JPH03249249A - Nonwoven fabric of olefin-based ultrathin yarn - Google Patents

Abstract

PURPOSE:To obtain the title nonwoven fabric useful for a filter, having excellent handleability, comprising specific polyolefin-based ultrathin yarn. CONSTITUTION:The objective nonwoven fabric comprising specific polyolefin- based ultrathin yarn having 0.1-5mum, preferably 0.5-4mum average yarn diameter and weight-average molecular weight (Mw) and number-average molecular weight (Mn) satisfying formula I and formula II.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an olefin-based ultrafine fiber nonwoven fabric, and more particularly to an olefin-based ultrafine fiber nonwoven fabric that is particularly excellent in filter applications and has good handling properties.

(Prior Art) Ultrafine fiber nonwoven fabrics have recently come to be obtained by melt blowing and are used for many purposes.

The heavy weight spinning method using the melt-blowing method is described in Industrial and Engineering Chemistry, Vol.
8, No. 8, pp. 1342-1346, 1956. The melt blowing method for polypropylene in Japan is disclosed in JP-A-50-46972 and JP-A-54-13.
No. 4177. These methods thermally degrade high molecular weight polymers (initial intrinsic viscosity of 1.4 or higher) by the time of spinning, and reduce the polymer to a low melt viscosity (with a shear rate of 700 to 350).
Since the method involves spinning with a melt viscosity of 50 to 300 poise at 1 second, the resulting nonwoven fabric has the drawbacks of large irregularities in fiber diameter and weak nonwoven fabric strength. A method for improving heat deterioration spots in piping is disclosed in Japanese Patent Application Laid-open No. 83-6107 and Japanese Patent Application Laid-open No. 1
It is disclosed in the publication No.-158581. These are based on a method of spinning with a melt viscosity below molecular weight reduction, and the resulting low molecular weight and wide molecular weight distribution (weight average molecular weight:
Mw, number average molecular weight; Mw is 50,000 as Mn
to 90,000, and the nonwoven fabric has an Mw/Mn of 4 to 6, but fiber diameter irregularities (particularly irregularities over time) become large due to addition irregularities of the molecular weight reducing agent, and it is difficult to control the viscosity.
There are problems such as the threads break easily due to the low viscosity, the strength of the nonwoven fabric is weak due to the low molecular weight, the additives cause an increase in back pressure, and the additives dissolve during use.

(Problems to be Solved by the Invention) The present invention overcomes the drawbacks of the conventional technology, reduces fiber diameter unevenness, improves the strength of the nonwoven fabric, and improves elution of additives, etc., and is particularly suitable for filter applications. An object of the present invention is to provide an olefin-based ultrafine fiber nonwoven fabric.

(Means for Solving the Problems) The present invention has found a solution by increasing the molecular weight slightly and narrowing the molecular weight distribution.In order to solve the problems, the following means are taken. be. That is, the present invention is based on the average fiber diameter force! This is an olefin-based ultrafine fiber nonwoven fabric characterized by being made of polyolefin ultrafine fibers having a diameter of 0°1 μm or more and 5 μm or less, and whose weight average molecular weight (Mw) and number average molecular weight (Mn) satisfy the following formula.

Mw≧5.0X10' Log (Mw/Mn)≦0.5791×Log (
Mw) -2,2916 The weight average molecular weight (Mw) of the fibers constituting the nonwoven fabric of the present invention is 50,000 or more, preferably 60,000 or more and 400,000 or less.

If the weight average molecular weight (Mw) is low, the strength of the nonwoven fabric will be low even if the ratio of weight average molecular weight to number average molecular weight (Mw/Mn) described below is satisfied, which is not preferable.

