JP2014124578A - Filtration material for filter and production method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filtration material for a filter having low pressure loss, a high collection rate of particles, particularly the particles with a particle diameter of about 0.1-0.3 μm and high durability and to provide a production method of the same.SOLUTION: A filtration material for a filter comprises: a PTFE fiber layer which is composed of a PTFE fiber having an average fiber diameter of 0.3-2 μm and whose basis weight is 1-45 g/m; and a fluorine resin nanofiber layer which is layered on the PTFE fiber layer, which has an average fiber diameter of 20-150 nm, which is composed of the fiber of a fluorine resin selected from the group consisting of PVDF, PFA, FEP and ETFE and whose basis weight is 0.05-0.2 g/m.

Description

  The present invention relates to a filter medium and a manufacturing method thereof, and more particularly to a filter medium suitable for use in clean room ventilation, turbine intake, and the like, and a manufacturing method thereof.

An air filter for collecting (capturing) fine particles in the air is required to collect particles with high efficiency and to have a low pressure loss.
Conventionally, various filter media have been developed. For example, in Patent Document 1, a polytetrafluoroethylene (hereinafter also referred to as “PTFE”) porous membrane, a breathable support material, and an electrospinning method are used. , A filter medium including a web layer made of polymer fibers is disclosed, and it is described that the average fiber diameter of the polymer fibers may be 10 nm to 5 μm. As a polymer, polyvinylidene fluoride (hereinafter referred to as “PVDF”) is also disclosed. And polyvinylidene fluoride-hexafluoropropylene copolymers ([0007], [0020], [0021], etc.).

  Patent Document 2 discloses a filter unit including a filter medium and a support frame that supports the filter medium, and the filter medium includes a PTFE porous membrane and fibers disposed so as to sandwich the porous membrane. And a non-woven fabric of a polymer (eg, polyethylene, polypropylene) having an average fiber diameter of about 0.02 to 1 μm formed by an electrospinning method. ([0005], [0017], [0018], etc.).

JP 2006-326579 A JP 2007-75739 A

  However, the conventional filter has room for further improvement in terms of collecting particles with a high collection rate, particularly particles having a particle size of about 0.1 to 0.3 μm. Moreover, in order to reduce the power consumption required for ventilation of an air conditioner or the like to which the filter is attached, that is, in order to save energy, it is necessary to reduce the pressure loss of the filter. Furthermore, it is desired to improve the durability of the filter.

  Accordingly, the present invention provides a filter medium having a low pressure loss, a high collection rate of particles, particularly particles having a particle size of about 0.1 to 0.3 μm, and a high durability, and the production of such a filter medium. It aims to provide a method.

The filter medium for the filter according to the present invention is:
A PTFE fiber layer having an average fiber diameter of 0.3 to 2 μm, made of polytetrafluoroethylene (hereinafter also referred to as “PTFE”) fiber, and having a basis weight of 1 to 45 g / m ² ;
Polyvinylidene fluoride (hereinafter also referred to as “PVDF”), tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer (hereinafter referred to as “PFA”) having an average fiber diameter of 20 to 150 nm, which is laminated on the PTFE fiber layer. ), Tetrafluoroethylene / hexafluoropropylene copolymer (hereinafter also referred to as “FEP”) and ethylene / tetrafluoroethylene copolymer (hereinafter also referred to as “ETFE”). It has a fluororesin nanofiber layer made of resin fibers and having a basis weight of 0.05 to 0.2 g / m ² .

The method for producing a filter medium according to the present invention includes a step of laminating the PTFE fiber layer and the fluororesin nanofiber layer.
The method for producing the filter medium may include a step of producing the fluororesin fiber by an electrospinning method from a spinning solution containing the fluororesin, an ionic surfactant, and a solvent.

  The filter medium for a filter according to the present invention has low pressure loss, a high collection rate of particles (particularly particles having a particle size of about 0.1 to 0.3 μm), and high durability. Moreover, according to the filter medium manufacturing method of the present invention, such a filter medium can be manufactured.

The present invention will be described in detail below.
The filter medium according to the present invention has a PTFE fiber layer and a fluororesin nanofiber layer laminated on the PTFE fiber layer.

