JPS61215771A - Electret melt blow nonwoven fabric - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electret melt-blown nonwoven fabric having a highly polarized and regularly charged charge structure on its surface.

[Conventional technology]

Hitherto, nonwoven fabrics made of electret fibers have been known (Japanese Patent Publication No. 124/1983), and according to this, high pressure is applied to fiber threads spun by melt blowing.
Charge particles collide with the fiber threads to charge the fiber surface,
A method has been proposed in which the fiber threads are collected on a conveyor to obtain an electret nonwoven fabric. However, the electroleft nonwoven fabric obtained by this method has the disadvantage that the orientation of polarized charges within the nonwoven fabric is random (irregular), which causes the charges to mutually weaken and the electric field strength to decrease over time. There was a problem that the benefits of switching to electric left would not be realized when switching to electric left.

That is, FIGS. 3 and 4 are cross-sectional views showing the polarization charge states of nonwoven fabrics obtained from these known electret fibers, and vector lines (arrows) showing the electric power direction of the charges charged on the nonwoven fabrics. Although this is a schematic diagram, it is clear from the diagram that the directions of polarized charges are random and their vector quantities cancel each other out.

[Problem that the invention seeks to solve]

The object of the present invention is to have a structure that is completely different from the above-mentioned known nonwoven fabric made of electretized fibers in its electretted electric field structure, and to provide stable fabrics that do not lose their high degree of charge over time. The purpose of the present invention is to provide a nonwoven fabric that exhibits electric left performance.

[Means for solving problems]

The object of the present invention is to have a charge on the surface, and the activation energy of the polarized charge constituting the charge is at least 0.
．． 2eV, the basis weight is 80g/rrr or less, and the apparent density is 0.05g/co! This can be achieved with an electret melt-blown nonwoven fabric having a fiber diameter of 20 microns or more and a fiber diameter of 20 microns or less.

The nonwoven fabric of the present invention is electroleft, that is, it has positive or negative charges on its surface, but the charges are polarized, and this polarized charge has an activation energy of 0°2 eV or more. It has characteristics.

That is, as shown in FIG. 5, this activation energy is a value expressed by the amount of electricity generated when polarized charges are depolarized as the temperature is increased.
This activation energy is measured by the measuring method shown in FIG. That is, FIG. 6 is a flow chart diagram of a measurement method for measuring the activation energy,
In the figure, 2 is an electret nonwoven fabric sample;
3 and 4 are electrodes, 5 is a temperature control device, 6 is a heating tank, 7 is a high-sensitivity thermometer, 8 is a data processing device, and 9 is a recorder. The nonwoven fabric sample 2 is placed in a heating bath 6 and connected via an electrode 3.4 to a sensitive thermometer. When the temperature of the heating tank 6 is raised at a constant temperature increase rate, for example, 5° C./min from room temperature to around the melting point of the fiber, the trapped charges are depolarized and a current flows. When this current is recorded by the recorder 9 via the data processing device 8, a current curve with respect to the rising temperature as shown in Fig. 6 is obtained.The value obtained by dividing the area of this current curve by the measurement area is the amount of polarized charge. be.

A plot of InJ versus 1/T is taken for the rising portion of each peak in this chart, and the activation energy (8E) of the polarized charge is calculated from the slope of the obtained straight line using the following formula.

InJ=C-ΔE/kT In the above formula, J is a depolarizing current prisoner, C is a constant, ΔE is activation energy (eV), k is Portzmann's constant, and T is temperature (6K).

This activation energy has a close relationship with the lifespan and durability of the electret, but the fact that the activation energy value of the nonwoven fabric of the present invention is at least 082 eV means that it has a lifespan that is not found in conventional electret nonwoven fabrics. This means that it is an electric left nonwoven fabric with excellent durability.

However, in the present invention, the nonwoven fabric has a basis weight of 80 g/rd or less and an apparent density of 0.05 g/c++.
! As described above, the nonwoven fabric is characterized in that the diameter of the fibers constituting it is 20 microns or less, and because the basis weight and appearance satisfy the density and fiber diameter, it satisfies the fabric performance and function inherent to nonwoven fabrics. , it can be used and developed for many purposes.

