JPH0533068B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention has good charge stability, low pressure loss,
The present invention relates to a mask with high collection efficiency.

[Conventional technology] Conventionally, as a mask using electret,
The one proposed in Japanese Patent Publication No. 59-124 is known. This is a method in which a sheet-like product is obtained by applying high pressure near a die for forming melt-blown fibers to electret the fibers.

In the fibrous sheet obtained by this method, the electret fibers are randomly dispersed to form a sheet-like material, so the orientation of polarized charges is random, and the charges are weakened by mutual polarized charges inside the sheet. , a countervailing inconvenience occurs. In addition, the electric field strength was also weak, and the stability of the charge over time was also reduced.

[Problems to be Solved by the Invention] An object of the present invention is to provide an electret mask with excellent charge stability not found in such conventional electret masks.
The present invention provides a mask having low pressure loss and high collection efficiency.

[Means for solving the problems] The mask of the present invention that achieves the above-mentioned object has 7
×10 ^-11 c/cm ² It has a polarization charge of more than 0.2eV and an activation energy of more than 0.2eV, and the average fiber system is
This mask is characterized in that an electrified melt-blown nonwoven fabric made of fibers of 10 μm or less and having a basis weight of 50 g/m ² or less is used for at least the inner material.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a perspective view showing an example of a mask according to the present invention, and FIG. 2 is a sectional view taken along line A-A' in FIG.

The mask 1 is composed of a mask body 2 made of a fibrous sheet and strings 3.

The mask body 2 is composed of an inner material 4 made of an electrified melt-blown nonwoven fabric and an outer material 5 covering the inner material 4. The outer material 5 is usually made of a fiber material other than the inner material 4, but is not particularly limited.

In the mask of the present invention, the outer material 5 is used to increase the airflow rate to collect coarse dust, and the inner material 4 is an electrified melt-blown nonwoven fabric with low pressure loss and good charge stability to collect fine dust. That's what I do.

FIG. 3 is a front view showing another example of the mask according to the present invention, and FIG. 4 is a sectional view taken along line BB' in FIG. 3. In the mask 6 shown in FIGS. 3 and 4, the mask body 2 is provided with a fold structure. The pleats 7 stretch when the mask is worn and fit closer to the face to prevent side leakage from the sides.

Further, the mask form is not limited to those shown in FIGS. 1 to 4, and may also be used in the form of a shaped mask 8 as shown in FIG. 5. This molded mask 8 has wide spaces between the nose 9 and mouth 10, so you won't feel stuffy at all.
Excellent shape retention.

In the present invention, having a charge on the surface means having a positive charge or a negative charge on the surface like a normal electret.

In order to obtain high performance using electrets, the amount of charge of the present invention is determined to be 7×10 ^-11 c/cm ² or more as the amount of polarized charge held within the electret-ized melt-blown nonwoven fabric. 2×
It is preferably 10 ⁻¹⁰ c/cm ² or more.

The melt-blown nonwoven fabric referred to in the present invention may be any material as long as it has an electrical resistivity of 10 ¹³ Ω·cm or more. Examples include fibrous materials formed from synthetic resins such as polyolefin, polyester, polycarbonate, polyfluorine resins, and vinyl chloride resins, as well as glass and other inorganic compounds. The above-mentioned fibrous form may be any form as long as a part thereof has a fibrous shape.

Furthermore, fibers coated with an organic compound having an electrical resistivity of 10 ¹³ Ω·cm or more, such as core-sheath type fibers, are also included.

The inner material of the mask used in the mask of the present invention has flexibility, ease of design for various uses,
It is important to use melt-blown nonwoven fabric because it is easy to mold.

The electric charge possessed by the electretted melt-blown nonwoven fabric of the present invention is characteristic in that the polarized charges constituting it have an activation energy of at least 0.2 eV.

This activation energy can be found from the chart in Figure 7, which records the amount of current generated by depolarization of polarized charges depending on temperature, but this energy is determined by the amount of electric charge in the electret. It indicates the depth of the trap and has a great impact on the lifespan and durability of the electret.

