JP3134964B2 - Ultrafine fiber nonwoven fabric and method for producing same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-woven fabric made of ultra-fine fibers, and more particularly to an ultra-fine fiber suitably used for a heat insulating material, a filter, a surgical drape, a bacterial barrier, etc. by utilizing the properties of the ultra-fine fibers. The present invention relates to a fibrous nonwoven fabric and a method for producing the same.

[0002]

2. Description of the Related Art Ultra-fine fiber non-woven fabrics include melt blow methods (JP-A-49-10258 and JP-A-49-4892).
1, non-woven fabrics made of ultrafine fibers having an average fiber diameter of 0.1 μm to 20 μm have been known.

[0003]

SUMMARY OF THE INVENTION These nonwoven fabrics include:
The sheet contained many bundled fibers formed by intertwining a plurality of fibers called ropes. As a means of solving this problem, it is possible to reduce the distance between the nozzle and the collector and collect the rope with a collector before the rope is formed in the air.However, when a nonwoven fabric is manufactured by a conventional method, a ball called a shot is used. Polymer often occurs, the texture of the sheet becomes rough, the cooling of the shot is delayed due to the thick fiber diameter of the shot, the fibers around the shot are melted by the sensible heat brought in by the shot, and In some cases, holes called pinholes were formed.

[0004] Further, the fusion of the fibers becomes large, so that when used as a filter, the permeation speed of the liquid or gas to be filtered increases. When used as a heat insulating material, there is a problem that the packing density is high due to the large number of fusion constraint points, the flexibility is low because the sheet is hard, and the air permeability is poor because the porosity is small. . A device for solving such a problem, that is, a method of adhering droplet particles to fibers to promote cooling has been considered (Japanese Patent Publication No. 60-22100). However, when the particles are attached to the droplets, the surface of the fibers and the nozzle surface are at a high temperature, so that the particles hardly come into contact due to the effect of thermophoresis, and it was not easy to send the particles to the fibers near the nozzle. Therefore, the diameter is 20μm to 100μ
It is necessary to use large droplet particles such as m and to cause inertial collision at a high speed.

By the way, when a large water droplet is put on a high-speed air stream and collides with a fiber, the air flow disturbs the fiber itself and the air flowing around the fiber, and the fiber is entangled with one another and is called a rope. There is a problem in that the spinning phenomenon such as yarn breakage or a ball-like object called a shot is generated by promoting the instability due to fiber vibration. Here, the solidification point of the fiber means that the temperature of the fiber is in a state of a glass transition temperature or a softening point and is in a state where it is substantially difficult to elongate.

[0006] Such yarn breaks, shots, and unevenness of thickness,
When used as a filter or a heat insulating material, there has been a problem that channeling or drifting of a fluid such as air or water is caused to significantly impair the performance. An object of the present invention is to solve such problems and to provide a microfiber nonwoven fabric suitable for a filter or a heat insulating material and a method for producing the same.

[0007]

The present invention adopts the following means in order to solve such problems. That is, according to the present invention, the value obtained by dividing the flow rate of air when applied with a pressure of 0.5 inch / cm ² of water by the area is made of ultrafine fibers having an average fiber diameter of 0.1 to 3.0 μm. 30 g / m ²
A microfiber nonwoven fabric or a molten polymer, characterized in that the basis weight is 0.5 to 4.5 cm / sec and the initial bubble generation pressure determined by the bubble point measurement method is 250 mmAq (water column) or more. In contact with a high-temperature high-speed traction fluid to produce a microfiber nonwoven fabric,
After the polymer is sufficiently pulled by the traction fluid and the thinning is completed, a droplet containing mist containing water droplets having a diameter of 20 μm or more and a number concentration of 5% or less in the gas atmosphere is mixed with the traction fluid. The method for producing a microfiber nonwoven fabric as described above, wherein the nonwoven fabric is applied so as not to come into contact with the nonwoven fabric.

