JP2002201560A - Polypropylene for ultrafine fiber melt-blown nonwoven fabric and nonwoven fabric and air filter each made therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polypropylene capable of producing ultrafine fiber melt- blown nonwoven fabric in high productivity, to provide such a melt-blown nonwoven fabric thus produced, and to provide an air filter made of the above nonwoven fabric and having high particulate collection efficiency. SOLUTION: This polypropylene for ultrafine fiber melt-blown nonwoven fabric has a melt flow rate of >=1,200 g/10 min and molecular weight distribution index (Mw/Mn) of <=2.5. The 2nd objective melt-blown nonwoven fabric with an average fiber diameter of <=2.0 μm is produced by melt blowing method using the above polypropylene. The other objective air filter is obtained by applying direct current voltage to the above melt-blown nonwoven fabric to give electret property, and the thus obtained air filter has particulate collection efficiency of >=99.97% and pressure loss of <=120 Pa each determined at a basis weight of 40 g/m2 based on JIS B9908 (at a wind velocity of 5 cm/s), respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene from which a melt-blown non-woven fabric made of ultrafine fibers can be obtained, a non-woven fabric made of the same, and an air filter.

[0002]

BACKGROUND OF THE INVENTION In recent years, nonwoven fabric production methods which have been used for various applications include a spunbond method and a meltblown method as methods for producing nonwoven fabrics.
Compared to spunbonded nonwoven fabrics with large fiber diameters and strength, meltblown nonwoven fabrics have a small fiber diameter, and utilize filters with a large specific surface area, thereby making use of the barrier properties due to the narrow gap between fibers. It is used for leak-proof members such as disposable diapers. In a melt-blown non-woven fabric, in order to further enhance these performances, the constituent fibers are required to be extremely fine.

[0003] In the production of melt blown nonwoven fabrics, polypropylene-based resins are mainly used as raw material resins. In order to improve the spinnability of the raw material resin, a high melt flow rate (MFR), for example, a material having a high melt flow rate of 300 g / 10 min or more is usually used as a raw material. It has been difficult to produce ultrafine fibers. That is, it is generally necessary to increase the resin temperature and the air flow rate, and at the same time, to extremely reduce the discharge amount in order to make the fibers ultrafine.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polypropylene capable of producing an ultrafine fiber melt-blown non-woven fabric with good productivity, a melt-blown non-woven fabric obtained by using the same, and an excellent particle collection rate comprising the non-woven fabric. An object of the present invention is to provide an air filter.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and as a result, by using propylene having a specific MFR and a molecular weight distribution (Mw / Mn), it has been found that ultrafine fibers can be produced with high productivity. The present inventors have found that a melt-blown nonwoven fabric can be obtained, and have reached the present invention.

That is, the present invention provides the following (1) to (4)
, A nonwoven fabric and an air filter. (1) Polypropylene for ultrafine fiber melt-blown nonwoven fabric having a melt flow rate of 1200 g / 10 min or more and a molecular weight distribution (Mw / Mn) of 2.5 or less.

(2) The polypropylene for ultra-fine fiber melt-blown nonwoven fabric according to (1), which is obtained by degrading polypropylene having a melt flow rate of 20 g / 10 minutes or less.

(3) A melt-blown nonwoven fabric having an average fiber diameter of 2.0 μm or less, obtained by a melt-blowing method using the polypropylene according to (1) or (2).

(4) After applying a DC voltage to form an electret, JIS B99 is applied at a basis weight of 40 g / m ² .
An air filter comprising the melt-blown nonwoven fabric according to the above (3), wherein the particle collection rate and the pressure loss measured according to the method described in No. 08 (measured air velocity 5 cm / sec) are 99.97% or more and 120 Pa or less, respectively.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the polypropylene for ultra-fine fiber melt-blown non-woven fabric according to the present invention, the melt-blown non-woven fabric obtained by using the same, and the air filter comprising the non-woven fabric will be described in detail. In the present invention, ultrafine fibers refer to fibers having a fiber diameter of 2.0 μm or less.

