JPH06123063A - Electret material divided into sea and island region and its production - Google Patents

Abstract

PURPOSE:To obtain an electret material having strong electric action on the outside and stable electric charge for a long period of time. CONSTITUTION:An electret material comprises positive and negative charges divided into a sea and an island regions on the surface wherein the whole area ratio of island region of positive or negative electric charge on the surface is 25-60%, the whole area ratio of sea region of the opposite electric charge on the back is 40-95% and the polarity of both the surface and the back is opposite polarity on the whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret material having a high charge density and good charge stability, which can be used in a wide variety of fields of filters, masks, wipers, caps, and sensors, and a method for producing the same.

[0002]

2. Description of the Related Art A conventional electret material is disclosed in Japanese Patent Laid-Open No. 52-
It was either positively or negatively polarized on the front and back surfaces as seen in Japanese Patent Publication No. 61794 and Japanese Patent Publication No. 56-47299, or positive and negative charges were randomly mixed.

In the former, charges are separated on the front and back sides,
In practice, there was a drawback that the electric action on the opposite charge was weakened.

Further, the latter has a drawback that random positive and negative charges cancel each other inside and an effective electric field cannot be obtained. The manufacturing method for obtaining these electret materials was a method in which a direct current voltage is applied to the materials for a long time as seen in Japanese Patent Publication No. 56-47299.

These methods have the drawback that an electret material having a high charge density and good charge stability cannot be obtained.

[0006]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to eliminate the above-mentioned weak point of external electric action and obtain an electret material having a stable charge for a long period of time.

[0007]

The electret material of the present invention is an electret material in which positive and negative charges are distributed in the sea-island domain and coexist on the surface, and the total area ratio of positive and negative charges in the island domain is 25. The electret material is characterized in that the total area ratio of the sea areas of opposite charges on the back surface is 40 to 95%, and the polarities of the front and back surfaces are different as a whole.

In the method for producing an electret material of the present invention, the electret material is placed between the electrodes, and a DC pulse voltage is applied to the electrodes so that positive and negative charges are mixed on the surface with sea-island domains. It is a manufacturing method characterized by obtaining a material.

[0009]

The present invention will be described based on embodiments.

FIG. 1 is an enlarged view in which the charged surface of the sea-island domain electret material 1 of the present invention obtained by negative pulse corona charging is visualized using negative toner. Tree-shaped island domain 2
Is a positive charge and sea area 3 is a negative charge.

FIG. 2 is an enlarged view in which the charged surface of the sea-island domain electret material 1 of the present invention obtained by positive pulse corona charging is visualized using positive toner. The dot-shaped island domain 4 has a negative charge, and the sea domain 5 has a positive charge.

FIG. 3 is an enlarged view in which the back surface of the sea-island domain electret material 1 of the present invention obtained by negative pulse corona charging is visualized using negative toner. The dendritic island domain 2 and the dot-shaped island domain 6 coexist with a positive charge, and the sea domain 3 exists with a negative charge. As shown in FIG. 3, such a sea-island domain of charges also appears on the back surface, which is the opposite surface to the charged surface.

The material of the present invention has a volume resistivity of 10 ¹³ Ω · c.
m or more is preferable, and for example, polypropylene resin, polyethylene resin, polycarbonate resin, fluorine resin, nylon resin, polyester resin, and other copolymer resin can be used.

Non-woven fabrics, woven fabrics, knitted fabrics, papers, films, sheets and the like can be used as the form, but a fiber product having irregularities and having many voids is preferable.

In this case, the finer the fineness, the smaller the size of one island area and the larger the total area ratio, so that the average fineness is 5 denier or less, preferably 0.5 denier or less, It is preferably 0.1d or less. In particular, the meltblown nonwoven fabric is preferable because it is composed of ultrafine fibers.

The basis weight of the material is preferably 100 g / m ² or less in order to increase the area of the island domain, and particularly 50 g / m 2.
² or less is good.

The total area ratio of the island area is 25 to 60%, preferably 33 to 60%, more preferably 35 to 60%. This measurement area was 5 × 5 cm, and the sample visualized with toner was subjected to computer image analysis to determine the island domain area. Further, the total area ratio of the sea area is calculated by the same method, and the area ratio is preferably 40 to 95%, more preferably 45 to 90%. When the visualization of the sea area is unclear by the toner method, the value obtained by subtracting the island area from the total area may be used as the sea area. The sea area may include neutral parts that are neither positive nor negative.

The island shape is formed of a dendritic shape, a dot shape, or a mixed figure of these. The size of one island area is 30 mm ² or less, preferably 15 m in the dendritic island area
m ² or less, and 3 mm ² or less, preferably 1.3 mm ² or less in a dot-shaped area.

