JP4792846B2 - Nonwoven manufacturing method - Google Patents

Description

  The present invention relates to a nonwoven fabric made of ultrafine fibers. In particular, the present invention relates to a high-performance nonwoven fabric that exhibits high collection and low pressure loss as an air filter.

  The melt blow method, which is one of the nonwoven fabric manufacturing methods, is generally made into a fiber by hot air jetting a thermoplastic polymer extruded from a spinneret, and formed into a web by utilizing the self-bonding property of the fiber. This method does not require a complicated process compared to other nonwoven fabric manufacturing methods such as the spunbond method, and since thin fibers of several tens to several microns can be easily obtained, the melt blown nonwoven fabric is a filter material for filter products. In particular, it is often used for air filter media.

  The performance required for the air filter is “high collection” capable of collecting a large amount of micro dust, and “low pressure loss” with low resistance when gas passes through the air filter.

  In order to obtain a filter medium having high collection performance, it is suitable that the melt blown nonwoven fabric to be formed has a fineness, but on the other hand, the pressure loss is increased by increasing the fiber density in the nonwoven fabric.

  Moreover, in order to obtain a filter medium with low pressure loss, it is suitable that the melt blown nonwoven fabric to be formed has a large fineness, but on the other hand, the gap between the fibers in the nonwoven fabric is widened, so that the collection performance is lowered. .

  Thus, “high collection” and “low pressure loss” are in a contradictory relationship, and a melt blown nonwoven fabric that satisfies these requirements at the same time has not been obtained in the prior art.

  For example, according to Patent Document 1, by increasing the average molecular weight of the fiber and narrowing the molecular weight distribution, the fiber diameter unevenness and the unevenness of the basis weight are reduced in the nonwoven fabric. Although it could be obtained, the pressure loss was high.

  According to Patent Document 2, an ultrafine fiber meltblown nonwoven fabric excellent in collection performance could be obtained by increasing the melt flow rate of the raw material and narrowing the molecular weight distribution, but the pressure loss is high. Met.

  Furthermore, according to Patent Document 3, by adjusting the raw material viscosity and the cloth-making conditions, a fine fiber melt-blown nonwoven fabric with fine filtration and fiber diameter variation (fiber diameter variation rate: CV%) is reduced, and the filtration accuracy is good. Although it could be obtained, the pressure loss was high.

  As described above, the conventional melt blown nonwoven fabric for air filter media is mainly used for the purpose of “high collection” and has a low fiber diameter variation rate and is a nonwoven fabric mainly composed of fine fibers. The pressure loss was high, and it was difficult to satisfy the requirements of air filter “high collection” and “low pressure loss” at the same time.

Patent Document 4 is known for non-woven fabric composed of ultrafine fibers. According to this, blend spinning of a mixture of polyvinyl alcohol and polyolefin is performed by a melt blow method, with polyvinyl alcohol as a sea component and polyolefin as an island component. A sea-island type composite fiber is obtained, and this composite fiber is processed with a water needle to remove sea components, thereby obtaining a nonwoven fabric with a basis weight of 50 g / m ² made of ultrafine fibers of 0.005 to 0.5 μm. It is not clear regarding the diameter fluctuation rate and filter performance. So far, no ultrafine fiber nonwoven fabric with a large fiber diameter variation rate is known.
Japanese Patent No. 2775959 JP 2002-151560 A JP-A-8-144166 JP-A-5-71006

  An object of the present invention is to provide a nonwoven fabric composed of ultrafine fibers and having a high fiber diameter variation rate, and to provide a nonwoven fabric that has a low pressure loss and excellent collection performance, and can be suitably used for an air filter. There is to do.

  In order to obtain a nonwoven fabric excellent in “high collection” and “low pressure loss”, the present inventors constituted (1) a nonwoven fabric with ultrafine fibers, for example, fibers refined to the nano-order level, (2) It was considered that the fiber diameter variation rate of the ultrafine fibers constituting the nonwoven fabric should be increased so that thick fibers and thin fibers exist simultaneously and uniformly. In this case, since the entire nonwoven fabric is composed of ultrafine fibers, the collection performance is improved, and since these ultrafine fibers have variations in fiber diameter, relatively thick fibers become beams in the nonwoven fabric. Creates voids to prevent an increase in pressure loss, and fine fibers that exist between thick fibers collect dust, satisfying both "high collection" and "low pressure loss" even when the nonwoven fabric has a low basis weight. A high performance nonwoven fabric is obtained.

