JPS636107A - Production of polypropylene ultrafine fiber - Google Patents

Abstract

PURPOSE:To produce the titled fiber web free from polymer globule and having a homogeneous weight distribution in the direction of width, by heat-melting polypropylene having a specific melt index and then extruding the molten polypropylene from an orifice of a nozzle at a specific melt viscosity. CONSTITUTION:Propylene with a melt index of 70-500g/10min under a load of 2,160g at 230 deg.C is melted, sent into a die and then extruded from orifice 4 maintaining the melt viscosity of the molten polypropylene in a nozzle 1 to <=50 poise. A heated gas is simultaneously blown against the extruded fibers at a high speed from jet slits 6 through gas headers 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing ultrafine, high-quality polypropylene fibers and webs thereof by a melt blowing method using a specific polypropylene resin as a raw material.

The ultrafine fiber web produced by the method of the present invention is widely used in fields such as medical and sanitary materials, civil engineering materials, agricultural materials, and general industrial materials, and in particular, various filters and batteries that take advantage of the characteristics of ultrafine fibers. Ideal for separators, wipers, etc.

[Conventional technology]

In recent years, nonwoven fabrics have been used in various fields because fabric structures can be obtained through a simpler process 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.
r-ing Chemistry) Volume 48, No. 8 (
P1342-1346).

A basic device and method was disclosed in 1956. Regarding the melt blowing method of polypropylene,
It is disclosed in JP-A-50-46972 and JP-A-54-134177. 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 with a melt viscosity of 50 to 300 poise. The technical idea is that, as described in this specification, as-made polymer resins (especially polypropylene) have high intrinsic viscosities (about 1.4
) and low melt flow rate (temperature 230℃, load 2.160
This high viscosity resin is thermally decomposed between the extruder and the nozzle orifice, resulting in an intrinsic viscosity of 0.6 to 1.
4. By lowering the melt viscosity to 50 to 300 poise, a high-quality nonwoven fabric can be produced without generating polymer beads (clumps of polymer resin that are not fiberized).

[Problem that the invention seeks to solve]

According to the study results of the present inventors, it has been found that the above-mentioned conventional technology has the following two important problems. That is,
The first problem is due to thermal degradation of the polymer resin from the extruder to the nozzle orifice. In the melt-blowing method, ultrafine fibers are often directly produced as a wide (approximately 0.5 to approximately 3 m for boat fishing) sheet-like material (web), but when obtaining this wide web, an extruder or later It is necessary to spread the molten polymer widthwise, particularly preferably in a die, until it reaches the orifice of the nozzle. In this process of widening, it is inevitable that the molten polymer will have a difference in residence time in some parts (eg, the center of the die and the ends of the die). If thermal degradation occurs in the die,
The degree of decomposition differs based on this difference in residence time, and this results in uneven melt viscosity of the polymer. Therefore, in general, the melt viscosity is lower in areas where the residence time is long, and the amount of polymer discharged from the orifice is large; conversely, the areas where the residence time is short are relatively high, and the melt viscosity is relatively high and the amount of polymer discharged is small. As a result, only a material with uneven basis weight distribution in the width direction can be obtained. Temperature unevenness in the width direction of the die also causes deterioration spots in the polymer in the width direction, and this also causes a problem in that only a web with large fabric weight unevenness in the width direction can be obtained. In addition, thermal deterioration produces polymer decomposition products, which partially gel and partially change the flow of the molten polymer, which also causes unevenness in the web. Furthermore, polymer decomposition products etc. adhere to the filter section in the melt line and the orifice of the nozzle.
There is also a problem in industrial production that continuous spinning for a relatively long time is impossible.

The second problem is that with the conventional techniques, there is a limit to the diameter of the fibers that can be obtained, and ultrafine fibers cannot be obtained. This is due to the conventional method of thermally degrading a polymer with a high degree of initial polymerization in the melt line, which naturally limits the melt viscosity that can be obtained, resulting in a relatively large value of 50 to 300 poise. It is caused by In this range of melt viscosity, the average fiber diameter is limited to a minimum of 1.0 μm.
Below this, especially 0.5 μm, cannot be obtained at all. For this reason, conventional technology' has limited applications and is not suitable for high-performance applications such as high-performance air filters.

