KR20130117793A - Highly uniform spunbonded nonwoven fabrics - Google Patents

Abstract

The present invention relates to high-uniform spunbonded nonwovens, as well as related fibers, products, machinery, and methods.

Description

High-Uniformity Spunbonded Nonwovens {HIGHLY UNIFORM SPUNBONDED NONWOVEN FABRICS}

35 U.S.C. In accordance with § 119 (e), this patent application claims U.S. Provisional Patent Application No. 61 / 393,232, filed Oct. 14, 2010, and U.S. Provisional Patent Application No. 61 / 497,241, filed June 15, 2011. Claim priority on the basis. The contents of these US patent applications are incorporated herein by reference.

The present invention relates to high-uniform spunbonded nonwovens, as well as related fibers, products, machinery, and methods.

Nonwovens formed from fibers thermally bonded to each other have been produced for a long time. Two common thermal bonding techniques are area bonding and point bonding. In area bonding, bonds are formed arbitrarily over the entire nonwoven at locations where the fibers of the nonwoven come into contact with each other. This can be accomplished by various methods, for example, by passing heated air, steam or other gas through an unbonded web of fibers to cause the fibers to melt and fuse with each other at the point of contact. Area bonding can also be realized by passing the web of fibers through a calender composed of two smooth steel rollers heated to soften and fuse the fibers. In point bonding, a web of fibers is passed through a heated calender nip with two nip rolls, one or more of the nip rolls having a surface with a extrusion pattern. Typically, one of the heated rolls is a patterned roll and the other roll is a cooperating roll with a smooth surface. As the web is moved through the calender rolls, the individual fibers are thermally bonded together at discrete point bond sites where the fibers contact the protrusions of the patterned roll but not at locations between the point bonding sites. Thus, the resulting fabric includes a bonding pattern.

U.S. Patent No. 5,665,300 U.S. Patent No. 3,338,992, US Patent No. 4,208,366, U.S. Patent No. 4,233,014 U.S. Patent No. 5,368,913 U.S. Patent No. 3,989,788

Unexpectedly, the inventors of the present invention have found that a wet nonwoven fabric is spunbonded fiber comprising a single polymer (a polymer having a single intrinsic viscosity) with a monomodal molecular weight distribution. improved tensile strength (eg, longitudinal or transverse) while having high surface uniformity (eg, with an M-4 web uniformity index of up to about 600), similar to wet laid nonwoven fabric or superior to wet nonwoven fabrics. And spunbonded nonwoven fabrics with lower production costs compared to wet nonwoven fabrics. Thus, spunbonded nonwovens can be used to replace wet nonwovens in certain applications (eg, membrane filtration media).

In one aspect, the present invention provides an article comprising a nonwoven fabric comprising a plurality of continuous fibers. Each fiber of the plurality of continuous yarns comprises a single polymer comprising a polyester. Continuous yarns are randomly bonded over a nonwoven substrate.

In yet another aspect, the present invention provides an article comprising a nonwoven fabric comprising a plurality of fibers. The nonwoven has a M-4 web uniformity index of up to about 600. The nonwoven has a unit weight of 34 gsm and the nonwoven has a tensile strength of at least about 10 pounds in the transverse direction as measured according to ASTM D4595-09.

In still another aspect, the present invention provides an article comprising a nonwoven fabric comprising a plurality of spunbonded fibers. The nonwoven has a M-4 web uniformity index of up to about 600.

In yet another aspect, the present invention provides an article comprising a nonwoven fabric comprising a plurality of fibers. When the nonwoven has a unit weight of 34 gsm, the nonwoven has a tensile strength of at least about 10 pounds in the transverse direction as measured according to ASTM D4595-09. Nonwovens do not include polymers having an inherent viscosity higher than about 0.64 dl / g.

In another form, the present invention provides a membrane filtration medium comprising one or more of the above mentioned articles.

In yet another aspect, the present invention provides a method for forming a non-bonded continuous yarn comprising the steps of: extruding a composition comprising a single polymer; And area bonding the unbonded continuous yarns to form a nonwoven fabric comprising a plurality of bonded continuous yarns. The single polymer comprises polyester.

Embodiments may include one or more of the following optional features.

Each fiber may comprise a single polymer that may include a polyester. For example, the single polymer may be polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyglycolide, polylactide, polycaprolactone, polyethylene adipate, polyhydroxyalkanoate Or copolymers thereof.

The single polymer may have an intrinsic viscosity of at least about 0.5 dl / g and / or at most about 0.7 dl / g.

At least some of the fibers may have a circular cross section. For example, the circular cross section may have an average diameter between about 6 μm and about 20 μm.

At least some of the fibers may have a trilobal, quadrulobal, pentalobal, or octalobal cross section. For example, such fiber cross sections may have an average diameter between about 1 μm and about 6 μm.

The fibers can be optionally bonded across the nonwoven substrate.

When the nonwoven has a unit weight of 34 gsm, the nonwoven can have a tensile strength of at least about 10 pounds in the transverse direction as measured according to ASTM D4595-09.

The nonwoven can have an M-4 web uniformity index of up to about 600.

The nonwoven can have an average pore size of at least about 5 μm and / or at most about 125 μm.

The nonwoven can have a thickness of at least about 50 μm and / or at most about 550 μm.

The nonwoven can have a bubble point of at least about 25 μm and / or up to about 200 μm.

The membrane filtration medium may be a reverse osmosis filtration medium.

The zone bonding step may include through-air bonding the unbonded continuous yarns to form a nonwoven substrate.

The zone bonding step may be carried out at a temperature of at least about 145 ° C and / or at most about 250 ° C.

Prior to areabonding the unbonded continuous yarns, the method may further comprise passing the unbonded continuous yarns through two or more draw rolls to form oriented fibers. have. For example, two draw rolls may each have a fiber speed of at least about 1,800 meters per minute.

After zonebonding the unbonded continuous yarns, the method may further comprise calendering the nonwoven substrate to form a calendared product. The calendering step may be performed at a temperature of at least about 145 ° C and / or at most about 215 ° C. The calendered product may comprise a membrane filtration medium.

The bonded continuous yarn may comprise spunbonded fibers.

Embodiments may provide one or more of the following advantages.

