WO2015093451A1

WO2015093451A1 - Filter

Info

Publication number: WO2015093451A1
Application number: PCT/JP2014/083173
Authority: WO
Inventors: 市川　太郎; 邦昭川辺; 武津田
Original assignee: 三井化学株式会社
Priority date: 2013-12-16
Filing date: 2014-12-15
Publication date: 2015-06-25
Also published as: TW201532655A

Abstract

　A filter comprising a polyethylene nonwoven, obtained by melt-blow molding an ethylene polymer composition having a weight-average molecular weight of 10,000-45,000, and a Z-average molecular weight of 65,000 or less.

Description

filter

The present invention relates to a filter.

Melt blown nonwoven fabric (also referred to as “meltblown nonwoven fabric”) is superior in flexibility, uniformity, and denseness because it can be formed from ultrafine fibers compared to a spunbond nonwoven fabric. For this reason, melt blown nonwoven fabrics are singly or laminated with other nonwoven fabrics, filters (liquid filters, gas filters, etc.), hygiene materials, medical materials, agricultural coating materials, earth and wood, building materials, oil adsorption It is used for materials, automobile materials, electronic materials, separators, clothing, packaging materials, and the like.

And it is known that the melt blown nonwoven fabric using polypropylene is excellent in high-performance precision filterability, chemical resistance, processability, fine particle rejection, and the like, and can be used for filters and the like (for example, Patent Document 1). reference).
In addition, as a method for obtaining a polyethylene non-woven fabric of fine fibers, a method of forming a resin composition containing polyethylene and polyethylene wax by a melt blow method has been proposed (for example, see Patent Document 2).
In addition, a resin composition containing polyethylene and polyethylene wax is molded by a melt blow method, and the resulting molded product (melt blow nonwoven fabric) is laminated with a spunbond nonwoven fabric composed of a composite fiber formed from polyester and an ethylene polymer. A method has been proposed (see, for example, Patent Document 3).

Patent Document 1: Japanese Patent Application Laid-Open No. 2010-125404 Patent Document 2: International Publication No. 2000/222219 Patent Document 3: International Publication No. 2012/111724

The present inventors examined using a polyethylene nonwoven fabric as a filter. When using polyethylene non-woven fabric as a filter, the content of additives (stabilizers, etc.) can be reduced compared to using polypropylene non-woven fabric as a filter. This is because it is considered that there is an advantage.
However, since it is difficult to obtain a thin polyethylene fiber in the prior art, if a polyethylene non-woven fabric is used as a filter, if the filter cannot be improved in performance, that is, a blocking rate against fine particles (hereinafter also referred to as “fine particle blocking rate”), It has been found that the filtration flow rate, or the balance between these, may not be sufficient.

For example, Patent Document 2 described above discloses that a melt-blown polyethylene nonwoven fabric having a fiber diameter of 2.8 μm can be obtained by molding a resin composition containing specific polyethylene and polyethylene wax by a melt-blowing method ( (See Example 2 of Patent Document 2). Moreover, the above-mentioned Patent Document 3 discloses that a melt blown polyethylene nonwoven fabric having a fiber diameter of 3.3 μm can be obtained.
However, as a result of studies by the present inventors, when trying to use these conventional melt blown polyethylene nonwoven fabrics as a filter, the fine particle blocking rate, the filtration flow rate, or the balance thereof may not be sufficient due to the large fiber diameter. It has been found.
Here, among the performances of the filter, the fine particle rejection rate and the filtration flow rate may be in a trade-off relationship. For this reason, from the viewpoint of improving the performance of the filter, it is desirable to improve the balance between the two, rather than significantly improving only one of the fine particle rejection rate and the filtration flow rate and sacrificing the other.

This invention is made | formed in view of the said situation, and makes it a subject to achieve the following objectives.
That is, an object of the present invention is to provide a filter made of a polyethylene non-woven fabric and having an excellent balance between the fine particle rejection rate and the filtration flow rate.

Means for solving the above problems are as follows.
<1> A filter comprising a polyethylene nonwoven fabric obtained by molding an ethylene polymer composition having a weight average molecular weight of 10,000 to 45,000 and a Z average molecular weight of 65,000 or less by a melt blow method.
<2> The filter according to <1>, wherein the polyethylene nonwoven fabric has an average fiber diameter of less than 2.8 μm.
<3> The filter according to <1> or <2>, wherein the ethylene polymer composition includes an ethylene polymer wax (b) having a weight average molecular weight of 15,000 or less.
<4> The filter according to <1> or <2>, wherein the ethylene polymer composition includes an ethylene polymer (a) having a weight average molecular weight of 10,000 to 45,000.
<5> The ethylene polymer composition is:
An ethylene polymer wax (b) having a weight average molecular weight of 15,000 or less;
An ethylene polymer (a) having a weight average molecular weight of 10,000 to 45,000 and a value higher than the weight average molecular weight of the ethylene polymer wax (b);
The filter according to <1> or <2>.
<6> The filter according to <5>, wherein the ethylene polymer (a) has a weight average molecular weight of 20,000 to 45,000.
<7> The filter according to any one of <1> to <6>, wherein an average pore diameter measured with a basis weight of 60 g / m ² is 20 μm or less.
<8> The filter according to any one of <1> to <7>, wherein the air permeability measured at a basis weight of 60 g / m ² is less than 15 cm ³ / cm ² / sec.
<9> The filter according to any one of <1> to <8>, wherein the blocking rate of polystyrene latex particles having a spherical particle diameter of 3.00 μm measured at a basis weight of 60 g / m ² is 10% or more.

According to the present invention, there is provided a filter made of a polyethylene non-woven fabric and having an excellent balance between the fine particle rejection rate and the filtration flow rate.

In this specification, the numerical range indicated by using “to” indicates a range including the minimum value and the maximum value described before and after “to”, respectively.

The filter of the present invention is a polyethylene obtained by molding an ethylene polymer composition having a weight average molecular weight (Mw) of 10,000 to 45,000 and a Z average molecular weight (Mz) of 65,000 or less by a melt blow method. Made of nonwoven fabric.
The filter of the present invention is a filter made of a polyethylene non-woven fabric and is excellent in the balance between the fine particle rejection rate and the filtration flow rate.

