JP2023012165A - Mask filter material and mask - Google Patents

Abstract

To provide a mask filter material capable of holding excellent collection performance even after repeated washing and being excellent in washing durability, and a mask.SOLUTION: There is provided a mask filter material made of non-woven fabric, in which the non-woven fabric comprises nanofiber having a fiber diameter of 100-1000 nm and heat-fusible binder fiber.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a filter medium for a mask and a mask which are excellent in washing durability and which can maintain excellent collection performance even after repeated washing.

Conventionally, masks have been used in various environments in daily life to prevent viruses, hay fever, and colds. Masks are required to have a high collection rate of viruses, pollen, and dust, and to have good breathability. Furthermore, in recent years, as the number of occasions to use masks has increased, there is a demand for not only disposable masks but also washing durability such that they can be used repeatedly after washing.

In general, there are many masks on the market that improve the collection rate while maintaining high breathability by subjecting the filter medium to electret processing. Electret processing is to collect particles by electrostatic force and improve the collection efficiency by electrifying the fibers constituting the filter medium. However, there is a problem that as the collected particles are deposited on the filter medium, the electric charges on the constituent fibers are neutralized and the electrostatic force is reduced. Furthermore, there is a problem that the loss of electric charges is accelerated by oil mist such as cigarette smoke and surfactants used in washing, resulting in a significant reduction in electrostatic force.

For example, Patent Literature 1 proposes a method of increasing the physical collection efficiency by mixing electret fibers having a small fiber diameter. However, since the diameter of the fibers used is on the order of microns, there is a problem that sufficient collection performance cannot be obtained when the electrostatic force is completely lost.
Patent document 2 proposes a filter medium for a mask containing nanofibers having a fiber diameter of 1000 nm or less, but it cannot be said to be satisfactory in terms of washing durability.

JP-A-10-46460 JP 2019-199668 A

The present invention has been made in view of the above background, and an object thereof is to provide a filter medium for a mask and a mask which are excellent in washing durability and which can maintain excellent collection performance even after repeated washing.

As a result of intensive research, the present inventors have invented a filter medium for a mask and a mask that can achieve the above-mentioned problems.

Thus, according to the present invention, there is provided "a filter material for a mask made of a nonwoven fabric, characterized in that the nonwoven fabric contains nanofibers having a fiber diameter of 100 to 1000 nm and heat-fusible binder fibers. .” is provided.
In this case, the nanofibers and/or the heat-fusible binder fibers are preferably polyester fibers, polyolefin fibers, or nylon fibers. The nonwoven fabric preferably contains 5% or more of the nanofiber based on the weight of the nonwoven fabric, and preferably contains 50% or more of the heat-fusible binder fiber based on the weight of the nonwoven fabric.

Moreover, in the mask filter material of the present invention, it is preferable that the basis weight is within the range of 20 to 80 g/m ² . Moreover, it is preferable that the tensile strength in the MD direction is 20 N/15 mm or more. Moreover, it is preferable that the elongation is 10% or more in both the vertical and horizontal directions. Moreover, it is preferable that the 0.3 μm particle collection rate after the static elimination treatment is 95% or more. Moreover, it is preferable that the 0.3 μm particle capture rate after the washing test is 95% or more. Moreover, it is preferable that the time for the water droplets to disappear after dropping the distilled water is 1 minute or less.
Further, according to the present invention, there is provided a mask using the filter medium for a mask.

ADVANTAGE OF THE INVENTION According to this invention, the filter medium for masks and the mask which are excellent in washing durability which can maintain the outstanding collection performance after repeated washing are obtained.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. The mask filter medium of the present invention is composed of nanofibers having a fiber diameter of 100 to 1000 nm (preferably 200 to 800 nm) and a nonwoven fabric containing heat-fusible binder fibers. In the nanofibers, if the fiber diameter is larger than 1000 nm, the collection performance may be lowered. Conversely, when the diameter is less than 100 nm, the fibers themselves have difficulty in dispersibility, and the fibers may aggregate to reduce the collection performance. Furthermore, the fibers may pass through the mesh in the papermaking process, making it difficult to form the sheet.