Hereinafter, the present invention will be described in detail. In the present invention, the average fiber diameter of the ultrafine fibers constituting the nonwoven fabric is from 0.1 μm to 3.0 μm, preferably from 0.5 μm to 3.0 μm .
0 μm. Fine fibers are indispensable for increasing the cooling efficiency, and if the fiber diameter is larger than this, the occurrence of shots cannot be suppressed. On the other hand, if the fibers are too thin, the effect of the mist will not be recognized much. The nonwoven fabric sheet having such a fiber diameter range has good performance in applications such as a filter and a heat insulating material that come into contact with a fluid.

The material of the polymer constituting the ultrafine fibers in the present invention may be a thermoplastic resin, and polypropylene, polyester, polyphenylene sulfide, polyamide, etc., which are generally used for melt-blowing, are often used. It is not particularly limited. Particularly recently, new polymers having biodegradability have appeared, and their use is also one of the preferable forms.

In the nonwoven fabric of the present invention, the maximum bubble point pressure by the bubble point method, that is, the initial bubble generation pressure determined by the bubble point measurement method is 250 mmA.
q (water column) or more, preferably 270 mmAq
It is necessary to be above. This makes it possible to obtain a well-balanced nonwoven fabric having a small micropore size (micropore size) formed by the fibers in the nonwoven fabric and having a low fluid permeation resistance.

The air permeability, which is inversely proportional to the passage resistance when the permeating fluid is air, is preferably 0.5 to 4.5 cm / sec in terms of a basis weight of 30 g / m ² , and more preferably 0.5 to 4.5 cm / sec.
7 to 4.5 cm / sec. This is preferable in terms of the characteristics of the filter and the heat insulating material.

This condition is inconsistent with the fact that the maximum bubble point pressure of the above-mentioned bubble point measurement method is large, and to achieve this, by devising a manufacturing method, it is possible to obtain a filtration accuracy which has been incompatible with the prior art. It has been found that a nonwoven fabric having an excellent balance between the two contradictory characteristics of the nonwoven fabric and the filtration speed can be obtained. That is, it was natural that the relationship between the air permeability and the initial bubble point pressure was such that as one became larger, the other became smaller, but the nonwoven fabric of the present invention became a sheet whose balun was very excellent, and a filter or heat insulating material. Suitable for applications such as bacterial barrier.

[0013] The non-woven fabric, which has less rope and string, and is excellent in flexibility, has a uniform pore size formed of fibers as compared with the conventional non-woven fabric, and has been found to exhibit characteristics suitable for filters, heat insulating materials, and the like. did. That is, since there is no rope, shot, or pinhole, there is no channeling, and the dead space where no fluid passes at all is significantly reduced. Therefore, the air permeability can be increased at the same maximum pore size, and the maximum pore size can be reduced at the same air permeability.

If the non-woven fabric has a dry heat shrinkage ratio of more than 3%, the fibers shrink when heated for the purpose of sterilization or cleaning of the heat insulating material when used as a filter medium, and the distribution of the fibers is reduced. However, it is not preferable because good filtration characteristics cannot be realized due to variation.

One of the methods for producing such a non-woven fabric exhibiting excellent filter and heat insulating properties is to contact the molten polymer with a high-temperature, high-speed traction fluid to sufficiently prepare the polymer in the process for producing a micro-fiber non-woven fabric. In order to facilitate cooling of the fibers after traction has been completed and thinning has been completed, a diameter of 0.1 m
A water droplet of 20 μm to 20 μm is applied by a nepliser or the like, and the cooling efficiency of the fiber can be improved by lowering the temperature of the traction fluid around the fiber and the atmosphere by using the latent heat of evaporation of the water droplet. This can be implemented by means for preventing the droplet from coming into contact with the fiber in the middle of falling. In addition, for the purpose of preventing the scattering of the fibers and for improving the releasability from the conveyor net, a method of applying a liquid such as water or a solvent to the completely solidified fibers, or a foaming agent or a hydrophilic agent for imparting new properties. A method for producing a nonwoven fabric using a method for applying a liquid droplet containing an agent or the like in combination is also preferable.

As a method for generating mist droplets used in the spinning process in order to express such excellent characteristics, a droplet generating device such as an atomizer or a nebulizer may be used. is not. Particularly preferably, a mist generator using ultrasonic waves is suitable for obtaining droplets having a small particle diameter.