In the above chart, the higher the temperature range where the peak appears, the greater the durability and stability of the electric left.
It is preferably in the high temperature range of 80° C. or higher, more preferably 130° C. or higher, and is extremely excellent not only in life but also in durability and stability.

Furthermore, the amount of polarization charge of the nonwoven fabric is directly related to the electrical performance of the electric nonwoven fabric, but the nonwoven fabric of the present invention
The polarization charge amount is at least 7X10-''c/ca!, preferably 2X10-''c/cd or more, more preferably 5X10-''c/ct1 or more.

Furthermore, since the electric field structure of the nonwoven fabric of the present invention has a structure in which the polarized charges are oriented in one direction, the electric field structure in which the polarized charges are distributed in a random direction is similar to the above-mentioned known electleft nonwoven fabric. The electric field structure is extremely stable compared to those having a polarization charge of at least 0.2 eV, and this is one of the major factors why the nonwoven fabric of the present invention has a highly polarized charge activation energy of at least 0.2 eV. It is.

FIG. 1 is a cross-sectional view showing one aspect of the charge state of fibers constituting the electret melt-blown nonwoven fabric of the present invention. In the figure, 1 indicates the nonwoven fabric, and 2 indicates the fibers constituting the nonwoven fabric. As shown in the figure, the nonwoven fabric of the present invention is polarized, with positive charges on one side and negative charges on the other side.

The direction of electric power generated by such polarized charges is schematically shown in FIG. 2 using vector lines (arrows). This structure is clearly different from the conventional electroleft nonwoven fabric shown in FIG. 3, which has an electric field structure in which the direction of polarized charges is random. That is,
Unlike nonwoven fabrics in which the direction of polarization is random, the charges on the nonwoven fabric do not cancel each other out, so it exhibits a stable electric left function over a long period of time.

The method for producing such an electrefted nonwoven fabric according to the present invention includes various known electreftable polymers, such as preferably polymers or glasses with an electrical resistivity of 16-+3Ω or more, other inorganic compounds, Specifically, polyolefin, polyester, polycarbonate, polyfluoride resin, vinyl chloride resin, etc. are used, and melt blowing is performed, that is, the fiber-forming material is discharged from a spinneret, and the spun discharged fiber yarn is produced. A nonwoven fabric is created by a method in which the threads are made into fibers at once by being accompanied by a high-speed air current, the fiberized threads are collected to make a nonwoven fabric, and then the obtained nonwoven fabric is made into an electreft, preferably the following method. It is better to convert it to electleft by

That is, FIG. 7 is a schematic diagram showing one embodiment of the apparatus used for producing the electret melt-blown nonwoven fabric of the present invention, and in the figure, 10 is the nonwoven fabric, 11 is the water electrode, and 1 is the nonwoven fabric.
Reference numeral 2 indicates a needle-like electrode, and a nonwoven fabric 10 that is made by melt blowing and satisfies the basis weight, apparent density, and fiber diameter specified in the present invention is a water electrode 1 that is maintained at an appropriate temperature.
A needle electrode 12 is connected to the surface of the nonwoven fabric on the opposite side of the water electrode 11, and a high voltage DC current is applied to convert the nonwoven fabric into an electroleft.

In this case, by increasing the contact area between the nonwoven fabric 10 and the water electrode 11, the nonwoven fabric can be made more effectively electleft.

The applied voltage varies depending on the fiber material constituting the nonwoven fabric and the distance between the electrodes, but for example, when the distance between the electrodes is 3CI+, the applied voltage is at least 10 KV, preferably 15 to 50 KV, and more preferably 25 to 40 KV. The applied voltage is preferably applied instantaneously or for a period of about 0.1 seconds or more, preferably 1 to 120 seconds.

As a high pressure application means, high pressure is applied directly to one side of the nonwoven fabric,
By performing double-sided treatment in which a negative high voltage is applied to the opposite side, the polarization of the electric charge can be further increased, and the high activation energy specified in the present invention can be easily imparted to the nonwoven fabric.