The activation energy measurement (thermal stimulation current measurement) is carried out by using electrodes 14 and 15 on both sides of the electret melt-blown nonwoven fabric 13 placed in a heating tank 12 having a temperature control device 11, as shown in FIG. The trapped charges are measured by firmly sandwiching the electrodes and connecting them to the high-sensitivity ammeter 16. In other words, when the temperature of the heating tank is raised at a constant temperature increase rate, for example, 5°C/min from room temperature to around the melting point, the trapped charges are It depolarizes and current flows. When this current is recorded on the recorder 18 via the data processing device 17, current curves for various temperature ranges are obtained (FIG. 7). The quotient obtained by dividing the area of this current curve by the area of the measurement sample is the amount of polarized charge (measurement area).

The rise of each peak in this chart follows the following formula, so for the rise of the peak
A plot of InJ versus 1/T is taken, and the activation energy of the polarized charge can be calculated from the slope of the obtained straight line.

InJ=C-ΔE/kT [where J: depolarization current (A) C: constant
ΔE: Activation energy (eV) k: Boltzmann constant T: Temperature (°K)] From the viewpoint of charge stability, it is important that the activation energy is at least 0.2 eV at the current peak above room temperature. be.

In other words, the larger the activation energy value,
The lifespan of the electret is excellent. This fact was brought about for the first time by the electret sheet of the present invention. For this reason, in the present invention, those having an activation energy of 0.5 eV or more, particularly preferably 0.7 eV or more, exhibit even more excellent heat resistance and chemical resistance.

The upper limit of the activation energy is generally said to be 4 to 5 eV for film sheets, but in the case of the fibers that are the subject of the present invention, according to the findings of the present inventors, this value is up to about 2 eV. . The value of this activation energy indicates the stability of the charge, that is, the depth (stability) of the charge, and is a parameter for withstanding long-term use of the mask as described above.

Furthermore, it is a fact brought about by the present invention that the higher the temperature range in which the peak occurs, the better the life of the electret.
℃, preferably 80℃ or higher, has better durability and stability. Most preferably 130℃
The above is excellent.

The electrical performance of the electrified melt-blown nonwoven fabric used in the present invention is better when the polarization charge amount is larger, and is at least 7×10 ^-11 c/cm ² , more preferably 2×10 ^-10 c/cm ² It is preferable to have a charge amount equal to or higher than that. Most preferably 5×10 ^-11 c/
^cm2 or more is appropriate.

According to the knowledge of the present inventors, the upper limit of the polarization charge amount is generally the air discharge limit, and the value is around 1×10 ⁻⁸ c/cm ² .

Another feature of the electrified melt-blown nonwoven fabric used in the present invention is that, as shown in FIGS. 8 and 9, the melt-blown nonwoven fabric has a polarization charge of
9 has an electric field structure oriented in one direction. Specifically, the melt-blown nonwoven fabric has the same type of charge on the same surface. In the present invention, there is no problem even if the melt-blown nonwoven fabric has different types of charges in the thickness direction as shown in FIG.

Ordinary electret fibers as shown in FIG. 11, which do not have such an electric field structure, do not have the above-mentioned characteristic electrical properties of the present invention. This point will be explained with reference to FIG.

FIG. 12 schematically shows, by vector lines (arrows), the directions of electric power generated by polarized charges possessed by the electret fibers constituting the conventional electret melt-blown nonwoven fabric of FIG. 11.
As is clear from this figure, the direction of polarization is random, and the electric field structure is such that the vector quantities are canceled out and reduced. For this reason, this type of electret cannot withstand long-term use, and tends to be extremely susceptible to the presence of chemicals and thermal stimulation.

In contrast, the electrified melt-blown nonwoven fabric used in the present invention has an electric field structure in which polarized charges are oriented in one direction, as is clear from FIGS. 8 and 9. This structural difference is the reason for exhibiting the above-mentioned durability and electrical properties.

The electrified melt-blown nonwoven fabric used in the present invention has excellent characteristics when used alone, but by collecting and laminating a plurality of such melt-blown nonwoven fabrics, it can have an even longer life and durability against external conditions. A high value can be obtained.

For example, FIG. 13 shows the state of the vector line of a structure in which three sheets of electret melt-blown nonwoven fabric are laminated to be used in the present invention.
The polarized charges 19 are aligned in the same direction. Although this is shown in the power vector line (arrow) diagram, in such a structure, the types of charges on the laminated surfaces of the laminated melt-blown nonwoven fabrics may be different from each other. For example, the first layer of melt-blown nonwoven fabrics may be stacked so that the vector lines are in opposite directions, or the vector lines between the melt-blown nonwoven fabrics may be arranged in opposite directions. In the case of the electrified melt-blown nonwoven fabric used in the present invention, the above-mentioned improvement in durability is achieved in all cases. This point is also a big difference from conventional electrified melt-blown nonwoven fabrics.

