JP2017519916A - Heat-stable meltblown web containing multilayer fibers - Google Patents

Abstract

A heat-stable meltblown fiber web comprising a plurality of meltblown multilayer fibers, wherein at least some of the meltblown multilayer fibers each comprise a first polymer with slow crystallization having a Tm of at least about 200 ° C. A heat-stable meltblown fibrous web comprising a first layer and at least one second layer comprising a fast crystallizing second polymer having a Tm of at least about 200 ° C.

Description

  Melt blowing is a process for forming a nonwoven fibrous web of thermoplastic polymer fibers. In a typical meltblowing process, one or more molten polymer streams are extruded through a die orifice and recovered to form a meltblown nonwoven fibrous web by refining with a focused stream of high velocity air ("blown" air). Formed fibers. Meltblown nonwoven fibrous webs are used in a wide variety of applications such as soundproofing, thermal insulation, filtration media, surgical drapes, and wipes.

In summary, this specification discloses a heat-stable meltblown fiber web, the web comprising a plurality of meltblown multilayer fibers, each of the at least selected meltblown multilayer fibers having a T _m of at least about 200 ° C. At least one first layer composed of a first polymer that is a slow crystallization polymer and at least one composed of a second polymer that is a fast crystallization polymer having a T _m of at least about 200 ° C. Including two second layers. These and other aspects of the invention will be apparent from the detailed description below. However, regardless of whether such subject matter was presented in the claims of the originally filed application or in the amended claims or otherwise during patent examination, The summary should not be construed as limiting the claimed subject matter in any way.

1 is a schematic cross-sectional side view showing an outline of some side surfaces of a representative heat-stable meltblown fiber web. 1 is a cross-sectional slice view of a typical meltblown multilayer fiber. FIG. 3 is a cross-sectional slice view of another representative meltblown multilayer fiber. FIG. 3 is a cross-sectional slice view of another representative meltblown multilayer fiber.

  Unless otherwise specified, all drawings and figures in this document are not to scale and are selected for the purpose of illustrating different embodiments of the invention. In particular, the dimensions of the various components are described only as exemplary terms unless otherwise indicated, and the relationship between the dimensions of the various components should not be inferred from the drawings. Like reference numbers in the various drawings indicate like elements. There may be several elements; in such cases, only one or more representative elements may be indicated by reference numbers, but such reference numbers apply to all such elements. It will be understood (in some cases the notation (for example) may be used to distinguish multiple equivalent elements for convenience for purposes of explanation). “Top”, “Bottom”, “Upper”, “Lower”, “Lower”, “Top”, “Front”, “Back”, “Outside”, “Inside”, “Up”, “ It should be understood that terms such as “under” and “first” and “second” may be used in this disclosure, but unless stated otherwise, these terms are used only in a relative sense. It is. In particular, for components that occur in equivalent plurals, the notations "first" and "second" may apply to the description order as described herein (this is , Regardless of whether one of the components is selected as described first).

  In this specification, the term “generally” used as a modifier for a characteristic or attribute, unless otherwise specified, is that the characteristic or attribute is immediately recognized by those skilled in the art, but is not Means that no exact match is required (eg, in the range of +/− 20% for quantifiable properties). Unless otherwise specified, the term “nearly” means a high degree of approximation (eg, within the range of +/− 10% for quantifiable properties), but again in absolute accuracy Or does not require an exact match. Terms such as identical, equal, uniform, constant, exact, etc. are understood to be within normal tolerances or measurement errors that apply to the particular environment, rather than requiring absolute accuracy or perfect match. Should be. Those skilled in the art will use terms such as “substantially no” and “substantially free of” as used herein, for example, on a large scale subjected to routine cleaning procedures. It will be understood that it does not exclude the presence of some amount of material (eg, 0.1% or less), as may occur when using a simple production facility.

Glossary A heat-stable web means a web that exhibits a heat shrinkage of less than 10% when tested, as described in the Examples herein.

  By meltblown fiber / web is meant a fiber / web prepared by meltblowing.

  Melt blowing means extruding the molten fiber forming material through a plurality of orifices in the die to provide a molten filament. The filament (essentially immediately after exiting the orifice) is contacted with a high velocity gas stream (eg, air) and the filament is refined into a (meltblown) fiber, which is then collected as described in detail later in this specification. To do.

  “Filament” means a melt stream of thermoplastic material extruded from a set of orifices, and fiber means a solidified filament. By web is meant a mass of recovered fibers, at least some of which are joined together to the extent that the web has sufficient mechanical integrity to be handled by conventional roll-to-roll equipment. Yes.

T _m means the crystalline melting point of a semi-crystalline polymer measured as described in the examples herein.

  As applied to semi-crystalline polymers, the terms “fast crystallization” and “slow crystallization” are defined herein below and explained in detail.

  By polymer is meant a material made of macromolecules having a number average molecular weight of at least about 10,000. The term “polymer” is used for convenience of description, specifically including copolymers, and unless otherwise specified, non-polymeric additives (often present in thermoplastic polymers for various purposes, for example). May further be included.

  Non-polymer means having a number average molecular weight of less than 10,000.

  By outside is meant the layer, surface or edge that provides the radially outermost portion of the multilayer fiber.

  Disclosed herein is a heat stable meltblown nonwoven fibrous web 1 as shown in the exemplary embodiment of FIG. The web includes a plurality of meltblown multilayer fibers 100. Multi-layer refers to at least one first layer 110 in which the fibers are composed of at least two layers, specifically a first polymer, and at least one second layer 150 composed of a second polymer. It means having. Multi-layer further means at least one of the first layer 110 and at least one of the second layer 150, each comprising an outer edge and / or a major outer surface. Thus, by definition, the term “multilayer fiber” specifically excludes so-called seascore fibers, and the core layer does not include the outer edge or major outer surface (eg, sporadic statistics). Excluding occurrences and defects above).

  FIG. 2 shows a cross-sectional slice of a representative bilayer multilayer fiber 100 (seen along a direction substantially aligned with the major axis of the multilayer fiber). The fiber 100 includes a first polymer layer 110 that includes a major outer surface 118 and an outer edge 116 (in this embodiment, the portion of the layer 110 referred to as the major outer surface and the outer edge). And may include a major inner surface 112). The fiber 100 further includes a second polymer layer 150, which includes a main inner surface 152 and an outer edge 156, which in this embodiment further includes a main outer surface 158. The major inner surface 152 of the second polymer layer 150 and the first major inner surface 112 of the first polymer layer 110 are in direct contact with each other at the inner interface 114.