That is, the nonwoven fabric of this invention which solves the said subject has the following structure.
(1) An easily soluble polymer is composed of a thermoplastic polymer by eluting a readily soluble polymer component of a nonwoven fabric composed of fibers that form a sea-island structure with a sea component and a thermoplastic polymer with an island component. A method for producing a nonwoven fabric, comprising obtaining a nonwoven fabric having a fiber diameter of 50 to 800 nm and a fiber diameter fluctuation rate of 55% or more.
(2) The method for producing a nonwoven fabric according to (1), wherein the easily soluble polymer is polylactic acid.
(3) The method for producing a nonwoven fabric according to (1) or (2), wherein the nonwoven fabric is produced by a melt blow method.
(4) The manufacturing method of the nonwoven fabric as described in said (1) which obtains the nonwoven fabric whose 0.5 g / m < ² > equivalent pressure loss is 0.5-10 Pa and whose QF value is 0.26 Pa < ^-1 > or more.
(5) The manufacturing method of the nonwoven fabric as described in said (1) which obtains the nonwoven fabric whose fabric weight is 1-15 g / m < ² > .
(6) The manufacturing method of the nonwoven fabric as described in said (1) which obtains the nonwoven fabric whose said thermoplastic polymer is either polyamide or polyolefin .

  According to the present invention, it is possible to provide a non-woven fabric that has a low pressure loss and at the same time has high collection.

  The nonwoven fabric of the present invention is a nonwoven fabric characterized by comprising a thermoplastic polymer and having an average fiber diameter of 50 to 800 nm and a fiber diameter fluctuation rate of 55% or more.

  Examples of the thermoplastic polymer in the present invention include polyamide, polyolefin, polyester, polyphenylene sulfide and the like. When the melting point of the thermoplastic polymer is 165 ° C. or higher, the heat resistance of the fiber is good, which is preferable. For example, polypropylene (PP) is 165 ° C, polyethylene terephthalate is 255 ° C, and nylon 6 (N6) is 220 ° C. The thermoplastic polymer used in the present invention is preferably either polyamide or polyolefin from the viewpoint of alkali resistance and electret properties. Further, the thermoplastic polymer may contain additives such as a weathering agent and an antioxidant. Further, other components may be copolymerized as long as the properties of the polymer are not impaired.

  The fibers constituting the nonwoven fabric of the present invention have an average fiber diameter of 50 to 800 nm. More preferably, it is 60-750 nm, More preferably, it is 70-700 nm. In general, the smaller the fiber diameter is, the higher the collection performance is. However, when the average fiber diameter is smaller than 50 nm, the strength of the nonwoven fabric is weakened, causing a problem in process passability. On the other hand, when the average fiber diameter is larger than 800 nm, the above-mentioned preferable effect brought about by the ultra-thinning becomes insufficient.

  The fiber diameter fluctuation rate is expressed as a percentage obtained by dividing the standard deviation of the fiber diameter by the average fiber diameter. The fiber diameter fluctuation rate is preferably 55% or more, more preferably 58% or more, and still more preferably. Is 60% or more. The smaller fiber diameter variation rate means that the variation of the fiber diameter constituting the nonwoven fabric is small. If the fiber diameter variation rate is less than 55%, the thick fiber and the thin fiber are present simultaneously. The effect on “low pressure loss” and “high collection” decreases, which is not preferable.

  In addition, the average fiber diameter and fiber diameter fluctuation | variation rate in this invention say the value calculated | required with the following method. That is, 30 measurement samples of 1 cm × 1 cm were collected from an arbitrary location of the nonwoven fabric, the magnification was adjusted to 80000 times with a scanning electron microscope, and each fiber surface photograph from the collected samples was 30 in total. Take a picture. Measure all fiber diameters in the photograph that can be clearly confirmed, and use the average value as the average fiber diameter. The fiber diameter fluctuation rate is obtained by dividing the standard deviation of the fiber diameter by the average fiber diameter.