The present inventors examined using a polyethylene nonwoven fabric as a filter.
However, since it is difficult to obtain a thin polyethylene fiber in the prior art, it has been found that when a polyethylene non-woven fabric is used as a filter, the fine particle rejection rate, the filtration flow rate, or the balance thereof may not be sufficient.
In contrast to the above-described conventional technology, the filter of the present invention is excellent in the balance between the fine particle blocking rate and the filtration flow rate while being a filter made of a polyethylene nonwoven fabric.
More specifically, in the filter of the present invention, the Mz of the ethylene-based polymer composition is 65,000 or less, and the polyethylene-based nonwoven fabric is molded by melt-blowing to form a polyethylene nonwoven fabric. The fiber diameter is easily reduced (preferably, the average fiber diameter of the polyethylene nonwoven fabric is easily reduced to less than 2.8 μm), and as a result, the balance between the fine particle rejection rate and the filtration flow rate is improved.

Moreover, in the filter of this invention, the intensity | strength of a polyethylene nonwoven fabric improves because Mw of the said ethylene-type polymer composition is 10,000 or more.
Moreover, in the filter of this invention, when Mw of the said ethylene-type polymer composition is 45,000 or less, the balance of a fine particle blocking rate and a filtration flow rate improves.

Moreover, since the filter of the present invention is a filter made of polyethylene nonwoven fabric, the content of additives (stabilizers and the like) in the resin can be suppressed as compared with a filter made of polypropylene nonwoven fabric. For this reason, according to the filter of this invention, elution of additives (stabilizer etc.) is suppressed.

In general, a support structure for supporting the filter (hereinafter also referred to as “filter support structure”) may be made of polyethylene resin for the purpose of reducing the eluted components.
In this regard, since the filter of the present invention is a filter made of a polyethylene nonwoven fabric, it is superior in heat sealability with a polyethylene filter support structure compared to a filter made of a polypropylene nonwoven fabric.

In general, when a filter is used for a living body or a food, the filter may be sterilized with an electron beam.
With regard to this electron beam sterilization treatment, the filter of the present invention is a filter made of a polyethylene nonwoven fabric, so that it is excellent in electron beam sterilization compared to a filter made of a polypropylene nonwoven fabric.
In this specification, “excellent in electron beam sterilization” means that deterioration, denaturation, odor, and the like are suppressed when electron beam sterilization is performed.

Furthermore, in the filter of the present invention, since the fiber diameter of the polyethylene nonwoven fabric can be reduced (preferably, the average fiber diameter of the polyethylene nonwoven fabric is less than 2.8 μm), the filter accuracy and the filter uniformity are improved.

<Z average molecular weight (Mz)>
Hereinafter, the Z average molecular weight (Mz) in this specification will be described.
In the following description, the Mz of the ethylene polymer composition will be mainly described. However, the definition of Mz of each polymer is the same as the definition of Mz of the ethylene polymer composition.
In this specification, Z average molecular weight (Mz) refers to the molecular weight defined by the following formula (1).
In general, Mz is considered to have a molecular weight more reflecting a high molecular weight component.

In the formula (1), Mi represents the molecular weight of the ethylene polymer composition, and Ni represents the number of moles of the ethylene polymer composition.

<Method for Measuring Z Average Molecular Weight (Mz) and Weight Average Molecular Weight (Mw)>
In the present specification, the ethylene polymer composition and the Z average molecular weight (Mz) of each polymer are values obtained from GPC measurement, and are values measured under the following conditions. More specifically, the Z average molecular weight (Mz) is obtained based on the following conversion method by creating a calibration curve using commercially available monodisperse standard polystyrene.
Moreover, in this specification, the weight average molecular weight (Mw) of an ethylene-type polymer composition and each polymer is also the value calculated | required from GPC measurement, and is the value measured on condition of the following. More specifically, the weight average molecular weight (Mw) is determined based on the following conversion method by creating a calibration curve using commercially available monodisperse standard polystyrene.

-Measurement conditions for Z average molecular weight (Mz) and weight average molecular weight (Mw)-
Apparatus: Gel permeation chromatograph Alliance GPC2000 (manufactured by Waters)
Solvent: o-dichlorobenzene Column: TSKgel column (manufactured by Tosoh Corporation) x 4
Flow rate: 1.0 mL / min Sample: 0.15 mg / mLo-dichlorobenzene solution Temperature: 140 ° C.
Molecular weight conversion: PE conversion / General calibration method

In addition, the coefficient of the Mark-Houwink viscosity formula shown below was used for calculation of general-purpose calibration.
Coefficient of polystyrene (PS): KPS = 1.38 × 10 ⁻⁴ , aPS = 0.70
Polyethylene (PE) coefficient: KPE = 0.06 × 10 ⁻⁴ , aPE = 0.70

<Ethylene polymer composition>
The ethylene polymer composition in the present invention has a weight average molecular weight (Mw) of 10,000 to 45,000 and a Z average molecular weight (Mz) of 65,000 or less.
The Mw of the ethylene polymer composition is preferably 10,000 to 30,000, more preferably 10,000 to 25,000.
The Mz of the ethylene polymer composition is preferably 60,000 or less, more preferably 57,000 or less, still more preferably 54,000 or less, and particularly preferably 50,000 or less.
The lower limit of the Mz of the ethylene polymer composition is not particularly limited, but the Mz of the ethylene polymer composition is preferably 10,000 or more, more preferably 20,000 or more.

The ethylene polymer composition preferably contains an ethylene polymer wax (b).
When the ethylene polymer composition contains the ethylene polymer wax (b), it becomes easier to reduce the average fiber diameter of the obtained polyethylene nonwoven fabric, and it is possible to obtain sufficient uniformity as a filter application. It becomes easier.

The ethylene polymer composition is not particularly limited as long as it satisfies the aforementioned weight average molecular weight and Z average molecular weight, but in addition to the ethylene polymer wax (b) or in place of the ethylene polymer wax (b). The ethylene polymer (a) may be contained.
When the ethylene polymer composition contains the ethylene polymer (a), it becomes easier to spin the resulting polyethylene nonwoven fabric and to obtain sufficient fiber strength.

The ethylene-based polymer composition may contain other components other than the above, if necessary, as long as the object of the present invention is not impaired.
Other components include ethylene polymer wax (b) and other polymers other than ethylene polymer (a), stabilizers (heat stabilizers, weather stabilizers, etc.), fillers, antistatic agents, hydrophilic Agents, water repellents, nucleating agents, slip agents, antiblocking agents, antifogging agents, lubricants, colorants (dyes, pigments, etc.), natural oils, synthetic oils and the like.
When the ethylene-based polymer composition includes other components, the other components that can be included in the ethylene-based polymer composition may be one type or two or more types.
However, the total content of the ethylene polymer wax (b) and the ethylene polymer (a) in the ethylene polymer composition is 80 mass from the viewpoint of more effectively achieving the effects of the present invention. % Or more is preferable, and 90% by mass or more is more preferable.

