JPH1147508A - Defoaming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and completely remove even fine foams within a short time independently of the viscosity of a foam-containing liquid body by degassing the foam-containing liquid and then capturing the foams. SOLUTION: A liquid 3 to be adjusted by being stirred and mixed by a mixing apparatus 2 in a liquid adjustment tank 1 contains large and small foams 4. The foam-containing liquid body 3 is sent to a defoaming apparatus 5 through a liquid sending pipe 10 by a liquid sending pump 11. The defoaming apparatus 5 is constituted of a degassing apparatus 6 and a filtering apparatus 7 and the foam-containing liquid body 3 is at first sent to the degassing apparatus 6. The degassing apparatus 6 is for decreasing the dissolved air amount in the foam-containing coating liquid 3 and mainly removes large foams in the liquid and carries out treatment to provide tolerance of air dissolving performance of the liquid. The foam-containing liquid 3 is then sent to the filtering apparatus 7. The filtering apparatus 7 captures fine foams in the foam- containing liquid body 3 which are not removed by the degassing treatment by the degassing apparatus 6 on the surface of a filter medium and removes the foams by dissolving them in the liquid.

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 liquid from a bubble-containing liquid containing bubbles.

[0002]

2. Description of the Related Art For example, coating liquids for various recording materials such as photographic light-sensitive materials, photosensitive printing plate materials, and magnetic materials are stirred and mixed at the time of preparation, and therefore contain a large amount of bubbles in the liquid. If it is used, pinholes or streak-like unevenness are formed on the coating film. Therefore, the coating liquid is used after removing bubbles in the liquid.

[0003] In order to remove such bubbles in the foam-containing liquid, a conventional method has been employed in which a difference in mass between the bubbles and the liquid is used to allow the bubble to remain in a defoaming tank for a predetermined time or a special flow path is formed. A bubble is floated on the liquid surface by passing through the inside of a defoaming tank, and defoaming after the floated bubble is naturally broken (for example, JP-A-56-97508). In addition to the method, a method for improving the defoaming efficiency by evacuating the inside of the defoaming tank (for example, JP-A-56-100610), and a method for breaking bubbles by applying ultrasonic vibration to the defoaming tank (For example, Japanese Patent Publication No. 47-6835) and the like.

[0004]

However, in the conventional defoaming method, in the defoaming method based on the difference in mass, when the viscosity of the contained liquid becomes high, it takes a long time for air bubbles to float. It becomes difficult. In this regard, although the degree of improvement can be improved to some extent by adding vacuum evacuation, it is necessary to considerably increase the degree of vacuum in the tank in order to completely remove even minute bubbles in the liquid. In addition, the size of the defoaming tank must be increased in accordance with the processing amount of the foam-containing liquid, and there is a disadvantage that the apparatus becomes large.

[0005] In the method using ultrasonic waves, high-output electrical equipment for driving ultrasonic generating means (ultrasonic vibrator or the like) is required, so that it cannot be applied to an explosive gas atmosphere, that is, an explosion-proof place. The device itself may be degraded or damaged in some cases by the vibration of the sound waves. Further, there is a disadvantage that the apparatus is more expensive than other methods because of the need for the ultrasonic wave generating means.

The present invention solves the above-mentioned drawbacks of the prior art. Even when the viscosity of the bubble-containing liquid is as low as several cp or as high as several hundred cp, it is possible to completely remove small bubbles in a short time. It is an object of the present invention to provide a defoaming method which can be defoamed, is inexpensive, and has no restriction on an application place.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, by filtering a coating solution after deaeration, the coating solution having a high viscosity has been obtained. However, they have found that even minute bubbles can be completely removed in a short time, and have completed the present invention. That is, the above object is achieved by a defoaming method of the present invention for removing bubbles in a foam-containing liquid, which comprises degassing the foam-containing liquid and then capturing the bubbles. You.
According to the above defoaming method, a sufficient margin is given to the air dissolving ability of the liquid by the deaeration treatment, and thereafter, by filtering, the bubbles having a diameter larger than the aperture of the filter medium to be used are completely removed. Therefore, by setting the degree of deaeration and the aperture of the filter medium, small bubbles can be completely and efficiently removed in a short time regardless of the viscosity of the bubble-containing liquid. Moreover, since expensive and high-powered devices such as an ultrasonic generator are not required for the treatment, the defoaming of the foam-containing liquid can be performed at low cost and without restriction on the installation location. .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The defoaming method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing an apparatus configuration for performing the defoaming method of the present invention. As shown in the drawing, in a liquid preparation tank 1, a liquid 3 prepared by stirring and mixing various additives as a raw material and a solvent with a stirrer 2 is used.
Contains a large amount of large and small bubbles 4 composed of air entrained by stirring and mixing. Hereinafter, this liquid is referred to as a bubble-containing liquid.

