JPH04163353A - Nonwoven fabric of olefin-based ultra-fine fiber - Google Patents

Abstract

PURPOSE:To provide the subject nonwoven fabric composed of an olefin-based ultra-fine fiber having respectively specified fiber diameter, coefficient of variation thereof, etc., excellent in distribution of fiber diameter and weight and free from pill-like parts, excellent in filter characteristics and useful as a filter, a buttery separator, etc. CONSTITUTION:An objective nonwoven fabric composed of an olefin-based fiber having <=0.1-5.0mum, preferably 0.5-3.5mum average fiber diameter, <=30% coefficient of variation (CV) thereof and <=5%, preferably <=3% coefficient of variation (CV) of weight in the crosswise direction, preferably having a random arrangement of the fiber and having 0.15-0.80g/cm<3> bulk density.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an olefin-based microfiber nonwoven fabric with excellent filter performance.

(Prior art) Non-woven fabrics produced by the melt-blowing method (hereinafter referred to as melt-blown non-woven fabrics) are disclosed in Japanese Patent Publication No. 43-20248, Japanese Patent Publication No. 30016-1972, and Japanese Patent Publication No. 44-128.
48 Publication, Special Publication No. 44-13210, Special Publication No. 4
It is disclosed in Japanese Patent Publication No. 4-22525, Japanese Patent Publication No. 44-25870, Japanese Patent Publication No. 44-25872, etc.

Regarding olefin-based m-fiber melt-blown nonwoven fabrics, JP-A-50-46972, JP-A-54-13417
No. 7, etc., all have extremely large fiber diameter distributions and cannot be used as filters.

In contrast, JP-A-1-156561 provides a nonwoven fabric with a good fiber diameter distribution, but the filtration performance is insufficient when used in high-performance air filter applications.

Furthermore, in Japanese Patent Application Laid-Open No. 63-6107, a melt-blown nonwoven fabric with excellent eye distribution has been obtained, but its filtration performance is insufficient when used in high-performance air filter applications.

(Problems to be Solved by the Invention) The present invention aims to solve the above-mentioned problems of the prior art and provide an olefin-based ultrafine fiber nonwoven fabric that exhibits excellent filtration performance when used as a filter.

(Means for Solving the Problem) That is, the present invention has an average fiber diameter of 0.1 to 5.0 μm, a fiber diameter variation rate (CV) of 30% or less, and a basis weight variation rate (CV) of 0.1 to 5.0 μm.
) is an ultrafine fiber nonwoven fabric consisting of 5% or less of olefin fibers.

The present invention will be explained in detail below.

The average fiber diameter of the olefin ultrafine fibers constituting the nonwoven fabric of the present invention is 0.1 to 5.0 μm, preferably 0.5 μm.
~3.5 μm. If it is less than 0.1 μm, the collection efficiency will be excellent when used as a filter, but the pressure loss will be significantly high, which is not preferable. Furthermore, the fiber tenacity also decreases, and as a result, the nonwoven fabric tenacity also decreases, which poses a problem in use. If it exceeds 5.0 μm, it becomes difficult to collect fine particles even if the bulk density is significantly increased, resulting in poor filter performance.

The variation rate (CV) of the fiber diameter of the olefin ultrafine fibers constituting the nonwoven fabric of the present invention is 3o% or less. If the coefficient of variation (CV) of fiber diameter exceeds 30%, the filter performance will be significantly inferior.

In the nonwoven fabric of the present invention, the distribution of the basis weight in the width direction is 5% or less, preferably 3% or less in terms of variation rate (CV'). 5
If it exceeds %, when used as a filter, the flow may be uneven and the performance may be deteriorated, which is not preferable.

The nonwoven fabric of the present invention consists of olefin-based microfibers,
It is necessary for the average fiber diameter, the variation rate (CV) of the fiber diameter, and the variation rate (CV) in the width direction to all be satisfied at the same time. If either of the negative conditions is not met, the filter performance will deteriorate.

The olefin fibers constituting the nonwoven fabric of the present invention are polypropylene (PP), polyethylene (PE), polybutene-1, and copolymers or blends thereof.

In particular, polypropylene, polybutene-1
is preferred. These polymers are preferably used because of their chemical resistance.