Here, the fiber diameter can be measured by taking a single fiber cross-sectional photograph at a magnification of 30,000 using a transmission electron microscope TEM. At that time, in a TEM having a length measurement function, the measurement can be performed by utilizing the length measurement function. Also, with a TEM that does not have a length measuring function, it is sufficient to make an enlarged copy of the photograph taken and measure it with a ruler after considering the scale. When the cross-sectional shape of the single fiber is an irregular cross-section other than a circular cross-section, the diameter of the circumscribed circle of the cross-section of the single fiber is used as the fiber diameter.

In the nanofibers, the aspect ratio (ratio L/D of fiber length L to fiber diameter D) is preferably in the range of 100-2500.

Examples of the fiber type of the nanofiber include polyester fiber, polyolefin fiber, and nylon fiber. Among them, polyester fibers are preferred. Polyesters forming polyester fibers include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate, and these as main repeating units, and isophthalic acid as other comonomer components. Aromatic dicarboxylic acids such as 5-sulfoisophthalic acid metal salts, adipic acid, aliphatic dicarboxylic acids such as sebacic acid, hydroxycarboxylic acid condensates such as ε-caprolactone, diethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene A copolymer obtained by further copolymerizing a glycol component such as glycol is preferred. It may be material-recycled or chemically-recycled polyester, or polyethylene terephthalate using a monomer component obtained from biomass, that is, a substance derived from organisms, as described in JP-A-2009-091694. Furthermore, polyesters obtained using a catalyst containing a specific phosphorus compound and titanium compound as described in JP-A-2004-270097 and JP-A-2004-211268 may also be used.

Although the method for producing the nanofiber is not particularly limited, International Publication No. 2005/
The method disclosed in 095686 is preferred. That is, in terms of the fiber diameter and its uniformity, the island component composed of the fiber-forming thermoplastic polymer and the polymer that dissolves more easily in an alkaline aqueous solution than the fiber-forming thermoplastic polymer (hereinafter referred to as "easily soluble It is preferable to use a conjugate fiber having a sea component, which is composed of a polymer, which is subjected to alkali weight reduction processing, and to dissolve and remove the sea component.

Here, when the dissolution rate ratio of the readily soluble alkaline aqueous solution polymer that forms the sea component to the fiber-forming thermoplastic polymer that forms the island component is 200 or more (preferably 300 to 3000), the island separation property is good. is preferable. If the dissolution rate is less than 200 times, the separated island component in the surface layer of the fiber cross section is dissolved while the sea component in the central part of the fiber cross section is dissolved, so that the sea component is dissolved due to the small fiber diameter. Despite the weight reduction, the sea component in the center of the fiber cross section cannot be completely dissolved and removed, leading to uneven thickness of the island component and solvent erosion of the island component itself, making it impossible to obtain fibers with a uniform fiber diameter. There is a risk.

Preferred examples of readily soluble polymers forming the sea component include polyesters, aliphatic polyamides, and polyolefins such as polyethylene and polystyrene, which are particularly good in forming fibers. More specific examples include polylactic acid, ultra-high molecular weight polyalkylene oxide condensed polymers, and polyester copolymers of polyalkylene glycol compounds and 5-sodium sulfoisophthalic acid, which are readily soluble in alkaline aqueous solutions and are therefore preferred. Here, the alkaline aqueous solution refers to potassium hydroxide, sodium hydroxide aqueous solution, and the like. Other combinations of sea components and solutions that dissolve the sea components include formic acid for aliphatic polyamides such as nylon 6 and nylon 66; Hydrocarbon-based solvents such as hot toluene and xylene for low-density polyethylene) and hot water for polyvinyl alcohol and ethylene-modified vinyl alcohol-based polymers can be mentioned as examples.

