TWI793815B - Face mask - Google Patents

Abstract

We offer masks that meet more stringent standards regarding capture performance and breathability. The mask has a mask body (2) covering the wearer's mouth and nose. The mask body portion comprises: an inner sheet (12), an outer sheet (13), and a filter sheet (11). The filter sheet is positioned between the inner sheet and the aforementioned outer sheet, and is formed by an electretized non-woven fabric. The filter sheet includes first fibers having a fiber diameter of 1 μm to less than 5 μm, and second fibers having a fiber diameter of 5 μm to less than 15 μm. The ratio of the first fiber in the filter sheet is larger than the ratio of the second fiber, and the ratio of the first fiber to the second fiber in the filter sheet is 90% or more of the filter sheet. The fiber density of the filter sheet is 0.03-0.10 g/cm ³ .

Description

Face mask

The present invention relates to masks.

Masks that cover the mouth and nose of the wearer are known. Masks are used to suppress the inhalation of germs, bacteria, dust, pollen, etc.; or to prevent the scattering of droplets caused by sneezing and coughing. In recent years, disposable masks using non-woven fabrics have also become common. As a filter material used in such a mask, for example, there is a filter material for a mask disclosed in Patent Document 1. [Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2008-86626

[Problem to be Solved by the Invention]

Recently, masks are expected to suppress inhalation of substances that have adverse effects on health such as fine particulate matter (PM2.5, etc.) in the atmosphere. In terms of the specifications of masks corresponding to PM2.5, there are DS2 specifications formulated by the Ministry of Health, Labor and Welfare of Japan, N95 specifications formulated by the National Institute of Occupational Safety and Health (NIOSH) in the United States, FFP2 specifications formulated by the EU, and national standardization in China. GB/T32610-2016 (Technical Specifications for Daily Protective Masks: Technical Specification of Daily Protective Mask) formulated by the Management Committee exists. Among them, although GB/T32610-2016 is a newly published specification in 2016, it has set stricter standards for capture performance and air permeability. In order to provide a mask (filter material) satisfying such a standard, there is room for improvement to existing masks (filter material) such as the filter for a mask of Patent Document 1. In addition, masks worn by humans are very different from air filters used in suction and exhaust equipment, etc., because the flow rate of gas during suction and exhaust is very different, so it is desirable to have a technology suitable for masks.

The object of the present invention is to provide a mask that satisfies stricter standards in terms of trapping performance and breathability. [Means to solve the problem]

The mask of the present invention, (1) is equipped with a mask body covering the wearer's mouth and nose, wherein the mask body includes: an inner sheet, an outer sheet, and a filter sheet, and the filter sheet is positioned on the aforementioned inner side An electretized nonwoven fabric is formed between the sheet and the outer sheet, and the filter sheet includes: first fibers having a fiber diameter of 1 μm or more and less than 5 μm; and fibers having a fiber diameter of 5 μm or more and less than 15 μm The ratio of the aforementioned first fiber in the aforementioned filter sheet is more than the ratio of the aforementioned second fiber, and the ratio of the aforementioned first fiber and the aforementioned second fiber in the aforementioned filter sheet is 90% of that of the aforementioned filter sheet As above, the fiber density of the filter sheet is 0.03 to 0.10 g/cm ³ .

Since this mask has the above-mentioned structure, compared with a mask that does not have the above-mentioned structure, the trapping performance and the breathability of mutually opposite characteristics can be balanced, that is, both can be improved together. Thereby, this mask can suppress the wearer from absorbing substances such as fine particulate matter (PM2.5) in the atmosphere, compared with a mask that does not have the above-mentioned structure. The main reasons for this are as follows. Assuming that if the fiber density of the filter sheet is constant, relatively increasing the proportion of fibers with small fiber diameters (1~5μm), the filter sheet as a whole can relatively increase the surface area of the fibers. As a result, the area of the surface of the fiber capable of retaining charge due to the electret treatment can be increased, and thus the amount of charge retained per unit basis weight can be increased. Thereby, the effect of the electret treatment is improved, and the collection performance of the filter sheet can be improved. However, on the other hand, if the filter sheet is formed using only fibers with a small fiber diameter, the distance between the fibers becomes narrow. In this case, the filter sheet becomes dense, thereby degrading the air permeability of the filter sheet. Here, in this mask, fibers with a large fiber diameter (5~15μm) and fibers with a small fiber diameter are mixed into the filter sheet. By incorporating fibers with large fiber diameters into the collection of fibers with small fiber diameters, voids are likely to be generated in the region where the fiber diameters vary greatly, that is, in the region around the fibers with large fiber diameters. Fibers tend to maintain their voids. As a result, there are proper voids in the filter sheet, and excessive narrowing of the distance between fibers can be suppressed. Compared with the case where only fibers with small fiber diameters are used, air permeability can be improved. Thereby, while improving the air permeability of the filter sheet, the collection performance can be improved. Here, if the fiber density of the filter sheet is relatively high, the formation of an electric field in the filter sheet by the electret treatment may be hindered by the fibers, and the electret treatment may not reach the inside of the filter sheet. At this time, a region that has not been electretized may be formed inside the filter sheet. Generally, the collection performance of the filter material that has not been treated with electret is reduced by a fraction compared with the filter material that has been treated with electret. Therefore, in a filter sheet having a relatively high fiber density, there are regions inside which do not contribute to the replenishment property (become an obstacle to air permeability). However, in this mask, the above-mentioned fibers with a large fiber diameter and fibers with a small fiber diameter are mixed, and the fiber density is made to an appropriate size (0.03~0.10g/cm ³ ), so that the electret treatment reaches the inside of the filter sheet In this way, the formation of regions that cannot be reached by electret treatment can be suppressed. Thereby, it is possible to eliminate a region that is not very helpful for the collection performance, and to improve the collection performance. By virtue of these synergistic effects, the trapping performance and air permeability can be balanced, that is, both can be further improved together.

The mask of the present invention may be the mask described in (1) above, wherein (2) the ratio of the first fiber to the second fiber in the filter sheet is 5:4 to 10:1. In this mask, the ratio of the first fiber to the second fiber is 5:4~10:1. Because the ratio of the first fiber is high enough, the above effect can be achieved more reliably, especially through electret The effect of improving the collection performance due to the increase in the charged area by the bulk treatment, and the effect of suppressing the decrease in air permeability due to the appropriate inclusion of fibers with a large fiber diameter. Thereby, it is possible to balance the trapping performance and the air permeability, that is, to further improve both.

The mask of the present invention may be the mask described in (1) or (2) above, wherein (3) the basis weight of the filter sheet is 5 to 20 g/m ² . In this mask, because the basis weight of the filter sheet has a predetermined condition, the above-mentioned effects, especially the way that the electret treatment reaches the inside of the filter sheet, suppresses the formation of regions that have not been treated with electret, and can be more reliable. The effect of improving the capture performance is achieved. Thereby, it is possible to balance the trapping performance and the air permeability, that is, to further improve both. At this time, in the mask 1 of the final product, a plurality of filter sheets 11 are laminated. As a whole, even if the basis weight of the plurality of filter sheets 11 exceeds 20 g/m ² , as long as the basis weight of the filter sheets 11 of each layer satisfies the above-mentioned range. The reason for this is that the electret treatment and the like can be sufficiently applied to the filter sheets 11 of each layer.

