JP2003181263A - Method of feeding liquid having thixotropy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To feed a liquid having thixotropy, particularly a liquid having high apparent viscosity. <P>SOLUTION: In the method of feeding the liquid having thixotropy, a magnetic coating material 10 of the liquid having thixotropy and stirred with a stirring impeller 12a rotating around a nearly vertical shaft in a tank 11 is discharged from a discharge port 11a located below the stirring impeller 12a and fed by a pump 15 arranged in the downstream side of the discharge port 11a. After the stirring impeller 12a is rotated at a prescribed number of rotation to lower the apparent viscosity of the magnetic coating material 10, the number of rotation is decreased or the rotation is stopped and when the magnetic coating material 10 starts to flow out from the discharge port 11a, the feeding is continued with the increase of the number of rotation of the stirring impeller 12a. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for feeding a liquid having thixotropy. 2. Description of the Related Art Generally, when liquid having thixotropy such as ink of a ballpoint pen or magnetic paint is fed, it is necessary to feed the liquid stored in the tank while stirring it with a stirring blade. There is. This is because the liquid having thixotropy increases in viscosity over time, and the liquid is allowed to be fed by lowering the apparent viscosity by stirring the liquid in the tank. [0003] The liquid stored in the tank is generally stirred by a stirring blade rotated about a substantially vertical axis, and discharged from a discharge port disposed below the stirring blade. A pump is installed downstream of the outlet,
Liquid feeding is continued by the driving force of the pump. Incidentally, the magnetic paint applied to the surface of a magnetic recording medium such as a magnetic tape or a magnetic disk has a composition in which a magnetic powder is mixed in a solvent. It is preferable for the performance of the magnetic recording medium to be coated. On the other hand, when the magnetic powder is made into fine particles, the magnetic paint tends to aggregate and the apparent viscosity increases. That is, in the case of a magnetic coating material in which magnetic powder is finely divided, it is necessary to increase the number of revolutions of the stirring blade and lower the apparent viscosity of the magnetic coating material in the tank to carry out liquid feeding. However, the liquid stirred by the stirring blade in the tank flows toward the inner wall of the tank by centrifugal force, and the liquid descending along the inner wall of the tank follows the center of the tank. Rise. For this reason, in the vicinity of the discharge port at the bottom of the tank, a pressure drop due to the upward flow of the liquid, that is, a suction negative pressure occurs. This negative pressure increases as the number of revolutions of the stirring blade increases, and in the case of a magnetic coating material in which the magnetic powder is finely divided as described above, it is difficult for the liquid to flow from the discharge port. In particular, when the liquid starts to flow from the discharge port of the tank, the solvent as priming water is previously placed downstream of the discharge port, and the liquid is stirred to some extent to reduce the apparent viscosity. However, in the case of a liquid whose apparent viscosity is higher than a certain level, a large negative pressure is generated at the bottom of the tank due to the high speed rotation of the stirring blade, so the liquid cannot be drawn out from the tank even by a solvent as priming water. The pump runs idle. When the pump idles, cavitation occurs in the solvent, and parts such as the rotor in the pump directly contact each other, causing deterioration and failure of the pump. In view of these problems, the present invention has been made. The present invention relates to a liquid having a thixotropic property that can easily start feeding even a liquid having a high apparent viscosity and a thixotropic property. An object is to provide a liquid feeding method. In order to solve the above-described problems, in the method for feeding a liquid having thixotropy according to the present invention, the liquid is stirred by a stirring blade rotating about a substantially vertical axis in a tank. A liquid having a thixotropic property, wherein the liquid having a thixotropic property is discharged from a discharge port located below the stirring blade and is fed by a pump disposed downstream of the discharge port, wherein the stirring is performed. After reducing the apparent viscosity of the liquid by rotating the blade at a predetermined number of rotations, the rotation number of the stirring blade is decreased or stopped, and when the liquid begins to flow out from the discharge port, the stirring blade The number of rotations is increased and the liquid feeding is continued. According to such a liquid feeding method, after the stirring blade is rotated at a predetermined rotational speed to lower the apparent viscosity of the liquid,
By reducing the rotation speed of the stirring blade or stopping the rotation, the negative pressure near the discharge port at the bottom of the tank is eliminated, and the pressure due to the weight of the liquid is directly applied to the discharge port. Therefore, the liquid starts to flow out from the discharge port, and thereafter, the number of rotations of the stirring blade is returned to the original and the liquid feeding is continued. As described above, in the present invention, the liquid discharge failure due to the negative pressure at the bottom of the tank can be prevented, so that deterioration due to idling of the pump can also be prevented. It should be noted that the timing of increasing the rotational speed again after decreasing or stopping the rotational speed of the stirring blade is preferably after the liquid feeding has stabilized, for example, when the liquid having a high apparent viscosity reaches the pump. If you increase the rotation speed of the agitating blade after it arrives, the driving force by the pump will be sufficiently high,
Stable liquid feeding becomes possible. Further, the rotational speed when the rotational speed of the stirring blade is increased again is not particularly limited, and may be set so as to satisfy the necessary characteristics as a liquid. DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic diagram of a liquid feeding device used in a liquid feeding method according to an embodiment of the present invention. The liquid feeding device 1 is a device that feeds the magnetic paint 10, which is a liquid having thixotropy stored in the tank 11, to the next process, for example, the application process of the magnetic paint 10 by the power of the pump 15. . The tank 11 is a substantially cylindrical container, and the lower part is thin in a cone shape.