The number of islands is about 20 to 5000 pieces / cm ²
Preferably, the dendritic domain density is 20 to 500 pieces / c.
m ² with a dot-like domain density of 100 to 5000 pieces / c
m ² .

More preferably, the dendritic domain density is 30.
~ 500 / cm ² , dot-like domain density is 300 ~ 5
000 pieces / cm ² , 20-3000 pieces / c when mixed
m ² .

The surface charge polarity of the electret material of the present invention is positive or negative as a whole, and the polarities are different between the front and back surfaces.

Regarding the polarities of the front and back surfaces, comparing the area ratios of the islands in the front and back surfaces, a surface having a large area ratio often becomes the charge polarity of the islands.

The polarity and the amount of charge were measured by the method shown in FIG. That is, the measurement sample 9 (5
(cm diameter), the voltage generated in the known capacitor 10 is measured with the electrometer 11 to measure the polarity and the amount of charge.

Charge amount (Coulomb / cm ² ) = C × V / S Here, C is a known capacitor (F), V is a voltage (V), and S is a sample area (cm ² ).

The charge amount of the present invention is 3 × 10 ⁻¹⁰ to 8 × 1.
0 ^-9 coulomb / cm ² (hereinafter abbreviated as "C / cm ² "), preferably 7 × 10 ^-10 to 8 × 10 ^-9 coulomb /
cm ² .

FIG. 5 shows a model diagram showing the method for producing the sea-island domain electret material of the present invention.

The electret material 12 is attached to the material 13
The material 11 is electretized by performing pulse corona charging from the loading electrode 17 connected to the high voltage generator 15 and the pulse generator 16 by being installed on the ground electrode 14 via the.

The pulse loading voltage is preferably 10 to 70 KV, and the distance between the electrodes is preferably 2 to 10 cm. The printing current is 0.01-0.3mA for negative current and 0.005-0.05 for positive current.
mA is used. The pulse loading time per pulse is 2 seconds or less, preferably 0.05 to 1 second, more preferably 0.05 to 1 second.
0.5 seconds is good. If the pulse loading time for one time is 2 seconds or more, a fine and uniform island domain with a large area ratio cannot be obtained. Also, if it is less than 0.05 seconds, the island domain cannot be obtained. The pulse dwell time is preferably 0.01 to 2 seconds.

The total pulse loading time including the rest time is 6
0 seconds or less, preferably 30 seconds or less, more preferably 1
It is preferably 0 seconds or less and 0.1 seconds or more.

The load polarity may be positive or negative, and both can be used from both sides. Further, it is more preferable to reprint the back surface after printing the front surface and to change the polarity at that time.

The attached material has a volume resistivity of 1 × 10 ¹ to 1 ×.
A semiconductor material of 10 ¹⁰ Ω · cm is preferable, and 1 × 10 6 is particularly preferable.
² to 1 × 10 ⁸ Ω · cm is preferable.

The electret material of the present invention obtained in this manner is stable because it has a mixture of charges and has a high charge density and can be used for a long period of time. For this reason the filter,
Suitable for masks, hair caps, wipers, etc.

[0033]

Example 1 An average fineness of PP (polypropylene) fiber having a volume resistivity of 1 × 10 ¹⁶ Ω · cm, 0.01 d, and a basis weight of 25 g / m 2.
The meltblown non-woven fabric of No. ² was electretized by the apparatus shown in FIG.

The applied electrode and the ground electrode were 5 cm, and the attached material was a carbon-containing polyethylene film having a volume resistivity of 1 × 10 ⁴ Ω · cm.

The pulse loading time is 0.1 seconds, the pulse rest time is 0.1 second, and the rest time is 3 seconds including the rest time.
A negative pulse corona charge of 0 kv was performed.

The surface of the obtained electretized nonwoven fabric was positively charged as a whole and the back surface was negatively charged, and the surface charge density was 2 × 10 ^-9 C / cm ² .

When the surface charge was visualized using a toner, dendritic positively charged domains were recognized as islands. As a result of computer image analysis, the total area ratio of islands was 36.
%, And the domain number density of the island portion was 51 pieces / cm ² .

On the other hand, in the visualization diagram with the toner on the back surface, a mixed pattern of dendrites and dots was recognized, and the negatively charged total area ratio of the sea area was 80% by image analysis.

When the performance as a filter was evaluated using this non-woven fabric, 0.3 μm particles and a wind speed of 1.5 m /
The collection efficiency was as high as 93% in minutes. Further, after storage for 3 months, the filter performance was measured again, but no deterioration was observed.

Example 2 The meltblown non-woven fabric used in Example 1 was set in the same apparatus with a pulse loading time of 0.2 seconds and a pulse rest time of 0.3 seconds, including the rest time of 5 seconds and -20 kv. It was electretized by negative pulse corona charging.