The mask of the present invention may also be the mask described in any one of the above (1) to (3), wherein (4) the average fiber diameter of the filter sheet is 2 to 5 μm. In this mask, the average fiber diameter is in the range of 2 to 5 μm, that is, within the range of the first fiber, it can be said that it is not too thin or too thick as a whole. That is, since fibers with a small fiber diameter and fibers with a large fiber diameter are present in an appropriate balance near the side with a small fiber diameter, the electretization treatment increases the charged area while suppressing the interaction between the fibers. When the interval becomes too narrow, the reduction of the air permeability of the filter sheet can be suppressed. Thereby, the trapping performance and the air permeability can be balanced, and both can be further improved together.

The mask of the present invention can also be the mask described in any one of the above (1) to (4), and (5) the aforementioned filter sheet is formed by a melt-blown non-woven fabric. Since this mask is formed of melt-blown non-woven fabric, the fiber diameter and fiber ratio of the above-mentioned first fiber and second fiber; the basis weight, thickness and density of the filter sheet can be easily formed to desired values. Thereby, it is possible to balance the trapping performance and the air permeability, that is, to further improve both.

The mask of the present invention may also be the mask described in any one of the above (1) to (5), wherein (6) the aforementioned filter sheet is laminated in two or more layers in the thickness direction of the aforementioned mask. This mask is the above-mentioned filter sheet which is laminated with two or more layers (multiple sheets) in the thickness direction to improve the trapping performance and air permeability. Thereby, it is possible to reduce the decrease in air permeability that may decrease depending on the number of layers of filter sheets, and to improve the collection performance more than that in the case of a single layer.

The mask of the present invention may also be the mask described in any one of the above (1) to (6), wherein (7) the fiber diameter distribution of the aforementioned first fiber has the first peak of the number of the aforementioned first fibers, and the aforementioned first fiber The fiber diameter distribution of the 2 fibers has the second peak of the number of the second fibers in the range where the fiber diameter is larger than 5 μm, and the number of the first fibers of the first peak in the filter sheet is higher than the second peak. The number of the aforementioned second fibers is more. In this mask, the second peak of the second fiber is 5 μm away from the fiber diameter that is the boundary between the first fiber and the second fiber. Therefore, there is a distance from the range of the first fiber and the first peak, and the first fiber at the first peak The number of fibers is more than that of the second fiber at the second peak. That is, the fibers of the filter sheet can be more clearly divided into the first group representing the first fibers represented by the first peak, and the second group representing the second fibers represented by the second peak. As a result, the fiber diameter distributions of the first fiber and the second fiber are close to each other, but continue to be separated from each other, and the first group of the first fiber maintains the effect of the electret treatment, while maintaining the collection performance, probably by The second group of the second fiber is more likely to generate voids, which can further reduce the pressure loss. In this way, the air permeability can be further improved without excessively changing the trapping performance of the filter sheet.

The mask of the present invention may also be the mask described in any one of the above (1) to (7), wherein (8) the aforementioned filter sheet has an average unit basis weight (g/m ² ) of 500C (coulombs) or more. Since this mask has the above-mentioned structure, it can hold a charge of more than 500C through electret treatment. Thereby, very high trapping performance can be obtained. [Effect of the invention]

According to the present invention, it is possible to provide a mask that satisfies stricter standards in terms of trapping performance and breathability.

[Mode for Carrying Out the Invention]

Hereinafter, the mask according to the embodiment will be described with reference to the drawings.

Fig. 1 shows the schematic diagram of the structural example of the mask 1 of embodiment. The mask 1 includes a mask main body 2 that covers the wearer's mouth and nose, and ear hooks 3 that can be hung on the wearer's ears. The mask body portion 2 includes: a left half sheet 2a covering the left half of the wearer's face, and a right half sheet 2a' covering the right half of the wearer's face. The left-half sheet 2a and the right-half sheet 2a' are integrated by joining opposite ends along the edge. The joining portion 2b is formed by, for example, thermal fusion, adhesive, or the like. At this time, since the edges of the end portions have a substantially convex curved shape, the integrated two sheets can form a concave three-dimensional shape (three-dimensional structure) with respect to the wearer's face. On both sides of the left and right sides of the mask body part 2, that is, at the end of the opposite side of the joint part 2b in the left half-face sheet 2a and the right half-face sheet 2a', respectively join the end of the earhook part 3. The joining portion 4 is formed by, for example, pressing, heat fusion, adhesive, or the like. The ear hook portion 3 is formed to extend outward from the left and right sides of the mask body portion 2 . The inside of the earhook part 3 is formed with openings 3a, 3a' extending from the mask main body 2 side toward its opposite side, and the wearer's ears are put into the openings 3a, 3a', and the mask 1 is installed on the wearing surface. By.

FIG. 2 is a partial sectional view of the mask 1 . This figure shows the mask body portion 2, that is, the cross-sectional structure of the left half sheet 2a and the right half sheet 2a'. The mouth mask body portion 2 is provided with: towards the face side when wearing, that is, toward the inner side sheet 12 of the inside, towards the outer side sheet 13 of the outer side when wearing and using, and the filter sheet 11 between the inner side sheet 12 and the outer side sheet 13. In addition, FIG. 2 has shown the case where the mask main body part 2 is equipped with the filter sheet 11 of 2 sheets laminated|stacked in the thickness direction. However, the mask main body 2 may be provided with only one filter sheet 11 or may be provided with three or more filter sheets 11 .

The inner sheet 12 and the outer sheet 13 hold the filter sheet 11 from both sides in the thickness direction, and maintain the shape of the mask main body 2 . From the functional point of view, the inner sheet 12 and the outer sheet 13 preferably have higher air permeability and higher rigidity than the filter sheet 11 . It is ideal that the inner sheet 12 has a good touch on the skin. The basis weight is, for example, 20 to 50 g/m ² , and the average fiber diameter is, for example, 10 to 50 μm. The material of the inner sheet 12 and the outer sheet 13 is not particularly limited as long as it satisfies the above-mentioned requirements, and examples thereof include nonwoven fabrics. For non-woven fabrics, for example, water needle non-woven fabrics, hot-air non-woven fabrics, spun-bonded non-woven fabrics, air-laid non-woven fabrics, melt-blown non-woven fabrics, flash-spun non-woven fabrics, heat-bonded non-woven fabrics, carded non-woven fabrics, or a combination of these of non-woven fabrics. As for the fibers constituting the nonwoven fabric, for example: natural fibers (examples: wool, cotton); regenerated fibers (examples: rayon, acetate); synthetic resin fibers (examples: polyethylene, polypropylene, polybutylene, Ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ionomer resin and other polyolefins; polyethylene terephthalate, polyethylene terephthalate, poly Polyesters such as propylene terephthalate and polylactic acid; polyamides such as Nylon, etc.), etc. The fibers constituting the nonwoven fabric may be composed of a single component, or may be composed of composite fibers such as core, sheath fibers, side-by-side fibers, and island/sea fibers. A single-layer nonwoven fabric may be used, or a laminate of single-layer nonwoven fabrics may be laminated (for example: SMS nonwoven fabric).