Examples of stabilizers include anti-aging agents such as 2,6-di-t-butyl-4-methyl-phenol (BHT); tetrakis [methylene-3- (3,5-di-t-butyl-4- Hydroxyphenyl) propionate] methane, β- (3,5-di-t-butyl-4-hydroxyphenyl) propionic acid alkyl ester, 2,2′-oxamide bis [ethyl-3- (3,5-di-t- Butyl-4-hydroxyphenyl) propionate], Irganox 1010 (hindered phenol-based antioxidant: trade name), etc .; fatty acid metals such as zinc stearate, calcium stearate, calcium 1,2-hydroxystearate Salt: Glycerol monostearate, glycerin distearate, pentaerythritol monos Areto, pentaerythritol distearate, polyhydric alcohol fatty acid esters such as pentaerythritol monostearate; and the like. A combination of these can also be used as the stabilizer.

Fillers include silica, diatomaceous earth, alumina, titanium oxide, magnesium oxide, pumice powder, pumice balloon, aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, dolomite, calcium sulfate, potassium titanate, barium sulfate, Examples thereof include calcium sulfite, talc, clay, mica, asbestos, calcium silicate, montmorillonite, pentonite, graphite, aluminum powder, and molybdenum sulfide. A combination of these can also be used as the filler.

When the ethylene polymer composition contains the ethylene polymer (a) and the ethylene polymer wax (b), when the ethylene polymer composition is produced, for example, the ethylene polymer (a) The ethylene-based polymer wax (b) and the above-mentioned other components as necessary can be mixed using various known methods.

<Ethylene polymer wax (b)>
The ethylene polymer wax (b) is a polymer having a relatively low molecular weight, that is, a wax-like polymer.

The ethylene polymer composition in the present invention preferably contains an ethylene polymer wax (b) having a weight average molecular weight (Mw) of 15,000 or less. The Mw of the ethylene polymer wax (b) is preferably 400 to 15,000, more preferably 400 to 14000, still more preferably 2000 to 13000, and particularly preferably 6000 to 13000.
When the Mw of the ethylene-based polymer wax (b) is 15,000 or less, it is easy to make the fibers of the obtained meltblown nonwoven fabric finer, and the filter performance (fine particle rejection rate, filtration flow rate, or fine particle rejection rate and filtration flow rate Balance, etc. The same shall apply hereinafter).
When the Mw of the ethylene polymer wax (b) is 400 or more, the strength of the resulting melt-blown nonwoven fabric can be further improved, and the bleed-out over time can be further suppressed.

The Z average molecular weight (Mz) of the ethylene polymer wax (b) is not particularly limited as long as the Z average molecular weight (Mz) of the ethylene polymer composition is 65,000 or less.
The Mz of the ethylene polymer wax (b) is preferably 700 to 40,000, more preferably 1000 to 30,000.
When the Mz of the ethylene-based polymer wax (b) is 40,000 or less, it is easy to make the fibers of the obtained melt blown nonwoven fabric finer, and the filter performance can be further improved.
When the Mz of the ethylene polymer wax (b) is 700 or more, the strength of the resulting melt-blown nonwoven fabric can be further improved, and the bleed-out with time can be further suppressed.

The content of the ethylene polymer wax (b) in the ethylene polymer composition is preferably 1% by mass to 100% by mass, more preferably 5% by mass to 100% by mass, and still more preferably 10% by mass. % To 100% by mass, particularly preferably 20% to 80% by mass.
When the content of the ethylene polymer wax (b) is in the above range, the balance of spinnability, fiber strength, fine particle rejection, and filtration flow rate is excellent.

When the content of the ethylene polymer wax (b) is less than 30% by mass, the Mw of the ethylene polymer composition is 45,000 or less and the Mz of the ethylene polymer composition is 65,000 or less. It is preferable to lower the Mw of the ethylene polymer wax (b) so that The Mw of the ethylene polymer wax (b) in this case is preferably 400 or more and less than 15,000, more preferably 1,000 or more and less than 13,000, and particularly preferably 1,000 or more and 8,000. Is less than.

When the content of the ethylene polymer wax (b) exceeds 70% by mass, the Mw of the ethylene polymer composition is 10,000 or more and the Mz of the ethylene polymer composition is 65,000 or less. It is preferable to increase the Mw of the ethylene polymer wax (b) so that In this case, the Mw of the ethylene polymer wax (b) is preferably 1,000 or more and less than 15,000, more preferably 3,000 or more and less than 15,000, and particularly preferably 5,000 or more and 15 or more. Less than 1,000.

The ethylene polymer wax (b) preferably has a softening point measured in accordance with JIS K2207 of more than 90 ° C. The softening point is more preferably 100 ° C. or higher.
When the softening point is 90 ° C. or higher, the heat resistance stability during heat treatment or use can be further improved, and as a result, the filter performance can be further improved.
Although the upper limit of the softening point is not particularly limited, an example of the upper limit is 145 ° C.

Examples of the ethylene polymer wax (b) include an ethylene homopolymer, a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, and the like.
When the ethylene-based polymer composition contains an ethylene-based polymer wax (b) and an ethylene-based polymer (a), and the ethylene-based polymer wax (b) is an ethylene homopolymer, an ethylene-based polymer composition The kneadability between the polymer wax (b) and the ethylene polymer (a) is excellent, and the spinnability is excellent.
Further, the ethylene polymer wax (b) that can be contained in the ethylene polymer composition may be a single type or a mixture of two or more types.

The density of the ethylene polymer wax (b) measured according to JIS K6760 is not particularly limited, but is, for example, 0.890 to 0.980 g / cm ³ , preferably 0.910 to 0.980 g / cm 3. ³ , more preferably 0.920 to 0.980 g / cm ³ , and particularly preferably 0.940 to 0.980 g / cm ³ .
The ethylene polymer composition contains an ethylene polymer wax (b) and an ethylene polymer (a), and the density of the ethylene polymer wax (b) is 0.890 to 0.980 g / cm ^3. In this case, the kneadability between the ethylene polymer wax (b) and the ethylene polymer (a) is excellent, and the spinnability and stability over time are also excellent.

