JP2013034941A - Oil proof filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter in which the reduction of efficiency in oil mist load is suppressed, high efficiency is maintained even when loosing electric charge, and the rise of air-flow resistance is suppressed.SOLUTION: The filter is constituted by laminating an electret fiber layer having oil repellency, and a sheet containing a porous material such as an activated charcoal or an oil absorbable layer being a fiber sheet comprising olefine base fiber or polyester base fiber.

Description

  The present invention relates to a filter used for air purification and its use.

  Conventionally, fiber layers made of various fiber materials have been used as filters used for air purification applications. These have the advantage that the ventilation resistance is lower than that of a filtration method using a membrane or a particle packed layer, and the lifetime of the filter is long because the porosity of the constituent materials is large. Further, since it is in the form of a sheet, the degree of freedom of deformation is high, and it is widely used in dust masks, various air conditioner elements, air purifiers and the like.

  The fiber layer filter captures particles on the constituent fibers by a mechanical collection mechanism such as blocking, diffusion, inertial collision, etc., but these mechanisms vary depending on the particle, fiber diameter and passing wind speed, but 0.1 to 0 It is known that the filter collection efficiency has a minimum value around 3 μm.

  In order to improve the efficiency at the above-mentioned minimum value, a method using electric attractive force in combination is known. For example, there are known a method of applying charge to the particles to be collected, a method of dielectric polarization when using a filter by placing a filter between the electrodes, and a method of utilizing electrostatic attraction by holding an electric charge in an insulating material. ing. A filter in which a stable charge is held in a filter-constituting fiber is preliminarily used as an electret filter, an electrostatic filter and the like because it only performs a predetermined charging process and does not require energy such as an external power source.

  However, the electret filter has a problem that the electrostatic attraction is reduced as the particles are collected. Especially when the oil mist adheres to the surface, the droplet covers the surface and causes leakage and neutralization of the charge itself. Therefore, there is a problem that the performance is suddenly lowered. In order to solve such a problem, it is known to use a filter having higher oil repellency than that of a normal electret filter, that is, having a surface tension.

  Since electret filters use hydrophobic polymers such as polyolefin, polyester, and polycarbonate, a method of mixing an additive having a perfluoro group in the resin to further improve oil repellency (for example, patent documents) 1), a method of surface treatment with a processing agent having a perfluoro group (see, for example, Patent Document 2), a method of substituting hydrogen in a fiber constituent material with fluorine (for example, see Patent Document 3), and the like. It is known to be resistant.

JP 2009-6313 A JP 2009-242550 A Japanese translation of PCT publication No. 2002-519483

When a conventionally known oil-repellent filter is used, the spread of oil mist on the fiber surface is suppressed, so that the efficiency drop is moderate with respect to the particle load. On the other hand, the increase in the contact angle of the droplets increases the rate of increase in ventilation resistance at the same load, and there is a problem that the droplets are blocked due to the connection between the droplets when loaded more than a certain amount. . Moreover, even if oil repellency is imparted, it is not possible to completely prevent the dissipation of charges and the decrease in filter efficiency. Therefore, a filter that exhibits a high mechanical collection efficiency even when charges are lost is desired.
This invention solves such a conventional subject, and it aims at suppressing the fall in efficiency in an oil mist load, and also suppressing a raise of ventilation resistance while maintaining high efficiency at the time of charge loss. .

In order to solve the above problems, the filter of the present invention has the following configuration.
(1) A filter in which an electret fiber layer having oil repellency and an oil absorbing layer are laminated.
(2) The filter according to (1), wherein the oil absorption layer comprises a porous material.
(3) The filter according to (1), wherein the oil absorbing layer is made of a fiber sheet.
(4) The filter according to (3), wherein an oil absorbing layer composed of a fiber layer is disposed on the upstream side.
(5) The filter according to any one of (1) to (4), wherein the electret fiber layer is composed of fibers having a fiber diameter of 1 μm or less.

  According to the present invention, it is possible to obtain a filter in which the efficiency is less reduced with respect to the oil mist load and the increase in ventilation resistance is suppressed.

  Specific examples of the present invention are illustrated below, but an optimal configuration is selected for each application in accordance with the gist of the present invention.

  The filter of the present invention is characterized in that at least one layer is composed of an electret fiber layer. The fiber layer is formed by forming a woven fabric, a nonwoven fabric, a cotton shape, or the like into an appropriate shape and thickness according to the application, and is preferably a nonwoven fabric for a filter application.