Among polyester-based polymers, polyethylene terephthalate-based copolymer having an intrinsic viscosity of 0.4 to 0.6 obtained by copolymerizing 6 to 12 mol% of 5-sodium sulfoisophthalic acid and 3 to 10% by mass of polyethylene glycol having a molecular weight of 4000 to 12000. Polymerized polyesters are preferred. Here, 5-sodium sulfoisophthalic acid contributes to improving hydrophilicity and melt viscosity, and polyethylene glycol (PEG) improves hydrophilicity. In addition, the higher the molecular weight of PEG, the more hydrophilic it is thought to be due to its higher-order structure. there is a possibility. Further, when the copolymerization amount is 10% by mass or more, the melt viscosity may decrease.

On the other hand, preferable examples of the sparingly soluble polymer forming the island component include polyamides, polyesters, polyphenylene sulfides, polyolefins, and the like. Specifically, for applications that require mechanical strength and heat resistance, polyesters such as polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and isophthalate having these as main repeating units acids, aromatic dicarboxylic acids such as 5-sulfoisophthalic acid metal salts, adipic acid, aliphatic dicarboxylic acids such as sebacic acid, hydroxycarboxylic acid condensates such as ε-caprolactone, diethylene glycol, trimethylene glycol, tetramethylene glycol, hexa A copolymer with a glycol component such as methylene glycol is preferred. Among polyamides, aliphatic polyamides such as nylon 6 (Ny-6) and nylon 66 (Ny-66) are preferred. In addition, polyolefins are resistant to acids and alkalis, etc., and have a relatively low melting point, so they can be used as a binder component after being taken out as ultrafine fibers. Preferred examples include low-density polyethylene, linear low-density polyethylene, isotactic polypropylene, ethylene-propylene copolymer, and ethylene copolymer of vinyl monomers such as maleic anhydride. In particular, polyesters such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene terephthalate isophthalate having an isophthalic acid copolymerization rate of 20 mol% or less, polyethylene naphthalate, or aliphatic polyamides such as nylon 6 and nylon 66 Since it has heat resistance and mechanical properties due to its high melting point, it can be applied to applications requiring heat resistance and strength compared to ultrafine fibrillated fibers made of polyvinyl alcohol/polyacrylonitrile mixed spun fibers. The island component is not limited to a circular cross section, and may be an irregular cross section such as a triangular cross section or a flat cross section.

The polymer forming the sea component and the polymer forming the island component may optionally contain delustering agents, organic fillers, and antioxidants as long as they do not affect the spinnability and physical properties of the main fiber after extraction. agents, heat stabilizers, light stabilizers, flame retardants, lubricants, antistatic agents, antirust agents, cross-linking agents, foaming agents, fluorescent agents, surface smoothing agents, surface gloss improvers, release improvers such as fluororesins, etc. There is no problem even if it contains various additives of.

In the sea-island composite fiber, the melt viscosity of the sea component during melt spinning is preferably higher than the melt viscosity of the island component polymer. In such a relationship, even if the composite mass ratio of the sea component is less than 40%, it is difficult for the islands to join together or for most of the island components to join together to make the fiber different from the sea-island composite fiber. .

A preferred melt viscosity ratio (sea/island) is in the range of 1.1 to 2.0, particularly 1.3 to 1.5. On the other hand, if it exceeds 2.0 times, the viscosity difference is too large and the spinning condition tends to decrease.

Next, the number of islands is preferably 100 or more (more preferably 300 to 1000). Further, the sea-island composite mass ratio (sea:island) is preferably in the range of 20:80 to 80:20. Within this range, the thickness of the sea component between the islands can be reduced, the sea component can be easily removed by dissolution, and the island component can be easily converted into ultrafine fibers, which is preferable. If the proportion of the sea component exceeds 80% by mass, the thickness of the sea component becomes too thick. easier.

