JP2545889B2 - Melt blown nonwoven - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a melt blower which exhibits high performance as a filter, particularly a heat-resistant and chemical-resistant filter, by specifying the size of constituent fibers, its polymer and thermal characteristics. It relates to a non-woven fabric.

(Prior Art) Demand for filters using ultrafine fiber non-woven fabric is increasing, and applications such as filtration of liquids and gases as well as electrets using dielectric polarization are being performed.

In the field of electrets, it has been proposed to form a film or sheet from an alpha-olefin polymer and utilize its dielectric constant to put it into practical use (JP-A-55-26700).
Issue).

On the other hand, in recent years, the melt-blowing method has been drawing attention as a method for producing an ultrafine fiber non-woven mat (JP-A-59-26561). Nonwoven fabrics produced by such a method are also used for filters.

(Problems to be solved by the invention) By the way, since polymers such as alpha-olefin have a relatively high crystallization rate, it is difficult to obtain an ultra-thin film or an ultra-fine fiber by the conventional melt molding method, and the performance of the obtained non-woven fabric is also high. It was unsatisfactory.

Further, the latter melt-plow method has many unsatisfactory points in various factors such as spinning temperature and index fluid temperature, and various improvements have been desired to obtain ultrafine fibers. In the melt-blowing method, the discharge amount per nozzle orifice is generally small, and the staying time of the molten polymer in the spinning machine is often extremely long. However, there is a problem that it is not desirable because

The present invention has been made by paying attention to the above problems, and its object is to provide a melt blown nonwoven fabric composed of ultrafine fibers excellent in thermal stability with less unevenness in fiber diameter distribution due to alpha-olefin. To do.

(Means for Solving Problems) The present invention takes the following means in order to solve the above problems. That is, the present invention is a melt-blown non-woven fabric formed of synthetic fibers consisting of an alpha-olefin polymer having a branched diameter side chain having a fiber diameter of 10 μm or less and a fiber diameter variation CV of 30% or less.
The melt-blown nonwoven fabric is characterized in that the dry heat shrinkage in the longitudinal and transverse directions at 0 ° C. is 3% or less. The present invention will be described in detail below.

The fiber diameter of the synthetic fiber constituting the nonwoven fabric according to the present invention is
It is 10 μm or less, preferably 8 μm or less, and more preferably 5 μm or less. When the fiber diameter exceeds 10μ, not only the nonwoven fabric, which is an aggregate of these fibers, becomes coarse, but the filtering performance as a filter deteriorates, and the surface area per weight decreases and the performance as an electret can be expected. It gets harder. Further, the fiber diameter unevenness CV of the synthetic fiber is 30%.
It should be below, and more preferably below 20%. When the fiber diameter unevenness CV exceeds 30%, the size of the free space formed when making a nonwoven fabric becomes uneven, not only the selectivity in filtration decreases but also the non-uniformity of the dielectric constant occurs in the electret. As a result, there is a variation in performance, which is not preferable.

Furthermore, when the nonwoven fabric is subjected to dry heat treatment at 160 ° C. for 30 minutes, the shrinkage rate in the machine direction and the transverse direction must be 3% or less, preferably 1%. It has been confirmed that those having a content of 3% or less exhibit excellent performance as a filter because they have excellent thermal dimensional stability. Incidentally, those having a shrinkage ratio of more than 3% have poor thermal dimensional stability and are completely unsuitable for use under heating and have poor filtration performance.

The properties required for the fibers constituting the non-woven fabric according to the present invention are as described above, but the performance as a non-woven fabric filter is further improved by using a specific polymer as shown below. That is, it is essential that the polymer used in the present invention is an alpha olefin polymer having a branched side chain, and specifically, poly 3 methyl butene 1, poly 4 methyl pentene 1 and the like. The characteristics of these polymers are that they are excellent in chemical resistance and excellent in heat resistance because they are olefin-based. Further, as described above, when a melt blow method is used for producing ultrafine fibers, one of the features is that unlike aliphatic polyesters and polyamides, deterioration or decomposition does not easily occur due to heat. Further, since the crystallization speed is extremely fast, a sufficient degree of crystallinity can be obtained by spinning, so that a stretching process or the like is unnecessary, and the property is determined only by spinning. Further, since the alpha olefin polymer has excellent electric insulation, it can be sufficiently applied to electret applications.

As a method for obtaining the ultrafine fibers used in the present invention, various methods capable of making ultrafine fibers such as a melt blowing method, a flash spinning method, a method of dissolving a sea-island fiber structure obtained by a composite spinning method can be adopted, but the most preferable method is melt blowing. Is the law.

