JPH11290611A - Ultrasonic defoamation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic defoaming method in which, in a system for coating a substrate with a liquid by a coating device, bubbles contained in the coating liquid are removed efficiently and in a short time even if the coating liquid is highly viscous and contains many bubbles to be removed in unit time. SOLUTION: An ultrasonic defoaming method in which a bubble-containing liquid is irradiated with ultrasonic waves to remove the bubbles comprises the steps of continuously modulating an ultrasonic oscillation frequency radiated from an ultrasonic vibrator 2 to provided predetermined frequency band widths centered at a reference frequency, and periodically continuously changing the sound pressure distribution of ultrasonic waves with which a liquid to be defoamed is irradiated. This change in the sound pressure distribution period mitigates or eliminates the standing waves in the liquid to be defoamed and slightly vibrates the bubbles in the liquid to be defoamed, thereby efficiently expediting the defoaming operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defoaming method for removing bubbles in a coating solution, and more particularly to an ultrasonic defoaming method for a coating solution for a photographic light-sensitive material.

[0002]

2. Description of the Related Art Generally, a coating liquid used for coating various liquids on a support is apt to generate bubbles by operations such as stirring, dispersion, and liquid sending performed before the coating step, and the coating liquid contains bubbles. When a coating solution is supplied to a coating apparatus, applied to a support, and dried, a foam failure such as a bubble streak or a pinhole occurs in the coating film, and a uniform and good coating film cannot be formed. Therefore, it is necessary to perform a sufficient defoaming treatment before the coating step. As a defoaming method used for such a purpose, for example, an ultrasonic wave described in JP-B-42-11875 is used. Known defoaming methods are known.

[0003] Ultrasonic defoaming means that when a liquid contained in a defoaming container or the like is irradiated with ultrasonic waves, a local sound pressure fluctuation field is generated in the liquid to be defoamed, and minute bubbles are instantaneously generated. So-called ultrasonic cavitation, which repeatedly occurs and disappears, is used to remove bubbles by using this effect. Many methods and apparatuses for removing bubbles have been proposed.

[0004] For example, as described in JP-B-57-6365, JP-A-59-92003, and JP-B-4-31722, a defoaming container having a fixed volume is removed. A foam liquid is introduced, and bubbles contained in the liquid to be defoamed and micro bubbles generated by ultrasonic irradiation are grown, crowded, and floated and separated, and usually subjected to defoaming treatment under atmospheric pressure or reduced pressure. You.

Also, Japanese Patent Publication No. Sho 51-5295, Japanese Patent Publication No. Sho 55-6405, Japanese Patent Application Laid-Open No. Sho 63-178807, Japanese Patent Application Laid-Open No. 5-92103, Japanese Patent Application Laid-Open No. Hei 6-110
No. 151 discloses that a liquid to be defoamed is continuously fed into a defoaming container having a fixed volume, and usually fine bubbles are removed under a pressure of 0.3 kg / cm ² or more. A method and an apparatus for dissolving and dissolving in it have been proposed.

Further, the method of floating and separating the bubbles and the method of dissolving and eliminating the bubbles in the liquid to be defoamed are simultaneously treated in separate defoaming containers, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 6-130.
A method and an apparatus described in Japanese Patent Application Laid-Open No. 547, Japanese Patent Application Laid-Open No. 8-318102 and the like are known.

[0007]

However, a coating solution containing various additives, such as a photographic light-sensitive material coating solution, has a property that the liquid itself easily foams and easily contains bubbles. In recent years, with the improvement of the coating method and the improvement of productivity, the viscosity of the coating liquid has been increased, and the amount of defoaming treatment per unit time tends to increase. Despite the proposed method,
The defoaming ability of the conventional method is still insufficient, so that a reliable and efficient ultrasonic defoaming treatment is required, and this is also an important technical problem.

[0008] In the conventional method, the reason why the defoaming ability is still insufficient is that when a liquid contained in a defoaming container is irradiated with ultrasonic waves at a constant ultrasonic frequency, a constant compressional wave is formed by ultrasonic vibration. As a result, a standing wave may be generated. This standing wave traps air bubbles in the liquid to be defoamed at a specific location, hinders the air bubbles from floating, and lowers the ability to dissolve and eliminate micro air bubbles. There was a problem that could not be removed.

