Vapor-permeable, substantially water-impermeable multilayer article

Abstract

This disclosure relates to an article (e.g., a vapor-permeable, substantially water-impermeable multilayer article) that includes a nonwoven substrate and a film supported by the nonwoven substrate. The film includes a polyolefin, a nanoclay, and a pore-forming filler.

Description

TECHNICAL FIELD

This disclosure relates to vapor-permeable, substantially water-impermeable multilayer articles, as well as related products and methods.

BACKGROUND

Polyolefin films that are rendered permeable to water vapor by using a filler and a stretching process are known. Such films are also known as breathable, i.e., having vapor permeability while maintaining a resistance to water. They can permit the passage of moisture vapor and air, while substantially preventing the passage of water.

SUMMARY

This disclosure is based on the findings that including a nanoclay (e.g., montmorillonite nanoclay) in a film containing a pore-forming filler (e.g., calcium carbonate) can provide an unexpected improvement in the flame retardancy of the film. Such a film can be combined with a nonwoven substrate to form a multilayer article with improved flame retardancy, which is suitable for use as a construction material (e.g., a housewrap or a roofwrap).

In one aspect, this disclosure features an article that includes a film containing a polyolefin, a nanoclay, and a pore-forming filler.

In another aspect, this disclosure features an article that includes a nonwoven substrate and a film supported by the nonwoven substrate, wherein the film includes a polyolefin, a nanoclay, and a pore-forming filler.

In another aspect, this disclosure features an article that includes a nonwoven substrate and a film supported by the nonwoven substrate, wherein the film has a maximum heat release time measured in a cone calorimetry test longer than that of a film having the same composition except that it does not include both a nanoclay and a pore-forming filler.

In another aspect, this disclosure features a construction material that includes at least one of the articles described above.

In still another aspect, this disclosure features a method of making an article. The method includes forming a laminate containing a nonwoven substrate and a film supported by the nonwoven substrate; and stretching the laminate to form the article. The film includes a polyolefin, a nanoclay, and a pore-forming filler.

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

The nanoclay can include montmorillonite clay.

The nanoclay can include particles having an average aspect ratio of from about 200 to about 500.

The film can include from about 0.1% by weight to about 20% by weight (e.g., about 2% by weight) of the nanoclay.

The polyolefin can include a polyethylene, a polypropylene, or a copolymer thereof. For example, the polyolefin can include a polyethylene selected from the group consisting of low-density polyethylene, linear low-density polyethylene, and high density polyethylene. In some embodiments, the film can further include a functionalized polyolefin.

The pore-forming filler can include calcium carbonate. In some embodiments, the film can include from about 30% by weight to about 70% by weight (e.g., about 50% by weight) of the calcium carbonate.

The film can further include an elastomer. For example, the elastomer can be a thermoplastic olefin elastomer (e.g., a propylene-ethylene copolymer). In some embodiments, the film can include from about 5% by weight to about 30% by weight of the elastomer.

The nonwoven substrate can include randomly disposed polymeric fibers, at least some of which are bonded to one another.

The article can have a moisture vapor transmission rate of at least about 35 g/m²/day when measured at 23° C. and 50% relative humidity (RH %).

When the article has a unit weight of 1.25 ounces per square yard (osy), the article can have a tensile strength of at least about 40 pounds in the machine direction as measured according to ASTM D5034 and/or at least about 35 pounds in the cross-machine direction as measured according to ASTM D5034.

The article can have a hydrostatic head of at least about 55 cm.

The film can have a maximum heat release time measured in a cone calorimetry test longer than that of a film having the same composition except for the nanoclay, the pore-forming filler, or both.

The article can be embossed.

The construction material can be a housewrap or a roofwrap.

Forming the laminate can include extruding the film onto the nonwoven substrate.

The laminate can be stretched at an elevated temperature (e.g., at least about 30° C.).

The laminate can be stretched in the machine direction or in the cross-machine direction.

The laminate can be stretched by a method selected from the group consisting of ring rolling, tentering, embossing, creping, and button-breaking.

The method can further include embossing the laminate prior to or after stretching the laminate.

The method can further include bonding randomly disposed polymeric fibers to produce the nonwoven substrate prior to forming the laminate.

Embodiments can provide one or more of the following advantages.

In some embodiments, including a nanoclay (e.g., montmorillonite nanoclay) in a film containing a pore-forming filler (e.g., calcium carbonate) can achieve a synergistic effect in the flame retardancy of the film as demonstrated by an unexpected increase in its maximum heat release time measured in a cone calorimetry test.

In some embodiments, one advantage of using an elastomer in a breathable film is that a multilayer article containing such a film can have both improved tensile strength and improved elongation.

In some embodiments, when the surface of the breathable film contains a polymer having a chemical structure similar to or the same as the chemical structure of a polymer in the surface of the nonwoven substrate, the multilayer article thus formed can have improved adhesion between the breathable film and the nonwoven substrate.

In some embodiments, stretching the laminate described above at an elevated temperature (e.g., at least about 30° C.) can unexpectedly improve the moisture vapor transmission rate of the multilayer article thus formed while still maintaining an appropriate hydrostatic head of the multilayer article.

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

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a vapor-permeable, substantially water-impermeable multilayer article.

FIG. 2 is a scheme illustrating an exemplary extruding process.

FIG. 3 is a scheme illustrating an exemplary ring-rolling apparatus.