Spunbonded nonwovens formed by zone-bonding fibers comprising a single polymer having a specific intrinsic viscosity value (eg, 0.60 dl / g to 0.64 dl / g) are high surface uniformity similar to or better than wet nonwovens. It can also have improved tensile strength (eg, longitudinal or transverse) and lower production costs compared to wet nonwovens.

One advantage of using a single polymer to make a nonwoven is that no additional binder polymer is required to bond the fibers, thus reducing manufacturing costs.

Other features and advantages of the invention will be apparent from the description, drawings, and claims.

1 is a perspective view of a spunbonded nonwoven fabric formed from continuous yarns made of a single polymer.
2 is a schematic illustration of an apparatus for producing spunbonded nonwovens.
FIG. 3 is a perspective view, cut away, of a portion of a filter system comprising the nonwoven fabric shown in FIG. 1. FIG.
4 is a perspective view illustrating a reverse osmosis membrane filter including the nonwoven fabric illustrated in FIG. 1.

1 is a perspective view illustrating a spunbonded nonwoven fabric 10 formed of a plurality of continuous yarns 12 bonded to each other through a plurality of irregular coupling portions 14 randomly distributed throughout the entire nonwoven fabric. As used herein, the term "nonwoven fabric" refers to a fabric comprising one or more layers of fibers bonded together in a knit or woven material in a non-identifiable manner. As used herein, the term "continuous fiber" refers to fibers formed in a continuous process that are not reduced before being incorporated into a fabric comprising continuous yarns. Nonwovens may be formed in a continuous process in which continuous yarns are provided in a fabric. Thereafter, the nonwoven can be cut to a specific size (with a particular length and width) and the continuous yarn may typically have a length that is equal to or greater than the length or width of the nonwoven. In contrast, staple fibers refer to fibers having a unique length that is reduced before being incorporated into the fabric and thus is different from and independent of the length or width of the fabric. The term “spunbonded fiber” as referred to herein refers to fibers that are extruded, drawn and laid on a moving substrate (eg, a moving belt). In general, nonwoven fabric 10 has a planar structure that is relatively flexible and porous.

In general, the fibers 12 are formed from a single polymer. As used herein, the term "single polymer" refers to a polymer that has the same chemical composition and includes molecules with a monomodal molecular weight distribution. Polymers with a monomodal molecular weight distribution referred to herein refer to polymers having only one unique molecular weight peak in the chromatogram of Gel Permeation Chromatography (GPC). As an example, fibers made from polymers having two different chemical compositions (eg, polyethylene and polyester) are not within the meaning of the term "single polymer" as defined herein. As another example, a fiber made of a polymer having the same chemical composition but having a multimodal molecular weight distribution (eg, a mixture of two polyethylene terephthalate polymers having two unique molecular weights in a GPC chromatogram) Is not within the meaning of the term "single polymer" as defined herein. In addition, polymers having molecules of the same chemical composition but with significantly different intrinsic viscosity values (eg, 0.61 dl / g and 0.67 dl / g) have a multimodal molecular weight distribution. Thus, such polymers are also not within the meaning of the term "single polymer" as defined herein.

Examples of single polymers that can be used in the fibers 12 are polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), Polyglycolide or polyglycolic acid (PGA), polylactide or polylactic acid (PLA), polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxyalkanoate (PHA), or copolymers thereof to be. Without being bound by theory, it is believed that fibers formed from polyester can provide adequate strength to nonwovens for use in filter media. The single polymer can be a homopolymer or a copolymer.

In general, fibers 12 are area bonded to form nonwoven fabric 10 with high-surface uniformity. Thus, nonwoven fabric 10 is formed including irregularly bonded portions 14 that are randomly distributed (ie without a bonding pattern) through the entire nonwoven at locations where the fiber will come into contact with another fiber. As a result, such nonwoven fabrics may be subjected to repeated bonding patterns, such as point bonding, such as by passing fibers through two heated nip rolls (one or more of which include the pattern). It may be different from the nonwoven fabric having the bonding pattern produced. In some embodiments, the nip rolls used in point bonding can have an arbitrary pattern. However, since the arbitrary pattern is repeated after the nip roll ends the cycle, the bonds in the formed nonwovens are therefore considered to have a pattern that is still within the meaning of the terms defined herein. Without being bound by theory, nonwoven fabric 12 produced by area bodning has a much higher surface uniformity (eg, a much higher M-4 web uniformity index than a fabric produced by point bonding). uniformity index), which is believed to be due to area bonding, while point bonding allows the fabric to have an indentation of fused fibers on the surface. Without being bound by theory, for use in membrane filtration medium, nonwoven fabrics prepared by zone bonding may be preferred, as it is believed that the nonwoven fabric may be porous over the entire surface. In contrast, fabrics produced by point bonding contain marks on the surface, thus preventing them from being filtered at these points and thus reducing the available filtration area, thereby increasing pressure drop and reducing filter life. Can be.

Region combining can be implemented in a variety of ways known in the art. As an example, the zone bonding is achieved by melting the fibers with each other at the points of contact by through-air bonding, ie, passing heated air, steam or other gas through the unbonded web of fibers. And may be implemented to be fused. As another example, area bonding is achieved by softening the fibers by passing them through calender bonding, that is, through a web of calenders consisting of two heated steel rollers heated. It may be soften and then implemented to be combined with each other.

Zone bonding is usually carried out at increased temperatures. For example, the fibers 12 may be at least about 145 ° C. (eg, at least about 155 ° C., at least about 175 ° C., at least about 195 ° C., at least about 215 ° C., or at least about 225 ° C.) up to about 250 ° C. (eg, Up to about 245 ° C., up to about 240 ° C., up to about 235 ° C., or up to about 230 ° C.). Typically, zone bonding is performed between about 225 ° C. and about 245 ° C. by using through-air bonding or between about 175 ° C. and about 245 ° C. by using flat calendering. Heating during the zone bonding process may be conducted by conduction (eg by using a heated roll in a calender bond process), convection (eg by using heated air in a pass-air bond process), or by vibration (eg by sonic welding). Can be implemented by In general, heat is provided uniformly to the entire fabric of the fiber. Without being bound by theory, since a single polymer used in the fiber 12 has a relatively low intrinsic viscosity (eg, about 0.60 dl / g to about 0.64 dl / g), the single polymer is at the temperature used in the zone bonds. It is believed that the fibers soften and consequently the fibers are bonded to each other at any point of contact and thus form a random bond substantially uniformly throughout the entire fabric without any bonding pattern. In contrast, fabrics made only by viscous bonding have a bond where fibers are in contact with protrusions on a patterned nip roll and the fibers remain unbonded at locations between the viscous sites. form bonds. As a result, the fabric produced by point bonding includes a bonding pattern.