The purpose of the present invention is to solve the above-mentioned problems in the conventional manufacturing method of polypropylene ultrafine fiber nonwoven fabric, and to produce high quality ultrafine fibers (average fiber diameter 0) without polymer beads and with excellent uniformity of distribution in the width direction. An object of the present invention is to provide a method for manufacturing a fibrous web (.1 to 5.0 μm). Another object of the present invention is to provide a method for producing polypropylene ultra-m fibers, which is advantageous in terms of productivity and cost because continuous spinning can be carried out stably for a long period of time.

[Means for solving the problems and their effects] In contrast to the conventional technology in which polymers with a high degree of polymerization are degraded in the melt line from the extruder to the orifice of the nozzle, The present invention was arrived at as a result of extensive research into ways to minimize in-line deterioration and at the same time achieve a lower melt viscosity that exceeds that of the prior art.

That is, the present invention provides a method of heating and melting a thermoplastic resin, then discharging it from an orifice of a nozzle, and injecting heated gas from near the opening end of the orifice to thin the discharged molten resin to form an ultrafine fiber group. In, the thermoplastic resin is polypropylene having a melt index of 70 to 500 g/10 minutes at a temperature of 230 ° C. and a load of 2.160 g, and the melt viscosity of the polypropylene resin in the nozzle is 50 poise or less. This is a method for producing ultrafine polypropylene fibers.

An example of the melt blowing method of the present invention will be explained with reference to FIG. A polypropylene polymer is melted by an extruder, fed into a die, and extruded through a number of spinning orifices (4) arranged in a row provided in a nozzle (1). The molten polymer is extruded from the orifice (4) via the polymer channel (3). At the same time, the heated high-speed gas supplied through the gas inlet (7) is injected from the slits (6) provided on both sides of the orifice through the gas header (5), and the extruded molten polymer is Spray on the flow. A gas header (5) and an injection slit (6) can be provided between the nozzle (1) and the lip (2) as shown. The extruded molten polymer is stretched into the shape of ultrafine fibers and solidified by the action of the high-speed airflow. The microfibers thus formed are deposited on a screen (collector) circulating between a pair of rotating rollers to form a random web. Steam, air, etc. are suitable as the gas, and the gas conditions include temperature 3.
00-400°C, preferably 320-380°C, pressure 1.5 kg/c+JG or more, preferably 2.5-5.
0 kg/c+d G. Extruder temperature is 170~
300℃, preferably 190-280℃, die temperature 1
The temperature is 90-340°C, preferably 200-330°C.

The term "polymer beads" as used herein refers to a bead-like polymer having a diameter of about 10 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. Detection is facilitated by observation using a microscope, or by dyeing the web as it is, or after increasing the fiber density by pressing, 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 (M
It is essential that the FR) is 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. When the melt index is below 70 g/10 min, as shown in the prior art described above, the melt viscosity in the orifice of the nozzle must be relatively low (50 to 300 poise) in order to obtain a web without polymer beads. In order to achieve this low melt viscosity, the polypropylene resin must be significantly degraded in the melt line, resulting in worsening of unevenness in the middle direction and poor continuous operation. On the other hand, if the melt index exceeds 500 g/10 minutes, the degree of polymerization of the polymer will be too low, and the strength of the resulting ultrafine fibers will be too low, causing a practical problem. As mentioned above, the polypropylene resin of the present invention has a melt index of 70 g to 500 g.
It is important that the temperature is within the range of g/10 minutes, and by selecting this polymer, it is possible to set the temperature of the polymer melt line from the extruder to the orifice of the nozzle and the blow gas temperature to be low (low). As a result, deterioration of the polymer can be kept to a minimum.As a result, a good web with a uniform basis weight distribution in the width direction can be obtained, and continuous stable production over a long period of time is possible.Moreover, it is possible to obtain a good web with a uniform basis weight distribution in the width direction. Because it is possible to further lower the polymer melt viscosity compared to conventional technology, it is now possible for the first time to produce ultra-fine webs that are of good quality without polymer beads and have an average fiber diameter of 0.5 μm or less, which was not possible with conventional technology. became.

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.

Organic peroxide tin compounds, sulfur compounds, and the like are known as molecular weight reducing agents. Specifically, the organic peroxides include 2,5-dimethyl-2,5-t-butylperoxyhexane, 2,5-dimethyl-2,5-t-butylperoxyhexene-3, and bis(1- t-butylperoxy-1
dialkyl peroxides such as -methylethyl)benzenedicumyl peroxide, hydroperoxides such as 2,5-dimethylhexane-2,5-sibide lobaroxide, p-menthane hydroperoxide, ketone peroxides, peroxides, etc. Among oxyesters, those having a half-life of more than 10 hours at 100°C are suitable. As a tin compound, (CJJSn
(OOC-CzHzs)3, (C4H9)zSn(0
0C-CzHzs)z, (CJs)zSn(OOC-(
:++Hz:+)z etc.General 2RI! 5n(OOCR'
)m (However, R and R' are an alkyl group of 01 to 18, an aryl group, or a cyclohexyl group, and j!=1.2
,3. Compounds of the formula (where m=1.2.3 and 1+m=4) are 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, and if this amount of molecular weight reducing agent is blended and heated to a temperature of 180°C to 300°C, the molecular weight of the polypropylene resin will be reduced. is reduced to the desired degree.