FIG. 4 is a plot illustrating the results of various multilayer articles in a cone calorimetry test.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

This disclosure relates to, for example, an article (e.g., a vapor-permeable, substantially water-impermeable multilayer article) containing a film (e.g., a breathable film) supported by a nonwoven substrate. The film can include a polyolefin, a nanoclay, a pore forming filler, and optionally an elastomer. The nonwoven substrate can be formed from polymeric fibers.

FIG. 1 is a cross-sectional view of a vapor-permeable, substantially water-impermeable multilayer article 10 containing a breathable film 12 supported by a nonwoven substrate 14.

A nanoclay can include a clay from the smectite family. Smectite nanoclays have a unique morphology, featuring one dimension in the nanometer range. An example of a smectite nanoclay is montmorillonite nanoclay. The montmorillonite nanoclay particle is often called a platelet, which has a sheet-like structure where the dimensions in two directions far exceed the particle's thickness. Other suitable nanoclays are disclosed, for example, in U.S. Pat. No. 6,414,070, and PCT Application Publication Nos. WO 00/66657 and WO 00/68312. Montmorillonite nanoclays are commercially available from Nanocor, Inc.

In some embodiments, the nanoclay used in the film 12 can be intercalated with an intercalant. An intercalate is a clay-chemical complex in which the space between parallel layers of the clay platelets has increased, e.g., by surface modification using an intercalant. An intercalant is a chemical capable of entering the space between clay platelets. Montmorillonite nanoclays containing an intercalant are also commercially available. An example of such a nanoclay is NANOMER 144P available from Nanocor, Inc.

In some embodiments, the nanoclay particles (i.e., nanoclay platelets) can have an average length or width of at least about 0.1 μm (e.g., at least about 0.5 μm) and/or at most about 1.5 μm (e.g., at most about 1.0 μm), while having an average thickness of at least about 0.5 nm (e.g., at least about 1 nm) and/or at most about 2 nm (e.g., at most about 1.5 nm). Thus, the nanoclay particle can have a large average aspect ratio (e.g., a ratio between length and thickness or a ratio between width and thickness). For example, the average aspect ratio of a nanoclay particle can be at least about 200 (e.g., at least about 250) and/or at most about 500 (e.g., at most about 400 or at most about 300).

The film 12 can include the nanoclay in an amount that can provide sufficient flame retardancy. For example, the film 12 can include from at least about 0.1% (e.g., at least about 0.5% or at least about 1%) to at most about 20% (e.g., at most about 15%, at most about 10%, at most about 5%, at most about 4% or at most about 3%) by weight of the nanoclay. In one example, the film 12 can include about 2% by weight of the nanoclay.

Without wishing to be bound by theory, it is believed that including a nanoclay (e.g., montmorillonite nanoclay) in a film containing a pore-forming filler (e.g., calcium carbonate) can achieve a synergistic effect in the flame retardancy of the film. The flame retardancy of a film can be characterized by the maximum heat release time measured in a cone calorimetry test according to ASTM E1354. As used herein, the term “maximum heat release time” refers to the time required for a heat-release curve (i.e., a curve of the heat-release rate of a film over the entire period of time of the cone calorimetry test) to attain its maximum value. In general, the longer the maximum heat-release time, the better the flame retardancy. As an example, when a polypropylene film includes either the nanoclay or the pore-forming filler (but not both), the film can have a maximum heat-release time measured in a cone calorimetry test shorter (e.g., by about 5-15%) than that of a polypropylene film without any additive (i.e., without the nanoclay or the pore-forming filler). Unexpectedly, when a propylene film includes both the nanoclay and the pore-forming filler, the film can have a maximum heat-release time measured in the cone calorimetry test longer (e.g., by at least about 5%) than that of a propylene film without any additive, which in turn is longer than that of a propylene film having either the nanoclay or the pore-forming filler. In other words, a propylene film including both the nanoclay and the pore-forming filler possesses significantly better flame retardancy than that of a polypropylene without any additive or with only of the nanoclay or the pore-forming filler. In addition, a multilayer article including the former film also possesses significantly better flame retardancy than a multilayer article including the latter films.

In some embodiments, the film 12 can have a maximum heat-release time measured in the cone calorimetry test at least about at least about 70 seconds (e.g., at least about 75 seconds, at least about 80 seconds, at least about 85 seconds, and at least about 90 seconds) and/or at most about 150 seconds (e.g., at most about 140 seconds, at most about 130 seconds, at least about 120 seconds, or at least about 110 seconds).

In some embodiments, the film 12 can have a maximum heat-release rate measured in the cone calorimetry test lower than that of a film without any additive (e.g., by at least about 30%) or a film containing the nanoclay or the pore-forming filler alone (e.g., by at least about 10%, at least about 20%, or at least about 25%). As used herein, the term “maximum heat release rate” refers to the maximum heat released by a sample per unit area per unit time. In general, the lower the maximum heat release rate, the better the flame retardancy. In some embodiments, the film 12 can have a maximum heat release rate measured in the cone calorimetry test at most about 450 kW/m² (e.g., at most about 400 kW/m², at most about 350 kW/m², or at most about 300 kW/m²) and/or at least about at most about 100 kW/m² (e.g., at most about 150 kW/m² or at most about 200 kW/m²).

The pore-forming filler in the film 12 can generate pores upon stretching (e.g., by using a ring-rolling process during the manufacture of the multilayer article 10) to impart breathability to the film 12 (i.e., to allow passage of vapor through the film 12).

