JP4391152B2 - Method for manufacturing electret body and charging device - Google Patents

Description

  The present invention relates to a method for manufacturing an electret body suitable for electretizing a structure made of a thermoplastic resin, and a charging device suitable for use in the manufacturing method.

  Conventionally, a structure made of a porous thermoplastic resin such as a woven fabric or a non-woven fabric has been used as a filtering material in order to remove dust and the like in the gas. Since such a filter medium mainly removes dust and the like by Brownian diffusion, shielding and inertial collision due to physical action, the smaller the aperture diameter of this type of structure, the smaller the dust and the like. Can be captured and removed automatically. As is well known, when dust having a predetermined particle diameter is captured and removed, the filtration efficiency increases as the aperture diameter of the filter material decreases, but at the same time the pressure loss increases. Therefore, the apparatus to which the filter medium is attached also has a problem that the operating cost of the apparatus becomes high because the air blowing capacity requires high performance, for example.

  As a technique for improving the contradictory problems between the filtration efficiency and the pressure loss described above, a structure made of a thermoplastic resin is electretized, and the structure is made into an electret body, so that substantially the same opening diameter is obtained. However, attempts have been made to achieve both high filtration efficiency and low pressure loss by capturing and removing smaller dust and the like by electrostatic action. As such electretization technology, electret bodies are widely used by corona charging utilizing discharge phenomenon in the atmosphere.

  Also, as a technique for adding a hindered amine compound to a thermoplastic resin constituting the structure for the purpose of stabilizing the applied charge after the structure described above is an electret body, Japanese Patent Laid-Open No. 1-287914 A gazette (hereinafter referred to as Patent Document 1) is known. In this publication, a polypropylene resin is disclosed as a thermoplastic resin, and a melt blown nonwoven fabric capable of preparing a sheet having a relatively small fiber diameter, and thus a relatively small opening diameter, is illustrated as an example of such a resin. Thus, a technique for obtaining an electret body with high efficiency and low pressure loss is disclosed.

  Furthermore, in Japanese Patent Application Laid-Open No. 11-510862 (hereinafter referred to as Patent Document 2), as a technique for producing an electret body, a non-woven web of thermoplastic non-conductive microfibers that can have a large amount of trapped charges is used. Of a thermoplastic microfiber for providing an electret filter medium comprising the steps of impinging a jet or water stream of water at a pressure sufficient to provide a filtration enhancing electret charge to the web and drying the web Techniques for producing electret bodies by a method for charging a nonwoven web are known.

  On the other hand, in Japanese Patent Application No. 2002-5233 (hereinafter referred to as Patent Document 3), the present applicant causes ultrasonic vibration to act on a structure made of a thermoplastic resin via a polar liquid, and the structure is designated as an electret body. The technology to do is proposed. According to this technique, the friction between the polar liquid and the structure made of the thermoplastic resin can be suppressed as compared with the case where the polar liquid is collided as in Patent Document 2 described above. Therefore, according to this application technique, for example, the orientation of the fibers constituting the meltblown nonwoven fabric is changed by the jet of water, and it is possible to suppress a decrease in dust collection efficiency due to movement of the fibers and opening of holes in the sheet. .

JP-A-1-287914

Japanese National Patent Publication No. 11-510862 Japanese Patent Application No. 2002-5233

  As described above, the present applicant, when electretizing a structure made of a thermoplastic resin, a technique for applying ultrasonic vibration in the polar liquid as a physical action of the polar liquid on the fibers constituting the structure. Focused on the continual investigation. As a result, by applying this technology under specific conditions, a technology capable of producing a superior electret body and a charging device suitable for use in this technology have been found, and the invention according to the present application has been completed. It was.

  Therefore, the object of the invention according to this application is to more effectively realize a charging effect due to a physical action by ultrasonic vibration when the structure made of a thermoplastic resin is electretized, and the structure is an electret body. An object of the present invention is to provide an electret body capable of realizing excellent filtration characteristics by suppressing structural damage during the process.

