JPS63319015A - Production of electret body - Google Patents

Abstract

PURPOSE:To obtain the titled electret body to be used for a high-performance filter by laminating the fibers consisting of polyolefin and having <=5mum mean diameter on a nonwoven fabric having >=10mu mean diameter, and then forming the laminate into an electret. CONSTITUTION:Polyolefin resin is melted by an extruder 2, and sent into a die 3 to form a group 5 of extra-fine fibers 5. The extruded molten polymer is drawn into the extra-fine fibers 5 having <=5mu means diameter, and solidified. The fibers are laminated on a nonwoven mat consisting of the fibers having >=10mu mean diameter, and introduced onto a screen 8. The laminated nonwoven fabric is impressed with a DC high voltage from an electrode 11 on a roll 10, and formed into an electret. Since the laminated filter is thus formed into an electret, the filter can be easily handled, and the productivity can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an electret body that can be used as a mounting material for an air filter, and particularly to a highly efficient method for producing an electret body that has high performance as an air filter.

[Conventional technology]

Polyolefin electret porous materials exhibit high collection efficiency when used in filter applications, and therefore have high industrial utility value, and many proposals have been made. In particular, recently, high-performance air filters made of electret nonwoven fabrics with fiber diameters of several microns have been developed, for example, in JP-A-60-168511.
JP-A-61-102476, JP-A-61-21102
It is disclosed in each publication No. 7.

[Problem that the invention seeks to solve]

However, although the above-mentioned air filter obtained by converting the nonwoven fabric with a fiber diameter of several microns into an electret has high performance as an air filter, the nonwoven fabric with a fiber diameter of several microns has a lot of fluff on the surface and is easily tangled between the nonwoven fabrics, making it difficult to handle. There are problems in that it is difficult and requires time and effort to convert into an electret. For this reason, there is a need for a method that can efficiently produce electret bodies having the above performance.

An object of the present invention is to solve the problems in the conventional techniques described above and provide a highly productive method for manufacturing an electret body.

[Means for solving problems]

The purpose of the present invention is to heat-melt and reduce the diameter of a polyolefin resin to form a fiber group with an average fiber diameter of 5μ or less, stack this on a nonwoven fabric mat made of fibers with an average fiber diameter of 10μ or more, and then convert it into an electret. This is achieved by a manufacturing method for electret bodies that is characterized by the following.

The polyolefin resin used in the present invention includes polyteropylene, ethylene-propylene copolymer, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, or mixtures thereof, and unsaturated polyolefin resins. Examples include those modified with caldic acid derivatives. Among polyolefins, polypropylene or ethylene-propylene block copolymer having a high melting point is preferred.

The invention will now be described in detail with reference to the accompanying drawings, which illustrate an example of a preferred apparatus for carrying out the method of the invention.

FIG. 1 shows a preferred apparatus 1 for carrying out the manufacturing method of the present invention.
An example of this is shown, and FIG. 2 shows the detailed structure of the melt blow die 3 used in the apparatus 1. As shown in FIG. 1, the polyolefin resin is melted by an extruder 2 and fed into a die 3 to form a pole #Im and a fiber group 5. That is, the molten polymer is extruded from a large number of spinning orifices 16 extending in a row over the nozzle 13 through a polymer flow path 15, as shown in FIG. At the same time, gas no. 9 Eve 4
The heated and high-speed gas supplied through the gas inlet 19 passes through the gas header 17 and is ejected from the injection slits 18 provided on both sides of the orifice 16.
A stream of molten polymer extruded from 6 is blown on. The gas header 17 and the injection slit 18 can be provided between the nozzle 13 and the lip 14, as shown in FIG.

The extruded molten polymer is elongated and solidified into the shape of ultrafine fibers 5 having an average fiber diameter of 5 μm or less by the action of a high-speed gas stream. Ultrafine fiber group 5F formed in this way
i In the conventionally known manufacturing method, a random web 6 is formed by depositing on a screen (collector) 8 circulating between a pair of rotating rollers, but in the manufacturing method according to the present invention, as shown in FIG. A nonwoven fabric mat 9 made of fibers with a fiber diameter of 10 μm or more is introduced onto the screen 8, and nine fibers are layered on this nonwoven fabric mat 9 by being stretched by a high-speed air current.