Hereinafter, one filter sheet 11 will be described. The filter sheet 11 is that when a gas such as air circulates in the filter sheet 11, it captures germs, bacteria, dust, pollen, or tiny particulate matter (PM2.5) that are about to pass through the filter sheet with the gas ( Hereinafter, it is simply referred to as "fine matter".) and collected. It is desirable that the filter sheet 11 has a higher trapping performance of minute substances than the inner sheet 12 and the outer sheet 13 .

The filter sheet 11 is formed of electretized nonwoven fabric. The electretized non-woven fabric captures tiny substances in the gas by electrostatic force and can be collected. Such a nonwoven fabric is obtained by subjecting the nonwoven fabric to electret treatment. Electret treatment is the treatment of injecting charge into the non-woven fabric of the dielectric body by means of DC corona discharge or high electric field. It is conceivable that the charge injected into the nonwoven fabric exists mainly near the surface of the fibers of the nonwoven fabric. The amount of charge injected into the nonwoven fabric can be controlled by the conditions of DC corona discharge and high electric field application, but it can also be controlled by the fiber diameter and fiber density of the nonwoven fabric. As the material of the electretized non-woven fabric, although the same material as the material of the inner sheet 12 and the outer sheet 13 can be used, a non-polar polymer is ideal, such as polypropylene, polyethylene, polystyrene, etc. ethylene, or a combination thereof.

The filter sheet 11 includes first fibers having a fiber diameter of 1 μm to less than 5 μm, and second fibers having a fiber diameter of 5 μm to less than 15 μm. The ratio of the first fiber and the second fiber in the filter sheet 11 (based on the number of fibers) is 90% or more of the filter sheet 11 . In other words, the ratio of the number of first fibers and second fibers to the number of fibers of the filter sheet 11 is 90% or more. The ratio is ideally above 95%. In addition, the ratio of the first fibers in the filter sheet 11 is larger than the ratio of the second fibers (based on the number of fibers). That is, in the filter sheet 11, the number of the first fibers is greater than the number of the second fibers. In addition, the ratio of the fibers other than the first fiber and the second fiber in the filter sheet 11 (based on the number of fibers) is about 0 to 10%, and ideally 0 to 5%. The fiber diameters of fibers other than the second fibers are, for example, about 0 to 1 μm and/or about 15 to 20 μm.

In this way, the present filter sheet 11 includes: first fibers (1-5 μm) with a small fiber diameter and second fibers (5-15 μm) with a large fiber diameter, and the ratio of the first fibers in the filter sheet 11 is set to be higher than that of the second fiber. The ratio of 2 fibers is higher for the following reasons. Assuming that the fiber density of the filter sheet 11 is constant and the ratio of the first fibers is relatively increased, the surface area of the fibers per unit volume of the filter sheet 11 as a whole can be relatively increased. By applying electret treatment to such a filter sheet 11, the area of the surface of the fiber that can hold charges can be increased, so the charge held per unit volume (if the thickness is constant, the average unit basis weight) can be increased. amount. Thereby, since the amount of minute substances that the filter sheet 11 can absorb by electrostatic force can be increased, the collection performance of the filter sheet 11 can be improved. However, when the filter sheet is formed using only the first fibers, the distance between the fibers becomes narrow. In this case, the fiber density of the filter sheet becomes too high, and the gas becomes difficult to pass through the filter sheet, thereby reducing its air permeability. Here, in the filter sheet 11 , second fibers having a large fiber diameter are mixed into the filter sheet 11 together with the first fibers. By incorporating the second fiber into the aggregate of the first fibers, the fiber diameter is greatly different between the second fiber and the surrounding first fibers. Because of the difference in fiber diameter, voids are easily generated in the area around the second fiber, and the voids are easily maintained by the second fiber. As a result, appropriate voids are formed in the filter sheet 11, and excessive narrowing of the distance between fibers can be suppressed, and air permeability can be improved compared with the case of using only fibers with small fiber diameters. Thereby, gas can easily pass through the filter sheet 11, thereby improving its air permeability. In this manner, since the present filter sheet 11 includes the first fibers and the second fibers, it is possible to improve the air-permeability of the filter sheet 11 while improving the collection performance. In this case, since the ratio of the first fiber is larger than the ratio of the second fiber, a sufficient effect of the electret treatment can be enhanced while ensuring an appropriate void.

However, the reason why the fiber diameter of the first fiber is set to 1 μm or more is because if there are more fibers with a fiber diameter of less than 1 μm, the fiber density of the filter sheet will be relatively high, and the voids around the second fiber will be blocked by the first fiber. The fibers are filled, so overall, the space for gas to pass through becomes smaller, and the air permeability decreases. The reason for setting the fiber diameter of the first fiber to less than 5 μm is that if there are more fibers with a fiber diameter of 5 μm or more, the surface area of the fiber will be relatively small, and the charge held in the electret-treated fiber will decrease, making the collection Performance drops. In addition, the reason why the fiber diameter of the second fiber is 5 μm or more and less than 15 μm is to make the range of the fiber diameter of the first fiber (1 to 5 μm) close to the range of the fiber diameter of the second fiber (5 to 15 μm). . Furthermore, the reason why the range of the fiber diameter of the first fiber (1 to 5 μm) is brought close to the range of the fiber diameter of the second fiber (5 to 15 μm) is derived from the following reason. If the two ranges deviate, even if the second fiber is mixed into the filter sheet, the void formed in the area where the fiber diameter greatly changes due to the mixing of the second fiber becomes excessively large, so that the first fiber is easy to enter, and as a result, the void Easily filled with 1st fiber. In this case, as a result, voids are reduced and air permeability is reduced. Thus making the two ranges close. The reason for setting the ratio of the first fiber and the second fiber in the filter sheet 11 (based on the number of fibers) to 90% or more of the filter sheet 11 is to allow the above-mentioned first fiber and the second fiber to be mixed. The resultant effect of balancing the trapping performance and air permeability is surely achieved in the filter sheet 11 .

Also, the fiber density of the filter sheet 11 is 0.030 to 0.10 g/cm ³ . The reason for this is as follows. Here, if the fiber density of the filter sheet is relatively high, that is, if the fiber density is greater than 0.10 g/cm ³ , the fibers may interfere with the formation of an electric field in the filter sheet due to electret treatment, and so on. Electret treatment cannot reach the inside of the filter sheet. At this time, a region that has not been electretized, that is, a region with relatively few charges may be formed inside the filter sheet. Generally, the collection performance of a filter material that has not been treated with electret is reduced to a fraction of that of a filter that has been treated with electret. Therefore, in a filter sheet having a relatively high fiber density, there are regions inside which do not contribute to the replenishment property (become an obstacle to air permeability). However, in this filter sheet 11, the fiber density is made into an appropriate size, at least 0.10 g/cm ³ or less, so that the electret treatment can reach the inside of the filter sheet, and the formation of electret treatment can be suppressed. reached area. Thereby, it is possible to eliminate a region that is not very helpful for the collection performance, and to improve the collection performance. Again, in this filter sheet 11, since the fiber density is set to an appropriate size, at least set to 0.10g/cm ^Below , the circulation of the gas becomes easy, so the gas is easily passed through the filter sheet 11, and its air permeability can be improved. performance. On the other hand, if the fiber density is relatively low, that is, if it is less than 0.03g/cm ³ , there will be too few fibers to capture microscopic substances, and the collection performance will decrease. Moreover, there will be concerns that the filter sheet cannot maintain its shape alone. , so it is not ideal. However, in this filter sheet 11, the fiber density is set to an appropriate size, at least 0.03 g/cm ³ or more, so as to prevent the collection performance of the filter sheet 11 from degrading and maintain the shape. In this way, since the fiber density of the filter sheet 11 is 0.03 to 0.10 g/cm ³ , the filter sheet 11 can improve the collection performance while improving the air permeability. The fiber density is ideally 0.05 to 0.08 g/cm ³ .