In order to solve the above problem, a method is provided in which a plurality of ultrasonic vibrators are provided opposite to each other on the bottom and side surfaces of the defoaming container, and ultrasonic irradiation waves emitted from the individual ultrasonic vibrators are mutually complemented. An apparatus has been proposed in, for example, JP-A-59-92003 and JP-A-5-92103.
However, these methods can improve the defoaming efficiency by increasing the ultrasonic irradiation amount per unit volume of the defoaming container, but cannot eliminate the standing wave itself. Even with the use of the apparatus, it has been difficult to efficiently and completely remove bubbles from the liquid to be defoamed.

Accordingly, an object of the present invention is to prevent a bubble failure caused by bubbles contained in a coating solution in a step of applying a liquid such as a coating solution of a photographic light-sensitive material to a support by a coating apparatus, and to provide a uniform liquid. It is an object of the present invention to provide a method for defoaming a coating solution in order to form a good coating film. Particularly, when the viscosity of the coating solution is high and the defoaming amount per unit time is large, It is an object of the present invention to provide an ultrasonic defoaming method for efficiently defoaming and removing air bubbles in a short time.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultrasonic defoaming method for irradiating a liquid containing air bubbles with ultrasonic waves to remove air bubbles from the liquid. This was basically achieved by an ultrasonic defoaming method characterized by continuously modulating the oscillation frequency of a sound wave to a predetermined frequency bandwidth around a reference frequency.

[0012] The solution generated in the liquid in the defoaming container by the solution means for continuously modulating the oscillation frequency of the ultrasonic wave emitted from the ultrasonic transducer to a predetermined frequency bandwidth around the reference frequency. To reduce and eliminate the standing ultrasonic waves
Bubbles in the liquid can be efficiently defoamed and removed in a short time.

[0013]

FIG. 5 is a model diagram showing an ultrasonic sound pressure distribution in a liquid to be defoamed and a defoaming action by a conventional general ultrasonic irradiation method. An ultrasonic wave 53 is transmitted from the ultrasonic vibrator 52 attached to the bottom of the defoaming container 51 to the liquid to be defoamed 54. An ultrasonic oscillator 5 for vibrating the oscillator at a constant frequency is connected to the ultrasonic oscillator 52. In the liquid to be defoamed 54, compression waves of ultrasonic irradiation are continuously formed, and a unique sound pressure distribution is generated. Point a
Indicates a maximum sound pressure band in which the sound pressure is positive, and point b indicates a minimum sound pressure band in which the sound pressure is negative. Generally, in the liquid to be defoamed 54 irradiated with ultrasonic waves, minute bubbles 56 are instantaneously generated in the minimum sound pressure band, and the process of repeating dissolution and extinction proceeds simultaneously. At this time, whether the generated air bubble moves to the process of growing or dissolving and disappearing is usually determined by the size of the air bubble, the pressure applied to the liquid to be defoamed 54, and the like. If the size of the bubbles is relatively small and the pressure applied to the liquid to be defoamed is high, the bubbles dissolve and disappear, and if the pressure is low, the bubbles grow. Therefore, when it is desired to dissolve and eliminate bubbles contained in the liquid to be defoamed, pressure may be applied to the liquid to be defoamed while irradiating ultrasonic waves. When it is desired to remove bubbles by floating while growing and crowding, the pressure may be reduced. Also,
If necessary, the liquid to be defoamed may be placed under reduced pressure to promote the generation of bubbles.

However, in the general ultrasonic irradiation method shown in FIG. 5, since the frequency oscillated from the ultrasonic transducer is a single frequency, the maximum sound pressure band and the minimum sound The sound pressure distribution formed by repetition of the pressure band is constant, and this causes a standing wave. When a standing wave is generated, the grown and crowded bubbles are trapped at a specific location in the liquid to be defoamed without floating or remain in the liquid to be defoamed without dissolving and disappearing. ,
Eventually, it is discharged out of the defoaming container 51 along with the liquid flow, and is sent to a coating device (not shown).