The nonwoven fabric 10 may have a relatively high Gurley stiffness in the longitudinal direction MD and / or in the transverse direction CD. The term "machine direction" as used herein refers to the direction of movement of an unbonded web, bonded web, or nonwoven during the production process. The length of the unbonded web, bonded web, or nonwoven is usually the dimension in the longitudinal direction. The term "cross-machine direction" as used herein refers to a direction perpendicular to the direction of movement of the unbonded web, bonded web, or nonwoven during the production or processing process. The width of the unbonded web, bonded web, or nonwoven is the dimension in the transverse direction. For example, nonwoven fabric 10 may have at least about 65 mg (eg, at least about 100 mg, at least about 200 mg, at least about 300 mg, or at least about 500 mg) up to about 1,800 mg (eg, up to about 100 mg) in the longitudinal direction. 1,600 mg, up to about 1,400 mg, up to about 1,200 mg, or up to about 1,000 mg). As another example, nonwoven fabric 10 may have at least about 45 mg (eg, at least about 80 mg, at least about 150 mg, at least about 250 mg, or at least about 400 mg) up to about 850 mg (eg, max. About 700 mg, up to about 6000 mg, up to about 500 mg, or up to about 400 mg). The strength of the nonwoven substrate referred to herein refers to the strength measured using a Gurley type tester according to ASTM D6125-97 (2002). Without being bound by theory, it is believed that the nonwoven fabric 10 produced by area bonding can have a higher Gurley strength than that of the nonwoven fabric produced by point bonding having the same unit weight.

Single polymers suitable for use in the fiber 12 have a relatively low intrinsic viscosity value. For example, a single polymer may contain up to about 0.7 dl / g (eg, up to about 0.69 dl / g, up to about 0.68 dl / g, up to about 0.67 dl / g, up to about 0.66 dl / g, up to about 0.65 dl / g) , Up to about 0.64 dl / g, up to about 0.63 dl / g, up to about 0.62 dl / g, up to about 0.61 dl / g, or up to about 0.60 dl / g) or at least about 0.5 dl / g (eg, at least about 0.52 dl / g, at least about 0.54 dl / g, at least about 0.56 dl / g, at least about 0.58 dl / g, or at least about 0.60 dl / g). Typically, a single polymer has an intrinsic viscosity value between about 0.60 dl / g and about 0.64 dl / g (eg, about 0.61 dl / g to about 0.63 dl / g). As used herein, the intrinsic viscosity referred to herein is measured according to the method described in ASTM D4603-03. Without being bound by theory, if a single polymer has an intrinsic viscosity that is too high (eg greater than about 0.7 dl / g), the polymer is generally at a level sufficient to form bonds between the fibers at the temperatures used in the zone bonds. Is not considered to soften. In addition, without being bound by theory, if a single polymer has an intrinsic viscosity that is too low (eg less than about 0.5 dl / g), the polymer may have sufficient tensile strength to form a nonwoven fabric that is strong enough for use in the filter medium. It is not believed to have.

Conventionally, spunbonded nonwovens formed by zone bonding are fibers comprising polymers having different chemical compositions (eg, polyethylene and PET homopolymers or PET copolymers and PET homopolymers) or inherently distinctly different chemical compositions. It is made of a fiber comprising a polymer having a viscosity value (eg polyethylene terephthalate having an intrinsic viscosity value of 0.61 dl / g and 0.67 dl / g). In these fibers, one or more of the polymers are used to provide the mechanical strength of the spunbonded nonwoven (eg, polymers having a relatively high intrinsic viscosity or relatively high melting point) and forming bonds between the fibers. As the binder for the above, one or more of the above polymers which can be easily softened at the bonding temperature are used (for example, a polymer having a relatively low intrinsic viscosity or a relatively low melting point). Unexpectedly, the inventors of the present invention have found that a single polymer having an intrinsic viscosity (eg, from about 0.60 dl / g to about 0.64 dl / g) has high surface uniformity (ie, significantly, as long as it is within the range discussed above. It has been found that fabrics made from such nonwovens are suitable for use as filter media, having a smooth surface) and can be zone bonded to form spunbonded nonwovens with sufficiently strong mechanical strength. Without being bound by theory, one advantage of using a single polymer to make a nonwoven fabric is that the fabric can be fabricated (eg, by adjusting the bonding and / or calendering temperature) to produce a fabric with improved web uniformity. It is contemplated that the area bonding and / or thermal calendering processes used to fabricate the PSA can be easily optimized while two or more polymers are used, which can be difficult to optimize. Also, without being bound by theory, according to another advantage of using a single polymer to make a nonwoven fabric, it is believed that no additional binder polymer is needed to bond the fibers and thus reduce manufacturing costs.

The cross sections of the fibers 12 may have different shapes as desired. In some embodiments, some or more of the fibers 12 may have a circular cross section (eg, a circular transverse cross section). In such embodiments, the fiber 12 having a circular cross section may have a maximum of about 20 μm (eg, at most about 18 μm, at most about 16 μm, or at most about 14 μm) to at least about 4.5 μm (eg, at least about 5 μm). , At least about 6 μm, at least about 7 μm, at least about 8 μm, or at least about 9 μm). In general, the average diameter of the fibers is correlated relative to the linear mass density of the fibers and this correlation may depend on the polymer used to form the fibers. For example, a fiber having a linear mass density of about 0.9 dtex (ie, about 1 dpf) corresponds to a fiber having an average diameter of about 10 μm when the fiber is made of polyester, and the fiber may be made of polypropylene. When corresponds to a fiber with an average diameter of about 12.5 μm. Accordingly, the fibers 12 having an average diameter described above may have a maximum of about 1.8 dtex (eg, at most about 1.6 dtex, at most about 1.44 dtex, or at most about 1.26 dtex) when the fiber 12 is made of polyester. And have a linear mass density between about 0.4 dtex (eg, at least about 0.45 dtex, at least about 0.54 dtex, at least about 0.63 dtex, at least about 0.72 dtex, or at least about 0.81 dtex). Without being bound by theory, due to fibers with relatively small average diameters (or relatively small linear mass densities), nonwovens have relatively good filtration efficiency and relatively high surface uniformity (ie, a relatively smoother surface). It is considered to be. On the other hand, if the average diameter of the fibers in the nonwoven fabric 10 is too small, such fabrics may have very high pressure drops, thus reducing the filtration performance of the fabrics.

