JP2535325B2 - Method for manufacturing woven polyolefin fabric - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electret sheet, which is firstly a polypropylene excellent in stability of electret characteristics such as long-term charge stability and also excellent in mechanical stability. The present invention relates to a method for producing an electret woven or knitted fabric.

[Prior Art] Conventionally, an electret nonwoven fabric made of polypropylene slit fibers (fibers obtained by splitting a polypropylene film) is known as described in JP-B-56-47299. However, the direction of the polarization charge in such a prior art electret has a random direction as shown in FIG.

Such a non-woven fabric usually does not exhibit the depolarizing current described below, and is insufficient to use the effect of the electret as a "face" having a certain size as an electret sheet body and to be used. Is.

This is because after the electretized film is split into a large number of fibrous materials, the fibrous materials are three-dimensionally combined to form a non-woven fabric. This means that the non-woven fabrics are oriented in random directions, and the polarization directions of the fibrous material in the non-woven fabrics are various.

For this reason, the electret non-woven fabric produced in this manner weakens the polarization charges inherently possessed by the individual fibrous substances to each other, so that an electret sheet forms an effective charge to the outside of the sheet. This leads to a drawback that the charge stability is not obtained and the charge stability is maintained for a long period of time, which also impairs the charge stability. Also,
Since it is in the form of a non-woven fabric, it is also poor in mechanical stability, and when used as a dustproof garment, wiper, etc., it is also inferior in durability as a fabric form.

[Problems to be Solved by the Invention] In view of the above points, an object of the present invention is to provide a method for producing a novel polypropylene electret woven or knitted fabric that can improve long-term stable maintenance of electric charge and mechanical stability. It is intended to be provided.

More specifically, it is intended to provide a method for producing an electret woven or knitted fabric that can fully exhibit its unique electret performance when evaluated as a sheet-shaped electret body.

[Means for Solving the Problem] The method for producing a polypropylene electret woven or knitted fabric of the present invention which achieves the above-mentioned object has the following constitution.

That is, a semiconductive liquid layer is provided on the ground electrode in contact with the ground electrode, and the semiconductive liquid layer is contacted on the semiconductive liquid layer, and 30% by weight or more of the polypropylene filament fiber A method for producing a polypropylene electret woven or knitted fabric, comprising: disposing a polypropylene woven or knitted fabric having a cover factor of 50% or more, and applying a high voltage with an electrode arranged above the polypropylene woven or knitted fabric.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing a polypropylene electret woven or knitted fabric of the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a schematic cross-sectional view showing an example structure of an electret woven fabric 3 composed of polypropylene multifilament warp yarns 1 and weft yarns 2, in which only + (plus) charges are present on the upper surface. Only − (minus) charges are substantially present on the lower surface. Such a woven fabric shows a state in which the directions of polarization charges are oriented in the thickness direction of the woven fabric as shown in FIG.

According to the method for producing a polypropylene electret woven / knitted fabric of the present invention, the surface and the back surface of the woven / knitted material are charged in this way, and the surface and the back surface of the woven / knitted material are polarized into positive and negative opposite charges. The purpose is to obtain a polypropylene electret woven or knitted fabric.

Such a polypropylene electret woven or knitted fabric,
When a high-voltage application process is performed on a woven or knitted material to be treated using the ground electrode and the application electrode, a semiconductive liquid layer such as water is provided on the ground electrode in contact with the ground electrode, and the semiconductive liquid layer is provided. It can be produced by placing the treated polypropylene woven or knitted fabric on top of the semiconductive liquid layer, and applying a high voltage to the treated polypropylene woven or knitted fabric by an electrode arranged above the treated polypropylene woven or knitted fabric.

According to the knowledge of the present inventors, in particular, a semiconductive liquid layer is provided on the ground electrode in contact with the ground electrode, and the semiconductive liquid layer is contacted on the semiconductive liquid layer. By arranging and treating the polypropylene woven or knitted fabric to be treated, there is an advantage that the charge injection is smoothly performed and a polarized electret having a high surface charge density can be obtained.

In the present invention, it is of primary importance to use the semiconductive liquid layer as described above, and at that time, as a polypropylene woven or knitted fabric for the reason described below,
The use of woven and knitted fabrics with 30% by weight or more of polypropylene filament fibers and a cover factor of 50% or more also makes it possible to obtain a high-performance electret that the front surface and the back surface are polarized into positive and negative opposite charges. It is an important thing to get stable.