  Nonwoven fabrics can be obtained by sheeting single-component short fibers, split short fibers, core-sheath composite short fibers by carding, airlaid, wet papermaking, etc. to obtain short fiber nonwoven fabrics, spunbond methods, meltblown methods, electro It is possible to use a conventionally known method such as a method of obtaining a long fiber nonwoven fabric by a spinning method or the like. Since a sheet having a fine fineness can be easily obtained by effectively using a mechanical collection mechanism, a melt blown method or an electrospinning method is preferable as a method for obtaining a nonwoven fabric, and the treatment of residual solvent is not required. From the viewpoint, the melt blown method and the melt electrospinning are most preferable.

  The electretization of the fiber layer is not particularly limited as long as desired characteristics can be obtained when the filter is used, and the fiber layer may be electretized either as a single fiber, during sheet molding, or after sheet molding. Also, as the electretization method, conventionally known methods such as polarization by high voltage, collision of charged ions, injection of charged particles, frictional charging, vapor and condensation, contact with spray liquid and collision charging can be used.

  The material used for the electret fiber layer is not particularly limited as long as it has desired characteristics, but it is preferably a synthetic resin material having high electrical resistance in consideration of processability to a fiber shape and the like. Specifically, the non-fluorine-based material is polyester, polycarbonate, polyamide, polyolefin, cyclic olefin, polyvinyl chloride, polyvinylidene chloride, etc., more preferably polyethylene, polybutene, polypropylene, polymethylpentene, polystyrene, cyclic olefin, etc. This is a polyolefin-based material, and since it has a good balance of hydrophobicity, electrical resistance, moldability, etc., an electret layer having excellent practical characteristics can be obtained.

  Since the above synthetic resin material does not substantially exhibit oil repellency, it is also preferable to use a synthetic resin material having a fluorine atom in advance, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer Copolymer (FEP), tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF) Tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (THV), and FEP, PFA, ETFE, PCTFE, PVDF, and THV are more preferable from the viewpoint of thermoplasticity.

  Conventionally known compounding agents and compounding compositions can be preferably used for the resin material in order to suppress deterioration of the resin itself and to further improve the charge stability of the electret fiber layer. For example, the compounding agent includes various metal salts, antioxidants, light stabilizers, and the like, and the compounding composition includes a polymer alloy obtained by mixing different resin components.

  When a non-fluorine resin is used for the electret fiber layer, it is characterized in that it is oil-repellent. Oil repellent treatment methods include mixing a fluororesin during fiber production, mixing a fluorine-based additive, forming a fiber or sheet, and then attaching a fluorine-based surface treatment agent, or coating the surface with a fluororesin. Conventionally known methods such as a method, a method of directly fluorinating the fiber surface with fluorine gas, and a method of grafting a fluorine compound can be preferably used. Among these, fluorination treatment after fiber production increases the degree of freedom of molding without being affected by the decomposition temperature and melt viscosity of the fluororesin, and is advantageous in terms of disposal treatment and production costs.

  The oil repellency of the material is preferably 40 mN / m or less, more preferably 35 mN / m or less, and more preferably 30 mN / m or less as the surface test solution tension required for penetration in the wetting tension test solution defined in JIS K6768 (1999). Is more preferable, and 25 mN / m or less is most preferable. These figures are DOP (surface tension: 31 mN / m) and PAO (for example, Emery 3004, surface tension: 29 mN / m), which are typical oil mists used in evaluation tests of dust masks and air conditioning elements, and oil in actual use environments. Considering durability against mist.

  The fiber diameter of the fiber used in the electret fiber layer of the present invention is preferably 0.001 to 100 μm, more preferably 0.005 to 20 μm, still more preferably 0.01 to 10 μm, and 0 Most preferably, the thickness is from 02 to 1 μm. The purpose of setting the fiber diameter in the above range is to reduce the ventilation resistance while increasing the mechanical collection efficiency.

  In the present invention, since it is intended to increase the efficiency of mechanical collection, the electret fiber layer may be a single manufacturing method or a uniform material made of a material, and the manufacturing method, the material, and two or more different fiber diameters may be used. A sheet material made of a material may be used.