In some embodiments, the fiber 12 has a polygonal-lobed shape (eg, trilobal, quadrulobal, pentalobal, or octagonal-). It may have a cross section (eg, transverse cross section) having a octalobal shape. Such fibers can be up to about 18 μm (eg, up to about 16 μm, up to about 14 μm, up to about 12 μm, or up to about 10 μm) to at least about 1 μm (eg, at least about 2 μm, at least about 3 μm, at least About 4 μm, at least about 6 μm, or at least about 8 μm). As used herein, the diameter of a polygonal-shaped fiber is the distance from the tip of the lobe across the center of the cross section to the end of the cross section on the other side of the center. Point. In addition, the fibers 12 having the sizes described above may range up to about 2.4 dtex (eg, up to about 2.2 dtex, up to about 2.0 dtex, up to about 1.8 dtex, or up to about 1.6 dtex) to at least about 0.45 dtex (eg, at least About 0.54 dtex, at least about 0.63 dtex, at least about 0.72 dtex, at least about 0.81 dtex, or at least about 0.9 dtex). Typically, fibers 12 having polygonal-section cross sections may have a linear mass density between about 1.6 dtex and about 2.2 dtex. Without being bound by theory, because fibers with polygonal-section cross-sections have a larger surface area per unit weight than fibers with circular cross-sections, relatively small dimensions (eg, relatively small diameters or relatively small linear mass densities) Polygon-cross section with cross section produces a nonwoven fabric with surface uniformity similar to that of nonwoven fabric produced by a fiber having a circular cross section with a relatively large dimension (eg, a relatively large diameter or a relatively large linear mass density). It is believed that it can be used to. As a result, nonwoven fabrics made from fibers having a polygonal cross-section can have better filtration efficiency and greater tensile strength than nonwovens made from fibers having a circular cross section.

The spunbonded nonwoven fabric 10 (eg having a unit weight of 34 grams per m ² (gsm) and / or having an area of 32 in ² ) is about 10 pounds in the longitudinal direction (eg, at least about 15 pounds, Tensile strength between at least about 20 pounds, at least about 25 pounds, or at least about 30 pounds) up to about 50 pounds (eg, up to about 45 pounds, up to about 40 pounds, up to about 35 pounds, or up to about 30 pounds). Can have Typically, the spunbonded nonwoven fabric 10 may have a tensile strength between about 20 pounds and about 40 pounds in the longitudinal direction. The spunbonded nonwoven fabric 10 (eg having a unit weight of 34 gsm and / or having an area of 32 in ² ) may have at least about 10 pounds (eg, at least about 15 pounds, at least about 20 pounds, Have a tensile strength between at least about 25 pounds, or at least about 30 pounds) and up to about 50 pounds (eg, up to about 45 pounds, up to about 40 pounds, up to about 35 pounds, or up to about 30 pounds). Typically, the spunbonded nonwoven fabric 10 may have a tensile strength between about 18 pounds and about 24 pounds in the longitudinal direction. As used herein, the tensile strength of the nonwoven fabric 10 is measured by the Grab Tensile method according to ASTM D4595-09. In general, spunbonded nonwoven fabrics having relatively high unit weights have increased tensile strength in both longitudinal and transverse directions. Without being bound by theory, it is believed that the spunbonded nonwoven fabric 10 has a significantly higher tensile strength per unit weight than wet laid nonwoven fabric in the longitudinal and / or transverse directions. Also, without being bound by theory, according to another advantage of the spunbonded nonwoven fabric 10, the spunbonded nonwoven fabric has a better fuzz ratio than the fuzz rating of a wet nonwoven fabric, which is a spunbone. Died nonwovens are made by continuous yarns (and thus have a minimum amount of fiber ends on the fabric surface) while wet nonwovens are usually made by yarns having fiber lengths between about 0.5 inches and about 3 inches (and thus It is believed to have a significant amount of fiber ends at the fabric surface.

In some embodiments, the spunbonded nonwoven fabric 10 may be up to about 3: 1 (eg, up to about 2.5: 1, up to about 2: 1, up to between tensile strength in the longitudinal direction and tensile strength in the transverse direction). About 1.5: 1, up to about 1.4: 1, up to about 1.2: 1) to at least about 1: 1 (eg, at least about 1.1: 1, at least about 1.3: 1, at least about 1.5: 1, or at least about 2: 1 It can have a ratio between).

The average pore size of the nonwoven fabric 10 may vary depending on the manner in which the fabric is made and the desired use of the fabric. The term “mean pore size” as used herein is defined as 1 in ² (ie, about 6.45) by Capillary Flow Porometer CFP 1200 AEX, available from Porous Materials, Inc., Ithaca, NY, USA. cm ² ) measured in the sample. For example, nonwoven fabric 10 may be used to form a calendared product (eg, a pool or spa, or a dryer sheet) having a reduced pore size. After the fabric is zone bonded, but before the fabric is calendered, at least about 35 μm (eg, at least about 45 μm, at least about 55 μm, at least about 65 μm, at least about 75 μm, or at least about 85 μm) And may have an average pore size of between about 125 μm (eg, up to about 120 μm, up to about 110 μm, up to about 100 μm, up to about 90 μm, or up to about 80 μm). As another example, the nonwoven fabric 10 may be at least about 5 μm (eg, after the fabric has been zone bonded and calendered to form a calendared product (eg, a filtration medium) having a reduced pore size). At least about 7 μm, at least about 9 μm, at least about 11 μm, at least about 13 μm, at least about 15 μm, or at least about 17 μm) up to about 25 μm (eg, up to about 23 μm, up to about 21 μm, up to About 19 μm, up to about 17 μm, or up to about 15 μm).