The electret melt-blown nonwoven fabric used in the present invention can be produced, for example, by the method shown in FIG.

That is, the specific resistance of the melt-blown nonwoven fabric 20 formed by a normal appropriate method is set at an appropriate temperature.
Place it on the water electrode 21 of 10 ³ Ω·cm. in this case,
It is preferable to increase the contact area between the melt-blown nonwoven fabric 20 and the electrode 21. A high voltage DC current is applied to the surface of the melt-blown nonwoven fabric on the opposite side of the water electrode 21 using a needle electrode 22 . A container 23 containing water in the water electrode 21 is made of a metal material.

The applied voltage varies depending on the type of material composing the melt-blown nonwoven fabric, its molecular structure, the thickness of the melt-blown nonwoven fabric, the shape of the needle electrode, the distance between the electrodes, etc. For example, when the distance between the electrodes is 3 cm,
At least 10KV, preferably 15-50KV, more preferably 25-40KV. Application time is usually
The time is 0.1 seconds or more, preferably 1.0 to 120 seconds.

In this case, it is recommended to apply a method of applying negative high pressure to one side of the melt-blown nonwoven fabric and applying positive high pressure to the opposite side to perform double-sided treatment. A melt-blown nonwoven fabric having the electrical properties of the invention can be easily obtained.

In addition, the melt-blown nonwoven fabric to be treated has a basis weight of 50g/
A material having a thickness of m ² or less is preferable because it is easier to achieve the object of the present invention. In particular, the inner material used as a mask must have a density of 50 g/m ² or less from the viewpoint of pressure loss. If it is larger than 50 g/m ² , the mask becomes stuffy and undesirable. It is easier to increase the amount of polarization charge when the fiber diameter is thinner than when it is thicker, and it is important to set the fiber diameter to 10 μm or less. The apparent density of melt-blown nonwoven fabric made of such fibers is
0.05 g/cm ³ or more, preferably 0.1 g/cm ³ or more,
The application efficiency can be increased, and the charge stability of the resulting electret can also be improved.

Other fiber materials used as the outer material of the mask do not have to be electrified or may be electrified, but pressure loss will be reduced if the fiber material is thicker than the inner material and has a lower apparent density. Preferable from the standpoint. The material and form are not limited, but from the viewpoint of collection efficiency, nonwoven fabrics and knitted fabrics are preferable.

When used as a molded mask, thermoplastic materials such as polyolefin organic polymers (polypropylene, polyethylene), polyester, polyfluorine compounds, etc. are suitable for the inner and outer materials. In addition, a nonwoven fabric structure is preferable from the viewpoint of easy moldability.

[Examples] Example 1 A melt-blown nonwoven fabric sheet made of polypropylene fibers with an average fiber diameter of 3.5 μm and having a basis weight of 18 g/m ² and an apparent density of 0.13 g/cm ³ was electretted using the apparatus shown in FIG. 14. . The temperature of the water electrode is 50
℃, the distance between the needle electrodes is 3 cm, and the applied voltage is -
The voltage was 30KV and the processing time was 60 seconds.

Next, this sheet is dried at room temperature, the sheet is turned over and placed on the water electrode, and this time the applied voltage is +
A treatment voltage of 20KV was applied for 60 seconds.

The peak temperatures of the depolarization current of the obtained electrified melt-blown nonwoven fabric were 92°C and 153°C,
The activation energy at each peak is
They were 0.55eV and 0.85eV. The amount of polarization charge of this melt-blown nonwoven fabric was 8.5×10 ^-10 c/cm ² , and the amount of polarization charge above 130° C. was 4.8×10 ⁻¹⁰ c/cm ² .

This electrified melt-blown nonwoven fabric was used as the inner material of the mask, and a short rayon fiber nonwoven fabric with an average diameter of 15 μm, a basis weight of 20 g/m ² , and an apparent density of 0.25 g/cm ² was used as the outer material.

The pressure loss of the outer material is under the condition of passing wind speed of 3 m/min.
It was 0.4 mmaq. The pressure loss of the inner material was 2.6 mmaq under the same conditions. Figure 1 shows the inner and outer materials.
A mask with a width of 18 cm and a height of 10 cm as shown in Figure 2 was made.