The first fiber and the second fiber are preferably made of the same material, more preferably formed by the same manufacturing method. In this way, the fiber diameter ranges of the first fiber and the second fiber are close to each other, and when the filter sheet 11 is charged by electret treatment, it can be charged (example: the amount of charge per unit area) Overall roughly uniform. That is, it is possible to suppress the situation that the charging method of the first fiber and the second fiber may be different from the so-called use of different materials and different manufacturing methods, and the occurrence of non-uniform charging in the filter sheet 11 may be caused.

With regard to the manufacturing method of the filter sheet 11 in the above-mentioned mask 1, for example, a melt-blown method, a flash spinning method, a spunbonding method, an air-flow forming method, an electrospinning method, etc. can be cited. However, from the viewpoint of efficiently and reliably producing the filter sheet 11 having the above characteristics, the melt blowing method is ideal. In the melt-blown method, as a method of producing the filter sheet 11 having the above-mentioned characteristics, for example, a method of controlling the characteristics of the polymer and the spinning conditions can be mentioned. Specifically, for example, the flow rate of the high-temperature gas blown to the polymer is increased in the T-die used for the first fiber of melt blown spinning, and the high-temperature gas blown to the polymer is increased in the T-die used for the second fiber. A method of reducing the flow rate of gas. Alternatively, as the T-die for melt-blown spinning, a method of using a T-die formed by mixing holes for the first fiber (small hole diameter) and holes (large hole diameter) for the second fiber in a predetermined ratio may be used. By these methods, it is possible to form a melt-blown nonwoven fabric in which the first fibers and the second fibers have a predetermined ratio. In this case, it is ideal that so-called two types of fibers, the first fiber and the second fiber, can be simultaneously formed using one T-die, and can be mixed at the same time of formation.

As explained above, this mouth mask 1 has the above-mentioned structure, and the above-mentioned effects that can be multiplied can be achieved in the filter sheet 11 . Therefore, compared with a mask that does not have the above-mentioned structure, this mask 1 can balance the trapping performance and the breathability of mutually opposite characteristics, and can allow both to be improved together. Thereby, this mouth mask 1, compares with the mouth mask that does not possess the above-mentioned structure, can restrain the wearer's suction of tiny particulate matter (PM2.5) and the like in the atmosphere to a very small amount.

As far as the ideal aspect of this embodiment is concerned, the ratio of the first fiber to the second fiber in the filter sheet 11 (based on the number of s-dimensions) is 5:4 to 10:1 (56%:44% ~91%: 9%) is ideal. That is, when the ratio of the first fiber to the second fiber is 5/4 (5:4) or more, it is preferable that the first fiber can be increased more than when it is smaller than this. Thereby, since the area where charge can be held by the electretization treatment can be increased, that is, the area where charge can be increased can be increased, so that the trapping performance can be relatively improved. On the other hand, when the ratio of the first fiber to the second fiber is 10/1 (10:1) or less, the second fiber can be increased more than that, which is preferable. This can further suppress the gap between the fibers from becoming too narrow, so that the air permeability can be further improved. In this way, the trapping performance and air permeability can be more reliably balanced and improved. The ratio of the first fiber to the second fiber (based on the number of fibers) is ideally 3:2 to 5:1 (60%: 40% to 83%: 17%), more ideally 5:3 to 3: 1 (63%: 37% to 75%: 25%).

In a preferred aspect of this embodiment, the basis weight of the filter sheet 11 is preferably 5 to 20 g/m ² . That is, when the basis weight is 5 g/m ² or more, it is preferable that the first fiber and the second fiber can be increased more than when it is smaller than this. Thereby, more fibers treated with electret can be increased, and the distance between fibers can be further suppressed from becoming too narrow, so that the collection performance and air permeability can be further improved. On the other hand, when the basis weight is 20 g/m ² or less, it is preferable that the thickness of the filter sheet 11 can be relatively reduced compared with the case where it is larger. Thereby, the electret treatment can be carried out in the inside of the filter sheet 11, and the formation of the non-electret treatment area can be suppressed, so that the collection performance can be further improved. In this way, the trapping performance and air permeability can be more reliably balanced and improved. At this time, the thickness of the filter sheet 11 is ideally 0.1-0.18 mm. When the thickness is 0.1 mm or more, it is preferable that more fibers treated with electret can be relatively increased compared with the case where the thickness is smaller than this. When the thickness is 0.18 mm or less, it is preferable that the electretization treatment can be extended to the inside of the filter sheet 11 and the formation of regions that are not electretized can be suppressed as compared with a larger thickness. At this time, the mask 1 of the final product is laminated with a plurality of filter sheets 11. As a whole, even if the basis weight of the plurality of filter sheets 11 exceeds 20g/m ² , as long as the basis weight of the filter sheets 11 of each layer meets the above range That's it. The reason for this is that the electret treatment and the like can be sufficiently applied to the filter sheets 11 of each layer.

In a preferred aspect of this embodiment, the average fiber diameter of the filter sheet 11 is preferably 2 to 5 μm. In the present mask 1, the average fiber diameter is in the range of 2 to 5 μm, that is, within the range of the first fibers, it can be said that it is not too thin or too thick as a whole. That is, since fibers with a small fiber diameter and fibers with a large fiber diameter are present in an appropriate balance near the side with a small fiber diameter, the electretization treatment increases the charged area while suppressing the interaction between the fibers. When the interval becomes too narrow, the reduction of the air permeability of the filter sheet can be suppressed. Thereby, it is possible to balance the trapping performance and the air permeability, that is, to further improve both. In other words, since the average fiber diameter is 2 μm or more, there may be few fibers having a smaller fiber diameter, for example, among the first fibers. As a result, the distance between the fibers is narrowed, and the gas is difficult to pass through the filter sheet, so that the so-called decrease in air permeability can be more reliably prevented. Also, since the average fiber diameter is 5 μm or less, there may be few fibers having a larger fiber diameter among the second fibers, for example. Thereby, it is possible to more reliably prevent a situation in which air permeability is reduced due to the fact that the voids formed by mixing the second fibers in the filter sheet become too large and the voids are filled with the first fibers. Also, from the same reason, it is desirable that the fiber diameter at which the number of fibers becomes the largest is approximately 2 to 5 μm.

In a preferable aspect of this embodiment, it is preferable that the filter sheet 11 is formed of a melt-blown nonwoven fabric. Since the mask 1 is formed of a melt-blown nonwoven fabric, the fiber diameters, fiber ratios, and fiber densities of the above-mentioned first fibers and second fibers can be easily formed to desired values. That is, the basis weight, thickness, and density of the filter sheet 11 can be easily set to desired values. Thereby, it is possible to balance the trapping performance and the air permeability, that is, to further improve both.

