JPH0813309A - Melt blow nonwoven fabric and its production - Google Patents

Abstract

PURPOSE:To obtain a melt blow nonwoven fabric with average fiber diameter changed smoothly in the thickness direction in such a state that the constituent fibers are mutually interlaced inside, good in filtration efficiency, excellent in long-term durability, thus suitable for various kinds of filtering media. CONSTITUTION:A polypropylene resin is fed from a hopper 3 to an extruder 1, where it is melted and then fed, via a splitting device 2, into 1st and 2nd dies 4,4' for forming fibers differing in diameter from each other followed by conducting a melt blow spinning, and the resultant 1st and 2nd fiber streams 7,7' are mutually superposed and accumulated on the collecting surface of a collector roll 6, thus obtaining the objective melt blow nonwoven fabric 8. For this nonwoven fabric, the fibers are mutually interlaced inside and the average fiber diameter phi1 on one surface is at 0.1-30mum, that phi2 on the other surface is to be 1/300 to 9/10 in the ratio phi2/phi1 and the fiber diameter as a whole is altered smoothly in the direction of the thickness of this nonwoven fabric 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a meltblown nonwoven fabric and a method for producing the same, and more particularly to a meltblown nonwoven fabric having good filtration efficiency and a long service life and a method for producing the same.

[0002]

2. Description of the Related Art In recent years,
Nonwoven fabrics have come to be used for various filter materials such as air filters and liquid filter materials, and the production amount thereof is increasing.

In such a nonwoven fabric, in order to obtain good filtration efficiency, it is preferable that the pore size on the inlet side is large and the pore size on the outlet side is small. Therefore, a non-woven fabric formed of thick fibers and a non-woven fabric formed of thin fibers are attached to each other. However, such a non-woven fabric has a stepwise increase in filtration resistance at the part where it is bonded, so that pressure loss occurs at that part, and it is easy to peel off from the part where it is bonded or to leave foreign matter such as dust. Therefore, there is a problem that the life is shortened.

Accordingly, it is an object of the present invention to provide a meltblown nonwoven fabric having good filtration efficiency and a long service life.

Another object of the present invention is to provide a method for producing the above meltblown nonwoven fabric.

[0006]

As a result of earnest research in view of the above object, the present inventors have found that a non-woven fabric having good filtration efficiency and long service life can be obtained by averaging one surface and the other surface. It is necessary to change the fiber diameters and make it possible for the average fiber diameters to change smoothly. Also, using a plurality of devices for melt-blowing fibers having different average fiber diameters, the fibers are discharged from these devices. It was found that a non-woven fabric in which the average fiber diameters of one surface and the other surface are different and the average fiber diameter is smoothly changed can be obtained by making the meltblown fiber streams overlap, and the present invention is obtained. Was conceived.

That is, the melt-blown nonwoven fabric of the present invention is characterized in that the average fiber diameter changes smoothly in the thickness direction in a state where the fibers are entangled in one nonwoven fabric.

Further, the method of the present invention for producing the above meltblown nonwoven fabric uses a plurality of devices for meltblowing fibers having different average fiber diameters, and meltblown fibers spun from nozzles of each meltblown device overlap before being accumulated. Each melt-blowing device is set as described above, and the melt-blowing fibers are thus deposited.

The present invention is described in detail below. [1] Meltblown Nonwoven Fabric The thermoplastic resin constituting the meltblown nonwoven fabric of the present invention is not particularly limited, and polyolefins such as polyethylene and polypropylene, polyethylene terephthalate,
Polyester such as polybutylene terephthalate, polyamide such as nylon 6, nylon 66 and nylon 46, polyvinyl chloride, polyvinylidene chloride, polystyrene, polycarbonate, polyvinylidene fluoride and the like can be used. In particular, it is preferable to use polyolefin and polyamide.