Steam, air, etc. are suitable as the gas used here, and the gas conditions include a temperature of 300 to 400°C.
, preferably 320-3.80°C, pressure 1.0/c
m2G or more, preferably 1.5 to 5.0 to 9/c! rL
It is 2G. The extruder temperature is 170-300°C, preferably 190-280°C, and the goo temperature is 190-340°C, preferably 200-330°C.

In order for the electret body of the present invention to achieve high collection efficiency as an air filter, it is necessary that the fiber diameter of the laminated random web 6 (hereinafter referred to as web) made of a laminated polyolefin resin be 5 μm or less. Preferably 4.0 to 0.1μ, more preferably 2.5 to 0.4μ
A range of μ is recommended.

In addition, the web has a basis weight of 5 to 2009/m2, preferably 10 to 1009/m, and a density of 0.02 to 0.30 g/c.
IIL2 preferably ranges from 0.04 to 0.269/an2.

Next, a nonwoven fabric mat having an average fiber diameter of 10 μm or more (hereinafter referred to as a nonwoven fabric mat) will be described. This nonwoven fabric mat is necessary to facilitate the handling of the web, to prevent surface fibers from becoming entangled when the laminate is wound into a roll, and to efficiently perform electret formation as described below. Furthermore, when laminating a web thereon, it is important that the high-pressure air flow easily passes through the nonwoven fabric mat, leaving only the web. Furthermore, when used as a filter, this nonwoven mat does not increase the pressure drop of the filter. More preferably, a range of 15μ to 200μ is used. The basis weight is 5 to 200 p,/m, preferably 10 to 100
An area of 97m2 is recommended.

Regenerated fibers and synthetic fibers are used as the fibers constituting the nonwoven mat. Regenerated fibers include rayon, polynojit, ki, and dera, which are made by dissolving the cellulose contained in wood pulp and linters with chemicals and then regenerating them into long, thin fibers.Synthetic fibers include polyester,
Examples include nylon, acrylic, polyolefin, etc.

These fibers can be made into nonwoven mats by various methods such as dry method, wet method, and direct method. Also, is there press processing on this? It is also possible to use products that have been subjected to a process such as a 9-inch process or a 9-inch process.

The pressure loss of the nonwoven fabric in which the random web of polyolefin is laminated on the nonwoven fabric mat is 5! It is desirable that it be 111H20 or less, preferably 41mH2O or less.

To convert laminated nonwoven fabrics into electrets, for example, one side of the nonwoven fabric can be grounded! 0.5~10c of this when brought into contact with the flat plate or roll 10 for poles! An electrode 11 is installed on the rL and a DC voltage is applied from a high-voltage power source 12. A needle electrode or a wire electrode is used as the discharge electrode, and a positive or negative DC voltage of 1 to 20 kV/cm is applied. It is carried out in a high electric field that generates a corona discharge. At this time, the temperature is from room temperature to 100°C.

In the case of a web with an average fiber diameter of 5μ or less, if the web is made into an electret alone, the three-dimensional connection of the web is weak, and it is very easy to fluff, so when charged, a part of the nonwoven fabric sticks to the ground electrode, causing the web to become electret. It was not possible to increase the pulling speed of the nonwoven fabric due to some peeling and fluff getting entangled with the electrode, and the residence time in the high electric field required several seconds or more. However, when using a laminated nonwoven fabric according to the present invention, it is possible to increase the drawing speed of the nonwoven fabric, and even more surprisingly, a high-performance electret body can be obtained with a residence time of less than 1 second in a high electric field. is now possible. In order to exhibit this effect more effectively, it is more preferable to use a nonwoven fabric mat made of nine fibers having polar groups, more preferably a nonwoven fabric mat made of recycled fibers.

In the apparatus shown in FIG. 1, the production of the laminated nonwoven fabric and the electret processing are performed continuously. However, the laminated nonwoven fabric may be wound once and then charged using another device. However, it is more preferable in terms of production efficiency to manufacture a nonwoven fabric and convert it into an electret before winding it up, as in the apparatus shown in FIG.

〔Example〕

Examples of the present invention will be shown below.

