JPS5921964B2 - electrified fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electret fiber obtained by converting a core-sheath-covered fiber, that is, a core-sheath type composite yarn, into an electret by a corona discharge method.

Even if a single fiber is brought into contact with a ground electrode and a corona is discharged from the needle-like electrode above, the single fiber is usually bent, so there are very few contact points with the ground electrode, and as a result, the amount of energy from the ground electrode is small. Less injection and generation of compensation charge.

For example, air molecules near the needle electrode are ionized by corona discharge, and electrons are injected by colliding with the fiber surface on the ground electrode.

Since this injected charge is an excess charge for the fiber, the back surface of the fiber must be positively charged due to the principle of charge compensation (the property of objects to try to neutralize electrically).

This positive charge is generated by electrons escaping from the back surface of the fiber via the ground electrode, but in reality, as mentioned above, there is insufficient contact with the ground electrode, so a sufficient compensation charge is not generated.

For this reason, the fibers gradually begin to become negatively charged due to the charge injected by corona discharge, repelling the injected electrons and inhibiting charge injection, resulting in a drawback that sufficient electretization cannot be achieved.

At the same time, since the electret fiber obtained in this way is formed by polarizing positive and negative charges on both the upper and lower surfaces of a single fiber, these charges attract each other along the circumferential surface of the fiber, and over time It has the disadvantage of being easily neutralized over time.

In other words, although it is impossible for positive and negative charges to penetrate inside the fiber and be neutralized, recombination occurs on the outer circumferential surface of the fiber, and attenuation of the electret charge is likely to occur.

The present inventors conducted various research in an attempt to obtain fibers with a large amount of surface charge and a long charge life, and as a result, the electrical resistivity was reduced to 1
The core is a good electrical conductor or semiconductor material adjusted to 0-3 to 1011 Ω, and a material with high electrical insulation properties and a resistivity of 1014 Ω or more, preferably 1016 Ω or more, such as a non-polar polymer compound, is used as the core. closely covering the sheath;
The electret fibers of the present invention, in other words, the fibrous electrets, were obtained by electretization using a suitable electretization method such as a corona discharge method.

When the sheath is made of an insulator with a high resistivity (e.g. non-polar polymer) and the core is made of a conductor with a low resistivity of a semiconductor or higher,
The electret charge, that is, the amount of surface charge is extremely large, making it possible to extend the charge life.

The reason for this becomes clear when compared with the above-mentioned electret formation of a single fiber.

In other words, if the core fiber is grounded or electrically connected to the outside during electret formation, when negative charge begins to be injected into the sheath fiber by corona discharge, the same amount of positive charge as the negative charge will be injected into the conductor. It is naturally generated on the surface of certain core fibers.

That is, the same amount of free electrons as the injected electrons escape from the core fiber to the conducting ground electrode, and as a result, positive charges are generated on the surface of the core fiber.

Therefore, during corona discharge, electret charges are formed on the surface of the sheath fiber, but the core-sheath fiber as a whole is electrically neutral, and sufficient electretization can be achieved without inhibiting charge injection as in the conventional case. It becomes possible to significantly increase the amount of surface charge.

In addition, in the completed electret core-sheath fiber, negative charges are formed on the outer circumferential surface of the shoe and positive charges are formed on the outer circumferential surface of the core, so in order to neutralize both charges, it is necessary to penetrate the inside of the sheath fiber, which is an insulator. There is no other choice but to recombine them, and in reality, this rarely happens.

From this, it is easily understood that the charge life is extremely long compared to the conventional one.

In the above explanation, for convenience, the shoe is assumed to be negatively charged and the core is positively charged, but the principle is the same even if the shoes are reversed.

The core used for this purpose is a mixture of carbon or a polymer compound with a conductive material, and the sheath is a non-polar polymer compound such as polyethylene, polypropylene, polyvinylidene fluoride, tetrafluoride, etc. Ethylene/ethylene copolymer and the like are suitable, but the cross-sectional shape of the core and sheath may be arbitrary, and the core may be hollow.

In addition, methods for closely covering the core with the sheath include a method of melting each material of the core and sheath, and discharging and compounding these melts from a spinneret to make a core-sheath type composite yarn, and a method of making a core-sheath type composite yarn. There are methods such as dipping or passing a core into a molten sheath material, and methods for converting a core-sheath type composite yarn into an electret include conventionally known thermal electret methods and electro-electret methods.
There are electret methods, radio electret methods, etc., and these can be used appropriately.