The melt blown nonwoven fabric of the present invention made of such a thermoplastic resin has an average fiber diameter of 0.1 to 1 on one side.
30 μm, preferably 0.2 to 20 μm, more preferably
It is 0.5 to 15 μm. The ratio of the average fiber diameter φ ₁ on one surface to the average fiber diameter φ ₂ on the other surface (φ ₂ / φ ₁ )
Is 1/300 to 9/10, preferably 1/60 to 5/6, and more preferably 1/5 to 2/3. If the ratio of the average fiber diameters (φ ₂ / φ ₁ ) is less than 1/300, the resulting nonwoven fabric cannot have sufficiently high filtration efficiency, while if it exceeds 9/10, the nonwoven fabric is used as a filter. It is not preferable since it will not be possible to obtain a sufficient filter life when used.

In the nonwoven fabric of the present invention, the average fiber diameter changes smoothly. Such a region where the average fiber diameter changes smoothly is formed by entanglement of fibers having different average fiber diameters. In particular, it is preferable that the ratio between fibers having different average fiber diameters changes from the one surface side to the other surface side.

In the region where the average fiber diameter changes smoothly, the total thickness of the non-woven fabric is 100%.
%, Particularly preferably 50% or more.

The melt blown nonwoven fabric of the present invention as described above preferably has the following physical properties. (1) The average pore diameter is 5 to 300 μm, especially 20 to 100 μm. (2) Average filling rate is 2 to 20%, especially 5 to 15%.

[2] Manufacturing Method Next, the method of the present invention for manufacturing the above-mentioned melt blown nonwoven fabric will be described.

FIG. 1 is a schematic view showing an apparatus used in the method for producing a meltblown nonwoven fabric of the present invention. In FIG. 1, the melt blow molding apparatus comprises an extruder 1, a hopper 3 for supplying a thermoplastic resin to the extruder 1, a flow dividing device 2 provided at the tip of the extruder 1, and a resin divided by the flow dividing device 2. And a first die 4 (which discharges the first fiber) and a second die 4 ′ (which discharges the second fiber), respectively, which are connected to the dies 4 and 4 ′ by heating gas transport pipes 5 and 5 ′. It has an air supply device (not shown), an air heater (not shown), and a collector roll 6 provided at a predetermined position from the tip of the die 4.

2 is a sectional view of the die 4 in FIG.
Shown in The die 4 includes an upper die plate 41, a lower die plate 42, an upper gas plate 43, and a lower gas plate 44.
Consists of By combining such respective parts, the orifice 11, the slits 12 and 13, and the upper air chamber 45 and the lower air chamber 46 communicating with the slits 12 and 13 are formed. Orifice 11
Is composed of a rear end portion, an intermediate portion and a front end portion, a resin inlet 47 is connected to the rear end portion, and a middle portion serves as a resin chamber 48. The upper air chamber 45 and the lower air chamber 46 are respectively provided with the heated gas transport pipe 5.
Is connected. It should be noted that heaters 14 and 15 for holding the orifice 11 at a temperature described later are embedded in the upper die plate 41 and the lower die plate 42.

In the apparatus as described above, the first die 4
And the diameter of the orifice 11 of the second die 4'is 0.1 to 3 m.
It is preferably m, especially 0.2 to 2 mm. If the diameter of the orifice is less than 0.1 mm, it is difficult to carry out a stable spinning operation because the pressure of the die rises. On the other hand, if it exceeds 3 mm, it is difficult to reduce the average diameter of the obtained fiber to 30 μm or less. Not preferable. The diameters of the orifices 11 of the dies 4 and 4'can be appropriately changed depending on the desired average fiber diameter as described later.

The temperature of the heated air (blow air) jetted from the slits 12 and 13 is 250 to 350 ° C., especially 260
A temperature of ~ 320 ° C is preferred.

Further, as shown in FIG. 3, the first and second dies 4, 4'have a predetermined distance (distance between orifices: T).
And the angle formed by each die (the angle formed by the orifice: x) is preferably within a predetermined range. Specifically, the distance (T) between the first and second dies 4, 4'is 300-
It is preferable that the angle (x) formed by each die (orifice) is 700 to 700 cm, especially 400 to 600 cm, and 5 to 180 °, particularly 30 to 70 °.