  The method for obtaining the nonwoven fabric of the present invention is not particularly limited, but a nonwoven fabric composed of fibers that form a sea-island structure in which an easily soluble polymer is a sea component and a thermoplastic polymer is an island component by a melt blow method. After being obtained, the nonwoven fabric of the present invention can be obtained by eluting the easily soluble polymer component of the nonwoven fabric with a solvent. At that time, a nonwoven fabric satisfying the above average fiber diameter and fiber diameter variation rate by optimizing the polymer species and composition ratio constituting the sea-island fibers and adjusting the spinning conditions such as polymer discharge rate, nozzle temperature, and air pressure. Obtainable.

Further, the nonwoven fabric of the present invention is excellent in low pressure loss and high collection performance, preferably 5 g / m ² equivalent pressure loss is 0.5 to 10 Pa, and QF value is 0.26 Pa ⁻¹ or more. . The QF value here is calculated by the following equation.
QF value (Pa ⁻¹ ) = − [ln (1- [collecting performance (%)] / 100)] / [pressure loss (Pa)]
“Capturing performance” in the formula represents the degree of capturing of 0.3 to 0.5 μm polystyrene particles under a through-air speed of 1.5 m / min, and the number D of particles on the upstream side of the nonwoven fabric and the downstream side From the number d of particles on the side, the following formula is used.
Collection efficiency (%) = [1- (d / D)] × 100
Further, the “pressure loss” is obtained by measuring a difference in static pressure between the upstream side and the downstream side under a through wind speed of 1.5 m / min with a pressure gauge.
Furthermore, “5 g / m ² equivalent pressure loss” is obtained by the following equation.
5 g / m ² equivalent pressure loss (Pa) = actual pressure loss (Pa) × 5 (g / m ² ) / actual weight (g / m ² )
By setting the average fiber diameter and the fiber diameter variation rate of the fibers constituting the nonwoven fabric of the present invention within the above-described range, that is, by forming the nonwoven fabric with ultrafine fibers having large fiber diameter variation, relatively thick fibers are contained in the nonwoven fabric. At the same time as a beam, a gap is formed to prevent an increase in pressure loss, and fine fibers existing between thick fibers collect dust, resulting in a pressure loss equivalent to 5 g / m ² and a low pressure loss as indicated by the QF value. And the nonwoven fabric excellent in the high collection performance can be obtained.

A more preferable range of the pressure loss corresponding to 5 g / m ² is 0.5 to 9 Pa, and more preferably 0.8 to 8 Pa. Further, QF value is more preferably at 0.28Pa ^-1 or more, further preferably 0.30 Pa ^-1 or less.

Moreover, since the nonwoven fabric of this invention is comprised with a nano-order extra fine fiber, since high collection performance is obtained, it exhibits excellent filter performance with a low basis weight. Therefore, it is preferable that the fabric weight of the nonwoven fabric of this invention is 1-15 g / m < ² >. More preferably, it is 1-12 g / m < ² >, More preferably, it is 2-10 g / m < ² >.

  The nonwoven fabric of the present invention can be obtained by eluting, with a solvent, a readily soluble polymer component of a nonwoven fabric composed of fibers that form a sea-island structure in which a readily soluble polymer is a sea component and a thermoplastic polymer is an island component. Is preferred. The readily soluble polymer that is a sea component is not compatible with the thermoplastic polymer that constitutes the island component and needs to have different solubility in a solvent. In order to elute the readily soluble polymer, it is preferable to use an aqueous solution as the solvent from the viewpoint of reducing environmental load, and specifically, an alkaline aqueous solution or hot water is preferably used. For this reason, examples of the readily soluble polymer include polymers that are alkali-hydrolyzed such as polyester and polycarbonate, and hot water-soluble polymers such as polyalkylene glycol and polyvinyl alcohol, and derivatives thereof. The solvent to be used may be appropriately selected in consideration of the solvent to be used. Among them, the easily soluble polymer is preferably polylactic acid from the viewpoint of excellent effect of increasing the fiber diameter variation.