<PTFE fiber layer>
Since the filter medium for a filter according to the present invention has the PTFE fiber layer, the filter medium is excellent in durability. Since the fiber diameter (pore diameter) of the PTFE fiber layer is large, large particles are collected and the filter medium (fluororesin nano There is an advantage of preventing clogging of the fiber layer).

  The average fiber diameter of the PTFE fibers constituting the PTFE fiber layer is 0.3 to 2 μm, preferably 0.5 to 2 μm, more preferably 0.5 to 1.5 μm. When the average fiber diameter is in this range, there are advantages that the particle collecting performance is excellent and the filtration resistance can be reduced. This average fiber diameter was selected by randomly selecting a scanning electron microscope (SEM) observation region for the PTFE fiber (group) to be measured, and then subjecting this region to SEM observation (magnification: 10,000 times). This is a value calculated based on the measurement results of 10 PTFE fibers selected for these PTFE fibers.

The basis weight of the PTFE fiber layer is 1 to 45 g / m ² , preferably 5 to 40 g / m ² , and more preferably 5 to 30 g / m ² . When the basis weight is in this range, the particle collection performance is excellent and the filtration resistance can be reduced.
Moreover, the thickness of the PTFE fiber layer is preferably 10 to 250 μm, and more preferably 20 to 100 μm.

(Method for producing PTFE fiber layer)
As a manufacturing method of the PTFE fiber layer, a conventionally known manufacturing method can be adopted. For example, the following method described in JP 2012-515850 A, that is,
A method of creating a PTFE fiber layer comprising:
Providing a dispersion comprising PTFE, a fiberizing polymer, and a solvent and having a viscosity of at least 50,000 cP;
Providing a load source and a device having a target at a distance from the load source;
Providing a voltage source to create a first charge at the load source and an opposite charge at the target, and electrostatically charging the dispersion by contacting the load source;
Collecting the electrostatically charged dispersion on the target to produce a mat precursor;
An electrospinning method such as a method including heating the mat precursor to form the PTFE mat by removing the solvent and the polymer to be fiberized can be employed.

During the electrospinning, the average fiber diameter tends to decrease by decreasing the humidity, decreasing the nozzle diameter, increasing the applied voltage, or increasing the voltage density.
The basis weight and thickness tend to increase by increasing the spinning time or increasing the number of spinning nozzles.

<Fluoropolymer nanofiber layer>
The fluororesin nanofiber layer is made of a fluororesin fiber selected from the group consisting of PVDF, PFA, FEP and ETFE (hereinafter also referred to as “fluororesin nanofiber”). Since the said fluororesin nanofiber layer consists of these resin, it is excellent in durability.

  The average fiber diameter of the fibers is 20 to 150 nm, preferably 20 to 100 nm, and more preferably 40 to 100 nm. When the average fiber diameter is in this range, there are advantages that the particle collecting performance is excellent and the filtration resistance can be reduced. The average fiber diameter was determined by randomly selecting a scanning electron microscope (SEM) observation region for the fluororesin fiber (group) to be measured, and performing SEM observation (magnification: 10,000 times) on this region. This is a value calculated based on the measurement results of 10 fluororesin fibers selected for the purpose.

Basis weight of the fluorine resin nanofiber layer, 0.05~0.2g / m ^2, preferably not 0.1 to 0.2 g / m ^2, more preferably a 0.1~0.15g / m ^2. When the basis weight is in this range, there are advantages that the particle collection performance is excellent and the filtration resistance can be reduced.
Further, the thickness of the fluororesin nanofiber layer is preferably 10 μm or less, more preferably 1 μm or less, and the lower limit may be, for example, about 0.1 μm.

(Method for producing fluororesin nanofiber layer)
The fluororesin nanofiber layer preferably has a merit that a fine and uniform fiber can be produced. From the spinning solution containing a fluororesin, an ionic surfactant and a solvent, the electrospinning (electrostatic spinning) method is preferably used. It is manufactured by manufacturing fluororesin nanofibers and accumulating them in a sheet form.

When producing the filter medium according to the present invention, fluororesin nanofibers may be accumulated in a sheet form on the PTFE fiber layer.
The fluororesin is contained, for example, in an amount of 5 to 60% by weight, preferably 10 to 50% by weight in the spinning solution, although it depends on the type of resin.