  FIG. 3 shows another exemplary multilayer fiber 100 (in this case, a five-layer fiber), again in cross-sectional slice view. The exemplary five-layer fiber 100 of FIG. 3 includes alternating first and second layers, a total of three first polymer layers 110 and two second polymer layers 150. Each of the first layers 110 includes at least one major inner surface 112 that is in direct contact with the major inner surface 152 of the second polymer layer 150 at the interface 114 (layers 110 and 150 on two such interface dates). Are identified as 114 and 114 ′, 112 and 112 ′ and 152 and 152 ′ in FIG. 3). In these general types of multi-layer fibers (eg, comprising at least three first layers 110 and at least two second layers 150), at least one of the first layers 110 becomes the inner first layer ( This means that such a first layer is sandwiched between two second layers 150 (shown as 110i in FIG. 3). At least one other first layer 110 may be the outer first layer (shown as 110e in FIG. 3), and the primary in direct contact with the primary inner surface 152 of the second layer 150 at the interface 114 There is another major surface that includes the inner surface 112 and is the major outer surface 118. By definition, the first layer 110 of multi-layer fibers exhibits an outer edge 116 (two such edges 116 and 116 'are shown in FIG. 3), a major outer surface 118, or both. (As described above) For example, in a multi-layer fiber having only a few layers, there is no clear boundary between the first layer part called the main outer surface and the part called the outer edge. It will be appreciated that the more layers there are, the more quickly the outer edge can be distinguished from the main outer surface (eg, the outer first layer). Also, by definition, the second layer 150 of multi-layer fibers exhibits an outer edge 156 (two such edges 156 and 156 'are shown in FIG. 3).

  FIG. 4 shows yet another representative multilayer fiber 100 (in this case fifteen-layer fiber) in cross-sectional slice view. The exemplary fifteen-layer fiber 100 of FIG. 4 comprises eight first polymer layers 110 (six inner layers and two outer layers) and seven second polymer layers 150. In more general terms, multi-layer fibers are at least n first layers, and at least n-1 second layers, at least n-2 second layers individually sandwiched between a pair of first layers. (Where n is a number from 3 to 51) (as used herein, sandwiched individually means that the other second layer is a specific pair of first layers) Meaning it does n’t exist in between).

  From the above description, as defined herein, a multi-layer fiber has at least one, often several (eg, 5, 10, or more) between the first layer 110 and the second layer 150. It will be appreciated that the inner interface (s) 114 extend substantially along the long axis of the multi-layer fiber without any predetermined and essentially uninterrupted interface. That is, in the multilayer fiber as defined herein, the first and second layers and the interface between them are essentially continuous and essentially the entire length of the multilayer fiber without interruption. Extending along (except for sporadic variations, breaks, etc. that are statistically understood to be present in any fiber produced in the actual meltblowing process). Thus, by definition, the multi-layer fibers disclosed herein are distinct from single-layer fibers comprising a polymer blend (where the two polymer phases are distributed, for example, almost randomly (eg, island-like, small One polymer phase, such as spherical, tendrils, etc. is dispersed between the other polymer phases)). One skilled in the art will recognize that such blended polymer fibers may exhibit a single polymer phase that extends along the long axis of the fiber to a certain extent, although such unstable and unpredictable occurrences are described herein. It will be understood that it cannot be equivalent to the predetermined multilayer fiber disclosed.

  In many embodiments, the interface 114 between the first layer and the second layer may, on average, be generally or even substantially planar (as depicted in FIGS. 2-4). As you can see). However, the depictions in FIGS. 2-4 are ideal, and in practice, the various layers, surfaces, and interfaces need not be strictly planar at any location, and the outer shape of the fiber 100 Note that does not necessarily have to be a perfect circle. In addition, a general type of multilayer fiber having two first layers 110 and one second layer 150 sandwiched therebetween is not shown in any of the figures, but the present disclosure is It will be understood that this includes a simple structure. Similarly, multi-layer fibers having an even number of second layers, or multi-layer fibers having as many or more second layers as the first layers are not shown in these figures, but such arrangements are also disclosed herein. Is included.

  In at least some embodiments, the first layer (s) 110 and the second layer (s) 150 are each single component layers. A single component layer means a layer having essentially the same composition over the thickness, width and length of the layer, and a single component layer is substantially in composition over the thickness, width and length of the fiber. As long as they are uniform (except for the sporadic statistical fluctuations that those skilled in the art understand are present in any practical manufacturing process). In some embodiments, the first polymer is the only polymer component of the first layer 110 and the second polymer is the only polymer component of the second layer 150.

  The average diameter of the meltblown multilayer fiber (eg, measured by optical microscopy using representative fiber sampling) may be in any desired range. Melt blow (eg, due to the tendency of high velocity “blowing” air to reduce the diameter of the melted filament) is particularly suitable for forming so-called microfibers (meaning fibers having an average diameter of 10 microns or less). It will be understood. Thus, in various embodiments, the average diameter of the meltblown multilayer fiber may be less than about 30, 20, 15, 10, 5, 2, or 1 micron. In further embodiments, the average diameter of the meltblown multilayer fiber may be at least less than about 0.5, 1, 2, or 5 microns.

Multilayer fiber 100 includes at least one layer 110 comprising a first polymer having a T _m of at least about 200 ° C. and at least one second layer 150 comprising a second polymer having a T _m of at least about 200 ° C. It is composed of This means that both the first polymer and the second polymer must be able to exhibit a crystalline melting point T _m (at least about 200 ° C.) under at least some conditions. That is, such polymers need to be able to form a significant number of crystalline domains (eg, under sufficiently slow cooling conditions), and the terms first polymer and second polymer can, eg, cool very slowly. It does not form any significant crystalline domains, and therefore does not contain essentially amorphous polymers that cannot exhibit a well-defined crystalline melting point. In various embodiments, the first polymer may exhibit a T _m of at least about 210, 220, 230, 240, 250, or 260 ° C. In various embodiments, the second polymer may exhibit a T _m of at least about 210, 220, 230, 240, 250, or 260 ° C.

  The first polymer and the second polymer differ in that the first polymer is a slow crystallization polymer and the second polymer is a fast crystallization polymer. In short, fast crystallization polymers are those where solidified meltblown fibers are generally exposed to a slower cooling process under the relatively rapid cooling conditions used in conventional meltblowing processes. By a polymer that forms crystalline domains at a rate fast enough to exhibit a degree of crystallinity similar to the wax value. In contrast, a slow crystallization polymer indicates that, under the cooling conditions used in conventional meltblowing processes, the solidified meltblown fibers are generally exposed to a slower cooling process. By a polymer that forms crystalline domains at a rate sufficiently slow to exhibit a crystallinity significantly lower than the wax value.