The polypropylene for ultra-fine fiber melt-blown nonwoven fabric according to the present invention has a melt flow rate (MFR) of 1200 g / 10 min or more, preferably 1200 to 3000.
g / 10 min, more preferably 1500 to 2500 g / 10
And the molecular weight distribution (Mw / Mn) is 2.5 or less, preferably 1.0 to 2.3, more preferably 1.0 to 2.0.
belongs to.

In the present invention, MFR is ASTM D
It was measured at a load of 2.16 kg and a temperature of 230 ° C. in accordance with 1238. In the present invention, the molecular weight distribution is expressed as weight average molecular weight (Mw) / number average molecular weight (M
n), and the measurement was performed by gel permeation chromatography (GPC) analysis under the following conditions. Sample preparation A sample was added to o-dichlorobenzene at 0.1% (w /
and the solution was completely dissolved at 140 ° C. The solution was filtered through a sintered filter having a pore size of 0.45 μm to obtain a sample for analysis. Apparatus Used and Measurement Condition Apparatus ALC / GPC 150-C Separation Column manufactured by Waters GMHHR-H (S) -HT30 cm × 2 manufactured by Tosoh Corporation GMH-HTL30 cm × 2 Mobile phase o-dichlorobenzene Detector Differential refractometer Flow rate 1.0ml / min. Column temperature 140 ℃ Injection volume 500μl

The polypropylene of the present invention may be a homopolymer of propylene or a random copolymer of propylene and another α-olefin. In the case of a copolymer, the other α-olefin used is preferably an α-olefin having 2 to 20 carbon atoms, and the content of the α-olefin structural unit is usually 30 mol% or less, preferably 10 mol%. It is as follows.

Specific examples of the α-olefin include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene,
Linear α-olefins such as 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene; 3-methyl-1-butene, 3-methyl-1-pentene;
3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl
1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl
And branched α-olefins such as 1-pentene, 4-ethyl-1-hexene and 3-ethyl-1-hexene. Among these, ethylene and 1-butene are preferable, and ethylene is particularly preferable. Such linear or branched α-olefins can be used alone or in combination of two or more.

The polypropylene of the present invention may be directly obtained by polymerizing or copolymerizing an olefin in the presence of a known Ziegler-type or metallocene-based olefin polymerization catalyst, but may have an MFR of 20 g / 10 min or less, and a MFR of 15 g or less. What is obtained by degrading polypropylene of / 10 minutes or less is preferable. Such a gradation increases the MFR,
The molecular weight distribution (Mw / Mn) becomes narrower, and by using the same, a melt-blown nonwoven fabric of ultrafine fibers can be obtained with high productivity.

As a method of degradation, for example, there is a method of melt-kneading in the presence of a radical generator, whereby polypropylene having a predetermined MFR and a molecular weight distribution can be obtained.

Here, the radical generator that can be used is an organic or inorganic one, and includes peroxides, hydroperoxides, peracids and the like which are generally used as radical polymerization initiators. Organic peroxides may be in liquid, solid or solid form with inorganic fillers. These are usually mixed with the polypropylene at a temperature at which the organic peroxide does not substantially decompose.

Specific examples include hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide; dicumyl peroxide, 2,5-dimethyl-di (t-
Butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-
Dialkyl peroxides such as butylperoxy) hexine-3; diacyl peroxides such as lauroyl peroxide and benzoyl peroxide; peroxyesters such as t-butylperoxyacetate and t-butylperoxylaurate; Ketone peroxides such as methyl ethyl ketone peroxide and methyl isobutyl ketone peroxide can be mentioned.

The amount of the radical generator to be added is appropriately determined in consideration of the MFR and the molecular weight distribution before and after the degradation, and is usually 0.01 to 10 parts by weight of polypropylene having a melt flow rate of 10 g / 10 minutes or less. ~ 1.0
0 parts by weight, preferably 0.05 to 0.50 parts by weight.

