BACKGROUND

A filter for a mask is conventionally known. This filter is one type of a filter for a gas having a function such as dust removal or filtration.

JP 4126679 describes an electret filter. The following description is in JP 4126679: "A filter, made by sequentially stacking an electretized melt-blown nonwoven fabric made from an ultrafine fiber of a fiber diameter of 7 to 15 μπι manufactured by melt-blowing a synthetic resin, a mixed web that is made by defibrating and mixing the electretized melt-blown nonwoven fabric and a fiber whose base material is wool of a fiber diameter of at least 15 μπι or more and folded in a cross-layer method, and a spunbond nonwoven fabric."

JP 4418906 describes a dust mask filter. The following description is in JP 4418906: "A dust mask filter, wherein in a range from a center to an outer periphery, an airflow resistance per unit area gradually decreases heading from the center to the outer periphery and a plurality of concentric circular pleats is folded and formed."

SUMMARY

If one sheet-shaped filter described in JP 4126679 is to be provided as-is to the mask, to increase filtering efficiency, an area of this filter needs to be increased. However, when the filter itself is enlarged, a viewing angle of a user comes to be narrowed, and it is therefore desirable to suppress external dimensions of the filter. In relation to this point, the filter according to JP 4418906 gains a surface area of the filter while suppressing the external dimensions by forming the concentric circular pleats. However, when this method is adopted, an escalation value of pressure resistance of the mask increases, and there is a possibility that breathability will be impaired. Moreover, forming pleats leads to increased manufacturing costs for the filter.

Therefore, desired is to provide a mask filter unit that can realize both suppression of pressure loss and improvement of filtering efficiency at the lowest cost possible.

A filter unit according to one aspect of the present invention is a filter unit for a mask that covers at least a portion of the face of a person, provided with: a charged filter that has an inflow surface through which air inflows, an outflow surface through which the air outflows, and a side surface that extends from the inflow surface to the outflow surface; wherein the charged filter is provided with a first layer and a second layer; the first layer is provided with a base and a plurality of solid protrusions that extends from a surface of the base and is adjacent to the second layer, the protrusions having a stem portion that has a root-side side surface and a tip-side side surface; the second layer is provided with a base; and a first angle, which is one angle from among an angle formed between the root-side side surface of the stem portion and the base of the first layer and an angle formed between the tip-side side surface of the stem portion and the base of the second layer, is 90° or more and less than 180° and a second angle, which is the other angle among these, is 45° or more and less than 180°.

In such an aspect, because a corner of a flow path of a gas is ensured to be wide on a root side and a tip side respectively of the stem portion of the protrusion, in the flow path, which is formed by two adjacent protrusions, the gas comes to travel not only near a center thereof but also near the corner, facilitating the gas flowing in the filter. Because the protrusion is solid, a layer structure of the filter can be stabilized and a flow path between the layers can continue to be maintained. Therefore, suppression of pressure loss and improvement of filtering efficiency can be realized. Additionally, because the charged filter can be made by a simple method of stacking layers, manufacturing costs of the filter unit can be suppressed.

According to one aspect of the present invention, it becomes possible to provide a mask filter unit that can realize both suppression of pressure loss and improvement of filtering efficiency at a low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating an example of a mask provided with a filter unit according to an embodiment.

FIG. 2 is a perspective view of a sheet (layer) used in the filter unit according to the embodiment.

FIG. 3a is a side view illustrating a protrusion 20 extending from a base 11.

FIG. 3b is a side view illustrating a protrusion 20 having a cap portion 22.

FIG. 4 is a diagram for describing a projection of the protrusion onto a virtual surface. FIG. 5 is a diagram illustrating several examples of the projection image of the protrusion.

FIG. 6 is a diagram illustrating several examples of the projection image of the protrusion.

FIG. 7 is a diagram for describing a relationship between a shape of the protrusion and filtering efficiency and pressure loss.

FIG. 8 is a diagram illustrating several examples of the projection image of the protrusion. FIG. 9 is a diagram illustrating several examples of the projection image of the protrusion.

FIG. 10 is a diagram illustrating several examples of the projection image of the protrusion.

FIG. 11 is a diagram illustrating several examples of the projection image of the protrusion.

FIG. 12 is a diagram illustrating several examples of the projection image of the protrusion.

FIG. 13 is a diagram illustrating an example of the sheet.

FIG. 14 is a diagram illustrating an example of the sheet.

FIG. 15 is a perspective view and a partial enlarged view of a filter unit according to the embodiment.

FIG. 16 is a perspective view and a partial enlarged view of a filter unit according to the embodiment.

FIG. 17 is a perspective view of a filter unit according to the embodiment.

FIG. 18 is a diagram illustrating an example of stacking.

FIG. 19 is a diagram illustrating an example of stacking.

FIG. 20 is a perspective view illustrating another example of a filter unit according to the embodiment.

FIG. 21 is a perspective view illustrating another example of a mask provided with the filter unit according to the embodiment.

FIG. 22 is an enlarged view of a filter housing portion illustrated in FIG. 21.

FIG. 23 is a table indicating results of examples and comparative examples.

FIG. 24 is graphs illustrating the results of the examples indicated in FIG. 23.

FIG. 25 is graphs illustrating the results of the examples indicated in FIG. 23.

FIG. 26 is graphs illustrating the results of the examples indicated in FIG. 23.

FIG. 27 is a table indicating results of examples and comparative examples.

DETAILED DESCRIPTION

An embodiment of the present invention is described in detail below with reference to the attached drawings. Note that in describing the drawings, identical or equivalent elements are labeled with the same reference signs and redundant description is omitted.

A structure of a filter unit according to the embodiment is described. A "filter unit" in the present specification is an article having a function of removing a fine particle (a minute solid or foreign matter) mixed in a gas (for example, air). As examples of the fine particle, dust, dirt, pollen, and the like can be mentioned; however, an object to be removed by the filter unit is not limited thereto, and the filter unit may remove any fine particle in the gas. The filter unit is used for a mask. A "mask" in the present specification is an article or a device that covers at least a portion of the face of a person (particularly, the nose and the mouth of the person) and is more specifically an article or a device provided with a portion that covers at least a portion of face of the person. One example of the mask provided with the filter unit is illustrated in FIG. 1. A mask 200 is described in detail below, but this mask 200 is provided with a filter unit lOOC. Air taken into the mask 200 for respiration of a user is inhaled by the user after passing through the filter unit lOOC.

The expressions, "filter unit for a mask" and "filter unit is used for a mask" signify that the filter unit relates to use of the mask in some aspect. More specifically, they signify that the filter unit is used as at least a portion of a function of the mask or to assist the function of the mask. A "mask provided with a filter unit" is a mask having a structure where air to be inhaled by a person (wearer of the mask) passes through the filter unit. Therefore, not only a mask where the filter unit is provided in a portion covering at least a portion (nose and mouth) of the face of the person but also a mask where the filter unit is provided to a component different from a component covering at least a portion (nose and mouth) of the face of the person (for example, respiration protection equipment with an electric fan) corresponds to the "mask" in the present specification.

The filter unit is provided with at least a charged filter. First, this charged filter is described in detail.

The charged filter is provided with a plurality of layers. At least a portion of the plurality of layers is formed by a sheet 10 illustrated in FIG. 2. The sheet 10 is a thin, plate-like member and is provided with a base 11 and a plurality of solid protrusions 20 disposed on the base 11. A "protrusion" in the present specification is a structure extending outward from one surface of the base 11. Moreover, in the present specification, the surface on which the protrusion 20 is present is defined as a front surface of the layer, the sheet 10, or the base 11 and a surface on which the protrusion 20 is not present is defined as a back surface of the layer, the sheet 10, or the base 11.

Dimensions of the sheet 10 (layer) are not limited and may be set based on any standard, such as a manufacturing process of the charged filter, dimensions of the filter unit, or dimensions of the charged filter. A length and a width of the sheet 10 can take on various values. For example, the length and the width of the sheet 10 can take on values of various ranges, from several centimeters to several decameters. Meanwhile, a thickness of the sheet 10 is set in consideration of, for example, both a dust removal effect (dust collection effect) and ensuring a flow path of the gas, but this thickness is also not limited. Here, the thickness of the sheet 10 is a distance from the back surface of the base 11 to the highest point of the protrusion 20. As one example, a lower limit of the thickness of the sheet 10 may be 60 μπι, 100 μπι, or 140 μπι, and an upper limit thereof may be 2,000 μπι, 900 μπι, or 600 μιη. Note that the thickness of the base 11 and a height of the protrusion 20 can be suitably set within a range of the thickness of the sheet 10. In a certain aspect, the height of the protrusion 20 can be made greater than the thickness of the base 11.