Polymers can be screened for the property of slow crystallization and fast crystallization in the following manner. The polymer samples, so as to erase all the heat history present in the sample, initially, may be exposed to a first heating step at a temperature above or the T _m of up to T _m. The sample, which has a standard thermal history and thus has been subjected to that thermal history, may then be slowly subjected to cooling (for this purpose, a cooling rate of 10 ° C./min can be used). ). The sample to well below T _m and up to T _m (e.g., to room temperature) to cool. Subsequently, the sample is _subjected to a second heating step at a temperature up to and above T _m (eg, 10 ° C./min). Thereafter, the heat of fusion and cooling crystallization is calculated from the data obtained from the second heating step, from which the degree of crystallinity (crystallinity%) is calculated (the above measurements and calculations are arbitrary suitable differentials). Using a scanning calorimeter “DSC” apparatus, for example, “DSC as Problem Solving Tool: Measurement of Percent Crystallinity of Thermoplastics” (Perkin-Elmer (2000)) (herein incorporated by reference in its entirety). Or may be implemented using the method outlined in

Similarly, another polymer sample, in order to erase all the heat history present in the polymer may be exposed to a first heating step at a temperature above the temperature or the T _m of up to T _m. This sample, which has a standard thermal history and has been imposed with that thermal history, can then be subjected to rapid cooling (for this purpose, a cooling rate of 200 ° C./min can be used). ). The second heating step is then performed and the crystallinity can be calculated for the rapidly cooled sample in the same manner as described above.

The crystallinity of the rapidly cooled sample and the slowly cooled sample can then be compared. A difference in crystallinity of at least about 20% under slow cooling conditions versus slow cooling conditions indicates a polymer that is slow to crystallize. As a specific example, poly (ethylene terephthalate) (PET) is typical of slow crystallization polymers as defined herein. PET can form crystalline domains, often (eg, after slow cooling from the lysate), a well-defined T _m in the range of about 250-260 ° C., and for example, 30-40% Or it may show crystallinity within a range higher than that. However, for example, when rapidly cooled from the melt as described above, PET may exhibit crystallinity in the range of less than 30% (often significantly below 30%).

  In contrast, poly (butylene terephthalate) is typical of fast crystallizing polymers and typically has a similar crystallinity (for example, each other, whether fast or slow cooling). Within about 10%).

As noted above, DSC screening can be useful in identifying potentially useful first and second polymers. However, for the purposes of this specification, the simplest method for identifying a semi-crystalline polymer as a first polymer or a second polymer (the first criterion, an identifiable T _m above 200 ° C. Is to produce a meltblown web composed of single component (non-multilayer) meltblown fibers of the polymer under evaluation. Melt blowing process conditions within the conventional range of melt blowing for that particular material (extruder temperature, die and blown air, blown air volumetric flow rate and linear velocity, die collector, as is well understood by those skilled in the art It is necessary to manufacture using distance etc. although it is not limited to these. (Examples of conventional meltblown conditions for certain polymers are found in the examples herein).

  The single component test web produced in this way can then be subjected to a heat shrink test, as disclosed in the examples herein. A polymer that exhibits less than 10% heat shrink as a single component meltblown web is a second polymer as defined herein (which also meets the other criteria disclosed herein) As far as). In various embodiments, the second polymer may exhibit a heat shrinkage of less than 8, 6, 4, or 2%. As a meltblown homopolymer web, a polymer that exhibits a thermal shrinkage of 10% or more is the first polymer as defined herein (this also meets other criteria disclosed elsewhere herein) As far as you can). In various embodiments, the first polymer may exhibit a thermal shrinkage of greater than about 20, 30, 40, or even 50%.

Suitable first polymers are, for example, polyesters (poly (ethylene terephthalate), poly (ethylene naphthalate), poly (trimethylene terephthalate), etc.), and at least some polylactic acid that can exhibit a T _m of greater than 200 ° C. It may be selected from (for example, those having a relatively high content of D-lactide). Any desired combination of such first polymers may be used. Suitable second polymers are selected from, for example, polyesters such as poly (butylene terephthalate), polyolefins such as polymethylpentene, and other polymers such as syndiotactic polystyrene, and any desired combinations thereof. May be.

  The first polymer and the second polymer may be present in a weight ratio of about 95: 5 to about 45:55 (first: second), which is the first polymer in the meltblown fibers of the web and Calculated based on the total weight of the second polymer, including any type of any polymer that may be present in the single component meltblown fibers present in addition to the multilayer fiber, but short It does not include any first polymer or second polymer that may be present in the fiber. In various embodiments, the weight ratio of the first polymer to the second polymer is at least about 50:50, 60:40, 70:30, 75:25, 80:20, 85:15, or 90:10. It may be. In further embodiments, the weight ratio of the first polymer to the second polymer is about 90:10, 85:15, 80:20, 75:25, 70:30, 60:40, or 50:50 or less. It may be.

  As described in more detail below, the arrangement disclosed herein allows a relatively small amount (weight percent) of the second polymer to be used while simultaneously using the first polymer alone. Significant advantages over superior performance are achieved. Such an arrangement within the multi-layer fiber may, for example, reduce the thickness of at least some of the second layers 150 (ie, the average distance between the major surfaces 152 and 152 ′ as shown in FIG. 3). It can be achieved by making it less than the thickness of at least some of the one layer 110 (ie, the average distance between the major surfaces 112 and 112 'as also shown in FIG. 3). Such methods can provide one or more second layers while minimizing the total amount of second polymer used relative to the total amount of first polymer used. Thus, in various embodiments, the ratio of the thickness of the first layer (s) 110 to the thickness of the second layer (s) 150 is about 1.2: 1, 1.5: 1. (In these calculations, the thickness of the outer layer having an arcuate major surface (eg, layer 110e in FIG. 3) is the same cross-sectional area as the outer layer). Can be the thickness of a rectangular area having

  Encapsulating one or more second layers in a second polymer that is rapidly crystallized allows the first polymer to be slow to crystallize even under relatively rapid cooling conditions that are mainstream in current meltblowing. It has been found that the crystallization of can be significantly accelerated. This can provide a solidified product comprising a first polymer with significantly increased crystallinity, resulting in, for example, more than if it is composed of a single component fiber of the first polymer A meltblown web can be provided that exhibits significantly lower heat shrinkage. Advantageously, this is, for example, as described above, so that the total weight ratio of the second polymer to the first polymer can be maintained at a relatively low concentration, for example a smaller number of second polymer layers and / or Alternatively, it can be achieved with a thinner second polymer layer. In many cases, such a second polymer is significantly more expensive than the first polymer, which can provide significant advantages.