As the spinneret used for melt spinning, any spinneret having a group of hollow pins or a group of fine holes for forming island components can be used. For example, a spinneret that forms a sea-island cross section by merging an island component pushed out from a hollow pin or a fine hole with a sea component flow designed to fill the gap and compressing this. good. The extruded islands-in-the-sea composite fiber is solidified by cooling air, and taken up by a rotating roller or an ejector set at a predetermined take-up speed to obtain an undrawn yarn. Although the take-up speed is not particularly limited, it is preferably 200 to 5000 m/min. If it is less than 200 m/min, productivity may deteriorate. On the other hand, if the speed is 5000 m/min or more, the spinning stability may deteriorate.

The obtained fibers may be directly subjected to the cutting process or the subsequent extraction process, depending on the use and purpose of the ultrafine fibers obtained after the sea component is extracted, or may be subjected to the desired strength, elongation, and heat shrinkage properties. For matching, it can be subjected to a cutting step or a subsequent extraction step via a stretching step and a heat treatment step. The drawing step may be a separate drawing method in which spinning and drawing are performed in separate steps, or a direct drawing method in which drawing is performed immediately after spinning in one step.

Next, the composite fiber is cut so that the ratio L/D of the fiber length L to the island diameter D is in the range of 100-2500. For such cutting, it is preferable to bundle tens to millions of tows and cut them with a guillotine cutter, a rotary cutter, or the like.

The fiber having the above fiber diameter is obtained by subjecting the composite fiber to alkali weight reduction processing. At that time, in the alkali weight reduction processing, the ratio of the fiber to the alkali solution (bath ratio) is preferably 0.1 to 5%, more preferably 0.4 to 3%. If the content is less than 0.1%, the fibers and the alkaline solution come into contact with each other frequently, but there is a possibility that processability such as drainage becomes difficult. On the other hand, if it is 5% or more, the amount of fibers is too large, and there is a possibility that the fibers may become entangled with each other during the alkali weight reduction process. The bath ratio is defined by the following formula.
Bath ratio (%) = (fiber mass (gr) / alkaline aqueous solution mass (gr) × 100)

Further, the processing time for alkali weight reduction processing is preferably 5 to 60 minutes, more preferably 10 to 30 minutes. If the time is less than 5 minutes, the alkali weight reduction may be insufficient. On the other hand, if it is 60 minutes or longer, even the island component may be reduced.
Also, in the alkali weight reduction process, the alkali concentration is preferably 2 to 10% by mass. If it is less than 2% by mass, there is a risk that the alkalinity will be insufficient and the rate of weight loss will be extremely slow. On the other hand, if it exceeds 10% by mass, the amount of alkali may be reduced too much, and even the island portion may be reduced.
The order of the cutting step and the alkali weight reduction step may be reversed so that the alkali weight reduction process is performed first, and then the cutting is performed.

It is preferable that the nanofiber is contained in an amount of 5% by weight or more (more preferably 5 to 30% by weight) based on the weight of the nonwoven fabric. In particular, it is important that the nonwoven fabric contains heat-fusible binder fibers in addition to the nanofibers. In this case, the content of the heat-fusible binder fiber is preferably 50% or more (more preferably 50 to 90% by weight, particularly preferably 70 to 85% by weight) based on the weight of the nonwoven fabric. Heat-fusible binder fibers form a fused network between fibers and play a role in forming the framework and strength of the nonwoven fabric. If the content of the heat-fusible binder is more than 90% by weight, the non-woven fabric may shrink due to tearing during the drying process, deteriorating the paper-making properties, or causing an increase in pressure loss due to the fused network. Conversely, if it is less than 50% by weight, the strength of the mask filter medium is low, and there is a risk that the washing durability will be low. Therefore, it is preferable that the heat-fusible binder fiber is contained in an amount of 50% by weight or more relative to the weight of the nonwoven fabric, and at this time, the nanofibers contained in an amount of 5% by weight or more relative to the weight of the nonwoven fabric can suppress shrinkage during the drying process, resulting in excellent papermaking properties. ,preferable. As a result, the strength and elongation of the filter medium itself can be increased, resulting in excellent washing durability.