Next, examples of the present invention will be described.

Example 1 A carbon fiber with a diameter of 50μ and a specific resistance of 2.3 x 10-2Ω was used as the core, and a specific resistance of 3.5 x 10 was used as the sheath material.
16 Ω Isotactic polypropylene (manufactured by Showa Yuka Co., Ltd., SH□ JL A L L O M E
A coating crosshead die is attached to the tip of an ordinary spinning extruder, and molten polypropylene is extruded into a 0.2 mm thick pipe from this die, and carbon fiber is placed in the center of the die. when the exit temperature of the molten polypropylene is about 230°C,
In the core-sheath type composite yarn 1 obtained at a spinning speed of 100 m/min, as shown in an enlarged view in FIG. 1, the core 1a has a diameter of 50 μm, and the outer diameter of the sheath 1b is 70 μm and the wall thickness is 10 μm. .

As shown in FIG. 2, this composite yarn 1 is passed through a feeding roller 2, and passed through the center of the corona electrode section 3, which is 2crIL away from the needle-like electrodes 3a, which are arranged radially in the vertical direction and arranged in many horizontal rows. , passed through an approximate Faraday gauge 4 and a take-up roller 5 to become an electret. The corona electrode part 3 has a length of 6 m, and the middle is partitioned by a heat insulating wall 6, covering the part on the feed roller 2 side. A heating section 7 is provided, a cooling section 8 is provided covering the part on the Faraday gauge 4 side, and a voltage of -10 KV is applied to the electrode section from a power source 9.
A corona discharge was applied to the composite yarn 1 traveling at a speed of 00 m/min for 1.8 seconds, and the surface charge density of the electret fiber 1' was measured using a Faraday gauge.
0-' coulomb/d was obtained.

In addition, when converting into an electret, the core can be grounded.

Example 2 Using the same equipment as in Example 1, powdered low-density polyethylene (ICU', :f, ALKATHENE) was used as the core material.
68300) and conductive furnace carbon (AK
The polypropylene of Example 1 was used as the sheath material, and the polypropylene of Example 1 was melted in a separate spinning extruder and sent to the spinning head. The exit temperature is approximately 230°C and the spinning speed is 100m/
The diameter of the core 1a is 50μ, the outer diameter of the sheath 1b is 70μ,
The wall thickness is 10μ.

Then, electrets were formed in the same manner as in Example 1, but the amount of furnace carbon added to the core material was changed, and the results obtained are as follows.

As a comparative example, the core material was 6-nylon (Amiran CM1031, Toshi Co., Ltd.) and the above-mentioned polypropylene, and the sheath material was crystalline polyethylene (Mitsui Yuka Co., Ltd., Ne
Example 2
A core-sheath type composite yarn having a core diameter of 50 μm and a sheath outer diameter of 70 μm was prepared by simultaneous spinning as shown in the figure below, and this was made into an electret as in Example 1. The results were as follows.

From these Examples and Comparative Examples, the specific resistance of the core is 10-4.
It can be seen that the core-sheath type composite yarn electret having a sheath resistivity of 10 14 Ω or more, preferably 10 16 Ω or more, has a high initial surface charge density.

Note that in these examples, the core is solid, but
The core is a liquid, such as water, ethyl alcohol, acetone, etc., which is filled into the hollow part of a fluorinated ethylene/ethylene copolymer, and then both ends are closed to create a core-sheath type composite yarn. When it was made into an electret by corona discharge, a high initial surface charge density of around 6.0 x 10-9 coulombs/- was obtained.

The electret fibers of these examples have a core 1
A is the opposite electrode, which is charged with the same amount and opposite polarity as the surface charge of the sheath 1b, and is separated by a high-resistance sheath, so it is difficult to neutralize and has a significantly long charge life.

Next, as mentioned above, the electret fiber of the present invention has a high initial surface charge density and a long charge life, so when cleaning products such as dusters and mops were manufactured and used, it showed excellent effects. I discovered something.

Core diameter 10 made in the same manner as Sample No. 1 of Example 2
As shown in Fig. 4, electret fiber 1' with 0μ and shoe outer diameter 140μ is cut into 15.7 cIrL, 20 of them are bundled to form sample 10, and twice the amount of dust t-(JIS 8 The sample was placed in a 500 ml plastic container with the sample test powder) and the container was shaken for 30 seconds.The sample was taken out and the amount of attached dust was measured, and the following results were obtained.