In order to achieve this object, according to the method of manufacturing an electret body according to the first invention of the present application, an ultrasonic vibration is applied to a structure made of a thermoplastic resin via a polar liquid to thereby change the electret body. In manufacturing, the distance between the ultrasonic oscillation member and the regulating member provided to face the ultrasonic oscillation member is less than 150 times the thickness of the structure under a 20 (g / cm ² ) compressive load , It is characterized by maintaining the temperature of the polar liquid at 40 ° C. or lower .

The charging device according to the second invention of the present application is a charging device for causing ultrasonic vibration to act on a structure made of a thermoplastic resin via a polar liquid. A pair of transport members provided in the structure transport direction and a pair of transport members for transporting the structure described above in a immersed state in a polar liquid stored in the bathtub, and the pair of transport members; An ultrasonic vibration generating portion including the provided ultrasonic oscillation member and a regulating member facing the ultrasonic oscillation member, and a variable fixing for adjusting and fixing the distance between the ultrasonic oscillation member and the regulating member And a cooling device for keeping the temperature of the polar liquid at 40 ° C. or lower .

According to the method of manufacturing an electret body according to the first invention of this application, in manufacturing an electret body by applying ultrasonic vibration to a structure made of a thermoplastic resin via a polar liquid, an ultrasonic oscillation member And the distance between the regulating member and the regulating member provided opposite thereto is less than 150 times the thickness of the structure under a compressive load of 20 (g / cm ² ), and the temperature of the polar liquid is 40 ° C. It is characterized by the following . For this reason, the vibration by the ultrasonic wave of the polar liquid is efficiently transmitted to the structure between the ultrasonic oscillation member and the regulating member opposed thereto, and an excellent charging effect can be realized by the liquid.

The charging device according to the second invention of this application is a charging device for causing ultrasonic vibration to act on a structure made of a thermoplastic resin via a polar liquid, wherein the polar liquid described above is used. A pair of transport members provided in the structure transport direction and a pair of transport members for transporting the structure described above in a immersed state in a polar liquid stored in the bathtub, and the pair of transport members; An ultrasonic vibration generating unit including the provided ultrasonic oscillation member, a regulation member facing the ultrasonic oscillation member, and adjusting and fixing the distance between the ultrasonic oscillation member and the regulation member described above variable fixing means is provided, further a comprising Ru constituting a cooling device for keeping the temperature of the polar liquid 40 ° C. or less.

  For this reason, in carrying out the manufacturing method according to the first invention of the present application described above, the distance between the ultrasonic oscillation member and the regulating member based on the design of the charging effect is defined for the structures having various thicknesses. And the electret body which has the outstanding filtration performance can be provided with high reproducibility. Further, the pair of conveying members provided in the apparatus of the present invention conveys the structure to a stable position with respect to the polar liquid region formed at a specific distance between the ultrasonic oscillation member and the regulating member. Can be supplied. Therefore, even if it is a structure which is easy to disturb fiber orientation, such as a nonwoven fabric, an electret body excellent in filtration performance and quality can be provided.

  Further, by narrowing the region formed by the two members, the ultrasonic output (energy) necessary for applying a predetermined charge amount can be reduced, and an efficient charging process can be performed. For this reason, it is also possible to extend the lifetime of apparatus parts, such as an ultrasonic oscillation member, for example.

In the method of manufacturing an electret body according to the first invention of the present application, an ultrasonic oscillation member is provided opposite to an ultrasonic oscillation member for applying ultrasonic vibration to a structure made of a thermoplastic resin via a polar liquid. The distance from the regulated member is less than 150 times the thickness of the structure body under 20 (g / cm ² ) compressive load. The thickness under the compression load mentioned here indicates a value measured according to “General Textile Testing Method” of JIS L 1096.