Examples of the heat-fusible binder fibers include undrawn fibers and composite fibers. Adhesive fibers are exemplified. Such heat-fusible fibers may be undrawn fibers (having a birefringence (Δn) of 0.05 or less) or composite fibers.

When heat-fusible fibers made of undrawn fibers are used, it is preferable to carry out calendering/embossing after papermaking, because a thermocompression bonding step is required after drying after papermaking. Examples of undrawn fibers include undrawn polyester fibers and undrawn polyphenylene sulfide fibers spun at a spinning speed of preferably 800 to 1200 m/min, more preferably 900 to 1150 m/min. Here, the polyester used for the unstretched fibers includes polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, and preferably polyethylene terephthalate and polytrimethylene terephthalate for reasons of productivity, dispersibility in water, and the like. is preferred. As the polyphenylene sulfide used for the unstretched fibers, any polyphenylene sulfide may be used as long as it belongs to the category called polyarylene sulfide resin. Examples of polyarylene sulfide resins include p-phenylene sulfide units, m-phenylene sulfide units, o-phenylene sulfide units, phenylene sulfide sulfone units, phenylene sulfide ketone units, phenylene sulfide ether units, and diphenylene sulfide units. , substituent-containing phenylene sulfide units, branched structure-containing phenylene sulfide units, and the like. Among them, those containing 70 mol % or more, particularly 90 mol % or more of p-phenylene sulfide units are preferable, and poly(p-phenylene sulfide) is more preferable.

On the other hand, among the heat-fusible binder fibers, the conjugate fiber has a polymer component (for example, amorphous copolyester) that is fused by heat treatment at 80 to 170° C. after papermaking and exhibits an adhesive effect in the sheath. It is preferable to use a core-sheath type conjugate fiber in which another polymer (for example, ordinary polyester such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, etc.) having a melting point higher than those of these polymers by 20°C or more is arranged in the core. . A core-sheath type conjugate fiber, an eccentric core-sheath type conjugate fiber, a side-by-side type conjugate fiber, etc. in which the binder component (low-melting-point component) forms all or part of the surface of the single fiber may also be used.

Here, the amorphous copolyester includes terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid, azelaic acid, dodecanoic acid, and 1,4-cyclohexane. acid component such as dicarboxylic acid, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, 1,4-cyclohexanediol, 1, It is obtained as a random or block copolymer with a diol component such as 4-cyclohexanedimethanol. Among them, it is preferable to use terephthalic acid, isophthalic acid, ethylene glycol and diethylene glycol, which have been widely used, as main components from the viewpoint of cost. Such copolyesters have a glass transition point in the range of 50 to 100° C. and do not exhibit a clear crystalline melting point.

Preferably, the nonwoven fabric is a wet-laid nonwoven fabric. As a method for producing such a wet-laid nonwoven fabric, it is preferable to use an ordinary Fourdrinier paper machine, a short wire paper machine, a cylinder paper machine, or a combination of a plurality of these machines to make multi-layered paper, followed by heat treatment. At that time, as a heat treatment process, either a Yankee dryer or an air-through dryer can be used after the papermaking process. Also, after heat treatment, calendering such as metal/metal roller, metal/paper roller, metal/elastic roller may be applied.

As a method for producing a nonwoven fabric having a multi-layered structure, for example, after obtaining a wet-laid nonwoven fabric as described above, it is preferable to bond the wet-laid nonwoven fabric using a calender or the like.
Furthermore, in addition to the nanofibers and the heat-fusible binder fibers, fibers having a large fineness of 0.1 dtex (fiber diameter of 3 μm) or more may be included. These fibers help disperse the nanofibers and become the skeleton of the nonwoven fabric to create a high void structure and contribute to low pressure loss. Polyester fibers such as those described above are preferable as the fibers having a large fineness because they have a uniform fiber diameter and good dispersibility.

