JP2007160137A - Electret filter medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electret filter medium which is manufactured easily and has high collection efficiency even if the pressure drop is low and to provide a manufacturing method thereof. <P>SOLUTION: The electret filter medium is characterized by effecting the electret processing by laminating a non-woven fabric which consists of polyester fiber together with a non-woven fabric which consists of polyolefin fiber. The manufacturing method of the electret filter medium is characterized by comprising at least following steps after laminating the non-woven fabric which consists of the polyester fiber and the non-woven fabric which consists of the polyolefin fiber to integrate them: a step of laminating the non-woven fabric containing the polyester fiber and the non-woven fabric consisting of the polyolefin and a step of imparting a polar solvent to the non-woven fabric filter medium and drying the same to effecting the electret processing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air filter for purifying air in a vehicle interior of an automobile, a railway vehicle, etc., an exhaust filter and a main filter for a vacuum cleaner, an air cleaner filter, an air conditioner filter, and an intake / exhaust filter for OA equipment. The present invention relates to a filter medium for an electret filter that can be used for a building air conditioner filter and the like, and a method for producing the same.

  An electret filter is an air filter that can effectively remove fine particles in the air by electrostatic force of electric charges semi-permanently fixed to fibers used for a filter medium. Therefore, high collection efficiency can be achieved with low pressure loss compared to conventional filters such as glass fiber that collect only with mechanical collection efficiency, and it is necessary to clean the air in the interior of automobiles and railway vehicles. Used in air filters, vacuum cleaner exhaust filters and main filters, air cleaner filters, air conditioner filters, OA equipment intake / exhaust filters, building air conditioning filters, clean room filters, and the like.

  As filter media for electret filters used in such applications, electret films are formed by electrifying non-woven fabrics such as polypropylene and polyethylene, or cast films made of resins such as polypropylene and polyethylene. The thing made into the split fiber with the fine cutter etc. is known. However, any of these filter media for electret filters has a problem that pressure loss increases when trying to improve the collection efficiency, and a load is imposed on the power source, resulting in consumption of wasted power.

  As a method for producing a high electret filter medium, for example, JP 2003-73971 (Patent Document 1) and JP 2003-205210 (Patent Document 2) describe a method of carrying a nonwoven fabric in water, which is called a hydrocharge method. Has been. These methods are certainly good methods because high electretization can be expected, but non-woven fabric made of a single thermoplastic resin is used, and pressure loss such as melt blow is high for producing non-woven fabric with high collection efficiency. There was a problem that electrets could only be applied to the nonwoven fabric of the manufacturing method.

Japanese Patent Application Laid-Open No. 2005-028273 (Patent Document 3) describes a non-woven sheet obtained by mixing or blending a polyolefin fiber material and an aliphatic polyester fiber material and processing them with a needle punch or the like to form an electret. This method successfully combines the weakness of electret stability of polyester fibers and the characteristics of polyolefin fibers that tend to produce electret performance, and has succeeded in producing a nonwoven fabric with high collection efficiency while maintaining low pressure loss. If mixed, there is a drawback that the production of the nonwoven fabric is limited to one type. For example, as a production method for increasing the collection efficiency, there is a melt blow method for producing ultrafine fibers of about 3 to 6 μm, but the pressure loss becomes high. On the contrary, the spunbond method and needle punch method can use fibers having a large fiber diameter, and thus have a relatively low pressure loss, but have a lower collection efficiency than melt blow. If nonwoven fabrics can only be produced by either of these methods, the electret performance is limited to one type despite the fact that two types of fibers are used to enhance the electret performance. Low pressure loss and high collection efficiency cannot be improved greatly.
JP 2003-73971 A JP 2003-205210 A JP 2005-028273 A

  In view of the background of such prior art, the present invention is to provide an electret filtering material that is easy to manufacture and has high collection efficiency even when pressure loss is low, and a method for manufacturing the same.

  The present invention employs the following means in order to solve such problems. That is, the electret filter material of the present invention is characterized in that a nonwoven fabric made of polyester fibers and a nonwoven fabric made of polyolefin fibers are bonded together and electret processed together.

Moreover, the manufacturing method of this electret filter material is characterized by comprising at least the following steps after bonding a nonwoven fabric made of polyester fiber and a nonwoven fabric made of polyolefin fiber together.
Bonding step: A step of bonding a nonwoven fabric containing polyester fibers and a nonwoven fabric made of polyolefin.
Electretization step: a step of applying a polar solvent to the bonded nonwoven filter medium and drying and electret processing.