The bubble-containing liquid 3 is sent to a defoaming device 5 by a liquid sending pump 11 through a liquid sending pipe 10. Defoaming device 5
Is composed of a deaerator 6 and a filter 7, and the bubble-containing liquid 3 is first sent to the deaerator 6. The deaerator 6 is a device for reducing the amount of dissolved air in the foamed coating liquid 3,
A process is mainly performed to remove relatively large bubbles in the liquid and to allow the liquid to dissolve in air. As a method of this deaeration, for example, there is a method of connecting a vacuum device to reduce the pressure in the tank. Dissolved air is precipitated by depressurization, the floating of bubbles in the liquid is promoted, and the bubbles reaching the liquid level are forcibly broken to reduce the dissolved air amount of the bubble-containing liquid 3 in a short time. It can be done. The degree of pressure reduction at this time does not need to be particularly high, since it is not the purpose of completely removing air bubbles unlike the conventional method using vacuum evacuation, and the degree of pressure reduction is not necessary. Although it depends on the degree of mind, a degree of vacuum of about several tens torr is sufficient. Further, it is also possible to use a gas-liquid separation membrane as the degassing means. In addition, any method can be used without particular limitation as long as it can reduce the amount of dissolved air in the liquid. The deaeration treatment by the deaerator 6 is desirably performed until the deaeration of the bubble-containing coating liquid 3 becomes 90% or less, preferably 80% or less of the saturated dissolved air amount. Thereby, the processing by the filtration device 7 at the next stage can be efficiently performed.

[0010] The bubble-containing liquid 3 is then sent to a filtration device 7. The filtering device 7 is a device for capturing fine bubbles in the bubble-containing liquid 3 that have not been removed by the degassing process in the degassing device 6 on the surface of the filter medium and dissolving them in the liquid to remove them. For example, a filter medium made of a synthetic resin nonwoven fabric, a wire mesh, a metal sintered body, a ceramic porous body, or the like is provided.
When passing through the filter medium, the bubbles in the bubble-containing liquid 3 come into contact with the openings of the filter medium and break or break up into smaller bubbles. Therefore, the openings of the filter medium must be smaller than the diameter of the bubble to be defoamed. The aperture of the filter medium to be used is appropriately selected depending on the type and application of the coating liquid. For example, when a thin film of submicron order is applied such as a photographic light-sensitive material or a magnetic paint for a magnetic recording medium and a uniform coating is required, extremely fine pinholes and unevenness are required in the coating. Even if 著 し く occurs, the product value is significantly reduced. Therefore, air bubbles having a diameter of 3 µm or less are completely removed by using a fine filter medium having a mesh of 3 µm or less as openings.
In the case of printing ink or the like that forms type, complete defoaming is not required as in the case of photographic photosensitive materials or magnetic paints for magnetic recording media, and it is also possible to use a filter medium having a coarse opening of about 30 μm mesh. it can. Thus, the filtering device 7
In the above, it is important to use a filter medium having an opening smaller than the diameter of the bubble to be defoamed.

The processing speed of the filtration device 7 varies depending on the type and filtering area of the filter medium to be used, the viscosity and type of the bubble-containing liquid 3, and the like, and is appropriately set. At the time of the actual treatment, it is desirable that the filter medium is immersed in the same liquid as the coating liquid in advance and the air inside the filter medium is evacuated. In addition, this filtration treatment has an advantage that impurities and insolubles contained in the bubble-containing liquid 3 can be removed simultaneously with the removal of bubbles.

The defoaming liquid 9 from which bubbles have been completely removed by the defoaming treatment in the defoaming device 5 as described above is stored in the storage tank 8 or continuously to a coating step (not shown). Sent.