The mask filter medium thus obtained preferably has a basis weight in the range of 20 to 80 g/m ² . If the basis weight is larger than this, the mask becomes heavy, and there is a possibility that the burden of wearing the mask becomes large. A smaller basis weight is preferable, but 20 g/m ² or more is preferable from the viewpoint of uniformity and strength of the nonwoven fabric.

In addition, the mask filter material preferably has a tensile strength of 20 N/15 mm or more (more preferably 20 to 100 N/15 mm) in the MD direction (preferably both longitudinally and laterally). If the tensile strength is small, the filter medium may be torn during washing, or the filter medium may deteriorate and the collection performance may deteriorate.

In addition, in the mask filter medium, it is preferable that the 0.3 μm particle trapping rate during static elimination after the isopropyl alcohol treatment is 95% or more. Taking into account the influence of cigarette smoke in daily life and the influence of surfactants during washing, it is preferable that the collection efficiency during static elimination does not decrease even during static elimination.

In addition, in terms of wearing comfort, the mask filter material preferably has an elongation of 10% or more (more preferably 12 to 50%) in both the vertical and horizontal directions.
Moreover, in the mask filter material, it is preferable that the 0.3 μm particle capture rate after the washing test is 95% or more. It is preferable that the collection performance does not deteriorate even when the mask is washed and used repeatedly.

Further, in the mask filter material, it is preferable that the water droplet disappears after dripping distilled water for 1 minute or less. In the case of a filter material for washing durability masks that has low water absorption and does not absorb water droplets, when water droplets are generated inside due to sweat, splashes, or condensation when used as a mask, the water droplets will remain and the mask will be uncomfortable. Doing so may cause rashes, etc. Therefore, it is preferable that the generated water droplets are immediately absorbed so that the water droplets do not remain inside the mask so that it can be comfortably used as a filter medium for a washing durable mask.
Since the filter medium for a mask of the present invention has the above structure, it can maintain excellent collection performance even after repeated washing.

Next, the mask of the present invention is a mask using the above filter medium for masks. In such a mask, the filter medium may be used alone, or may be used in combination with a nonwoven fabric base material or woven or knitted fabric made of various types of spunbond or thermal bond. Such masks may be provided with ear straps, bands, hooks, or the like.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples. Physical properties in the examples were measured by the following methods.

(1) Fiber diameter Using a transmission electron microscope TEM (equipped with length measurement function), a fiber cross-sectional photograph was taken at a magnification of 30,000 times and measured. However, as the fiber diameter, the diameter of the circumscribed circle in the cross section of the single fiber was used (average value of 5 samples).

(2) Fiber length Using a scanning electron microscope (SEM), the ultrafine short fibers (short fibers A) before dissolution and removal of the sea component were laid on a substrate, and the fiber length L was measured at 20 to 500 times (sample Average value of number 5). At that time, the fiber length L was measured using the length measurement function of the SEM.

(3) Basis weight The basis weight was measured based on JIS P8124 (method for measuring metric basis weight of paper).

(4) Thickness The thickness was measured according to JIS P8118 (Method for measuring thickness and density of paper and cardboard). The measurement load was 75 g/cm ² , the number of samples was 5, and the average value was obtained.

(5) Tensile strength and elongation It was carried out based on JIS P8113 (Tensile strength of paper and cardboard and test method).

(6) Collection rate Atmospheric dust (0.3 to 5 μm) passes through the sample at a speed of 5.1 cm / sec with a particle measuring device (Rion Co., Ltd. particle counter KC-01 (0.3 to 5 μm)). The number of 0.3 μm particles in the air dust collected by the sample was measured when the sample was left, and the collection rate was calculated by 100% from the number of 0.3 μm particles in the air dust.

(7) Pressure loss (pressure loss)
The differential pressure relative to atmospheric pressure was read from the gauge when atmospheric dust (0.3-5 μm) was passed through the sample at a velocity of 5.1 cm/sec.