The bubble point of the nonwoven fabric 10 can be changed as desired. The term "bubble point" referred to herein refers to the maximum pore size measured in 1 in ² (ie, about 6.45 cm ² ) samples by Capillary Flow Porometer CFP 1200 AEX, available from Porous Materials, Inc. Point to. For example, the nonwoven fabric 10 may comprise at least about 75 μm (eg, at least about 85 μm, after the fabric is zone bonded but before calendering, to form a calendared product having a reduced pore size). Bubble points between at least about 95 μm, at least about 105 μm, or at least about 115 μm) up to about 200 μm (eg, up to about 190 μm, up to about 180 μm, up to about 170 μm, or up to about 160 μm). Can have As another example, the nonwoven fabric 10 may be at least about 25 μm (eg, after the fabric has been zone bonded and calendered to form a calendared product (eg, a filtration medium) having a reduced pore size). At least about 30 μm, at least about 35 μm, at least about 40 μm, or at least about 45 μm) up to about 50 μm (eg, up to about 45 μm, up to about 40 μm, up to about 35 μm, or up to about 30 μm) It can have a bubble point in between.

In addition, the thickness of the nonwoven fabric 10 can also be changed as desired. For example, the nonwoven fabric 10 may have at least about 200 μm (eg, at least about 250 μm, after the fabric has been zone bonded but before calendering, to form a calendared product having a reduced pore size). At least about 300 μm, at least about 350 μm, or at least about 400 μm) up to about 550 μm (eg, at most about 500 μm, at most about 450 μm, at most about 400 μm, or at most about 350 μm). Can be. As another example, the nonwoven fabric 10 may be at least about 50 μm (eg, after the fabric has been zone bonded and calendered to form a calendared product (eg, a filtration medium) having a reduced pore size). At least about 75 μm, at least about 100 μm, at least about 125 μm, or at least about 150 μm) up to about 250 μm (eg, up to about 225 μm, up to about 200 μm, up to about 175 μm, or up to about 150 μm) It can have a thickness between.

The nonwoven fabric 10 may have various unit weights depending on the desired use. For example, non-woven fabric 10 m, at least 15 g (gsm) (e.g., at least about 34 gsm, at least about 51 gsm, at least about 68 gsm, at least about 85 gsm, at least about 102 gsm, or at least about 136 per ^second gsm) up to about 260 gsm (eg, up to about 255 gsm, up to about 238 gsm, up to about 221 gsm, up to about 204 gsm, up to about 187 gsm, up to about 170 gsm, up to about 153 gsm, up to about 136 gsm, Or up to about 119 gsm). As used herein, unit weight of nonwoven fabric 10 is measured according to ASTM D3776-96.

In general, nonwoven fabric 10 has high surface uniformity. The surface uniformity (smoothness) of the nonwoven 10 can be quantified using the M-4 web uniformity index.

As used herein, the M-4 web uniformity index is determined by the four physical properties of the nonwoven fabric (ie, thickness, unit weight, bubble point, and average pore size) and is obtained by the general method described below: A specific number of samples (eg 30 samples) having a specific area (eg 1 in ² , ie an area of about 6.45 cm ² ) are evenly selected across the nonwoven fabric where the M-4 web uniformity index should be determined. Taken. Odd samples must be selected in the longitudinal and transverse directions. Samples should not be selected based on their visual appearance. After selecting the samples, the thickness, unit weight, bubble point, and average pore size of each sample are measured. Then, the average value of each property is obtained. For example, when using 30 samples, dividing the sum of the thickness values of all samples (ie t1 + t2 + t3 + ... + t30) by the number of samples (ie 30) yields an average thickness t Lose. The mean values of the other properties are calculated in the same way. A random value is pre-selected for each property, which will be referred to as a "normalized value" in the future. Normal values for thickness, unit weight, bubble point, and average pore size are 178 μm, 34 gsm, 27.41 μm, and 9.09 μm, respectively. The M-4 web uniformity index values referred to herein are all calculated according to the normal values just mentioned. However, for all samples to be compared, other normal values for the property may also be used for comparison, as long as the same normal value is used for each property.

After the average value of each property of the samples is obtained, the "normalized factor" for each property is also calculated by dividing the normal value selected for each property by the average value. For example, if the average thickness of the samples is 190.5 μm, the normalization factor is 0.934 (ie 178 μm / 190.5 μm = 0.934).

Then, by multiplying the actual measurement of the properties (e.g., thickness) of each sample by the normalization coefficient obtained above, a "normalized test value" for each property of each sample is calculated. For example, in the above example where the normalization coefficient is 0.934 for the thickness of the samples, the normal experimental value of the thickness of each sample is calculated by multiplying the actual measurement of the thickness of each sample by 0.934.

After the normal experimental values of each property of all samples are obtained, using the following formula, the "normal standard deviation (normal STDEV)" of the normal test values of each property is calculated:

Where x ₁ , x ₂ , ..., and x _N are normal experimental values of the properties of all samples, N is the number of samples, μ is the mean of x ₁ , x ₂ , ... and x _N (x ₁ Calculated by + x ₂ + ... + x _N ) / N, σ is the normal STDEV of the property.

Then, using the following formula, the M-4 web uniformity index is calculated:

M-4 web uniformity index = (normal thickness STDEV + normal unit weight STDEV + normal bubble point STDEV + normal mean pore size STDEV) x 100. More details on obtaining M-4 web uniformity index for nonwoven fabric (10) The description is described in the Examples section below.

In general, fabrics with a relatively low M-4 web uniformity index have a more uniform surface (ie, a relatively smoother surface) than fabrics with a relatively high M-4 web uniformity index. As one example, using the method described above, nonwoven fabric 10 may be at most about 600 (eg, at most about 575, at most about 550, at most about 525, at most about 500, at most about 475, at most about 450, at most about 425). , Or up to about 400) to at least about 75 (eg, at least about 150, at least about 200, at least about 250, at least about 300, at least about 350, or at least about 400). have. For example, nonwoven 10 may have an M-4 web uniformity index between about 100 and about 600 (eg, about 150 to about 575 or about 200 to about 550). Without being bound by theory, the nonwoven fabric 10 may have a M-4 web uniformity index that is comparable to or better than that of the wet nonwoven fabric, which is generally the most uniform surface among nonwoven fabrics produced by currently known methods. Is considered to have.