The distance between the dies 4, 4'and the collector roll 6 is preferably 100 to 600 cm, more preferably 200 to 400 cm. The distance between the dies 4, 4'and the collector roll 6 is 100c
When it is less than m, it becomes difficult to sufficiently entangle the fibers,
On the other hand, if it exceeds 600 cm, the fiber flow is disturbed, and the fibers are completely solidified during deposition, which makes it difficult to obtain a nonwoven fabric in which the fibers are sufficiently entangled with each other, which is not preferable.

In such a melt blow molding apparatus, the resin forming the non-woven fabric is transferred from the hopper 3 to the extruder 1.
After being melted and kneaded, they are supplied to the first and second dies 4, 4'by the flow dividing device 2. The resin supplied to the first die 4 is discharged from the orifice 11 via the inlet 47. At this time, the discharged molten resin is extremely thinned by the heated air jetted at high speed from the slits 12 and 13. The first fiber stream 7 generated here is collected on a collecting surface such as the rotating collector roll 6.
On the other hand, the resin supplied to the second die 4'is also extremely thinned, and the second fiber stream 7'is accumulated on the collecting surface of the rotating collector roll 6 or the like.

Since the first and second dies 4, 4'are installed at predetermined intervals and angles as shown in FIG. 3, at least one of the first fiber stream 7 and the second fiber stream 7'is provided. The parts are entangled by the time they reach the collector roll 6 (collection surface). The ratio of this entanglement can be appropriately set depending on the distance and angle between the first and second dies 4 and 4 ', but the total amount of melt blown fibers discharged from the dies 4 and 4'is 100% by weight. 5 to 70% by weight, preferably 20 to
40% by weight.

If the ratio of entanglement is less than 5% by weight, the area of the non-woven fabric obtained is not so smoothly changed, and the filtration resistance is changed step by step with the non-woven fabric. Foreign matter tends to remain. On the other hand, if the entanglement ratio exceeds 70% by weight, the life of the filter cannot be extended.

In this way, a part of the fiber flow discharged from the two dies is deposited while being entangled,
First, the first fibers with a large average fiber diameter are deposited independently (7
a), then the fiber stream in which the first fiber and the second fiber are entangled with each other is deposited (7b), and finally, the second fiber having a small average fiber diameter is independently deposited (7c). The nonwoven fabric 8 of the present invention can be obtained. When 7b is examined in detail, the meltblown fibers are sprayed and discharged as shown in FIG. 3, but the distribution is not uniform in any of the diffused parts, and shows a normal distribution. Therefore, the amount of fibers is small at the ends of the fiber streams 7 and 7'and is large at the center. Therefore, the proportion of the second fibers gradually increases from the state in which the first fibers occupy the majority, and therefore the average fiber diameter changes smoothly in 7b.

The discharge amount of the first and second fibers can be adjusted by adjusting the inflow amount of the resin into the first and second dies 4, 4'by the flow dividing device 2, respectively.

The melt-blown nonwoven fabric of the present invention thus obtained can be subjected to post-treatments such as heat setting with a heating roll, infrared irradiation, and induction heating.

Although the method of manufacturing the melt-blown nonwoven fabric of the present invention has been described above by taking the case of using two dies as an example, the present invention is not limited to this and the number of dies may be three or more. Further, for example, two or more extruders may be used, and dies may be connected to the respective extruders, and the fiber streams made of the same or different resins may be discharged therefrom, respectively. Thus, fibers having a large average fiber diameter (first fibers) are not discharged from the die 4 and fibers having a small average fiber diameter are not discharged from the die 4 ', and vice versa. However, when three or more dies are used, it is preferable to install them so that the average fiber diameter changes sequentially.

[0028]

In the present invention, a plurality of devices for melt-blowing fibers having different average fiber diameters are used, and melt-blown non-woven fabrics are manufactured by stacking the melt-blown fiber flows discharged from these devices so that they are superposed. The obtained non-woven fabric has different average fiber diameters on one surface and the other surface, and the average fiber diameter changes smoothly inside the surface.