The pore-forming filler can have a low affinity for and a lower elasticity than the polyolefin component or the optional elastomer component. The pore-forming filler can be a rigid material. It can have a non-smooth surface, or have a surface treated to become either hydrophobic or hydrophilic.

In some embodiments, the pore-forming filler is in the form of particles. In such embodiments, the average value of the maximum linear dimension (e.g., the diameter) of the filler particles can be at least about 0.5 micron (at least about 1 micron or at least about 2 microns) and/or at most about 7 microns (e.g., at most about 5 microns or at most about 3.5 microns). Without wishing to be bound by theory, it is believed that a filler with a relatively small average value of the maximum linear dimension (e.g., from about 0.75 to 2 microns) can provide a better balance of compoundability and breathability than a filler with a relatively large average particle size.

The pore-forming filler in the film 12 can be any suitable inorganic or organic material, or combinations thereof. Examples of the inorganic fillers include calcium carbonate, talc, clay, kaolin, silica diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, aluminum hydroxide, zinc oxide, magnesium oxide, calcium oxide, magnesium oxide, titanium oxide, alumina, mica, glass powder, glass beads (hollow or non-hollow), glass fibers, zeolite, silica clay, and combinations thereof. In some embodiments, the pore forming filler in the film 12 includes calcium carbonate. In some embodiments, the inorganic pore-forming filler can be surface treated to be hydrophobic so that the filler can repel water to reduce agglomeration of the filler. In addition, the pore-forming filler can include a coating on the surface to improve binding of the filler to the polyolefin in the film 12 while allowing the filler to be pulled away from the polyolefin when the film 12 is stretched or oriented (e.g., during a ring-rolling process). Exemplary coating materials include stearates, such as calcium stearate. Examples of organic fillers that can be used in film 12 include wood powder, pulp powder, and other cellulose-type powders. Polymer powders such as TEFLON powder and KEVLAR powder may also be included as an organic pore-forming filler. The pore-forming fillers described above are either available from commercial sources or can be readily prepared by methods known in the art.

The film 12 can include a relatively high level of the pore-forming filler as long as the level of the filler does not affect the formation of the film 12. For example, the film 12 can include from at least about 30% (e.g., at least about 35%, at least about 40%, or at least about 45%) to at most about 70% (e.g., at most about 65%, at most about 60%, or at most about 55%) by weight of the pore-forming filler (e.g., calcium carbonate). In some embodiments, the film 12 can include about 50% by weight of the pore-forming filler. Without wishing to be bound by theory, it is believed that, if the film 12 does not include a sufficient amount (e.g., at least about 30% by weight) of the pore-forming filler, the film may not have an adequate moisture vapor transmission rate (MVTR) (e.g., at least about 35 g/m²/day when measured at 23° C. and 50 RH %). Further, without wishing to be bound by theory, it is believed that, if the film 12 includes too much (e.g., more than about 70%) of the pore-forming filler, the film 12 may not be uniform or may have a low tensile strength.

The polyolefin in the film 12 facilitates formation of the film. As used here, the term “polyolefin” refers to a homopolymer or a copolymer made from a linear or branched, cyclic or acyclic alkene. Examples of polyolefins that can be used in film 12 include polyethylene, polypropylene, polybutene, polypentene, and polymethylpentene.

Exemplary polyethylene include low-density polyethylene (e.g., having a density from 0.910 g/cm² to 0.925 g/cm²), linear low-density polyethylene (e.g., having a density from 0.910 g/cm² to 0.935 g/cm²), and high-density polyethylene (e.g., having a density from 0.935 g/cm² to 0.970 g/cm²). High-density polyethylene can be produced by copolymerizing ethylene with one or more C₄ to C₂₀ α-olefin. Examples of suitable α-olefins include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, and combinations thereof. The high-density polyethylene can include up to 20 mole percent of the above-mentioned α-olefin comonomers. In some embodiments, the polyethylene suitable for use in the film 12 can have a melt index in the range of from about 0.1 g/10 min to about 10 g/10 min (e.g., from about 0.5 g/10 min to 5 g/10 min).

Polypropylene can be used in the film 12 by itself or in combination with one or more of the polyethylene polymers described above. In the latter case, polypropylene can be either copolymerized or blended with one or more polyethylene polymers. Both polyethylene and polypropylene are available from commercial sources or can be readily prepared by methods known in the art.

In some embodiments, the film 12 can further include a functionalized polyolefin (e.g., functionalized polyethylene or polypropylene), such as a polyolefin graft copolymer. Examples of such polyolefin graft copolymers include polypropylene-g-maleic anhydride and polymers formed by reacting PP-g-MAH with a polyetheramine. In some embodiments, such a functionalized polyolefin can be used a compatibilizer to minimize the phase separation between the components in the film 12 and/or to improve adhesion between the film 12 and the nonwoven substrate 14. The compatibilizer can be at least about 0.1% (e.g., at least about 0.2%, at least about 0.4%, at least about 0.5%, at least about 1%, or at least about 1.5%) and/or at most about 30% (e.g., at most about 25%, at most about 20%, at most about 15%, at most about 10%, at most about 5%, at most about 4%, at most about 3%, or at most about 2%) of the total weight of film 12.