As illustrated in example (a) in FIG. 3, the protrusion 20 of the present embodiment is provided with at least a stem portion 21 extending from the front surface of the base 11. As illustrated in example (b) in FIG. 3, the protrusion 20 may be provided with a cap portion 22 formed on a tip of this stem portion 21, and in this situation, the protrusion 20 exhibits a mushroom shape overall. In fact, a shape of the protrusion 20 is not limited to the example of FIG. 3, and as described below, various shapes are conceivable. An upper surface of the protrusion 20 (that is, an upper surface of the stem portion 21 or the cap portion 22) may be flat or wavy (that is, jagged).

Dimensions of the base 11 and the protrusion 20 are not limited. For example, the thickness of the base 11, the height of the protrusion 20, a height of the stem portion 21, a maximum width of a bottom of the stem portion 21, a width of the tip of the stem portion 21, a maximum width of the cap portion 22, and a protrusion amount of the cap portion 22 from the stem portion 21 may all be freely set. Moreover, a density of the protrusions 20 on the base 11 is also not limited. For example, this density may be about 60 to about 1,550 per square centimeter, about 125 to 690 per square centimeter, or about 200 to about 500 per square centimeter.

A material of the sheet 10 is a thermoplastic resin, and a thermoplastic resin suited to extrusion molding can be used. The thermoplastic resin includes a polyester such as

poly(ethylene terephthalate); a polyamide such as nylon; a polyolefin such as poly(styrene- acrylonitrile), poly(acrylonitrile-butadiene-styrene), or polypropylene; a plasticized polyvinyl chloride; and a copolymer or blend thereof. For example, a polypropylene resin (PP), a mixture of a polypropylene resin (PP) and a polyethylene resin (PE), and an ethylene-vinyl acetate copolymer (EVA) resin can be mentioned as specific examples. In a situation of using the mixture of the PP and the PE, the PP and the PE may be mixed at a weight ratio of about 95:5 to 30:70. Generally, when an amount of the PP increases, the protrusion 20 tends to become hard. Conversely, when the amount of the PP decreases, the protrusion 20 becomes soft. The PP may be a homopolymer or a copolymer. As an example of the PE, low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and the like can be mentioned. Materials of the base 11 and the protrusion 20 in the sheet 10 may be the same material or different materials.

Two examples concerning a manufacturing method of the sheet 10 are illustrated in the present embodiment.

One is a method described in JP 2005-514976U. In this method, first, by extruding the thermoplastic resin from an extrusion die having an opening cut by electrical discharge machining, a strip is formed where a plurality of rail-shaped ribs having a cross-sectional shape of the protrusion is lined up on a base sheet. Next, this strip is pulled by a roller in a cooling tank filled with a cooling liquid such as water. Next, by making an incision in a width direction in each rib at a plurality of positions separated from each other along a longitudinal direction of the rib, for each rib, a plurality of portions corresponding to a thickness of the protrusion is formed. After cutting the rib, the base sheet of the strip is stretched by a predetermined stretch ratio. Specifically, the base sheet is stretched along the longitudinal direction of the rib between a first pair of nip rollers and a second pair of nip rollers driven at mutually different surface speeds. In this process, the base sheet may be stabilized by cooling one of the second pair of nip rollers, which is positioned downstream, while heating the base sheet by heating one of the first pair of nip rollers, which is positioned upstream. By this stretching, a space arises between a plurality of portions of the rib, and this portion becomes the protrusion 20.

The other example is a method described in JP 2008-532699U. In this method, first, by a template having a large number of through holes or by extrusion molding using an extruder, a band-shaped base material is formed where a plurality of columnar bodies forming a plurality of original shapes of the protrusion is lined up on the front surface. Note that the protrusion having the cap portion can be formed by smashing a tip portion of each columnar body by a calender roller while heated. By this process, one sheet 10 is obtained.

An electret treatment is applied to the sheet 10. The layer applied with the electret treatment functions as a charged layer, and the charged filter is obtained. The electret treatment is a treatment that charges the sheet 10 by a corona discharge, heating and cooling, spraying charged particles, or the like. By charging the sheet 10, an effect of dust removal or filtration of each layer can be increased.

Various shapes of the protrusion 20 are described below. Characteristics of the shape of the protrusion 20 can be discovered when the protrusion 20 is viewed from the side. In the present embodiment, as illustrated in FIG. 4, the characteristics of the shape of the protrusion 20 are illustrated using an outer edge of a projection image P obtained by projecting the protrusion 20 onto a virtual surface V orthogonal to the base 11. The virtual surface V is set to intersect a direction in which the gas flows, and this signifies that the virtual surface V is set in an aspect that blocks the flow of the gas. FIG. 5 to 12 are projection images of various protrusions 20; in these diagrams, to facilitate description, the projection image is labeled with the same reference signs as those of the protrusion. Both a first outer edge 23 and a second outer edge 24 of the projection image illustrated in FIG. 5, 6, and 8 to 12 are an outer edge corresponding to a side surface of the stem portion 21. In the present embodiment, in the side surface of the stem portion 21, a portion that includes a connection portion with the base 11 is referred to as a "root-side side surface" and a portion that includes the tip of the stem portion 21 is referred to as a "tip-side side surface." Moreover, in several patterns, a reference line L is illustrated that indicates an extension direction of the stem portion 21. This reference line L is a line that connects midpoints between the first outer edge 23 and the second outer edge 24. In each pattern in FIG. 5 to 12, the base 11 on a lower side corresponds to a base of a first layer, the stem portion 21 (protrusion 20) corresponds to a protrusion of the first layer, and the base 11 on an upper side (base 11 of an adjacent layer) corresponds to a base of a second layer.

In pattern 1, the protrusion 20 is not provided with the cap portion 22 and is formed from only the stem portion 21. The stem portion 21 exhibits a straight columnar shape. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. It can also be said that the first outer edge 23 and the second outer edge 24 extend along the reference line L. An angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°, and an angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is also 90°. Note here that the angles θ, φ in the present specification are angles corresponding to a shape of the flow path of the gas (space) and not angles relating to the solid stem portion 21 itself. An individual "flow path" in the present specification is a space formed between two adjacent protrusions 20. The angles θ, φ are measured in the projection image of the protrusion 20. By setting the angles θ, φ to be right angles, the gas also travels near each corner; therefore, the gas flowing in the flow path is facilitated, which in turn enables suppression of pressure loss of the charged filter. Moreover, because the gas also travels near the corner of the flow path, the minute particle in the gas can be collected even in the corner of the flow path or a portion near this corner. In this manner, the angles θ, φ are crucial elements that affect a flowability of the gas and a value of pressure loss and can also affect filtering efficiency.

Pattern 2 illustrates the protrusion 20 with the cap portion 22 provided on the tip of the stem portion 21 illustrated in pattern 1. In the present specification, regardless of whether the cap portion 22 is provided, the angle φ indicating a shape of the corner of the flow path is the angle formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer and is therefore also 90° in this pattern 2. In this manner, the presence of the cap portion 22 does not affect a determination of the angle φ. In the patterns illustrated below, description is given based on an aspect of the protrusion 20 where the cap portion 22 is not had.

In pattern 3, the stem portion 21 exhibits a tapered shape that tapers toward the tip. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is obtuse. Meanwhile, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is acute but is set to be 45° or more. By setting the angle Θ to be obtuse, travel of the gas near the corner corresponding to this angle Θ is further facilitated.

Moreover, even if the angle φ is acute, if this angle is 45° or more, no less than a certain amount of the gas travels even near the corner corresponding to the angle φ. Therefore, similarly to patterns 1, 2, overall, the gas flowing in the flow path is facilitated overall, which in turn enables suppression of pressure loss of the charged filter. Moreover, because the gas also travels near the corner of the flow path, the minute particle in the gas can be collected even in the corner of the flow path or a portion near this corner.

In pattern 4, the stem portion 21 exhibits a tapered shape that tapers toward the bottom. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is acute but set to be 45° or more. Meanwhile, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is obtuse. By setting the angle φ to be obtuse, travel of the gas near the corner corresponding to this angle φ is further facilitated.