As polylactic acid, poly (D-lactic acid), poly (L-lactic acid), a copolymer of D-lactic acid and L-lactic acid, or a blend thereof is preferably employed. The weight average molecular weight of the polylactic acid-based resin is preferably 50,000 or more, more preferably 100,000 or more from the viewpoint of improving spinnability. Further, from the viewpoint of facilitating fiber diameter reduction, it is preferably 200,000 or less, and more preferably 150,000 or less.
In the present invention, the thermoplastic polymer constituting the sea-island fiber together with the easily soluble polymer is preferably either a polyamide from the viewpoint of alkali resistance or a polyolefin from the viewpoint of electret properties. In the case of polyamide, nylon 6, nylon 66, nylon 6-10, nylon 12 and copolymers thereof can be used alone or in combination. In the case of polyolefin, polyethylene, polypropylene, and copolymers thereof can be used alone or in combination. Among these, nylon 6 or polypropylene is more preferably used because it has a small melting point difference from polylactic acid, has high affinity, and good spinnability when composite spinning.

  Moreover, when the nonwoven fabric of this invention is comprised mainly from a polypropylene, it is preferable that the nonwoven fabric of this invention is electretized. The electretization method is not particularly limited, but a corona charging method or a method of electretization by applying water to the nonwoven fabric sheet and drying it (for example, JP 9-501604 A, The method described in Japanese Unexamined Patent Publication No. 2002-249978 and the like is preferably used. In the case of the corona charging method, an electric field strength of 15 kV / cm or more, preferably 20 kV / cm or more is suitable.

  Further, from the viewpoint of improving weather resistance and improving electret performance, it is preferable that the nonwoven fabric of the present invention contains at least one selected from the group consisting of hindered amine compounds and triazine compounds.

  As the hindered amine compound, poly [(6- (1,1,3,3-tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) ((2,2,6,6- Tetramethyl-4-piperidyl) imino) hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino)] (manufactured by Ciba Geigy, Chima Soap 944LD), dimethyl-1- (2-hydroxyethyl succinate) ) -4-Hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (Ciba Geigy, Tinuvin 622LD), 2- (3,5-di-tert-butyl-4-hydroxybenzyl) -2-n -Butyl malonate bis (1,2,2,6,6-pentamethyl-4-piperidyl) (manufactured by Ciba Geigy, Tinuvin 144) and the like.

As the triazine-based additive, the poly [(6- (1,1,3,3-tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) ((2,2 , 6,6-tetramethyl-4-piperidyl) imino) hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino)] (manufactured by Ciba-Geigy, Chimersoap 944LD), 2- (4,6 -Diphenyl-1,3,5-triazin-2-yl) -5-((hexyl) oxy) -phenol (manufactured by Ciba Geigy, Tinuvin 1577FF) and the like. Among these, hindered amine compounds are particularly preferable.
Although content of a hindered amine type compound or a triazine type compound is not specifically limited, It is preferable that it is the range of 0.5-5 weight%, and it is more preferable that it is the range of 0.7-3 weight%.

  Further, in addition to the above compounds, usual additives such as heat stabilizers, weathering agents, polymerization inhibitors, etc., which are generally used for non-woven sheets of electret processed products may be added.

  Although the manufacturing method of the nonwoven fabric of this invention is not specifically limited, From the point of obtaining the ultrafine fiber with a large variation in fiber diameter, the following method is preferably employed.

  That is, the nonwoven fabric of the present invention is preferably manufactured through a spinning step by a melt blow method, and is composed of fibers that form a sea-island structure in which an easily soluble polymer is a sea component and a thermoplastic polymer is an island component. After obtaining the nonwoven fabric, the nonwoven fabric of the present invention can be obtained by eluting the readily soluble polymer component of the nonwoven fabric with a solvent. In order to obtain a nonwoven fabric composed of ultrafine fibers with large fiber diameter variations, sea island fibers can be obtained by optimizing the polymer species and composition ratio of sea island fibers and adjusting spinning conditions such as polymer discharge rate, nozzle temperature, and air pressure. Optimization of the average fiber diameter is important and will be described in detail below.