Optionally, the film 12 can include an elastomer (e.g., a thermoplastic olefin elastomer) to improve the elasticity of the film. Examples of suitable elastomers include vulcanized natural rubber, ethylene alpha olefin rubber (EPM), ethylene alpha olefin diene monomer rubber (EPDM), styrene-isoprene-styrene (SIS) copolymers, styrene-butadiene-styrene (SBS) copolymers, styrene-ethylene-butylene-styrene (SEBS) copolymers, ethylene-propylene (EP) copolymers, ethylene-vinyl acetate (EVA) copolymers, ethylene-maleic anyhydride (EMA) copolymers, ethylene-acrylic acid (EEA) copolymers, and butyl rubber. A commercial example of such an elastomer is VERSIFY (i.e., an ethylene-propylene copolymer) available from Dow (Midland, Mich.). The film 12 can include from about 5% (e.g., at least about 6% or at least about 7%) to at most about 30% (e.g., at most about 25%, at most about 20%, or at most about 15%) by weight of the elastomer. Without wishing to be bound by theory, it is believed that one advantage of using an elastomer in the film 12 is that the multilayer article 10 containing such a film can have both improved tensile strength (e.g., by at least about 5% or at least about 10%) and improved elongation (e.g., by at least about 20% or at least about 50%).

The nonwoven substrate 14 can be formed from any suitable fibrous materials. As used herein, the term “nonwoven substrate” refers to a substrate containing one or more layers of fibers that are bonded together, but not in an identifiable manner as in a knitted or woven material.

The nonwoven substrate 14 can be formed from any suitable polymers. Exemplary polymers that can be used to form the nonwoven substrate 14 include polyolefins and polyesters. Examples of suitable polyolefins include polyethylene, polypropylene, and copolymers thereof, such as those in the film 12 described above. Examples of suitable polyesters include 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), and a copolymer thereof.

The nonwoven substrate 14 can be formed from single component fibers, i.e., fibers containing a polymer having a single chemical structure (e.g., a polymer described in the preceding paragraph such as a polyethylene, a polypropylene, or a polyethylene terephthalate). In some embodiments, the nonwoven substrate 14 can include single component fibers made from polymers having the same chemical structure but different characteristics (e.g., molecular weights, molecular weight distributions, density, or intrinsic viscosities). For example, the nonwoven substrate 14 can include a mixture of a low-density polyethylene and a high-density polyethylene. Such fibers are still referred to as single component fibers in this disclosure.

The nonwoven substrate 14 can also be formed from multicomponent fibers, i.e., fibers containing polymers with different chemical structures (such as two different polymers described above). For example, the nonwoven substrate 14 can be formed from a mixture of a polypropylene and a polyethylene terephthalate. In some embodiments, a multicomponent fiber can have a sheath-core configuration (e.g., having a polyethylene terephthalate as the core and a polypropylene as the sheath). In some embodiments, a multicomponent fiber can include two or more polymer domains in a different configuration (e.g., a side-by-side configuration, a pie configuration, or an “islands-in-the-sea” configuration).

In some embodiments, the surface of the nonwoven substrate 14 can contain a polymer having a chemical structure similar to (e.g., the same type as) or the same as the chemical structure of a polymer in the surface of the film 12. As an example, a polyolefin (e.g., a polyethylene or propylene) is of the same type as and similar to another polyolefin (e.g., a polyethylene or propylene). Without wishing to be bound by theory, it is believed that such a film and substrate can have improved adhesion between these two layers. For example, when the nonwoven substrate 14 is formed from single component fibers, the fibers can be made from a polyolefin, which has a chemical structure similar to or the same as the polyolefin in the film 12. When the nonwoven substrate 14 is formed from multicomponent fibers (e.g., having a sheath-core configuration), the polymer in the fibers that contacts the film 12 (e.g., the polymer in the sheath) can have a chemical structure similar to or the same as the chemical structure of one of the polymers in the film 12. Both examples described above can result in a multilayer article with improved adhesion between the film and the nonwoven substrate.

The nonwoven substrate 14 can be made by methods well known in the art, such as a spunlacing, spunbonding, meltblowing, carding, air-through bonding, or calendar bonding process.

In some embodiments, the nonwoven substrate 14 can be a spunbonded nonwoven substrate. In such embodiments, the nonwoven substrate 14 can include a plurality of continuous fibers, at least some (e.g., all) of which are bonded (e.g., area bonded or point bonded) with each other through a plurality of intermittent bonds. The term “continuous fiber” mentioned herein refers to a fiber formed in a continuous process and is not shortened before it is incorporated into a nonwoven substrate containing the continuous fiber.

As an example, the nonwoven substrate 14 containing single component fibers can be made by using a spunbonding process as follows.

After the polymer for making single component fibers is melted, the molten polymer can be extruded from an extruding device. The molten polymer can then be directed into a spinneret with composite spinning orifices and spun through this spinneret to form continuous fibers. The fibers can subsequently be quenched (e.g., by cool air), attenuated mechanically or pneumatically (e.g., by a high velocity fluid), and collected in a random arrangement on a surface of a collector (e.g., a moving substrate such as a moving wire or belt) to form a nonwoven web. In some embodiments, a plurality of spinnerets with different quenching and attenuating capability can be used to place one or more (e.g., two, three, four, or five) layers of fibers on a collector to form a substrate containing one or more layers of spunbonded fibers (e.g., an S, SS, or SSS type of substrate). In some embodiments, one or more layers of meltblown fibers can be inserted between the layers of the above-described spunbonded fibers to form a substrate containing both spunbonded and meltblown fibers (e.g., an SMS, SMMS, or SSMMS type of substrate).