Without being bound by theory, it is believed that as one advantage of the spunbonded nonwoven fabric 10, the surface uniformity is improved while the fiber size is reduced compared to the conventional spunbonded nonwoven fabric. As a result, the spunbonded nonwoven fabric 10 has improved filtration efficiency compared to conventional spunbonded nonwoven fabrics when used as membrane filtration media. In addition, spunbonded nonwoven fabric 10 may have improved surface uniformity that is comparable to or better than that of wet nonwoven fabric (generally better than that of conventional spunbonded nonwoven fabrics). Tensile strength and fabrication cost reduced. Thus, spunbonded nonwoven fabric 10 may be used to replace wet nonwovens in certain applications (eg, membrane filtration media).

The spunbonded nonwoven 10 can be made of one or more (eg, two, three, four, or five) nonwoven material layers. For example, the nonwoven fabric 10 may be made of one spunbonded fiber layer comprising the single polymer mentioned above. As another example, the nonwoven fabric 10 may be made from more than one spunbonded fiber layer, each of the spunbonded fiber layers comprising fibers made of the same single polymer, but having different physical properties, such as voids. Size, fiber size, or bond density.

2 illustrates an apparatus for producing a spunbonded nonwoven 10. As shown in FIG. 2, the apparatus comprises first and second spin beams 22 arranged in series mounted on an endless moving conveyor belt 24. The illustrated device has two spin beams, but other device shapes having only one spin beam or three or more spin beams may be used. Each beam extends widthwise in the transverse direction and each beam is arranged continuously in the longitudinal direction. Each beam is supplied with a molten polymer (eg, a single polyester with one inherent viscosity) from one or more extruders (not shown in FIG. 2). Spinnerets with orifices formed to produce a continuous filament are mounted on each spin beam 22.

The newly extruded filaments are then cooled and solidified by contact with a quench air flow. The filaments are then drawn and attenuated by the device 26 using methods known in the art, such as mechanical drawing methods or pneumatic drawing methods (eg, slot drawing methods). For example, when the devices 26 can include a drawn roll, the filaments can be mechanically attenuated. Methods of mechanically drawing filaments are known in the art and are described, for example, in US Pat. No. 5,665,300. As another example, when device 26 includes an attenuator device, the filaments may be pneumatically damped and drawn. For example, when the device 26 includes a slotted attenuator, the filaments may be slot drawn. Filament slot drawing methods are known in the art and are described, for example, in US Pat. Nos. 3,338,992, 4,208,366, 4,233,014, and 5,368,913.

Thereafter, the damped and drawn filaments may be arbitrarily arranged on the advancing conveyor belt 24 to form a web. The filaments can then be zone bonded at increased temperatures to provide web consistency and strength. Typically, zone bonding includes passing a web through a heated calender consisting of two smooth steel rollers or a step in which heated steam, air, or other gas passes through the web, causing the filaments to stick and fuse together. .

Specifically, as shown in FIG. 2, the web of unbonded filaments can be guided through a steam consolidator 32, an example of which is shown in US Pat. No. 3,989,788. The web may be in contact with saturated steam used to soften the filaments. The web can then be delivered to a hot air bonder 34 so that it can be bonded. In general, the temperature used in this bonding process is significantly higher than the temperature used in the curing machine and the properties desired in the product (eg, strength, dimensional stability or strength) and the tack temperature of the polymer used in the fiber. Can follow. For example, when the fiber comprises polyethylene terephthalate, the cured web is typically exposed to air at a temperature of 140 to 250 ° C. (eg, 215 to 250 ° C.) during the bonding process. During the curing and bonding process, the fibers soften and become tacky, forming fusion bonds at the locations where the fibers contact each other. This nonwoven is a region bonded fabric having a random bonding site distributed substantially uniformly throughout the entire fabric. The bond site provides the required sheet properties such as burst strength and tensile strength. Once the web is engaged, it can pass through the winding device 36 on an exit roll.

The combined web can be further calendared to form a calendared product. The calendering process can be performed by passing the bonded web through a heated calender with three or more smoothing rollers (eg, steel rollers and nylon rollers). For example, when the nonwoven fabric 10 is made of polyester, the calender can be up to about 215 ° C. (eg, up to about 205 ° C., up to about 195 ° C., up to about 185 ° C., or up to about 175 ° C.) to at least about 145 Heating at a temperature between about ° C (eg, at least about 150 ° C, at least about 160 ° C, at least about 170 ° C, or at least about 180 ° C). These processes range from about 9.14 m / min to about 91.4 m / min (ie, from about 10 to about 100 yards / minute) and from about 525 to about 4903 Newtons per roll width of 1 centimeter. Pressure between about 300 and about 2,800 pounds (PLI) per inch of roll width. As a specific example, nonwoven fabric 10 made of polyethylene terephthalate with an inherent viscosity of 0.61 dl / g has a calendering speed of about 50 m / min (ie, about 55 yards / minute) of about 1,962 per roll width of 1 centimeter. It can be calendered at about 171 ° C. under a pressure of Newton (ie, about 1,120 PLI) to form a calendered product. Without being bound by theory, it is believed that the calendering process can further reduce the pore size and thickness of the nonwoven fabric 10 and increase the surface uniformity (ie, surface smoothness) of the fabric.