The ethylene-based polymer wax (b) may be produced by any of a production method by polymerization of a low molecular weight polymer or a monomer that is usually used, or a production method in which a molecular weight is reduced by heat degradation of a high molecular weight ethylene polymer. What was manufactured by the method may be sufficient and the manufacturing method in particular of ethylene-type polymer wax (b) is not restrict | limited.

From the viewpoint of easily adjusting Mw and Mz of the ethylene polymer wax (b) according to Mw and Mz of the target ethylene polymer composition, the ethylene polymer wax (b) is: It is preferably produced using a metallocene catalyst.

Further, from the viewpoint of improving the fine particle rejection rate and the filtration flow rate of the filter, the ethylene polymer wax (b) is preferably produced using a metallocene catalyst.
The reason why the fine particle rejection rate and the filtration flow rate of the filter are improved when the ethylene polymer wax (b) produced using the metallocene catalyst is used is not clear, but the ethylene produced using the metallocene catalyst This is probably because the lower molecular weight component is reduced in the system polymer wax (b). That is, in this case, it is considered that the low molecular weight component considered to be easily crystallized among the ethylene polymer compositions is reduced. For this reason, when the fiber is solidified when the melt is discharged from the spinneret in the spinning process, and the discharged melt is blown off with a high-speed, high-temperature air stream sprayed from the periphery of the spinneret. It can be considered that the fiber can be effectively drawn because the time of the above can be delayed, and as a result, the fine particle rejection rate and the filtration flow rate can be improved.

Furthermore, when a metallocene catalyst is used, the Mz of the ethylene polymer wax (b) can be lowered, so that the Mz of the ethylene polymer composition can also be lowered. It is preferable because fiberization becomes easy.

The metallocene catalyst is not particularly limited, and examples thereof include those described in JP-A-2007-246832.
Suitable metallocene catalysts (olefin polymerization catalysts) include, for example, transition metal metallocene compounds selected from Group 4 of the periodic table, organoaluminum oxy compounds, compounds that react with the metallocene compounds to form ion pairs, And an olefin polymerization catalyst comprising at least one compound selected from organic aluminum compounds.

<Ethylene polymer (a)>
The ethylene polymer composition in the present invention may contain an ethylene polymer (a).
The Z average molecular weight (Mz) of the ethylene polymer (a) is not particularly limited as long as the Z average molecular weight (Mz) of the ethylene polymer composition is 65,000 or less, preferably 30,000 to 70,000, more preferably 30,000 to 65,000.
When the Mz of the ethylene-based polymer (a) is 70,000 or less, it is easy to make the fibers of the obtained melt-blown nonwoven fabric finer, and the filter performance can be further improved.
The intensity | strength of the melt blown nonwoven fabric obtained as Mz of an ethylene-type polymer (a) is 30,000 or more can be improved more.

The weight average molecular weight (Mw) of the ethylene polymer (a) is not particularly limited as long as the weight average molecular weight (Mw) of the ethylene polymer composition is 10,000 to 45,000, but preferably 10,000. 50,000 to 50,000, more preferably 10,000 to 40,000, and further preferably 15,000 to 35,000.
When the Mw of the ethylene-based polymer (a) is 45,000 or less, it is easy to make the fibers of the obtained melt-blown nonwoven fabric finer, and the filter performance can be further improved.
The intensity | strength of the melt blown nonwoven fabric obtained as Mw of an ethylene-type polymer (a) is 10,000 or more can be improved more.

When the ethylene polymer composition contains an ethylene polymer wax (b) having an Mw of 15,000 or less and the ethylene polymer (a), the Mw of the ethylene polymer (a) is 10,000. It is preferably 45,000 and higher than the Mw of the ethylene polymer wax (b). In this case, the Mw of the ethylene polymer (a) is preferably 20,000 or more, and more preferably 25,000 or more. In this case, the upper limit of Mw of the ethylene polymer (a) is preferably 50,000, more preferably 40,000, and further preferably 35,000.

The ethylene polymer (a) content in the ethylene polymer composition is such that the ethylene polymer composition has a weight average molecular weight of 10,000 to 45,000 and a Z average molecular weight of 65,000 or less. Although there is no particular limitation as long as it is, it is preferably 0% by mass to 99% by mass.
The content of the ethylene polymer (a) is more preferably 0% by mass to 95% by mass, still more preferably 0% by mass to 90% by mass, and further preferably 20% by mass to 80% by mass.
When the content of the ethylene polymer (a) is in the above range, the balance of spinnability, fiber strength, fine particle rejection, and filtration flow rate is excellent.

When the content of the ethylene polymer (a) is less than 30% by mass, the Mw of the ethylene polymer (a) is increased so that the Mw of the ethylene polymer composition is 10,000 or more. It is preferable to do.
When the content of the ethylene polymer (a) exceeds 70% by mass, the Mw of the ethylene polymer composition is 45,000 or less and the Mz of the ethylene polymer composition is 65,000 or less. Thus, it is preferable to lower Mw and Mz of the ethylene-based polymer.

Examples of the ethylene polymer (a) include ethylene homopolymers and copolymers of ethylene and other α-olefins.
The density of the ethylene polymer (a) measured according to JIS K6760 is not particularly limited, but the density is, for example, 0.870 to 0.980 g / cm ³ , preferably 0.900 to 0.00. It is 980 g / cm ³ , more preferably 0.920 to 0.975 g / cm ³ , and particularly preferably 0.940 to 0.970 g / cm ³ .
When the density of the ethylene-based polymer (a) is 0.870 g / cm ³ or more, durability, heat resistance, strength, and stability over time of the resulting melt-blown nonwoven fabric tend to be further improved.
When the density of the ethylene polymer (a) is 0.980 g / cm ³ or less, the heat-sealability and flexibility of the resulting melt-blown nonwoven fabric tend to be further improved.

Here, the density of the ethylene-based polymer (a) is such that the strand obtained at the time of measuring a melt flow rate (MFR) at 190 ° C. under a load of 2.16 kg is heat-treated at 120 ° C. for 1 hour, and takes 1 hour to room temperature It is a numerical value obtained by measuring with a density gradient tube after slow cooling.

The ethylene polymer (a) is preferably a crystalline resin produced and sold under the names of high pressure method low density polyethylene, linear low density polyethylene (LLDPE), medium density polyethylene, high density polyethylene, and the like.