In addition, thread breakage is more likely to occur during spinning, so if the fiber diameter is large, beads may be generated, and if the fiber diameter is small, powdery material may be scattered or contained in nonwoven fabrics, causing contamination and filtration. This is undesirable as it causes a decrease in performance. Furthermore, the weight average molecular weight (Mw
) and number average molecular weight (Mn) Log (Mw/Mn)
is preferably less than or equal to 0.5791×Log (Mw) −2,2918, that is, the molecular weight distribution becomes narrower as the weight average molecular weight (Mw) becomes lower, and the fibers are highly oriented. Perhaps because of this, it became possible to improve the strength of the nonwoven fabric. In addition, since thread breakage is eliminated, there is no contamination of beads or powdery substances, and filtration accuracy is improved. Moreover, surprisingly, the weight average molecular weight (
Mw) and number average molecular weight (Mn), that is, Log
When (Mw/Mn) is within the range of the invention, yarn diameter unevenness is significantly improved. The reason is not clear, but it is assumed that because the molecular weight distribution is narrow, appropriate elongation resistance is required, and because there are few melt viscosity irregularities, it becomes difficult to break and traction irregularities are less likely to occur. Note that Mw/Mn is 3.
It is preferably 1 or less. Weight average molecular weight (M
w) and the number average molecular weight (Mn) Log (Mw/M
Non-woven fabrics made of the fibers mentioned in n) have poor non-woven strength and are difficult to handle, resulting in defective products, and filtration accuracy deteriorates due to uneven fiber diameters and the formation of pores due to beads. There are concerns about problems with filter performance, such as when powder or beads fall off, causing contamination.

In addition, the weight average molecular weight (M w ) and number average molecular weight (Mn) as used in the present invention are determined in terms of polystyrene using a Gerber Mueishi Nikko chromatograph (manufactured by Nippon Waters Co., Ltd., 150C).

The average fiber diameter of the fibers constituting the nonwoven fabric of the present invention is 0.1
μm or more and 5 μm or less, preferably 0.5 μm or more and 4 μm
It is as follows. As is well known, the thinner the fiber diameter, the more fine particles can be filtered out, but when the average fiber diameter is less than 0.1 μm, the pressure loss becomes extremely high, so a nonwoven fabric with strong strength is required. On the contrary, it becomes weaker and may cause problems such as bursting, which is undesirable. When it exceeds 5 μm, the filtration efficiency deteriorates, making it unsuitable for high-performance filters.

The olefin fibers referred to in the present invention include polypropylene,
Fibers made of polyethylene, polybutene-1, polypentene-1, etc., and modified polymers thereof.

A preferable fiber material for the present invention is disclosed in Japanese Patent Application Laid-open No. 1-156561.
Examples include those that do not contain particulate matter, decomposing agents, etc. shown in (2), and more preferably those that contain only some antioxidants. Particularly preferred from the viewpoint of fiber forming properties are polypropylene, polybutene 1, and the like. When used in a gas filter, charging performance can improve the collection performance.

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/cJ or more, more preferably 0.15 g/ca or more. Life and collection ability can be improved by stacking fibers with different fiber diameters and bulk densities.

The basis weight of the nonwoven fabric of the present invention is not particularly limited, but from the viewpoint of shape retention, it is preferably 5 g or more.

Moreover, 120 g// or less is preferable.

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

An example for obtaining the nonwoven fabric of the present invention will be shown below.

The polymer used in the present invention preferably has a narrow molecular weight distribution. In addition, those with a large molecular weight (Mw 150
000 or more) preferably satisfies the following formula.

L o g (Mw/Mn)≦0.854×Log (
Mw) -3,701 Polypropylene with 0.05% antioxidant added is melted in an extruder and a fixed amount is supplied to a nozzle via a metering pump. It is preferable to remove foreign matter with a filter to prevent yarn breakage during the process. Further, in order to eliminate the difference in thermal history within the conduit up to the nozzle, it is preferable to perform migration using a static mixer or the like.

In addition, the residence time up to the nozzle orifice is preferably within 10 minutes in order to control thermal decomposition, and is preferable in order to prevent further decomposition.
280℃ or higher, and 230℃ or higher for polybutene-12
The temperature is 70°C or less. If a large amount of stabilizer is not added, it is preferable to spin it at least up to the melting point +150°C. In this way, the polymer having a uniform melt viscosity can be uniformly discharged from the orifice without being thermally degraded as much as possible.

At the same time, heated fluid is blown onto the tip of the orifice to elongate and thin the molten polymer, which is then cooled and solidified by the low-temperature fluid drawn in by the accompanying flow, collected and stacked on the suctioned net to create a random fiber arrangement. Form a nonwoven fabric. The heating fluid is preferably steam, air, nitrogen gas, or the like. The temperature of the heating fluid is 250°C or more and 400°C or less, preferably 30°C
0℃ or more and 380℃ or less, the pressure of the heating fluid is 0.5kg
/cJ or more, preferably 0.8kg/cJ or more4k
g/cJ or less. Note that it is preferable that the temperature unevenness of the fluid be 5° C. or less, and the ejection pressure unevenness (measurable with a pitot tube) be 10 m/sec or less in terms of velocity. If it is out of the above range, the unevenness of the fiber diameter becomes large, or if it is significant, balls or powder are generated due to thread breakage, making the nonwoven fabric unsuitable for filters.