A plurality of intermittent bonds can subsequently be formed between at least some of the fibers (e.g., all of the fibers) randomly disposed on the collector to form a unitary, coherent, nonwoven substrate. Intermittent bonds can be formed by a suitable method such as mechanical needling, thermal bonding, ultrasonic bonding, or chemical bonding. Bonds can be covalent bonds (e.g., formed by chemical bonding) or physical attachments (e.g., formed by thermal bonding). In some embodiments, intermittent bonds are formed by thermal bonding. For example, bonds can be formed by known thermal bonding techniques, such as point bonding (e.g., using calender rolls with a point bonding pattern) or area bonding (e.g., using smooth calender rolls without any pattern). Bonds can cover between about 6 and about 40 percent (e.g., between about 8 and about 30 percent or between about 22 and about 28 percent) of the total area of the nonwoven substrate 14. Without wishing to be bound by theory, it is believed that forming bonds in the nonwoven substrate 14 within these percentage ranges allows elongation throughout the entire area of the nonwoven substrate 14 upon stretching while maintaining the strength and integrity of the substrate.

Optionally, the fibers in the nonwoven substrate 14 can be treated with a surface-modifying composition after intermittent bonds are formed. Methods of applying a surface-modifying composition to the fibers have been described, for example, in U.S. Provisional Application No. 61/294,328.

The nonwoven substrate thus formed can then be used to form multilayer article 10 described above. A nonwoven substrate containing multicomponent fibers can be made in a manner similar to that described above. Other examples of methods of making a nonwoven substrate containing multicomponent fibers have been described in, for example, U.S. Provisional Application No. 61/294,328.

The multilayer article 10 can be made by the methods known in the art or the methods described herein. For example, the multilayer article 10 can be made by first applying the film 12 (e.g., a film containing a polyolefin, a nanoclay, and a pore-forming filler) onto the nonwoven substrate 14 to form a laminate. The film 12 can be applied onto the nonwoven substrate 14 by extruding (e.g., cast extrusion) a suitable composition (e.g., a composition containing a polyolefin, a nanoclay, and a pore forming filler) at an elevated temperature to form a film onto the nonwoven substrate 14. In some embodiments, the just-mentioned composition can be extruded (e.g., by tubular extrusion or cast extrusion) to form a web, which can be cooled (e.g., by passing through a pair of rollers) to form a precursor film. A laminate can then be formed by attaching the precursor film to the nonwoven substrate 14 by using, for example, an adhesive (e.g., a spray adhesive, a hot-melt adhesive, or a latex-based adhesive), thermal bonding, ultrasonic bonding, or needle punching.

In some embodiments, the multilayer article 10 can include multiple (e.g., two, three, four, or five) films supported by the nonwoven substrate 14, at least one of the films is the film 12 described above. Each of the films other than the film 12 can include one or more polymers and one or more pore-forming fillers described above with respect to the film 12. Optionally, one or more of the films other than the film 12 can include a nanoclay described above with respect to the film 12. In some embodiments, the nonwoven substrate 14 can be disposed between two of the multiple films. In some embodiments, all of the films can be disposed on one side of the nonwoven substrate 14.

FIG. 2 is a scheme illustrating an exemplary process for making a laminate described. As shown in FIG. 2, a suitable composition (e.g., a composition containing a polyolefin, a nanoclay, and a pore-forming filler) can be fed into an inlet 26 of an extruder hopper 24. The composition can then be melted and mixed in a screw extruder 20. The molten mixture can be discharged from extruder 20 under pressure through a heated line 28 to a flat film die 38. Extrusion melt 40 discharging from the flat film die 38 can be coated on the nonwoven substrate 14 from a roll 30. The coated substrate can then enter a nip formed between rolls 34 and 36, which can be maintained at a suitable temperature (e.g., between about 10-120° C.). Passing the coated substrate through the nip formed between the cooled rolls 34 and 36 can quench the extrusion melt 40 while at the same time compressing the extrusion melt 40 so that it contacts the nonwoven substrate 14. In some embodiments, the roll 34 can be a smooth rubber roller with a low-stick surface coating while the roll 36 can be a metal roll. A textured embossing roll can be used to replace the metal roll 36 if a multilayer article with a textured film layer is desired. When the extrusion melt 40 is cooled, it forms the film 12 laminated onto the nonwoven substrate 14. The laminate thus formed can then be collected on a collection roll 44. In some embodiments, the surface of the nonwoven substrate 14 can be corona or plasma treated before it is coated with the extrusion melt 40 to improve the adhesion between the nonwoven substrate 14 and the film 12.

The laminate formed above can then be stretched (e.g., incrementally stretched or locally stretched) to form the vapor-permeable, substantially water-impermeable multilayer article 10. Without wishing to be bound by theory, it is believed that stretching the laminate generates pores around the pore-forming filler in the film 12 that allow water vapor to pass through. The laminate can be stretched (e.g., incrementally stretched) in the machine direction (MD) or the cross-machine direction (CD) or both (biaxially) either simultaneously or sequentially. As used herein, “machine direction” refers to the direction of movement of a nonwoven material during its production or processing. For example, the length of a nonwoven material can be the dimension in the machine direction. As used herein, “cross-machine direction” refers to the direction that is essentially perpendicular to the machine direction defined above. For example, the width of a nonwoven material can be the dimension in the cross-machine direction. Examples of incremental stretching methods have been described in, e.g., U.S. Pat. Nos. 4,116,892 and 6,013,151.