Although the reason why such an effect is obtained is not always clear, a plurality of dies are used to discharge meltblown fibers having different average fiber diameters,
Since these fibers are overlapped, it is considered that, in the overlapped portion, the ratio of the other fibers gradually increases from the state in which one meltblowing device has many fibers.

[0030]

The present invention will be described in more detail by the following examples. Examples 1 to 3 Homopolypropylene (manufactured by Tonen Kagaku Co., Ltd., S215) was used to produce a meltblown nonwoven fabric under the manufacturing conditions shown in Table 1 by the apparatus shown in FIG. The thickness, air permeability, average pore diameter, average fiber diameter on one side, average fiber diameter on the other side, NaCl efficiency, pressure loss and filter characteristics of the obtained meltblown nonwoven fabric were measured. The results are shown in Table 2.

Comparative Examples 1 and 2 Melt blown fibers discharged from the first die and the second die were not bulky in the same manner as in the examples except that the angle formed by the dies was 0 ° and the distance between the dies was 50 cm. Do 2
A melt blown non-woven fabric made of fibers having different average fiber diameters was produced. The thickness, air permeability, average pore diameter, average fiber diameter on one side, average fiber diameter on the other side, NaCl efficiency, pressure loss and filter characteristics of the obtained meltblown nonwoven fabric were measured. The results are shown in Table 2.

Comparative Example 3 Nozzle temperature 300 ° C., orifice diameter 0.3 μm, discharge rate 3 kg
/ h, air temperature of 310 ℃, and air discharge rate of 5 Nm ³ / min, the take-off speed is changed to 0.34 mm and 0.38 respectively.
A non-woven fabric having a thickness of mm was prepared. One nonwoven fabric has an average fiber diameter of 6 μm, and the other nonwoven fabric has an average fiber diameter of 4 μm.
It was m. Two of these non-woven fabrics were bonded together with an adhesive to form one non-woven fabric. The properties of the resulting nonwoven fabric are shown in Table 2.

Table 1 Manufacturing conditions Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Nozzle temperature (° C) 300 300 300 300 300 First die Orifice diameter (μm) 0.3 0.3 0.3 0.3 0.3 Discharge rate (Kg / min) 3 4.2 6 6 5 Air temperature (℃) 310 310 310 310 310 Air discharge rate ⁽¹⁾ 2 3 4 6 3 Second die orifice diameter (μm) 0.3 0.3 0.3 0.3 0.3 Discharge rate ( kg / min) 3 3 3.5 8 15 Air temperature (℃) 310 310 310 310 310 Air discharge rate ⁽¹⁾ 2 3 3 6 3 Distance between first die and second die (cm) ⁽²⁾ 50 50 50 50 50 Angle between first die and second die (°) ⁽³⁾ 50 50 45 0 0 Distance between die and collector roll (cm) 40 40 40 40 40 Entanglement ratio (%) ⁽⁴ ) ⁾ 30 30 35 0 0

Note) (1) Amount of air discharged per 1 g of resin component (unit is Nm ³ / min). (2) Distance between orifices. (3) Angle formed by the direction of the orifice. (4) Weight of entangled portion (overlapping portion) / (total discharge amount of first die + total discharge amount of second die) × 100 (wt%)

Table 2 Physical Properties Example 1 Example 2 Example 3 Thickness (mm) 0.655 0.554 0.531 Air permeability ⁽¹⁾ 42.5 105.2 36.3 Average pore diameter ⁽²⁾ (μm) 20.7 36.1 21.8 Average fiber diameter ⁽³⁾ (Μm) One side φ ₁ 0.8 6 10 The other side φ ₂ 0.5 3 2 NaCl efficiency ⁽⁴⁾ 37.97 11.08 40.77 Pressure loss ⁽⁵⁾ 1.8 0.6 1.8 Filter characteristics ⁽⁶⁾ 0.265 0.196 0.291