In a preferred aspect of this embodiment, the filter sheet 11 is preferably laminated in two or more layers in the thickness direction of the mask 1 . This mouth mask 1, owing to be the above-mentioned filter sheet 11 that trapping performance and air permeability are promoted together in thickness direction lamination more than two layers, so, can suppress the descending of the air permeability that may decline according to the lamination number of filter sheet 11, Moreover, the collection performance can be further improved compared with the case of a single layer. Thereby, the mask 1 with significantly improved trapping performance can be obtained while suppressing the decrease of air permeability as much as possible.

In a preferred aspect of the present embodiment, the filter sheet 11 preferably has a charge amount of 500 C (coulombs) or more per unit basis weight (g/m ² ). Due to the more charge, more tiny substances can be captured. Since the mask 1 has the above-mentioned predetermined structure of the first fiber, the second fiber, etc., the average unit basis weight (g/m ² ) of the electret treatment can hold an electric charge of 500C or more. Thereby, very high trapping performance can be obtained. It is more preferable that the average unit basis weight (g/m ² ) of the filter sheet 11 has a charge amount of 600C or more. In addition, although the upper limit is not particularly limited, an average unit basis weight (g/m ² ) of 1000C or less is desirable in view of the influence of static electricity on the human body.

In terms of other embodiments, in the filter sheet 11 of the mouth mask 1, the fiber diameter distribution of the first fibers is preferably the first peak with the number of the first fibers in the range of greater than 1 μm and less than 5 μm. Furthermore, the fiber diameter distribution of the second fibers preferably has a second peak with the number of second fibers in the range of fiber diameters greater than 5 μm and less than 15 μm. Furthermore, it is desirable that the number of first fibers of the first peak in the filter sheet 11 is larger than the number of second fibers of the second peak. However, the fiber diameter distribution is exemplified by a histogram showing the relationship between the fiber diameter and the number of fibers. The histogram is a graph showing the number of fibers (frequency or frequency) by fiber diameter class (data interval). The width of the fiber diameter class (the width of the data interval) is set to k [μm] (k is an integer of 4/2 or less) considering that the range of the fiber diameter of the first fiber is 4 μm (5 μm-1 μm). .

Here, the fiber diameter distribution of the first fiber has the first peak, which means that the histogram shows the highest number of fibers (frequency or frequency) in the plurality of data intervals included in the range of the fiber diameter of the first fiber. Data range of values. Similarly, the fiber diameter distribution of the second fibers has a second peak, which means that among the plurality of data intervals included in the range of the fiber diameters of the second fibers in the histogram, there is a data interval in which the number of fibers shows the highest value. In addition, having a second peak in the range where the fiber diameter is greater than 5 μm refers to the remaining plural data intervals including the smallest data interval including 5 μm (example: 5 μm to less than 6 μm) among the plurality of data intervals including the second fiber A data interval (example: a data interval including a fiber diameter of 6 μm or more) has a second peak. In other words, it indicates that the second peak is away from the boundary (5 μm) between the first fiber and the second fiber, and the second peak does not exist in the data interval adjacent to the boundary (example: 5 μm to less than 6 μm), but in the data away from the boundary In a section (example: any data section including a fiber diameter of 6 μm or more), the second peak exists. Therefore, a minimum value of the number of fibers may exist in any of the data intervals from the data interval smaller than the second peak to the boundary (5 μm). Visually, between the first peak and the second peak of the number of fibers, there may be a so-called low peak of the number of fibers slightly closer to the second peak than the boundary. If the fiber diameter distribution of the first fiber and the fiber diameter distribution of the second fiber are respectively set to be roughly convex or roughly bell-shaped, the low peak of the number of fibers becomes clear if the two are properly separated, but, If the two are close, the low peak of the number of fibers becomes unclear. Therefore, the degree of proximity between the two can be judged from the clarity of the existence of the low peak (minimum value).

In the mask 1 of other above-mentioned embodiments, the second peak of the second fiber is away from the fiber diameter 5 μm as the boundary of the first fiber and the second fiber, so it exists away from the range of the first fiber and the first peak, The number of first fibers at the first peak is greater than the number of second fibers at the second peak. That is, the fibers of the filter sheet 11 can be more clearly classified into the first group of first fibers represented by the first peak and the second group of second fibers represented by the second peak. As a result, although the fiber diameter distribution of the first fiber and the fiber diameter distribution of the second fiber are close to each other, they continue to separate from each other, and the effect of the electret treatment is maintained in the first group of the first fiber, and the collection performance is maintained. , it is probably easier to generate voids in the second group of the second fibers, which can further reduce the pressure loss. In this way, the air permeability can be further improved without excessively changing the trapping performance of the filter sheet.

Here, in the histogram, the second peak has a data section in the range of more than 5 μm and less than 15 μm. However, although the fiber diameter distribution of the first fiber and the fiber diameter distribution of the second fiber are close to each other, from the viewpoint of being appropriately separated from each other, it is ideal that the second peak exists in a data interval in the range of greater than 6 μm and less than 12 μm. A data interval in the range of 10 μm is more desirable. Also, from the same viewpoint, the difference between the first peak (data interval) and the second peak (data interval) is preferably 2 μm to 10 μm, and 3 μm to 8 μm.

In addition, in this specification, various values are measured by the following method.

(1) Fiber diameter and average fiber diameter Use any one of the following method 1~method 2. (method 1) Ten samples of vertical x horizontal = 5 mm x 5 mm were cut out from arbitrary locations on the sheet to be measured. Then, a scanning electron microscope (VE-7800 manufactured by KEYENCE Co., Ltd.) was used to take one picture of the surface of the sample at a magnification of 500 times, and a total of 10 pictures were taken. The fiber diameters of a predetermined number (example: 10) of fibers are measured on the outermost surface in each photograph. Each fiber diameter is measured with an effective figure of 0.01 μm. Moreover, the value obtained by dividing the total fiber diameter of each fiber by the measured number of fibers was defined as the average fiber diameter. (method 2) Ten samples of vertical x horizontal = 5 mm x 5 mm were cut out from arbitrary locations on the sheet to be measured. Then, a scanning electron microscope (VE-7800 manufactured by KEYENCE Co., Ltd.) was used to photograph the cross-section of the sample one by one at a magnification of 500 times, and a total of 10 photographs were taken. The fiber diameters of all the fibers with clear cross-sections were measured on the outermost surface in each photograph. In addition, in the case of an ellipse, an indeterminate shape, etc., the smallest diameter is used as the fiber diameter. Each fiber diameter is measured with an effective figure of 0.01 μm. Moreover, the value obtained by dividing the total fiber diameter of each fiber by the measured number of fibers was defined as the average fiber diameter.

(2) Collection Efficiency and Pressure Loss One sample with a diameter of 120 mm was cut out from an arbitrary place on the sheet to be measured. And, in mask performance testing machine AP-9000 type (manufactured by Shibata Scientific Co., Ltd.), the sample is installed on the special fixture of the testing machine (measurement range 100mmφ=filter sheet diameter 100mm). After that, in a space containing NaCl: 0.06 to 0.1 μmφ particles adjusted to a concentration of 0.5 mg/m ³ (example: air), the gas is sucked through the sample at a flow rate of 85 L/min, and the gas before passing the sample is measured. The particle concentration and pressure of the sample, and the particle concentration of the gas after passing through, calculate the collection efficiency for one minute from the difference in particle concentration, and calculate the pressure loss from the difference in pressure. Capture efficiency is an index of capture performance, which means that the higher the capture efficiency, the higher the capture performance. Pressure loss is an indicator of air permeability, the lower the pressure, the higher the air permeability.