Exemplary stretching methods include ring rolling (in the machine direction and/or the cross-machine direction), tentering, embossing, creping, and button-breaking. These methods are known in the art, such as those described in U.S. Pat. No. 6,258,308 and U.S. Provisional Application No. 61/294,328.

In some embodiments, the laminate described above can be stretched (e.g., incrementally stretched) at an elevated temperature as long as the polymers in the laminate maintain a sufficient mechanical strength at that temperature. The elevated temperature can be at least about 30° C. (e.g., at least about 40° C., at least about 50° C., or at least about 60° C.) and/or at most about 100° C. (e.g., at least about 90° C., at least about 80° C., or at least about 70° C.). Without wishing to be bound by theory, it is believed that stretching the laminate described above at an elevated temperature can soften the polymers in the film 12 and the nonwoven substrate 14, and therefore allow these polymers to be stretched easily. In addition, without wishing to be bound by theory, it is believed that stretching the laminate described above at an elevated temperature can increase the MVTR by increasing the number of the pores, rather than the size of the pores (which can reduce the hydrostatic head (i.e., resistance of water) of the multilayer article). As a result, it is believed that stretching the laminate described above at an elevated temperature can unexpectedly improve the MVTR of the resultant multilayer article while still maintaining an appropriate hydrostatic head of the multilayer article.

FIG. 3 illustrates an exemplary ring-rolling apparatus 320 used to incrementally stretch the laminate described above in the cross-machine direction. The apparatus 320 includes a pair of grooved rolls 322, each including a plurality of grooves 324. The grooves 324 stretch the laminate described above to form the multilayer article 10. In some embodiments, one or both of the rolls 322 can be heated to an elevated temperature (e.g., between about 30° C. and about 100° C.) by passing a hot liquid through the roll 322. The laminate described above can also be incrementally stretched in the machine direction in a similar manner. It is contemplated that the laminate can also be incrementally stretched using variations of the ring-rolling apparatus 320 and/or one or more other stretching apparatus known in the art.

In some embodiments, the laminate described above can be embossed prior to or after being stretched (e.g., by using a calendering process). For example, the laminate can be embossed by passing through a pair of calender rolls in which one roll has an embossed surface and the other roll has a smooth surface. Without wishing to be bound by theory, it is believed that an embossed multilayer article can have a large surface area, which can facilitate vapor transmission through the multilayer article. In some embodiments, at least one (e.g., both) of the calender rolls is heated, e.g., by circulating a hot oil through the roll.

In some embodiments, the multilayer article 10 can have a suitable MVTR based on its intended uses. As used herein, the MVTR values are measured according to ASTM E96-A. For example, the multilayer article 10 can have a MVTR of at least about 35 g/m²/day (e.g., at least about 50 g/m²/day, at least about 75 g/m²/day, or at least about 100 g/m²/day) and/or at most about 140 g/m²/day (e.g., at most about 130 g/m²/day, at most about 120 g/m²/day, or at most about 110 g/m²/day) when measured at 23° C. and 50 RH %. For instance, the multilayer article 10 can have a MVTR of between 70 g/m²/day and 140 g/m²/day.

In some embodiments, the multilayer article 10 can have a sufficient tensile strength in the machine direction and/or the cross-machine direction. The tensile strength is determined by measuring the tensile force required to rupture a sample of a sheet material. The tensile strength mentioned herein is measured according to ASTM D5034 and is reported in pounds. In some embodiments, the multilayer article 10 can have a tensile strength of at least about 40 pounds (e.g., at least about 50 pounds, at least about 60 pounds, at least about 70 pounds, or at least about 80 pounds) and/or at most about 160 pounds (e.g., at most about 150 pounds, at most about 140 pounds, at most about 130 pounds, or at most about 120 pounds) in the machine direction. In some embodiments, the multilayer article 10 can have a tensile strength of at least about 35 pounds (e.g., at least about 40 pounds, at least about 50 pounds, at least about 60 pounds, or at least about 70 pounds) and/or at most about 140 pounds (e.g., at most about 130 pounds, at most about 120 pounds, at most about 110 pounds, or at most about 100 pounds) in the cross-machine direction.

As a specific example, when the multilayer article 10 has a unit weight of 1.25 ounce per square yard, it can have a tensile strength of at least about 40 pounds (e.g., at least about 45 pounds, at least about 50 pounds, at least about 55 pounds, or at least about 60 pounds) and/or at most about 100 pounds (e.g., at most about 95 pounds, at most about 90 pounds, at most about 85 pounds, or at most about 80 pounds) in the machine direction, and at least about 35 pounds (e.g., at least about 40 pounds, at least about 45 pounds, at least about 50 pounds, or at least about 55 pounds) and/or at most about 95 pounds (e.g., at most about 90 pounds, at most about 85 pounds, at most about 80 pounds, or at most about 75 pounds) in the cross-machine direction.

In some embodiments, the multilayer article 10 can have a sufficient elongation in the machine direction and/or the cross-machine direction. Elongation is a measure of the amount that a sample of a sheet material will stretch under tension before the sheet breaks. The term “elongation” used herein refers to the difference between the length just prior to breaking and the original sample length, and is expressed as a percentage of the original sample length. The elongation values mentioned herein are measured according to ASTM D5034. For example, the multilayer article 10 can have an elongation of at least about 5% (e.g., at least about 10%, at least about 20%, at least about 30%, at least about 35%, or at least about 40%) and/or at most about 100% (e.g., at most 90%, at most about 80%, or at most about 70%) in the machine direction. As another example, the multilayer article 10 can have an elongation of at least about 5% (e.g., at least about 10%, at least about 20%, at least about 30%, at least about 35%, or at least about 40%) and/or at most about 100% (e.g., at most about 90%, at most about 80%, or at most about 70%) in the cross-machine direction.

