JP2008138299A - Melt blown non-woven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a melt blown non-woven fabric, in spite of consisting mainly of an aliphatic polyester, excellent in spinning stability and having an extremely small dry heat shrinkage. <P>SOLUTION: This melt blown non-woven fabric consisting of a sea island type conjugate fiber constituted by a sea component of the aliphatic polyester and an island component of any of a polyamide or polyolefin is provided by having 0 to 5% range each of dry shrinkages in length direction and width direction of the non-woven fabric under a condition of 100°C×3 min. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a melt blown nonwoven fabric having an aliphatic polyester as a main component, excellent spinning stability, and low dry heat shrinkage.

  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. Widely used in battery separators and the like.

  Polypropylene has mainly been used as the resin used for melt blown nonwoven fabrics, but recently, from the viewpoint of reducing environmental impact, research on biodegradable polymers using natural resources as a raw material has been active. Polylactic acid (hereinafter abbreviated as PLA), which is a kind of aliphatic polyester, has attracted attention from the viewpoints of mechanical properties and costs. However, when PLA is produced into a non-woven fabric by the melt-blowing method, the melt-blowing method is not substantially stretched, so that the orientation and crystallization of the polymer chain does not proceed, so that there is a problem that the thermal shrinkage is large. A number of proposals have been made for PLA melt-blown nonwoven fabrics, but no proposal for improving heat shrinkage has been made. For polyester-based melt blown nonwoven fabrics, the following proposals have been made.

  For example, a polyester-based ultrafine fiber nonwoven web made of a mixture of an amorphous polyester-based polymer and a crystalline polypropylene-based polymer has been proposed (Patent Document 1). However, since the main component is not a biodegradable polymer, it does not contribute at all to the reduction of environmental impact, and since it is a simple mixture, it is assumed that the size of the polyolefin-based polymer will vary greatly, and spinning stability It is thought that it is inferior to.

  A low-shrinkage melt blown nonwoven fabric composed of a mixed polymer of polyethylene terephthalate and polyolefin polymer has been proposed (Patent Document 2). Again, for the same reason as described above, there is no reduction in environmental load, and it is considered that the spinning stability is poor.

As described above, there has been no actual proposal for obtaining a melt-blown nonwoven fabric that has an aliphatic polyester or an aliphatic polyester as a main component and has excellent spinning stability and low thermal shrinkage.
JP 7-138863 A JP-A-5-51852

  An object of the present invention is to provide a melt blown nonwoven fabric having an aliphatic polyester as a main component, excellent in spinning stability, and extremely low dry heat shrinkage.

The nonwoven fabric of this invention which solves the said subject has the following structure.
(1) A meltblown nonwoven fabric composed of a sea-island type composite fiber composed of aliphatic polyester as an ocean component and polyamide or polyolefin as an island component, wherein the meltblown nonwoven fabric is warped under conditions of 100 ° C. × 3 minutes. A melt blown nonwoven fabric characterized in that the dry heat shrinkage of each is in the range of 0 to 5%.

  (2) The melt blown nonwoven fabric according to (1), wherein the island component polyamide or polyolefin has a domain size of 50 to 800 nm.

  (3) The melt blown nonwoven fabric according to (1) or (2), wherein the weight ratio of the aliphatic polyester / polyamide or polyolefin is 55/45 to 95/5.

  (4) The melt blown nonwoven fabric according to any one of (1) to (3), wherein the aliphatic polyester is polylactic acid, the polyamide is nylon 6, and the polyolefin is polypropylene.

  According to the present invention, it is possible to obtain a melt blown nonwoven fabric having an aliphatic polyester as a main component, excellent spinning stability, and extremely low dry heat shrinkage.