The degradation is carried out, for example, by mixing polypropylene and a radical generator in a predetermined ratio by a method such as dry blending, and using a extruder or the like at a melting temperature of 200 to 300 ° C., preferably 220 to 280 ° C. This is performed by melt-kneading. This gives the polypropylene of the invention.

In the polypropylene of the present invention, in addition to the radical generator, various additives that can be blended with the polypropylene resin, such as antioxidants, weather stabilizers, antiblocking agents, slip agents, antistatic agents, coloring agents, etc. Can be blended.

The melt blown nonwoven fabric of the present invention is produced by a melt blow method using the above polypropylene. Meltblowing is a process in which molten resin is extruded directly from a number of orifices into two converging high-speed heated air streams of air to draw and narrow the molten resin and collect it on a moving screen. In this method, the fiber diameter of the fibers constituting the melt-blown nonwoven fabric is mainly determined by the melting temperature (melt viscosity) of the resin, the air flow rate, and the discharge amount of the resin. Therefore, in order to produce microfibers by the conventional method, it is necessary to increase the melting temperature, the air flow rate, and reduce the discharge rate, depending on the conditions, the thread breaks, so-called fly or shot occurs, Deteriorate the appearance of the product.

When a non-woven fabric is produced by the melt blow method using the polypropylene of the present invention, a single-hole discharge rate of 0.1 wt.
When produced at a flow rate of ³ g / min or more and a high-speed air flow of 500 Nm ³ / hr / m or less, a melt blown fiber having an average fiber diameter of 2.0 μm or less can be obtained.

Further, using the polypropylene of the present invention,
If the nonwoven fabric is manufactured by the melt blow method, when manufactured at a resin temperature of 280 ° C., meltblown fibers having an average fiber diameter of 2.0 μm or less can be obtained.

This can be considered as follows. The polypropylene of the present invention has an MFR suitable for the production of a melt-blown nonwoven fabric and, at the same time, has an extremely narrow molecular weight distribution.
No yarn breakage occurs when obtaining ultrafine fibers of μm or less, and no fly or shot due to the yarn breakage is observed, so that production can be performed with high productivity.

The melt-blown nonwoven fabric according to the present invention is produced by the above-mentioned melt-blowing method.
The average fiber diameter of the constituent fibers is 2.0 μm or less, preferably 0.5 to 1.9 μm, and more preferably 0.8 to 1.8.
μm, and the apparent density is usually 0.05 to
0.30 g / cm ³ , especially 0.07 to 0.20 g / cm ³
cm ³ is preferable in that excellent filter performance can be exhibited. If necessary, a confounding process may be performed in a subsequent step. Examples of the confounding method include hot embossing using an embossing roll, confounding by fusion using ultrasonic waves, and confounding using fusion of fibers by hot air through.

Such a melt-blown nonwoven fabric according to the present invention has an extremely fine fiber diameter, and when used as a filter, has an excellent particle collection rate. That is, after applying a DC voltage to the obtained melt-blown nonwoven fabric to form an electret, the JIS B99 is applied at a basis weight of 40 g / m ² .
The particle collection rate measured by the following method according to the method described in No. 08 is 99.97% or more, and the pressure loss at that time is 120 Pa
It is as follows.

The measurement of the particle collection rate was performed using an apparatus schematically shown in FIG. First, an aerosol generator (manufactured by Nippon Kagaku Kogyo Co., Ltd.) 21 sends NaCl particles (particle size:
m) was supplied through a cleaning filter 22 into a chamber 23 into which clean air was introduced. N in the chamber
After the concentration of aCl becomes constant (2 to 6 × 10 ⁶ / cm ³ ), the aspirator 24 sucks in the direction of the arrow through the filter sample 25 arranged at the bottom of the chamber 23,
The NaCl particle concentrations C _IN and C _OUT on the upstream 26 and downstream 27 sides of the filter sample 25 when the wind speed passing through the filter became a constant speed (5 cm / sec) were measured by a particle counter (KC-01B manufactured by Rion) 2.
8a and 28b, and the particle collection rate was determined by the following equation. 29 is a flow meter, 30 is a flow control valve. Particle collection rate (%) = (1−C _OUT / C _IN ) × 100

The pressure loss was measured at the same time as the particle collection rate. Upstream 26 of filter sample 25
And a differential pressure gauge (KD1 manufactured by Yamatake Honeywell Co., Ltd.)
46) was attached and the test was performed under the condition of a wind speed of 5 cm / sec.