  The method for obtaining the nonwoven fabric composed of fibers forming such sea-island structure by the melt-blowing method is not particularly limited. Two types of polymer chips are mixed and supplied to the extruder hopper of the melt-blowing machine, and extruded. Kneading in-machine and feeding directly to the die, or blending two types of polymer in advance with a kneading extruder or stationary kneader to produce a polymer alloy chip, which is melted in the extruder Although the method of supplying to a nozzle | cap | die part is mentioned, The latter method is preferably employ | adopted from the effect with respect to ultrafine fiber formation and fiber diameter variation of an island component polymer.

  Here, in order to obtain nano-order ultrafine fibers, it is important to control the island size of the island polymer in the sea-island fiber that is the precursor of the nonwoven fabric of the present invention. Here, the island size means the diameter of the island polymer portion in the sea-island fiber cross section. Since the diameter of the ultrafine fiber is determined by the island size in the precursor in addition to the melt blow spinning conditions, the kneading of the polymer to be alloyed becomes very important.

  Regarding the preparation of the polymer alloy chip, a specific guideline for kneading depends on the polymer to be combined, but when using a kneading extruder, it is preferable to use a biaxial extrusion kneader, and use a static kneader. In this case, the number of divisions is preferably 1 million or more. Moreover, in order to avoid blend spots and fluctuations in the blend ratio over time, it is preferable to measure each polymer independently and supply the polymers to the kneading apparatus independently. At this time, the polymer may be supplied separately as a chip, or may be supplied separately in a molten state. Also, two types of polymers may be supplied to the root of the extrusion kneader, or a side feed that supplies one component from the middle of the extrusion kneader.

  When a twin screw extrusion kneader is used as the kneading apparatus, it is preferable to achieve both high kneading and suppression of the polymer residence time. The screw is composed of a feeding part and a kneading part, but it is preferable that the kneading part length is 20% or more of the effective screw length, so that high kneading can be achieved. In addition, when the kneading part length is 40% or less of the effective screw length, excessive shear stress can be avoided and the residence time can be shortened, and thermal degradation of the polymer and gelation of the polyamide component, etc. are suppressed. be able to. In addition, by positioning the kneading part on the discharge side of the twin-screw extruder as much as possible, it is possible to shorten the residence time of the mixed word and suppress the reaggregation of the island polymer. In addition, when strengthening kneading, it is possible to provide a screw having a backflow function for sending the polymer in the reverse direction in an extrusion kneader.

  Furthermore, as a vent type, the decomposition gas during kneading is sucked or the water content in the polymer is reduced to suppress polymer hydrolysis, and the amount of amine end groups in polyamide and carboxylic acid end groups in polyester is also suppressed. Can do.

In addition, the b ^* value of the L ^* a ^* b ^* color system, which is an index of coloration of the blend polymer chip, is preferably 10 or less, so that the color tone when fiberized can be adjusted, which is preferable. In addition, when using a hot water-soluble polymer as an easily soluble component, it generally has poor heat resistance and is likely to be colored due to its molecular structure, but it is possible to suppress coloring by an operation for shortening the residence time as described above. .

  Further, in order to finely disperse the island component of the blend polymer chip, a combination of polymers is also important.

In order to make the fiber cross section made of the thermoplastic polymer as an island component close to a circle, the island polymer and the sea polymer are preferably incompatible. However, it is difficult for the island polymer to be sufficiently finely dispersed by a simple combination of incompatible polymers. For this reason, it is preferable to optimize the compatibility of the polymer to be combined, but one index for this purpose is the solubility parameter (SP value). The SP value is a parameter reflecting the cohesive strength of substances defined by SP value = (evaporation energy / molar volume) ^1/2 , and a polymer alloy having good compatibility can be obtained between those having close SP values. There is sex. The SP value is known for various polymers, and is described, for example, in “Plastic Data Book”, edited by Asahi Kasei Amidus Corporation / Plastics Editorial Department, page 189. It is preferable that the difference between the SP values of the two polymers is 1 to 9 (MJ / m ³ ) ^{1/2 because} it is easy to achieve both circularization of island domains and ultrafine dispersion due to incompatibility.