In the nonwoven fabric of the present invention, the constituent olefin microfibers are arranged in a random arrangement. It is preferable that the fibers are randomly arranged in the form of ultrafine fibers or single fibers, as this significantly increases the collection efficiency.

The bulk density of the nonwoven fabric of the present invention is not particularly limited, but from the viewpoint of maintaining filtration accuracy and shape retention, it is preferably 0.05 g/am or more, more preferably 0.15 g/c.
a to J: 0, 80 g l cnt or less.

In order to obtain the ultrafine nonwoven fabric of the present invention, it is particularly preferable to use a melt blowing method.

An example of the melt blowing method of the present invention will be explained below.

The melt blowing method is based on a known method, but because it is necessary to obtain a nonwoven fabric with a sharp fiber distribution and basis weight distribution, it is necessary to eliminate unevenness in the polymer's discharge, viscosity, and temperature, as well as flow rate and temperature unevenness in the traction fluid. must be minimized as much as possible. In order to meet these conditions, the heaping machine, head, and nozzle used are designed to have no dead space. Further, in order to suppress thermal decomposition of the polymer, the residence time up to the nozzle orifice is preferably within 10 minutes, more preferably within 5 minutes. Furthermore, it is preferable that the spinning temperature be as low as possible in order to suppress thermal decomposition of the polymer. For example, for polypropylene, 250°C or more and 290'C
It is. In addition, the head and nozzle are heated uniformly by ensuring sufficient heat retention and by devising the structure and control method of the heater so that there are no temperature variations. Further, it is preferable to make the diameter of the nozzle orifice as small as possible to increase the discharge linear velocity and to reduce the draft ratio due to the traction fluid.

Next, in this way, the polymer with as uniform a melt viscosity as possible is uniformly discharged from the nozzle orifice, and at the same time, a heated high-velocity traction fluid is sprayed onto the stream of the discharged molten polymer to form the molten polymer into ultra-fine particles. The fibers are elongated and thinned into fibers, cooled and solidified, and then collected and laminated on a net to form a randomly arranged nonwoven fabric. Suitable traction fluids include steam, air, nitrogen, and the like. Unevenness in the flow rate of the traction fluid causes traction unevenness, so it is necessary to uniformly distribute the traction fluid. For example, it is necessary to take aerodynamic measures such as enlarging the header of the supply section and dividing the supply port into multiple sections. The flow rate difference of traction fluid is 50 m/s
ec or less, preferably 20 m/sec or less.

Towing fluid'? ! 01 degree unevenness is undesirable because it causes both flow rate unevenness and melt viscosity unevenness of the polymer. Preferred traction fluid temperature difference is within 10°C, more preferably 5°
It is within C. The temperature of the traction fluid should be 250°C or above 40°C.
Below 0°C, preferably above 300'C and below 380°C, the pressure of the traction fluid is above 0.5 k (H/ca,
Preferably it is between 0.8 and 14 kg/cJ.

When the traction fluid is ejected from the lip surface, it attracts entraining flow from the surroundings, thereby creating turbulence, resulting in a distribution and fiber diameter distribution on the eye side. In order to reduce turbulence caused by the entrained flow, it is preferable that the widthwise side surfaces restrict the inflow of the entrained flow. Furthermore, when the fibers laminated on the net are moved by the fluid, the basis weight distribution becomes uneven, so an appropriate amount of suction is required to prevent this. If the distance from the nozzle surface to the net is too short, it will cause fusion, and if it is too long, the fibers will become entangled with each other, making it easy to form strings.
0 cm to 60 cm is suitable. Also, in order to make the fiber arrangement random, it is preferable to take it out on a flat net surface. Since the nonwoven fabric of the present invention has appropriate strength, it can be used as it is as a filter, but it can also be pressed to increase its bulk density and strength.

The nonwoven fabric of the present invention is preferably used as a filter when the bulk density is 0.15 g/cm, especially preferably 0.30 to 0.
, 70 g/cut. If the bulk density is high, the filtration accuracy will be improved, or if it exceeds 0.80 g/cnt, the pressure drop will be significantly increased. Further, embossing, ultrasonic processing, etc. can be performed as necessary. It can also be converted into an electret by corona discharge to improve filter performance.