The droplet size used in the present invention is 2
It is necessary that the number concentration of droplets of 0 μm or more is 5% or less. More preferably, it does not exceed 15 μm. Large particles of 20 μm or more are larger than the diameter of the fiber to be manufactured, and they adhere to the fiber by inertial collision and cause cooling unevenness of the fiber, thus causing the fiber diameter to become thicker or thinner due to stress concentration. Or let it. The thickness unevenness of the fiber, which is considered to be caused by mist water droplets of 20 μm or more adhering to the fiber, is reflected in the CV% (fiber diameter standard deviation divided by the average value and expressed as a percentage), which is the fiber diameter variation. Experiments have shown that reducing the droplets with a large mist diameter reduces CV% by at least 5-10%. In addition, the presence of large droplets tends to cause problems such as disturbing the flow of the entrained flow, and the adhesion of droplets to a nozzle surface or the like to lower the temperature.

When the generation of droplets of 20 μm or more cannot be suppressed by the mist generator, it is possible to use an impactor to separate the droplets from the balance between inertia and drag. By any chance
5% in number concentration even if particles of 20 μm or more are mixed
Below, the effect is small. Particles smaller than 0.1 μm have no problem even if they are present, but it has been found that the latent heat is small and the effect on the present invention is extremely small.

The mist droplets thus generated are consumed to cool down the temperature of the entrainment and traction fluids.
In other words, the entrainment flow loses the necessary amount of latent heat due to the evaporation of the droplets. By this cooling, it is possible to prevent the fiber diameter from being increased and the sheet from being wrinkled due to the relaxation due to the contraction of the fibers and the effect of the polymer elongation recovery as a viscoelastic body. In addition, a phenomenon in which the end of the sheet is warped upward on the support may be observed for the same reason, but improvement can be achieved by applying mist.

The distance between the spinneret and the collector (also called a support or a collector) is preferably between 6 cm and 30 cm. Further, the distance is preferably between 8 cm and 25 cm. It is preferable to increase the distance from the viewpoint of cooling. However, as the distance increases, the number of ropes formed by entanglement of a plurality of fibers increases. When the rope is present, it is considered that the distribution of the fibers becomes sparse in the vicinity of the rope, so that the drift is likely to occur, and the texture is not smooth.

On the other hand, when the distance between the nozzle and the collector is reduced, the number of shots that are cut into balls in the course of thinning of the polymer increases and the texture of the sheet is significantly reduced. Also, cooling is delayed due to the thickness of the fibers, and the fibers around the fall are melted to form pinholes, which adversely affects filter performance and the like. It has been extremely difficult to obtain such a sheet with very few shots and ropes until now, but it has become possible for the first time by providing a mist. Note that the distance between the nozzle and the collector needs to be increased as the amount of single-hole discharge of the polymer increases.
That is, when the discharge amount of the polymer single hole increases, the distance at which the thinning is completed increases, and the amount of heat brought in by the polymer and the accompanying air flow increases, so that pinholes are easily generated. If the single hole discharge rate is less than 0.5 g / min. Per hole, it is necessary to optimize conditions such as lowering the temperature of the entrained air flow entrained in the jet without applying mist. Although the occurrence of shots can be considerably suppressed by optimizing the conditions, it is possible to obtain a better nonwoven fabric by applying mist.

In the present invention, a mist is applied in the vicinity of the collector in order to prevent scattering of the fibers, or a method of applying a liquid such as water to completely solidified fibers for post-processing by dipping a sheet or the like. Is one of preferred modes. In addition, a method of adding a liquid such as a foaming agent or a hydrophilizing agent to the mist droplets in order to impart new characteristics is also one of the preferable embodiments. In this case, the particle size of the droplet is not particularly limited, but a large droplet of 20 μm or more is a preferable form for suppressing scattering of the fiber. Also, 2
Droplets of less than 0 μm are effective in uniformly applying a drug such as a foaming agent or a hydrophilizing agent. The application of these agents by post-processing is easy and quick, while the uniformity is poor due to the slow entry of the droplets into the micropores and the processing time is required. Even when the agent is not sufficiently applied by the mist, the effect of increasing the wetting speed during post-processing is also recognized.