Furthermore, melt viscosity is also important, and if the polymer forming the island is set lower, the island polymer is likely to be deformed by shearing force, so that the island polymer is likely to be finely dispersed, which is preferable from the viewpoint of making ultrafine fibers. . However, if the island polymer is excessively low in viscosity, it tends to be seamed and the blend ratio with respect to the whole fiber cannot be increased. Therefore, the island polymer viscosity is preferably 1/10 or more of the sea polymer viscosity. At this time, the melt viscosity is a value at a shear rate of 121.6 sec ⁻¹ at the die surface temperature during spinning.
Moreover, the ratio of the easily soluble polymer and the thermoplastic polymer of the sea-island fiber used in the present invention is preferably 10/90 to 90/10% by weight because of the effect of the island component polymer on ultrafine fiber and fiber diameter variation. More preferably, it is 20 / 80-90 / 10, More preferably, it is 50 / 50-80 / 20 weight%.

  As spinning conditions in the melt blow method, there are polymer discharge amount, nozzle temperature, air pressure, etc., but in order to obtain ultrafine fibers, the average fiber diameter of sea-island fibers which are precursors of the nonwoven fabric of the present invention is 1 to 15 μm. Thus, these conditions may be adjusted as appropriate. In general, the fiber diameter of the nonwoven fabric obtained by the melt-blowing method inherently varies due to the characteristics of the production method, but in the case of the nonwoven fabric of the present invention, the dispersion of the island component fiber diameter in the sea-island fibers is added to this, so A fiber having a larger variation than that obtained by the melt blow method is obtained. Furthermore, when the sea component polymer is polylactic acid, the effect becomes more prominent.

  The production method of the present invention makes it possible to obtain a nonwoven fabric composed of nano-order ultrafine fibers having large fiber diameter variations by optimizing the polymer and spinning conditions as described above.

  The nonwoven fabric of the present invention can be used as a filter medium. The filter medium is suitable for high-performance applications such as air filters in general, air-conditioning filters, air cleaner filters, and automobile cabin filters, but the application range is not limited thereto.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, it is not limited to these Examples. The characteristic values used in the examples are measured by the following measuring method.

(1) Weight per unit area The weight of a 15 cm × 15 cm sheet was measured, and the obtained value was converted to a value per 1 m ² to obtain a basis weight (g / m ² ).

(2) Average fiber diameter, fiber diameter fluctuation rate 30 measurement samples of 1 cm × 1 cm were collected from any location of the nonwoven fabric, the magnification was adjusted to 80000 times with a scanning electron microscope, and the fiber surface from the collected samples A total of 30 photos were taken, one for each photo. All of the photographs in which the fiber diameter was clearly confirmed were measured, and the average value was taken as the average fiber diameter. The fiber diameter fluctuation rate was obtained by dividing the standard deviation of the fiber diameter by the average fiber diameter.

(3) Collection performance, pressure loss 15 cm × 15 cm measurement samples were collected at 10 places in the longitudinal direction of the nonwoven fabric, and each sample was measured with the collection efficiency measuring apparatus shown in FIG. In this collection efficiency measuring apparatus, a dust storage box 2 is connected to an upstream side of a sample holder 1 for setting a measurement sample M, and a flow meter 3, a flow rate adjusting valve 4 and a blower 5 are connected to a downstream side. In addition, the particle counter 6 is used for the sample holder 1, and the number of dusts on the upstream side and the number of dusts on the downstream side of the measurement sample M can be measured via the switching cock 7. Furthermore, the sample holder 1 includes a pressure gauge 8 and can read the static pressure difference between the upstream and downstream of the sample M. In measuring the collection efficiency, a 0.309U 10% polystyrene solution (manufacturer: Nacalai Tech) is diluted 200 times with distilled water and filled in the dust storage box 2. Next, the sample M is set in the holder 1, and the air volume is adjusted by the flow rate adjusting valve 4 so that the filter passing speed is 1.5 m / min, and the dust concentration is 10,000 to 40,000 pieces / 2.83 × 10 ^{−. 4} m ³ (0.01 ft ³ ) was stabilized, and the number of dusts D upstream of the sample M and the number of dusts d downstream were measured 10 times per sample with a particle counter 6 (manufactured by Lion, KC-01B). Based on JIS K-0901, the collection efficiency (%) of 0.3 to 0.5 μm particles was determined by the following formula. The average value of 10 samples was taken as the final collection performance.