  The present invention, which is the subject, namely, a melt blown nonwoven fabric that has an aliphatic polyester as a main component, has excellent spinning stability and has an extremely low dry heat shrinkage rate, has been intensively studied, and the sea component is aliphatic polyester and the island component is polyamide or Using a raw material mixed polymer mixed with a polymer blend made of the above specific polymer to make a sea-island type composite fiber composed of any of the polyolefins, we tried to make a nonwoven fabric by the melt blow method. It was clarified to solve the problem.

  The present invention will be described in detail below.

  First, the melt blown nonwoven fabric produced by the melt blow method, which is the main configuration of the present invention, will be described. The melt blow method, which is one of the nonwoven fabric production methods, generally involves hot air injection of a molten thermoplastic polymer extruded from a spinneret. Is formed into a web by using the self-bonding property of the molten fiber.

  The melt blown nonwoven fabric of the present invention is composed of a sea-island composite fiber having a sea-island structure composed of aliphatic polyester as a sea component and polyolefin or polyamide as an island component. The sea-island type composite fiber referred to in the present invention has a multi-core type core-sheath structure, that is, when the cross section of the sea-island type composite fiber is viewed, the aliphatic polyester that is a sea component contains a large number of islands. Any structure having a structure that covers all of the component polyolefins or polyamides may be used. In particular, it is preferable that the aliphatic polyester and the polyolefin or polyamide are composed of what is mixed by a so-called polymer blend.

  As the aliphatic polyester constituting the sea component, polylactic acid, polyglycolic acid, polyhydroxybutyrate, polyhydroxybutyrate valerate, or a blend, copolymer, modified product or the like thereof can be used.

  Among them, polylactic acid is most preferable from the viewpoint of heat stability. As such 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 preferable. The weight average molecular weight of polylactic acid is preferably 50,000 to 250,000, and more preferably 70,000 to 200,000. When the polylactic acid has a weight average molecular weight of less than 50,000, yarn formation is difficult due to low viscosity, and spinnability is poor. On the other hand, when the weight average molecular weight exceeds 250,000, the viscosity is so high that it is difficult to reduce the fiber diameter.

  Moreover, as polyolefin which comprises an island component, polypropylene, polyethylene, these copolymers, and its modified material can be used individually or in mixture. Moreover, as polyamide which comprises an island component, nylon 6, nylon 66, nylon 6-10, nylon 12, these copolymers, and its modified material can be used individually or in mixture. Among these, polypropylene and nylon 6 are particularly preferable because they have a small melting point difference from polylactic acid, and thus have high affinity for polymers and good spinnability when composite-spun. The blended polymer after blending may contain additives such as particles, flame retardants and antistatic agents, and other components are copolymerized within a range that does not impair the properties of the polymer as an island component. May be.

Here, the weight ratio of aliphatic polyester to be blended with polyolefin or polyamide (aliphatic polyester / (polyolefin or polyamide)) is preferably in the range of 55/45 to 95/5, more preferably 60/40 to 90 /. 10. If the weight ratio of the polyolefin or polyamide of the island component exceeds 45/100, it is not preferable because the aliphatic polyester may not exhibit its biodegradability, and if it is too low, less than 5/100 The aliphatic polyester of the sea component is dominant, and the properties of the polyolefin or polyamide of the island component cannot be sufficiently exhibited, which is not preferable.
The sea-island type composite fiber made of aliphatic polyester and polyolefin or polyamide in the present invention is a sea-island type composite fiber containing many island components in order to use a mixed polymer made of a polymer blend as a raw material. It is not a structure of a laminated type, a multi-leaf type composite, a radial laminated structure or the like.
The number of islands in the sea-island type composite fiber is preferably 10 or more, more preferably 20 or more, and still more preferably 30 or more. If the number of islands is 10 or more, it is preferable because the blending effect of polyolefin or polyamide can be fully utilized. From the viewpoint of spinnability, it is important to uniformly control the island polymer domain size (island size) in the sea-island composite fiber. Here, the domain size refers to the diameter of the island polymer portion in the cross section of the sea-island type composite fiber. The domain size is preferably 50 nm or more, more preferably 50 nm or more, and even more preferably 50 nm or more, since a general fiber diameter used in a melt blown nonwoven fabric is 20 μm or less. Moreover, 800 nm or less is preferable, More preferably, it is 700 nm or less, More preferably, it is 600 nm or less. This is because if the domain size is larger than 50 nm, the characteristics of polyolefin or polyamide can be fully utilized, and if the domain size is 800 nm or less, stable spinning can be performed.