If the distance between the nozzle and the take-up net is short, fusion will occur.
If it is not long, it will stall and there will be a lot of string canes. The preferred distance is 40c1 to 60cm.

Further, in order to arrange the fibers in a random arrangement suitable for filters, it is preferable to take the fibers on a flat surface.

The unevenness of the fabric weight is determined by how the fibers fall on the flow of fluid, and by whether or not the laminated fibers are blown away by the fluid. In order to reduce the turbulence of the ejected fluid and entrained flow,
Preferably, the medial side surface restricts the inflow of fluid.

It is preferable that there be no unevenness in the orthogonal direction so that the inflowing entrained flow is not disturbed.

Appropriate suction is required to avoid being blown away by the flowing fluid. Further, it is preferable to restrict the flow path of the ejected fluid so as not to increase the amount of ejected fluid, or to suction the ejected fluid midway through the flow.

The nonwoven fabric laminated in this way has less unevenness in fiber diameter (preferably reaching CV<20%) and less unevenness in fabric weight (
The nonwoven fabric is ideal for filter applications (preferably reaching a CV<3%).

The nonwoven fabric of the present invention is strong and can be used as a filter as it is, but it can be pressed to increase its bulk density and strength. Further, heat treatment, embossing, ultrasonic processing, etc. can be performed as necessary. In addition, the collection performance can be improved by converting it into an electret by corona discharge or the like.

(Examples) The present invention will be explained in more detail below using Examples, but the present invention is not limited to these Examples.

The main characteristic values specified in the text and used in the examples are as follows.

■ Average fiber diameter (μm), variation rate (VC%) Width direction of nonwoven fabric: IO locations, arbitrarily sampled, 300% using a scanning electron microscope (SEM)
Photographs are taken at 5 points at 0x magnification, and the diameters of the 5 fibers at point L are measured. The average value (X
) and standard deviation (σ, -1). The rate of variation (CV) is determined by the formula below.

Variation rate = [(σ, -+)/(X))xlOO% Rectangular direction: Sample at every 501 W and find in the same way as in the width direction.

Values are indicated by XTCVT for differentiation.

■ Non-woven fabric strength (g/c) Take 5 samples of length 24cm x width 2cm in each width and longitudinal direction, stretch and cut with Tensilon with a gripping width of 2cra (stretching speed 100%) and measure the maximum strength at that time. Calculate the average value of the 5 points by converting it into 1 cm.

■ Bulk density (g/cJ) Calculated from the thickness and area weight measured under a load of 50 g/cJ.

■ Collection efficiency, pressure loss JIS Z-8901 test dust The collection efficiency and pressure drop were measured using

Example I Melt index (hereinafter referred to as MI) according to the method of JIS K-8785: 300 g/10 minutes Mw: 1100
00. Mw/Mn: 3.9, antioxidant 0.05% by weight
The contained polypropylene was melted by heating and melt blown under the following conditions.

The spinning temperature is 280℃, the nozzle diameter is 0.15m, the pitch between the holes is 0.7mm, and the single hole discharge rate is 0.2g/min.The traction fluid is air at 330℃. The fibers were supplied to the tip of the orifice at a pressure of 3.5/dG (inside the nozzle), collected on a suctioned moving net under the nozzle, and then wound up through a pressing roller. The temperature difference of the heated air jetting out from the lip is 8°C over 100 am, the flow velocity difference is 10 m/s,
No powdery matter was observed.

Note that the entrained flow inflow from the nozzle side (width direction) was cut by a regulating plate. In addition, a regulating plate was attached in the width direction of the net surface (1.2 times the nozzle width) to prevent scattering of ffi.