Table 2 (continued) Physical Properties Comparative Example 1 Comparative Example 2 Comparative Example 3 Thickness (mm) 0.75 0.624 0.517 Air permeability ⁽¹⁾ 31.2 80.4 27.1 Average pore diameter ⁽²⁾ (μm) 31.2 57.6 24.8 Average fiber diameter ⁽³⁾ (μm) One surface side φ ₁ 0.8 6 6 Other surface side φ ₂ 0.5 3 4 NaCl efficiency ⁽⁴⁾ 33 8.5 29.55 Pressure loss ⁽⁵⁾ 2.0 0.8 2.9 Filter characteristics ⁽⁶⁾ 0.20 0.11 0.121

(1) Air permeability: Measured according to JIS L1095 (unit: cc / cm ² / sec). (2) Average pore diameter: measured with a porometer. (3) Average fiber diameter: SEM (scanning electron microscope)
The measurement was performed on one surface, the other surface, the inner layer (entangled portion), and the entire nonwoven fabric. (4) Unit:% / at 5 cm / s. (5) Unit: mmAg / at 5 cm / s. (6) Filter characteristic = ln (1 / P) / pressure loss. P = 1- (NaCl efficiency).

As shown by the NaCl efficiency, pressure loss and filter characteristics in Table 2, the melt blown non-woven fabrics of Examples 1 to 3 have an initial efficiency when used as a filter as compared with the melt blown non-woven fabrics of Comparative Examples 1 to 3. Was good and the life value was large. When the cross section of the meltblown nonwoven fabric of Example 1 was observed by SEM (500 times), the average fiber diameter of the average fiber diameters changed smoothly.
Boundaries and the like did not exist inside.

[0039]

As described in detail above, in the present invention, a plurality of devices for melt-blowing fibers having different average fiber diameters are used, and the melt-blown fiber streams discharged from these devices are piled up so as to be superposed. Since the melt-blown non-woven fabric is produced in this manner, the resulting non-woven fabric has different average fiber diameters on one side and the other side, and the average fiber diameter changes smoothly inside. Such a melt-blown nonwoven fabric of the present invention is suitable for various filters such as battery separators and heat-resistant filters.

[Brief description of drawings]

FIG. 1 is a schematic view showing an apparatus for producing a meltblown nonwoven fabric of the present invention.

FIG. 2 is a cross-sectional view of a die of the apparatus for manufacturing the melt-blown nonwoven fabric of FIG.

FIG. 3 is a schematic view showing the intervals and angles of the dies and the state of entanglement of the meltblown nonwoven fabric in the apparatus for producing the meltblown nonwoven fabric of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Extruder 2 ... Flow dividing device 3 ... Hopper 4 ... First die 4 '... Second die 5, 5' ... Heated gas transport pipe 6 ... Collector Roll 7, 7 '... Fiber flow 8 ... Nonwoven fabric 11 ... Orifice 12, 13 ... Slit 14, 15 ... Heater 41 ... Upper die plate 42 ... Lower die plate 43. ..Upper gas plate 44 ... Lower gas plate 45 ... Upper air chamber 46 ... Lower air chamber 47 ... Inlet 48 ... Resin chamber

Claims (3)

[Claims] 1. A melt blown non-woven fabric, characterized in that the average fiber diameter changes smoothly in the thickness direction in a state where the fibers are entangled in one non-woven fabric. 2. The melt blown nonwoven fabric according to claim 1, wherein the average fiber diameter φ ₁ of the fibers on one surface of the nonwoven fabric is 0.
1 to 30 μm, the average fiber diameter φ ₂ of the fibers on the other surface is 1/300 to 9 / with respect to the average fiber diameter φ ₁ of the fibers on the one surface.
A melt blown nonwoven fabric having a ratio of 10 (φ ₂ / φ ₁ ). 3. The method for producing a meltblown nonwoven fabric according to claim 1 or 2, wherein a plurality of devices for meltblowing fibers having different average fiber diameters are used, and meltblown fibers spun from nozzles of each meltblowing device are used. A method characterized in that each melt-blowing device is set so as to be overlapped with each other before being accumulated, and the melt-blown fibers are thereby deposited.