(8) Static Elimination Treatment Static elimination treatment was performed based on the isopropyl alcohol (IPA) saturated vapor exposure method of JISB9908:2011 (Performance test method for ventilating air filter units and ventilating electrostatic precipitators).

(9) Water Absorption After 5 μL of distilled water was dropped on the sample, the time for water droplets to disappear was measured. When the water droplets disappeared in 1 minute or less, it was evaluated as ◯ (acceptable), and when the water droplets remained even after 5 minutes or more, it was evaluated as x (failed).

(10) Washing test Washed by the C4M method of JISL1930:2014 (home washing test method for textile products), and hung and dried by the A method. This method was performed for each number of washes (L).

[Example 1]
10% by weight of nanofiber (polyester fiber) with a fiber diameter of 400 nm and a fiber length of 0.4 mm, 10% by weight of a microfiber (polyester fiber) with a fiber diameter of 12.6 μm and a fiber length of 5.0 mm, and a fiber diameter of 12.6 μm× A polyester nonwoven fabric composed of 80% by weight of a core-sheath composite heat-fusible binder fiber (polyester fiber) having a fiber length of 5.0 mm is produced by a wet papermaking method and dried with a Yankee dryer (120 ° C.) to form a wet nonwoven fabric. A filter medium for a mask was obtained. Table 1 shows the evaluation results.

Such a washing-resistant mask filter medium contains 80% by weight of heat-fusible binder fibers, and thus has excellent strength and elongation. Furthermore, since it contains nanofibers, it is possible to achieve both high collection efficiency and low pressure loss. In addition, the collection mechanism does not deteriorate with electret processing but with nanofibers, so the collection performance does not deteriorate even after static electricity is removed.

[Example 2]
20% by weight of nanofibers (polyester fibers) with a fiber diameter of 700 nm and a fiber length of 0.5 mm, and 80% by weight of core-sheath composite heat-fusible binder fibers (polyester fibers) with a fiber diameter of 12.6 μm and a fiber length of 5.0 mm A polyester nonwoven fabric consisting of was produced by a wet papermaking method and dried with a Yankee dryer (120° C.) to obtain a filter medium for a mask made of the wet nonwoven fabric. Table 1 shows the evaluation results.
As in Example 1, excellent strength and elongation were obtained with the heat-fusible binder fiber. In addition, nanofibers achieve both high collection performance and low pressure loss, and performance does not deteriorate even after static elimination.

[Example 3]
The filter medium of Example 1 was knitted fabric 1 (basis weight: 148 g/m ² , thickness: 0.48 mm) made of Nanofront (registered trademark) manufactured by Teijin Frontier Co., Ltd. and knitted fabric made of Ecopure (registered trademark) manufactured by Teijin Frontier Co., Ltd. 2 (weight per unit area: 146 g/m ² , thickness: 0.44 mm). Table 2 shows the evaluation results.
Since this filter medium contained 80% by weight of heat-fusible binder fibers, it was excellent in washing durability and retained its collection performance even after washing 30 times.

[Example 4]
10% by weight of nanofibers (polyester fibers) with a fiber diameter of 400 nm and a fiber length of 0.4 mm, 60% by weight of microfibers (polyester fibers) with a fiber diameter of 12.6 μm and a fiber length of 5.0 mm, and a fiber diameter of 12.6 μm× A polyester nonwoven fabric composed of 30% by weight of a core-sheath composite heat-fusible binder fiber (polyester fiber) having a fiber length of 5.0 mm is produced by a wet papermaking method and dried with a Yankee dryer (120 ° C.) to form a wet nonwoven fabric. A filter medium for a mask was obtained. Table 1 shows the evaluation results.
Although it has excellent collection performance due to the inclusion of nanofibers, the strength and elongation are slightly low due to the small amount of heat-fusible binder fibers.