  Further, by encapsulating one or more second polymers in the form of one or more layers as described herein, the second polymer and the first polymer are homogenized, eg, in the form of a polymer blend. It has been found that the crystallization of the first polymer can be accelerated better than when it is physically mixed (for example, dissolved blend). This is a surprising result. One skilled in the art will recognize that the accelerating effect of the second polymer provides a nucleation site for the first polymer (rapidly crystallized) at the interface between the second polymer and the first polymer. Would be expected to be obtained from the surface. Thus, by mixing the second polymer and the first polymer as a blend, between the first polymer in multiple parcel forms (eg, from whiskers or globules to possibly macromolecular segments). This is expected in the layer form disclosed herein because the second polymer is expected to be dispersed in this, resulting in a significantly greater second polymer surface area between the first polymers. It is expected to be much more effective at accelerating crystallization of the first polymer compared to the case of containing two polymers. However, the examples presented herein show that when the weight ratio of the second polymer to the first polymer is similar or even lower, the multilayer meltblown fibers disclosed herein are better than blended polymer meltblown monolayer fibers. Also indicates that it is considered to exhibit low heat shrinkage. For this reason, this is an unexpectedly advantageous result.

  In some embodiments, the web 1 may additionally include optional short fibers 200, as shown in the exemplary embodiment of FIG. In the web 1, the short fibers 200 are distributed throughout the network of meltblown fibers and mixed within the network of meltblown fibers. In various embodiments, the short fibers 200 may comprise at least about 5, 10, 20, 30, or 40 wt% of the total weight of the web's fiber material (eg, meltblown fibers and short fibers). In further embodiments, the short fibers 200 may comprise up to about 60, 50, 40, 30 or 20 wt% of the total weight of the fiber material of the web.

  Regardless of these specific manufacturing processes or compositions, the short fibers are usually mechanically cut to a specific predetermined or discernable length and added to the nonwoven web in solidified form. The length of the short fibers is often much shorter than the length of the meltblown fibers, and in various embodiments may be about 1-8 cm, or about 2.5 cm-6 cm. The average fiber diameter of the short fibers is often on average greater than about 15 μm, and in various embodiments may be greater than 20, 30, 40, or 50 μm. Thus, in many embodiments, the average fiber diameter of the short fibers may be at least about 2, 4, or 8 times the average diameter of the meltblown multilayer fibers.

  In some embodiments, the short fibers may include a synthetic polymer material. In some embodiments, the short fibers may include natural fibers (eg, selected from fibers derived from bamboo, cotton, wool, jute, agave, sisal, coconut, soybean, linen, etc.). If desired, at least some compositions of short fibers can be used during the molding process such that they can be melt bonded to each other and / or to meltblown fibers (eg, to form a molded article comprising a meltblown web). May be selected). Alternatively, it can be made from materials that have properties (eg, melting points) that do not bond to each other or to meltblown fibers during the molding process.

  Suitable staple fibers may be prepared, for example, from any suitable polyester and copolymers thereof, polyolefins such as polyethylene, polypropylene and copolymers thereof, polyamides, or any combination thereof. The short fibers may be crimped fibers such as those described in US Pat. No. 4,118,531 (Hauser). The crimped fibers may have a continuous wavy, crimped or jagged shape along the length. The short fibers may include crimped fibers including, for example, about 10-30 crimps / cm. The short fibers may be single component fibers or multicomponent fibers.

  Various other components may be present in the web 1, particularly in the meltblown multilayer fiber 100, as required for various purposes. For example, any desired type of particulate additive may be present in the web 1. In particular, when the web 1 is used for filtration purposes, particulate additives such as any suitable adsorbent, catalyst agent, chemical reactant and the like may be present. The meltblown multi-layer fiber 100 may have any suitable auxiliary components present therein, among others. Such components may be present, for example, in the first polymer and / or second polymer described above when obtained, and also include, for example, processing additives, antioxidants, UV stabilizers. In addition, flame retardant additives may be included. In some embodiments, the first polymer can include one or more non-polymer nucleating agents (eg, melt additives), such as various stearic acids, carboxylates, nitrogen-containing heterocycles. It may be selected from formula aromatic compounds and the like. However, in certain embodiments, the first polymer comprises less than about 5, 2, 1 or 0.5 wt% of any non-polymer nucleating agent. In certain embodiments, the first polymer is substantially free of any non-polymer nucleating agent.

In some further embodiments, the web 1 is added in the form of a separate layer of multilayer fibers, or blended with a first polymer or a second polymer (eg, as a melt additive), etc. And may contain at least some amount of polymer nucleating agent. Such materials may include, for example, polyester-sulfonates, certain polyolefins such as polypropylene, polyethylene, and copolymers and blends thereof. However, it will be appreciated that some of such materials may exhibit a T _m of less than 200 ° C. and therefore cannot be considered the second polymer disclosed herein. However, such materials can still provide advantages as long as they are not present in amounts that unacceptably affect, for example, the heat shrinkage of the resulting web. Thus, in various embodiments, the multilayer fiber 100 may include up to about 5, 2, 1 or 0.5 wt% of any polymeric nucleating agent. In certain embodiments, the multilayer fiber 100 is substantially free of any polymeric nucleating agent.

In some embodiments, it may be advantageous to minimize the amount of polymeric material that exhibits a T _m of less than 200 ° C. in the meltblown fibrous web. (In this context, the term “polymer material exhibiting a T _m of less than 200 ° C.” specifically refers to any polymer segment of such material that may be present in the copolymer, not just the homopolymer chain of the polymer material. including). Thus, in various embodiments, any polymeric material having a T _m of less than 200 ° C. is about 20, 10, 5, 2, based on the total fiber material of the web (including, for example, short fibers). 1 or less than 0.5 wt%. In a further embodiment, meltblown fiber web does not contain a polymeric material having a T _m of a less than 200 ° C. substantially. In some embodiments, it can be particularly useful to minimize the amount of polymeric material that exhibits a T _m of less than 200 ° C. in the meltblown fibers of the web. Thus, in various embodiments, any polymeric material having a T _m of less than 200 ° C. is about 20, 10, 5, 2, 1 in the web meltblown fibers (including any non-multilayer meltblown fibers, etc.). Or it exists in less than 0.5 wt%. In a further embodiment, meltblown fibers of the web are substantially free of polymeric material having a T _m of a less than 200 ° C..

  In various embodiments, the web 1 disclosed herein has a thermal shrinkage (measured as disclosed in the examples herein) of less than about 10, 8, 6, 4, 2 or 1%. May be shown. As discussed herein, such characteristics may provide significant advantages in certain applications.

