CA2329604A1

CA2329604A1 - Breathable housewrap and process of making same

Info

Publication number: CA2329604A1
Application number: CA 2329604
Authority: CA
Inventors: Gregory W. Lynn; Jeffrey M. Hansbro
Original assignee: Individual
Current assignee: Celotex Corp
Priority date: 2000-04-05
Filing date: 2000-12-27
Publication date: 2001-10-05
Also published as: MXPA00012887A

Abstract

A liquid water-impermeable, water vapor-permeable composite comprising a porous, fibrous sheet adhered to a film of a vapor permeable, liquid impermeable polymer, the composite having a water vapor transmission rate of at least about 35 g/m2 per day and a hydrostatic head of at least about 55 cm H20.

Description

BREATHABLE HOUSEWRAP AND
PROCESS OF MAKING SAME
BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to a breathable housewrap composite constructed from a water vapor-permeable and liquid water-impermeable film and a water vapor-and liquid water-permeable substrate having high strength.

2. Description of the Prior Art Fibrous substrates that are vapor-permeable and water-impermeable have long been sought for a wide variety of uses. The ordinary substrates are usually unsuitable for such uses because they are porous and constitute a poor barrier to liquids. Barrier properties can be improved by laminating a barner film onto the substrate.
While the film itself generally renders the laminate impermeable to the passage of both liquids 1 S and gases and vapor, microporous films can be produced from the virgin film with a pore size which is small enough to prevent transfer of liquids but large enough to permit transfer of gas and liquid vapors.
There are various methods of creating microporous films, such as perforating a film by electrical discharge or by preparing and drawing a film containing a filler material which then may be removed or crushed to provide pores in the film.
U.S.
Pat. No. 5,762,643 discloses a method wherein a vacuum coating process can be used to extrude a vapor permeable, liquid impermeable material onto a three-dimensional apertured substrate using a vacuum or pressure differential. The method is used to make a breathable polymeric composite for such products as disposable absorbent articles, sleeping bag liners and the like.
It is known to use breathable composites made of a breathable film laminated to a fibrous substrate as air infiltration barriers in building construction.
These materials are generally placed over the perimeter walls of a building prior to the application thereover of a decorative finish layer, e.g., brick or vinyl siding. Such "housewrap" products substantially prevent the passage therethrough of air, while allowing the passage of water vapor. Specific examples of such fabrics are described in U.S. Pat. Nos. 4,684,568, 4,929,303, 5,554,246, 5,593,768, and 5,773,123.