(3) The amount of charge in the sheet Measurement is performed by thermally stimulated charge decay (Thermally Stimulated Chagrge Decay: TSCD method), that is, a sample of vertical x horizontal = 50 mm x 50 mm is cut out from an arbitrary position of the sheet to be measured. Then, place the sample on a hot plate and heat it from 20°C to 140°C at a constant rate of temperature increase, measure the temperature and surface potential of the sample, and calculate the charge of the sample from the graph of surface potential and temperature.

(4) Basis weight, thickness, and fiber density of the sheet. Basis weight of the sheet: Ten samples of 5 cm x 5 cm were cut out from an arbitrary position of the sheet to be measured. In addition, the sample is dried in an environment of 100° C. or higher, and then the mass of the sample is measured. The measured mass % was divided by the area of the sample to calculate the basis weight of the sample. The average value of the basis weights of 10 samples was taken as the basis weight of the sheet.・Thickness of the sheet: Using a thickness gauge type FS-60DS (manufactured by Daiei Chemical Seiki Seisakusho Co., Ltd.) equipped with a gauge head of 15 cm ² , the thickness of the sheet was measured under a measuring load of 3 g/cm ² . The thicknesses of three arbitrary places of the sheet to be measured are measured, and the average value of the thicknesses of the three places is taken as the thickness of the sheet.・Fiber density of the sheet: The fiber density of the sheet is calculated by dividing the basis weight of the sheet obtained by the above method by the thickness of the sheet obtained by the above method.

(5) Fiber Diameter Distribution (Histogram) In the method (1) above, each fiber diameter is measured for a predetermined number n fibers of the filter sheet 11 to obtain n fiber diameter data. Next, the range R (=max-min) of the fiber diameter is calculated from the difference between the maximum value max and the minimum value min of the fiber diameter among n pieces of fiber diameter data. Next, the range R is divided by n ^0.5 , the quotient k is rounded to an integer value in μm, and this is taken as the interval (width) h of the data interval (level). Next, the starting point for classifying the data intervals is set to 0 μm, and the interval h is added to the value of the starting point, and each data interval up to the data interval including at least the maximum value is determined. Next, the horizontal axis is the data interval (fiber diameter), and the vertical axis is the frequency ratio (ratio of the number of pieces), that is, the number of pieces in each data section/the total number of pieces x 100 (%), and a columnar shape is made. picture. However, the histograms ( FIG. 3 , FIG. 4 and FIG. 5 ) of Example 1, Comparative Example 1, and Example 5 described later are as follows. n is 100 (~400), and max and min are 15 μm and 1 μm, respectively. Then, R=15-1=14 was calculated, k=1.4 (~0.7) was obtained from R/n ^0.5 =14/100 ^0.5 (~400 ^0.5 ), and h=1 μm. Then, a histogram was created by setting the starting point for classifying data intervals as 0 μm. In the created histogram, the maximum value of the frequency (ratio) in the plurality of data intervals ranging from 1 μm to 5 μm in the range of the first fiber was defined as the first peak (data interval). In addition, in a plurality of data intervals of 5 μm to less than 15 μm as the range of the second fiber, the maximum value of the frequency (ratio) is taken as the second peak (data interval). [Example]

The filter sheets for the mask 1 were evaluated as follows, assuming a case of using one sheet and a case where two sheets were stacked and used. Table 1 summarizing the evaluation results is described on the last page. Hereinafter, it will be described in detail.

(1) Case of one filter sheet (Example 1) As a sample of Example 1, a filter sheet 11 (one sheet, single layer) formed of a melt-blown nonwoven fabric having a basis weight of about 10 g/m ² was prepared. For the filter sheet 11, the fiber diameter and average fiber diameter, basis weight, thickness and fiber density, electric charge, collection efficiency and pressure loss were measured. As a result, the ratio of the number of the first fiber (fiber diameter 1 to 5 μm) was 73%, the ratio of the number of the second fiber (fiber diameter 5 to 15 μm) was 27%, and the ratio of the number of the first fiber and the second fiber The ratio of number is 100% (>90%), the average fiber diameter is 4.12μm, the basis weight is 10.5g/m ² , the thickness is 0.150mm, the fiber density is 0.070g/cm ³ , the average unit basis weight ((g/ m ² ) ^-1 ) has a high charge of 629.3C.

FIG. 3 is a histogram showing the fiber diameter distribution (based on the number of fibers) of the filter sheet 11 of Example 1. FIG. The horizontal axis represents the data interval, and represents the fiber diameter per 1 μm from 0 μm. For example, the data section "1" μm includes fiber diameters ranging from 0 μm to 1 μm. The vertical axis represents the frequency of each data interval, and the ratio (%) of the number of fibers in each data interval to the number of fibers in the entire data interval is represented on a scale of 1%. Round below the decimal point. In the filter sheet 11 of Example 1, the frequency is very high in the data interval of the fiber diameter of 2 to 4 μm, and the frequency is the highest in the data interval of 4 μm in particular. That is, the first peak exists in the data interval of 4 μm. On the other hand, the second peak exists in the data interval of 6 μm. Therefore, the second peak exists in the data interval adjacent to the boundary (5 μm) between the first fiber and the second fiber.

On the other hand, with respect to the filter sheet 11, the collection efficiency and pressure loss were measured. In addition, in the measurement of collection efficiency and pressure loss, the data will not change due to the presence or absence of the inner sheet 12 and the outer sheet 13, so the collection efficiency and pressure loss of the filter sheet 11 can be regarded as the collection efficiency and pressure loss of the mouth mask 1. Pressure loss (same below). As a result, the collection efficiency was very high at 83.3%, and the pressure loss was very low at 38Pa. That is, it is clear that the filter sheet 11 of Example 1 has good trapping performance and air permeability.

(Example 2) As a sample of Example 2, a filter sheet 11 (one sheet, single layer) formed of a melt-blown nonwoven fabric having a basis weight of about 7 g/m ² was prepared. Furthermore, with respect to the filter sheet 11, the basis weight, thickness, and fiber density, collection efficiency, and pressure loss were measured. As a result, the basis weight was 7.3 g/m ² , the thickness was 0.110 mm, and the fiber density was 0.066 g/cm ³ . In addition, since Example 1 is the same as the production method, it is conceivable that the ratio of the number of first fibers, the ratio of the number of second fibers, and the average fiber diameter are approximately the same.

On the other hand, with respect to the filter sheet 11, the collection efficiency and pressure loss were measured. As a result, the collection efficiency was extremely high at 87.5%, and the pressure loss was extremely low at 29 Pa. That is, it is known that the filter sheet 11 of Example 2 also has good trapping performance and air permeability.

(Example 5) As a sample of Example 5, a filter sheet 11 (one piece, single layer) formed of a melt-blown nonwoven fabric having a basis weight of about 10 g/m ² and a relatively large proportion of first fibers was prepared. For the filter sheet 11, the fiber diameter and average fiber diameter, basis weight, thickness and fiber density, electric charge, collection efficiency and pressure loss were measured. As a result, the ratio of the number of first fibers (fiber diameter 1 to 5 μm) was 81%, the ratio of the number of second fibers (fiber diameter 5 to 15 μm) was 18%, the average fiber diameter was 3.34 μm, and the basis weight It is 10.5g/m ² , the thickness is 0.150mm, and the fiber density is 0.070g/cm ³ .

