JPH01156561A - Polypropylene extremely fine fiber nonwoven fabric - Google Patents

Abstract

PURPOSE: To obtain a nonwoven fabric having excellent filter performances and tenacity, high qualities free from polymer ball, most suitable for various kinds of high-performance filters, comprising a PP ultrafine having an average fiber diameter, an average molecular weight and a molecular weight distribution in specific ranges. CONSTITUTION: This nonwoven fabric comprises a PP ultrafine fiber having 0.1-5.0 μm average fiber diameter, 5.0×10<4> <=Mw <=9.0×10<4> average molecular weight and 4.0<=Mw /Mn <=6.0 (Mw is a weight-average molecular weight, Mn is a number-average molecular weight). Most preferably the objective nonwoven fabric has 10-300 g/cm<2> weight and 0.08-0.30 g/cm<3> bulk density. The melt index of the PP resin is most preferably 100-300 g/10 minutes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polypropylene ultrafine fiber nonwoven fabric, and more particularly to a high quality polypropylene ultrafine fiber nonwoven fabric that has excellent filter performance and strength and is free of polymer beads.

The polypropylene ultrafine fiber nonwoven fabric of the present invention is widely used in fields such as medical and sanitary materials, civil engineering materials, agricultural materials, and general industrial materials, but it is especially suitable for various high-performance filters that take advantage of the characteristics of ultrafine fibers. Can be used.

[Conventional technology]

In recent years, nonwoven fabrics have been used in a variety of fields because fabric structures can be obtained through simpler processes than woven or knitted fabrics, and because of their excellent properties.

In particular, nonwoven fabrics made of ultrafine fibers obtained by melt blowing have been developed for many uses including filters.

For information on spinning polymers using the melt blow method, see Industrial and Engineering Chemistry.
ringChemistry) Volume 48, No. 8 (P1
342-1346), 1956, disclosed the basic apparatus and method.

Further, the melt blowing method for polypropylene is disclosed in JP-A-50-46972, JP-A-50-46972, JP-A-54-54-34177. These methods include thermally degrading a thermoplastic resin having an initial intrinsic viscosity of at least 1.4 from the extruder to the orifice of the nozzle in the presence or absence of a free radical generating compound. , the intrinsic viscosity of the polymer resin in the orifice of the nozzle is 0.6 to 1.4.
This is a method for producing a melt-blown nonwoven fabric having a melt viscosity of 50 to 300 poise. The idea is that as-made polymer resins (especially polypropylene) have high intrinsic viscosities (at least about 1.
4) and low melt flow rate (temperature 230℃, load 2.16
This high viscosity resin is thermally decomposed between the extruder and the nozzle orifice, resulting in an intrinsic viscosity of 0.6 to 0.0 g.
1.4. By lowering the melt viscosity to 50 to 300 voids, a high-quality nonwoven fabric can be produced without generating polymer balls (clumps of polymer resin that are not made into fibers).

[Problems to be solved by the invention] In the prior art described above, in order to obtain a high-quality ultrafine fiber nonwoven fabric without polymer beads, it is necessary to thermally degrade the polymer to lower the melt viscosity before it reaches the orifice. Therefore, the strength of the obtained nonwoven fabric was only low. In addition, with the conventional method, only filters with relatively low performance could be obtained, and in particular, they could not be used as-is for high-performance air filter applications.

The purpose of the present invention is to solve the above-mentioned problems with conventional ultrafine propylene fiber nonwoven fabrics, and to provide a high quality polypropylene microfiber nonwoven fabric that has excellent filter performance, high strength, and is free from polymer beads.

[Means for solving the problems and their effects] The present inventors have found that when the average molecular weight and molecular weight distribution (M, /M, ratio) of polypropylene ultrafine fibers are within a specific range, the strength is high and the polymer The present invention was completed based on the discovery that high-quality ultrafine fibers without beads can be obtained, and surprisingly, the filter performance of this nonwoven fabric is significantly improved.

That is, in the present invention, the average fiber diameter is 0.1 to 5. On, it is a polypropylene ultrafine fiber nonwoven fabric made of polypropylene ultrafine fibers having an average molecular weight within the range of the general formula below.