In the present invention, "the front surface and the back surface of the woven and knitted material are polarized into positive and negative charges opposite to each other" means that
As shown in Fig. 4, if the front side is positive, the back side is negative,
Alternatively, if the front side is negative, the back side is positive, meaning that each has an opposite charge. That is, on the front surface and the back surface, positive and negative charges are not substantially mixed, and according to the manufacturing method of the present invention, a polypropylene electret woven or knitted fabric having such electret characteristics can be manufactured. .

When confirming the effect of the present invention, whether or not positive and negative charges are not substantially mixed on the front surface and the back surface is confirmed by a commercially available measuring device as in the following method. When using, to measure the surface potential of the electretized polypropylene woven or knitted on each of the front surface or the back surface, a curve showing the electric potential,
This can be performed by checking whether or not the recording is performed substantially only on the positive side area or on the negative side area on the recording paper.

That is, the surface potential on the front surface or the back surface is
For example, 3 mm of a grounded conveyor belt (stainless steel flat plate) that runs continuously at a running speed of 1 m / min.
In the upper space, install the surface electrometer and probe connected to the chart recorder, and then measure the diameter of the object to be measured 133 mm.
The circular polypropylene electret woven or knitted article is placed so as to be in close contact with the conveyor belt surface, and the central portion of the polypropylene electret woven or knitted article is run immediately below the probe, and the surface potential value detected at that time is recorded on the recording paper. Then, it is possible to confirm whether or not the curve showing the electric potential is recorded only on the positive side area or on the negative side area on the recording paper. The instruments and measurement conditions that can be used for the confirmation are as follows.

Surface potential meter: Name ELECTOSTATIC VOLTMETER type ISOPROVER 244 type (Made by Monroe, USA) (Probe type: 1017) Recorder: Name Technicoder type 3047 (Yokogawa Electric Co., Ltd.) Recording paper traveling speed: 60 cm / min Conveyor belt : Material Stainless steel flat plate (thickness 0.5m
m × width 20 cm) Further, in the present invention, the “woven or knitted fabric” refers to a woven fabric or a knitted fabric.

FIG. 2 shows a schematic diagram of an electret knitted fabric 5 made of polypropylene filament yarn 4 and having polarized electric charges oriented, that is, polarized on the surface and the back of the woven or knitted material to have opposite positive and negative charges. It is a thing.

According to the method for producing a polypropylene electret woven or knitted fabric of the present invention, the activation energy of the polarization charge is preferably 0.3 eV or more, more preferably 0.5 eV or more, and the polarization charge amount is preferably 1 × 10 ⁻¹⁰ coulomb. /
cm ² or more, more preferably 3 × 10 ^-10 coulomb / c
A high-performance polypropylene electret woven or knitted fabric having m ² or more can be produced. That is, in order to obtain such a high activation energy of the polarization charge and the value of the polarization charge amount, it is essential that the front and back surfaces of the woven or knitted fabric have opposite positive and negative charges as described above. Of.

The reason why polypropylene fiber is used in the method of the present invention is that polypropylene fiber has a high volume resistivity of 10 ¹⁶ Ω · cm and is nonpolar, and therefore has extremely good charge stability. Further, since polypropylene has water repellency, it is possible to maintain a stable electric charge even under the influence of moisture, which is an essential requirement for the fiber material of the present invention.
In this sense, according to the findings of the present inventors, it is important to use a polypropylene woven or knitted fabric composed of 30% by weight or more of polypropylene filament fibers.

According to the method for producing a polypropylene electret woven or knitted fabric of the present invention, as an example of a specific mode of performing the electret treatment, for example, the mode shown in FIG. 5 can be used.

That is, it can be obtained by putting semi-conductive water 7 in the earth electrode container 6, placing the polypropylene woven or knitted fabric 8 thereon, and applying a high-voltage application process with the needle electrode 9 to form an electret. Providing the semiconductive liquid layer on the ground electrode by directly contacting the ground electrode in this manner is extremely important from the viewpoint of realizing a stable high voltage application process.

Here, although not limited to the water electrode, the use of the water electrode firstly increases the actual contact area between the electrode and the woven or knitted fabric having unevenness due to the overlap of the warp yarn and the weft yarn, and This is a very preferable method because it is possible to inject a sufficient compensation charge into the woven or knitted material from the electrodes.