Here, sample number 1.2.3 is when the corona voltage is 16KV, sample 4.5 is when the corona voltage is 110KV, and the dust adhesion rate is the dust adhesion sample weight - sample initial weight x 100 sample initial weight It is.

However, the core-sheath type composite yarn of this electret l-formed fiber 1' before being converted into electret was processed into a 15.7C fiber as described above.
The results of a single test conducted in the same manner as described above with 20 pieces cut into fIL and bundled together are as follows, and it can be seen that the dust adhesion rate of the product of the present invention is extremely high, and therefore, the dust removal effect is excellent.

Moreover, if the product of the present invention is washed by putting it in water after dust has adhered to it, the amount of surface charge will be reduced, so the adhered dust can be easily removed, but if the product is taken out and dried,
As shown in the table below, the amount of surface charge gradually recovers, so it can be used as a dust removal tool for a long time, and when the amount of surface charge decreases below a certain standard, it can be restored by converting it to electret again. have.

, Furthermore, the electret fiber 1' of the present invention has a fifth
As shown in the figure, the inside of the frame 11 is made of mesh, non-woven fabric, or cloth.
The gas filter 12 can be made by stretching it in a shape or the like.

That is, if a gas, for example air, is passed through the intersecting gap of the electret fibers 1' having surface charges, the airborne dust is charged to the opposite polarity due to the surface charges and is attracted and adsorbed to the fibers. Since the fibers are semi-permanently charged, there is no need for electrical equipment to supply voltage, and since the capture is electrical rather than mechanical, the filter structure is an open type rather than a filled type, resulting in low pressure loss. When floating dust adheres to and accumulates on the fiber surface of the filter, as with dust control products, washing with water temporarily reduces the amount of surface charge, making it easy to remove the dust, and drying after washing restores the amount of surface charge, so it can be repeated repeatedly. In addition, it can be used
If the amount of surface charge falls below a certain standard, it can be turned into an electret again and used like new.

FIG. 6 is a semi-logarithmic graph showing the change over time (life span) of the surface charge density of the electret core-sheath fiber, where the vertical axis is the surface charge density and the horizontal axis is the number of days elapsed.

The sheath fibers are all made of polypropylene, and the core fiber materials are copper wire (solid line), carbon tetrachloride (dotted line), polypropylene (dotted chain line), air or hollow fiber (double chain line), and tetrafluorinated ethylene/ethylene heptafilament. The surface charge density was measured for about 30 days on five core-sheath fibers consisting of five types.

The initial electretization conditions were 10 KV and 60 volts at room temperature.
corona discharge for seconds.

As is clear from the figure, the copper wire with the lowest specific resistance as the core material has the longest charging life.

At the same time, this means a longer service life as the specific resistance decreases, but if a highly rigid metal is used as the core material, it is difficult to process it into fibers.

Therefore, for the purposes of the present invention, the most suitable core material is a material in which conductive powder, such as carbon powder, is added to carbon fiber or resin to provide a conductivity meter.

The electret fiber of the present invention can be used to make various products using knitted and woven hats.

[Brief explanation of drawings]

Figure 1 is an enlarged perspective view with one end of the core-sheath composite yarn cut away, Figure 2 is a partially cutaway principle diagram of the corona discharge electretization device, and Figure 3 is a cross-sectional view taken along line A-A in Figure 2. , FIG. 4 is an elevational view of a bundle of electret fibers of the present invention,
FIG. 5 is an elevational view of the gas filter of the present invention, and FIG. 6 is a semi-logarithmic graph showing changes in surface charge over time. 1... core-sheath type composite yarn, 1a... core of the thread, 1b... sheath of the thread, 1'... electretized fiber', 3...Corona electrode part, 3
a...acicular electrode, 4...Faraday
Gauge, 10...Electret fiber bundle, 1
2... Gas filter.

Claims (1)

[Claims] 1. A core made of carbon fiber or conductive powder added to a resin, each having an electrical resistivity adjusted to 10-3 to 10-11 Ω, and a resin covering this core. done1
An electret fiber for cleaning, characterized in that a core-sheath composite fiber consisting of a sheath of 0.14Ω or more is made into an electret by a corona discharge method. 2. An electret fiber for cleaning, characterized in that the electret fiber for cleaning according to claim 1 is woven into a planar lattice shape.