Here, the nonwoven fabric to be electlefted by the above method is made of ultrafine fibers with a fiber diameter of 20 microns or less, preferably 10 microns or less, and has a uniform sheet unevenness fluctuation rate of 10% or less, preferably 6% or less. It is desirable to use a melt-blown nonwoven fabric to form a nonwoven fabric. However, the basis weight of the nonwoven fabric is 80 g/rd or less, preferably 50 g/rd or less, and the apparent density is 0.05 g/cd or more, preferably 0.1 g/cd.
By satisfying such basis weight and apparent density, it is possible to make the polarized charge amount thick (and to make an electric-left nonwoven fabric with high application efficiency and good charge stability). It is.

〔Effect of the invention〕

In the electret melt-blown nonwoven fabric of the present invention, the electric charges on the nonwoven fabric are mutually stable for a long period of time,
Moreover, because it has a large activation energy, it is less likely to lose its charge even when exposed to chemicals or heat, and exhibits excellent durability.

This nonwoven fabric has uniformity, mechanical and physical properties equivalent to or better than ordinary nonwoven fabrics, and since it is made of ultrafine fibers, it has excellent flexibility and drape properties, so it can be used in many different types. It can be used for various purposes.

Hereinafter, the effects of the present invention will be specifically explained using Examples and Comparative Examples.

Example 1 Polypropylene was spun by a melt blow spinning method,
The fabric weight is 18g/r made of fibers with an average diameter of 3.5μm.
d. A nonwoven fabric with an apparent density of 0.13 and a sheet unevenness fluctuation rate of 4.4% was prepared and made into an electret using the apparatus shown in FIG.

The conditions for electretization are that the temperature of the water electrode is 50
℃, the distance between the needle electrodes was 3 cm, and the applied voltage was -30K.
V, treatment time was 30 seconds. After this electlefting treatment, the nonwoven fabric was dried, turned over, placed on a water electrode, and electlefted again at +20 KV for 30 seconds. The current peaks of the electred non-uniformity thus obtained are 92°C and 153°C, and the activation energies at the respective peaks are 0.54 eV and 0.8
6 eV, and the amount of polarization charge is 8.5 Xl0-”c/-
Met.

This nonwoven fabric was left in an atmosphere of 20° C. and 65% RH for one month, and the durability of electlefting was examined. As a result, no substantial decrease in polarization charge amount was observed.

Comparative Example 1 In Example 1, a DC high voltage of 140 KV was applied to the fiber yarn spun by the melt blow method, and the electrode gap was 4 cs), and charged particles were made to collide with the fiber yarn to electroleft the fiber yarn. The electroleft fiber yarns were collected to create a nonwoven fabric.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one aspect of the charged state of the fibers constituting the electret melt-blown nonwoven fabric according to the present invention, FIG. 2 is a schematic diagram showing, by vector lines, the direction of electric power generated by polarized charges in the nonwoven fabric, and FIG. 3 is a cross-sectional view showing the charged state of a conventional electret nonwoven fabric, FIG. 4 is a schematic diagram showing the direction of polarization charges of the same nonwoven fabric using vector lines, FIG. 5 is a relationship between depolarization current and temperature, and FIG. 6 is a flowchart diagram of the method for measuring activation energy, No. 7
The figure is a schematic diagram showing an apparatus for producing an electret melt-blown nonwoven fabric of the present invention. l...Nonwoven fabric, 2...Fiber.

Claims (6)

[Claims] (1) It has a charge on its surface, the activation energy of the polarized charge constituting the charge is at least 0.2 eV, the basis weight is 80 g/m^2 or less, and the apparent density is 0.05 g/cm.
An electret melt-blown nonwoven fabric having a fiber diameter of ^3 or more and a fiber diameter of 20 microns or less. (2) In claim 1, the amount of polarized charge at least at a temperature equal to or higher than room temperature is 7×10^-^
An electret melt-blown nonwoven fabric having a velocity of 1^1 coulomb/cm^2 or more. (3) The electret melt-blown nonwoven fabric according to claim 1 or 2, wherein the depolarization temperature of polarized charges is at least 40°C. (4) In any one of claims 1 to 3,
An electret melt-blown nonwoven fabric in which the average diameter of the fibers constituting the nonwoven fabric is 10 microns or less. (5) In any one of claims 1 to 4,
An electret melt-blown nonwoven fabric whose sheet unevenness fluctuation rate is 10% or less. (6) In any one of claims 1 to 5,
An electret melt-blown nonwoven fabric whose constituent fibers are polypropylene polymer fibers.