Next, the ultrasonic defoaming method according to the present invention will be specifically described. The feature of the present invention is that the oscillation frequency of the ultrasonic wave is continuously modulated in a predetermined frequency bandwidth around the reference frequency, so that the period of the sound pressure distribution of the ultrasonic wave applied to the defoaming liquid is changed. The purpose of the present invention is to provide a continuous change to relax or extinguish an ultrasonic standing wave. The period of the sound pressure distribution of ultrasonic irradiation is the continuation of the so-called ultrasonic vibration, where the vibration wave of the ultrasonic vibrator is transmitted through the liquid to be defoamed and periodically repeats the maximum sound pressure band and the minimum sound pressure band. This means that the standing wave generated by ultrasonic irradiation is reduced or eliminated by continuously changing the period of the sound pressure distribution in the liquid to be defoamed. FIG. 1 is a model diagram showing a sound pressure distribution and a defoaming action in a liquid to be defoamed according to the present invention, in which a transmission frequency is continuously modulated to a predetermined frequency bandwidth around a reference frequency. . An ultrasonic wave 3 is transmitted from the ultrasonic vibrator 2 attached to the bottom of the defoaming container 1 to the liquid 4 to be defoamed. The ultrasonic oscillator 2 is connected to an ultrasonic transmitter 5 capable of continuously modulating the oscillator to a predetermined frequency bandwidth around a reference frequency. In the liquid to be defoamed 4, compression waves of ultrasonic irradiation are continuously formed, and a predetermined sound pressure distribution is generated. However, with time, the maximum sound pressure band point c and the minimum sound pressure band point d This sound pressure distribution moves in the liquid to be defoamed little by little. By the action of the sound pressure distribution that moves with the passage of time, bubbles are quickly degassed without remaining in the liquid to be defoamed.

The defoaming action of the present invention will be described in more detail. In the method in which bubbles are grown and crowded by lowering the pressure applied to the liquid to be defoamed and floated and separated, the period of the sound pressure distribution of the irradiated ultrasonic waves changes continuously, and the sound pressure distribution is defoamed. Moves little by little in the liquid. At this time, the bubbles move in small increments in accordance with the fluctuation of the sound pressure distribution, and the bubbles frequently crowd and fuse with each other. While crowding, and sometimes clustering in the form of a bunch of grapes, it floats quickly against the liquid flow in the defoaming container and completes separation. Also, in the method of dissolving and eliminating bubbles by increasing the pressure applied to the liquid to be defoamed, small bubbles generated by ultrasonic irradiation quickly move in the liquid to be defoamed in small increments and are efficiently and uniformly covered. Dissolves and disappears in the defoaming solution.

The reference frequency according to the present invention is a frequency that is the center of a transmission frequency for irradiating ultrasonic waves while continuously modulating the ultrasonic wave from the ultrasonic oscillator 2 into the liquid 4 to be defoamed to a predetermined frequency bandwidth. Usually, a frequency of 10 KHz or more and 500 KHz or less can be used. Further, as the ultrasonic vibrator in the present invention, for example, a piezoelectric vibrator made of a component such as lead zirconate titanate, barium titanate or the like, which has been subjected to waterproof treatment, can be suitably used.

According to the present invention, continuously modulating a predetermined frequency bandwidth means that the frequency of ultrasonic oscillation is continuously and alternately modulated on a low frequency side and a high frequency side around a reference frequency. This means that the modulation period is represented by the number of times of modulation per unit time. As an example, when a frequency modulation bandwidth of 5% is set with respect to a reference frequency of 40 KHz, the low frequency side of 39 KHz and
The high-frequency side of KHz is continuously and alternately modulated, and continuously modulated at a predetermined modulation period, for example, 100 times per second, so that the sound pressure distribution in the liquid to be defoamed is continuously moved in small increments. Foam efficiency can be increased. In the present invention,
The bandwidth of the frequency to be modulated is set to 0.
It is preferable to use a range of 1% to 100%, and particularly preferable to use a range of 1% to 50% with respect to the reference frequency value. Further, it is preferable to use the modulation cycle of the ultrasonic irradiation in the range of once to 2,000 times per second. These frequency bandwidths and modulation periods are appropriately determined according to the shape and size of the defoaming container, the liquid properties such as the viscosity and composition of the liquid to be defoamed, and the amount of bubbles and dissolved air contained in the liquid to be defoamed. Can be determined.

According to the present invention, the ultrasonic energy applied to the liquid to be defoamed may be in the range of 0.05 to 100 W / cm ² , preferably 0.1 to 10 W / cm ² , but at a single frequency. As compared with the conventional method of defoaming, a good defoaming effect can be obtained with relatively low ultrasonic energy.