First, the structure made of a thermoplastic resin to which this method invention is applied can be used in various forms as long as it is a porous material conventionally known as a filter material, such as woven fabric, knitted fabric, It is preferable to apply to structures made of fibers such as nonwoven fabric. In particular, as a thermoplastic resin constituting this structure, a volume specific resistance value of 10 ¹⁴ (Ω · cm) or more, more preferably 10 ¹⁶ (Ω · cm), for the purpose of imparting an effective charge amount to filtration characteristics. What shows the above volume specific resistance value is suitable. In addition, the upper limit of this volume specific resistance value is not specifically limited. This volume resistivity value is measured by a “volume resistivity measurement device” used in an insulation resistance test by a three-terminal method in accordance with “General Thermosetting Plastic Testing Method” defined in JIS K 6911. Is the number obtained. Examples of the thermoplastic resin corresponding to the volume resistivity value include polyolefin resins (for example, polyethylene resins, polypropylene resins, polymethylpentene resins, polystyrene resins, etc.), polytetrafluoroethylene resins, and polyvinylidene chloride. Examples thereof include a resin, a polyvinyl chloride resin, and a polyurethane resin. Among these, polyolefin resin is particularly suitable because it has a high volume resistivity and is excellent in processability to fibers and the like, and in particular, polypropylene resin or polymethylpentene resin is excellent in heat resistance. An electret body suitable as a filter medium can be obtained.

Further, the “ultrasonic oscillation member and the regulating member provided opposite to the ultrasonic oscillation member” referred to in the present invention will be described in detail as a charging device according to the second invention of the present application described later. The distance is set to be less than 150 times the thickness of the structure under a 20 (g / cm ² ) compressive load. The lower limit of this distance depends on the apparent thickness of the electretized structure itself in the polar liquid. For this reason, although not particularly limited, in the case of electretization, when these members are conveyed to the surface of the structure in a state of contact, there is a possibility that physical damage will be caused to the surface of the obtained electret. Therefore, the distance between these members is preferably equal to or greater than the apparent thickness of the structure in a swollen state in the polar liquid.

  Further, as the thermoplastic resin constituting the structure according to the present invention, a hindered amine compound, an aliphatic metal salt (for example, a magnesium salt of stearic acid, An aluminum salt of stearic acid and the like) and one or more compounds selected from unsaturated carboxylic acid-modified polymers can also be contained. Among these series of compounds, hindered amine compounds are particularly preferable in that the charge amount increases as disclosed in Patent Document 1 described above.

  Specific examples of such hindered amine compounds include poly [{(6- (1,1,3,3-tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) {(2, 2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}}, dimethyl-1- (2-hydroxyethyl) succinate -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, 2- (3,5-di-tert-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1, 2,2,6,6-pentamethyl-4-piperidyl) and the like.

  The content of the compound capable of increasing the chargeability with respect to such a structure is not particularly limited, but relative to the total mass of the thermoplastic resin constituting the structure or the electret body to be obtained. , And preferably contained in a weight of 0.01 to 5 (mass%). When the content of the compound is less than 0.01 (mass%), the effect on the charging characteristics due to the addition tends to be small, and the content is preferably 0.05 (mass%) or more. Moreover, when the content exceeds 5 (mass%), the strength of the fibers constituting the structure or electret body tends to be remarkably reduced, and more preferably the content is 2.5 (mass%). The following is preferable.

  In addition, in carrying out the present invention, it is preferable to use a polar liquid having a lower electrical conductivity. The electric conductivity referred to here is a numerical value obtained by a measurement method defined in JIS K 0101 “Industrial water test method” or JIS K 0552 “Electrical conductivity test method of ultrapure water”. Examples of the polar liquid include water, alcohol, acetone, and water in which ammonia is dissolved. In particular, water is excellent in the working environment for electretization, and in the final stage of preparing the electret body. This is preferable because it can avoid ignition or ignition during drying.

  Furthermore, as a structure to be electretized by applying the method of the present invention, a nonwoven fabric prepared by a melt blow technique widely used for filter media having a relatively thin fiber diameter can be employed. This melt blown nonwoven fabric can have a predetermined fiber diameter distribution in terms of design of filtration characteristics. Moreover, the said nonwoven fabric is said that the entanglement state of fibers is comparatively loose, and the movement of the fiber with respect to a physical external force is comparatively large. Therefore, among electretization techniques that are charged by contact friction with a polar solvent, for example, in the present method invention, charging by ultrasonic vibration in which the movement of the polar solvent is small compared to the conventional technique by contact friction with a high-pressure water stream. Therefore, it is possible to effectively avoid the deterioration of quality after electretization and the phenomenon that a predetermined filter medium design is changed.