  ADVANTAGE OF THE INVENTION According to this invention, even if a manufacturing process is easy and a pressure loss is low, an electret filter material with high collection efficiency can be provided.

  The present invention has been intensively studied on the above-mentioned problem, that is, an electret filter material that is easy to manufacture and has a high collection efficiency even when pressure loss is low, and a nonwoven fabric made of polyester fiber and a nonwoven fabric made of polyolefin fiber are bonded together. Later, when electret processing was performed together, it was found that the attenuation of electric charge on the nonwoven fabric side made of polyester fiber was suppressed, and the electret life was prolonged, and it was not possible until now. The present inventors have found that an electret filter medium with a low pressure loss and a high collection efficiency can be provided, and have reached the present invention.

  Hereinafter, the best embodiment of the present invention is a spunbond nonwoven fabric as a nonwoven fabric made of polyester fibers, a polyolefin blown fiber, a melt blown nonwoven fabric made of polypropylene fibers, and both nonwoven fabrics bonded together with a moisture curable urethane resin. An electret processed non-woven fabric will be described as an example.

The nonwoven fabric composed of the polyester fiber according to the present invention may be a polyester fiber alone, a composite of another fiber and a polyester fiber, or a fiber having a core-sheath structure in which the polyester fiber is exposed on the sheath side. In addition, for the production of nonwoven fabrics, wet nonwoven fabrics, resin bond dry nonwoven fabrics, thermal bond dry nonwoven fabrics, spunbond dry nonwoven fabrics, needle punch dry nonwoven fabrics, water jet punch dry nonwoven fabrics, melt blow dry dry nonwoven fabrics or flash spinning dry dryers. A nonwoven fabric or the like can be used, but a spunbond dry nonwoven fabric is preferably used because a nonwoven fabric with a low basis weight is relatively easy to produce, has high strength, and has high productivity. Basis weight of such nonwoven fabric is about ^10g / ^{m 2 ~100g} / m 2 is preferred. If the basis weight is less than 10 g / m ² , the shape as a nonwoven fabric cannot be maintained, and it is difficult to bond the nonwoven fabric made of polyolefin fibers. On the other hand, if the basis weight exceeds 100 g / m ² and increases too much, the pressure loss of the nonwoven fabric increases, making it unsuitable as a filter medium.

The nonwoven fabric composed of polyolefin fibers according to the present invention may be either a single polyolefin fiber, a composite of other fibers and polyester fibers, or a fiber with a core-sheath structure in which the polyolefin fibers are exposed on the sheath side. As such a polyolefin fiber, a polypropylene fiber is particularly preferable because it can be easily subjected to electret processing. In addition, as a nonwoven fabric made of such polyolefin fibers, wet nonwoven fabric, resin bond dry nonwoven fabric, thermal bond dry nonwoven fabric, spun bond dry nonwoven fabric, needle punch dry nonwoven fabric, water jet punch dry nonwoven fabric, melt blow dry dry Although what is manufactured with various manufacturing methods, such as a nonwoven fabric or a flash spinning type dry nonwoven fabric, can be used, the nonwoven fabric manufactured by the melt blow method which can make collection efficiency high is preferable. Basis weight of the nonwoven fabric made of such polyolefin fibers 2 to 100 g / ^{m 2} approximately ^{10 g} / m are preferred. If the basis weight is less than 10 g / m ² , the shape as a nonwoven fabric cannot be maintained, and it is difficult to bond with a nonwoven fabric made of polyester fiber. If the basis weight exceeds 100 g / m ² , the nonwoven fabric is aerated. The amount decreases and is not suitable as a filter medium.

  Moreover, you may add an additive to a nonwoven fabric for the improvement of electret performance. As such an additive, it is preferable to blend at least one hindered amine-based additive or triazine-based additive.

  Of the above two types of additives, the hindered amine-based additive may be 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)) (manufactured by Ciba-Geigy, Chimersoap 944LD ), Dimethyl succinate-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (manufactured by Ciba Geigy, Tinupin 622LD), 2- (3,5-di- t-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl) (manufactured by Ciba-Geigy, Tinupin 144) It is.

  Examples of the triazine-based additive include the aforementioned 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)) (manufactured by Ciba Geigy, Chimerthop 944LD), 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-((hexyl) oxy) -phenol (manufactured by Ciba Geigy, Tinupin 1577FF) and the like. Among these, it is particularly preferable to use a hindered amine-based additive.