A recent change in building regulation requires that all housewraps which are sold as weather resistive barriers must exhibit a pronounced liquid water impermeability in addition to being vapor permeable. Specifically, the housewrap must pass the hydrostatic water penetration test (AATCC-127) at 55 cm head of for 5 hrs., both initial and post-accelerated aging testing, and also pass the water vapor transmission test (ASTM E-96, Method B) at >_ 35 g/m2 per day, while maintaining strength and other important properties.
It would be highly desirable if a method could be found for producing a vapor-permeable, liquid water-impermeable fabric which additionally has the other properties desired in a wrap material for residential and commercial buildings.
OBJECTS OF THE INVENTION
It is accordingly an object of the invention to produce a breathable composite of a fibrous sheet and a thermoplastic film on a high-speed production line.
It is another object of the invention to produce such composite having a combination of properties required for housewrap applications, such as high tensile strength at break, liquid water-impermeability and water vapor-permeability.
SUMMARY OF THE INVENTION
The foregoing and other objects have been achieved and the drawbacks of the prior art have been overcome by the present invention which provides a composite of a fibrous substrate or sheet adhered to a polymeric film. The composite is particularly useful as a housewrap because it has superior water vapor-permeability and liquid water-impermeability, and high strength and tear-resistance. The composite is suitably formed by coating a vapor permeable, liquid impermeable polymeric material, which is conveniently in extruded or film form, onto the top surface of a fibrous substrate and applying a vacuum to the bottom surface of the coated substrate.
The polymeric material is supplied at a sufficiently high temperature for good bonding to the fibrous substrate. The composite can be formed in a simple one step process on a single production line, as described in U.S. Pat. No. 5,762,643, whose teachings with respect to a vacuum assisted coating of a thin vapor permeable, liquid impermeable material on a substrate are incorporated herein by reference.
The composite sheet of the invention has a low air permeability, expressed as Gurley-Hill porosity, e.g., greater than 400 seconds, and a superior water vapor transmission rate, i.e., at least about 35 g/m2 or 5.0 perms in 24 hours according to ASTM E96 Method B, and low liquid water permeability, i.e., a hydrostatic head pressure of at least about 55 cm H20 according to AATCC standard 127-1985. The tensile strength of the composite sheet is at least 20 lb/in in both the machine and transverse directions according to ASTM D-882. According to an advantageous embodiment of the invention, the composite sheet has a water vapor permeability high enough to assure the satisfactory passage of water vapor from a building construction but not so high as to result in excessive penetration of vapor into the building and a resultant moisture accumulation and structural damage therein.
The fibrous substrate may be an organic and/or inorganic material, such as a polyolefin, a polyester, glass, rayon, cellulose and nylon, and blends thereof.
Examples of preferred substrates are polyester mats, glass mats and non-woven and woven fabrics, with a suitably high porosity or open area, e.g. >_30%. The fibrous substrate advantageously has an initial moisture vapor transmission of at least 500, more preferably at least 700 to 1,000 g/m2 /day, and most preferably at least g/m2/day.
Suitable breathable polymeric films used in the inventive composite have a water vapor transmission rate, as determined in accordance with ASTM E96 Method B, of at least about 40 g/m2 per day, preferably at least about 60 g/m2 per day, and more preferably at least about 95 g/m2 per day, and resistance to air permeability not less than about 200 Gurley seconds, preferably not less than about 500 Gurley seconds. Preferred polymeric films used in the composite of the invention are polyacrylics.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a side schematic elevation of an apparatus suitable for producing a breathable housewrap in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The laminate of the present invention advantageously is a woven or nonwoven web composite comprising at least one layer of a fibrous web and at least one layer of a breathable polymeric film. In a preferred embodiment, the web is a nonwoven fibrous material which has been formed without weaving and which is composed of individual fibers, filaments, or threads which are bonded in a substantially random fashion. The nonwoven fabrics used in the invention may be any of the high strength variety known in the art and must be bondable to the breathable film without adversely affecting the water vapor permeability or the resistance to air permeability of the breathable film, i.e., fabrics or webs generally having a suitably open mesh to avoid totally covering the surface area of the breathable film coated thereon.
Advantageously, the open area of the fibrous material is about 35-70%, preferably 40-60%, and more preferably about 45%.
In general, any suitable thermoplastic resin can be used in making the fibrous nonwoven webs, including polyolefins of branched and straight-chained olefins such as low density polyethylene, linear low density polyethylene, high density polyethylene, polypropylene, polybutene, combinations thereof and the like.
The term "polyolefins" is meant to also include homopolymers, copolymers and blends of polymers prepared from at least 50 wt % of an unsaturated hydrocarbon monomer.