  In the present invention, an oil absorbing layer is laminated on an electret fiber layer having oil repellency. Oil mists generally added in the filter field include DOP, PAO, DEHS as test particles, tobacco smoke, cooking oil, lubricating oil, agricultural chemicals, etc. as components loaded in the use environment. When used as a fiber layer, even if a low energy material such as polyethylene or polypropylene is used, the penetration and diffusion of droplets occurs.

  The material of the oil-absorbing layer is not particularly limited as long as it absorbs and transfers the droplets captured in the oil-repellent layer, but a sheet containing a porous material such as activated carbon, zeolite, pulp or processed on the surface, polypropylene fiber, It is preferable to use a fiber sheet made of polyethylene fiber, polystyrene fiber, polyamide fiber, polyacrylonitrile fiber, polyester fiber, polycarbonate fiber, cellulose fiber, rayon fiber or the like. More preferred are fiber sheets made of olefin fibers such as polypropylene fibers, polyethylene fibers, polystyrene fibers or polyester fibers, and most preferred are polypropylene fiber sheets.

  When using a fiber sheet for the oil-absorbing layer, it is also preferable to use one type or a combination of two or more types of fibers, and an appropriate material can be selected from the viewpoint of ventilation resistance and collection of coarse particles.

  The material used for the oil absorbing layer can be either a non-electretized material or an electretized material, and is preferably an electretized material.

  The type of fiber sheet used in the oil absorbing layer is not particularly limited as long as the desired configuration can be obtained, but the sheet is formed by a method such as a thermal bond method, a spun bond method, a spun lace method, an electrospinning method using a melting method and a solution method. Material can be used.

  The fiber constituting the fiber sheet used in the oil absorbing layer preferably has a fiber diameter of 0.005 to 100 μm, more preferably 0.01 to 20 μm, and still more preferably 0.5 to 5 μm. Most preferably, it is 1-10 micrometers.

The fiber diameter used for the oil repellent layer and the oil absorbing layer can be selected depending on the particles to be collected and the use environment, but the fiber used for the oil repellent layer is preferably finer.
More preferably, the fiber used for the oil repellent layer is a nanofiber having a fiber diameter of 1 μm or less, and the lipophilic layer is preferably a microfiber having a fiber diameter of about 1 μm to 10 μm.

The intention of this combination is with the following effects in mind.
First, by using nanofibers with a small fiber diameter, it is possible to increase the mechanical collection efficiency at the same ventilation resistance, and it is possible to improve the minimum collection efficiency when the charge is lost. .
Second, when nanofibers are used as a single layer, it is difficult to ensure the oil mist retention capacity because the interfiber distance and the volume of the filter medium are small. Rise is suppressed.
Third, nanofibers and microfibers have different minimum collection particle sizes at the same wind speed, and the minimum collection efficiency of microfibers has a maximum transmittance of about 0.3 μm, whereas the minimum collection efficiency of nanofibers Has a maximum transmittance of about 0.1 μm, so that the collection performance is complementary. Therefore, the minimum collection performance at the time of charge disappearance can be improved and the filter performance can be improved with respect to an object having a number mode diameter in a specific range such as test mist, tobacco smoke, and environmental oil mist.

  The filter of the present invention achieves efficiency improvement and long life against oil mist by combining at least one pair of oil-repellent layer and oil-absorbing layer, and can be used in combination with other components as necessary. That is, it is also preferable to use in combination with a prefilter layer, a fiber protective layer, a reinforcing member, a functional fiber layer, and the like.

  Examples of the prefilter layer and the fiber protective layer include a spunbond nonwoven fabric, a thermal bond nonwoven fabric, and urethane foam. Examples of the reinforcing member include a thermal bond nonwoven fabric and various nets. Examples thereof include a colored fiber layer for the purpose of viruses and identification and design. Providing these functions to the oil-absorbing layer is also preferable as a method for reducing thickness and ventilation resistance.

  The filter of the present invention can be widely used in filter applications for removing oil mist. For example, it can be widely used for dust and gas masks, household air purifiers, ventilation systems for buildings and vehicles, and protection of various devices.

