heating the liquid in the tank 1 include indirect heating using a jacket, direct fire heating, and blowing live steam into the liquid, but the present invention is not limited to this.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, the content of this invention is not restricted to these Examples.

  The dissolution apparatus shown in FIG. 1 was used. In a tank with a heating jacket with a capacity of 1600 liters, 1270 liters of pure water was weighed and kept at 45 ° C. Both a high-speed stirrer having a sawtooth disk plate and a pulverizer (PUB Vibro Reactor) installed outside the tank were operated at 60 Hz, and the inside of the tank was stirred. Co., Ltd. PVA235: average polymerization degree 3500, saponification degree 88%) 92 kg was added. The liquid (mixed liquid of pure water and PVA) circulated between the tank and the pulverizer, and was discharged from a discharge port installed so as to approximately coincide with the swirling flow direction by the high-speed stirrer. Simultaneously with the start of addition, the temperature of the heating jacket is set to 95 ° C., and the temperature in the tank is increased to 70 ° C. After the temperature of the liquid reaches 70 ° C., both the high-speed stirrer and the pulverizer are set to 30 Hz. The operating frequency was changed, and at the same time, the liquid temperature was cooled to 60 ° C. and kept warm.

(Comparative Example 1)
As a typical example of PVA dissolution, the tank is filled with pure water kept at 25 ° C., and PVA is gradually added and dispersed sufficiently in a state where the tank is stirred. went. The temperature rise of the liquid in the tank was started after dispersing for 30 minutes after the addition of PVA. A pulverizer was not used.

(Comparative Example 2)
In Comparative Example 1, dissolution was performed in the same manner as Comparative Example 1 except that the pure water at the time of PVA addition was changed to 45 ° C.

(Comparative Example 3)
In Example 1, dissolution was performed in the same manner as in Example 1 except that the discharge direction of the liquid circulated from the pulverizer was arranged in the direction opposite to the swirl flow direction by the high-speed stirrer.

(Comparative Example 4)
In Example 1, dissolution was performed in the same manner as in Example 1 except that the direction of discharge of the circulated liquid from the pulverizer was directed vertically downward.

(Comparative Example 5)
In Example 1, dissolution was performed in the same manner as in Example 1 except that the liquid discharge port circulated from the pulverizer was arranged so as not to be immersed in the liquid.

  In the dissolution methods of the above-described Examples and Comparative Examples, the solubility, the state of foaming, and the residual state of undissolved materials were evaluated by the following methods and criteria.

<Solubility>
After collecting the liquid in the tank and removing undissolved substances by filtration, the solid content concentration in the liquid was measured by the absolutely dry method. The start of addition of PVA is taken as the dissolution start time, and the time when the solid content concentration of the liquid in the tank reaches 99.5% of the theoretical solid content concentration of the measured pure water and the added PVA is taken as the completion of dissolution. The time was evaluated. The results are shown in Table 1.

<Bubbled state>
The height from the upper end of the tank inner wall to the liquid surface at the time of completion of dissolution was measured, and foaming was evaluated based on the degree of foam mixing in the liquid. In addition, it evaluated on the following references | standards on the basis of the height to the liquid surface by the dissolution method of PVA of the comparative example 1 which is a general dissolution method.
○: Suppression of foaming was observed (the height of the liquid surface decreased)
Δ: Same as standard (the height of the liquid surface is the same)
×: Bubble generation increased (the height of the liquid surface increased)

<Undissolved>
After dissolution was completed, the liquid was discharged, and undissolved PVA remaining in the tank was visually observed.

  As is apparent from the above results, the dissolution method of the present invention is less foamed, no undissolved material remains, and shortens the time required for dissolution, as compared with Comparative Example 1 which is a conventional general dissolution method. . On the other hand, in Comparative Example 2, a large amount of undissolved material remained, and dissolution was not completed. Comparative Examples 3 and 4 in which the discharge direction of the liquid circulated from the pulverizer was changed were inferior in solubility, dissolution time, and foaming suppression. In Comparative Example 5, bubbles were often generated when the liquid was discharged into the tank, and the experiment was stopped due to overflow of bubbles from the tank.

  The method for dissolving a granular material of the present invention can be suitably used in the field of ink jet recording paper and the like produced by applying a solution containing a water-soluble polymer on a support.

It is a schematic diagram of the dissolving device of the present invention. It is a top view of a tank. It is a principle diagram of a high-pressure emulsifier. It is a principle diagram of a spiral pin mixer. It is a principle diagram of a vibro reactor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tank 2 Liquid supply pipe | tube 4 Crushing device 7 Discharge port 9 in a liquid supply pipe into a tank 9 Stirring blade 10 Heating mechanism 21 Direction of liquid swirl flow by a stirring blade 22 Direction of liquid discharge into a tank

Claims (2)

  A method in which a liquid in which a powder and a solvent are mixed is circulated between a tank equipped with a stirring device and a pulverizer to dissolve the powder, and the circulated liquid is transferred from the pulverizer to the tank. The discharge port of the liquid feed pipe for returning to the tank is immersed in the liquid in the tank, and the discharge direction of the liquid discharged from the discharge port is substantially the same direction as the swirl flow direction of the liquid in the tank by the stirring device A method for dissolving a granular material, characterized by comprising:   The method for dissolving a granular material according to claim 1, wherein the granular material is polyvinyl alcohol having an average degree of polymerization of 2000 to 5000, and the solvent is water.

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