  Next, with reference to the drawings, a preferred embodiment of the charging device according to the second invention of the present application will be described with reference to a part of the above-described method invention. FIG. 1 is a schematic perspective cross-sectional view of a charging device according to the present invention, focusing on the side of the device that intersects the conveyance direction of a structure. In the figure, hatching of the cross section of each component is omitted, and components having the same function are denoted by the same reference numerals.

  First, in FIG. 1, a structure 12 made of a thermoplastic resin to be electret is conveyed and supplied from a supply roll 10 to a bathtub 16 in which a polar liquid 14 is accommodated. At this time, the structure 12 is guided into the liquid 14 by being supported by a transport member 18 a that is upstream in the transport direction and is immersed in the polar liquid 14. Here, the structure 12 may not be wound in the form of a roll, and may be in the form of being introduced into the polar liquid 14 via the conveying member 18a, for example, in the form of a sheet following the production line of the melt blown nonwoven fabric. Moreover, although the one roll-shaped form is illustrated as the conveyance member 18a, it can also be designed as arbitrary suitable members, such as a conveyor. In particular, a roll-shaped member may be additionally provided so as to face the conveying member 18a so as to sandwich the structure 12, and in this case, in the structure 12 prior to the action of ultrasonic vibration, It is also possible to eliminate the air remaining on the surface and realize a better charging process.

  Next, the structural body 12 passes between the regulating member 20 provided on the bottom side of the bathtub 16 and the ultrasonic oscillation member 22 facing the regulating member 20. Here, the ultrasonic oscillation member 22 is a member corresponding to a horn of a generally known ultrasonic generator. The ultrasonic generator 24 in FIG. 1 illustrates a configuration including the member 22, a power unit 26, a converter 28, a booster 30, and the like.

  In addition, the structure 12 that has been transported between the regulating member 20 and the ultrasonic oscillation member 22 is guided out of the polar liquid 14 via the transport member 18b, dried by a drying device (not shown), and then electret body. Rolled up as As described above, the transport member 18a and the transport member 18b are a pair of members respectively disposed on the upstream side and the downstream side in the structure transport direction, and between the regulation member 20 and the ultrasonic oscillation member 22. It is responsible for keeping the transport area constant.

  Here, the distance between the regulating member 20 and the ultrasonic oscillation member 22 will be described with reference to FIG. FIG. 2 is a schematic perspective sectional view showing, in an enlarged manner, the device portions of the members arranged opposite to each other in the charging device shown in FIG. In the drawing, the structure is not shown for easy understanding of the description.

As shown in FIG. 2, the regulating member 20 and the ultrasonic oscillating member 22 are disposed to face each other with a distance D as a region to be processed while conveying the structure. This distance D is variously adjusted and fixed according to the thickness of the above-described structure under a 20 (g / m ² ) compressive load. For such adjustment and fixing, one or both of the regulating member 20 and the ultrasonic oscillating member 22 is combined with, for example, a rack (a linear part provided with a serrated notch) and a gear, not shown. A variable fixing means is provided to fix the distance D between the members for a specific structure, and in cooperation with the conveying members 18a and 18b, the structure 12 being conveyed and the members 20 and / or Alternatively, damage to the structure 12 due to contact with 22 can be avoided.

  Furthermore, the structure 12 receives the action of ultrasonic vibration while containing the polar liquid 14. Therefore, the capacity of the polar liquid 14 in the bathtub 16 tends to decrease by continuing the processing. In order to eliminate such a loss of polar liquid and realize a stable ultrasonic vibration process, a liquid level sensor is provided in the bathtub 16 and a variable fixing means interlocked with the sensor is used to convey the structure 12. It is good also as a structure which can carry out a conveyance process with the depth of a polar liquid with a fixed position.