FIG. 5 is a histogram showing the fiber diameter distribution (based on the number of fibers) of the filter sheet 11 of Example 5. FIG. About the horizontal axis and the vertical axis, it is the same as that of FIG. 3 . In the filter sheet 11 of Example 5, the fiber diameter distribution of the first fibers (1 to 5 μm) has the highest frequency in the data interval of 2 μm, and therefore has the first peak in the number of fibers in the data interval of 2 μm. On the other hand, the fiber diameter distribution of the second fiber (5 to 15 μm) has the highest frequency in the data section of 7 μm where the fiber diameter is larger than 5 μm, and therefore has the second peak in the number of fibers in the data section of 7 μm. Therefore, the minimum value of the number of fibers exists in the data interval of 6 μm from the data interval smaller than 7 μm to the data interval up to the boundary (5 μm). There is a difference of 5 μm between the data interval of the first peak and the data interval of the second peak. In other words, the second peak of the second fiber is away from the fiber diameter of 5 μm, which is the boundary between the first fiber and the second fiber, and thus exists away from the range of the first fiber and the first peak. That is, the second peak exists in the data interval where there is no boundary (5 μm) adjacent to the first fiber and the second fiber (distance). Therefore, compared with the filter sheet 11 of Example 1, the filter sheet 11 of Example 5 can be more clearly divided into the first group of the first fibers represented by the first peak and the representative group represented by the second peak. Group 2 of the 2nd fiber. Furthermore, the frequency (ratio of the number of fibers) of the first peak in the filter sheet 11 is higher than the frequency (ratio of the number of fibers) of the second peak of the second peak. The frequency (ratio of the number of items) is about 31% of the first peak, about 5% of the second peak.

On the other hand, with respect to the filter sheet 11, the collection efficiency and pressure loss were measured. As a result, the collection efficiency was a very high 79.6%, and the pressure loss was a very low 37Pa. That is, it is clear that the filter sheet 11 of Example 5 has good trapping performance and air permeability similar to the filter sheet 11 of Example 1.

(Comparative Example 1) A filter sheet (one piece, single layer) formed of a melt-blown nonwoven fabric produced by a production method different from that of Examples 1 and 2 and having a basis weight of about 20 g/m ² was prepared as a comparative example 1 sample. For the filter sheet, measure the fiber diameter and average fiber diameter, basis weight, thickness and fiber density, electric charge, collection efficiency and pressure loss. As a result, the ratio of the number of first fibers (fiber diameter 1 to 5 μm) was 45%, the ratio of the number of second fibers (fiber diameter 5 to 15 μm) was 55%, the average fiber diameter was 5.44 μm, and the basis weight It is 21.5g/m ² , the thickness is 0.196mm, the fiber density is 0.11g/cm ³ , and the charge amount per unit basis weight ((g/m ² ) ^-1 ) is as low as 481.7C.

4 is a histogram showing the fiber diameter distribution (based on the number of fibers) of the filter sheet of Comparative Example 1. FIG. About the horizontal axis and the vertical axis, it is the same as that of FIG. 3 . In the filter sheet of Comparative Example 1, in the data interval of the fiber diameter of 3 to 7 μm, the overall frequency is about the same high, and in particular, the frequency is the highest in the data interval of 6 μm. That is, the first peak exists in the data intervals of 3 μm and 4 μm. On the other hand, the second peak exists in the data interval of 6 μm. Therefore, the second peak exists in the data interval adjacent to the boundary (5 μm) between the first fiber and the second fiber.

On the other hand, the collection efficiency and pressure loss were measured for the filter sheet. As a result, the collection efficiency was as low as 65.9%, and the pressure loss was as high as 68 Pa. That is, it turns out that the filter sheet collection performance and air permeability of Comparative Example 1 are not as good as in Examples 1, 2, and 5.

In addition, when comparing the sample of Example 1 with the sample of Example 2, since the production method is the same, it is conceivable that the ratio of the number of first fibers, the ratio of the number of second fibers, and the average fiber diameter are approximately the same, The fiber density is almost the same, however, regarding Example 2, it can be seen that the collection efficiency and pressure loss are improved. The reason is that with regard to the collection efficiency, if compared with the filter sheet 11 of Example 1, although the fiber density of the filter sheet 11 of Example 2 is about the same, but because the thickness is thinner, it is conceivable that it is due to the electret treatment. Spread to the inside of the filter sheet 11 of Example 2. Also, regarding the pressure loss, since the filter sheet 11 of Example 2 is thin, it is conceivable that gas passes through easily.

Comparing the sample of Example 5 with the sample of Example 1, although the production method is the same, the proportion of the first fiber is relatively large, so although the average fiber diameter is relatively smaller, the fiber density is almost the same. . However, for the sample of Example 5, the pressure loss was lower than that of the sample of Example 1. Although the fiber diameter distributions of the first fiber and the second fiber are close to each other, they continue to separate. This is presumably because voids are more likely to be formed in the area around the second fiber, and the pressure loss can be further reduced.

On the other hand, if the samples of Examples 1, 2, and 5 are compared with the sample of Comparative Example 1, since the manufacturing methods are different, the ratio of the number of the first fibers, the ratio of the number of the second fibers, and the average Fiber diameter and fiber density are different. Therefore, compared with the filter sheet of Comparative Example 1, the collection efficiency and pressure loss of the filter sheets 11 of Examples 1, 2, and 5 are improved. That is, since the above-mentioned various effects can be achieved by having the structure of the present filter sheet 11, it can be seen that both the trapping performance and the air permeability are improved, and they are improved. Furthermore, from the aforementioned differences that are useful for improving the collection performance and air permeability, it can be seen that the proportion of the first fibers in the filter sheet 11 is preferably greater than the proportion of the second fibers. Also, it can be seen that the ideal fiber density is about 0.030 to 0.10 g/cm ³ . Furthermore, it can be seen that the ratio of the first fiber to the second fiber in the filter sheet 11 (on the basis of the number of fibers in the X dimension) is about 5:4 to 10:1, which is ideal. Furthermore, it can be seen that the basis weight of the filter sheet 11 is about 5-20 g/m ² is ideal. It can be seen that the average fiber diameter of the filter sheet 11 is preferably about 2 to 5 μm. It can be seen that the average charge amount per basis weight ((g/m ² ) ^-1 ) of the filter sheet 11 is preferably about 500C or more. It can be seen that the data interval in which the second peak exists in the range of more than 6 μm and less than 12 μm is ideal. It can be seen that the difference between the data interval of the first peak and the data interval of the second peak is preferably 2 μm or more and 10 μm or less.

(2) In the case of 2 filter sheets (Example 3) Two filter sheets 11 of Example 1 were prepared, and the filter sheets 11 laminated in the thickness direction were used as samples of Example 3. The collection efficiency and pressure loss were measured for the filter sheet 11 laminated thereon. As a result, it was found that the collection efficiency was very high at 97.1%. That is, it can be seen that the filter sheet 11 of Example 3 has further improved collection performance and pressure loss. In addition, since two filter sheets 11 are stacked, the pressure loss is approximately twice the value of the pressure loss when there is one filter sheet 11 , that is, it is as high as 84Pa. However, since the value of the pressure loss is small when there are one filter sheet 11, it can be seen that even when there are two filter sheets 11, the value of the pressure loss is not so large.