  As mentioned above, the meltblown fibers defined above are used for the nonwoven web disclosed herein. Those skilled in the art will know that the meltblown process, and the meltblown fibers and meltblown nonwoven webs formed by such processes, for example, processes such as melt spinning, and such as meltspun fibers and meltspun (eg, spunbonded) nonwoven webs, etc. It will be understood that this is distinct from the product produced. The terms “meltspinning” and “meltspun” are used to extrude a melted filament through a set of orifices, followed by a space (moving airflow) to assist in cooling the filament. (Which may be included) is a technical term that refers to forming a fiber by passing the filament through to cool and solidify the filament to form a fiber. Thereafter, the cooled filament is passed through a drafting device to at least partially draft the filament (e.g., to draw orientation and improved physical properties). For this reason, meltblown involves the extrusion of molten filaments into a high velocity focused air stream introduced by an air outlet opening (eg, an air knife) placed in close proximity (eg, within 1 cm) to the extrusion orifice. Melt spinning can be distinguished from meltblown. Those skilled in the art will appreciate that meltblown and melt spinning impart to fibers and webs thus obtained different properties (eg of molecular orientation and physical properties obtained) (even if the fibers / webs are of similar composition). It will be appreciated that, for this reason, meltblown fibers and meltspun fibers are easily distinguishable from each other.

  For this reason, the meltblown fiber described herein is a meltblown die from which molten multilayer filaments can be discharged, immediately after leaving the meltblown die orifice so that the filaments are thinned into meltblown fibers, Devices for impinging high velocity "blowing" air on the molten multilayer filament, collectors for recovering meltblown fibers, and various other equipment customarily used for meltblown (eg, extruders, temperature control devices, etc.) It may be manufactured by using.

  Such devices are described, for example, in “Superfine Thermoplastic Fibers” Industrial Engineering Chemistry, Vol. 48, 1342 et seq. (Et sec) (1956) "(van Wente) or the title" Manufacture of Superfine Organic Fibers "published on May 25, 1954 (Report No. 4364 of the World Research, A. Lab. , Boone, CD, and Fluharty, EL). Such an apparatus may be modified for the specific purpose of producing multi-layer meltblown fibers, for example, supplying first and second flow streams of molten polymer to a feed block, respectively, There may be provided first and second extruders that combine the first and second flow streams into a single layered flow stream, followed by distribution of the single layered flow stream into a plurality of orifices. Methods and apparatus that can be used to produce multilayer meltblown fibers are discussed in further detail, for example, in US Pat. Nos. 5,207,790 and 5,232,770 (Joseph). Multilayer fibers produced in this way are, for example, blended polymer monolayer fibers that are blended with two melted polymers in a single extruder into a single blend flow stream and then extruded through a normal orifice. It is clear that there is a distinction. The multilayer fiber produced in this way is a sheet of material in which a first molten polymer stream is extruded from a first inner orifice and a second molten polymer stream is extruded from a second orifice that annularly surrounds the inner orifice. It will be further clear that it is distinct from the score fiber.

  In some embodiments, meltblown multilayer fibers may be collected on a flat surface (eg, a porous collection belt or net) or on the surface of a single collection drum. In other embodiments, the meltblown multilayer fibers may be collected, for example, in a gap between the focused collection surfaces that are between the first collection drum and the second collection drum. Such an arrangement allows the meltblown fibers 100 to be present in the web 1 with at least a general or substantially “C” shaped cross-sectional structure. Such an arrangement (described in detail herein in US Pat. No. 7,476,632 (Olson), which is hereby incorporated by reference in its entirety) may, for example, be bulky and / or other beneficial. The improvement of the characteristic etc. can be brought about.

  In some embodiments, short fibers may optionally be incorporated into the meltblown web, as described above. This may be done, for example, by injecting a short fiber air suspension into the fine filament / fiber air suspension (they are solidified while the molten filament is moving from the die orifice to the collector). The process of forming fibers in this way is a statistical process, so the terms “filament” and “fiber” are somewhat synonymous at this stage of the process). Thereby, a mixed air flow of the multilayer meltblown fiber and the short fiber can be formed, and this airflow can be collided with the collector to collect the mixed multilayer meltblown fiber and the short fiber as a fiber lump. it can. Apparatus and processes for injecting short fibers into, for example, a meltblown fiber stream are described in further detail in, for example, US Pat. No. 7,989,371 (Angadjivand) and US Pat. No. 4,118,531 (Hauser).

  In some embodiments, at least some short fibers can function as binding fibers, as described above. Alternatively, or in addition, at least some meltblown fibers may be bonded (eg, melt bonded) to each other (eg, depending on the recovery method, etc.). If desired, any suitable post-bonding process may be used (eg, point bonding by a calendaring operation or the like).

  The meltblown fiber web described herein can be applied to manufactured articles such as insulation and sound insulation articles, liquid filters and gas filters (eg, webs, sheets, scrims, fabrics, etc. of any suitable thickness, dimensions, etc.) As well). Although any suitable usage is envisioned, the heat shrink resistance of the meltblown web may make such articles particularly suitable for use in relatively high temperature environments. Such articles may find use in a wide range of applications (eg, sound insulation and / or insulation of vehicles or building components), such as in protective devices or clothing. Such meltblown webs may be particularly useful in thermal insulation articles and / or high temperature soundproofing articles, but in some applications (eg, automotive bonnet liners) such articles may serve both roles. Please note that. The meltblown fiber web 1 may be advantageous for the formation of certain articles and may be combined with any desired additional layers (eg, scrim layers, front layers, etc.). The web 1 may be processed (eg, molded, cut, etc.) with any such additional layers to form an article of a particular structure.

List of Exemplary Embodiments Embodiment 1 is a heat stable meltblown fiber web comprising a plurality of meltblown multilayer fibers, wherein at least selected meltblown multilayer fibers each have a T _m of at least about 200 ° C. At least one first layer composed of a first polymer that is a slow polymer and at least one first layer composed of a second polymer that is a fast crystallizing polymer having a T _m of at least about 200 ° C. And an average weight ratio of the first polymer to the second polymer of the meltblown multilayer fiber is about 45:55 to about 95:05, and the heat stable meltblown fiber web is less than about 10% Shows thermal shrinkage.

Embodiment 2 is a web according to embodiment 1, the first polymer showed the T _m of at least about 240 ° C., the second polymer exhibits a T _m of a least about 240 ° C.. Embodiment 3 is the web of any one of embodiments 1-2, wherein the average weight ratio of the first polymer to the second polymer of meltblown fibers is from about 60:40 to about 90:10. . Embodiment 4 is the web of any one of embodiments 1-3, wherein the average weight ratio of the first polymer to the second polymer of the meltblown fibers is from about 70:30 to about 80:20. . Embodiment 5 is the web according to any one of Embodiments 1 to 4, wherein the first polymer is poly (ethylene terephthalate), poly (ethylene naphthalate), poly (lactic acid), poly (trimethylene). Terephthalate), and a polyester selected from the group consisting of combinations thereof. Embodiment 6 is the web described in any one of Embodiments 1 to 4, and the first polymer is poly (ethylene terephthalate). Embodiment 7 is the web according to any one of Embodiments 1-6, wherein the first polymer is substantially free of non-polymer nucleating agents.