General formula % Formula % (However, in the above formula, Mw represents a weight average molecular weight, and Mn represents a number average molecular weight.)

The weight average molecular weight (M
, ) is 5.0X10' to 9.0X10', preferably 5.5X10' to 8.5 XIO', particularly preferably 6, OXIO' to 8. OXIO'. When Mw is smaller than 5.0×10 4 , the strength of the nonwoven fabric decreases because the fiber strength decreases. On the other hand, if it is larger than 9.0x10', only a nonwoven fabric with many polymer beads will be obtained, and such a nonwoven fabric will have a significantly reduced filter performance. M, is 5.
0X10' to 9.0X10', the filter performance becomes high (, high strength, high quality ultrafine fiber nonwoven fabric without polymer beads. Also, the weight average molecule !t (M, ), which is an index of molecular weight distribution. Ratio of number average molecular weights (M, , ),
M, /M, 1 is 4.0 to 6.0, preferably 4.5 to 5
．． It is 5. M, /M, is particularly important, and this is 4.
If it is less than 0, the filter performance of the nonwoven fabric will deteriorate. On the other hand, if it is larger than 6.0, the filter performance will be significantly reduced, and high-quality ultrafine fibers without polymer beads will not be obtained. When Mw/M is in the range of 4.0 to 6.0, the filter performance is significantly improved. The reason for this is not necessarily clear, but nonwoven fabrics within this range have no polymer beads, small variations in the fiber diameter of the ultrafine fibers, and a sharp fiber diameter distribution. Since there are very few fibers in the form of bundles, and the dispersibility of single fibers is significantly improved, the filter performance is significantly improved, and it also has the effect of increasing the strength of the nonwoven fabric. considered to be a thing. The fiber diameter distribution of ultrafine fibers is not necessarily a normal distribution (in particular, ultrafine fibers obtained by melt blowing often have a tailing distribution toward larger fiber diameters), but this distribution Standard deviation value (σnμm,
), M, /M, as referred to in the present invention, is 4. O~
The one with 6.0 has σ,, μm, of 0.10 trm or less, especially in the range of 0.20 to 0.50 m, whereas M, /
If M is outside the range of the present invention, the standard deviation value σ of the fiber diameter
, lμm, was found to be 0.80 m or more, generally 1.00- or more. Note that M, and M, l
was determined from a polystyrene standard conversion number using a gel permeation chromatograph (GPC: 150C manufactured by Nippon Waters).

Mw/M is a measure of molecular weight distribution, M,/M.

The smaller the value, the narrower the molecular weight distribution.

The average fiber diameter of the polypropylene fibers constituting the nonwoven fabric of the present invention is from 0.1 to 5.0, preferably from 0.5 to 4.
．． 0, particularly preferably 1.0 to 3.5 tna. When it is less than 0.1, it is flexible but the fiber strength is low, and as a result, the nonwoven fabric strength is also low. Furthermore, it was found that the filter performance also deteriorated.

This is considered to be due to deterioration in single fiber dispersibility.

On the other hand, if it is more than 5.0, the filter performance and flexibility will be significantly reduced. In addition, since this ultrafine fiber has an extremely small fiber diameter, it is difficult to measure the average length of the fiber, but it is preferably 30 length or more, and in most cases 100 to 500 length.

The basis weight of the polypropylene nonwoven fabric of the present invention is 5 to 500.
g/rd is preferred, more preferably 10-300
It is g1rd. Below 5 g/rrr, the strength and filter performance of the nonwoven fabric decreases. On the other hand, 500 g
/m' or more, the collection efficiency is high, but on the other hand, the pressure loss tends to become too high.

In addition, the bulk density of the nonwoven fabric of the present invention is 0.05 to 0.50 g.
/d is preferred, especially 0.08-0.30 g/c
d is preferred. If it is less than 0.05 g/cd, the strength of the nonwoven fabric will be low, and if it is more than 0.50 g/cd, the pressure loss will be high. The strength and filter performance of non-woven fabrics are
It is related to both the basis weight and bulk density of nonwoven fabric, with basis weight 5-500 g/rd, bulk density 0.05-0.5
Even better effects can be obtained if both of the conditions are satisfied.