Other α-olefins copolymerized with ethylene include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1- Examples thereof include α-olefins having 3 to 20 carbon atoms such as tetradecene, 1-hexadecene, 1-octadecene and 1-eicocene.
The ethylene polymer (a) that can be contained in the ethylene polymer composition may be one kind or a mixture of two or more kinds.

The melt flow rate (MFR) of the ethylene polymer (a) is not particularly limited as long as it can be mixed with the ethylene polymer wax (b) to produce a melt blown nonwoven fabric.
The MFR of the ethylene polymer (a) is preferably 10 to 250 g / 10 minutes, more preferably 20 to 200 g / 10 minutes, and further preferably 50 to 50% from the viewpoint of fine fiber diameter and spinnability. 200 g / 10 min.
Here, MFR of the ethylene-based polymer (a) refers to a value measured under conditions of a load of 2.16 kg and 190 ° C. in accordance with ASTM D1238.

As the ethylene polymer (a), various known production methods, for example, a polymer obtained by a high-pressure method, or a polymer obtained by using a Ziegler catalyst or a metallocene catalyst (for example, a polymer obtained by a medium-low pressure method). Can be used.
Among them, from the viewpoint of easily adjusting each of Mw and Mz of the ethylene polymer (a) according to Mw and Mz of the target ethylene polymer composition, the ethylene polymer (a) is: It is preferably produced using a metallocene catalyst.
When a metallocene-based catalyst is used, the Mz of the ethylene polymer (a) can be particularly lowered, so that the Mz when the ethylene polymer composition is obtained is also low, and it is easy to make the polyethylene nonwoven fabric finer. This is preferable.

For the production of the ethylene polymer (a), conventionally known catalysts such as JP-A-57-63310, JP-A-58-83006, JP-A-3-706, JP-A-3476793, Magnesium-supported titanium catalyst described in Kaihei 4-218508, JP-A-2003-105022, etc., WO 01/53369, WO 01/27124, JP-A-3-19396 The metallocene catalyst described in JP-A No. 02-41303 or the like can be suitably used.

<Polyethylene non-woven fabric>
The polyethylene nonwoven fabric in the present invention is a nonwoven fabric (melt blown nonwoven fabric) formed by molding the above-described ethylene polymer composition by a melt blow method.

The average fiber diameter of the polyethylene nonwoven fabric in the present invention is preferably less than 2.8 μm. More preferably, it is 2.5 μm or less.
When the average fiber diameter is less than 2.8 μm, the uniformity of the obtained polyethylene nonwoven fabric becomes better, and the fine particle blocking rate and filtration flow rate when used as a filter are further improved.
Although there is no restriction | limiting in particular in the minimum of the average fiber diameter of a polyethylene nonwoven fabric, The said average fiber diameter is 0.5 micrometer or more, for example, Preferably it is 1.0 micrometer or more.

The basis weight of the polyethylene nonwoven fabric is preferably 0.5 g / m ² or more, more preferably 3 to 80 g / m ² , still more preferably 5 to 60 g / m ² , and further preferably 6 to 40 g / m 2. ² .
The intensity | strength improves more that the fabric weight of a polyethylene nonwoven fabric is 0.5 g / m < ² > or more. For this reason, for example, post-processing such as lamination becomes easier.
When the basis weight of the polyethylene nonwoven fabric is 80 g / m ² or less, fine fibers are more easily obtained.

On the other hand, when it is used in applications where high barrier properties are not required, such as hygiene materials, and where flexibility, heat sealability, and lightness are mainly required, the range of the weight of the polyethylene nonwoven fabric is, for example, 0.5 to It may be 5 g / m ² , more preferably 0.5 to 3 g / m ² .

The polyethylene nonwoven fabric in the present invention has a maximum pore size measured at a basis weight of 60 g / m ² , preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less.

The polyethylene nonwoven fabric in the present invention has an average pore diameter measured at a basis weight of 60 g / m ² , preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less.
Although there is no restriction | limiting in particular in the minimum of the said average pore diameter, From a viewpoint of improving a filtration flow rate, the said average pore diameter becomes like this. Preferably it is 1 micrometer or more, More preferably, it is 2 micrometers or more.

A polyethylene nonwoven fabric satisfying at least one of an average fiber diameter of less than 2.8 μm and an average pore diameter of 20 μm or less measured at a basis weight of 60 g / m ² has a spherical particle diameter of 3 when used in a filter. This is preferable in that the blocking rate of 0.000 μm polystyrene latex is easily 10% or more (more preferably 20% or more, more preferably 25% or more).
Furthermore, when the polyethylene nonwoven fabric satisfying at least one of the above is used for a filter,
It is also preferable in that the filtration flow rate at a filtration pressure of 0.1 MPa is easily set to 0.7 L / min / cm ² .

The polyethylene nonwoven fabric in the present invention preferably has an air permeability measured at a basis weight of 60 g / m ² of 15 cm ³ / cm ² / sec or less. In the nonwoven fabric having an air permeability of 15 cm ³ / cm ² / sec or less, the dispersion of ultrafine fibers becomes uniform and the average pore diameter tends to be small. For this reason, when used in a liquid filter, there is a tendency that the blocking rate of the fine particles is increased.
On the other hand, the air permeability is preferably 0.1 cm ³ / cm ² / second or more, and more preferably 1 cm ³ / cm ² / second or more. By setting the air permeability to 0.1 cm ³ / cm ² / second or more, the flow rate is increased when used in a liquid filter. That is, it becomes easy to finish filtration at an appropriate time.

The polyethylene nonwoven fabric in the present invention preferably has a blocking rate of polystyrene latex having a spherical particle diameter of 3.00 μm measured at a basis weight of 60 g / m ² of 10% or more, more preferably 20% or more, and 25%. It is still more preferable that it is above.
The upper limit of the blocking rate may be 100% or less, but is preferably 95% or less from the viewpoint of balance with the filtration flow rate.

<Method for producing polyethylene nonwoven fabric>
The polyethylene nonwoven fabric in this invention can be manufactured with the manufacturing method (melt blow method) of a well-known melt blown nonwoven fabric using the said ethylene polymer composition.
As the melt blow method, specifically, for example, an ethylene polymer composition is melt-kneaded with an extruder or the like, and the melt (molten resin) is discharged from a spinneret having a spinning nozzle and around the spinneret. The web (polyethylene non-woven fabric) is manufactured by blowing off with a high-speed and high-temperature air stream sprayed from the substrate and depositing it as a self-adhesive microfiber on the collection belt to a predetermined thickness.