(Examples) The present invention will be further explained below with reference to Examples, but the present invention is not limited to these Examples.

The method for measuring physical property values used in the following explanation is shown below.

■ Average fiber diameter (μm), variation rate (%) The nonwoven fabric was photographed using a scanning electron microscope at a magnification of 2000 times E4. We randomly selected 100 f&bricks from the photos, measured their diameters, and measured the average value (X) and standard deviation (σ□
-1) is calculated. The rate of variation (CV) was determined using the following formula.

Variation rate (CV) = (σn,,1/×)×100 (
%) ■ Non-woven fabric strength (g/cm) ゛ Length of non-woven fabric in vertical and width directions 24 cm each
Take 5 samples of x width 2cIII, grip length 2cm
The specimen was stretched and cut using a tennron, the maximum strength at that time was measured, and the average value of the five points was converted to 1 cm.

■ Fabric weight is the rate of variation (%) Take a sample of the nonwoven fabric in the width direction with a width of 2 am x length of 10 cm, measure the weight of each, calculate the average value and standard deviation, and calculate [(standard deviation) / (average value )]X100 (
%) is the fluctuation rate.

■ Bulk density (g/c return) The thickness measured under a load of 50 g/c+if and the grain side were calculated from the amount = 9-.

(2) 17D collection efficiency and pressure loss Collection efficiency and pressure loss were measured using JIS Z-8901 test test.

Example 1 Polypropylene having a melt index (hereinafter referred to as M) of 300 at a temperature of 230° C. and a load of 2.160 g was heated and melted using a presser and melt-blown under the following conditions.

Orifice diameter 0.15+n+n, pitch between orifices Q
, using a 7mm1 nozzle, a single hole discharge rate of 0.2 g/min, and a spinning temperature of 280°C.
Using air at 0°C1 supply pressure 3 and 0 kg/cm, the molten polymer was purified by pulling, and the temperature was 60 cm from the nozzle surface.
The fibers were collected and wound up by the suction net at the o+ position. The inflow of entrained flow from the side of the nozzle was cut by a regulating plate. The average fiber diameter of the obtained nonwoven fabric was 1.
The 2 tt m 1 fiber diameter distribution (CV) was 15%. The average weight is 30g/ca, and the variation rate is 3% on the eye side.
Bulk density is 0, 15 g/cJ, -10=Nonwoven fabric strength is vertical! 540g/cm, width direction 480
g/am. Moreover, this non-woven fabric was flexible and of good quality, containing no foreign material at all. The collection efficiency of this nonwoven fabric was 99.5%, and the pressure loss was 10 GiH20.

Examples 2 to 3, Comparative Examples 1 to 3 Melt blowing was performed in the same manner as in Example 1, using various polypropylenes with different MI and varying the discharge amount, spinning temperature, traction fluid temperature, and pressure. The nonwoven fabrics shown in the table were obtained.

As is clear from Table 1, the nonwoven fabrics within the scope of the present invention are excellent in both filter performance and strength.

Moreover, it can be seen that materials other than those according to the present invention are not preferable for filter applications.

(Effects of the invention) The olefin-based ultrafine fiber nonwoven fabric of the present invention is extremely fine with an average fiber diameter of 0.1 to 5.0 μm, has excellent fiber diameter distribution and basis weight distribution, and does not contain beads. Therefore, it shows extremely excellent filter performance.

The nonwoven fabric of the present invention is particularly suitable as a high-performance filter, but has other applications such as battery separators,
It is also suitable for disposable applications such as medical supplies, sanitary materials, and clean room supplies, as well as for 7m kA storage.

Patent applicant: Toyobo Co., Ltd.

Claims (2)

[Claims] 1. The average fiber diameter is 0.1 to 5.0 μm or less, the fiber diameter variation rate (CV) is 30% or less, and the width direction basis weight variation rate (C
An olefin-based ultrafine fiber nonwoven fabric characterized by comprising V) of 5% or less of olefin-based fibers. 2. Olefin fibers are arranged randomly, and the bulk density is 0.15 g/cm^3 or more, 0.80 g/cm
The olefin-based ultrafine fiber nonwoven fabric according to claim 1, which has a particle diameter of ^3 or less.