In the nonwoven fabric of the present invention, it is more preferable that the ultrafine fibers are randomly dispersed in the form of single fibers, since this significantly improves the filter performance. Further, although it is preferable that the nonwoven fabric of the present invention is made of polypropylene fiber alone, it may be a mixture of fibers of different materials, powder, etc.

It is particularly preferable to use a melt blowing method to obtain the ultrafine fiber nonwoven fabric of the present invention. An example of the melt blowing method of the present invention will be explained below.

Polypropylene polymer is melted by an extruder, fed into a die, and extruded through a number of spinning orifices arranged in a row in a nozzle. Molten polymer is forced out of the orifice through a polymer channel.

At the same time, the heated high-speed gas supplied through the gas inlet is injected through the gas header through slits provided on both sides of the orifice, and is blown onto the stream of extruded molten polymer. A gas header and injection slit can be provided between the nozzle and the lip. The extruded molten polymer is pulled into the shape of ultrafine fibers by the action of the high-speed airflow, thinned, and solidified. The microfibers thus formed are deposited on a screen (collector) circulating between a pair of rotating rollers to form a random web. Gases include steam,
Air is suitable, and the gas conditions include a temperature of 300℃.
~400°C, preferably 320~380°C, pressure 1.
0 kg/cdG or more, preferably 1.5 to 5.0 kg/
c+JG. Extruder temperature is 170-300°C, preferably 190-280°C, die temperature is 190-340°C
, preferably) or 200 to 330°C.

The term "polymer beads" as used herein refers to a bead-like polymer having a diameter of several times to 500 times the diameter of the web-constituting fibers, or a knob-like polymer formed at the ends or intermediate portions of the fibers. Many of these polymer beads are extremely small and cannot be seen with the naked eye. Observe using a microscope or
Or use the web as is or press the web,
Detection is facilitated by increasing fiber density by calendering, entangling, or other means. If a large number of these polymer beads exist, the applications are greatly restricted, and in particular, they cannot be used as high-performance filters or battery separators.

The polypropylene resin used in the present invention has a temperature of 230
Melt index at ℃, load 2.160 g (
MFR) is preferably in the range of 70 to 500 g/10 minutes, most preferably 100 to 300 g/10 minutes. Melt index is used as an indicator of the melt viscosity and degree of polymerization of a polymer. Further, the molecular weight distribution of the polypropylene resin used in the present invention is not particularly limited, but M, /M is 3. O~7
．． 0, especially D 4.0 to 6.0 (7) is preferable in terms of blowability. When using such polypropylene resin,
Weight average molecular weight (M, ), molecular weight distribution (M,
/M, ), the average fiber diameter is 0.1 to 5.0 ts, and a high-quality ultrafine fiber web without polymer beads can be easily obtained.

Polypropylene resin with a high melt index as described above can be produced by polymerization, but it is also possible to produce it by adding a molecular weight reducing agent to polypropylene resin and heating it to an appropriate temperature to reduce the molecular weight. is convenient.

As molecular weight reducers, organic peroxides such as tinned organic peroxides, metals, sulfur compounds, etc. are known. Specifically, the organic peroxides include 2,5-dimethyl-2,5-t-butylperoxyhexane, 2,5-dimethyl-2,5-t-butylperoxyhexene-3, and bis(1- t-butylperoxyμ
dialkyl peroxides such as m,-methylethyl)benzenedicumyl peroxide;2. Hydroperoxides such as b-dimethylhexane-2,5-cybidrobar oxide and p-menthane hydroperoxide, ketone peroxides, and peroxyesters whose half-life at 100°C exceeds 10 hours. is appropriate. As a tin compound, (C,H
,)Sn(OOCHc+ +Ib5) 3, (C411
J, 5n(OOC-CzHzs)z, (Ct, ll5)
General formula Re S such as zSn(OOC+ CzHz3)z
n (OOCR”)s (However, R and R' are 01
~Cll1 is an alkyl group, aryl group, or cyclohexyl group, where l=1.2.3, m=1.2.3, and 1+m=
4) is suitable. Suitable sulfur compounds include 2-mercaptobenzothiazoles such as dibenzothiazyl disulfide, 2-mercaptobenzothiazole zinc salt and copper salt, and cyclohexylbenzothiazyl sulfenamide. The amount of molecular weight reducing agent used is preferably 0.01 to 0.5% by weight based on the polypropylene resin.
Heating to a temperature of 80°C to 300°C reduces the molecular weight of the polypropylene resin to a desired degree.