FIG. 1 shows a melt blow nozzle used for producing the nonwoven fabric of the present invention. In FIG. 1, 1 is a polymer discharge pipe, 2 is an orifice hole, 3 is a heating fluid outlet, and 4 is a heating fluid temperature detecting end. L is the lip width. However, even if the melt-blowing method is applied as it is, it is not found that the ultrafine fibers satisfying the above-mentioned required performance are found, and in that case, the spinning temperature is set to a temperature 10 ± 5 ° C. higher than the melting point of the raw material resin, Index fluid temperature is 20 ±
It is necessary to set the temperature higher by 5 ° C. for extension, and it is desirable that the flow velocity of the index fluid is set to around Mach 1. For example, when poly-3 methylbutene 1 is used as the raw material resin, the most preferable conditions are a spinning temperature of 290 ° C and an indexing fluid temperature of about 300.
° C. The discharge amount per single hole may be arbitrarily set according to the target fiber diameter, but when obtaining a fiber diameter of 10 μ or less, 0.1 to 0.01 g / min is preferable, and 0.05 to 0.02 g / min is preferable. . The fiber group spun under such a condition is hung while being three-dimensionally crossed on a sucked drum or net, and the fibers are appropriately entangled to form a nonwoven fabric. The distance between the spinning nozzle and the drum or net is such that fibers are not closely entangled to form a string, that is, a distance sufficient for stacking while crossing three-dimensionally due to the spread and turbulence of the accompanying index fluid. For example, it is set to about 30 to 60 cm. If necessary, the non-woven fabric may be pressed lightly with a heating roller or the like, or may be embossed to adjust the apparent bulk density.

(Embodiment) Embodiment 1 A melt blow nozzle (orifice hole 2: 0.
15 mmΦ, the lip width of the heated fluid outlet 3 is 300 μ), and the poly 3 methylbutene 1 having a melt index value of 10 g / 10 min at 300 ° C. is spun at the discharge rate shown in Table 1 and the heated fluid outlet 3 The temperature of the detection end 4 is 30
Melt blow is performed while supplying heated air at 0 ° C at a pressure of 2.2 kg / cm ² , and 1 m at a position 40 cm away from the nozzle discharge end.
The spun fibers were collected on a net moving at a speed of / min to obtain a nonwoven fabric having a basis weight of 150 g / m ² (Examples 1, 2, 3 and Comparative Example 1).

The spinning temperature using polyethylene terephthalate,
Nonwoven fabrics were prepared in the same manner as in Example 1 except that the single hole discharge amount was changed to the value shown in Table 1 (Comparative Examples 2 and 3). Examples 1, 2, 3
The characteristics of the non-woven fabrics obtained in Comparative Examples 1, 2, and 3 are shown in Table 1. Using these non-woven fabrics as industrial bag filters, collection efficiency and dimensional stability under heating conditions were evaluated, and the results are also shown in Table 1.

The fiber diameter, fiber diameter unevenness, longitudinal shrinkage, transverse shrinkage, etc. in Table 1 were measured in the following manner.

Fiber diameter: The non-woven fabric was photographed by an electron micrograph, and 100 fibers were randomly selected from the enlarged photograph and the diameter (d
Measure i) and obtain the average value by the following formula.

Fiber diameter unevenness: The variation is obtained according to the following formula from the fiber diameter (di) obtained in the same manner as above.

Longitudinal shrinkage (%) and horizontal shrinkage (%) Mark the 10cm x 10cm mark on the surface of the non-woven fabric at 160 ℃, 3
After the heat treatment at 0 minutes, the marked line interval (lcm) is read and the shrinkage in the longitudinal and lateral directions is obtained by the following formula.

Collection efficiency In coal dust collection including SO _x etc., SO _x concentration before and after collection was compared and evaluated by the magnitude of filtration resistance. A circle indicates a large concentration difference and a high collection efficiency, and a cross indicates a small concentration difference and a low collection efficiency. Δ indicates an intermediate performance.

Heat resistance The degree of deformation when the bag filter was suspended in an atmosphere of 200 ° C was evaluated. ○ does not deform when used for a long time, ×
Indicates a state in which the suspension is extremely unusable.

In Example 1, the single-hole discharge amount was small, so the fiber diameter was small, and the fiber diameter unevenness was small, so the collection efficiency was good, and the heat resistance was good due to the resin. In Example 2, the fiber diameter was slightly thicker because the single hole discharge rate was rather large, but the collection efficiency and heat resistance were good. In Example 3, since the lip width was large and the fluid pressure was large, the fiber diameter unevenness was large and the collection efficiency was slightly lowered, but it was reasonably good. In Comparative Example 1,
The resin was the same as in Examples 1, 2 and 3, but the fiber diameter was large due to the large single hole discharge rate and the collection efficiency was poor. In Comparative Examples 2 and 3, the resin was polyethylene terephthalate. The heat resistance was low.

(Effects of the Invention) Since the nonwoven fabric of the present invention is made of fibers of a specific polymer, and further has a fiber diameter and a fiber diameter unevenness within a specific range, and has a dry heat shrinkage ratio below a certain level. In addition, the collection efficiency is excellent and the heat resistance is excellent, and the remarkable effect that the electret is widely used not only in the filter field but also in the field is obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of a melt blow nozzle used in the present invention. 2 ... Orifice hole, 3 ... Heating fluid outlet.

Claims (1)

(57) [Claims] 1. A fiber diameter is 10 μ or less, and a fiber diameter unevenness CV is 30%.
A meltblown non-woven fabric formed of a synthetic fiber composed of an alpha-olefin polymer having a branched side chain as described below, which has a dry heat shrinkage ratio of 3% or less in the longitudinal and transverse directions at 160 ° C.