Moreover, even if the angle Θ is acute, if this angle is 45° or more, no less than a certain amount of the gas travels even near the corner corresponding to the angle Θ. Focusing on the shape of the flow path, because pattern 4 is substantially the same as pattern 3, similarly to pattern 3, suppression of pressure loss and improvement of filtering efficiency can be realized.

In pattern 5, the stem portion 21 exhibits a tapered shape that tapers toward the tip. With both the first outer edge 23 and the second outer edge 24, an entirety thereof curves so as to be convex toward an inner portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle formed between the base 11 and an auxiliary line M) is obtuse. Meanwhile, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is 90°. By setting the angle Θ to be obtuse, travel of the gas near the corner corresponding to this angle Θ is further facilitated.

Moreover, by setting the angle φ to be a right angle, travel of the gas near the corner corresponding to this angle φ is also facilitated. In this manner, by setting the angles of the corners of the flow path to be 90° or more and setting a portion of these angles to be obtuse, pressure loss of the charged filter can be further suppressed and more of the minute particle in the gas can be collected.

In pattern 6, the stem portion 21 exhibits a tapered shape that tapers toward the bottom.

With both the first outer edge 23 and the second outer edge 24, an entirety thereof curves so as to be convex toward an inner portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°. Meanwhile, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer (angle formed between the adjacent base 11 and the auxiliary line M) is obtuse. By setting the angle φ to be obtuse, travel of the gas near the corner corresponding to this angle φ is further facilitated. Moreover, by making the angle Θ to be a right angle, travel of the gas near the corner corresponding to the angle Θ is also facilitated. Focusing on the shape of the flow path, because pattern 6 is substantially the same as pattern 5, similarly to pattern 5, suppression of pressure loss and improvement of filtering efficiency can be realized.

In pattern 7, the stem portion 21 exhibits a shape where a central portion in the extension direction thereof is tapered. With both the first outer edge 23 and the second outer edge 24, the entirety thereof curves so as to be convex toward the inner portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle formed between the base 11 and an auxiliary line M) is obtuse. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer (angle formed between an auxiliary line N and the adjacent base 11) is also obtuse. In this manner, by setting the angles of all corners of the flow path to be obtuse, travel of the gas is further facilitated near all corners of the flow path; therefore, pressure loss of the charged filter can be further suppressed and more of the minute particle in the gas can be collected.

In pattern 8, the stem portion 21 exhibits a shape where the central portion in the extension direction is tapered. The entirety of the first outer edge 23 is formed by straight lines and is bent so as to be convex toward the inner portion of the projection image. The second outer edge 24 is also of a shape similar to that of the first outer edge 23. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is obtuse. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is also obtuse. Because the angles of all corners of the flow path are obtuse, similarly to pattern 7, travel of the gas is further facilitated near all corners of the flow path; therefore, pressure loss of the charged filter can be further suppressed and more of the minute particle in the gas can be collected.

In patterns 1 to 8, with the angle formed between the base 11 and the root-side side surface of the stem portion 21 and the angle formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer, the first angle that is one angle among these is set to 90° or more and less than 180° and the second angle that is the other angle among these is set to 45° or more and less than 180°. In this manner, by widening the angle of the corner of the flow path of the gas, travel of the gas is facilitated even near the corner of the flow path and pressure loss of the charged filter is suppressed. In conjunction therewith, the minute particle in the gas is collected even in the corner of the flow path or the portion near this corner; therefore, filtering efficiency also improves.

Flow of the gas is smoother in a situation where the angle of the corner of the flow path is a right angle rather than acute and further smoother in a situation where this angle is obtuse rather than a right angle. In a situation where the angles of the corners of the flow path are all a right angle (see patterns 1, 2), because the gas also travels near each corner, flow of the gas in the flow path is facilitated. In a situation where a portion of the corners of the flow path is acute at 45° or more and the angle of the remaining corner is obtuse (see patterns 3, 4), viewing the flow path overall, the gas flows favorably; therefore, pressure loss can be suppressed to an extent equivalent to or greater than the situation where the angles of the corners of the flow path are all a right angle. In a situation where a portion of the corners of the flow path is a right angle and the angle of the remaining corner is obtuse (see patterns 5, 6), pressure loss can be suppressed further than the situation where the angles of the corners of the flow path are all a right angle. In a situation where all corners of the flow path are set to be obtuse (see patterns 7, 8), because the gas flows favorably in all portions of the flow path, pressure loss can be further suppressed.

Patterns 1, 3, and 7 are further compared with reference to FIG. 7. FIG. 7 is a diagram that illustrates a cross-sectional shape of a flow path 90 of the gas formed by two adjacent protrusions 20 for these three patterns. It is assumed that an area of the cross-sectional shape of the flow path 90 is the same in these three patterns. At this time, a length of a line segment (frame) F demarcating the cross-sectional shape is longer in pattern 3 than in pattern 1 and longer in pattern 7 than in pattern 3. Because the length of this line segment F can be said to represent a surface area when a depth of the filter is also taken into consideration, it can be said that the longer the line segment F, the lesser the pressure loss. With pattern 3, while the angle of a portion of the corners of the flow path is acute, because the line segment F is longer than in pattern 1, it can be said that pressure loss due to the filter surface area is lower than that of pattern 1. In this manner, a high and low of pressure loss between pattern 1 and pattern 3 depends on a balance between the angle of the corner of the flow path 90 and the length of the line segment F (surface area). With pattern 7, because the angles of the corners of the flow path 90 are all obtuse and the line segment F is longer than in patterns 1, 3, it can be said that pressure loss is lower than in patterns 1, 3.

The shape of the stem portion 21 is not limited if, with the angle formed between the base 11 and the root-side side surface of the stem portion 21 and the angle formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer, the first angle that is one angle from among these is set to 90° or more and less than 180° and the second angle that is the other angle from among these is set to 45° or more and less than 180°. Various shapes of the stem portion 21 are illustrated below.

In pattern 9, the stem portion 21 exhibits a shape where the central portion in the extension direction is tapered at a plurality of locations. Both the first outer edge 23 and the second outer edge 24 curve so as to be convex toward the inner portion of the projection image at two locations. Defining these two locations as concave portions, a region surrounded by these concave portions is convex toward an outer portion of the projection image. Therefore, in this example, only a portion of the first outer edge 23 and only a portion of the second outer edge 24 are convex toward an inner side of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle formed between the base 11 and the auxiliary line M) is 90°. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer (angle between the auxiliary line N and the adjacent base 11) is also 90°.

In pattern 10, a root side of the stem portion 21 is a straight columnar shape, and a remaining portion of the stem portion 21 exhibits a tapered shape that tapers toward the tip. A root side of the first outer edge 23 and the second outer edge 24 is a straight line and can also be said to extend along the reference line L. In contrast, a tip side of the first outer edge 23 and the second outer edge 24 curves so as to be convex toward the outer portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer (angle between the auxiliary line M and the adjacent base 11) is acute at 45° or more.

In pattern 11, the stem portion 21 exhibits a shape where the central portion in the extension direction thereof is tapered. With both the first outer edge 23 and the second outer edge 24, the central portion thereof curves so as to be convex toward the inner portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle formed between the base 11 and the auxiliary line M) is 90°. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer (angle between the auxiliary line N and the adjacent base 11) is also 90°.

In pattern 12, the stem portion 21 exhibits a shape where the central portion in the extension direction is tapered at a plurality of locations. Both the first outer edge 23 and the second outer edge 24 are formed by straight lines and are bent so as to be convex toward the inner portion of the projection image at two locations. Defining these two locations as concave portions, the region surrounded by these concave portions is convex toward the outer portion of the projection image. Therefore, in this example, only a portion of the first outer edge 23 and only a portion of the second outer edge 24 are convex toward an inner side of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is obtuse. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is also obtuse.

Patterns 13 to 15 are examples where the projection image of the stem portion 21 is not linearly symmetrical. In pattern 13, the stem portion 21 exhibits a tapered shape that tapers toward the bottom. The first outer edge 23 is neither bent nor curved and is a straight line.

Meanwhile, with the second outer edge 24, the entirety thereof curves so as to be convex toward the inner portion of the projection image. An angle 0 _a formed between the base 11 and the root side of the first outer edge 23 (root-side side surface of the stem portion 21) is 90°. An angle 0b formed between the base 11 and the root side of the second outer edge 24 (root-side side surface of the stem portion 21) is also 90°. An angle (p _a formed between the tip side of the first outer edge 23 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer is also 90°. An angle q¾ formed between the tip side of the second outer edge 24 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer (angle between the auxiliary line M and the adjacent base 11) is obtuse.