Collection efficiency (%) = [1- (d / D)] × 100
However,
d: 10 times measurement total number of downstream dust D: 10 times measurement total number of upstream dust Further, the pressure loss was obtained by reading the static pressure difference between the upstream and downstream of the sample M at the time of collecting efficiency measurement with a pressure gauge 8. The average value of 10 samples was taken as the final pressure loss.

(4) Pressure loss equivalent to 5 g / m ^{2 The} pressure loss obtained in the above item (3) was converted into a pressure loss equivalent to 5 g / m ² by the following formula.
5 g / m ² equivalent pressure loss (Pa) = actual pressure loss (Pa) × 5 (g / m ² ) / actual weight (g / m ² )
(5) QF value The QF value was calculated by the following formula.
QF value (Pa ⁻¹ ) = − [ln (1- [collection efficiency (%)] / 100)] / [pressure loss (Pa)]
Example 1
Melt viscosity 500Pa · s (230 ℃, shear rate 121.6sec ^-1), and polylactic acid having a melting point of 170 ° C., a melt viscosity 300Pa · s (230 ℃, shear rate 121.6sec ^-1), nylon 6 having a melting point of 220 ° C. Was kneaded at 230 ° C. at a blend ratio of 6/4 with a biaxial extrusion kneader to obtain a polymer alloy chip.

Using this tip, a nozzle having a discharge hole with a diameter of 0.4 mm (hole pitch: 1 mm, number of holes: 151 holes, width: 150 mm), melt discharge method, polymer discharge rate of 32 g / min, nozzle temperature A nonwoven fabric having a basis weight of 7.5 g / m ² was obtained by spraying under conditions of 230 ° C. and an air pressure of 0.05 MPa and adjusting the collection conveyor speed.

Next, this nonwoven fabric was treated with alkali to elute the polylactic acid component, and after obtaining a nonwoven fabric with a basis weight of 3 g / m ² , the characteristic values were measured and shown in Table 1.

Example 2
Polylactic acid having a melt viscosity of 350 Pa · s (230 ° C., shear rate of 121.6 sec ⁻¹ ) and a melting point of 170 ° C., and polypropylene having a melt viscosity of 300 Pa · s (230 ° C., shear rate of 121.6 sec −1) and a melting point of 165 ° C. A triazine compound Kimasorb 944 (made by Ciba Geigy) added at 1 wt% was kneaded at 230 ° C. at a blend ratio of 8/2 with a biaxial extrusion kneader to obtain a polymer alloy chip.

Using this tip, the same die as in Example 1 is used, and the polymer is ejected under the conditions of a polymer discharge rate of 32 g / min, a nozzle temperature of 230 ° C., and an air pressure of 0.20 MPa by the melt blow method to adjust the collection conveyor speed. As a result, a nonwoven fabric having a basis weight of 15 g / m ² was obtained.

Next, this nonwoven fabric was treated with alkali to elute the polylactic acid component, and after obtaining a nonwoven fabric with a basis weight of 3 g / m ² , the characteristic values were measured and shown in Table 1.

Example 3
The nonwoven fabric obtained in Example 2 was subjected to electret treatment with an applied voltage of 25 kV / cm by the corona charging method, and then the characteristic values were measured and shown in Table 1.

Comparative Example 1
Polyvinyl alcohol having a melt viscosity of 450 Pa · s (230 ° C., a shear rate of 121.6 sec ⁻¹ ) and a melting point of 180 ° C. and the polypropylene used in Example 2 were mixed in the form of chips at a blend ratio of 5/5. Using this mixed tip, the same die as in Example 1 was used to inject the polymer at a discharge rate of 32 g / min, a nozzle temperature of 230 ° C., and an air pressure of 0.2 MPa by the melt blow method to adjust the collection conveyor speed. As a result, a nonwoven fabric having a basis weight of 5 g / m ² was obtained.

Next, this nonwoven fabric was treated with hot water to elute the polyvinyl alcohol component, and after obtaining a nonwoven fabric with a basis weight of 3 g / m ² , the characteristic values were measured and shown in Table 1.