The collection efficiency in the examples was calculated by calculating the particle concentration before and after the nonwoven fabric using quartz dust with an average particle diameter of 0.45 μm at a speed of 301/min, and by calculating the ratio thereof. Particle concentration was measured using a light scattering light intensity integration method. Moreover, the pressure loss was measured by measuring the pressure difference between the upstream and downstream sides of the nonwoven fabric using a differential pressure diaphragm.

Issummer's melt flow register w - (Jd below MFR) is at a temperature of 230°C according to ASTM-D 1238.
, Measured under load 2.16 to 9 conditions, unit? -! 9/10
It's a minute.

The density of the nonwoven fabric was determined using the formula below.

Examples 1 to 6 Comparative Examples 1 to 2 A polypropylene resin with an MFR of 215 was introduced in an extrusion manner, heated and melted, and melt-blown under the following conditions.

O, :3+wφ with 1■ pitch on the nozzle provided in the die
200 orifices were arranged in one row, and molten I remer was discharged from these orifices at a discharge rate of 10.19/min/orifice. Heated steam was injected from slits on both sides of this orifice to draw and thin the blown molten polymer, and the fiber group was collected on a nonwoven fabric mat introduced onto a moving net conveyor to form a web with a width of 20 cWL.

The extruder temperature is 210°, the die temperature is 290°C, and the gas temperature is 3.
The temperature was 70°C and the gas pressure was 5.0 kg/α2G.

This laminated nonwoven fabric was installed on the ground electrode roll and 3cWL of this installed at the end of the net conveyor fc 1 c
The sample was introduced into a charging section consisting of four rows of needle electrodes arranged at m pitches, and a high voltage was applied to produce elm chloret. At this time, Table 1 shows the shape of the nonwoven fabric mat used and the nine PP web laminated on the mat.
Shown below. In addition, Table 2 shows the results of measuring the winding speed and applied voltage of the laminated nonwoven fabric and its performance as a filter. For performance measurement, the nonwoven fabric made of stacked stones after 2 hours of operation was used.

Table 2 below: Comparative Example I A polypropylene resin with an MFR of 215 was put into an extruder, heated and melted, and melt-produced under the following conditions.

The nozzle installed in the die has a pitch of 0.3m.
There are 200 φ orifices lined up in a row, and the molten polymer is discharged from these orifices at a rate of 0. I N /min/
It was discharged through an orifice. Heated steam was injected from slits on both sides of this orifice to draw and thin the blown molten polymer, and the fiber group was collected on a moving net conveyor to form a web with a width of 20 cIIL. Conditions such as extruder temperature were the same as in Example 1. When this PP web was directly introduced into the charging section at a speed of 0.4 m/min and a high voltage was applied under the same conditions as in Example 1, a part of the web wrapped around the earth electrode roll and operation could be started in about 5 minutes. It's gone. In addition, the collection efficiency of this web was 52.1%, and the pressure loss was 4. :3w
It was a substance with low performance as wH2O.

Comparative Example 2 A PP web was produced in the same manner as Comparative Example 1 and wound up without being introduced into the charging section. This was introduced into the charging section at a speed of 0.3 m/min. +6kv to prevent spark discharge due to fluff
When a voltage of /crIL was applied, the time required to wrap the earth around the pole roll was reduced, and continuous operation for up to 30 minutes was possible. Collection efficiency #-j of this web is 76.5%, pressure loss is 4.1
(2) It was still lower than H20 and Example 1.

〔Effect of the invention〕

Since the method for manufacturing an electret body according to the present invention is configured as described above, a high-performance electret body can be manufactured with high production efficiency.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of an apparatus used to carry out the manufacturing method according to the present invention, and FIG. 2 is a longitudinal sectional view of a melt blowing die used in the apparatus of FIG. 1. 2... Extruder, 3... Melt blow die, 6...
Random web, 8...Screen, 9...Nonwoven fabric mat, 10...Roll for grounding, 16...Spinning orifice, 18...Gas slit.

Claims (1)

[Claims] 1. After heating and melting the polyolefin resin, it is thinned to form a fiber group with an average fiber diameter of 5μ or less, and this is made into a fiber group with an average fiber diameter of 10μ or less.
A method for producing an electret body, which is characterized by laminating it on a nonwoven mat made of fibers of μ or more and then converting it into an electret.