At this time, the deposited web can be entangled as necessary.
Examples of the method of entanglement of the deposited web include a method of thermocompression bonding using an embossing roll and a flat roll (metal roll, rubber roll); a method of fusing by ultrasonic waves; and a fiber entanglement using a water jet Various methods such as a method; a method of fusing by hot air through; a method of using a needle punch;
Among these, for the purpose of improving the uniformity of the nonwoven fabric and obtaining a uniform filter, a method of thermocompression bonding using a flat roll having a uniform surface or a method of fusing by hot air through is preferable.

On the polyethylene nonwoven fabric according to the present invention, at least one of a short fiber nonwoven fabric and a long fiber nonwoven fabric, such as cotton, cupra, rayon, polyolefin fiber, polyamide fiber, and polyester fiber, is included within the range not hindering the object of the present invention. Furthermore, you may laminate | stack.

For example, in order to reinforce the strength, a method of forming a laminate by integrating the polyethylene nonwoven fabric (melt blown nonwoven fabric) and the spunbond nonwoven fabric in the present invention can be selected. Specifically, for example,
(A) After forming a melt-blown nonwoven fabric by directly depositing fibers obtained from an ethylene-based polymer composition by a melt-blowing method on a previously obtained spun-bonded nonwoven fabric, the spun-bonded nonwoven fabric and the melt-blown nonwoven fabric are heat embossed, etc. A method of producing a two-layer laminate by fusing
(B) a method for forming a melt blown nonwoven fabric by directly depositing fibers obtained from an ethylene polymer composition by a melt blow method on a previously obtained spunbond nonwoven fabric;
(C) A method for producing a laminate by superimposing a previously obtained spunbond nonwoven fabric and a separately produced meltblown nonwoven fabric, and fusing both nonwoven fabrics by heating and pressing, etc.
However, it is not limited to these methods.

<Filter>
The filter of the present invention comprises the polyethylene nonwoven fabric (melt blown nonwoven fabric).
The filter of the present invention may be composed of a single layer of the polyethylene nonwoven fabric, or may be composed of a laminate in which two or more layers of the polyethylene nonwoven fabric are laminated.
The laminate may be simply a laminate of two or more layers of the polyethylene nonwoven fabric.
The basis weight of the filter of the present invention can be appropriately determined depending on the use of the filter, but is usually in the range of 5 to 200 g / m ² , preferably 10 to 150 g / m ² .

When manufacturing the filter of this invention, you may perform a calendar process using the flat roll which used the metal roll and the rubber roll, for example in order to control a hole diameter small.
It is preferable to change the clearance or pressure between the flat rolls as appropriate according to the thickness of the polyethylene nonwoven fabric so that there are no voids between the fibers of the nonwoven fabric.
Further, when the heat treatment is performed during the calendering treatment, it is desirable that the roll surface temperature is hot-pressed in the range of 15 ° C. to 70 ° C. lower than the melting point of the fibers of the polyethylene nonwoven fabric.
When the roll surface temperature is 15 ° C. or more lower than the melting point of the fibers of the polyethylene nonwoven fabric, the filter performance is further improved.

The filter of the present invention is composed of the polyethylene nonwoven fabric, and if necessary, by laminating a nonwoven fabric having a larger fiber diameter than the polyethylene nonwoven fabric (filter), or a nonwoven fabric having a large average pore diameter, to the filter of the present invention, The lifetime of the filter can be extended. In order to increase the strength of the filter, a spunbonded nonwoven fabric or a net-like material may be laminated on the filter of the present invention.

In the filter of the present invention, the average pore diameter, air permeability, and preferable ranges of the blocking rate of polystyrene latex particles having a spherical particle diameter of 3.00 μm are respectively the average pore diameter, air permeability, and spherical particle diameter of 3 in the aforementioned polyethylene nonwoven fabric. This is the same as the preferable range of the blocking rate of 0.000 μm polystyrene latex particles.

Further, the filter of the present invention is subjected to secondary processing such as gear processing, printing, coating, laminating, heat treatment, shaping processing, water repellent treatment, hydrophilic treatment, etc. within the range not impairing the object of the present invention. There may be.

Since the filter of the present invention has a thin fiber diameter and excellent uniformity, it can be widely applied as a liquid filter and a gas filter. The filter of the present invention is particularly suitable as a liquid filter.
Moreover, since the filter of this invention has favorable heat-sealability with a polyethylene raw material, it can be applied to a filter using a polyethylene filter support structure.
Further, since the filter of the present invention can be sterilized with an electron beam, it can be applied to filters for various biological uses and filters for foods.

In addition, the polyethylene nonwoven fabric in the present invention can be developed for uses described in “Basic knowledge of nonwoven fabric” issued by the Japan Nonwoven Fabric Association, but is excellent in flexibility because it is made finer than conventional polyethylene nonwoven fabric. In addition, it is excellent in uniformity, denseness, and barrier properties. Therefore, it can be suitably used for paper diapers, sanitary napkins, various sanitary materials, clothing, and protective clothing.
In addition, since the polyethylene nonwoven fabric in the present invention has good post-processability such as heat sealability, it can be used as a material for easy adhesion, such as automobile interior materials, various backing materials, daily life materials, industrial materials, deoxygenated materials. It can be applied to daily life materials such as medicines, warmers, warm ships, masks, CD (compact disc) bags, food packaging materials, and clothing covers.
In addition, since polyethylene resin is stable to electron beams and gamma rays irradiated during sterilization and sterilization, the polyethylene nonwoven fabric in the present invention is used in gowns, caps, masks, drapes, gauze, lab coats, curtains used in hospitals, etc. It can be particularly suitably used as a material for sheets, sheets, pillow covers, etc.
Furthermore, since the polyethylene nonwoven fabric in the present invention is made of fine fibers and has sufficient gaps in the nonwoven fabric, it is suitable for oil adsorbents, wipers, sound absorbing materials, heat insulating materials, cushioning materials, surface protective materials, etc. Can be used.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

In the examples and comparative examples, the following measurements and evaluations were performed.

(1) Measurement of average fiber diameter (μm) Using an electron microscope (S-3500N manufactured by Hitachi, Ltd.), a photograph of a melt blown nonwoven fabric (filter) was taken at a magnification of 1000 times. In the photograph taken, 100 fibers were arbitrarily selected, and the width (diameter) of the fibers was measured. The average of the obtained measurement results was defined as the average fiber diameter.