[Comparative Example 1]
70% by weight of microfiber (polyester fiber) with a fiber diameter of 3 μm and a fiber length of 3.0 mm, and 30% by weight of a core-sheath composite heat-fusible binder fiber (polyester fiber) with a fiber diameter of 12.6 μm and a fiber length of 5.0 mm A polyester nonwoven fabric consisting of was produced by a wet papermaking method and dried with a Yankee dryer (120° C.) to obtain a filter medium for a mask made of the wet nonwoven fabric. Table 1 shows the evaluation results.
The strength and elongation are low due to the small amount of heat-fusible binder fiber. In addition, since it does not contain nanofibers, its collection efficiency is low and its performance as a mask is low.

[Comparative Example 2]
A commercially available mask was disassembled and the meltblown nonwoven filter media was taken out and evaluated. Although this filter medium achieved both a high collection rate and a low pressure drop by electret processing, the collection rate was greatly reduced after static elimination. Moreover, when distilled water was dripped, water droplets remained even after 5 minutes or more, indicating low water absorption. Electret-processed filter media have low performance reliability and are not preferable for use in various environments or for repeated use.

[Comparative Example 3]
The knitted fabric 1 (basis weight 148 g / m2, thickness 0.48 mm) made of Nanofront manufactured by Teijin Frontier Co., Ltd. in Example 3 and the knitted fabric 2 made of Teijin Frontier Co., Ltd. Ecopure (registered trademark) (basis weight 146 g / ^m ) , thickness 0.44 mm), and the four corners were sewn with a sewing machine to be integrated. Table 2 shows the evaluation results.
Since it is composed only of knitted fabric, its collection performance is low and its performance as a mask is low.

[Example 5]
The filter medium of Example 4 was knitted fabric 1 (basis weight: 148 g/m ² , thickness: 0.48 mm) made of Nanofront (registered trademark) manufactured by Teijin Frontier Co., Ltd. and knitted fabric made of Ecopure (registered trademark) manufactured by Teijin Frontier Co., Ltd. 2 (weight per unit area: 146 g/m ² , thickness: 0.44 mm). Table 2 shows the evaluation results.
Since this filter medium contained only 30% by weight of the heat-fusible binder fiber, its washing durability was low, and after 30 washings, the collection performance was greatly reduced. This is because the strength and elongation of the filter material are low, and the deterioration of the filter material progresses due to washing, resulting in a decrease in performance.

INDUSTRIAL APPLICABILITY According to the present invention, there are provided a filter medium for a mask and a mask which are excellent in durability to washing, which can maintain excellent collection performance even after repeated washing, and which are of great industrial value.

Claims (11)

A filter material for a mask made of a nonwoven fabric, characterized in that the nonwoven fabric contains nanofibers having a fiber diameter of 100 to 1000 nm and heat-fusible binder fibers. 2. The filter medium for a mask according to claim 1, wherein said nanofibers and/or heat-fusible binder fibers are polyester fibers, polyolefin fibers, or nylon fibers. 3. The filter medium for a mask according to claim 1, wherein the nonwoven fabric contains 5% or more of the nanofibers based on the weight of the nonwoven fabric. The mask filter medium according to any one of claims 1 to 3, wherein the nonwoven fabric contains 50% or more of the heat-fusible binder fiber based on the weight of the nonwoven fabric. The filter medium for a mask according to any one of claims 1 to 4, which has a basis weight within the range of 20 to 80 g/m ² . The mask filter medium according to any one of claims 1 to 5, having a tensile strength in the MD direction of 20 N/15 mm or more. The mask filter medium according to any one of claims 1 to 6, which has an elongation of 10% or more in both the vertical and horizontal directions. The mask filter medium according to any one of claims 1 to 7, wherein the 0.3 µm particle collection rate after static elimination treatment is 95% or more. The mask filter medium according to any one of claims 1 to 8, which has a 0.3 µm particle trapping rate of 95% or more after a washing test. 10. The filter medium for a mask according to claim 1, wherein the water drop disappears for 1 minute or less after dropping distilled water. A mask using the mask filter medium according to any one of claims 1 to 10.