In pattern 14, the stem portion 21 exhibits a tapered shape that tapers toward the tip. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. The angle 0 _a formed between the base 11 and the root side of the first outer edge 23 (root-side side surface of the stem portion 21) is obtuse. The angle 0b formed between the base 11 and the root side of the second outer edge 24 (root-side side surface of the stem portion 21) is 90°. The angle (p _a formed between the tip side of the first outer edge 23 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer is acute at 45° or more. The angle (pb formed between the tip side of the first outer edge 24 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer is 90°.

In pattern 15, the stem portion 21 exhibits a tapered shape that tapers toward the tip. With the first outer edge 23, the entirety thereof curves so as to be convex toward the inner portion of the projection image. Meanwhile, with the second outer edge 24, the entirety thereof curves so as to be convex toward an outer side of the projection image. The angle 0 _a formed between the base 11 and the root side of the first outer edge 23 (root-side side surface of the stem portion 21) (angle between the base 11 and an auxiliary line Ma) is obtuse. The angle 0b formed between the base 11 and the root side of the second outer edge 24 (root-side side surface of the stem portion 21) (angle between the base 11 and an auxiliary line Mb) is 90°. An angle (p _a formed between the tip side of the first outer edge 23 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer is also 90°. The angle (pb formed between the tip side of the second outer edge 24 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer (angle between the auxiliary line N and the adjacent base 11) is acute at 45° or more.

As illustrated in pattern 16, the stem portion 21 may include a branch 25 in an

intermediate portion thereof. In the illustrated example, the branch 25 is formed on both the first edge portion 23 and the second edge portion 24, but a position and number of branches 25 are not limited to this example. An angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°, and an angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is also 90°.

In patterns 17 to 20, when viewed in the projection image, the stem portion 21 is bifurcated and as a result is of an aspect where a gap 26 is present. With the stem portion 21, the root side may be bifurcated, the tip side may be bifurcated, or both sides may be bifurcated. While the gas can also flow in the gap 26, "flow path" defined as above in the present specification is a concept that does not include the gap 26.

In pattern 17, the stem portion 21 exhibits a tapered shape that tapers toward the tip. With both the first outer edge 23 and the second outer edge 24, the entirety thereof curves so as to be convex toward the inner portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle formed between the base 11 and an auxiliary line M) is obtuse. The angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is 90°.

In pattern 18, the root side of the stem portion 21 is a straight columnar shape, and a remaining portion of the stem portion 21 exhibits a tapered shape that tapers toward the tip. A root side of the first outer edge 23 and the second outer edge 24 is a straight line and can also be said to extend along the reference line L. In contrast, a tip side of the first outer edge 23 and the second outer edge 24 curves so as to be convex toward the outer portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer (angle between the auxiliary line M and the adjacent base 11) is acute at 45° or more.

In pattern 19, the stem portion 21 exhibits a straight columnar shape. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. Alternatively, it can also be said that the first outer edge 23 and the second outer edge 24 extend along the reference line L. An angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°, and an angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is also 90°.

In pattern 20, the stem portion 21 exhibits a shape where the central portion in the extension direction thereof is tapered. The gap 26 is present on both the root side and the tip side. With both the first outer edge 23 and the second outer edge 24, the entirety thereof curves so as to be convex toward the inner portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle formed between the base 11 and an auxiliary line M) is obtuse. Moreover, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 1 1 of the adjacent layer (angle formed between an auxiliary line N and the adjacent base 11) is also obtuse.

Patterns 21 to 23 are aspects formed with one or more holes 27 that penetrate in a direction orthogonal to the extension direction of the stem portion 21 (such a hole is simply referred to as a "through hole" hereinbelow). A position and dimensions of an individual through hole 27 is not limited. While the gas can also flow in the through hole 27, "flow path" defined as above in the present specification is a concept that does not include the through hole 27.

In pattern 21, the stem portion 21 exhibits a tapered shape that tapers toward the bottom. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is acute but set to be 45° or more. Meanwhile, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is obtuse.

In pattern 22, the stem portion 21 exhibits a tapered shape that tapers toward the tip. With both the first outer edge 23 and the second outer edge 24, the entirety thereof curves so as to be convex toward the inner portion of the projection image. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle formed between the base 11 and an auxiliary line M) is obtuse. The angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is 90°.

In pattern 23, the stem portion 21 exhibits a tapered shape that tapers toward the tip and is not linearly symmetrical. With the first outer edge 23, the entirety thereof curves so as to be convex toward the outer side of the projection image. Meanwhile, the second outer edge 24 is neither bent nor curved and is a straight line. The angle 0 _a formed between the base 11 and the root side of the first outer edge 23 (root-side side surface of the stem portion 21) (angle between the base 11 and an auxiliary line M) is 90°. An angle 0b formed between the base 11 and the root side of the second outer edge 24 (root-side side surface of the stem portion 21) is also 90°. The angle (p _a formed between the tip side of the first outer edge 23 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer (angle between the auxiliary line N and the adjacent base 11) is acute at 45° or more. The angle (pb formed between the tip side of the first outer edge 24 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer is 90°.

In pattern 24, the stem portion 21 exhibits a tapered shape that tapers toward the tip. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. In this example, a large number of minute holes 28 is formed in the stem portion 21, and the stem portion 21 is therefore porous. While the gas can also flow in the hole 28, "flow path" defined as above in the present specification is a concept that does not include the hole 28. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is obtuse.

Meanwhile, the angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is acute but is set to be 45° or more.

Further examples of the shape of the protrusion 20 are illustrated as patterns 25 to 28. In pattern 25, the stem portion 21 exhibits an oblique columnar shape. Both the first edge 23 and the second edge 24 do not bend or curve and are a straight line. Alternatively, similarly to pattern 1, it can also be said that the first outer edge 23 and the second outer edge 24 extend along the reference line L. The angle 0 _a formed between the base 11 and the root side of the first outer edge 23 (root-side side surface of the stem portion 21) is obtuse. The angle 0b formed between the base 11 and the root side of the second outer edge 24 is acute at 45° or more. The angle (p _a formed between the tip side of the first outer edge 23 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer is acute at 45° or more. The angle q¾ formed between the tip side of the second outer edge 24 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer is obtuse. In pattern 26, the stem portion 21 exhibits a columnar shape curved in an arc shape. The first outer edge 23 and the second outer edge 24 extend along the reference line L. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 (angle between the base 11 and the auxiliary line M) is 90°. The angle (p _a formed between the tip side of the first outer edge 23 (tip-side side surface of the stem portion 21) and the base 11 of the adjacent layer (angle between the auxiliary line N and the adjacent base 11) is acute but set to be 45° or more. The angle (pb formed between an outer edge corresponding to the upper surface of the stem portion 21 and the base 11 of the adjacent layer is acute at 45° or more.

In pattern 27, the stem portion 21 exhibits a columnar shape curved in a J shape. The angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°. In a portion of the stem portion 21 that contacts the base 11 of the adjacent layer, the angle φ formed between the side surface of the stem portion 21 and the base 11 of the adjacent layer (angle between the auxiliary line M and the base 11) is acute but set to be 45° or more.

In pattern 28, the stem portion 21 exhibits a columnar shape where a central vicinity is curved. The first outer edge 23 and the second outer edge 24 extend along the reference line L. An angle Θ formed between the base 11 and the root-side side surface of the stem portion 21 is 90°, and an angle φ formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer is also 90°.

In this manner, the shapes of the protrusion 20 and the stem portion 21 are not limited if, with the angle formed between the base 11 and the root-side side surface of the stem portion 21 and the angle formed between the tip-side side surface of the stem portion 21 and the base 11 of the adjacent layer, the first angle that is one angle from among these is set to 90° or more and less than 180° and the second angle that is the other angle from among these is set to 45° or more and less than 180°. A lower limit of the first angle may be 100°, 110°, 120°, 130°, 140°, 150°, 160°, or 170°, and an upper limit thereof may be 100°, 110°, 120°, 130°, 140°, 150°, 160°, or 170°. Moreover, a lower limit of the second angle may be 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, 140°, 150°, 160°, or 170°, and an upper limit thereof may be 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, 140°, 150°, 160°, or 170°.