Examples of such polyolefins include polyethylene, polystyrene, polyvinyl chloride, polyvinyl acetate, polyacrylic acid, polyethyl acrylate, polyacrylamide, polyacrylonitrile, polyisoprene and the like.
The fibrous substrate is preferably a nonwoven polyolefin such as, for example, low or high density polyethylene and polypropylene, and preferably low density or high density polyethylene, more preferably high density polyethylene. The substrate suitably has an elongation (ASTM D1682) less than about 30%; a break load (ASTM D882) of at least about 20 lb/in, preferably at least about 25 lb/in, and more preferably at least about 30 lb/in, and a basis weight of about 0.9 to 1.5 oz/yd2.
Some preferred substrates are believed to be prepared from HDPE films having outer layers of low density polyethylene coextruded on the exterior of the HDPE core. The films are fibrillated, and the resulting fibers are spread in at least two transverse directions at a strand count of about 6-10 per inch. The spread fibers are then cross laminated by heat to produce a nonwoven fabric of 3-5 mils with equal MD and TD strength. These fabrics have excellent strength properties in both MD
and TD for reinforcing the breathable film, and an open structure to avoid substantially blocking the surface area of the breathable film when laminated thereto.
Especially suitable substrates for use in the laminate of the present invention are nonwoven HDPE/LDPE fabrics commercially available under the trade designation CLAFT"" from Amoco-Nisseki Claf Incorporated.
The fibrous substrate and the breathable film are bonded together to form the breathable composite of the invention. The bonding process is suitably carned out by applying a polymer onto the high strength substrate using the vacuum-processing step which is described in U.S. Pat. No. 5,762,643. The polymer is extruded onto the top surface of the fibrous substrate and a vacuum is applied to the bottom surface. The vacuum pulls the polymeric coating against the substrate and into its openings. The coating is applied at an elevated temperature and in sufficient amount to effect its bonding with the substrate.
The extrusion process provides a thin coating of a monolithic (nonporous) film which is vapor permeable and liquid impermeable. 'The vacuum is applied long enough and at a sufficiently high pressure so that the coating is pulled against the substrate for strong bonding and advantageously at least partial penetration into the openings of the substrate without creating holes in the coating. While the temperature of the applied coating is also elevated to create a strong bond, it must not be so high that degradation of the substrate or polymer will result.
The composition and density of the monolithic or non-microporous films of the invention may be easily adjusted to achieve the desired barrier properties. The vacuum assisted application may be accomplished with a variety of polymers, including copolyesters, polyacrylics, polyolefins, and ethylene vinyl acetate copolymers. The usual additives such as processing aids, UV stabilizers, antioxidants, pigments, anti-block agents, etc. may be used in the polymers.
The breathable films used in the inventive composite are derived especially from acrylic polymers. In a preferred embodiment, the breathable films are derived from acrylic copolymers. The copolymers may be formed by polymerizing olefins with one or more alpha, beta ethylenically unsaturated acids such as acrylic and methacrylic acids or alkyl esters of said acids, such as those made with C~ to CS
alcohols. Blends of the copolymers) may be employed. Examples of the copolymers are ethylene acrylic acid, ethylene ethyl acrylate, ethylene methyl acrylate, ethylene methyl methacrylate, ethylene butyl acrylate, ethylene methacrylic acid, and the like.
The ethylene alkyl acrylate copolymers typically contain about 5-50 wt % alkyl acrylate and about 95-50 wt % ethylene, preferably about 10-40 wt % alkyl acrylate and about 90-60 wt % ethylene, and more preferably about 15-40 wt % alkyl acrylate and about 85-60 wt % ethylene. A particularly preferred copolymer contains about 20 wt % alkyl acrylate and about 80 wt % ethylene.
The coating material is generally applied at a thickness of about 0.6 mil to 1.5 mils. A preferred range is from about 0.8 mil to 1.3 mils. The density of the coating is suitably about 0.5 to 1.2, preferably about 0.94 to 0.97 g/cm3. The water vapor transmission rate of the coated composite is preferably less than about 490 g/m2 per day, more preferably less than about 315 g/m2 per day, and most preferably less than about 140g/m2 per day.
With reference to FIG. 1, a substrate 10, which in a preferred embodiment is a nonwoven polyolefin fabric, advances from a supply roll 11. Another means to supply the substrate is by a film forming cast extrusion process. The substrate 10 is passed over a drum 12 having a plurality of openings 13 extending through its surface. Other conveying means, such as a conveyor belt with openings, can be used.
Simultaneously, a copolymer is melted in a conventional extruder (not shown), extended through a slot die 14 in the form of a sheet of molten copolymer 15, and deposited at an elevated temperature through opening 16 of the die onto the substrate 10. The opening 16 is suitably less than 12 inches, preferably about 2-3 inches, from the top surface of the substrate 10 as it passes over the drum 12.
A vacuum chamber 17, preferably within the drum 12, creates a vacuum and, as the copolymer 15 is applied to the substrate 10, the vacuum causes the coating copolymer to be pulled against the top surface of substrate 10 to form composite material 18 which is then wound on a roll 19. At least one other roll 20, such as an idler roll and/or cooling roll, can be used.