  Embodiment 8 is the web according to any one of Embodiments 1 to 7, wherein the second polymer is selected from the group consisting of poly (butylene terephthalate), polymethylpentene, and syndiotactic polystyrene. .

  Embodiment 9 is the web according to any one of Embodiments 1 to 8, wherein at least selected multilayer fibers are each sandwiched between at least a pair of first layers and each of them. A second layer. Embodiment 10 is the web according to any one of embodiments 1-8, wherein at least selected multilayer fibers each comprise at least three first layers and at least two second layers, each The second layer is individually sandwiched between the pair of first layers. Embodiment 11 is the web according to any one of Embodiments 1-8, wherein at least selected multilayer fibers each comprise at least 5 first layers and at least 4 second layers, each The second layer is individually sandwiched between the pair of first layers. Embodiment 12 is the web according to any one of embodiments 1-8, wherein at least selected multilayer fibers each comprise at least n first layers and at least n-1 second layers. At least n-2 of the second layer is individually sandwiched between the first layers, and n is a number from 7 to 51.

  Embodiment 13 is the web according to any one of embodiments 1 to 12, wherein the first layer is a single component layer and the second layer is a single component layer. Embodiment 14 is the web of any one of embodiments 1-13, wherein the plurality of meltblown fibers collectively exhibit an average fiber diameter of less than about 10 micrometers.

  Embodiment 15 is the web of any one of embodiments 1-14, wherein the web further comprises short fibers, the short fibers being about 5 wt% to about 50 wt% based on the total weight of the web's fibrous material. Occupy.

  Embodiment 16 is the web of any one of embodiments 1-15, wherein the web exhibits a heat shrinkage of less than about 6%. Embodiment 17 is the web of any one of embodiments 1-15, wherein the web exhibits a heat shrinkage of less than about 2%.

Embodiment 18 is the web of any one of embodiments 1 to 17, the meltblown fibers of the web, including any polymeric material exhibiting a T _m of a less than 200 ° C. to about 5 wt% or less. Embodiment 19 is the web of any one of embodiments 1 to 17, the meltblown fibers of the web are substantially free of any polymeric material which exhibits a T _m of a less than 200 ° C..

  Embodiment 20 is an article comprising the thermally stable meltblown fiber web according to any one of embodiments 1-19, the article comprising a heat insulating article, a soundproof article, a fluid filtration article, or a combination thereof. Selected from the group.

  Embodiment 21 is the article of embodiment 20, which is a soundproof article that exhibits a thermal shrinkage of less than about 5%.

Embodiment 22 extrudes a molten multilayer flow stream from an orifice of a melt blow die to form a molten multilayer filament, refines the molten multilayer filament with a high velocity gas stream to form a multilayer meltblown fiber, and as a fiber mass Recovering a multilayer meltblown fiber, wherein at least selected multilayer meltblown fibers of the mass from which the fiber flow stream is recovered are each a slowly crystallizing polymer having a T _m of at least about 200 ° C. At least one first layer composed of a first molten polymer and at least one second layer composed of a second molten polymer that is a fast crystallizing polymer having a T _m of at least about 200 ° C. And a layer.

  Embodiment 23 is the method of embodiment 22, wherein the thin multilayer filament forms an air suspension of multilayer meltblown fibers, and the method injects an air suspension of short fibers into the air suspension of the multilayer fiber. And collecting the mixed multilayer meltblown fibers and short fibers as a fiber mass. Embodiment 24 is a method according to any one of embodiments 22 to 23, wherein the method combines at least some fibers of the fiber mass together to form a heat-stable meltblown fiber web. Further includes.

  Embodiment 25 is a web as described in any one of Embodiments 1-19 manufactured by the method as described in any one of Embodiments 22-24. Embodiment 26 is an article according to any one of embodiments 20-21, manufactured by a method according to any one of embodiments 22-24.

Test Method Heat Shrink Heat shrink melt blown webs can be obtained using three samples of 10 cm x 10 cm. The dimensions of each sample are measured both in the machine direction (MD) and in the cross direction (CD) before and after being placed in a 180 ° C. Fisher Scientific Isotemp Oven (or equivalent) for 15 minutes. The shrinkage of each sample is calculated for MD and CD using the following formula:

式中、L_０は試料の初期長さであり、Ｌは試料の最終長さである。平均収縮値を計算し、報告する。

Where L ₀ is the initial length of the sample and L is the final length of the sample. Average shrinkage value is calculated and reported.

T _m (crystalline melting point)
The T _m of the polymer sample can be obtained using a TA Instruments Q2000 Modulated Differential Scanning Calorimeter (MDSC) or equivalent. Weigh the sample and place it in a compatible aluminum pan. A first heat is applied to heat the sample to a temperature above the estimated T _m of the sample, and then the sample is cooled at a sufficiently slow rate (eg, 10 ° C./min) to cause crystallization. After these preheating / cooling steps, for example, a second heat is applied at a heating rate of 10 ° C./min, and the heat flow is observed. Crystalline melting point T _m is as reliably understood by those skilled in the art, as the vertex of the primary melting peak which is well-defined (if such a peak is present), can be obtained from the second heat data.

Meltblown web manufacturing apparatus and manufacturing method Meltblown web is a Went, Van A. et al. , “Superfine Thermoplastic Fibers” ((Industrial Engineering Chemistry, Vol. 48, page 1342 et seq. (1956)) and Naval Research Laboratories, report No. 4364, date of 5th of May, 54, 1954 Wente, Van. A. Boone, C.I. D. , And Fluharty, E .; Manufactured by using equipment and processes similar to those described in (L.). This apparatus used an extruder equipped with a gear pump to control the melt flow of the polymer and distributed the melt flow to a melt blow die having an annular smooth orifice with a 5: 1 length to diameter ratio. The orifices were arranged linearly on the die surface at intervals of 10 orifices / cm. A feed device (air knife) was provided on the die surface to impinge "blown" air onto the melt filament at high speed in a focused manner, essentially immediately after the air melt filament was discharged from the orifice of the meltblowing die.

  In the multilayer fiber embodiment, the apparatus is equipped with two extruders (generally in a manner similar to that disclosed in Example 1 of US Pat. No. 5,207,970), and the discharge rate of each extruder is independent. Each extruder has a gear pump so that it can be controlled and each extruder is a splitter feedblock similar to that described in US Pat. Nos. 3,480,502 (Chisholm) and 3,487,505 (Shrenk) Improved to be configured to feed a melt extrusion. The splitter feed block was configured to deliver a multilayer molten polymer stream to the meltblowing die, generally as described above.