A zero discharge port 11a is provided. The shape of the tank 11 is not particularly limited, and may be a box shape, for example. Inside the tank 11, a stirrer 12 is installed from above along the axis of the tank 11, that is, the vertical axis.
The stirrer 12 has a rotating shaft disposed at the axis of the tank 11, and a stirring blade 12 a is fixed to the lower end of the rotating shaft. And the stirring blade 12a is arrange | positioned so that it may rotate in the bottom vicinity of the tank 11 so that stirring of the magnetic coating material 10 can be performed even if the magnetic coating material 10 in the tank 11 decreases. The stirring blade 12a may be a general disper type or dissolver type stirring blade, but is not limited thereto. The number and position of the stirring blades 12a are not limited, and a plurality of stirring blades may be provided on the same axis, or a plurality of stirring blades may be rotated about a plurality of axes. The discharge port 11a of the tank 11 is connected to a discharge pipe 13
It is communicated to. The discharge pipe 13 is connected to a liquid pump 15 such as a trochoid pump, and the outlet of the pump 15 is connected to a delivery pipe 14 that feeds the magnetic paint 10 to the next step. A valve 16 is provided in the middle of the discharge pipe 13 so that the speed of liquid feeding can be adjusted and the liquid feeding can be started and stopped. By using the liquid delivery apparatus 1 having the above-described configuration, the liquid delivery method having thixotropy according to the present invention is carried out as follows. Note that FIG.
These are the graphs which showed the time change of the rotation speed of the said stirring blade 12a, and the outflow speed of a magnetic coating material. First, after cleaning the tank 11, the discharge pipe 13 and the delivery pipe 14, the valve 16 is opened and a solvent (not shown) as priming water is put into the tank 11. Then, the solvent passes through the discharge pipe 13 by its own weight and is supplied until it enters the pump 15. As the solvent used at this time, it is desirable to use a solvent having a viscosity as high as possible with its own weight and a viscosity that flows quickly. However, since this solvent is mixed in the magnetic paint 10 in a small amount, it is better to use the same material as the solvent of the magnetic paint 10. When the solvent enters the pump 15, the valve 16 is closed and the supply of the solvent is stopped. Next, as much magnetic paint 10 as is used is supplied into the tank 11 and stored. The magnetic coating material 10 is, for example, a material in which ferromagnetic powder is dispersed in a binder solution of an organic solvent, and has thixotropic properties. That is, when this magnetic paint 10 is left standing, the apparent viscosity becomes high and does not flow, but when sheared by stirring or the like,
It has the property that the apparent viscosity is lowered and becomes fluid. Next, in order to reduce the viscosity of the magnetic coating material 10 so that the liquid can be fed, the stirring blade 12a is rotated at a predetermined rotational speed (time t1). This rotational speed is appropriately set according to the characteristics of the magnetic paint 10. Generally, the finer the magnetic powder in the magnetic coating material 10, the higher the apparent viscosity and the higher the speed at which the apparent viscosity increases. Therefore, it is necessary to rotate the stirring blade 12a at a high rotational speed. When the stirring blade 12a is rotated, the magnetic paint 1
0 flows like the arrow shown in FIG. That is, with the rotation of the stirring blade 12a, the magnetic paint 10 is mixed with the stirring blade 12a.
It flows outward in the radial direction of a. On the upper side of the stirring blade 12 a, the magnetic paint 10 that has flowed in the radial direction collides with the inner peripheral wall of the tank 11, then rises along the inner peripheral wall of the tank 11, and along the liquid surface near the liquid surface of the magnetic paint 10. It gathers in the center, further descends along the axis of the tank 11, and returns to the vicinity of the center of the stirring blade 12a. On the other hand, under the stirring blade 12a, the magnetic coating material 10 that has flowed in the radial direction collides with the inner peripheral wall of the tank 11, and then gathers in the vicinity of the discharge port 11a along the inner peripheral wall and the bottom wall of the tank 11 and discharges at the lower end. Exit 11a
When it gathers, it rises rapidly and returns to the lower surface of the stirring blade 12a. When the magnetic coating material 10 is stirred in the tank 11 by the stirring blade 12a, the magnetic coating material 10 circulates in this way. Therefore, a suction negative pressure is generated by a strong upward flow in the vicinity of the discharge port 11a. In this case, when the magnetic powder is fine particles, the number of revolutions of the stirring blade 12a must be increased, which causes the magnetic coating material 10 to be prevented from flowing out from the discharge port 11a. Next, in the liquid feeding method having thixotropy according to this embodiment, the magnetic paint 10 in the tank 11 is used.