The electretization can be performed by applying a DC voltage to the melt-blown nonwoven fabric.
The applied DC voltage value is appropriately selected according to the shape of the electrodes to be used, the distance between the electrodes, and the like, and the amount of charge required for the electretized nonwoven fabric, the processing speed, and the like. For example, when the distance between the electrodes is 8 mm, at least -5 kV,
Preferably, a DC voltage of -6 to -20 kV is applied to the nonwoven fabric.

The application of the DC voltage may be performed according to any method, and is not particularly limited. For example, a method in which a nonwoven fabric is passed between a pair of electrodes to which a DC voltage is applied, a method in which a corona discharge or a pulsed high voltage is applied to the surface of the nonwoven fabric, and the front and back surfaces of the nonwoven fabric are held by another dielectric and the direct current is applied to both surfaces. Any method such as a method of applying a high voltage may be used.

The air filter is processed into a pleated shape in order to increase the ventilation area and increase the collection efficiency by using the above-mentioned melt-blown non-woven fabric as a filter material, or is processed into a honeycomb shape in order to reduce the pressure loss. It is formed and manufactured by combining those units.
Since the air filter of the present invention uses the above-mentioned melt-blown nonwoven fabric as a filter material, it has an excellent particle collection rate.

The melt blown nonwoven fabric according to the present invention is also suitably used for dust masks, wipers, disposable caps, battery separators, disposable diapers, breast milk pads, masks, liquid filters, oil adsorbents and the like.

[0034]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples, but the present invention is not limited to these examples. In addition, the measuring method and evaluation method of the physical property etc. used in the following Examples were performed as follows.

(1) Average fiber diameter From a magnified photograph of a nonwoven fabric sample taken at a magnification of 1000 with an electron microscope, 50 fibers were randomly selected, and their fiber diameters were measured using calipers. As the average fiber diameter. (2) Apparent density The basis weight and thickness of the nonwoven fabric sample were measured according to JIS L1906, and the apparent density was calculated by the following equation. Apparent density = weight / thickness

(3) Presence or absence of flies and shots The state of scattering of fibers (fly) caused by yarn breakage during melt blow molding and the presence or absence of resin blocks (shots) which are not converted into fibers but are granulated and mixed into the nonwoven fabric are determined. Observe visually,
Those in which they were not observed were indicated by ○, and those in which they were observed were indicated by x.

Example 1 0.18 parts by weight of dicumyl peroxide was added to 100 parts by weight of untreated polypropylene having an MFR of 14 g / 10 minutes, and degraded at 240 ° C. to give an MFR of 1200 g / 10 minutes. And a polypropylene having a molecular weight distribution (Mw / Mn) of 2.3. Using this polypropylene, a nonwoven fabric was produced by a melt blow method under the conditions of a resin temperature of 280 ° C., a single hole discharge rate of 0.3 g / min, and an air flow rate of 400 Nm ³ / hr / m.
g / m ² melt blown nonwoven fabric was produced. Table 1 shows the measurement results of the nonwoven fabric together with the evaluation results of the filter performance (particle collection rate and pressure loss).

(Example 2) Using the same untreated polypropylene as in Example 1, 0.23 parts by weight of dicumyl peroxide was added, degraded at 260 ° C.
A polypropylene having an R of 1500 g / 10 min and a molecular weight distribution (Mw / Mn) of 2.2 was obtained. Using this polypropylene, the resin temperature is 280 ° C and the single hole discharge amount is 0.3g / mi.
n, a nonwoven fabric was produced by a melt blow method under the conditions of an air flow rate of 400 Nm ³ / hr / m, to produce a melt blown nonwoven fabric having a basis weight of 40 g / m ² . Table 1 shows the results of the nonwoven fabric.