Representative Example (Example 1)
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced using the apparatus and general method described above and operated as described below. The first polymer was a poly (ethylene terephthalate) (PET; 0.54 intrinsic viscosity) resin obtained from Nan Ya Plastics Corporation (America, Livingston, NJ) under the trade name N211. The second polymer was poly (butylene terephthalate) (PBT) (trade name Valox-195-1001) obtained from SABIC Innovative Plastics, Pittsfield, MA.

  The first and second extruders delivered PET and PBT melt streams to the feedblock, respectively. The gear pump was adjusted to deliver a polymer melt at a weight ratio of 75: 25 / PET: PBT to the feedblock and maintain a total polymer processing rate of 0.175 kg / hr / cm die width with the meltblowing die. The die is held at about 305 ° C., the feed block is held at about 305 ° C., and for the first and second extruders, the melt temperature of the extruder (near the discharge end of each extruder barrel). Were held at about 305 ° C. and 270 ° C., respectively. The air knife gap width of the blowing air supply device was about 0.76 mm, and the high-speed blowing air temperature was maintained at a set point of about 400 ° C. and a pressure suitable for producing a uniform web. The melt stream was alternately merged into a five-layer melt stream upon ejection from the feedblock, with the first, third and fifth layers being PET and the second and fourth layers being PBT.

The meltblown multilayer fibers thus formed were collected on an air permeable belt with a DCD (die / collector distance) of about 38 cm. The fiber mass formed in this way showed sufficient mechanical integrity and functioned as a self-supporting nonwoven web, and the second bonding operation was not performed. The meltblown multilayer fiber was composed of five alternating layers (three first PET layers and two second PBT layers). Meltblown multilayer fiber showed an average diameter of less than about 10 micrometers, meltblown fiber web had a basis weight of about 130 g / m ^2.

(Example 2)
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a manner generally similar to Example 1. However, the gear pump was adjusted to deliver a molten polymer with a 50:50 weight ratio of PET to PBT. Both the die and the feed block were held at about 280 ° C, and the melting temperatures of the first extruder and the second extruder were held at about 280 ° C and 270 ° C, respectively. The temperature of the high-speed blowing air was maintained at a set point of about 390 ° C. The thus formed meltblown multilayer fiber was collected at a DCD (die / collector distance) of about 30.5 cm. Meltblown multilayer fiber shows a mean diameter less than about 10 micrometers, meltblown fiber web had a basis weight of about 130 g / m ^2.

(Example 3)
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a manner generally similar to Example 1. However, the second polymer was not poly (butylene terephthalate) but polymethylpentene (PMP; obtained from Mitsui Chemicals, Rye Brook, NY under the trade name TPX). The first polymer: second polymer (PET: PMP) weight ratio was about 75:25 and the meltblown die maintained a total polymer processing rate of 0.14 kg / hr / cm die width.

Both the die and the feed block were held at about 300 ° C., and the melting temperatures of the first and second extruders were about 285 ° C. and 300 ° C., respectively. The temperature of the high-speed blowing air was kept at the set point of about 400 ° C. The meltblown multilayer fibers thus formed were collected at a DCD (die / collector distance) of about 15 cm. The meltblown multilayer fiber was composed of five alternating layers (three first PET layers and two second PMP layers). Meltblown multilayer fiber shows a mean diameter less than about 10 micrometers, meltblown fiber web had a basis weight of about 90 g / m ^2.

Example 4
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a manner generally similar to Example 3. However, the first to second (PET: PMP) weight ratio was about 90:10.

(Example 5)
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a manner generally similar to Example 3. However, the first to second (PET: PMP) weight ratio was about 80:20.

(Example 6)
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a manner generally similar to Example 3. However, the first to second (PET: PMP) weight ratio was about 70:30.

(Example 7)
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a manner generally similar to Example 3. However, the first to second (PET: PMP) weight ratio was about 60:40.

The webs of Examples 4-7 contained meltblown multilayer fibers having a basis weight of about 90 g / m ^{2 and} having an average diameter of less than about 10 micrometers.

(Example 8)
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a conventional manner similar to Example 3. However, the splitter feed block was configured such that the multilayer fiber included 17 alternating layers (eight first PET layers and nine second PMP layers). The PET: PMP weight ratio was maintained at about 75:25. Both the die and the feed block were held at about 300 ° C., and the melting temperatures of the first and second extruders were held at about 285 ° C. and 300 ° C., respectively. The temperature of the high-speed blowing air was kept at the set point of about 400 ° C. The meltblown multilayer fibers thus formed were collected at a DCD (die / collector distance) of about 15 cm.

Example 9
A meltblown fiber web comprising a plurality of meltblown multilayer fibers was produced in a manner generally similar to Example 3. However, the splitter feed block was configured such that the multilayer fiber included two alternating layers (one first PET layer and one second PMP layer). The PET: PMP weight ratio was maintained at about 75:25. The die and feedblock were both held at about 300 ° C., and the melting temperatures of the first and second extruders were held at about 285 ° C. and 300 ° C., respectively. The temperature of the high-speed blowing air was kept at the set point of about 400 ° C. The meltblown multilayer fiber thus formed was collected with a DCD (die / collector distance) of about 15 cm.

The webs of Examples 4-9 exhibited a basis weight in the range of about 90 g / m ² and contained meltblown multilayer fibers having an average diameter of less than about 10 micrometers.

Comparative Example Comparative Example 1
The meltblown nonwoven web was produced using processing conditions generally similar to those of Example 1. However, no splitter feedblock was used and all meltblown fibers were the first polymer, specifically poly (ethylene terephthalate) (PET, obtained from Nan Ya Plastics Corporation (America, Livingston, NJ) under the trade name N211. Intrinsic viscosity 0.54) A single-layer fiber made of resin.

  The extruder gear pump was adjusted to deliver molten PET polymer at a processing rate of about 0.175 kg / hr / cm die width. The die was held at about 305 ° C and the feedblock was held at about 305 ° C, and the extruder melt temperature was held at about 305 ° C. The air knife gap width of the blowing air supply device was about 0.76 mm, and the high-speed blowing air temperature was maintained at a set point of about 400 ° C. and a pressure suitable for producing a uniform web. The meltblown multilayer fibers thus formed were collected with a DCD of about 38 cm.