In some embodiments, the multilayer article 10 can have a sufficient hydrostatic head value so as to maintain sufficient water impermeability. As used herein, the term “hydrostatic head” refers to the pressure of a column of water as measured by its height that is required to penetrate a given material and is determined according to AATCC 127. For example, the multilayer article 10 can have a hydrostatic head of at least about 55 cm (e.g., at least about 60 cm, at least about 70 cm, at least about 80 cm, at least about 90 cm, or at least about 100 cm) and/or at most about 900 cm (e.g., at most about 800 cm, at most about 600 cm, at most about 400 cm, or at most about 200 cm).

The multilayer article 10 can be used in a consumer product with or without further modifications. Examples of such consumer products include construction materials, such as a housewrap or a roofwrap. Other examples include diapers, adult incontinence devices, feminine hygiene products, medical and surgical gowns, medical drapes, and industrial apparels.

While certain embodiments have been disclosed, other embodiments are also possible.

In some embodiments, an effective amount of various additives can be incorporated in either the film 12 or the nonwoven substrate 14. Suitable additives include pigments, antistatic agents, antioxidants, ultraviolet light stabilizers, antiblocking agents, lubricants, processing aids, waxes, coupling agents for fillers, softening agents, thermal stabilizers, tackifiers, polymeric modifiers, hydrophobic compounds, hydrophilic compounds, anticorrosive agents, and mixtures thereof. In certain embodiments, additives such as polysiloxane fluids and fatty acid amides can be included to improve processability characteristics.

Pigments of various colors can be added to provide the resultant multilayer article 10 that is substantially opaque and exhibits uniform color. For example, the multilayer article 10 can have a sufficient amount of pigments to produce an opacity of at least about 85% (e.g., at least about 90%, at least about 95%, at least about 98%, or at least about 99%). Suitable pigments include, but are not limited to, antimony trioxide, azurite, barium borate, barium sulfate, cadmium pigments (e.g., cadmium sulfide), calcium chromate, calcium carbonate, carbon black, chromium(III) oxide, cobalt pigments (e.g., cobalt(II) aluminate), lead tetroxide, lead(II) chromate, lithopone, orpiment, titanium dioxide, zinc oxide and zinc phosphate. Preferably, the pigment is titanium dioxide, carbon black, or calcium carbonate. The pigment can be about 1 percent to about 20 percent (e.g., about 3 percent to about 10 percent) of the total weight of the nonwoven substrate 14 or the film 12. Alternatively, the pigment can be omitted to provide a substantially transparent multilayer article.

In some embodiments, certain additives can be used to facilitate manufacture of the multilayer article 10. For example, antistatic agents can be incorporated into the nonwoven substrate 14 or the film 12 to facilitate processing of these materials. In addition, certain additives can be incorporated in the multilayer article 10 for specific end applications. For example, anticorrosive additives can be added if the multilayer article 10 is to be used to package items that are subject to oxidation or corrosion. As another example, metal powders can be added to provide static or electrical discharge for sensitive electronic components such as printed circuit boards.

The nonwoven substrate 14 or the film 12 can also include a filler. The term “filler” can include non-reinforcing fillers, reinforcing fillers, organic fillers, and inorganic fillers. For example, the filler can be an inorganic filler such as talc, silica, clays, solid flame retardants, Kaolin, diatomaceous earth, magnesium carbonate, barium carbonate, magnesium sulfate, calcium sulfate, aluminum hydroxide, zinc oxide, magnesium hydroxide, calcium oxide, magnesium oxide, alumina, mica, glass powder, ferrous hydroxide, zeolite, barium sulfate, or other mineral fillers or mixtures thereof. Other fillers can include acetyl salicylic acid, ion exchange resins, wood pulp, pulp powder, borox, alkaline earth metals, or mixtures thereof. The filler can be added in an amount of up to about 60 weight percent (e.g., from about 2 weight percent to about 50 weight percent) of the nonwoven substrate 14 or the film 12.

In some embodiments, the surface of the nonwoven substrate 14 or the film 12 can be at least partially treated to promote adhesion. For example, the surface of the nonwoven substrate 14 or the film 12 can be corona charged or flame treated to partially oxidize the surface and enhance surface adhesion. Without wishing to be bound by theory, it is believed that the multilayer article 10 having enhanced surface adhesion can enable printing on its surface using conventional inks. Ink-jet receptive coating can also be added to the surface of the multilayer article 10 to allow printing by home or commercial ink jet printers using water based or solvent based inks.

The following examples are illustrative and not intended to be limiting.

Example 1

The following multilayer article samples were used in a cone calorimetry test according to ASTM E1354: (1) TYPAR (i.e., a polypropylene spunbonded nonwoven substrate available from Fiberweb, Inc.) coated with a film containing polypropylene alone, (2) TYPAR coated with a film containing polypropylene and a NANOMER 144P nanoclay available from Nanocor, Inc., (3) TYPAR coated with a film containing polypropylene and calcium carbonate, and (4) TYPAR coated with a film containing polypropylene, the above-mentioned NANOMER 144P nanoclay, and calcium carbonate. The NANOMER 144P nanoclay was 2% of the total weight of the films in samples (2) and (4), and the calcium carbonate was 50% of the total weight of the films in samples (3) and (4). For each sample, the film was coated onto TYPAR by extrusion coating.