The average fiber diameter of the obtained nonwoven fabric was 1.2 μm (CV12
%), Mw: 90000. Mw/Mn: 3゜6,
Fabric weight: 30 g/d, fabric weight irregularities (1 length for every 2 cm in the width direction)
Cut the nonwoven fabric into 0cm pieces, measure the weight of each piece, and average value: W
and standard deviation: σfi-1, fluctuation rate: (W/σ,
, -1) indicated by X100) 3%, bulk density 0°15g/c
J, longitudinal fiber variation (CVT) was 14%. The strength of the nonwoven fabric was 540 g/cm in the width direction and 480 g/am in the longitudinal direction.

This nonwoven fabric has a collection rate of 0.3 μm particles of 99.6% and a pressure loss of 12 mmH2O.

Example 2 A nonwoven fabric was prepared using polyethylene having an average molecular weight of 2,000,000 and changing the net speed, but using the same conditions as Example 1 except for the other conditions. The average fiber diameter of the nonwoven fabric is 4.8 μm.
(CVIO%) + Mw: 5000000, Mw
/Mn: 7.57. Fabric weight 88 g/rl, fabric weight unevenness 4%, bulk density 0.08 g/J1 longitudinal fiber accounting C
VTII%, the strength in the width direction was 3310 g/am, and the strength in the longitudinal direction was 2895 g/cm.

The collection rate of 0.3 μm particles of the nonwoven fabric was 82%, and the pressure loss was 5 μm H20. Note that there were no beads on the nonwoven fabric. It can be seen that the nonwoven fabric of the present invention exhibits extremely strong strength and excellent filtration performance.

Examples 3 to 4, Comparative Examples 1 to 4 Using various polypropylenes with different MI and molecular weight distribution, various spinning temperatures, discharge rates, traction fluid temperatures, and pressures were used, and the other conditions were the same as in Example 1 to produce ultrafine fiber nonwoven fabrics. I got it.

The results obtained are shown in Table 1.

As is clear from Table 1, it can be seen that the products within the scope of the present invention have excellent filtration performance, strong strength, and are optimal as filter materials. Also, those that are outside the scope of the present invention are not preferred as filters.

Comparative Example 5 V
The mixture was mixed for 2 hours using a mold mixer and pelletized using a pelletizer to obtain pellets with an MI of 250. This resin was spun at a spinning temperature of 290°C, a fluid temperature of 370°C, and a fluid pressure of 2.5 k.
g/cJ A nonwoven fabric was obtained in the same manner as in Example 1 except for G.

The obtained nonwoven fabric had an average fiber diameter of 1.3 μm (CV48%
, CVt 79%) Mw: 58000. Mw/Mn
: 4, ol basis weight 31 g/d (CVI 2%
), width direction strength 158g/am, longitudinal direction strength 127
g/cm, and contained microbeads. Furthermore, when the vehicle was picked up, a significant amount of powder was scattered.

The collection rate of this nonwoven fabric is 42%, and the pressure loss is 10w-H2O.
The filter performance was poor.

Example 5 The nonwoven fabric obtained in Example 1 was heated to a bulk density of 0.
The filtration performance was investigated using an aqueous solution containing latex standard particles of 1 μm and 1% concentration by weight. The nonwoven fabric of the present invention is 100%
I was able to remove it. The evaluation was performed by comparing particles in the filtrate with RO water using an in-liquid particulate meter.

Comparative Example 6 The nonwoven fabric obtained in Comparative Example 5 was evaluated for filtration performance in the same manner as in Example 5. The removal rate of 1 μm particles was 42%.

A further problem was that powdery substances were contained in the filtrate.

(Effects of the Invention) The nonwoven fabric of the present invention has characteristics such as a small average fiber diameter, low fiber accounting, strong nonwoven fabric, and no powdery or clumped substances, resulting in improved filtration accuracy and filtration efficiency. It has excellent properties and has good filter processability, making it ideal for various high-performance filter materials.

Due to the above-mentioned characteristics, the nonwoven fabric of the present invention is suitable for use in separators, wipers, heat insulating materials, barrier materials, and many other industrial materials, and can exhibit useful functions.

Claims (1)

[Claims] 1. An olefin-based ultrafine fiber nonwoven fabric characterized by being made of polyolefin-based ultrafine fibers having an average fiber diameter of 0.1 μm or more and 5 μm or less, and a weight average molecular weight (Mw) and a number average molecular weight (Mn) satisfying the following formula. Mw≧5.0×10^4 Log(Mw/Mn)≦0.5791×Log(Mw)
-2.2916