(Example 4) Two filter sheets 11 of Example 2 were prepared, and the filter sheets 11 laminated in the thickness direction were used as samples of Example 4. The collection efficiency and pressure loss were measured for the filter sheet 11 laminated thereon. As a result, it was found that the collection efficiency was as high as 98.4%. That is, it can be seen that the filter sheet 11 of Example 4 has further improved collection performance and pressure loss. In addition, since two filter sheets 11 are stacked, the pressure loss is approximately twice the value of the pressure loss when there is one filter sheet 11 , that is, it is as high as 60 Pa. However, since the value of the pressure loss is small when there are one filter sheet 11, it can be seen that even when there are two filter sheets 11, the value of the pressure loss is not so large.

(Example 6) Two filter sheets 11 of Example 5 were prepared, and the filter sheets 11 laminated in the thickness direction were used as samples of Example 6. The collection efficiency and pressure loss were measured for the filter sheet 11 laminated thereon. As a result, it was found that the collection efficiency was as high as 95.4%. That is, it can be seen that the filter sheet 11 of Example 6 has further improved collection performance and pressure loss. In addition, since two filter sheets 11 are stacked, the pressure loss is approximately twice the value of the pressure loss when there is one filter sheet 11 , that is, it is as high as 75 Pa. However, since the value of the pressure loss is small when there are one filter sheet 11, it can be seen that even when there are two filter sheets 11, the value of the pressure loss is not so large. Furthermore, in Example 6, although the fiber diameter distributions of the first fiber and the second fiber are close to each other, the separation of the two distributions continues, and while ensuring a gap, two filter sheets 11 are laminated to make the flow of fine particles The road (gap) becomes longer. Therefore, gas can easily flow through the flow path (void), and it is difficult for fine particles to pass through the void. Thus, compared with the sample of Example 3, the sample of Example 6 does not change the collection efficiency much (97.1%→95.4%: minus 1.8 percentage points), and the pressure loss can be reduced (84Pa→75Pa: minus 11%). That is, while maintaining the effect of the electret treatment in the first group of the first fibers, it is likely that voids are more likely to be generated in the second group of the second fibers, thereby further reducing the pressure loss.

(comparative example 2) Two filter sheets of Comparative Example 1 were prepared, and the filter sheets laminated in the thickness direction were used as samples of Example 2. The collection efficiency and pressure loss of the laminated filter sheets are measured. As a result, it was found that the collection efficiency was as high as 85.3%. That is, it can be seen that the filter sheet 11 of Comparative Example 2 has further improved collection performance and pressure loss. However, since two filter sheets are laminated, the pressure loss is about twice the value of the pressure loss when there is one filter sheet, that is, the height is 111Pa. Since the value of the pressure loss is large when there is one filter sheet, it can be seen that the value of the pressure loss becomes very large when there are two filter sheets.

In the specifications of masks (filter sheets), for example, the specifications of GB/T32610-2016, it is required to have a collection efficiency of more than 90% and a pressure loss of 90Pa or less in the so-called (2) evaluation method of collection efficiency and pressure loss. The characteristics of the same characteristics. One filter sheet 11 in Example 1, Example 2, and Example 5 showed values very close to 83.3%, 87.5%, and 79.6% in terms of collection efficiency, respectively, but did not reach 90% at all. However, as shown in Example 3, Example 4, and Example 6, it can be found that by laminating two filter sheets 11 of Example 1, Example 2, and Example 5, the collection efficiency can be obtained respectively. Such as 97.1%, 98.4% and 95.4% are so-called extremely good characteristics that meet the requirements of more than 90%. Furthermore, it can be seen that the pressure loss exhibits good characteristics, such as 84Pa, 60Pa, and 75Pa, which satisfy the requirement of 90Pa or less, respectively. That is, it can be found that by laminating two filter sheets 11 of Example 1, Example 2, and Example 3, a mask 1 that can satisfy the specifications of GB/T32610-2016 can be formed. In addition, for Comparative Example 2, even if two filter sheets of Comparative Example 1 are stacked, the collection efficiency becomes 85.3%, but it cannot meet the so-called requirement of 90% or more, and the pressure loss is 111Pa, which cannot meet the so-called requirement of 90Pa or less. In these cases, as a method for further improving the collection performance and air permeability, it is shown that the use of a thick filter sheet with an electret treatment applied by laminating two or more layers The method of chemically treating thin filter sheets is the most effective.

The absorbent article of the present invention is not limited to the respective embodiments described above, and can be appropriately combined, modified, and the like within a range that does not depart from the object and spirit of the present invention.

1: mask 2: Mask body 3: Ear hook 11: filter sheet 12: Inner sheet 13: Outer sheet

[FIG. 1] A schematic diagram showing a structural example of the mask of the embodiment. [FIG. 2] It is a partial sectional view of the mask shown in FIG. 1. [FIG. 3] It is a graph of the fiber diameter distribution of the filter sheet of Example 1. [FIG. [FIG. 4] It is a graph of the fiber diameter distribution of the filter sheet of the comparative example 1. [FIG. [FIG. 5] It is a graph of the fiber diameter distribution of the filter sheet of Example 5. [FIG.

2: Mask body

11: filter sheet

12: Inner sheet

13: Outer sheet

Claims (8)

A mask is a mask with a mask body that covers the wearer's mouth and nose, wherein the mask body includes: an inner sheet, an outer sheet, and a filter sheet, and the filter sheet is located between the inner sheet and the outer The sheets are formed of electretized non-woven fabric, the filter sheet includes: first fibers having a fiber diameter of 1 μm to less than 5 μm, and second fibers having a fiber diameter of 5 μm to less than 15 μm, the aforementioned The ratio of the aforementioned first fiber in the filter sheet is more than the ratio of the aforementioned second fiber, the ratio of the aforementioned first fiber and the aforementioned second fiber in the aforementioned filter sheet is more than 90% of the aforementioned filter sheet, and the ratio of the aforementioned filter sheet The fiber density is 0.03-0.10 g/cm ³ , and the first fiber and the second fiber are formed of the same material. The mask according to claim 1, wherein the ratio of the first fiber to the second fiber in the filter sheet is 5:4 to 10:1. The mask according to claim 1 or 2, wherein the basis weight of the filter sheet is 5-20 g/m ² . The mask according to claim 1 or 2, wherein the average fiber diameter of the filter sheet is 2-5 μm. The mask according to claim 1 or 2, wherein the aforementioned filter sheet is formed of melt-blown non-woven fabric. The mask according to claim 1 or 2, wherein the filter sheet is laminated with more than two layers in the thickness direction of the mask. As the mask of claim 1 or 2, wherein the fiber diameter distribution of the aforementioned 1st fiber has the 1st peak of the number of bars of the aforementioned 1st fiber, The fiber diameter distribution of the aforementioned second fibers has a second peak of the number of the aforementioned second fibers, and the fiber diameter of the fibers is in a range larger than 5 μm, The number of the first fibers of the first peak in the filter sheet is greater than the number of the second fibers of the second peak. The mask according to claim 1 or 2, wherein the aforementioned filter sheet has an average charge per unit basis weight (g/m ² ) of 500C or more.

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