As the fluororesin, PVDF and ETFE are preferable, and PVDF is particularly preferable because there is a merit that a thin and uniform fiber can be easily manufactured.
Examples of the ionic surfactant include a fluorine-based surfactant (that is, a surfactant having a fluorine atom. For example, an ammonium salt of an acid having a perfluoroalkyl group), a hydrocarbon-based surfactant (with a main chain). Surfactants composed of alkyl groups), silicone surfactants (surfactants having silicon atoms), and the like.

  If it is a commercial item as said fluorosurfactant, it is a footgent (registered trademark) 100 (anionic fluorosurfactant), a footgent (registered trademark) 310 (cationic fluorosurfactant). (Neos Co., Ltd.), Megafac F114 (anionic fluorosurfactant, DIC Corp.), Surflon S-231 (amphoteric fluorosurfactant, Asahi Glass Co., Ltd.), etc. .

The surfactant is contained in the spinning solution in an amount of, for example, 0.1 to 10% by weight, preferably 1 to 5% by weight.
According to the method for producing the fluororesin nanofibers by the electrospinning method, since the spinning solution contains an ionic surfactant, the stability of the spinning solution against the electric charge is increased during electrospinning, and thus the fluororesin fiber It is considered that the diameter can be reduced. By using the fluorosurfactant as the ionic surfactant, it is considered that the stability of the spinning solution during electrospinning can be particularly enhanced.

  The solvent is not particularly limited as long as it can dissolve the fluororesin, and examples thereof include dimethylacetamide, dimethylformamide, tetrahydrofuran, methylpyrrolidone, xylene, acetone, chloroform, ethylbenzene, and cyclohexane. These solvents may be used individually by 1 type, and may be used as a mixed solvent which combined 2 or more types.

The solvent is contained in the spinning solution in an amount of, for example, 30 to 90% by weight, preferably 45 to 85% by weight.
The spinning solution may further contain an additive such as a viscosity modifier.

The spinning solution can be produced by mixing the above-described fluororesin, surfactant, solvent, and if necessary, an additive by a conventionally known method.
Examples of preferred embodiments of the spinning solution include the following spinning solution (1).

Spinning solution (1): Spinning solution containing 5 to 30% by weight, preferably 10 to 20% by weight of PVDF, and 1 to 10% by weight, preferably 2 to 5% by weight of ionic surfactant When performing electrospinning Is preferably 5 to 50 kV, more preferably 20 to 40 kV.

The tip diameter (outer diameter) of the spinning nozzle is preferably 0.1 to 2.0 mm, more preferably 0.2 to 1.0 mm, and still more preferably 0.20 to 0.85 mm.
More specifically, for example, when the spinning solution (1) is used, the applied voltage is preferably 10 to 50 kV, more preferably 20 to 40 kV, and the tip diameter (outer diameter) of the spinning nozzle is used. ) Is preferably 0.2 to 0.85 mm.

  The average fiber diameter is obtained by using the spinning solution having a low concentration (fluororesin concentration), decreasing the humidity, decreasing the nozzle diameter, increasing the applied voltage, or increasing the voltage density during electrospinning. It tends to be smaller.

On the other hand, the proportion of the fluororesin fibers having a specific range of fiber diameters is determined by using the spinning solution having a high concentration (fluororesin concentration), increasing the humidity, increasing the nozzle diameter, and the applied voltage during electrospinning. There is a tendency to increase by decreasing or decreasing the voltage density.
The basis weight and thickness tend to increase by increasing the spinning time or increasing the number of spinning nozzles.

<Filter media for filters>
The filter medium for a filter of the present invention can be used as a filter for collecting particles contained in various filtration fluids (for example, gas, liquid, etc.). The filter medium of the present invention is particularly suitable as a filter medium for air filters. When used in this way, the pressure loss is low, the collection rate of particles having a diameter of about 0.1 to 0.3 μm is high, and the durability is high. The nature is also high. For example, the pressure loss is 160 Pa or less, preferably 150 Pa or less, the 0.1 μm particle capture rate is 99.9% or more, preferably 99.99% or more, and the 0.3 μm particle capture rate is 99.9% or more, preferably Is 99.99% or more. In addition, these physical property values are values when measured by a method employed in Examples described later. Further, the shrinkage ratio ((dimension before heat treatment−dimension after heat treatment) / dimension before heat treatment) by heat treatment (120 ° C., heating for 60 minutes), which is an index of durability, is, for example, 1% or less, preferably 0 .1% or less.