The ultrasonic defoaming method according to the present invention can be suitably used for defoaming a coating solution such as a photographic light-sensitive material coating solution. It may be used in any process of application. Further, the defoaming method according to the present invention may be a mode in which the coating liquid is continuously supplied to the ultrasonic defoaming device to perform defoaming treatment, and then continuously supplied to the coating device, or may be relatively large. A system in which batch processing is performed at a time in a defoaming tank or the like may be employed. Further, the shape and size of the defoaming container used in the present invention are not particularly limited in obtaining the effects of the present invention, for example, as proposed in Japanese Patent Publication No. 57-6365 and the like. A cylindrical defoaming tank having an opening at the upper end of a container for storing a coating liquid, or a defoaming container comprising a tube as proposed in Japanese Patent Application Laid-Open No. 59-92003. In addition, Tokubo Sho 5
As described in JP-A-5-6405, JP-A-61-50608, etc., a pipe is arranged and housed in a spiral or loop shape in an ultrasonic wave propagating liquid tank, and the coating liquid is sent to the pipe. A defoaming device or the like for performing a defoaming treatment by liquid can be used. Further, a general circular or square tank or a defoaming tank having an ultrasonic vibrator mounted on a tank may be used.

FIG. 2 shows a flow of an experimental apparatus for confirming the defoaming effect according to the present invention. In the figure, 21 is a coating liquid preparation tank, 22 is a liquid feed pump, and 23 is an ultrasonic defoamer. Device. The coating liquid (liquid to be defoamed) 24 stored in the preparation tank 21 is subjected to an ultrasonic defoaming device 23 by a pump 22.
Supplied to The gas-liquid mixing device 2 is provided on the primary side of the pump 22.
6 is attached, and bubbles of an arbitrary amount and size can be mixed into the coating liquid. Bubbles detectors 27 and 28 are attached to the primary side and the secondary side of the ultrasonic defoaming device 23 to detect bubbles mixed in the gas-liquid mixing device 26 and bubbles after the ultrasonic defoaming process. Can be. A pressure indicator 2 is provided between the ultrasonic defoaming device 23 and the bubble detector 28.
5 and a control valve 29 are attached, and the internal pressure of the ultrasonic defoaming device 23 can be adjusted. The purpose of this experiment is to evaluate the defoaming ability.

[0022]

EXAMPLES Next, the ultrasonic defoaming method of the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

Example 1 The above-described experimental apparatus shown in FIG. 2 was used to compare the defoaming effect between the case where the ultrasonic defoaming method according to the present invention was applied and the case where the conventional ultrasonic defoaming method was applied. did.

The ultrasonic defoaming apparatus in this embodiment is shown in FIG.
An ultrasonic defoaming device 30 was used in which an ultrasonic vibrator 32 was arranged in the circumferential direction toward the center of the tube on the outer surface of a circular tube 31 holding the tube axis shown in the vertical direction. The coating solution sent by the pump is supplied to a defoaming tube 33 mounted inside the tube 31.
Is supplied to the supply port 34 and defoamed in the defoaming pipe 33. A discharge port 35 is provided at a lower portion of the defoaming tube 33, and the defoaming-treated coating solution can be continuously discharged. Between the pipe body 31 and the defoaming pipe 33, the temperature-regulated water is supplied to the inlet 3
The temperature of the coating solution in the defoaming tube 33 is controlled by circulating from the position 6. Ultrasonic waves emitted from the ultrasonic oscillator 32 propagate through the temperature-regulated water and are irradiated into the defoaming tube 33. Note that a conical tube 37 made of a transparent material is attached to the upper part of the defoaming tube 33 so that the defoaming behavior can be easily observed.

The specifications and operating conditions of the ultrasonic defoaming apparatus common to the examples according to the present invention and the comparative examples are as follows. 1. 1. Ultrasonic oscillator Transmission frequency: 40 KHz Output: 300 W, 500 W, 800 W, 1200 W 2. Defoaming tube Inner diameter: 115 mmΦ Length: 1000 mm Internal pressure: 0.2 kg / cm ² Defoaming liquid 8% gelatin solution Surfactant: 5% sodium di-2-ethylhexylsulfosuccinate solution was added at 1% to the total amount of gelatin solution. Thickener: Na polystyrene sulfonate was added, and the gelatin solution was adjusted to 20 C.P. and 60 C.P. 4. Blended bubbles Size: 30 to 500 µm Blended amount: 3 to 30 ml / min

Table 1 shows an embodiment of the ultrasonic defoaming method according to the present invention. The defoaming process is performed by continuously modulating the ultrasonic oscillation to a bandwidth centered on a reference frequency of 40 KHz.
The viscosity of the gelatin solution, the amount of liquid to be introduced into the defoaming tube, and the oscillation output are changed, and the detection signal of the bubble detector provided on the primary and secondary sides of the defoaming tube is used to detect the oscillation per oscillation output of the ultrasonic oscillator. The foamable flow rate was evaluated. The defoamable flow rate refers to the amount of introduced liquid in which bubbles are not detected by the bubble detector 28 provided on the secondary side of the ultrasonic defoaming device 23. As a comparative example, a defoaming treatment was performed under the same conditions as in the example of the present invention except that ultrasonic oscillation was performed at a single frequency of 40 KHz. FIG. 4 shows the results.