Nonwoven fabric 10 can be used in a wide range of applications. For example, the uncalendered nonwoven 10 can be used as a support for filtration media (eg, pool and spa filtration media), dryer sheets, or fiber reinforced plastics. Representative filtration media include pool and spa filtration media and large air filtration systems, gas turbine filtration systems, window covers (eg blinds), liquid filtration systems (eg wastewater or drinking water filtration systems), HEPA filtration systems, vacuum bag filtration systems, Fuel filtration systems, oil filtration systems, battery separators, and / or media used in pulse cleaning applications. As another example, calendered nonwoven fabric 10 can be used in membrane filtration media (eg, support in filtration media, such as reverse osmosis filtration media), garments, dryer sheets, and towels. . Representative filtration media include ultra-filtration media, micro-filtration media, and reverse osmosis filtration media. Such filtration media may be one or more layers (eg, nonwoven layers, filtration membranes, or films) different from the nonwoven fabric 10 to control dirt holding capacity or filtration efficiency. )). These layers can be calendered with the nonwoven fabric 10 (eg, using the calendering process described above) to form a filtration medium. For example, when calendared nonwoven fabric 10 is used as a support in a reverse osmosis filtration medium (eg, for desalination or pharmaceutical separation), the reverse osmosis membrane is used to separate molecules of different sizes. It may be attached to the nonwoven fabric 10.

3 is a perspective view of a representative filter system 100 that includes a filter housing 101, a filter cartridge 102, an inner screen 108, and an outer screen 103. Nonwoven fabric 10 is arranged in filter cartridge 102. During use, gas or liquid enters the filter system 100 through the opening 104 and then passes through the inner screen 108, the nonwoven 10, and the outer screen 103. The gas then exits the filter assembly 100 through the opening 106. Nonwoven 10 may optionally be pleated into any of a variety of shapes (eg, paneled or cylindrical).

4 is a perspective view illustrating a reverse osmosis membrane filter 200 that includes a filter housing 202 and a reverse osmosis membrane medium 204. The medium 204 includes a nonwoven fabric 10 and a reverse osmosis membrane supported by the nonwoven fabric 10. Medium 204 and housing 202 together form feed channel 206 through which feed liquid passes. Media 204 also forms a permeate channel 208 where filtered liquid is collected through the permeate channel. During use, the feed liquid can be delivered into the feed channel 206 under high pressure so that the permeation step obtained by filtration through the membrane medium 204 can be implemented through the permeate channel 208.

The examples below are illustrative and not intended to be limiting. The contents of all publications (eg patents, patent applications, and articles) cited herein are incorporated by reference in their entirety. In particular, this patent application is cited with reference to the contents of US Provisional Patent Application No. 61 / 393,232, which is a concurrent application.

Example  1: single The polymer  Nonwoven fabric

The following spunbonded nonwovens were prepared using a single polyethylene terephthalate (PET) homopolymer with an intrinsic viscosity of 0.62 dl / g, which were:

(1) an uncalendered nonwoven fabric comprising 1.1 dpf fibers having a round cross section;

(2) an uncalendered nonwoven fabric comprising 1.9 dpf fibers having a triangular cross-section;

(3) an uncalendered nonwoven fabric comprising 2.4 dpf fibers having a triangular cross-section;

(4) calendared nonwoven fabric comprising 1.1 dpf fibers with round cross section;

(5) calendared nonwoven fabric comprising 1.9 dpf fibers having a triangular-cross section; And

(6) A calendered nonwoven fabric comprising 2.4 dpf fibers having a triangular cross-section.

Specifically, the polymer was dried at 140 ° C. for 5 hours and then extruded using an extruder having a spinneret having 2,310 round holes with a diameter of 0.009 inches to prepare a nonwoven fabric (1), and 0.004 inches by 0.011 inches. Nonwoven fabrics (2) and (3) were prepared by extrusion using an extruder having a spinneret including 1,080 triangular-section holes with dimensions of. Non-woven fabrics (1), (2), and (3) were produced using this extrusion throughput, that is, yields of 95, 75, and 95 pounds per hour. This spinning speed was kept constant at 2,733 yards per minute at both yields. The drawn fibers were dispersed on a moving laydown belt moving at a speed of 90 yards per minute. The web was then cured by partial bonding using hot steam. The filaments were then zone bonded together at 235 ° C. to form nonwoven fabrics (1), (2), and (3). The nonwoven fabrics (1), (2), and (3) are then calendered using a three-roll (i.e. two steel rolls and one nylon roll) calendar to produce the nonwoven fabrics (4), (5), And (6) were prepared respectively. Specifically, the nonwoven fabric was first drawn around one steel roll, nipped between the steel roll and the nylon roll on one side, then drawn around the nylon roll, and nipped again by the other steel roll.

The properties of the nonwoven fabrics (1)-(6) were measured by the methods described herein and summarized in Tables 1 and 2 below. In Tables 1 and 2, air perm was measured according to ASTM D737-04; Thicknesses were measured according to ASTM D 1777-96 and Mullens were measured according to ASTM D3786-09; Unit weight was measured according to ASTM D3776-96; MD dry heat shrinkage (DHS) and CD DHS were measured according to ASTM D2259-02; MD tension and CD tension were measured on samples with an area of 32 in ² according to ASTM D4595-09; MD rupture and CD rupture were measured on samples with an area of 32 in ² according to ASTM D 1424-09; M-4 web uniformity was measured according to the methods described herein.

Fabrics made from microfibers (ie, fibers with relatively small denier values) are generally known to exhibit better surface smoothness. However, as shown in Tables 1 and 2, fabrics made from fibers with relatively high denier values and triangular cross-sections showed relatively low M-4 web uniformity indices and thus relatively small deniers. Values and surface smoothness were better than fabrics made from fibers with round cross sections. In other words, the results described above indicate that fabrication of nonwovens with fibers with triangular-section cross-sections can significantly improve the surface smoothness of the fabric without reducing fiber size (which can reduce the tensile properties of the fabric). Shows.

In addition, as shown in Table 1, the uncalendered nonwoven fabrics (2) and (3) exhibited an M-4 web uniformity index of about 555, which is the M-4 uniformity of wet nonwoven fabrics made of the same material. It is similar to or better than the gender index. However, the uncalendered nonwoven fabrics (2) and (3) have significantly higher tensile strengths than those of wet nonwoven fabrics made of the same material with the same unit weight.

Nonwovens (1)-(6) by LMS Technologies (Bloomington, Minnesota, USA) using liquid filtration efficiency experiments using latex beads as latex beads as challenge particles and a liquid flow rate of 1 liter per minute The liquid filtration efficiency of) was measured. Nonwovens (1)-(6) by LMS Technologies (Bloomington, Minnesota, USA) using an air fractional efficiency experiment using potassium chloride as the challenge particle and air flow rate of 100 liters per minute. The air filtration efficiency of was measured. Prior to the experiment, the potassium chloride particles were neutralized in a radioactive chamber by generating the same positive and negatively charged particles so that the total charge was zero. ). This process eliminates the variability created by excessively positive or positively charged particles.