As generally shown in FIG. 1, a series of four coating films were dispensed at a temperature of 490° F to 500° F from slot die 14 onto a substrate 10 being fed to rotating drum 12 at 120 feet per minute and subjected to the relative vacuum pressure given in Table I below. Rotating drum 12 was located two inches below slot die 14 of the extruder.

In each run, substrate 10 was a nonwoven web of high density polyethylene/low density polyethylene with an open spacing of approximately 42%
(Amoco-Nisseki Claf HS-1310.) Each film 15 was formed from pellets of an ethylene methyl acrylate copolymer containing about 80% ethylene and 20% ethylene methyl acrylate (Chevron 2220), and was applied at the thickness given in Table I.
The composite 18 formed from film 15 and substrate 10 was wound on take-up roll 19.
The physical properties of the resultant composites are given in Table II
below. The adhesion of each film to the substrate was excellent.

The procedure of Example 1 was repeated except that a series of four coating films were dispensed at a temperature of 550°F to 570°F, each film being an ethylene methyl acrylate copolymer containing about 80% ethylene and 20% ethylene methyl acrylate (Exxon Optema TC 110) having minor amounts of auxiliary additives, and the substrate 10 was fed to rotating drum 12 at 100 feet per minute. The adhesion of each film to the substrate was excellent. Each film of Runs 5 to 8 was applied at the thickness and pressure given in Table III, and the physical properties of the resultant composites are given in Table IV.
TABLEI
RUN CONDITIONS
Run Film Thickness Vacuum Pressure*
(mil) (in Hg) 1 1.0 0.5 to 0.7 2 0.7 0.5 to 0.7 3 1.3 0.5 to 0.7 4 1.3 2.0 to 2.1 *In East and West directions, respectively.

TABLE II
COMPOSITE PROPERTIES
Pro a Test Run 1 Run 2 Run 3 Run 4 HydrostaticAATCC- Pass Pass Pass Pass Head 127*

(modified) WVTR, ASTM E96 5.3 6.2 3.0 3.6 Perms (Method B) Tensile ASTM 23.0/25.0 23.0/25.023.0/25.0 23.0/25.0 Strength, D882 lb/in (MD/CD) Gurley Tappi T460ImpermeableImpermeableImpermeableImpermeable Hill Porosity, sec/100 ml of air *55 cm H20 column for 5 hours.
TABLE III
RUN CONDITIONS
Run Film Thickness Vacuum Pressure*
_(mil) (in Hg) 0.9 2.6 to 2.7 6 p,9 2.6 to 2.7 7 1.0 2.6 to 2.7 g 1.0 2.6 to 2.7 *In East and West directions, respectively.
TABLE IV
COMPOSITE PROPERTIES
Pro er Test Run 5 Run 6 Run 7 Run 8 Grammage, Tappi T410 5 8.1 gm/m2 WVTR, ASTM E96 6.0 5.7 5.1 5.3 Perms (Method B) Mullen ASTM 84.1 Burst , D751 psi Tensile ASTM 22/27 Strength, D882 lb/in (MD/CD) Pro er Test Run 5 Run 6 Run 7 Run 8 Gurley Tappi T460 Impermeable Hill Porosity, sec/100 ml of air Steiner ASTM E84 0/25 Tunnel (flame spread/

smoke) HydrostaticAATCC- Pass Pass Pass Pass Head 127*

(modified) *55 cm H20 column for 5 hours.