  As a method for measuring the domain size, the obtained melt-blown nonwoven fabric is alkali-treated to elute the polylactic acid component, and then 30 1 cm × 1 cm measurement samples from any location of the nonwoven fabric composed only of island components The sample is collected, the magnification is adjusted to 80000 times with a scanning electron microscope, and a total of 30 fiber surface photographs are taken from the collected sample. Everything in the photograph where the fiber diameter can be clearly confirmed is measured, and the average value can be obtained as the domain size.

  In order to obtain a sea-island type composite fiber having such a uniform and fine sea-island structure, kneading of the polymer is very important. The method will be described below.

In order to produce a sea-island type composite fiber having a uniform and fine sea-island structure as described above, it is preferable to first employ a method in which a blend polymer chip in which island components are finely dispersed is prepared, and then this chip is melt-spun. . Regarding the preparation of the blend polymer 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, using 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, the kneading part is positioned on the discharge side of the twin-screw extruder as much as possible, so that the residence time of the mixed word can be shortened and re-aggregation of the island polymer can be suppressed. 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. .

  In order to finely disperse the island component of the blend polymer chip, the combination of the polymers is also important. In the present invention, as described above, the sea component is selected from aliphatic polyester and the island component is selected from polyamide or polyolefin. It is constituted by a specific combination of use.

  In order to make the cross section of the fiber made of either the island component polyamide or polyolefin 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 that reflects 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 SP values close to each other. there is a possibility. 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.

  Next, the melt blown nonwoven fabric of the present invention will be described in detail.

The basis weight of the melt blown nonwoven fabric of the present invention is preferably 10 g / m ² or more, more preferably 13 g / m ² or more. Moreover, Preferably it is 200 g / m < ² > or less, More preferably, it is 100 g / m < ² > or less. When the basis weight of the nonwoven fabric is less than 10 g / m ² , the web tends to break easily, which is not preferable. If the basis weight of the nonwoven fabric exceeds 200 g / m ² , the collection becomes unstable, which is not preferable.

  As the basis weight of the nonwoven fabric here, a value obtained by measuring the melt blown nonwoven fabric of the present invention according to 5.2 of JIS L1906 (2000 version) was used as the basis weight.

The fiber diameter of the sea-island composite fiber of the present invention is preferably 1 μm or more. On the other hand, 20 micrometers or less are preferable, More preferably, it is 15 micrometers or less, More preferably, it is 10 micrometers or less. If the fiber diameter is less than 1 μm, shots are likely to occur and spinning is unstable, which is not preferable. On the other hand, if it exceeds 20 μm, the unevenness of the sheet tends to be unfavorable.
As a method for measuring the fiber diameter, 30 measurement samples of 1 cm × 1 cm are taken from an arbitrary location on the nonwoven fabric sheet, and when the fiber diameter is about 1 to 5 μm, the magnification is 3000 times with a scanning electron microscope. When the fiber diameter is about 5 to 10 μm, the magnification is adjusted to 2000 times. Further, when the fiber diameter is 10 to 20 μm, the magnification is adjusted to 1000 times. A total of 30 images can be taken one by one, all of the photographs in which the fiber diameter can be clearly confirmed are measured, and an average value can be obtained as the average fiber diameter.

  In addition, the cross-sectional shape of the fiber is not limited at all, and a round shape, a hollow round shape, or an irregular shape such as an X shape, a Y shape, or a multi-leaf shape is preferably used. A round shape is most preferable.