Next, the melt blown non-woven fabric is turned upside down and the pulse loading time is 0.2 seconds and the pulse rest time is 0.3 seconds.
It was electretized by a positive pulse corona charge of +20 kv for 5 seconds including a rest time in seconds.

The obtained electretized non-woven fabric is negatively charged on the front side (positive pulse corona charged side surface) and positively on the back side, and the surface charge density is 4 × 10 ^-9 C / cm ^2.
Met.

Negatively charged dot-shaped island domains were recognized on the surface, and the island domain total area ratio was 45% and the island domain number density was 45%.
The number was 0 / cm ² .

On the back surface, the negatively charged portion was recognized as a dot-shaped island area, and the total area ratio of the positively charged portion was 70%.

When a filter evaluation using this nonwoven fabric was carried out under the same conditions as in Example 1, a high collection efficiency of 96% was exhibited. Further, the filter performance was measured again after storage for 6 months, but no decrease was observed.

Comparative Example 1 The melt-blown nonwoven fabric used in Example 1 was prepared by removing the pulse generator from the apparatus of Example 1 at −20 kv for 3 seconds.
It was electretized by continuous corona charging. The surface of the obtained non-woven fabric was positively charged and the back surface was negatively charged, and the surface charge density was 2 × 10 ⁻¹⁰ C / cm ² .

As a result of visualizing the charged state using the toner, island domains were recognized on the surface, but the number was small and the island domain total area ratio was 15%.

The performance of this non-woven fabric as a filter was 83% under the same conditions as in Example 1.

[Brief description of drawings]

FIG. 1 is a model diagram showing a sea-island domain electret material of the present invention.

FIG. 2 is a model diagram showing a sea-island domain electret material of the present invention.

FIG. 3 is an enlarged view in which the back surface of the sea-island domain electret material 1 of the present invention obtained by negative pulse corona charging is visualized using negative toner.

FIG. 4 is a model diagram showing a method of measuring polarity and charge amount.

FIG. 5 is a model diagram showing a method for producing a sea-island domain electret material of the present invention.

[Explanation of symbols]

 1: Sea island domain electret material of the present invention 2: Positively charged dendritic island domain 3: Negatively charged sea domain 4: Negatively charged dot island domain 5: Positively charged sea domain 6: Positively charged Island area 7: Electrode 8: Electrode 9: Sample 10: Known capacitor 11: Electrometer 12: Electret sample 13: Attached material 14: Earth electrode 15: High voltage generator 16: Pulse generator 17: Mark Load electrode

Claims (16)

[Claims] 1. An electret material in which positive and negative charges are distributed over a sea-island domain and coexist on the surface, and the total island area ratio of positive or negative charges on the surface is 25 to 60%, and on the back side. An electret material having a total area ratio of opposite charges of 40 to 95% and having opposite polarities as a whole on the front and back surfaces. 2. The electret material according to claim 1, wherein the graphic of the island domain has a dendritic shape, a dot shape, or a mixed drawing shape thereof. 3. The surface charge density is 3 × 10 ⁻¹⁰ to 8 × 10 ^−9.
The electret material according to claim 1, which is coulomb / cm ² . 4. The electret material according to claim 1, wherein the electret material is made of fibers. 5. The electret material according to claim 1, wherein the electret material is a non-woven fabric. 6. The electret material according to claim 5, wherein the constituent fibers of the non-woven fabric have an average fineness of 0.1 denier or less. 7. The number density of island domains is 20 to 5000 pieces / cm.
Electret material according to claim 1, wherein the ^2. 8. The electret material according to claim 1, wherein the maximum area of one island area is 30 mm ² or less. 9. A dendritic island domain number density of 20 to 500 /
The electret material according to claim 1, wherein the electret material is cm ² . 10. The electret material according to claim 1, wherein the island domains are dot-shaped, and the dot-shaped island domain number density is 100 to 5000 cells / cm ² . 11. An electret material having a sea-island domain and positive and negative charges mixed on the surface, wherein an electret material is placed between electrodes and a DC pulse voltage is applied to the electrodes. Manufacturing method. 12. A volume resistivity of 10 ^-1 to 10 ^-1 on the ground electrode.
^The method for producing an electret material according to claim 11, wherein an attached material of ¹⁰ Ω · cm is installed and a DC pulse voltage is applied. 13. The method for producing an electret material according to claim 11, wherein the pulse loading time is 2 seconds or less. 14. The method for producing an electret material according to claim 11, wherein the pulse dwell time is 2 seconds or less. 15. The method for producing an electret material according to claim 11, wherein the applied voltage is 10 to 70 KV. 16. The method for producing an electret material according to claim 11, wherein both positive pulse loading and negative pulse loading are performed when the DC pulse is applied.