For example, according to the method using such a water electrode, it is possible to achieve the phenomenon that the contact area between the water electrode and the surface of the woven or knitted material is significantly increased, which causes the front and back surfaces of the woven or knitted material to have positive and negative opposite charges. In addition, as a woven or knitted product, an electret woven or knitted product having a polarization charge amount value and a polarization charge activation energy value of a certain level or more can be easily manufactured as desired.

That is, according to the knowledge of the present inventors, a woven or knitted fabric whose surface is necessarily uneven due to the yarn bending structure in the woven or knitted fabric is used as a material sheet, and as described above, In order to obtain an electret woven or knitted fabric having a polarization charge amount value and a polarization charge activation energy value of a certain level or more, the area where the electrode and the woven or knitted fabric surface are substantially in contact with each other by some means. It is also important to adopt a method of increasing the size of the wire, that is, a method of preventing fibers or threads that are not affected by the electrode from existing as much as possible. From this viewpoint, it is important that the cover factor of the woven or knitted fabric used in the method for producing a polypropylene electret woven or knitted fabric of the present invention is 50% or more. The value of the cover factor of 50% or more of such a woven or knitted fabric can be said to be a part of a wide range known as a cover factor value that a general woven or knitted fabric can have, but in combination with a specific electretization method. It is a new finding that a remarkable effect is obtained, and it is difficult to perform stable high-voltage application treatment when the cover factor value is less than 50%.

Also, the large cover factor of 50% or more means
It is also effective in maintaining a stable charge by increasing the electretized surface area as much as possible to increase the polarization charge amount. Further, since high voltage can be applied, the charge trap becomes deeper, which is important in increasing activation energy.

The cover factor value is the area of the bright area made by transmitting light and B, and the area of the shadow area made by the light being blocked by the fiber by making a shadow of the sample (10 cm x 10 cm) using a magnifying projector. Is obtained by the following equation, where C is C.

Cover factor (%) = C / (B + C) × 100 In the present invention, the yarn form of the polypropylene fiber is such that the electret woven or knitted fabric using filaments such as multifilament or monofilament that do not have fluff on the surface has charge stability. It is preferable from the point of view, and it is necessary to use filament fiber in the present invention. It is considered that this is because spun yarn or the like has innumerable fluffs on the yarn surface, and the fluffs become an impeding factor at the time of charge injection by applying a high voltage.

In addition, the yarn form, in combination with the cover factor value of the woven or knitted material described above, also affects the state in which water such as the water electrode penetrates into the woven or knitted material, so that the yarn cross-sectional shape is substantially It is important to have a circular shape.For example, a super-flat yarn such as a slit yarn cannot be infiltrated with water when air enters, or conversely, it is In some cases, it is not suitable for continuous treatment or the like, which is not preferable because it may be excessively dipped in.

Here, a method of measuring each value of the activation energy and the polarization charge amount will be described. These characteristics can be determined by a thermally stimulated depolarization current measuring device.

As shown in FIG. 6, this device strongly sandwiches both sides of the electret woven / knitted fabric 12 (sample area: 12.5 cm ² ) installed in a heating tank 11 having a temperature control device 10 with electrodes 13 and 14. , This electrode is connected to the high-sensitivity ammeter 15 for measurement. That is, when the temperature of the heating tank is raised at a constant rate, for example, from room temperature to near the melting point at 5 ° C./minute, the trapped charges are depolarized and a current flows. When this current is recorded in the recorder 17 via the data processor 16, current curves for various temperature regions can be obtained (Fig. 7). The quotient obtained by dividing the area of this current curve by the area of the measurement sample is the polarization charge amount.

In this chart, the rising of each peak follows the formula below.
The 1 / T plot is taken, and the activation energy of the polarization charge can be calculated from the slope of the obtained straight line.

In J = C-ΔE / KT [wherein J: depolarizing current (A) C: constant ΔE: activation energy (eV) K: Boltzmann constant T: temperature (° K)] [Example] Implementation Example 1 Polypropylene multifilament (500 denier)
Is used for warp and weft threads, and the warp thread density is 80 threads / inch,
Prototype satin fabric with a weft density of 57 threads / inch. The cover factor of the fabric was 99%.