Further, the molecular weight distribution of the polypropylene used in the present invention is not particularly limited, but those with Mw/Mn (ratio of weight average molecular weight to number average molecular weight) of 5 or less, particularly 3 to 4, are good for spinnability etc. It is advantageous.

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, it is an essential requirement to use a polypropylene resin having a high melt index as described above, but in addition to this requirement, in the present invention, in addition to this requirement, the polypropylene resin is It has been found that even better results can be obtained by using a polypropylene resin whose crystallization onset temperature when cooled at a rapid rate is 120° C. or higher.

The crystallization initiation 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 is added to the polypropylene resin in an amount of 0.05 to 0.
It can be easily obtained by adding about 5% 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. To give a more specific example, as the inorganic fine powder, alumina, silica, etc. having a particle size of 5 μm or less are effective. Aliphatic and aromatic dicarboxylic acids and their anhydrides or their metal salts include adipic acid Na, AJ salt, sebacic acid Na, Al,
ni salt, benzoic acid Na, ni salt, para-t-butylbenzoic acid Al salt, para-t-butylbenzoic acid Ti, Cr salt, monophenylacetic acid AI! , salt, etc. are particularly effective.

As a condensate of benzaldehyde and polyhydric alcohol,
Dibenzylidene sorbitol, dibenzylidene xylidol, dibenzylidene perseitol, monobenzylidene sorbitol, dibenzylidene mannitol, 1.3
, 2.4-di(alkylbenzylidene)sorbitol,
1,3,2°4-di(alkoxybenzylidene) sorbitol, alkyl-substituted dibenzylidene sorbitol, and the like are useful.

It is also possible to add and mix the crystal nucleating agent to the polypropylene resin during the melting process, but from the viewpoint of uniformity of mixing, it is desirable to uniformly disperse the crystal nucleating agent in the polypropylene resin beforehand and then subject it to the melting process. .

The crystallization initiation temperature is preferably 120°C or higher and as close to the crystal melting point as possible, but the upper limit of the crystallization initiation temperature that can be achieved by blending the above-mentioned crystal nucleating agent is generally about 135°C.

The polypropylene resin used in the present invention whose crystallization initiation temperature is 120°C or higher exhibits superior effects compared to ordinary polypropylene resin whose crystallization initiation temperature is around 115°C. That is, virtually no thermal fusion occurs between the ultrafine fibers constituting the resulting web, resulting in extremely high filter performance and flexible waves. Furthermore, a web with a sharper fiber diameter distribution of ultrafine fibers can be obtained, resulting in uniformity and better filter performance. It is surprising that such a remarkable effect can be obtained even if the crystallization initiation temperature is only about 5° C. higher than that of ordinary polypropylene resins. Although the reason for this is not fully elucidated, it is believed that the addition of the crystal nucleating agent causes rapid solidification of at least the surface layer of the fiber.

In the present invention, the melt viscosity of the polypropylene resin in the nozzle is set to 50 poise or less. More preferably, it is 40 poise or less. By using the polypropylene resin specified in the present invention, this low melt viscosity can be obtained without significant deterioration in the polymer melt line after the extruder. 2.5 kg/aJ of this low melt viscosity molten polymer
0 or more, preferably 3. Okg/crA 0.5 when discharged into a high-speed gas flow injected at a high pressure of 0 or more
Super pf of ~0.1μm that could not be obtained with conventional technology
It has been found that a 1-fine fibrous web is obtained. Such ultra-fine fiber webs not only improve the performance of conventional products such as filters and puffy separators, but also
It has the potential to develop new fields of application, and has great industrial significance.

〔Example〕

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

Incidentally, in the examples, the density unevenness in the width direction is a value measured as follows. 5 cm in the width direction from a 1.5 m wide web
Cut a 20cm sample in the X length direction, measure the weight of this sample (n#3Q), and find the difference between the maximum and minimum (R)
is the ratio (%) divided by the average value (x).