(2) The average pore size of at basis weight 60 g / ^{m 2} ([mu] m) of measuring melt blown nonwoven fabric (filter) adjusted to basis weight 60 g / ^{m 2} by laminating at the number of layers shown in Table 1, after adjustment Test pieces were collected from the melt blown nonwoven fabric (filter).
The collected specimen is immersed in a fluorine-based inert liquid (trade name: Florinart, manufactured by 3M) in a temperature-controlled room with a temperature of 20 ± 2 ° C. and a humidity of 65 ± 2% as defined in JIS Z8703 (standard condition at the test site). Then, an average pore size (μm) of the test piece was measured using a capillary flow porometer “Model: CFP-1200AE” manufactured by Porous materials, Inc.

(3) rejection of at basis weight 60 g / ^{m 2} (percent) and flow rate (L / min) measured melt blown nonwoven fabric (filter), the basis weight 60 g / ^{m 2} by laminating at the number of layers shown in Table 1 Adjusted as follows.
Further, a test liquid was prepared in which polystyrene latex particles having a spherical particle diameter of 3.00 μm (hereinafter simply referred to as “particles”) were dispersed in a 60% by volume IPA aqueous solution at a concentration of 0.01% by mass.
Next, this test solution was filtered through the filter adjusted so as to have a basis weight of 60 g / m ² . This filtration was performed under a filtration pressure of 0.1 MPa using a filtration device (TSU-90B manufactured by ADVANTEC).
The concentration (C0) of the particles in the test solution (stock solution) before filtration and the concentration (C1) of the particles in the test solution (filtrate) after filtration were measured, respectively, and the rejection rate was obtained by the following equation. .
Blocking rate (%) = [(C0−C1) / C0] × 100 (%)
Here, both C0 and C1 were obtained by counting and measuring the number of particles using a precision particle size distribution measuring device (Beckman Coulter Multisizer 3).
The term “rejection rate” used herein refers to the rejection rate of fine particles. More specifically, it refers to the rejection rate of polystyrene latex particles having a spherical particle diameter of 3.00 μm measured at a basis weight of 60 g / m ² .

The filtration flow rate (L / min) was adjusted using the above filtration device (TSU-90B manufactured by ADVANTEC) so that the 50 cc test liquid had a basis weight of 60 g / m ² under a filtration pressure of 0.1 MPa. It was determined by measuring the time when it passed through the filter.

(4) air permeability at basis weight 60 g / ^{m 2} a ^(cm 3 / cm ² / sec) measured melt blown nonwoven fabric (filter), so as to be basis weight 60 g / ^{m 2} by laminating at the number of layers shown in Table 1 Adjusted. Five test pieces of 20 cm × 20 cm were collected from the adjusted melt blown nonwoven fabric (filter).
The amount of air passing through each test piece (cm ³ / cm ² / sec) was measured in accordance with JIS L1096 (8.27.1 A method; Frazier type method), and the amount of air in the five test pieces The average value of was obtained. The average value obtained was defined as “air permeability (cm ³ / cm ² / sec)” in Table 1.
Here, the measurement of the air amount (cm ³ / cm ² / sec) of each test piece is performed in a temperature-controlled room with a temperature of 20 ± 2 ° C. and a humidity of 65 ± 2% as defined in JIS Z8703 (standard state of test place). The fragile type tester was used.

(5) Evaluation of heat sealability One piece of nonwoven fabric sample 10 cm long × 10 cm wide was cut out from the melt blown nonwoven fabric (filter). At this time, the flow direction of the melt-blown nonwoven fabric was the longitudinal direction of the nonwoven fabric sample.
The cut-out nonwoven fabric sample was laminated | stacked with the 25-micrometer-thick polyethylene film, and it heat-sealed with the hot plate heat-sealing machine. At this time, as the upper seal bar, a sticker with a silicone rubber having a width of 5 mm and a thickness of 2 mm was used, and as the upper seal bar, a sticker with a silicone rubber having a width of 25 mm and a thickness of 2 mm was used. The heat seal conditions were a heat seal temperature of 110 ° C., a heat seal pressure of 2 kg / cm ² , and a heat seal time of 1.0 second.
Next, the heat sealability was visually evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: When an operation of peeling the heat-sealed nonwoven fabric sample and the polyethylene film is performed, the base material breaks down and the heat sealability is excellent.
B: Although the base material is not destroyed even if an operation of peeling the heat-sealed nonwoven fabric sample and the polyethylene film is performed, both peel easily.
C: Even if heat-sealed, the nonwoven fabric sample and the polyethylene film do not adhere at all, and the heat-sealability is poor.

(6) Evaluation of electron beam sterilization Ten pieces of nonwoven fabric samples 20 cm long × 20 cm wide were cut out from the melt blown nonwoven fabric (filter).
The obtained 10 nonwoven fabric samples were stacked, and the stacked nonwoven fabric samples were irradiated with an electron beam at an intensity of 45 kGy.
Next, sensory evaluation of electron beam sterilization was performed according to the following evaluation criteria.
-Evaluation criteria-
A: Neither deterioration of the nonwoven fabric sample, discoloration of the nonwoven fabric sample, nor odor is observed even by electron beam irradiation.
B: At least one of deterioration of the nonwoven fabric sample, discoloration of the nonwoven fabric sample, and odor is recognized by electron beam irradiation.

[Example 1]
<Manufacture of melt blown nonwoven fabric (filter)>
Ethylene copolymer by metallocene catalyst as ethylene polymer (a) [manufactured by Prime Polymer Co., Ltd., product name: Evolu H (registered trademark) SP50800P, density: 0.951 g / cm ³ , MFR: 135 g / 10 Min] 50 parts by mass and an ethylene polymer wax by a metallocene catalyst as an ethylene polymer wax (b) [Mitsui Chemicals, product name Excellex (registered trademark) 40800, density: 0.980 g / cm ³ , weight average molecular weight (Mw): 6,900, Z average molecular weight (Mz): 12,900] and 50 parts by mass of the mixture (ethylene polymer composition) by molding by a melt blow method, a melt blown nonwoven fabric (MB) (polyethylene nonwoven fabric) was produced.
Specifically, the melt resin of the ethylene polymer composition was discharged at 220 ° C. at a rate of 0.1 g / min per single hole, and melt spinning was performed by a melt blow method to obtain a microfiber. The melt blown nonwoven fabric (MB) (polyethylene nonwoven fabric) having a basis weight of 7.5 g / m ² was obtained by depositing the microfibers on the collecting surface.
The obtained melt blown nonwoven fabric (MB) (polyethylene nonwoven fabric) was used as a filter, and the above-described measurement and evaluation were performed.
The results are shown in Table 1.