This woven fabric was electretized by applying a treatment for 40 seconds at −30 KV and a distance between electrodes of 3 cm (water electrode temperature: 50 ° C.) by the embodiment and method shown in FIG.

It can be confirmed that the surface and the back surface of the thus obtained electret fabric are polarized into positive and negative opposite charges, and the activation energy is 0.52 eV, 149 at a peak temperature of 92 ° C.
It shows an activation energy of 0.82 eV at the peak temperature of ℃,
It was an excellent electret sheet body (woven fabric) having a polarization charge amount of 12 × 10 ⁻¹⁰ coulomb / cm ² .

When such a woven fabric obtained according to the present invention was allowed to stand at 20 ° C. and 100% RH for 2 months and then the above electret properties were re-evaluated, almost no deterioration in the properties was observed.

Comparative Example 1 For comparison, an electret fiber sheet was manufactured using a nonwoven fabric.

That is, a polypropylene nonwoven fabric sheet having a basis weight of 18 g / m ² and an apparent density of 0.136 g / cm ³ composed of polypropylene fibers having an average fiber diameter of 3.5 μm was electretized by the method shown in FIG.

The temperature of the water electrode was 50 ° C, the distance between the needle electrode and the needle electrode was 3 cm as in Example 1, the applied voltage was -30 kv, and the treatment time was 6
It was set to 0 seconds.

Then, this sheet was dried, and the sheet was turned over and further electretized at +20 kv.

The electret nonwoven fabric thus obtained can be confirmed that the front and back surfaces thereof are polarized into positive and negative opposite charges, and the peak current values are 92 ° C and 153 ° C. Energy is 0.55eV,
0.85eV, polarization charge is 8.5 × 10 ^-10 coulomb / cm ²
Met.

As is clear from the results of the comparative example and the above-described example, the filament woven fabric has a smoother plane than the non-woven fabric sheet, and thus a higher polarization charge amount can be obtained.

EFFECTS OF THE INVENTION According to the method for producing a polypropylene electret woven / knitted fabric of the present invention, it is excellent in that the front surface and the back surface thereof are substantially polarized into positive and negative opposite charges even though the structure is relatively simple. It is possible to manufacture a polypropylene electret woven or knitted fabric having characteristics as an electret sheet body.

The polypropylene electret woven or knitted product obtained by the present invention has a water repellent effect that polypropylene has, and is not easily affected by humidity, and can also maintain a stable charge for a long period of time, and also has strong mechanical strength. It can be used in a wide range of fields such as filters, dustproof clothing, wipers, gloves and hats.

[Brief description of drawings]

1 is a cross-sectional view showing an example of a polypropylene electret fabric obtained by the method of the present invention, FIG. 2 is a perspective view showing an example of a polypropylene electret knitted fabric obtained by the method of the present invention, FIG. 3 and FIG. Is a model diagram showing peeling (orientation) of polarization charge, FIG. 5 is a schematic diagram showing one embodiment of an electretization device that can be used for carrying out the method for producing a polypropylene electret woven or knitted fabric of the present invention, and FIG. 6 is FIG. 7 is a schematic diagram showing an apparatus for measuring activation energy, and FIG. 7 is a diagram showing an example of the relationship between depolarization current and temperature. 1: Warp yarn, 2: Weft yarn 3: Woven fabric, 4: Filament yarn 5: Knitted fabric, 6: Earth electrode container 7: Water, 8: Polypropylene woven fabric 9: Needle-shaped electrode

Claims (2)

(57) [Claims] 1. A semiconductive liquid layer is provided on the ground electrode in contact with the ground electrode, and the semiconductive liquid layer is contacted on the semiconductive liquid layer, and 30% by weight or more is obtained. A method for producing a polypropylene electret woven or knitted fabric, characterized in that a polypropylene woven or knitted fabric composed of polypropylene filament fibers and having a cover factor of 50% or more is arranged, and high voltage is applied by an electrode arranged above the polypropylene woven or knitted fabric. . 2. The front and back surfaces of the woven or knitted material are polarized into positive and negative opposite charges, the polarization charge amount is at least 1 × 10 ^-10 coulomb / cm ² , and the activation energy of the polarization charge is at least 0.3 eV. The method for producing a polypropylene electret woven or knitted fabric according to claim 1, wherein the polypropylene electret woven or knitted fabric described above is produced.