A shape of the upper surface of the protrusion 20 that is substantially parallel to the base 11 (the upper surface of the stem portion 21 or the upper surface of the cap portion 22) may be freely established. For example, the shape of this upper surface may be a circle, an ellipse, a rectangle, or a start shape. Alternatively, the shape of this upper surface may be any polygon, such as a triangle or a hexagon, or a more complex shape. A specific disposition aspect of the plurality of protrusions 20 on the base 11 is not limited. For example, the protrusions 20 may be disposed in a grid, in a zigzag pattern, or randomly. The disposition aspect of the protrusions 20 is not limited thereto and may be any pattern as long as the flow path of the gas can be formed.

The protrusions 20 may be disposed on the base 11 evenly or unevenly. For example, in the base 11, a protrusion region where the protrusions 20 are present and a flat region where the protrusions 20 are not present may coexist. Shapes of the protrusion region and the flat region are not limited and may be freely established (for example, a rectangle, a circle, an ellipse, a star shape, any polygon, a stripe shape, a grid, a wave shape, or a combination of such a plurality of types of shapes). By using a thin plate-like member different from the sheet 10 as a base material and affixing the sheet 10 on a portion of this base material, the protrusion region, where the sheet 10 is affixed, and the flat region, where the sheet 10 is not affixed, may be formed. Because the gas flows smoothly in the flat region, pressure loss of the charged filter can be further suppressed overall.

Alternatively, in one base 11, a region where the protrusions 20 are dense (dense region) and a region where the protrusions 20 are sparse (sparse region) may coexist. Shapes of the dense region and the sparse region are not limited and may be freely established (for example, a rectangle, a circle, an ellipse, a star shape, any polygon, a stripe shape, a grid, a wave shape, or a combination of such a plurality of types of shapes). The dense region and the sparse region may be formed by using a thin plate-like member different from the sheet 10 as the base material and affixing the sheet 10 where the protrusions 20 are dense on a portion of this base material by adhesion or welding and affixing the sheet 10 where the protrusions 20 are sparse on a remaining portion by a similar method. Because the gas flows more smoothly in the sparse region than in the dense region, pressure loss of the charged filter can be further suppressed overall.

A plurality of types of protrusions may be provided on one base 11. For example, on one base, protrusions of different dimensions may be provided, protrusions of different shapes (patterns) may be provided, or protrusions of different dimensions and shapes may be provided.

A slit or an opening may be formed in the base 11. The term, "slit" in the present specification is a concept that includes a slit-shaped groove and a slit-shaped through portion. The term, "groove" in the present specification indicates a state where an incision provided in one surface of the base 11 does not penetrate to the other surface. This groove may be formed on the front surface or the back surface of the base 11. The term, "through portion" in the present specification indicates a state where a hole or an opening provided in the base 11 penetrates from one surface to the other surface. In the present specification, a slit-shaped groove and a slit- shaped through portion may be collectively referred to simply as a "slit." In the present embodiment, a linear slit is illustrated, but the slit may be any shape; for example, a slit of a wave shape, a peak shape, an uneven shape, or the like may be formed in the base 11. FIG. 13 illustrates an example of a slit 13 formed in the base 11, and FIG. 14 illustrates an example of an opening 14 formed in the base 11, but aspects of the slit and the opening are various, as described below.

The slit can be formed by any conventionally-used method (for example, by a blade or laser cutting). Meanwhile, the opening can be formed by, for example, widening the base 11 formed with a slit-shaped through portion in a direction orthogonal to a slit column. As a means of widening the base 11, a machine such as a tenter or a roller, a manual operation, and the like can be mentioned. Alternatively, the opening may be formed without widening the base 11 but by cutting out a desired shape from the base 11.

The slit is disposed freely. For example, slits that continuously extend from one side vicinity to an opposite side vicinity of the base 11 may be lined up at predetermined intervals. Alternatively, the slits may be disposed in a zigzag pattern or in a grid. Moreover, a density of the slits in the base 11 overall does not need to be constant, and in one base 11 there may be a portion where the slits are sparse and a portion where the slits are dense.

A length of an individual slit is not limited. Moreover, the lengths of individual slits in one base 11 may be uniform, or slits of different lengths may coexist. An interval between two adjacent slits in an extension direction of the slits is also not limited, and the interval between two adjacent slits in a direction orthogonal to this extension direction is also not limited.

Moreover, these intervals may be uniform or not uniform in one base 11.

The slit may extend so as to be parallel to one side of the base 11 or may be formed so as to incline at any angle Θ (0° < Θ < 90°) relative to the side of the base 11.

The opening is also disposed freely. For example, openings that continuously extend from one side vicinity to an opposite side vicinity of the base 11 may be lined up at

predetermined intervals. The openings may be disposed in a zigzag pattern or in a grid. In one base 11, a portion where the openings are sparse and a portion where the openings are dense may coexist. An interval between two adjacent openings is not limited, and these intervals may be uniform or not uniform. Moreover, the opening may be formed diagonally relative to a side of the base 11. In this manner, similarly to the situation of the slit, various modifications are conceivable for the disposition of the opening. A shape of the opening is not limited and may be, for example, a rectangle, a rhombus, a circle, an ellipse, a rectangle, a star shape, a wave shape, or another polygon. Moreover, openings of a plurality of shapes may coexist in one base 11.

The slit and the opening may coexist. Obviously, dispositions of individual slits and openings may be freely established.

The charged filter according to the present embodiment is provided with a plurality of layers. Providing the plurality of layers, that is, a stacked structure, can be obtained by stacking the plurality of layers. Specifically, this may be done by bending or winding one sheet 10 or by stacking a plurality of sheets 10. The plurality of layers may be formed by winding after connecting different types of sheets 10, and the plurality of layers can also be formed by winding or stacking a sheet made from the plurality of layers. An adhesion layer or an adhesive layer may be provided on the upper surface of the protrusion 20 (that is, the upper surface of the stem portion 21 or the cap portion 22), and by this, shifting when stacking can be prevented.

The filter unit according to the present embodiment may be made from only the charged filter. FIG. 15 to 17 illustrate examples of the charged filter and the filter unit made from only the charged filter.

FIG. 15 illustrates a filter unit 100 made from a cylindrical charged filter 110. The charged filter 110 is obtained by winding one band-shaped sheet 10 into many layers. One of two circular surfaces in which a large number of flow paths 90 is present is an inflow surface through which the air inflows and the other is an outflow surface through which this air outflows. In FIG. 15, the depicted surface is an inflow surface 111 and an opposite surface thereof is an outflow surface 112. Moreover, the charged filter 110 has a side surface 113 that extends from the inflow surface 111 to the outflow surface 112.

A "side surface" of the charged filter is a surface that intersects both the inflow surface and the outflow surface of the charged filter and is a surface where at least a portion is formed based on the front surface or the back surface of the sheet (for example, the sheet 10 illustrated in FIG. 2). A plurality of protrusions 20 is lined up on any virtual line extending from the inflow surface to the outflow surface of the charged filter. Therefore, the side surface of the charged filter has a certain length or more, and this signifies that the charged filter has a thickness of an extent where a person can recognize it as a three-dimensional structure. Here, the thickness of the charged filter is the length of this side surface along a direction from the inflow surface to the outflow surface. The side surface of the charged filter may be formed by the front surface or the back surface of the sheet itself. Alternatively, the side surface of the charged filter may be formed in an aspect where at least a portion of the front surface or the back surface of the sheet is covered by another member. FIG. 15 illustrates an example where an entirety of the side surface 113 of the charged filter is formed by the back surface of the sheet itself.

In a situation of making the charged filter 110, the sheet 10 may be wound in many layers around a cylindrical member serving as an axis of the charged layer or the sheet 10 may be wound without using this cylindrical member. In a situation where the slit or the opening is formed in the base 11, a rigidity of the sheet 10 itself decreases such that the sheet 10 more flexibly deforms, a work of tightly winding the sheet 10 is thereby facilitated, and a charged filter 110 where two adjacent layers are more reliably adhered can be made. By adjusting the dimensions or the shape of the slit or the opening formed in the sheet 10, a flexibility of the sheet 10 can be suitably changed according to an attribute of the charged filter (manufacturing method, application scenario, or the like). In a situation where the sheet 10 formed with the opening is used, the gas flows smoothly in a region where this opening is present because no protrusion is present; therefore, pressure loss of the charged filter can be further suppressed overall. This leads to diversification of a control of the flow path in the filter and enabling of product design according to usage.