[Examples 2 to 3]
In Example 1, the mass ratio of the ethylene copolymer and the ethylene polymer wax and the basis weight of the melt blown nonwoven fabric (MB) (polyethylene nonwoven fabric) were the same as in Example 1, except that the basis weight was as shown in Table 1. The operation was performed. The results are shown in Table 1.

[Example 4]
In Example 3, a melt blown nonwoven fabric (polyethylene nonwoven fabric) was obtained in the same manner as in Example 3 except that the mass ratio of the ethylene copolymer and the ethylene polymer wax was changed as shown in Table 1. The obtained melt blown nonwoven fabric (polyethylene nonwoven fabric) was calendered by pressurizing at 5 m / min and 1 MPa with a rubber flat roll and a metal flat roll heated to 60 ° C.
The measurement and evaluation mentioned above were performed using the melt blown nonwoven fabric (polyethylene nonwoven fabric) after a calendar process as a filter. The results are shown in Table 1.

[Example 5]
In Example 3, 100 parts by mass of an ethylene polymer composition was added to an ethylene polymer wax produced by a Ziegler catalyst as an ethylene polymer wax (b) [product name: High Wax 800P (registered trademark) manufactured by Mitsui Chemicals, Inc. ), Density: 0.973 g / cm ³ , weight average molecular weight (Mw): 12,700, Z average molecular weight (Mz): 25,700] The same operation as in Example 3 except that the mass was changed to 100 parts by mass. went. The results are shown in Table 1.

[Example 6]
In Example 3, 50 parts by mass of an ethylene copolymer (Evolue H (registered trademark) SP50800P) was mixed with an ethylene copolymer using a metallocene catalyst (manufactured by Asahi Kasei Co., Ltd., product name: Creolex (registered trademark), density: 0.951 g / cm ³ , MFR: 150 g / 10 min] The same operation as in Example 3 was performed except that the content was changed to 50 parts by mass. The results are shown in Table 1.

[Comparative Example 1]
In Example 2, 60 parts by mass of an ethylene copolymer (Evolue H (registered trademark) SP50800P) was added to an ethylene copolymer by Ziegler catalyst [manufactured by Prime Polymer Co., Ltd., product name: Neozex 50302 (registered trademark), density]. : 0.950 g / cm ³ , MFR: 30 g / 10 min] The operation was performed in the same manner as in Example 2 except that the weight was changed to 60 parts by mass and the basis weight was changed as shown in Table 1. The results are shown in Table 1.

[Comparative Example 2]
In Example 3, the melt blown nonwoven fabric was obtained in the same manner as in Example 3 except that 100 parts by mass of the ethylene polymer composition was changed to 100 parts by mass of the ethylene polymer wax (product name Excellex (registered trademark) 40800). Although the strength of the nonwoven fabric was low, the nonwoven fabric could not be collected.

[Comparative Example 3]
In Example 6, Example 6 except that 100 parts by mass of the ethylene-based polymer composition was changed to 100 parts by mass of an ethylene copolymer (manufactured by Asahi Kasei Corporation, product name: Creolex (registered trademark)). The same operation was performed. The results are shown in Table 1.

[Comparative Example 4]
In Example 1, 100 parts by mass of the ethylene-based polymer composition was changed to 100 parts by mass of a propylene homopolymer (MFR: 25 g / 10 min), the temperature at the time of discharge was changed to 300 ° C., and the basis weight is shown in Table 1. The same operation as in Example 1 was performed except that it was as shown. The results are shown in Table 1.
In Table 1, for convenience, the physical property values of the propylene homopolymer are listed in the “ethylene polymer (a)” column and the “ethylene polymer composition” column.

As shown in Table 1, an example comprising a polyethylene nonwoven fabric (melt blown nonwoven fabric) formed by melt-blowing an ethylene polymer composition having an Mw of 10,000 to 45,000 and an Mz of 65,000 or less. The filters 1 to 6 were excellent in the balance between the fine particle rejection rate and the filtration flow rate. The filters of Examples 1 to 6 were also excellent in heat sealability and electronic sterilization properties.
On the other hand, in Comparative Examples 1 and 3 in which Mz of the ethylene-based polymer composition exceeds 65,000, both the fine particle blocking rate decreased.
In Comparative Example 2 where the Mw of the ethylene polymer composition was less than 10,000, as described above, the strength of the nonwoven fabric was low, and the nonwoven fabric could not be collected.
Moreover, in the comparative example 4 which used the propylene polymer instead of the ethylene polymer composition, the filtration flow rate was low, and it was inferior to heat seal property and electronic sterilization property.

The disclosure of Japanese application 2013-259495 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims

A filter comprising a polyethylene non-woven fabric obtained by molding an ethylene polymer composition having a weight average molecular weight of 10,000 to 45,000 and a Z average molecular weight of 65,000 or less by a melt blow method.
The filter according to claim 1, wherein the polyethylene nonwoven fabric has an average fiber diameter of less than 2.8 μm.
The filter according to claim 1 or 2, wherein the ethylene polymer composition contains an ethylene polymer wax (b) having a weight average molecular weight of 15,000 or less.
The filter according to claim 1 or 2, wherein the ethylene polymer composition contains an ethylene polymer (a) having a weight average molecular weight of 10,000 to 45,000.
The ethylene polymer composition is:
An ethylene polymer wax (b) having a weight average molecular weight of 15,000 or less;
An ethylene polymer (a) having a weight average molecular weight of 10,000 to 45,000 and a value higher than the weight average molecular weight of the ethylene polymer wax (b);
The filter of Claim 1 or Claim 2 containing this.
The filter according to claim 5, wherein the ethylene polymer (a) has a weight average molecular weight of 20,000 to 45,000.
The filter according to any one of claims 1 to 6, wherein the polyethylene nonwoven fabric has an average pore diameter of 20 µm or less measured at a basis weight of 60 g / m 2 .
The filter according to any one of claims 1 to 7, wherein the polyethylene non-woven fabric has an air permeability of 15 cm 3 / cm 2 / sec or less measured at a basis weight of 60 g / m 2 .
The filter according to any one of claims 1 to 8, wherein the polyethylene nonwoven fabric has a blocking rate of polystyrene latex particles having a spherical particle diameter of 3.00 µm measured at a basis weight of 60 g / m 2 of 10% or more.