Embodiments of the present invention will be described below.
(Filter test method)
The collection test for oil mist was carried out by the following method.
Load condition Load particle: Durasyn 164 (PAO: poly α-olefin Emery3004 equivalent)
Generator: TOPAS ATM-226 (Generated particle size around 0.3μm)
Load area: 50mmφ
Wind speed: 10cm / s
Load: 40 mg / min (0.055 mg / L: 21.1 g / m ² / min)
Efficiency meter conditions Evaluation particle: Atmospheric dust Measurement method: Light scattering counting method (range 0.3-0.5μm)
Evaluation wind speed: 10cm / s
The collection efficiency of the filter was calculated from the number of particles on the upstream side and downstream side according to the following equation.
Filter collection efficiency (%) = (1− (number of downstream side ÷ number of upstream side)) × 100
(Oil repellent test method)
The oil repellency test was carried out by the following test.
Test solutions of 30, 35, 40, 45, and 50 mN / m were prepared according to the formulation specified in JIS K6768 (1999). The osmosis | permeation degree was observed by leaving still 100 micrometers with the micropipette for microbe tests. When it exists as a droplet, the filter surface tension is assumed to be less than that value.
(Filter performance index)
QF values were used as a filter performance comparison. It shows the collection performance per unit ventilation resistance.
QF = (-Ln (number of downstream side ÷ number of upstream side)) ÷ ventilation resistance

Example 1
Fluorine-based oil repellent finishing agent (AG-manufactured by Asahi Glass Co., Ltd.) mixed with isopropyl alcohol (IPA) -water solution to a polypropylene sheet having a basis weight of 30 g / m ² , an average fiber diameter of 3 μm and a thickness of 0.25 mm obtained by the melt blown method E092) was infiltrated and then dried. The adhesion amount was 1 g / m ² and had an oil repellency of 30 mN / m or less. After the electretization treatment, the same unprocessed sheet (oil absorbing property of 35 mN / m or more) and a mesh-like adhesive resin were used for bonding. The initial efficiency was 99% and the ventilation resistance was 110 Pa. The efficiency after oil mist loading was 95%, and the ventilation resistance was 135 Pa. Moreover, the static elimination product efficiency of the laminated sheet was 45%, and the QF value was 0.0054.

(Example 2)
Fluorine-based oil repellent finishing agent (AG-E092 manufactured by Asahi Glass Co., Ltd.) mixed with IPA solution to a polypropylene sheet having a basis weight of 8 g / m ² , an average fiber diameter of 0.6 μm and a thickness of 0.1 mm obtained by the melt blown method. It was immersed and dried. The adhesion amount was 0.3 g / m ² and had oil repellency of 30 mN / m or less. After the electret treatment, the same unprocessed sheet (oil absorbing property of 35 mN / m or more) and a mesh-like adhesive resin were used for bonding. The initial efficiency was 99.5% and the ventilation resistance was 135 Pa. The efficiency after oil mist loading was 95%, and the ventilation resistance was 155 Pa. Moreover, the static elimination product efficiency of the laminated sheet was 81%, and the QF value was 0.012.

(Comparative Example 1)
The configuration of Example 1 was the same except that the oil repellent treatment was not performed.
The initial efficiency was 99% and the ventilation resistance was 110 Pa, but the efficiency after loading with oil mist was 48% and the ventilation resistance was 130 Pa. Moreover, the static elimination product efficiency of the laminated sheet was 45%, and the QF value was 0.0054.

(Comparative Example 2)
In the configuration of Example 2, only the fluorine processed sheet was used for the test. The initial efficiency was 99% and the ventilation resistance was 80 Pa, but the efficiency after loading with oil mist was 90% and the ventilation resistance was 280 Pa. Further, the efficiency of the static elimination product of the sheet alone was 70%, and the QF value was 0.015.

  In Comparative Example 1, the decrease in efficiency is larger than that in Example 1. In Comparative Example 2, the ventilation resistance is remarkably increased and the efficiency is greatly reduced compared to Example 2. Further, it can be seen that Example 2 gives high efficiency even in a state where no charge is present.

  It can be widely used in filter applications for removing oil mist. For example, it can be widely used for dust and gas masks, household air purifiers, ventilation systems for buildings and vehicles, and protection of various devices.

Claims (5)

  A filter in which an electret fiber layer having oil repellency and an oil absorbing layer are laminated.   The filter according to claim 1, wherein the oil absorbing layer comprises a porous material.   The filter according to claim 1, wherein the oil absorbing layer comprises a fiber sheet.   The filter according to claim 3, wherein an oil absorbing layer made of a fiber layer is disposed on the upstream side.   The filter according to any one of claims 1 to 4, wherein the electret fiber layer is composed of fibers having a fiber diameter of 1 µm or less.