To fix the charged filter 1 10, a film having contractility (shrink film) alone may be used without using a bonding agent or an adhesive. Specifically, the charged filter 110 is fixed by covering an outer peripheral surface of the charged filter 110 by the shrink film. For example, in a situation where a heat shrink tube is adopted as the shrink film, by heating this heat shrink tube after placing this tube on the outer peripheral surface of the charged filter 110, the tube shrinks to hold in the charged filter 110 from an outer side. As an example of a material of the heat shrink tube, polyethylene terephthalate (PET) and biaxially-oriented polystyrene (BOPS) can be mentioned. Alternatively, the charged filter 110 may be held in from the outer side by winding the charged filter 110 with the shrink film while applying a tensile force on the shrink film.

FIG. 16 illustrates a filter unit 100 A made from a charged filter 110A. The charged filter

11 OA is obtained by stacking the plurality of sheets 10. In this situation, the charged filter 110A may be formed by stacking a plurality of sheets 10 of the same shape, or the charged filter 110A may be completed by trimming the side surface of the charged filter after stacking the plurality of sheets 10. One surface in which the flow path 90 is present is the inflow surface through which the air inflows, and an opposite side of this surface is the outflow surface through which this air outflows. In FIG. 16, the depicted surface is an inflow surface 111 A and an opposite surface thereof is an outflow surface 1 12A. Moreover, the charged filter 110A has a side surface 113A that extends from the inflow surface 111 A to the outflow surface 112A. FIG. 16 illustrates an example where a portion of the side surface 113 A of the charged filter is formed by the front surface or the back surface of the sheet itself and the remaining side surface 113 A is formed by stacking the sheets. The charged filter 110A illustrated in FIG. 16 is a rectangular parallelepiped, but a shape of the charged filter 11 OA is not limited thereto and may be a cylinder, an elliptical cylinder, any polygonal column, or a more complex shape.

FIG. 17 illustrates a filter unit 100B made from a charged filter HOB that includes a conical portion. The charged filter 11 OB is obtained by pulling a center (portion corresponding to a winding core) after winding one band-shaped sheet 10 into many layers. One surface in which the flow path is present is the inflow surface through which the air inflows, and an opposite side of this surface is the outflow surface through which this air outflows. In FIG. 17, the depicted surface is an inflow surface 11 IB and an opposite surface thereof is an outflow surface 112B.

Moreover, the charged filter HOB has a side surface 113B that extends from the inflow surface 11 IB to the outflow surface 112B. FIG. 17 illustrates an example where an entirety of the side surface 113B of the charged filter is formed by the back surface of the sheet itself.

In this manner, charged filters of various shapes can be made from one or a plurality of sheets 10. In either case, the charged filter according to the present embodiment has a large number of flow paths through which the gas flows (see the flow path 90 illustrated in the enlarged portions in FIG. 15 and 16). A lower limit of the thickness of the entirety of the charged filter (flow path length of the filter) may be 3 mm or 5 mm, and an upper limit thereof may be 1,000 mm, 600 mm, 150 mm, or 100 mm. A lower limit of a diameter of the charged filter may be 10 mm or 50 mm, and an upper limit thereof may be 500 mm, 300 mm, 200 mm, or 120 mm.

A stacking method of the sheet 10 is not limited. For example, as illustrated in FIG. 18, the sheet may be stacked so an apex portion (highest point) of the protrusion 20 of a certain layer contacts the back surface of an adjacent layer. Alternatively, as illustrated in FIG. 19, a process may be repeated of stacking the first layer and the second layer so the protrusion 20 of the first layer and the protrusion 20 of the second layer adjacent to the first layer face each other and stacking the first layer and a third layer so the back surface of the first layer and the back surface of the third layer adjacent to the first layer make contact. In this situation, a charged filter is obtained where the plurality of sheets 10 is stacked to line up in a sequence of base, protrusion, protrusion, base, base, protrusion, protrusion, base, .... A charged filter of a shape such as that illustrated in FIG. 16 can be formed by, for example, folding one sheet 10 in a zigzag pattern. In the example of FIG. 19, the above angle Θ is an angle formed between the root-side side surface of the protrusion 20 of the first layer and the base of the first layer. Moreover, the above angle φ is an angle formed between the tip-side side surface of the protrusion 20 of the first layer and the base of the second layer— more specifically, an angle formed between a virtual extension line of the tip-side side surface of the protrusion 20 of the first layer and the base of the second layer.

When the charged filter is viewed facing the inflow surface or the outflow surface of the charged filter, the protrusions 20 may be aligned along the stacking direction, may be arranged in a zigzag pattern, or may be disposed randomly.

The charged filter may be provided with a plurality of types of layers where shapes or the like of the solid protrusions are different from each other. That is, in this situation, the first layer and the second layer are layers of types different from each other; between the first layer and the second layer, the sheet material may differ and shapes, dimensions, or densities of the protrusion may differ.

The filter unit may be further provided with a filter other than the charged filter. For example, the filter unit may be further provided with an inflow-side filter provided on a side of the inflow surface of the charged filter. Alternatively, the filter unit may be further provided with an outflow-side filter provided on a side of the outflow surface of the charged filter.

Alternatively, the filter unit may be provided with the charged filter, the inflow-side filter, and the outflow-side filter. A filter unit lOOC illustrated in FIG. 20 is provided with the charged filter 110 illustrated in FIG. 15, an inflow-side filter 120, and an outflow-side filter 130. Hereinbelow, the inflow-side filter and the outflow-side filter may be collectively referred to as an "additional filter."

The additional filter may contact the inflow surface or the outflow surface of the charged filter, and a gap may be formed between the additional filter and the inflow surface or outflow surface. A plurality of additional filters may be provided on the side of the inflow surface or the outflow surface.

A structure, a material, and a function of the additional filter are not limited. For example, the additional filter may be a nonwoven fabric filter that is electret treated (that is, a charged additional filter) or a nonwoven fabric filter where no electret treatment is applied. The additional filter may include activated carbon that performs removal or deodorization of an organic component, may include an absorbent such as a zeolite or an aluminosilicate, and may include a deodorizing catalyst such as copper-ascorbic acid. Alternatively, the additional filter may include a desiccant such as silica gel, a zeolite, calcium chloride, or activated alumina; may include a disinfectant of a UV disinfectant type or the like; and may include an aromatic such as glyoxal, methacrylic ester, or a fragrance. Alternatively, the additional filter may have an ozone removal agent including a metal such as an oxide supported on a carrier such as alumina, silica alumina, zirconia, diatomaceous earth, silica zirconium, or titania. Structures, materials, and functions of the additional filter may be the same or different across the inflow-side filter 120 and the outflow-side filter 130. For example, both filters may be selected so pressure loss is lower in the outflow-side filter 130 than in the inflow-side filter 120. Alternatively, both filters may be selected so filtering efficiency (for example, filtering efficiency measured by the Japanese national testing standard, "Testing According to Dust Mask Regulations (Notice No. 88)"; EN 143 (EFR) 2000; EN 149 (FFR) 2001; or NIOSH (42 CFR 84)) is higher in the outflow-side filter 130 than in the inflow-side filter 120.

The charged filter has a thickness of an extent where a person can recognize it as a three- dimensional structure. In contrast thereto, the additional filter may have a structure where a person can recognize it as a flat structure (for example, a sheet shape) or a three-dimensional structure similar to that of the charged filter. The charged filter may be thicker than at least one additional filter or thicker than all additional filters. Alternatively, the charged filter may be thinner than at least one additional filter or thinner than all additional filters. Alternatively, the charged filter and the additional filter may have the same thickness. In any case, because the charged filter has a dense stacked structure having a certain thickness, it can continue to maintain a shape thereof by itself. Therefore, when applying to a mask, there is no need to use another member to maintain the shape of the charged filter. This is an advantageous point compared to the filter described in JP 4418906 above, that is, the filter formed with pleats.

Next, several examples of a mask provided with the filter unit are described. The mask 200 in FIG. 1 described above is an example of a mask that provides the filter unit in a portion that covers at least a portion of the face of a person. FIG. 21 illustrates an example of a mask that provides the filter unit to a component different from a component covering at least a portion of the face of a person. FIG. 22 is a partial enlarged view of FIG. 21. Masks 200, 300 illustrated in these diagrams are but examples, and it should be noted that the filter unit according to the present invention can be applied to various masks.