Example 1 Bis(1-t-butylperoxy-1-methylethyl)benzene was added to polypropylene powder with a melt index of 10 g/10 min (measured according to AST-1238) at a temperature of 230°C and a load of 2,160 g. 0.07
and 0.2 weight percent of di-benzylidene sorbitol were added and mixed uniformly, and then passed through a heated extruder to obtain a melt index of 206 g/10 minutes and a melting rate of 10" C/ Polypropylene pellets were obtained which had a crystallization initiation temperature of 125°C and a melting point of 165°C when cooled at a rate of 1.5 min.The polypropylene resin thus obtained was charged into an extruder and melted by heating, and the following conditions were applied. It was melt-produced.

0.3 as with 1 fl pitch to the nozzle installed in the die
There are 1,500 φ orifices lined up in one row, and the molten polymer is discharged from these orifices at a rate of 10.2 g/ff.
min/orifice. Heated steam was injected from slits on both sides of the orifice to form a traction wire from the molten polymer, and the fiber group was collected on a moving net conveyor to form a web with a width of 1.5 m and a basis weight of 50 g/rd. Extruder temperature is 210'C, Gui temperature is 290'C, gas temperature is 370'C, gas pressure is 5.0kg/cdG.
Met. Further, the polymer melt viscosity in the nozzle orifice was 2o poise.

The obtained web had an average fiber diameter of 0.4 μm and was of good quality, containing no polymer beads.

The fabrication unevenness in the width direction of this web was good at 15% in R/x, and even after 20 days of continuous operation, no polymer balls were generated.
Almost no deterioration in the level of eye spots was observed, and a good spinning condition could be maintained.

Comparative Example 1 When a polypropylene resin with a melt index of 10 g/10 min at a temperature of 230° C. and a load of 2.160 g was melt-blown in the same manner as in Example 1, the average fiber diameter was as thick as 3.5 μm, and there were many polymer beads. It was a bad one. The melt viscosity at the nozzle orifice at this time was 500 poise.

Comparative Example 2゜The polypropylene resin used in Comparative Example 1 was heated to an extruder temperature of 35°C.
Melt blowing was carried out under the same conditions as in Example 1, except that the polypropylene resin was thermally degraded at 0° C. and the Goo temperature was 350° C. The melt viscosity at the nozzle orifice at this time was 100 poise.

The average fiber diameter of the obtained web was 1.2 μm, and the unevenness in the width direction was 35%, which was poor. Furthermore, when continuous operation was carried out, polymer beads frequently appeared after 4 days and the level of eye spots exceeded 50%, resulting in a defective product.

(Effects of the invention) According to the method of the present invention, it is possible for the first time to minimize the deterioration of the resin in the melt line from the extruder to the orifice of the nozzle. It is an advantageous manufacturing method in terms of cost as it allows a uniform wide web to be obtained and can be operated continuously for a long period of time.In addition, it is possible to lower the melt viscosity of the polymer in the nozzle, making it possible to reduce the viscosity of the polymer melt in the nozzle. 5 not obtained
A high-quality ultra-fine polypropylene fiber web with an extremely small average fiber diameter of 0 to 0.1 μm, especially 0.5 am to 0.1 μm, and no polymer beads can be obtained, and can be used in high-performance filters and other wide range of applications. It is possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a melt blowing die used to carry out the method of the present invention. 1...Spinning nozzle, 2...'J-/p, 3
... Polymer flow path, 4... Orifice, 5...
・Gas header, 6...Gas injection slit, 7...
・Gas inlet.

Claims (3)

[Claims] (1) After heating and melting the thermoplastic resin, it is discharged from an orifice of a nozzle, and a heated gas is injected from near the opening end of the orifice to blow the flow of the discharged molten resin to make it thinner, thereby forming a group of ultrafine fibers. In the method, the thermoplastic resin is heated at a temperature of 230°C and a load of 2,160g.
A method for producing ultrafine polypropylene fiber, characterized in that the polypropylene has a melt index of 70 to 500 g/10 minutes, and the melt viscosity of the polypropylene resin in the nozzle is 50 poise or less. (2) The manufacturing method according to claim 1, wherein the polypropylene resin crystallization initiation temperature is 120° C. or higher when cooled from a molten state at a rate of 10° C./min using a differential scanning calorimeter (DSC). (3) The average fiber diameter of the polypropylene microfiber is 0.
The manufacturing method according to claim 1, wherein the thickness is 1 to 5.0 μm.