  The filter medium of the present invention is preferably used with the PTFE fiber layer facing the upstream side of various filtration fluids and the fluororesin nanofiber layer facing the downstream side. The PTFE fiber layer collects particles having a large particle diameter by directing the PTFE fiber layer having a larger fiber diameter of the fluororesin fiber constituting the layer to the upstream side than the fluororesin nanofiber layer. It works as a pre-filter that prevents clogging of the fluororesin nanofiber layer, and can prevent performance deterioration of the filter medium.

  The filter medium of the present invention is produced by a production method including a step of forming the fluororesin nanofiber layer on at least one surface of the PTFE fiber layer. When the PTFE fiber layer is directed upstream and the fluororesin nanofiber layer is directed downstream as described above, the fluororesin nanofiber layer is formed only on one surface of the PTFE fiber layer. It is preferable to do.

  The filter medium for a filter of the present invention may be configured such that the PTFE fiber layer and the fluororesin nanofiber layer are each composed of two or more layers. In that case, two or more layers having different average diameters of fibers constituting each layer are used. The PTFE fiber layer may be composed of two or more fluororesin nanofiber layers having different fiber materials and average diameters.

  The PTFE fiber layer and the fluororesin nanofiber layer may be melt-bonded, and may be bonded by providing an adhesive layer between these layers, or may be melt-bonded or provided with an adhesive layer. It is also possible to simply stack them without using them.

  The filter medium of the present invention may further include a support layer. When the filter medium of the present invention is provided with a support layer, it is preferably laminated in the order of PTFE fiber layer, fluororesin nanofiber layer, support layer, or support layer, PTFE fiber layer, fluororesin nano The fiber layer and the support layer are laminated in this order.

  As the support layer, a conventionally known support layer in a filter medium such as a filter medium for air filters can be used, which has better air permeability than the PTFE fiber layer and the fluororesin nanofiber layer, and has an average fiber diameter, for example. Examples thereof include a glass nonwoven fabric, a cellulose nonwoven fabric, a polyolefin nonwoven fabric, a nylon nonwoven fabric, a polyester nonwoven fabric, an aramid nonwoven fabric, and a fluororesin nonwoven fabric composed of fibers of about 3 to 50 μm. Among these, from the viewpoint of durability, it is preferable to use a glass nonwoven fabric or a fluororesin nonwoven fabric.

  The filter medium for the filter may be subjected to conventionally known processing within a range not impairing its performance, for example, may be subjected to pleating.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these Examples.
<Measurement method>
Various physical properties of the fluororesin fibers and filter media prepared in Examples and Comparative Examples were measured by the following methods.

1. For each fluororesin fiber (group) produced in the fluororesin examples and comparative examples, a region for SEM observation was randomly selected, and this region was observed with SEM (device: S-3400N (manufactured by Hitachi High-Technologies Corporation). ), Magnification: 10,000 times), 10 fluororesin fibers were randomly selected, and the average (arithmetic average) fiber diameter was determined based on the measurement results of these fluororesin fibers.

2. Filter media (weight)
The basis weight of each layer was measured according to JIS L 1913 (2010). At this time, the basis weight of the fluororesin nanofiber layer was calculated from the difference between the weight of the PTFE fiber layer and the weight of the filter medium formed by integrating the fluororesin nanofibers on the PTFE fiber layer.

(Particle collection rate, pressure loss)
About each filter medium manufactured by the Example and the comparative example, the particle collection rate was measured according to JIS B 9908. At this time, a filter medium cut into a size of 200 mm × 200 mm was used instead of the filter unit, and atmospheric dust (including dust having a particle diameter of 0.10 μm to 2.0 μm) was used as measurement dust. When measuring the particle collection rate, the air flow rate was set to a surface velocity of 5.3 cm / s. In addition, it measured for the layer which the number described in Table 1 among each layer which comprises the filter medium for filters was set to the upstream.
Further, along with this measurement, the pressure difference (that is, pressure loss) between the upstream side and the downstream side of the filter medium was measured with a fine differential pressure gauge.