  Furthermore, the temperature of the polar liquid 14 tends to rise by continuously receiving the action of ultrasonic vibration. For this reason, it is preferable to use a cooling device or the like and keep the temperature low within a range where the liquid does not solidify, and the temperature of the polar liquid is preferably 40 ° C. or lower.

  In addition, as is well known, the dimensions of the regulating member 20 and the ultrasonic oscillation member 22 in the conveyance direction are such that the ultrasonic waves propagate substantially radially from the end face of the oscillation member, so that the dimensions of the opposing surfaces are not necessarily matched. It is not necessary to arrange. Similarly, the dimensional relationship between the width of the structure (dimension in the depth direction in the drawing) and the regulating member 20 and / or the ultrasonic oscillation member 22 can be variously selected. Moreover, although the flat member was illustrated as a suitable form of the control member 20, it can also be arrange | positioned as a cylindrical shape which has a predetermined curvature, or an elliptical roll shape.

  Furthermore, the material of each member constituting this device is made of stainless steel having corrosion resistance to the polar liquid used, such as the material of the device configuration, shape, arrangement relationship and numerical conditions, etc. Various design changes and modifications can be made within the scope of the design of the electret body and the object of the present invention.

  Hereinafter, the method and apparatus according to the present invention will be described in more detail as examples with reference to the evaluation results of electret bodies as a preferred application example. In addition, this invention is not limited only to these Examples.

First, when applying the present invention, an evaluation result of the distance D between the regulating member 20 and the ultrasonic oscillation member 22 according to the present invention described with reference to FIG. 1 will be described. First, as a structure made of a thermoplastic resin, a commercially available hindered amine “CHIMASORB 944FD” (manufactured by Ciba Specialty Chemicals Co., Ltd.) is used for a commercially available polypropylene resin having a volume resistivity of about 10 ¹⁶ (Ω · cm). , Registered trademark) containing 1.0 (mass%) of the entire resin, a melt blown nonwoven fabric (surface density 20 (g / m ² ), average fiber diameter 5 (μm)) was prepared.

With respect to the structure thus obtained (hereinafter referred to as structure 1), the electric conductivity of 3.2 (μS / cm) as a polar liquid in the bathtub 16 of the charging device shown in FIG. (° C.) pure water (corresponding to secondary distilled water subjected to distillation and ion exchange) is accommodated, the amplitude of ultrasonic waves generated from the ultrasonic oscillation member 22 is 0.5 (μm), and the transport speed of the structure 1 (m / min), the distance D between the regulating member 20 and the ultrasonic oscillating member 22 is subjected to ultrasonic vibration with various values shown in Table 1 in the subsequent stage, and after passing through a predetermined drying The electret bodies of Example 1, Example 2, and Comparative Example 1 were obtained. The thickness of the structure used here under a 20 (g / cm ² ) compressive load was 0.3 (mm). A commercially available device with a rated output of 600 (W) was used as the ultrasonic generator 24, and ultrasonic vibration with a frequency of 19.5 kHz was applied.

In evaluating the electret bodies according to these examples, the collection efficiency E (%) was measured under the condition of a surface wind speed of 10 (cm / sec) using atmospheric dust having a particle size of 0.3 to 0.5 (μm). did. In addition, as an evaluation result, from the pressure loss ΔP (Pa) and the collection efficiency E (%) under the condition of the surface wind speed 10 (cm / sec) before the start of the collection efficiency measurement test, the following formula 1 (however, The γ value was calculated on the basis of “ln” is a natural logarithm), and 100 γ was obtained as a value of 100 times.
γ = −ln (1-E / 100) / ΔP
In general, the larger this value, the better the collection efficiency and the lower the pressure loss.

As can be understood from Table 1 above, using the method and apparatus of the present invention, the distance D between the regulating member 20 and the ultrasonic oscillation member 22 is less than 50 mm, that is, in a polar liquid with respect to these members. By realizing less than 150 times the thickness of the structure of 20 (g / cm ² ) under compressive load, an electret body excellent in both collection efficiency and pressure loss can be realized using 100γ as an index. I was able to. Further, it is generally known that a melt blown nonwoven fabric using polypropylene has a property of being difficult to wet with water. In each of the above-described examples, the wettability with respect to the polar liquid immediately after the processing was confirmed for each sample obtained after the charging process. In Example 1 and Example 2, the obtained electret bodies were all good. However, in the electret body according to the comparative example, a part not wetted was observed.