The results of the cone calorimetry test are illustrated in FIG. 4. As shown in FIG. 4, when sample (2) (which includes a polypropylene film containing a nanoclay) and sample (3) (which includes a polypropylene film containing calcium carbonate, i.e., a pore-forming filler) exhibited a maximum heat release time about 5-15% shorter than that of sample (1) (which includes a polypropylene film without any additive). Unexpectedly, sample (4) (which includes a polypropylene film containing both the nanoclay and the calcium carbonate) exhibited a maximum heat release time at least about 5% longer than that of sample (1) and therefore also longer than those of samples (2) and (3). In general, a material having a longer maximum release time possesses better heat retardancy.

Example 2

The tensile strength and elongation of the following multilayer article samples were measured according to ASTM D5034: (1) TYPAR (i.e., a polypropylene spunbonded nonwoven substrate having a unit weight of 1.9 ounces per square yard available from Fiberweb, Inc) coated with a film containing polypropylene and calcium carbonate and (2) TYPAR coated with a film containing polypropylene, calcium carbonate, and VERSIFY (a propylene-ethylene elastomer available from The Dow Chemical Company). For each sample, the film was coated onto TYPAR by extrusion coating.

The results of the above tests are summarized in Table 1 below.

TABLE 1
				Elon-	Elon-
Sam-		Tensile	Tensile	gation	gation
ple	Components	MD (Lbs)	CD (Lbs)	MD (%)	CD (%)
(1)	TYPAR coated with	90.7	98.1	25.7	21.6
	70 wt % PP/30 wt %
	CaCO3
(2)	TYPAR coated with	100.3	106.9	31.1	33.3
	50 wt % PP/20 wt %
	VERSIFY/30 wt %
	CaCO3

As shown in Table 1, sample (2) unexpectedly exhibited improved tensile strength and elongation in both the machine and cross-machine directions.

Other embodiments are in the claims.

Claims

1. An article, comprising: (i) a breathable film comprising a polyolefin, a nanoclay, and a pore-forming filler, wherein the breathable film comprises pores around the pore-forming filler; and(ii) a nonwoven substrate, wherein the breathable film is supported by the nonwoven substrate;wherein the nanoclay comprises particles having an average aspect ratio of from about 200 to about 500; andwherein the article has a moisture vapor transmission rate of at least about 35 g/m2/day to at most about 140 g/m2/day when measured at 23° C. and 50 RH % and an elongation of at least about 5% to about 100% as measured according to ASTM D5034.

2. The article of claim 1, wherein the nanoclay comprises montmorillonite clay.

3. The article of claim 1, wherein the nanoclay has an average thickness of from about 0.5 nm to about 2 nm.

4. The article of claim 2, wherein the breathable film comprises from about 0.1% by weight to about 20% by weight of the nanoclay.

5. The article of claim 1, wherein the polyolefin comprises a polyethylene, a polypropylene, or a copolymer thereof.

6. The article of claim 5, wherein the polyolefin comprises a polyethylene selected from the group consisting of low-density polyethylene, linear low-density polyethylene, and high-density polyethylene.

7. The article of claim 5, wherein the breathable film further comprises a functionalized polyolefin.

8. The article of claim 1, wherein the pore-forming filler comprises calcium carbonate.

9. The article of claim 8, wherein the breathable film comprises from about 30% by weight to about 70% by weight of the calcium carbonate.

10. The article of claim 1, wherein the breathable film further comprises an elastomer.

11. The article of claim 10, wherein the elastomer is a thermoplastic olefin elastomer.

12. The article of claim 11, wherein the elastomer is a propylene-ethylene copolymer.

13. The article of claim 1, wherein the nonwoven substrate comprises randomly disposed polymeric fibers, at least some of the fibers being bonded to one another.

14. The article of claim 1, wherein, when the article has a unit weight of 1.25 osy, the article has a tensile strength of at least about 40 pounds in the machine direction as measured according to ASTM D5034.

15. The article of claim 1, wherein, when the article has a unit weight of 1.25 osy, the article has a tensile strength of at least about 35 pounds in the cross-machine direction as measured according to ASTM D5034.

16. The article of claim 1, wherein the article has a hydrostatic head of at least about 55 cm.

17. The article of claim 1, wherein the article is embossed.

18. A construction material, comprising the article of claim 1.

19. The construction material of claim 18, wherein the construction material is a housewrap or a roofwrap.

20. The article of claim 1, wherein: the nanoclay comprises particles of montmorillonite clay having an average thickness of from about 0.5 nm to about 2 nm;the polyolefin comprises a polyethylene, polypropylene, or a copolymer thereof; andthe pore-forming filler comprises calcium carbonate.

21. The article of claim 20, wherein the breathable film is supported by a nonwoven substrate comprising randomly disposed polymeric fibers, at least some of the fibers being bonded to one another.

22. The article of claim 21, wherein: the article has a unit weight of 1.25 osy;

23. The article of claim 22, further comprising a thermoplastic olefin elastomer.

24. The article of claim 1, wherein the breathable film comprises a first breathable film, and the article further comprises a second breathable film comprising nanoclay and pore-forming filler; and wherein the nonwoven substrate is disposed between the first breathable film and the second breathable film.

25. The article of claim 1, wherein the moisture vapor transmission rate comprises at least about 35 g/m2/day to at most about 110 g/m2/day when measured at 23° C. and 50 RH %.