As for polypropylene, a homocrystalline polymer of propylene has excellent spinnability, but a copolymer containing 1 mol % or less of an olefin such as ethylene can also be used.

In the present invention, even better results can be obtained by using a polypropylene resin whose crystallization initiation temperature is 120°C or higher when cooled from a molten state obtained by a differential scanning calorimeter (D SC') at a rate of 10°C/min. It will be done.

The crystallization start temperature of normal polypropylene resin is 115℃
For polypropylene resins with a crystallization initiation temperature of 120°C or higher, an inorganic or organic compound called a crystal nucleating agent should be added at a rate of 0.05 to 0.5 to the polypropylene resin.
It can be easily obtained by adding approximately % by weight. Typical crystal nucleating agents include fine powders of inorganic substances such as silica, aliphatic and aromatic dicarboxylic acids and their anhydrides, and their metal salts, benzaldehyde and its ring substituted products, and polyhydric alcohols with a valence of 5 or more. A condensate of , etc. can be used.

Polypropylene resins whose crystallization initiation temperature is 120 ÷ or higher have substantially no heat fusion between the ultrafine fibers that make up the obtained web, compared to ordinary polypropylene resins whose crystallization start temperature is around 115°C. This method is preferable because it provides a flexible web with extremely high filter performance.

The web obtained by the melt blowing method of the present invention has appropriate strength and can be used as it is for filter materials, etc., but it can also be pressed to increase bulk density and strength. Further, if necessary, heat pressing, embossing, ultrasonic bonding, etc. can be performed. It is also possible to improve the filter performance by converting it into an electleft using a corona discharge method or the like.

(Examples) The present invention will be further explained below with reference to Examples, but the present invention is not limited to these Examples.

Prior to the description of Examples, methods for measuring physical property values used in the following description will be shown below.

■Appearance density (g/cd): 130g/c+J
This value is calculated by measuring the thickness under a constant load and calculating the basis weight.

◎Tensile strength (g/cm): length 20cm x width 1
A cm sample is taken and stretched and cut using a tensilon with a gripping length of 1 cm, and the maximum force at that time is determined.

◎Average fiber diameter (voice), standard deviation (voice) Ten arbitrary points on the sample were examined using an electron microscope at a magnification of 2000.
Take 5 photos at double magnification. Any 1 per photo
Measure the diameter of 0 fibers and do this for 10 photographs. Obtain the fiber diameter measurements of a total of 50 fibers and calculate the average value (x)
and standard deviation (σ7μm, ).

◎ Collection efficiency and pressure are reduced to 0.3 for JIS Z-8901 test dust type 13 B method.
Measurements were made by measuring the dust collection efficiency and pressure drop of a trend-average stearic acid aerosol.

Polypropylene powder with melt index log/10 min (measured according to ASTM 01238) at a temperature of 230°C and a load of 2.160 g was mixed with bis(1-butylperoxyμm, -methylethyl)benzene. 0
．． After adding 0.7 weight percent and 0.2 weight percent of di-benzylidene sorbitol and mixing uniformly, the mixture was passed through a heated extruder to obtain a melt index of 206 g/10 minutes and a temperature of 10°C from the molten state in DSC. Polypropylene pellets having a crystallization onset temperature of 125°C and a melting point of 165°C when cooled at a rate of 1/min were obtained. The polypropylene resin thus obtained was put into an extruder, heated and melted, and melt blown under the following conditions.

The nozzle provided in the die has one row of 0.3 lφ orifices in one pitch. The molten polymer was discharged from these orifices at a discharge rate of 0.2 g/min/orifice. Heated steam is injected from the slits on both sides of this orifice, and the molten polymer is made into a draw wire.The fiber group is collected on a moving net conveyor, and after pressing, it is 1.5 m wide and has a basis weight of s o g/ =, a web with a bulk density of 0.14 g/ctA. Extruder temperature is 210℃, Gui temperature is 290℃, gas temperature is 370℃,
Gas pressure was 2.5 kg/col G.