  Next, evaluation results when the electric conductivity of the polar liquid is variously changed when the present invention is applied will be described. In this evaluation, the pure water (electric conductivity 3.2 (μS / cm), temperature 25 (° C.)) and industrial water (collected in Ibaraki Prefecture) were collected from the above melt-blown nonwoven fabric. Example 3 and implementation which carried out the process by ultrasonic vibration, each accommodated as each polar liquid in the bathtub 16 of the apparatus shown in FIG. 1 mentioned above using the temperature of 160 (μS / cm) and the temperature of 25 (° C.). For the electret body of Example 4, 100γ was determined. In addition to the difference in the polar liquid used, the amplitude condition of the ultrasonic wave was unified to 9 (μm), and the conveyance speed of the structure was unified to 0.7 (m / min). The evaluation method and the like are as described above.

  As can be understood from this result, an excellent electret body could be obtained as the electric conductivity of the polar liquid was lower.

Next, evaluation results when the temperature of the polar liquid 14 is variously changed when the present invention is applied will be described. In this evaluation, ultrasonic vibrations were applied to the melt blown nonwoven fabric described above, with the temperature of pure water (electric conductivity 3.2 (μS / cm)) as various values shown in Table 3 in the subsequent stage, The electret body of Example 5, Example 6, and the reference example was obtained through drying. In addition to the difference in temperature of the polar liquid used, the ultrasonic amplitude condition was unified to 9 (μm), and the conveyance speed of the structure was unified to 0.7 (m / min). The evaluation method and the like are as described above.

  As can be understood from this result, an excellent electret body could be obtained as the temperature decreased in the range where the polar liquid did not solidify.

FIG. 1 is a diagram showing a configuration example of a device of the present invention by a schematic perspective section, FIG. 2 is a schematic perspective sectional view showing the apparatus partially enlarged to explain the present invention.

Explanation of symbols

10: supply roll,
12: structure (made of thermoplastic resin),
14: Polar liquid,
16: Bathtub
18a, 18b: conveying member,
20: restriction member,
22: Ultrasonic oscillation member,
24 : Ultrasonic generator,
26: Power unit,
28: Converter,
30: Booster,
D: Distance between the regulating member and the ultrasonic oscillation member.

Claims (6)

When manufacturing an electret body by applying ultrasonic vibration to a structure made of a thermoplastic resin via a polar liquid, the distance between the ultrasonic oscillation member and a regulating member provided facing the ultrasonic vibration member is The manufacturing method of the electret body characterized by making it less than 150 times the thickness under 20 (g / cm < ² >) compressive load of the said structure, and keeping the temperature of the said polar liquid below 40 degreeC.   The method for producing an electret body according to claim 1, wherein the structure has a volume resistivity of 1014 Ω · cm or more.   The method for producing an electret body according to claim 1, wherein the structure has a volume resistivity of 1016 Ω · cm or more.   The structure according to claim 1, wherein the structure contains one or more compounds selected from hindered amine compounds, fatty acid metal salts, and unsaturated carboxylic acid-modified polymers. The manufacturing method of the electret body in any one.   The said structure is a melt blown nonwoven fabric, The manufacturing method of the electret body in any one of Claims 1-4 characterized by the above-mentioned. A charging device for applying ultrasonic vibration to a structure made of a thermoplastic resin via a polar liquid, the bathtub for containing the polar liquid, and the polar liquid contained in the bathtub In order to transport the structure in the immersion state, a pair of transport members provided in the structure transport direction, an ultrasonic vibration generation unit including an ultrasonic oscillation member provided between the pair of transport members, And a variable fixing means for adjusting and fixing the distance between the ultrasonic oscillation member and the regulating member, and further for maintaining the temperature of the polar liquid at 40 ° C. or lower. A charging device comprising a cooling device .

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