The performance of this mask was measured according to JIS-T851 (dust mask). The particles used were 0.3 μm polystyrene standard latex (polystyrene uniform latex particles manufactured by Dow Chemical Company, USA). In addition, a light scattering aerosol counter (manufactured by Hitachi, Ltd.: AN105 type) was used as a particle counter to measure the collection efficiency of the mask.

As a result, the pressure loss of this Max is 3.2 mmaq,
The collection efficiency was 96.8%, showing excellent properties.

Example 2 Using the inner and outer materials used in Example 1, a mask with the fold structure shown in FIGS. 3 and 4 was produced. The dimensions of the mask were 18 cm in width and 10 cm in height, with a fold width of 1 cm and 3 folds in the vertical direction.
The pressure loss of this mask is 3.4 mmaq, and the collection efficiency is
It was 97.5%.

Example 3 The same electrified melt-blown nonwoven fabric as used in Example 1 was used for the inner material, and the outer material had an average diameter.
A mask was made by thermoforming using a polypropylene spunbond nonwoven fabric with a diameter of 21 μm and a basis weight of 20 g/m ² .

The pressure loss of this mask is 3.8 mmaq, and the collection efficiency is
It was 93.5%.

Comparative Example 1 A mask was made in the same manner as in Example 1, except that a non-woven fabric similar to the polypropylene melt-blown non-woven fabric used in Example 1 but not electrified was used for the inner material.

The performance of this mask was a pressure loss of 3.2 mmaq, which was the same value as Example 1, but the collection efficiency was 52.0%, which was significantly inferior.

[Effects of the Invention] The mask of the present invention uses an electrified melt-blown nonwoven fabric with a stable charge for a long time as an inner material, so it can achieve high collection efficiency that cannot be obtained with conventional masks even with low pressure loss. can. Target objects to be collected are airborne substances such as dust, bacteria, viruses, and pollen.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a mask according to the present invention, FIG. 2 is a sectional view taken along line A-A' in FIG. 1, and FIG. 3 is a perspective view showing another example of a mask according to the present invention. Front view, Figure 4 is B- in Figure 3.
FIG. 5 is a sectional view taken along line B', FIG. 5 is a sectional view showing still another example of the mask according to the present invention, and FIG.
The figure is a schematic diagram showing a device for measuring polarization charge amount and activation energy, Figure 7 is a depolarization current curve shown by the electret melt-blown nonwoven fabric of the present invention, and Figure 8 is an example of the electret melt-blown nonwoven fabric of the present invention. FIG. 9 is a schematic diagram showing the polarization charge state of the cross section of the nonwoven fabric. FIG. 9 is a schematic diagram showing the power vector line (arrow) of the fiber in FIG. 8. FIG. 10 is another example of the electrified melt-blown nonwoven fabric of the present invention. FIG. 11 is a schematic diagram showing the polarization charge state of the fiber in the cross section of a conventional electret fiber sheet. FIG. 12 is a schematic diagram showing the power vector line of the fiber in FIG. 11. Fig. 13 is a schematic diagram showing the state of vector lines of a structure in which the electrified melt-blown nonwoven fabric of the present invention is laminated in three layers.
The figure is a schematic cross-sectional view showing an example of an apparatus for producing the electret melt-blown nonwoven fabric of the present invention. 1, 6, 8: Mask, 2: Mask body, 4: Inner material, 5: Outer material, 7: Fold part.

Claims (1)

[Claims] A fiber having a polarization charge of 17×10 ^-11 c/cm ² or more, an activation energy of 0.2 eV or more, and an average fiber diameter of 10 μm or less, with a basis weight of 50
A mask characterized in that an electrified melt-blown nonwoven fabric of g/m ² or less is used for at least the inner material. 2. Claim 1, wherein the electrified melt-blown nonwoven fabric is an olefin fiber nonwoven fabric.
Mask as described in section. 3. The mask according to claim 1, wherein the electrified melt-blown nonwoven fabric has a depolarization temperature of at least 40°C. 4. The mask according to claim 1, wherein the average fineness of the inner material is smaller than the average fineness of the outer material. 5 Activation energy of polarization charge of inner material is 0.2eV
2. A mask according to claim 1, wherein a plurality of the above electrified melt-blown nonwoven fabrics are laminated. 6. The mask according to claim 1, wherein the outer material is an electret fiber sheet. 7. The mask according to claim 1, wherein both the inner material and the outer material have a pleated structure.