[0023]

【Example】

Examples 1 to 4 The present invention will be specifically described with reference to the following examples.
It does not limit the embodiments of the present invention at all. Several types of ultrafine fibers having different fiber diameters were produced by melt blow method using polypropylene having a melt index of 300 or 1000 as a traction fluid and air. The injection pressure of air was 2.0 to 3.0 kg / cm ² at the original pressure, the discharge amount of the polymer was 0.1 to 1.0 g / min per single hole, and the temperature of the air and the polymer were as shown in Table 1. At this time, air provided with a droplet mist having a maximum particle size of 8 to 20 μm immediately below the nozzle surface was blown uniformly on the fibers before being collected by the collector. Table 1 shows the obtained results.

[0024]

[Table 1]

As is evident from Table 1, the nonwoven fabrics of Examples 1 to 4 had no shot having a fiber diameter of 0.5 to 10 μm and had a good balance between air permeability and filtration performance.
Further, by adding a thick hydrophilizing agent to the mist,
About 50%, the wetting rate of the aqueous post-processed material increased. In addition, the following method was used for the measuring method. The same applies to the comparative example. Fiber diameter Ten images were taken at three arbitrary positions on the sheet at a magnification of 1000 times using a scanning electron microscope. The fiber diameter was measured at 100 points at each position from the photograph, and the average value was obtained. Bubble point was measured according to ASTM 316-70. As a liquid to be used, a special grade reagent isopropanol was used, and the pressure when the first bubble was generated with the increase in pressure was determined. Air permeability (Fragile) The measurement was performed according to ASTM D737. The value obtained by dividing the air permeability at a 0.5 inch water column pressure by the cross-sectional area to obtain the air permeability was converted to a basis weight of 30 g / m 2. Particle size The measurement was performed using a commercially available dust counter (Rion type KC14). Dry heat shrinkage Measured at an appropriate temperature of about 60 to 80% of the melting point, such as 130 ° C for polypropylene and 160 ° C for polyester. Filtration accuracy Using the same device as used for measuring the particle diameter, supply the air to the filter medium at 5.3 cm / sec,
The population concentration and outlet concentration of m particles were measured, and the difference between the difference and the inlet concentration was defined as the filtration accuracy.

Comparative Examples 1-4 Spinning was carried out under the same conditions as in Examples 1-4, without applying mist. The results are shown in Table 2.

As is clear from Table 2, the balance between the bubble point pressure and the air permeability was poor, and the effect of the mist application was newly recognized.

[0028]

[Table 2]

Example 5, Comparative Example 5 The sheets of Example 2 and Comparative Example 2 were subjected to a calender press treatment to adjust the filling ratio to 0.6. When the performance as a liquid filter was measured, the results shown in Table 3 were shown. The liquid phase collection efficiency was as follows: 0.47 μm of monodispersion, 0.02 wt% of polystyrene latex was filtered at a linear speed of 3 cm / min, and the inlet and outlet concentrations were measured. It means the divided value.

[0030]

[Table 3]

[0031]

EFFECT OF THE INVENTION It is made of ultrafine fiber, and has a bubble point pressure,
The effect is to provide a nonwoven fabric having a good balance between air permeability and filtration accuracy, and a method for reliably producing this nonwoven fabric.

Claims (2)

(57) [Claims] An average fiber diameter of 0.1 to 3.0 μm is made of ultrafine fibers, and the flow rate of air when a pressure of 0.5 inch / cm ² of water is applied is divided by the area to obtain 30 g. / m a 0.5 ~ 4.5 cm / sec ² basis weight terms, and microfine fiber nonwoven fabric first bubble generation pressure obtained by the bubble point measurement method is characterized in that it is 250 mmAq (water column) or . 2. A method for producing a microfiber nonwoven fabric by bringing a molten polymer into contact with a high-temperature, high-speed traction fluid, wherein the polymer is sufficiently drawn by the traction fluid to complete the thinning.
In the surrounding gas atmosphere, which is mixed with the traction fluid, a diameter of 20
Fiber containing mist containing water droplets of μm or more in number concentration of 5% or less
The method for producing a microfiber nonwoven fabric according to claim 1, wherein the non-woven fabric is applied so that the droplets do not come into contact with the non-woven fabric.