  Regarding the dry heat shrinkage rate of the melt blown nonwoven fabric of the present invention, it is important that the vertical and horizontal are within the range of 0 to 5%, preferably 4% or less, more preferably, at 100 ° C. for 3 minutes. Is 3% or less. When the dry heat shrinkage rate is 0%, there is no dimensional change. For example, when used as a filter medium, the filter performance does not change. There are various advantages such as no occurrence. On the other hand, when the dry heat shrinkage rate exceeds 5%, the pressure loss increases with respect to the filter performance, and when it is bonded to a film, an aggregate, etc., peeling tends to occur, which is not preferable.

  As a method for measuring the dry heat shrinkage rate, in the method of JIS L1906 5.9.1, the temperature in the apparatus was set to 100 ° C., and the dry heat shrinkage rate was obtained.

  In the present invention, the reason why a melt blown nonwoven fabric having excellent spinning stability and low dry heat shrinkage is obtained is a sea-island type composite fiber using an aliphatic polyester as a sea component and a polyolefin or polyamide as an island component. By using a homogeneously blended polymer, the amorphous component of the sea component moves due to heating, and even if it tries to shrink, the polyolefin or polyamide of the island component inhibits it, thereby suppressing molecular migration and minimizing thermal shrinkage. It is estimated that

  Next, the manufacturing method of the melt blown nonwoven fabric of this invention is demonstrated.

  The manufacturing method by the melt blow method melts the raw material with an extruder, extrudes it from a die in which discharge holes are arranged in a row, and refines it by hot air jetted from hot air jet grooves provided on both sides of the die discharge hole. Then, it is collected on a collection conveyor while cooling to form a sheet.

  In the production method of the melt blow method, the following conditions are adopted in order to stably obtain the melt blow nonwoven fabric of the present invention. That is, polylactic acid is used as the aliphatic polyester of the sea component, polypropylene is used as the polyolefin of the island component, and nylon 6 is used as the polyamide of the island component, and a polymer in which these are uniformly blended is employed. As described above, a blend polymer chip in which these are uniformly blended is prepared, and the chip is melted to form a nonwoven fabric by a melt blow method. The temperature at the time of melting is preferably 220 to 260 ° C, more preferably 225 ° C to 255 ° C, and most preferably 230 ° C to 250 ° C. When spinning at less than 220 ° C., spinning with nylon 6 lowers the melting point of nylon 6 and unfavorably lowers the spinning stability. On the other hand, if the spinning temperature exceeds 260 ° C., the polylactic acid is decomposed and the spinning stability is deteriorated. In addition, about discharge amount, cooling conditions, etc., it sets suitably so that it may become a desired nonwoven fabric.

  Although the use application of the melt blown nonwoven fabric of this invention is not restrict | limited at all, It is preferably used for the filter medium of various filters, a battery separator, etc.

  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) Thirty measurement samples of 1 cm x 1 cm are collected from an arbitrary place on the nonwoven fabric sheet with an average fiber diameter. If the fiber diameter is about 1 to 5 µm, the magnification is adjusted to 3000 times with a scanning electron microscope. The photo size is taken so that at least 15 μm or more in both vertical and horizontal directions. When the fiber diameter is about 5 to 10 μm, the magnification is adjusted to 2000 times, and the photograph is photographed so that at least both the vertical and horizontal sizes are 20 μm or more. Further, when the fiber diameter is 10 to 20 μm, the magnification is adjusted to 1000 times, and the photograph is photographed so that at least both the vertical and horizontal sizes are 40 μm or more. In each of the 30 samples collected, 30 were taken one by one, and all of the photographs in which the fiber diameter could be clearly confirmed were measured, and the average value was taken as the average fiber diameter.