The mask 200 illustrated in FIG. 1 is provided with a main body 210 that covers the face (more specifically, the nose and the mouth) of the user and a strap 220 for bringing the mask main body 210 into close contact with the face. The strap 220 is installed to the mask main body 210 by being passed through a pair of slots 211 (only one slot is illustrated in FIG. 1) formed on both side surfaces on an outer side of the mask main body 210. The strap 220 may be made by a material having elasticity so the mask main body 210 can be brought into close contact with the face of the user.

The mask main body 210 exhibits a substantially hemispherical shape and can thereby ensure a space necessary for respiration in a vicinity of the nose and the mouth of the user. As long as the space necessary for respiration can be ensured on an inner side of the mask main body 210 (side facing the face of the user), an external form of the mask main body 210 is not limited and may be any shape, such as a cone or a column. Near an apex portion of this hemispherical shape, which comes to be positioned in front of the nose and the mouth of the user, a filter housing portion 230 for housing the filter unit is provided. In FIG. 1, as an example, the filter unit lOOC is illustrated, but the filter unit 100 or 100B may be used instead.

An edge portion 212 of the mask main body 210 that contacts the face during use may have flexibility, and in this situation, an adhesion of the mask main body 210 to the face can be increased. Meanwhile, an apex-portion side of the mask main body 210 where the slot 21 1 and the filter housing portion 230 are provided may be hard. For example, by making the edge portion 212 of the mask main body by a rubber and making other portions by a synthetic resin, the adhesion of the mask main body 210 can be increased while ensuring the space necessary for respiration on the inner side of the mask main body 210.

In FIG. 1, the filter housing portion 230 is provided with a housing 231 that receives the filter unit lOOC and an annular stopping portion 232 for preventing the filter unit lOOC from flying out from the housing 231. The filter unit lOOC is set in the mask 200 by disengaging the stopping portion 232, placing the filter unit lOOC in the housing 231, and afterward fitting the stopping portion 232 to the housing 231.

In FIG. 1, the filter housing portion 230 exhibits a cylindrical shape, but a shape of the filter housing portion 230 may be freely set to match the filter unit. For example, the filter housing portion may be a tubular shape with a square cross section to match the filter unit 100 A, and in this situation, a shape of the stopping portion is substantially square. Alternatively, the filter housing portion may be a tubular shape with a triangular cross section, and in this situation, the shape of the stopping portion is substantially triangular.

The mask 300 illustrated in FIG. 21 is provided with a hood 310 that covers an entire head portion of the user, a hose 320 that extends from this hood 310, and a filter housing portion 330 that connects to one end of the hose 320 and is provided with an electric fan. The air taken into the filter housing portion 330 by the electric fan flows into the hood 310 through the hose 320, and the user inhales this flowing air.

In the example of FIG. 21 and 22, the filter housing portion 330 exhibits a tubular shape.

A connection port 331 to which the hose 320 connects and an intake port 332 for air formed on an opposite side of this connection port 331 are connected by a flow path 333 formed by an inner wall of a substantially cylindrical shape. The filter unit is disposed in this flow path 333. Note that the electric fan that is not illustrated is disposed on an inner side of the intake port 332. In FIG. 22, as an example, the filter unit 100 is illustrated, but the filter unit 100B or lOOC may be used instead. The side surface 113 of the filter unit 100 (charging filter 110) contacts the inner wall of the flow path 333. Air entering from the intake port 332 by the electric fan passes through the filter unit 100 provided in the filter housing portion 330 (more specifically, the flow path 90) and afterward flows in the hose 320.

In FIG. 21 and 22 the flow path 333 exhibits a cylindrical shape, but a shape of the flow path in the filter housing portion may be freely set to match the filter unit. For example, a cross- sectional shape of the flow path in a situation of being viewed along a direction in which the air flows may be rectangular to match the filter unit 100 A.

The mask 300 is a type of respiration protection equipment with an electric fan. A mask of a direct-coupling type without a hose and where the electric fan and the filter housing portion are built into the face contact body also exists, and obviously, the filter unit according to the present invention can be built into this direct-coupling-type mask.

An aspect of providing the filter unit to the mask is not limited to the above example, and a system of installing the filter unit is not limited as long as all air that is taken in passes through the filter unit. For example, a structure is possible where the cylindrical inner wall in the filter housing portion (inner wall of the flow path) and the side surface of the filter unit do not make contact.

EXAMPLES

The present invention is described specifically below based on examples, but the present invention is not limited thereto.

Using polypropylene (PP) that includes polyethylene (PE) as the material, the sheet for forming the charged filter is formed. Each protrusion is provided with the stem portion and the cap portion and is therefore of a shape corresponding to example (b) in FIG. 3. The projection image of the stem portion obtained by projection onto the virtual surface corresponds to pattern 3 or 5 above. The thickness of the base is made to be about 0.1 mm to about 0.3 mm, the height of each protrusion is made to be about 0.3 mm or about 0.45 mm, and the maximum width of the tip portion of the stem portion of each protrusion is made to be about 0.1 to about 0.2 mm. The protrusions are formed on the base so the individual protrusions are disposed in a grid at intervals of about 0.8 mm. Next, the electret treatment is applied to the sheet. A time of a heating process (100°C) in the electret treatment is 5 seconds, a time of a cooling process is also 5 seconds, and an applied voltage is 13.5 KV. The sheet applied with the electret treatment is wound up in a roll shape (effective diameter: about 79 mm or about 84 mm), and by cutting this roll into a thickness of 18 mm or 25 mm, the charged filter of the cylindrical shape is obtained. In addition to the above cylindrical charged filter, three types of charged circular additional filters A to C are prepared. The additional filters A to C are all sheet-shaped, and an effective diameter is made to be about 79 mm or about 84 mm.

• Additional filter A: Charged filter for air purification made by 3M.

• Additional filter B: BMF (blown microfiber) filter made by 3M.

• Additional filter C: Mixed fiber filter.

Eight examples and three comparative examples (comparative examples 4 to 6) are prepared by these filters or by combining these filters. Moreover, three types of dust masks (including a corresponding filter) are prepared as comparative examples 1 to 3. Details of examples 1 to 8 and comparative examples 1 to 6 indicated in FIG. 23 and 27 are given below.

• Examples 1 to 6: A filter unit of a three-layer structure where the additional filter A is disposed on the inflow surface of the charged filter and the additional filter B is disposed on the outflow surface of the charged filter. Combinations of the effective diameter of the filter unit and the height and the thickness of the protrusion of the charged filter are as indicated in FIG. 23 or FIG. 27.

• Examples 7, 8: A filter unit made from the charged filter alone. Combinations of the effective diameter, the thickness, and the height of the protrusion are as indicated in FIG. 27.

• Comparative example 1 : A commercial dust mask that uses a flat filter and this filter.

• Comparative example 2: A commercial dust mask that uses a flat filter and this filter.

• Comparative example 3 : A commercial dust mask that uses a pleated filter and this filter.

• Comparative examples 4, 5: A filter unit of a two-layer structure made from the

additional filters A, B. The effective diameter is as indicated in FIG. 27.

• Comparative example 6: A filter unit made from the additional filter C. The effective diameter is as indicated in FIG. 27.

With these examples and comparative examples, pressure loss, filtering efficiency, and inhalation resistance of the mask overall (only for comparative examples 1 to 3) for the filter units alone are evaluated. Pressure loss and inhalation resistance are both values indicating energy loss when a fluid passes through an article, but in the present specification, the term, "pressure loss" is used relative to the filter unit, and the term, "inhalation resistance" is used relative to the mask overall.

In evaluating pressure loss and inhalation resistance, a measuring device made by Sibata Scientific Technology Ltd. (AP-632F) is used. Pressure loss is a pressure difference between the inflow-surface side and the outflow-surface side of the filter when the air is flowed at a flow rate of 40 LPM (liters per minute), and the unit thereof is Pascals (Pa). As pressure loss or inhalation resistance, in FIG. 23 to 27, a value denoted as "pressure loss" or "inhalation resistance" and a value denoted as "escalation value of pressure loss" or "escalation value of inhalation resistance" are sought. The value denoted as "pressure loss" or "inhalation resistance" in FIG. 23 to 27 is a value obtained by performing a test of flowing air at the flow rate of 40 LPM (liters per minute) through the filter before filtration (filter of the examples and the comparative examples itself). Meanwhile, the value denoted as "escalation value of pressure loss" or "escalation value of inhalation resistance" in FIG. 23 to 27 is a value obtained by performing a test of flowing air at the flow rate of 40 LPM (liters per minute) through the filter after 100 mg of sodium chloride (NaCl) are loaded to provide clogging.