Comparative Example 2
Shrinkage data show that all fibers are monolayer fibers consisting of a second polymer, specifically poly (butylene terephthalate) (PBT) obtained from SABIC Innovative Plastics (Pittsfield, MA) under the trade name Valox-195-1001. Obtained from a meltblown nonwoven web. Although process conditions were not obtained, it was thought that the conventional (single-layer fiber) meltblown apparatus and process conditions were used. Also, the reported heat shrinkage measurements of this material are a heat shrinkage test slightly different from the procedure described above (PCT Patent Application No. PCT / CN2014080901 (Chen et al.), Attorney Docket No. 75424WO003, title “THEMALLY”. STABLE NONWOVEN WEB COMPRISING MELTBLOW BLENDED-POLYMER FIBERS ”). For example, the sample was held at 170 ° C. for 15 minutes rather than at 180 ° C. for 15 minutes. Thus, the shrinkage number of Comparative Example 2 may not be accurately compared with other data, but Comparative Example 2 is still useful in showing the general trends disclosed herein. is there.

  The thermal shrinkage of various examples and comparative examples is reported in Table 1.

Other Embodiments The foregoing examples are provided by available records and are provided for clarity of understanding only, and are not to be construed as making unnecessary limitations thereto. The tests and test results described in the examples are not predictive and are intended to be exemplary, and it is possible to expect that the results obtained will vary due to changes in the test method. All quantitative values in the examples should be understood to be approximate in terms of the well-known tolerances included in the procedure used.

  It will be apparent to those skilled in the art that certain exemplary elements, structures, features, details, configurations, etc. disclosed herein can be modified and / or combined in many embodiments. All such variations and combinations are not merely exemplary designs contemplated by the inventors to be within the boundaries of the contemplated invention and selected to serve as exemplary illustrations. Accordingly, the scope of the present invention should not be limited to the specific exemplary structures described herein, but rather at least the structures described by the language of the claims and structures corresponding to those structures. Expand to. Any elements positively cited herein as alternatives may be expressly included in the claims or excluded from the claims in any desired combination. Any element or combination of elements described herein in an open-ended language (eg, including and derivatives thereof) includes a closed-end language (eg, consisting of and a derivative thereof) and a partially closed-end language (Eg, consisting essentially of, and derivatives thereof, etc.). Various theories and possible mechanisms may be discussed herein, but in any case, such discussion is not intended to limit the claimed subject matter. In the event of any inconsistencies or inconsistencies between the present specification as set forth and the disclosures of all documents incorporated herein by reference, the specification as set forth takes precedence. To do.

Claims (24)

A heat-stable meltblown fibrous web comprising a plurality of meltblown multilayer fiber, melt blown multilayer fibers at least selected, respectively, composed of a first polymer crystallinity is slow polymers having a T _m of a least about 200 ° C. And at least one second layer composed of a second polymer that is a fast crystallizing polymer having a T _m of at least about 200 ° C., and
The meltblown multilayer fiber exhibits an average weight ratio of the first polymer to the second polymer of about 45:55 to about 95:05, and the heat-stable meltblown fiber web has less than about 10% heat A heat-stable meltblown fiber web that exhibits shrinkage. The web of claim 1, wherein the first polymer exhibits a T _m of at least about 240 ° C. and the second polymer exhibits a T _m of at least about 240 ° C.   The web of claim 1, wherein the meltblown fibers have an average weight ratio of the first polymer to the second polymer of about 60:40 to about 90:10.   The web of claim 1, wherein the meltblown fibers have an average weight ratio of the first polymer to the second polymer of about 70:30 to about 80:20.   The first polymer is a polyester selected from the group consisting of poly (ethylene terephthalate), poly (ethylene naphthalate), poly (lactic acid), poly (trimethylene terephthalate), and combinations thereof. As described in the web.   The web of claim 1, wherein the first polymer is poly (ethylene terephthalate).   The web of claim 1, wherein the first polymer is substantially free of non-polymer nucleating agents.   The web of claim 1, wherein the second polymer is selected from the group consisting of poly (butylene terephthalate), polymethylpentene, and syndiotactic polystyrene.   The web of claim 1, wherein at least selected multilayer fibers each include at least a pair of first layers and a second layer individually sandwiched therebetween. Each of the at least selected multilayer fibers includes at least three first layers and at least two second layers, each second layer being individually sandwiched between a pair of first layers. The web of claim 1.   At least selected multilayer fibers each comprise at least five first layers and at least four second layers, each second layer being individually sandwiched between a pair of first layers. The web of claim 1.   Each of the at least selected multilayer fibers comprises at least n first layers and at least n-1 second layers, wherein at least n-2 of the second layers are between the first layers. The web of claim 1, wherein the web is sandwiched individually and n is a number 7-51.   The web of claim 1, wherein the first layer is a single component layer and the second layer is a single component layer.   The web of claim 1, wherein the plurality of meltblown fibers collectively exhibit an average fiber diameter of less than about 10 micrometers.   The web of claim 1, wherein the web further comprises short fibers, wherein the short fibers comprise from about 5 wt% to about 50 wt% based on the total weight of the fibrous material of the web.   The web of claim 1, wherein the web exhibits a heat shrinkage of less than about 6%.   The web of claim 1, wherein the web exhibits a heat shrinkage of less than about 2%. Wherein the meltblown fibers of the web may include any polymer material that exhibits the T _m of less than 200 ° C. to about 5 wt% or less, according to claim 1 web. Wherein the meltblown fibers of the web are substantially free of any polymeric material which exhibits a T _m of a less than 200 ° C., according to claim 1 web.   The article comprising the heat stable meltblown fiber web of claim 1, wherein the article is selected from the group consisting of a thermal insulation article, a soundproof article, a fluid filtration article, or a combination thereof.   21. The article of claim 20, wherein the article is a soundproof article that exhibits a thermal shrinkage of less than about 5%. Extruding a molten multilayer flow stream through an orifice of a meltblowing die to form a molten multilayer filament;
Thinning the molten multilayer filament with a high-speed gas stream to form a multilayer meltblown fiber;
Recovering the multilayer meltblown fiber as a fiber mass, comprising:
Wherein at least selected multi-meltblown fibers of the flow stream mass of collected fibers, respectively, at least composed of a first polymer obtained by melt crystallization is slow polymers having a T _m of a least about 200 ° C. one a first layer of, including, at least one second layer comprised of a second polymer melt is a polymer crystallization is faster with a T _m of a least about 200 ° C., method.   The thinned multi-layer filament forms an air buoyant flow of multi-layer meltblown fibers and injects the air buoyant flow of short fibers into the air buoyant flow of the multi-layer fibers; and the mixed multi-layer meltblown fibers and short fibers 23. The method of claim 22, further comprising recovering as a fiber mass.   23. The method of claim 22, further comprising combining at least some of the fibers of the fiber mass together to form a heat stable meltblown fiber web.

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