(3) Domain size (average diameter of island components)
The resulting melt-blown nonwoven fabric was treated with alkali to elute the polylactic acid component, and then 30 1cm x 1cm measurement samples were taken from any location of the nonwoven fabric composed only of island components and magnified with a scanning electron microscope Is adjusted to 80,000 times, and a total of 30 photographs of the fiber surface are taken from the collected samples, one each so that the photograph size is 5 μm or more for both vertical and horizontal. All of the photographs in which the fiber diameter was clearly confirmed were measured, and the average value was taken as the domain size (average diameter of island components).

(4) Dry heat shrinkage In the method of JIS L1906 5.9.1, the value obtained by setting the temperature in the apparatus to 100 ° C. was defined as the dry heat shrinkage.

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. Were 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, 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 30 g / m ² was obtained by spraying at 230 ° C. and an air pressure of 0.05 MPa and adjusting the collection conveyor speed. Looking at the cross section of one fiber constituting the melt blown nonwoven fabric, it was a sea-island type composite fiber having an island component average diameter of 187 nm.

  The characteristic values of the nonwoven fabric are shown in Table 1.

Example 2
Melt viscosity 350Pa · 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), mp 165 ° C. polypropylene ( 1% by weight of triazine compound Kimasorb (R) 944 (manufactured by Ciba Geigy)) was kneaded at 230 ° C. at a blend ratio of 8/2 with a biaxial extrusion kneader to obtain a polymer alloy chip It was.

Using this tip, the same die as in Example 1 is used to inject the polymer at a discharge rate of 32 g / min, a nozzle temperature of 240 ° C., and an air pressure of 0.03 MPa by the melt blow method to adjust the collection conveyor speed. As a result, a nonwoven fabric having a basis weight of 25 g / m ² was obtained. Similarly to Example 1, the cross section of one constituent fiber of the melt blown nonwoven fabric was a sea-island type composite fiber having an island component average diameter of 154 nm.

  The characteristic values of the nonwoven fabric are shown in Table 1.

Comparative Example 1
A nonwoven fabric having a basis weight of 30 g / m ² was obtained by the melt blow method in the same manner as in Example 1 except that only the polylactic acid chip used in Example 1 was used as the raw material polymer. The characteristic values of the nonwoven fabric are shown in Table 1.

Comparative Example 2
A nonwoven fabric having a basis weight of 25 g / m ² was obtained by the melt blow method in the same manner as in Example 2 except that only the polylactic acid chip used in Example 1 was used as the raw material polymer. The characteristic values of the nonwoven fabric are shown in Table 1.

  As is clear from Table 1, in Examples 1 to 3, in which nonwoven fabrics were produced by melt blown polymer alloy chips produced using polylactic acid as the sea component and nylon 6 or polypropylene as the island component, the spinnability was also good. A melt blown nonwoven fabric having a very low dry heat shrinkage ratio was obtained.

  On the other hand, the melt blown nonwoven fabrics of Comparative Examples 1 and 2 in which polylactic acid was produced using only a single component had extremely high dry heat shrinkage.

  According to the present invention, a melt blown nonwoven fabric having an aliphatic polyester as a main component and an extremely low dry heat shrinkage ratio can be obtained. This melt blown nonwoven fabric can be preferably used for filter media of various filters, battery separators, etc. Is not limited to these.

Claims (4)

A melt blown non-woven fabric comprising sea-island type composite fibers composed of aliphatic polyester as the sea component and polyamide or polyolefin as the island component, wherein the melt blown non-woven fabric has a length and width of 100 ° C. for 3 minutes. A melt blown nonwoven fabric having a dry heat shrinkage in the range of 0 to 5%. The melt blown nonwoven fabric according to claim 1, wherein the island component polyamide or polyolefin has a domain size of 50 to 800 nm. The melt blown nonwoven fabric according to claim 1 or 2, wherein a weight ratio of the aliphatic polyester / polyamide or polyolefin is 55/45 to 95/5. The melt blown nonwoven fabric according to any one of claims 1 to 3, wherein the aliphatic polyester is polylactic acid, the polyamide is nylon 6, and the polyolefin is polypropylene.