In evaluating filtering efficiency, a measuring device made by TSI (model 8130) is used. Two types of tests are used for filtering efficiency: one where sodium chloride (NaCl) is used, assuming dry dust, and one where dioctyl phthalate (DOP) is used, assuming an oil mist.

In the test using NaCl, a dimension of NaCl indicated by a particle count median diameter is about 0.06 to 0.10 μ, and a geometric standard deviation of this dimension is less than 1.8. The flow rate is made to be 85 LPM, and a time until 100 mg of NaCl is finished being provided to the airstream is made to be a test time.

In the test using DOP, a dimension of DOP indicated by a particle count median diameter is 0.15 to 0.25 μπι, and a geometric standard deviation of this dimension is less than 1.6. A concentration of DOP in the airstream is made to be about 100 mg/m ³ (15% fluctuation range) or less. The flow rate is made to be 85 LPM, and a time until 200 mg of DOP is finished being provided to the airstream is made to be a test time.

A filtering efficiency E (%) is obtained by the following formula, with a particle concentration in the airstream before passing through the filter being C _a (mg/m ³ ) and a maximum particle concentration in the airstream after passing through the filter (mg/m ³ ) being Cb.

FIG. 23 is a table indicating test results for examples 1 to 6 and comparative examples 1 to 3. "A" and "B" in the table respectively signify the additional filter A and the additional filter B. Note that in this table, "filter" is intended to include the filter unit. Because the filter used in comparative example 3 is a filter that includes concentric circular pleats such as that described in JP 4418906 above, a thickness and apparent filter outer diameter are indicated in the table. In comparative examples 1 to 3, pressure loss and the escalation value of pressure loss of the filter unit are calculated by respectively calculating inhalation resistance and the escalation value of inhalation resistance of the mask overall and thereafter subtracting inhalation resistance and the escalation value of inhalation resistance due to a mask face piece. In FIG. 23, an effective area and an apparent area of the filter unit are also described. The effective area is a total surface area of a filter unit surface assumed to directly receive the flowing air. The apparent area is an area of the inflow surface when the filter is viewed in a state of opposing the inflow surface of the filter and is sought by measuring a filter area (comparative examples 1, 2) or being calculated from the apparent filter outer diameter (comparative example 3 and examples 1 to 6). Because the filter of comparative example 3 is a pleated filter, the effective area is greater than the apparent area. Meanwhile, in comparative examples 1, 2 and examples 1 to 6, the effective area and the apparent area are the same value.

FIG. 24 is graphs illustrating the pressure loss (Pa), the filtering efficiency of NaCl (%), the filtering efficiency of DOP (%), and the escalation value of pressure loss (Pa) of examples 1 to 6 in FIG. 23 in relation to the height of the protrusion (mm). The horizontal axis of each graph is the height of the protrusion. As illustrated in this diagram, it is made clear that when the height of the protrusion increases, pressure loss and the escalation value thereof decrease and filtering efficiency also tends to decrease.

FIG. 25 is graphs illustrating the pressure loss (Pa), the filtering efficiency of NaCl (%), the filtering efficiency of DOP (%), and the escalation value of pressure loss (Pa) of examples 3 to 6 in FIG. 23 in relation to the effective diameter (mm). The horizontal axis of each graph is the effective diameter. As illustrated in this diagram, it is made clear that when the effective diameter of the filter increases, pressure loss and the escalation value thereof decrease. Filtering efficiency slightly increases, but it is made clear that a difference due to a change in the effective diameter is small.

FIG. 26 is graphs illustrating the pressure loss (Pa), the filtering efficiency of NaCl (%), the filtering efficiency of DOP (%), and the escalation value of pressure loss (Pa) of examples 1, 2, 5, and 6 in FIG. 23 in relation to the thickness (mm). The horizontal axis of each graph is the thickness. As illustrated in this diagram, it is made clear that when the thickness increases, pressure loss and the escalation value thereof increase and filtering efficiency also increases.

FIG. 27 is a table indicating test results for examples 1 to 8 and comparative examples 4 to 6. "A," "B," and "C" in the table respectively signify the additional filter A, the additional filter B, and the additional filter C. In this table as well, "filter" is intended to include the filter unit. Note that the value, "600<" that is the "escalation value of pressure loss" in comparative example 6 is an approximate value sought by calculation from an area ratio. As described above, a filter unit according to one aspect of the present invention is a filter unit for a mask that covers at least a portion of the face of a person, provided with: a charged filter that has an inflow surface through which air inflows, an outflow surface through which the air outflows, and a side surface that extends from the inflow surface to the outflow surface; wherein the charged filter is provided with a first layer and a second layer; the first layer is provided with a base and a plurality of solid protrusions that extends from a surface of the base and is adjacent to the second layer, the protrusions having a stem portion that has a root- side side surface and a tip-side side surface; the second layer is provided with a base; and a first angle, which is one angle from among an angle formed between the root-side side surface of the stem portion and the base of the first layer and an angle formed between the tip-side side surface of the stem portion and the base of the second layer, is 90° or more and less than 180° and a second angle, which is the other angle among these, is 45° or more and less than 180°.

Furthermore, a mask according to one aspect of the present invention is provided with the above filter unit.

In such an aspect, because a corner of a flow path of a gas is ensured to be wide on a root side and a tip side respectively of the stem portion of the protrusion, in the flow path, which is formed by two adjacent protrusions, the gas comes to travel not only near a center thereof but also near the corner, facilitating the gas flowing in the filter. Because the protrusion is solid, a layer structure of the filter can be stabilized and a flow path between the layers can continue to be maintained. Therefore, suppression of pressure loss and improvement of filtering efficiency can be realized. Additionally, because the charged filter can be made by a simple method of stacking layers, manufacturing costs of the filter unit can be suppressed.

In this manner, the charged filter used in the filter unit according to one aspect of the present invention can ensure high filtering efficiency while suppressing pressure loss and an escalation value thereof to be low. Moreover, being able to suppress escalation of pressure loss in the charged filter signifies that the charged filter is less likely to be clogged and a product life of the filter unit can therefore be extended.

Furthermore, in the above aspect, suppression of pressure loss and maintenance of high filtering efficiency can be realized while suppressing an apparent area of the filter unit. Being able to make the apparent area of the surface unit small signifies that even in a situation where the filter unit is provided in front of the face of the user a field of vision of this person is not obstructed. Therefore, in the above aspect, it can be said that favorable suppression of pressure loss and high filtering efficiency can be realized without blocking the field of vision of the user. Moreover, a process of increasing an effective area such as pleating the filter unit is also unnecessary, and the charged filter can be made by merely winding or stacking the sheet;

therefore, suppression of manufacturing costs can also be expected.

Moreover, because a filter unit according to one aspect of the present invention can make a width of the filter (thickness or flow path length) long and is of a structure where clogging is less likely to occur even if the width (thickness or flow path length) of the filter is made long, a filter unit can be obtained having a different structure and performance from a filter unit using a nonwoven fabric (for example, having a long product life).

In a filter unit according to another aspect, an inflow-side filter provided on a side of the inflow surface may be further provided.

In a filter unit according to another aspect, an outflow-side filter provided on a side of the outflow surface may be further provided.

By using at least the inflow-side filter or the outflow-side filter, filtering efficiency of the filter unit can be further increased.

In a filter unit according to another aspect, the second layer may be further provided with a plurality of solid protrusions that extends from a surface of the base of the second layer.

In a filter unit according to another aspect, an entirety of two outer edges of a projection image obtained by projecting the stem portion onto a virtual surface orthogonal to the base of the first layer does not have to be convex toward an outer side of the projection image.

In this situation, a flow path can be ensured to be wider; therefore, travel of air is further facilitated. Therefore, pressure loss can be further suppressed.

The present invention is described in detail above based on an embodiment thereof. However, the present invention is not limited to the above embodiment. With the present invention, various modifications are possible within a scope that does not depart from the spirit thereof.

The filter unit according to the present invention may be used for a mask of any shape.

Therefore, the filter unit according to the present invention may be applied to any mask other than the masks 200, 300 in the above embodiment.