  The amount of the hindered amine-based additive or triazine-based additive is not particularly limited, but is preferably in the range of 0.5 to 5% by weight, more preferably in the range of 0.7 to 3% by weight. Good. If the addition amount of these additives is less than 0.5% by weight, it is difficult to obtain a desired high level electret performance. Moreover, when it mix | blends so much that it exceeds 5 weight%, it is unpreferable since it will worsen a fiber-forming property and film forming property, and will become disadvantageous also in cost.

In the electret filter material of the present invention, the reason why the nonwoven fabric made of polyester fiber and the nonwoven fabric made of polypropylene fiber are combined is that the charged columns are separated. In particular, it is known that a material made of a thermoplastic resin having a volume resistivity of 10 ¹⁴ Ω · cm or more, such as polypropylene, is easily affected by electrets. Even if the electret is unstable, it has been clarified that the electret is stable and the charge is not easily attenuated when there is a stable electret such as polypropylene nearby.

  The “volume resistivity value” in the present invention is measured by a volume resistivity measurement apparatus used for an insulation resistance test by a three-terminal method in accordance with “General Thermosetting Plastic Test Method” defined in JIS K 6911. This is the value obtained.

  Hereinafter, preferred embodiments of the method for producing an electret filter material of the present invention will be described in detail for each step.

1. Lamination process It is the process of bonding the nonwoven fabric containing a polyester fiber and the nonwoven fabric consisting of polyolefin.

  That is, as a method of laminating two types of non-woven fabric, there are a method of spraying a moisture curable urethane resin by a spray method, a method of spraying a thermoplastic resin, a heat-fusible fiber, and pasting them through a heat path. A method will not be specifically limited if a nonwoven fabric can be bonded together. However, since the use application is a nonwoven fabric used for a filter, a laminating method that causes an increase in pressure loss is not preferable. In this respect, the spray method using a moisture-curable urethane resin is a preferable method because it can bond two non-woven fabrics without pressing, so that the increase in pressure loss at the time of bonding is small.

2. Electret process It is the process of electret-processing the nonwoven fabric filter material bonded together by the front process.

  That is, as the electret processing method, an electro electret, a thermal electret, a radio electret, a mechano electret, a photo electret, a magnet electret, or the like can be used. Moreover, since the performance of the electret which applies the electret by the hydrocharge method which sprays polar solvents, such as a pure water and an organic solvent employ | adopted in recent years, sprays on a nonwoven fabric etc. or vibrates etc. becomes high, it is preferable. As the polar solvent used at this time, it is preferable to use pure water from the viewpoint of productivity such as drainage.

  The order in which the electrets are applied must be at least after the bonding step. As a result of diligent research, the inventors of the present invention do not mix the fibers and perform the electret processing after the bonding process, so that the electret performance does not decrease even if a material that decreases the stability of the electret is used. I found. That is, it has been found that the charge attenuation on the nonwoven fabric side made of polyester fibers is suppressed, and that the electret life is prolonged, which is extremely surprising. If the electret is applied before bonding, the electret performance of the polyester fiber is lowered because the electret has low stability.

  Moreover, when electretization is performed by a hydrocharge method, it is necessary to pass through a drying process after that. Drying is performed until the moisture contained in the nonwoven fabric sheet reaches the official moisture content. The drying temperature is preferably 130 ° C. or less, more preferably 120 ° C. or less, and further preferably 100 ° C. or less. The dried sheet should be quickly discharged from the dryer so as not to deactivate the electret effect after drying. For example, the dried sheet is preferably discharged within 30 minutes at a drying temperature of 100 ° C. or higher. Further, the lower limit of the drying temperature is preferably 80 ° C. or higher because if the temperature is too low, it takes too much time to dry and the productivity is deteriorated.

  Since the electret filter material of the present invention is manufactured as described above, that is, it can be formed into a sheet by combining a low-pressure loss spunbond method and a high collection efficiency melt-blow method. It is possible to produce an electret filtering material having a low collection loss and a high collection efficiency as compared with the conventional method of producing a nonwoven fabric by mixing.

  In addition, by applying electret processing after bonding, even if a non-woven fabric made of polyester fiber with low electret stability is used, it is affected by the stable non-woven fabric with high electret performance, extending the performance and life of the electret. Can be maintained. As a result, electret performance can be maintained even for non-woven fabrics with low electret stability, and an electret filter material with high collection efficiency can be provided with a lower pressure loss than that obtained by superposing non-woven fabric sheets that have been electret-processed independently. .