The average fiber diameter of the obtained web was 1.4 tna, σ7μ
m, was 0.284, and was soft and of good quality, containing no polymer beads at all. M of ultrafine fiber is 6.5'
X10', Mw/M, is 4.8, the collection efficiency of this web is 96%, the pressure drop is excellent at 1311 II z O, and the tensile strength is 430 g / cts.
Met.

Examples Example 1 except that the amount of bis(1-t-butylperoxyμm, -methylethyl)benzene added was varied.
In the same manner as above, various polypropylene resins having different melt indexes and molecular weight distributions were obtained. Using this resin, melt blowing was performed in the same manner as in Example 1 except that the blow gas temperature and pressure were varied to obtain ultrafine fiber webs having the average molecular weights shown in Table 1. The web weight is 100 g/n (and the bulk density is O, 13 g/c
+J, the average fiber diameter was 2.0 tones. The results are shown in Table 1.
Shown below.

As is clear from Table 1, it can be seen that within the average molecular weight range of the present invention, a high quality web free of polymer beads and excellent in both filter performance and tensile strength can be obtained.

The polypropylene pellets of JLf Ikuhama Example 1 were used and the blow gas temperature and pressure were varied to obtain webs with different average fiber diameters. Other conditions were the same as in Example 1. The results are shown in Table 2. The web had a basis weight of 50 g/m and a bulk density of 0.20 g/cd.

Also, M of ultra-fine fiber. Is it 6.8~? , 7 XIO'
,M.

7M, ranged from 4.5 to 5.5.

As is clear from Table 2, it can be seen that the ultrafine fiber web of the present invention having an average fiber diameter within the range is excellent in both filter performance and tensile strength.

Below is a margin of 91 N. A polypropylene resin with a melt index of 10 g/10 minutes at a temperature of 230° C. and a load of 2.160 g is melt blown in the same manner as in Example 1 to obtain a basis weight of 80 g/1.
m, a web with a high density of 0.15 g/ci was obtained.

The average fiber diameter of this web is 5.51B@,σ,,μm,
It was a defective product with a score of 2.02 and a large number of polymer beads. M of this fiber. is 11×104, M,, 7M
, , was 6.7, the collection efficiency of the web was 58%, and the pressure loss was poor at 4 mmt120.

Comparison 1 The polypropylene resin used in Comparative Example 1 was heated to an extruder temperature of 35
Melt blowing was carried out under the same conditions as in Example I except that the polypropylene resin was thermally degraded at 0° C. and the temperature was 350° C.

The average fiber diameter of this web is 2.5μIII, σnμm,
was on the order of 1.30, and there were many polymer beads.

The M of this fiber is 6.5 x 10', M, 7M,
was 3.4, the collection efficiency of the web was 74%, and the pressure loss was poor at 7 mmH2O.

〔Effect of the invention〕

The polypropylene ultrafine fiber nonwoven fabric of the present invention has an extremely thin average fiber diameter of 0.1 to 5.0 μm, and the molecular weight distribution of the ultrafine fibers is in a small range. The fibers had a sharp fiber diameter distribution, excellent single-filament dispersibility, and extremely high filter performance (especially collection efficiency).Furthermore, the average molecular weight of the ultrafine fibers was also appropriate. By finding this range, we were able to obtain a high-quality nonwoven fabric with excellent strength and no polymer beads, and at the same time, we were able to further improve the filter performance.

The nonwoven fabric of the present invention is particularly suitable as a high-performance filter material, but it is also suitable for various uses such as battery separators, sanitary materials, wipers, industrial materials such as building materials, and clothing such as insulation clothing and dustproof clothing. be.

Claims (1)

[Claims] 1. A polypropylene ultrafine fiber nonwoven fabric comprising polypropylene ultrafine fibers having an average fiber diameter of 0.1 to 5.0 μm and an average molecular weight within the range of the following general formula. General formula: 5.0×10^4≦M_w≦9.0×10^44.0≦
M_w/M_n≦6.0 (however, in the above formula, M_w represents the weight average molecular weight and M_n represents the number average molecular weight).