Claims

1. A liquid water-impermeable, water vapor-permeable composite comprising a porous, fibrous sheet adhered to a film of a vapor permeable, liquid impermeable polymer, the composite having a water vapor transmission rate of at least about 35 g/m2 per day and a hydrostatic head of at least about 55 cm H2O.

2. The composite of claim 1 wherein the fibrous sheet is a nonwoven material.

3. The composite of claim 1 wherein the fibrous sheet comprises a nonwoven polyolefin.

4. The composite of claim 1 wherein the fibrous sheet comprises a nonwoven polyethylene or polypropylene or a combination thereof.

5. The composite of claim 4 wherein the fibrous sheet comprises a combination of high density polyethylene and low density polyethylene.

6. The composite of claim 1 wherein the fibrous sheet has a basis weight of about 0.95 to 1.25 oz/yd2.

7. The composite of claim 1 wherein the fibrous sheet has a tensile strength of at least about 20 lb/in in both the machine and transverse directions.

8. The composite of claim 1 wherein the Gurley-Hill porosity of the composite is greater than 400 sec.

9. The composite of claim 1 wherein the polymeric film has a thickness of about 0.6 mil to 1.5 mils.

10. The composite of claim 1 having water vapor transmission rate of from about 35 g/m2 per day to 490 g/m2 per day.

11. The composite of claim 1 having water vapor transmission rate of from about 35 g/m2 per day to 140 g/m2 per day.

12. The composite of claim 1 wherein the fibrous sheet has an open area of about 35-70%.

13. The composite of claim 1 wherein the fibrous sheet has an open area of about 40-60%.

14. A liquid water-impermeable, water vapor-permeable composite comprising a porous, fibrous sheet adhered to a film of a vapor permeable, liquid impermeable polymer, the composite having a water vapor transmission rate of at least about 35 g/m2 per day and a hydrostatic head of at least about 55 cm H2 0, and the composite being formed by the steps of supplying the polymer at an elevated temperature on the top surface of the sheet to form a coating of the polymer on the surface of the sheet, and applying a vacuum to the bottom surface of the coated sheet so that the coating is pulled against and into the openings of the sheet, the polymer temperature and vacuum pressure being sufficient to create a strong bond between the fibrous sheet and the polymeric coating without creating holes in the coating.

15. The composite of claim 14 wherein the fibrous sheet is a nonwoven material.

16. The composite of claim 14 wherein the fibrous sheet comprises a nonwoven polyolefin.

17. The composite of claim 14 wherein the fibrous sheet comprises a nonwoven polyethylene or polypropylene or a combination thereof.

18. The composite of claim 17 wherein the fibrous sheet comprises a combination of high density polyethylene and low density polyethylene.

19. The composite of claim 14 wherein the fibrous sheet has a basis weight of about 0.95 to 1.25 oz/yd2.

20. The composite of claim 14 wherein the fibrous sheet has a tensile strength of at least about 20 lb/in in both the machine and transverse directions.

21. The composite of claim 14 wherein the Gurley-Hill porosity of the composite is greater than 400 sec.

22. The composite of claim 14 wherein the polymeric coating has a thickness of about 0.6 mil to 1.5 mils.

23. The composite of claim 14 wherein the composite has a water vapor transmission rate of from about 35 g/m2 per day to 490 g/m2 per day.

24. The composite of claim 14 wherein the composite has a water vapor transmission rate of from about 35 g/m2 per day to 140 g/m2 per day.

25. The composite of claim 14 wherein the fibrous sheet has an open area of about 35-70%.

26. The composite of claim 14 wherein the fibrous sheet has an open area of about 40-60%.