When the apparent viscosity of the valve 16 reaches a predetermined value, the valve 16
Open. This predetermined apparent viscosity varies depending on the purpose of use of the magnetic coating material 10 and may be determined by the apparent viscosity required in the subsequent coating application step. If the rotation of the stirring blade 12a is maintained after the valve 16 is opened, the magnetic paint 10 does not flow out due to the pressure drop in the vicinity of the discharge port 11a.
The rotational speed of 2a is gradually decreased (time t2). Here, the rotation speed of the stirring blade 12a may be set to 0 (see the broken line in FIG. 2). When the rotational speed of the stirring blade 12a is lowered to some extent, if the magnetic coating material 10 flows out from the discharge port 11a, the rotational speed of the stirring blade 12a is maintained (time t3). The rotational speed at which the magnetic paint 10 flows out can be known in advance if the conditions such as the magnetic paint and the stirring blade are determined and tested before making the product. I do not care. Next, when the magnetic coating material 10 has flowed to the pump 15, the power of the pump 15 becomes sufficiently large thereafter, so that the rotational speed of the stirring blade 12a is increased (time t4). Thereafter, the liquid feeding is continued while maintaining the desired rotation speed according to the required characteristics of the magnetic coating material 10 (time t5). Here, even if the magnetic paint 10 does not wait until the pump 15 reaches the pump 15, depending on the viscosity of the solvent previously put in the pump 15, the magnetic paint 10 is applied by utilizing the inertia of the magnetic paint 10 flowing out. Since it can be withdrawn from the tank 11, the rotational speed of the stirring blade 12a may be increased immediately after the time t3, that is, immediately after the magnetic coating material 10 flows out. As described above, in the liquid feeding method having thixotropy according to the present embodiment, it is possible to feed even a liquid having a high apparent viscosity. In addition, since the liquid can be fed only by controlling the rotation speed of the stirring blade 12a using the conventional liquid feeding device, there is almost no equipment investment, and the magnetic paint containing the magnetic powder of fine particles can be used. Liquid feeding becomes possible. Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment. For example, in the above-described embodiment, the magnetic paint is taken as an example, but not limited to the magnetic paint, any liquid having thixotropy can be applied to any liquid feeding,
In particular, it can be suitably used when applied to a liquid having a high apparent viscosity. Moreover, the liquid feeding apparatus to which the present invention is applied is not limited to the liquid feeding apparatus 1 described above, and other elements may be appropriately added. Even in the case where there are a plurality of stirring blades, the present invention can be suitably applied if there is an outlet at the bottom of the tank where the negative pressure below it is generated. As described above in detail, according to the present invention,
It is possible to easily feed a liquid having thixotropic properties, particularly a liquid having a high apparent viscosity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a liquid feeding device used in a liquid feeding method according to an embodiment of the present invention. 2 is a graph showing temporal changes in the number of revolutions of the stirring blade and the outflow speed of the magnetic coating material from the discharge port of the liquid delivery device shown in FIG. 1; [Explanation of symbols] 10 Magnetic paint 11 Tank 11a Discharge port 12a Stirring blade 15 Pump

Continued front page    F-term (reference) 4D075 AC84 AC94 BB16X CA24                       DA04 DA08 DC28 EA31                 4F042 AA08 AA22 BA05 BA12 CA05                       CA06 CB02 CB11                 4G078 AA26 AB05 BA05 CA01 CA20                       DA00                 5D112 AA05 BB18

Claims (1)

What is claimed is: 1. A thixotropic liquid stirred by a stirring blade rotating about a substantially vertical axis in a tank is discharged from a discharge port located below the stirring blade. A method for feeding a liquid having thixotropy that is fed by a pump arranged downstream of an outlet, wherein the stirring viscosity is lowered after the apparent viscosity of the liquid is lowered by rotating the stirring blade at a predetermined rotational speed. Reduce the rotation speed of the blade or stop the rotation, and when the liquid begins to flow out from the discharge port, the liquid supply with thixotropic property is characterized by continuing the liquid supply by increasing the rotation speed of the stirring blade Method.