Example 3 Using untreated polypropylene having an MRF of 2 g / 10 min and dicumyl peroxide in an amount of 0.35
Parts by weight, degraded at 240 ° C,
MFR 2000g / 10min, molecular weight distribution (Mw / Mn)
Was 1.9. A melt blown nonwoven fabric was manufactured in the same manner as in Example 2 using this polypropylene. Table 1 shows the results of the nonwoven fabric.

Comparative Example 1 Dicumyl peroxide was added in an amount of 0.10 part by weight to 100 parts by weight of untreated polypropylene having an MFR of 300 g / 10 minutes, and degraded at 240 ° C. to give an MFR of 900 g / 10 minutes. A polypropylene having a molecular weight distribution (Mw / Mn) of 3.5 was obtained. A melt blown nonwoven fabric was manufactured in the same manner as in Example 2 using this polypropylene. Table 1 shows the results of the nonwoven fabric.

Comparative Example 2 A melt blown nonwoven fabric was manufactured in the same manner as in Comparative Example 1 except that the melt blown nonwoven fabric was molded at 310 ° C. Table 1 shows the results of the nonwoven fabric. (Comparative Example 3) Melt blown nonwoven fabric was molded at an air flow rate of
Except at 0 Nm ³ / hr / m, a melt blown nonwoven fabric was produced in the same manner as in Comparative Example 1. Table 1 shows the results of this nonwoven fabric.
Shown in

Comparative Example 4 A melt-blown nonwoven fabric was produced in the same manner as in Example 2 using untreated polypropylene having an MFR of 1300 g / 10 min and a molecular weight distribution (Mw / Mn) of 4.5. Table 1 shows the results of the nonwoven fabric. (Comparative Example 5) A melt blown nonwoven fabric was manufactured in the same manner as in Example 1 except that the melt blown nonwoven fabric was formed at a single hole discharge rate of 0.2 g / min. Table 1 shows the results of the nonwoven fabric.

[0043]

[Table 1]

[0044]

When the polypropylene of the present invention is used for the production of a nonwoven fabric by the meltblowing method, ultrafine meltblown fibers can be produced with high productivity. The meltblown nonwoven fabric made of such fibers can be used in addition to an air filter having an excellent particle collection rate. It can be applied to dust mask, wiper, disposable cap, battery separator, disposable diaper, breast milk pad, mask, liquid filter, oil absorbent, etc.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an apparatus used for measuring a particle collection rate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 21 Aerosol generator 22 Cleaning filter 23 Chamber 24 Suction device 25 Filter sample 26 Upstream 27 Downstream 28a, 28b Particle counter 29 Flowmeter 30 Flow control valve

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shigeyuki Motomura 1 Asahi-cho, Yokkaichi-shi, Mie Mitsui Chemicals Co., Ltd. Terms (reference) 4D019 AA01 BA13 BB03 BC01 DA03 4D054 AA11 BC16 4L047 AA14 AB07 AB08 BA09 BA23 BB02 CB10 CC12

Claims (4)

[Claims] An ultrafine fiber melt-blown nonwoven polypropylene having a melt flow rate of at least 1200 g / 10 min and a molecular weight distribution (Mw / Mn) of at most 2.5. 2. The polypropylene for ultra-fine fiber melt-blown nonwoven fabric according to claim 1, which is obtained by degrading polypropylene having a melt flow rate of 20 g / 10 minutes or less. 3. A melt-blown non-woven fabric having an average fiber diameter of 2.0 μm or less, obtained by a melt-blowing method using the polypropylene according to claim 1 or 2. 4. After applying a DC voltage to form an electret, the JIS B9908 is applied at a basis weight of 40 g / m ² .
The particle collection rate and the pressure loss measured in conformity with (measured wind speed 5 cm / sec) are 99.97% or more, respectively.
An air filter comprising the melt-blown nonwoven fabric according to claim 3, which is at most 20 Pa.