In addition, the fabric was prepared using the same method as described above, except that the fabric was made using a PET copolymer having an inherent viscosity of 0.71 dl / g and a PET homopolymer having an inherent viscosity of 0.64 dl / g. As a comparative example, Reemay 2024 was prepared. In addition, by the above mentioned experiments, the liquid and air filtration efficiency of Reemay 2024 was measured. The results are summarized in Tables 3 and 4 below.

As shown in Tables 3 and 4, the air filtration efficiency of the nonwoven fabrics (1)-(3) for filtering particles of 0.3-0.5 microns is somewhat lower than the air filtration efficiency of Reemay 2024 for filtering particles of the same size. Except, nonwoven fabrics (including a single polymer) (1)-(6) showed significantly higher filtration efficiency than Reemay 2024 (comprising two polymers with different intrinsic viscosity values).

Other embodiments are described in the claims.

Claims (35)

In the article,
The article comprises a nonwoven fabric comprising a plurality of continuous yarns,
Each fiber of the plurality of continuous yarns comprises a single polymer, the single polymer comprises polyester, and the continuous yarns are optionally bonded across the nonwoven substrate. In the article,
The article comprises a nonwoven fabric comprising a plurality of fibers,
The nonwoven has a M-4 web uniformity index of up to about 600, the nonwoven has a unit weight of 34 gsm, and the nonwoven has a tensile strength of at least about 10 pounds in the transverse direction as measured according to ASTM D4595-09. article. In the article,
The article comprises a nonwoven fabric comprising a plurality of spunbonded fibers,
The nonwoven fabric has an M-4 web uniformity index of up to about 600. In the article,
The article comprises a nonwoven fabric comprising a plurality of fibers,
When the nonwoven has a unit weight of 34 gsm, the nonwoven has a tensile strength of at least about 10 pounds in the transverse direction as measured according to ASTM D4595-09, and the nonwoven is a polymer having an intrinsic viscosity higher than about 0.64 dl / g. Article does not include. 5. The method according to any one of claims 2 to 4,
Wherein each fiber comprises a single polymer. 5. The method of claim 4,
An article characterized in that the single polymer comprises polyester. 7. The method according to any one of claims 1, 5 and 6,
Single polymers are polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyglycolide, polylactide, polycaprolactone, polyethylene adipate, polyhydroxyalkanoate, or noses thereof An article characterized in that it is a polymer. The method according to any one of claims 1 and 5 to 7,
And wherein the single polymer has an inherent viscosity of up to about 0.7 dl / g. The method according to any one of claims 1 and 5 to 8,
And wherein the single polymer has an inherent viscosity of at least about 0.5 dl / g. 10. The method according to any one of claims 1 to 9,
At least some of the fibers have a circular cross section. The method of claim 10,
Wherein the circular cross section has an average diameter between about 6 μm and about 20 μm. 10. The method according to any one of claims 1 to 9,
At least some of the fibers have a cross section of a triangular-section, a tetragonal-section, a pentagonal-section, or an octagonal-section. The method of claim 12,
Wherein the cross section has an average diameter between about 1 μm and about 6 μm. 14. The method according to any one of claims 2 to 13,
Wherein the fibers are optionally bonded across the nonwoven substrate. The method according to any one of claims 1, 3 and 5 to 13,
When the nonwoven has a unit weight of 34 gsm, the nonwoven has a tensile strength of at least about 10 pounds in the transverse direction as measured according to ASTM D4595-09. The method according to any one of claims 1 and 4 to 15,
The nonwoven fabric is characterized in that it has an M-4 web uniformity index of up to about 600. 17. The method according to any one of claims 1 to 16,
The nonwoven fabric has an average pore size of up to about 125 μm. The method according to any one of claims 1 to 17,
The nonwoven fabric has an average pore size of at least about 5 μm. 19. The method according to any one of claims 1 to 18,
The nonwoven fabric has a maximum thickness of about 550 μm. 20. The method according to any one of claims 1 to 19,
The nonwoven fabric has a thickness of at least about 50 μm. 21. The method according to any one of claims 1 to 20,
The nonwoven fabric has a bubble point of up to about 200 μm. 22. The method according to any one of claims 1 to 21,
The nonwoven fabric has a bubble point of at least about 25 μm. 23. An article comprising the article of any of claims 1 to 22, wherein
Said product is a membrane filtration medium. 24. The method of claim 23,
The product is a reverse osmosis filtration medium. Extruding a composition comprising a single polymer to form a plurality of unbonded continuous yarns, said single polymer comprising polyester;
Zone-bonding the unbonded continuous yarns to form a nonwoven fabric comprising a plurality of bonded continuous yarns. 26. The method of claim 25,
The domain bonding step includes passing-air bonding unbonded continuous yarns to form a nonwoven substrate. 27. The method of claim 25 or 26,
Wherein the zone bonding step is performed at a temperature of up to about 250 ° C. 28. The method according to any one of claims 25 to 27,
Wherein the zone bonding step is carried out at a temperature of at least about 145 ° C. 17. 29. The method according to any one of claims 25 to 28,
Prior to area bonding the unbonded continuous yarns, the method further comprises passing the unbonded continuous yarns through at least two drawing rolls to form oriented fibers. . 30. The method of claim 29,
Two drawing rolls each having a fiber speed of at least about 1,800 meters per minute. 31. The method according to any one of claims 25 to 30,
After zonebonding the unbonded continuous yarns, the method further comprises calendering the nonwoven substrate to form a calendared product. 32. The method of claim 31,
The calendaring step is performed at a temperature of up to about 215 ° C. 32. The method of claim 31,
The calendaring step is performed at a temperature of at least about 145 ° C. 34. The method according to any one of claims 31 to 33,
The calendered product comprises a membrane filtration medium. The method according to any one of claims 25 to 34, wherein
The bonded continuous yarn comprises spunbonded fibers.

Images