Hereinafter, the defoaming method of the present invention will be further clarified by giving examples. (Examples 1 and 2 and Comparative Examples 1 and 2) A 9% by weight aqueous solution of polyvinyl alcohol (PVA) was prepared using a stirrer. This PVA aqueous solution contained a large amount of large and small bubbles in the liquid, and the viscosity was measured to be 39 cp. Then, this PVA aqueous solution was treated according to the defoaming apparatus shown in FIG. First, the PVA aqueous solution was degassed. This degassing process is performed by "DMS" manufactured by Japan Gore-Tex Corporation.
-1F "to a vacuum of 40 torr,
The aqueous solution A was treated so that the dissolved air amount was 1.5 ppm (equivalent to a degassing degree of 20%). Next, a filtration treatment was performed. This filtration process is performed by NMS01 manufactured by Pall Corporation.
-L ₁ G16H ”, a filter material having a filtration area of 510 cm ² and a mesh size of 3 μm (Example 1) and a mesh size of 30 μm (Example 2) was loaded with a liquid flow rate of 1 liter / min. I went in. The filter medium was previously immersed in an aqueous PVA solution to remove the internal air. The number of bubbles remaining in the PVA aqueous solution subjected to each of the above treatments was measured by an ultrasonic bubble detector. As a result of the measurement, air bubbles having a diameter of 30 μm or more and air bubbles having a diameter of 30 μm or less are classified, and the remaining numbers of the air bubbles are shown in Table 1.

For comparison, when the same PVA aqueous solution as in Example 1 was used and neither the deaeration nor the filtration was performed (Comparative Example 1), neither the deaeration nor the filtration was performed.
When 20 liters were placed in a container having a diameter of 30 cm and left for 30 minutes (Comparative Example 2), the number of remaining bubbles was counted. Table 1 also shows the measurement results.

[0015]

[Table 1]

From Table 1, the number of residual bubbles in the examples is much smaller than the number of residual bubbles in the comparative example, confirming the effectiveness of the defoaming method of performing the filtration treatment after the deaeration treatment according to the present invention.
Further, in all of the examples, bubbles having a diameter of 30 μm or more were completely removed, and in Example 2 using a 3 μm mesh filter medium, bubbles having a diameter of 30 μm or less were completely removed. And the diameter of the bubble to be removed was confirmed.

(Examples 3 to 5) In order to investigate the influence of the degree of deaeration, the degree of deaeration is 96%, 90% and 70% in Example 1 (using a 30 μm mesh filter medium). When the degree of vacuum and the processing time were adjusted as described above, the deaeration treatment was performed. As a result, it was recognized that the higher the degree of deaeration, the lower the number of bubbles was (see Table 2).

[0018]

[Table 2]

Further, when the treatments of Examples 1 and 2 were performed on a PVA aqueous solution having a viscosity of 150 cp, the same results as described above were obtained.

As described above, the defoaming method of the present invention has been mainly described by taking a coating liquid as an example. Of course, the defoaming method of the present invention can be applied to other liquids containing bubbles, such as low-viscosity liquids to high-viscosity liquids. It is applicable to various foam-containing liquids up to the liquid.

[0021]

As described above, according to the defoaming method of the present invention, fine bubbles in the liquid can be completely removed efficiently in a short time regardless of the viscosity of the liquid. . In addition, the defoaming of the foam-containing liquid can be performed at low cost without being restricted by the installation location during the treatment.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an apparatus configuration for performing a defoaming method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid preparation tank 3 Bubble-containing liquid 4 Bubbles 5 Defoaming device 6 Deaerator 7 Filtering device

Claims (3)

[Claims] 1. A defoaming method for removing bubbles in a liquid from a bubble-containing liquid containing bubbles, the method comprising degassing the bubble-containing liquid and then capturing the bubbles. 2. The defoaming method according to claim 1, wherein the air bubbles are trapped by using a filter medium having an aperture smaller than the diameter of the air bubbles to be defoamed. 3. The degassing process according to claim 1, wherein the deaeration treatment is performed so that the amount of dissolved air in the bubble-containing liquid is 90% or less of the saturated dissolved air amount of the bubble-containing liquid. Foam method.