(durability)
The durability of the filter media was evaluated by the following method.
A filter medium was cut into a size of 200 mm in length and 200 mm in width to prepare a sample. This sample was heat-treated by being left unfixed in an electric furnace maintained at 120 ° C. for 60 minutes. Thereafter, the sample was taken out from the electric furnace, air-cooled to room temperature, and the vertical length (a) and the horizontal length (b) were measured as dimensions after the heat treatment. Based on vertical length (A = 200 (mm)) and horizontal length (B = 200 (mm)) before heat treatment, and vertical length (a) and horizontal length (b) after heat treatment Thus, the shrinkage ratio in the vertical direction and the horizontal direction was calculated from the following formula.

[Example 1]
(1a. Production of PTFE fiber layer)
A 30 μm thick PTFE fiber layer made only of PTFE fibers was produced by a conventionally known method (electrospinning method). Table 1 shows the average fiber diameter of the obtained PTFE fiber and the physical properties of the PTFE fiber layer.

Furthermore, a 20 cm × 20 cm square glass nonwoven fabric as a support layer (average fiber diameter 20 μm, thickness 0.15 mm, basis weight 40 g / m ² , trade name: Grabest (registered trademark) SYS-041, manufactured by Olivest Co., Ltd.) The PTFE fiber layer was laminated on one of the surfaces without bonding.

(1b. Manufacture of PVDF nanofiber layer / manufacture of filter media)
14% by weight of PVDF (polyvinylidene fluoride, weight average molecular weight: 275,000, manufactured by Aldrich), an anionic fluorosurfactant (Furgent (registered trademark) 100, manufactured by Neos Co., Ltd.) as a surfactant, the following A spinning solution containing 3% by weight of “F100”) and 83% by weight of dimethylacetamide (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd., hereinafter also referred to as “DMAc”) as a solvent was prepared.

  This spinning solution was filled in a solution filling part of an electrospinning apparatus (ES-2300 (device name), manufactured by Huence Co., Ltd.) and subjected to electrospinning for 10 minutes by applying a voltage of 40 kV to produce PVDF fibers. At this time, the PTFE fiber layer laminated on the glass nonwoven fabric produced in 1a above was used as a collector, and electrospinning was performed while moving the spinning nozzle, whereby the PTFE fiber layer and the glass nonwoven fabric were moved on the glass nonwoven fabric. A filter medium for a filter in which a PVDF nanofiber layer having a uniform thickness made of PVDF fibers was laminated was manufactured. The tip diameter (outer diameter) of the spinning nozzle was 0.2 mm (gauge: 30 G), and the distance from the tip of the spinning nozzle to the collector was 19 cm.

(1c. Manufacture of filter media having filter layers on both sides)
Further, the filter medium for the filter and the PVDF nanofiber layer are placed on one surface of a 20 cm × 20 cm square glass nonwoven fabric (Gravest (registered trademark) SYS-041, manufactured by Olivest Co., Ltd.) as a support layer. It laminated | stacked, without adhering through.

  Table 1 shows the average fiber diameter of the obtained PVDF fibers, the basis weight of the PVDF nanofiber layer, and the characteristics of the filter medium (the characteristics of the filter medium were measured with the support layers on both sides).

  Moreover, the filter medium for a filter by which the said PTFE fiber layer and PVDF nanofiber layer were laminated | stacked on the glass nonwoven fabric by the method similar to said 1a and 1b was manufactured, and the durability was evaluated. The results are shown in Table 2.

[Example 2]
When manufacturing the PVDF nanofiber layer, the weight of PVDF contained in the spinning solution is changed to 17% by weight, the weight of DMAc is changed to 80% by weight, and the tip diameter of the spinning nozzle is set to 0.4 mm (gauge: 27G). Except having changed, operation similar to Example 1 was performed and the filter medium for filters (filter medium for filters which has a support layer on both surfaces) was manufactured.