[Measuring method]
(1) Dust Collection Performance Test Air dust was passed through the obtained nonwoven fabric at a wind speed of 6.5 m / min, and the efficiency of 0.3 micron particles was measured using a Rion particle counter KC-01D.

(2) Pressure loss test Air having a temperature of 23 ° C. and a humidity of 50% RH was blown into the duct at a speed of 6.5 m / min. At that time, the differential pressure between the upstream side and the downstream side of the fiber sheet was measured with a digital manometer MA2-04P manufactured by MODUS.

[Example 1]
A spunbonded nonwoven fabric with a fabric weight of 18 g / m ² made of polyester fiber (product number R-055 made by Mitsui Chemicals) and a melt blown nonwoven fabric with a fabric weight of 15 g / m ² made of polypropylene fiber (Tremicron (R) made by Toray Fine Chemicals) It was sprayed on the polypropylene nonwoven fabric side by the urethane resin spray method, and the polyester nonwoven fabric was bonded together.

  The bonded nonwoven fabric sheet was electret processed by a hydrocharge method in which pure water was applied to the nonwoven fabric sheet, and dried at 120 ° C. for 3 minutes to obtain a nonwoven fabric of Example 1. The resulting nonwoven fabric had a dust collection performance of 61.5% and a pressure loss of 4.4 Pa.

[Example 2]
Spunbond nonwoven fabric made of polyester fiber with a basis weight of 18 g / m ² (product number R-055 manufactured by Mitsui Chemicals) and melt blow of 12 g / m ² made of polypropylene fiber (Tremicron® made by Toray Fine Chemical Co., Ltd.) The nonwoven fabric was sprayed on the polypropylene nonwoven fabric side by a moisture curable urethane resin spray method, and the polyester nonwoven fabric was bonded.

  The bonded nonwoven fabric sheet was subjected to electret processing by a hydrocharge method, and dried at 120 ° C. for 3 minutes to obtain a nonwoven fabric of Example 2. The resulting nonwoven fabric had a dust collection performance of 56.9% and a pressure loss of 3.6 Pa.

[Comparative Example 1]
Only a spunbond nonwoven fabric having a basis weight of 18 g / m ^{2 made} of polyester fiber (product number R-055 manufactured by Mitsui Chemicals, Inc.) was electret processed and dried in the same manner as in Example 1 to prepare a nonwoven fabric. The nonwoven fabric had a dust collection performance of 3.0% and a pressure loss of 0.3 Pa.

Only a melt blown nonwoven fabric having a basis weight of 15 g / m ² made of polypropylene fiber (Tremicron (R) manufactured by Toray Fine Chemical Co., Ltd.) was electret processed in the same manner as in Example 1 and dried to prepare a nonwoven fabric. The nonwoven fabric had a dust collection performance of 54.0% and a pressure loss of 3.9 Pa.

  A non-woven fabric of Comparative Example 1 was used as a non-woven fabric obtained by simply overlapping the two non-woven fabrics. The laminated nonwoven fabric had a dust collection performance of 56.5% and a pressure loss of 4.2 Pa.

  In Example 1, although the pressure loss is slightly higher than that of the overlapped sheet of Comparative Example 1, the collection efficiency is 5% or more, and the performance of performing the electret processing after bonding is higher than applying the electret individually. It turns out that it improves.

  Moreover, although Example 2 has a collection efficiency of substantially the same level as Comparative Example 1, it can be seen that a low pressure loss is achieved by lowering the basis weight of the polypropylene nonwoven fabric. From this, it can be made by applying the electret after pasting together the one with high collection efficiency if it has the same pressure loss than the single electret, and the one with low pressure loss if it has the same collection efficiency. I understand that.

  The present invention can be used for air filter applications.

Claims (4)

An electret filtering material, wherein a nonwoven fabric made of polyester fiber and a nonwoven fabric made of polyolefin fiber are bonded together and electret processed together. The electret filter material according to claim 1, wherein the nonwoven fabric made of polyolefin fibers is a melt blown nonwoven fabric. A method for producing an electret filter material, comprising a non-woven fabric made of polyester fiber and a non-woven fabric made of polyolefin fiber bonded together and integrated through at least the following steps.
Bonding step: A step of bonding a nonwoven fabric containing polyester fibers and a nonwoven fabric made of polyolefin.
Electretization step: a step of applying a polar solvent to the bonded nonwoven filter medium and drying and electret processing. The electret filtration according to claim 3, wherein the laminating step is performed by laminating with at least one adhesive selected from a thermoplastic resin, a heat-fusible fiber, and a moisture-curing urethane resin. A method of manufacturing the material.