[0027]

[Table 1]

As is clear from the comparison result of the defoamable flow rate shown in FIG. 4, the ultrasonic defoaming method according to the present invention has a higher defoaming ability than the conventional method, and particularly has a high viscosity of 60 C.P. It can be seen that the liquid also maintains an excellent defoaming effect. Further, when the defoaming behavior in the present example was observed with a transparent conical tube portion attached to the upper part of the defoaming tube, the ultrasonic defoaming method according to the present invention showed that fine bubbles were defoamed at the upper part of the defoaming tube. While it was confirmed that bubbles that grew large and crowded bubbles quickly rose together while vibrating little by little in the pipe, bubbles did not grow so large in the conventional defoaming method. Also less. It was also observed that the amount of air bubbles that floated was small and the speed was low, confirming that the defoamable flow rate of the present invention was high.

Next, the coating liquid of 60 C.P.
Table 2 shows the results of the defoaming treatment under the condition of 0 W while changing the frequency modulation bandwidth and the modulation period according to the present invention. It can be seen that under all conditions, the defoaming ability is higher than that of the conventional defoaming method.

[0030]

[Table 2]

Example 2 From the equipment specifications and operating conditions used in Example 1, the present invention was carried out under the same conditions as in Table 3 except that the internal pressure of the defoaming tube was changed to 0.7 kg / cm ^2. To confirm the defoaming effect. As is clear from the defoamable flow rate in Table 3, even under the condition where the defoaming tube is pressurized, the defoaming ability is higher than that of the conventional defoaming method.

[0032]

[Table 3]

[0033]

As described above, in the ultrasonic defoaming method according to the present invention, the oscillation frequency of the ultrasonic wave is modulated continuously in a predetermined frequency band around the reference frequency.
The bubbles in the liquid to be defoamed can be efficiently removed, and the defoaming ability can be greatly improved as compared with the conventional method of simply defoaming at a single frequency.

Therefore, in a coating liquid such as a photographic light-sensitive material coating liquid having a property of easily foaming and easily containing air bubbles, the viscosity of the coating liquid is increased, and the amount of defoaming treatment per unit time is increased. Also, after performing the defoaming treatment of the coating liquid using the ultrasonic defoaming method according to the present invention before the coating step, by supplying the coating liquid to the coating apparatus, the coating film is free from bubble defects such as bubble streaks and pinholes. A uniform and good coating film can be formed.

Further, as can be seen from the examples, the ultrasonic defoaming method according to the present invention can greatly reduce the output of the ultrasonic defoaming device in order to obtain the same defoaming effect as the conventional defoaming method. This has the advantage that it is possible to suppress erosion (erosion) on the surface of the defoaming container caused by strong ultrasonic irradiation. That is, the running cost required for operation and maintenance of the ultrasonic deaerator can be reduced.
Secondary effects can also be created.

[Brief description of the drawings]

FIG. 1 is a model diagram of an ultrasonic sound pressure distribution in a liquid to be defoamed and a defoaming action in an ultrasonic defoaming method using the present invention.

FIG. 2 is a schematic explanatory view of one embodiment of an experimental apparatus according to the present invention.

FIG. 3 is a schematic cross-sectional view of an example of an ultrasonic defoaming device used for defoaming treatment in the present invention.

FIG. 4 is a comparison diagram of the amount of defoamable liquid between an example of the ultrasonic defoaming method according to the present invention and a comparative example of the conventional ultrasonic defoaming method.

FIG. 5 is a model diagram of ultrasonic sound pressure distribution in a liquid to be defoamed and defoaming action by a conventional ultrasonic defoaming method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Model defoaming container 2 Ultrasonic transducer 3 Ultrasonic irradiation wave 5 Ultrasonic oscillator 21 Adjustment tank 22 Liquid feed pump 23 Ultrasonic defoaming device 33 Defoaming tube

Claims (2)

[Claims] 1. An ultrasonic defoaming method for irradiating a liquid containing air bubbles with ultrasonic waves to remove air bubbles from the liquid, wherein the oscillation frequency of the ultrasonic waves emitted from the ultrasonic vibrator is set to a reference frequency. An ultrasonic defoaming method characterized by continuously modulating a predetermined frequency bandwidth at the center. 2. The ultrasonic defoaming method according to claim 1, wherein the liquid is a coating solution for a silver halide photographic material.