  Table 1 shows the average fiber diameter of the obtained PVDF fibers, the basis weight of the PVDF nanofiber layer, and the characteristics of the filter medium (the characteristics of the filter medium were measured with the support layers on both sides).

[Comparative Example 1]
Porous PTFE layer (“sa-PTFE ^TM series” manufactured by Nippon Valqua Industries, Ltd.), average pore diameter 0.88 μm on a 20 cm × 20 cm square glass nonwoven fabric (Gravest (registered trademark) SYS-041, manufactured by Olivest Co., Ltd.) ) Was laminated without adhering to each other to produce a filter medium. Table 1 shows the characteristics of the obtained filter medium.

[Comparative Example 2]
The same operation as 1a of Example 1 was performed to produce a laminate composed only of a glass nonwoven fabric and a PTFE fiber layer, and this was used as a filter medium. Table 1 shows the characteristics of the filter medium.

[Comparative Example 3]
The spinning solution was changed to a spinning solution containing 25% by weight of PVDF, 3% by weight of F100, and 72% by weight of DMAc, and the tip diameter (outer diameter) of the electrospinning nozzle was set to 0.8 mm (gauge: 21G). A filter medium (filter medium having a support layer on both sides) was produced by performing the same operation as in Example 1 except that was changed to 3 minutes. Table 1 shows the average fiber diameter of the obtained PVDF fibers, the basis weight of the PVDF nanofiber layer, and the characteristics of the filter medium (the characteristics of the filter medium were measured with the support layers on both sides).

[Comparative Example 4]
Except that the collector was changed to a porous PTFE layer (“Poreflon (registered trademark) membrane series” manufactured by Sumitomo Electric Industries, Ltd., average pore diameter: 1 μm), the same operation as in Examples 1a and 1b was performed to produce a filter medium. Durability was evaluated. The results are shown in Table 2.

(Production example of fluororesin fiber)
[Production Example 1-1]
A spinning solution containing 17% by weight of PVDF (weight average molecular weight: 275,000, manufactured by Aldrich) as a fluororesin, 3% by weight of F100 and 80% by weight of DMAc as a solvent was prepared.

This spinning solution was filled in a solution filling part of an electrospinning apparatus (ES-2300 (device name), manufactured by Huence Co., Ltd.), applied with a voltage of 40 kV, and subjected to electrospinning for 30 minutes to produce a fluororesin fiber. . The tip diameter (outer diameter) of the spinning nozzle was 0.8 mm (gauge: 21 G), and the distance to the collector (aluminum foil) was 13 cm.
Table 3 shows the average fiber diameter of the obtained fluororesin fibers.

[Production Examples 1-2 to 1-7]
A PVDF fiber was produced by performing the same operation as in Production Example 1-1 except that various conditions were changed as described in Table 3. These average fiber diameters are also shown in Table 3.

Claims (3)

A PTFE fiber layer comprising polytetrafluoroethylene fibers having an average fiber diameter of 0.3 to ² μm and a basis weight of 1 to 45 g / m ² ;
Polyvinylidene fluoride, tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer and ethylene laminated on the PTFE fiber layer and having an average fiber diameter of 20 to 150 nm A filter medium for a filter comprising a fluororesin fiber selected from the group consisting of tetrafluoroethylene copolymers and a fluororesin nanofiber layer having a basis weight of 0.05 to 0.2 g / m ² . A PTFE fiber layer comprising polytetrafluoroethylene fibers having an average fiber diameter of 0.3 to ² μm and a basis weight of 1 to 45 g / m ² ;
A group consisting of polyvinylidene fluoride, tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, tetrafluoroethylene / hexafluoropropylene copolymer and ethylene / tetrafluoroethylene copolymer having an average fiber diameter of 20 to 150 nm. The manufacturing method of the filter medium for filters of Claim 1 including the process of laminating | stacking the fluororesin nanofiber layer which consists of the fiber of the fluororesin chosen from these, and a fabric weight is 0.05-0.2 g / m < ² >.   The method for producing a filter medium for a filter according to claim 2, comprising a step of producing a fiber of the fluororesin by an electrospinning method from a spinning solution containing the fluororesin, an ionic surfactant and a solvent.