Comparative Example 2
A blend polymer chip was obtained in the same manner as in Example 1 except that the polylactic acid and polypropylene used in Example 1 had a blend ratio of 4/6.

A nonwoven fabric having a basis weight of 5 g / m ² was obtained by the melt blow method in the same manner as in Example 1 except that this chip was used and the collection conveyor speed was adjusted.

Next, this nonwoven fabric was treated with alkali to elute the polylactic acid component, and after obtaining a nonwoven fabric with a basis weight of 3 g / m ² , the characteristic values were measured and shown in Table 1.

Comparative Example 3
The polypropylene used in Example 1 was used as a raw material without blending with other polymers, and the same die as in Example 1 was used, and the polymer discharge rate was 32 g / min, the nozzle temperature was 280 ° C., and the air pressure was 0 The nonwoven fabric having a basis weight of 10 g / m ² was obtained by spraying under the condition of 2 MPa and adjusting the collection conveyor speed. Next, this nonwoven fabric was subjected to electret treatment with an applied voltage of 25 kV / cm by the corona charging method, and then the characteristic values were measured and shown in Table 1.

  In Examples 1 to 3 in which polymer alloy chips made using polylactic acid as the sea component and nylon 6 or polypropylene as the island component were used for melt blow spinning, a nonwoven fabric satisfying both the average fiber diameter and the fiber diameter variation rate was obtained. They showed a low pressure drop and a high QF value.

  On the other hand, in Comparative Example 1 in which polyvinyl alcohol was used as the sea component and polypropylene was used as the island component and blend spinning was performed by the melt blow method, although the ultrafine fibers were obtained, the fiber diameter variation rate was a low value. The pressure loss was higher than that of Example 3, which is a basis weight, and the QF value was also low.

  In Comparative Example 2, which uses the same polymer as in Example 1 but has a low sea ratio, a nonwoven fabric that satisfies both the average fiber diameter and the fiber diameter fluctuation rate cannot be obtained, exhibits low collection performance, and has a low QF value. Value.

  In Comparative Example 3 in which the polymer blend was not performed, nano-order ultrafine fibers could not be obtained, and the fiber diameter variation rate was also a low value. The QF value was also low.

  As described above, when the polymer species, the polymer blend method, and the sea-island ratio constituting the sea-island fiber do not satisfy the predetermined condition, the fiber structure in the range specified in the present invention cannot be obtained, and the pressure loss and the QF value are satisfied at the same time. A sheet was not obtained.

  According to the present invention, a non-woven fabric having a low pressure loss and high collection performance can be obtained. This non-woven fabric can be preferably used for an air filter as a filter medium, but its application range is not limited thereto.

It is a schematic diagram showing a measuring device of collection performance and pressure loss.

Explanation of symbols

1: Holder 2: Dust storage box 3: Flow meter 4: Flow control valve 5: Blower 6: Particle counter 7: Switching cock 8: Pressure gauge M: Measurement sample

Claims (6)

Easily soluble polymer sea component by the easily soluble polymer component composed nonwoven from fibers thermoplastic polymer forms a sea-island structure of the island component is eluted by a solvent, consists of a thermoplastic polymer, the average fiber diameter A method for producing a nonwoven fabric, comprising obtaining a nonwoven fabric having a fiber diameter variation rate of 55% or more at 50 to 800 nm . The method for producing a nonwoven fabric according to claim 1 , wherein the easily soluble polymer is polylactic acid. The method for producing a nonwoven fabric according to claim 1 or 2 , wherein the nonwoven fabric is produced by a melt blow method. 5g / m ² The equivalent pressure loss is 0.5 to 10 Pa and the QF value is 0.26 Pa. ^-1 The manufacturing method of the nonwoven fabric of Claim 1 which obtains the nonwoven fabric which is the above. The basis weight is 1-15g / m ² The manufacturing method of the nonwoven fabric of Claim 1 which obtains the nonwoven fabric which is. The manufacturing method of the nonwoven fabric of Claim 1 which obtains the nonwoven fabric whose said thermoplastic polymer is either polyamide or polyolefin.

Images